vfd

LCI CHANNELS FOR VFD - COMPENDIUM OF FAULTS

Page 1 of 95

EQUIPMENT : LOAD COMMUTATED INVERTER (VFD)

DOCUMENT : COMPENDIUM OF FAULTS/ALARMS

DOCUMENT NO. : 441/COMPEND/LCI REV.054 DTD.30/0812/0607

When referring to a solution for a problem, the particular category of

Fault /Alarm is to be seen. Further please also read General checks,

Checks for ground fault, Load Commutation Failure, Load PLL Fault and

SEM Earthing document at the end of this document.


Page 2 of 95

REVISION HISTORY SHEET

NATURE OF CHANGE

REV.NO./ DATE PREPARED BY CHECKED BY APPROVED BY

FIRST ISSUE

UPDATED UPTO 09.06.04





00 /25.03.04

01 /09.06.04

02 /10.03.05

03 /30.08.05

04 /30.08.06

05 /30.12.07


Page 3 of 95


Page 5 of 95

Category Sl.no. Problem Solution MISC 1. Small crack observed in base of 1 no. CT in Load

Break Switch Panel.

Failure of CTs.

The primary connections on the CTs are such that load of

the Cu bars is coming on the CTs. Therefore necessary to

provide flexible connection on one side of the CT.

Customer opined that failure may be due to thermal

stresses.

This point was taken care of when replacement of Load

Break Switch with Contactor was done.

MISC 2. Gaskets on doors have gaps at many places resulting

in air being sucked through these gaps also.

Customer opined that replacement of gaskets necessary.

Gaskets replaced at places wherever required.

MMI FOR VFD 3. MMI remains out of service due to “Communication

Link failure”.

MMI s/w hanging problem.

Defective line driver replaced by a new one.

Demultiplexer channels at control room were not working.

Same repaired.

One wire of RS232 port was found disconnected, same

rectified.

One reed relay card to be replaced (failed during

troubleshooting). MMI system put on-line bypassing Drive

status and Reset command from PC.

Replaced reed relay card. Problem solved.

Corrected version of software installed. Became OK.

MISC 4. 6A Ch-2 tripped on electrical fault.

Current hunting was observed in Ch-1 and tripped on

R phase Overcurrent.

When Ch-2 of ID Fan 6A trips, current/voltage

hunting is observed in the Ch-1 and it also trips.

Motor foundation vibration found higher compared

to other motors.

1. “LMARG” changed from 25° to 30°. No change

observed.

2. “FLALEN” and “FLASEN” changed to TRUE. No

change observed.

3. Changed parameters “CRGAIN, FRGAIN, FRTC,

PLLTOL, LIMARG”. No change observed.

4. Finally by changing PLLMODE from 60 to 25, problem


Page 6 of 95

was solved.

SHORTED

MOTOR

WINDING

5. 6A Ch-2 trips with message “Shorted motor

winding.” Ch–1 stopped after current hunting

observed.

However, current drawn continues to be higher than

other fans due to poor p.f.

NLCB card in Ch-2 found defective. Card replaced and

problem solved.

MISC 6. Tripping of channels due to Loose connections of

cards on SEM rack.

Proposal for installing Anti-vibration pads on blower

support in panel. Concurrence given by BHEL for the

same.

Anti-vibration pads put and SEM lock bars installed.

Problem solved.

MISC 7. Frequent failure of NPPB card. Heat dissipated by

bleeder res. is high. Bleeder resistor installed on

PSFF just behind mother board NPPB.

Proposal by customer to install bleeder resistor outside

PSFF module.

Customer asked to check VFD room temperature and clean

the mesh filter on C&EXE panel. Bleeder resistor can be

mounted outside only if above remedies do not work.

Temperature in VFD Room rectified. Problem solved.

MISC 8. Self Test halts at No.23 even though channel is

healthy.

BHEL requested customer to furnish a print-out of self

test program to study the problem.

Customer asked to adjust offset zero on NLIB load card

FAB, FBC & FCA with BAL1 and BAL2 pots on NLCB

Allowed tolerance is 30mV. Problem solved.

MISC 9. UPS supply tripping on trf. inrush current.

120/120VAC, 1ph, trf. with 2P & 2S windings, 1 sec.

Winding found defective.

Spec. for trf. given by EDN to TEC with msg. to procure

trf. locally. Screen to be provided between primary and

Sec. of trf. and Screen to be earthed to panel frame.

Changed transformer. Problem solved.

MISC 10. 6A Ch-1 tripped , Ch-2 not responding to speed

lower command from CRT. Current and speed of ID

fan stuck. 6A taken out of service manually and 6B

taken into service. SRCLSC found to be 0.7 instead

of 1.0 in other channels.

Parameter SRCLSC changed to 1.0 as in scheme.

4-20mA speed signal is not being recd. by Ch-1 or Ch-2.

Problem in I&C system solved. 6A taken into service.


Page 7 of 95

MISC 11. Erosion of cooling tubes at the tip of the

tubeshoot at O/B side of ID Fan motors. Resulted

in passing of external air into motor body. Motor is

CACA cooled.

Customer proposed to replace all cooling tubes (1980

tubes). Asked for advise.

Referred to contact BHEL/EMRP-Mumbai for further

action.

MISC 12. ID 6A Ch1 – oscillating and load currents on

contactor not balanced. 1 phase current missing.

Source currents balanced. 0IA load NLIB

negative humps missing.

Told to change HPTF card in LTM1 or LTM4.

Pulse was missing in LTM4. Changed HPTF card. Problem

solved.

MISC 13. Repeated faults in drive due to loose connection on

SEM Rack.

Recommended to install lock bars to secure control cards

in the racks. SEM Lock bar installed. Problem solved.

MMI FOR VFD 14. MMI getting hung frequently. Line drivers OK.

After PC rebooting the MMI PC, communication

gets re-established.

If power goes OFF, sometimes MMI PC hangs as told by

customer. EDN suggested to put the MMI PC on UPS so

that this will not occur. MMI put on UPS. Problem solved.

MISC 15. ID Fan 6A taking high current (400A), current of

both channels hunts in the range 320-400A.

Higher current is due to higher LMARG and LIMARG as

motor p.f is lower. Adjusted SRGAIN such that hunting of

speed and current stops. Problem solved.

LOAD PLL FAULT 16. 6C1 tripping on “Load PLL fault”. Gate test OK. Self

test OK upto 40. Channel goes back to service

every time after tripping.

Additional to Load PLL fault, MP alarm also coming.

IMOK of HMPG and NLCB missing. Missing Leds

come on after reset.

6C1 started as slave channel after swapping HMPG

with 6C2. Load current does not come immediately

but hunts a lot. Also LED ‘0’ on HRDA card (for

MAMS) flickers. Firing of load thyristors also

flickers. Flickering stops after sometime and

channel becomes OK. Channel trips after few days.

HRDA, HROA, NLCB replaced. NLIB Source & Load

replaced.

Tripping freq. increased.

EDN Suggested

1. To install lock bar of SEM. HMPG/DMPB may be loose

in its slot.

2. Clean HMPG/DMPB and pins on mother board by air

blowing.

Load current hunting may be due to MTRFMIN and FLUXS

values being slightly different than actual requirement.

Suggested to lower the values of MTRFMIN and FLUXS in

steps of 0.01 and if not sufficient again in steps of 0.05.

Problem may be due to slight drift of NLIB load side flux

calibration over the years of service.


Page 8 of 95

Also asked to check SEM earthing as per SEM Earthing

document. Problem solved by adjusting offset zero to less

than 30mV on NLIB using source volts and also earthing

SEM as per document.

LOAD PLL FAULT 17. 6C1- Trips on Load PLL Fault on load. Increased LMARG from 20° to 25°.

Problem solved.

SOURCE

OVERCURRENT &

LOAD

OVERCURRENT

18. After starting the channel, as soon as current and

voltage started building up, channel tripped on

Source Overcurrent, Load Overcurrent and

Microprocessor Alarm.

On taking trial, current and speed developed OK.

On reaching 90-100rpm, channel tripped again on

Microprocessor alarm. LBS O/C relay operated,

Lock out of Source breaker operated and tripped

the breaker. IMOK LEDs of HMPG and NLCB not

glowing.

Firing cards on all thyristor legs of Source and Load side

were checked. Found that jack plug on one of the source

side cards was not fixed properly. Same rectified and

plugs of all cards were thoroughly checked.

All cards removed and cleaned and checked for any

abnormal marks or heating on the cards. Found OK. Dust

accumulation was completely removed. Channel trial taken

and found OK. Changeover trials taken for both the

channels and found OK. Fan taken into service.

MISC

REV.04

19. Severe hunting of currents in Master and Slave

channels when speed is brought to near minimum

speed.

ID Fan functions normally during service when unit is

generating full load. Also all the waveforms of voltages and

currents in both channels found OK. Found that rubber

blocks in the coupling had deteriorated. Rubber blocks

changed. Problem solved.

SOURCE

UNDERVOLTAGE

R05, 0207, VI

20. Current hunting over a certain speed. At this time,

INVLIM sets to 384 (256+128). 256=STOP,

128=SOURCE UNDERVOLTAGE. Boiler under

shutdown.

Shorted LBKRS TBs on IOMA (Source breaker input).

Problem persisted. Checked Earthing of SEM and panel.

Found OK. Since boiler was under shutdown, channel run

independently. Found that the hunting problem was related

to current and not to voltage.

Changed HLCB, NLIB Source, NSFC source. Problem still

persisted. All waveforms of current, flux, voltages found

OK. CT phasing on Source side OK. Found that NLIB

Source and NLIB load were interchanged. As the


Page 9 of 95

compensation resistance for reactances are different in

DLIB Source and Load, this was giving rise to wrong

position of interrupts on HLCB during higher currents.

Wrong interrupt position was causing very high current for

extremely short duration, giving rise to Source

undervoltage. Swapped the Source and Load DLIB cards.

Channel taken into service. Problem solved.


Page 10 of 95

Category Sl.no. Problem Solution LOAD

COMMUTATION

FAILURE

1. Channel trips on Load Commutation failure 1. HPTF card in LTM3 found faulty when doing crowbar

test. HTPF card replaced. Problem solved.

2. BHEL has suggested to maintain control room

temperature at 25°C.

MISC

2. 1 no. motor burnt out.

Replaced by spare motor available at site. All tests

while taking new motor into service done by

customer with telephone support from BHEL-EDN.

Lead from stator was found melted out. Connections were

wrongly crimped. Connections Brazed and motor ready.

Kept ready for service.

LOAD

OVERCURRENT

3. Channel tripping once a week with message “Load

Overcurrent”. 2 out of 3 flags in VFD Overcurrent

Relay have operated. Channel starts after resetting

and starting.

Suggested to

1. Operate Overcurrent relay manually and check for

same message print-out on printer.

2. Short the relay contact which is in series with load

contactor aux. contact going to IOMA.

3. Change Load NSFC card.

NSFC load card was changed and problem solved.

LOAD

COMMUTATION

FAILURE &

SHORTED

MOTOR WINDING

4. Channel tripping with fault message “Load

Commutation failure” and “Shorted motor winding”

Firing pulse LED on one card in source bridge

(HPTF) was not steady and was flickering.

Suggested to

1. Change NSFC load card

2. Checking of all connectors and RC filter circuits on

load side.

3. Check power bridge on load side.

HTPF card on source side changed and problem solved.

GROUND FAULT 5. Ground fault in both channels of 4B. In one channel one load side capacitor was faulty. In the

other channel, the neutral grounding of R-C circuit was

not OK. Problem in both channels solved.


Page 11 of 95

MISC 6. Chattering of MAMS relay in slave channel. Adjusted offset zero in NLIB Load FAB,FBC,FCA by back

charging from Master. Problem solved.

MISC 7. HMPGDMPB in 4B1 giving Bushog after few hours

in service.

HMPG/DMPB card replaced.

Problem solved.

GROUND FAULT 8. VFD Ground Fault problem in slave channel. See text on ground fault at the end of this document.

Cable insulation was found faulty on cable from contactor

to motor during hi-pot test to earth. Problem solved.

MISC 9. Master and Slave both start and run individually. At

minimum speed, slave does not take load when

paralleled with Master channel.

Back-charged slave with source breaker open and load

Contactor closed. Adjusted FAB, FBC, FCA on NLIB-load

on slave with that of Master.

Slave channel paralleled. OK. Problem solved.

MISC 10. Ch-1 tripped but no annunciation on the door

mounted printer or at remote C&I.

Initially suspected that "Stop" command was being issued

from C&I system, but found this was not true. Channel

selector switch and Local/Remote switch on IOMA were

bypassed but trippings continued. Trippings were reported

at regular intervals.

Laptop PC was then connected to HMPG. Found that

Microprocessor was getting reset every time the drive

tripped. This was evident from the Laptop display.

This could happen only if LVSH from PSFF goes "High".

PSFF supply was cleaned by blowing air. Channel put into

service and no trippings observed.

PSFF changed as per customer requirement. No further

trippings observed.

MISC 11. 1. After overhauling, when ID Fan-B was started, it

became ON & OFF many times on its own. When fan

speed was increased, it became normal. Again when

the channel was started after station tripping, same

problem occurred. 2. When Ch-2 was started,

Drive received ON command and took load also, but

Problem is that Ch-2 is not going to LMODE=3. The

reason is that the flux levels in the machine is lesser than

the values set for FLUXS and MTRFMIN.

Following suggested:

During the next shutdown, backcharge Ch-2 and adjust

NLIB Load Flux values to the same as in Ch-1. Also please


Page 12 of 95

OFF status did not go from the desk, while RUN

indication was appearing on the VFD panel. Then,

Ch-1 was started first and Ch-2 started

thereafter. Now drive started normally.

check the FLUXS, MTRFMIN and FRSTART values in Ch-2

are the same as in Ch-1.

Start motor from Ch-2 and please check motor goes to

LMODE=3.

SPD and SPM pots on NLCB do not matter for proper

starting of the drive.

SHORTED MOTOR

WINDING

12. Ch-1 tripped on Shorted Motor Winding. Ch-2 made Master and Ch-1 Slave. Adjusted Load flux in

NLIB Load in Ch-1 same as in Ch-2. Channel taken into

service. Problem solved.

LOAD

COMMUTATION

FAILURE

R05, 0807, PH

13. Channel trips on Load Commutation failure as soon

as it is paralleled.

Invoked Gate test and found that 1 no. LED on HPTF Load

side Pulse transformer card was not glowing. Replaced card

and re-checked under Gate test mode. LED glowing OK.

Channel taken into service. OK.

LOAD

COMMUTATION

FAILURE

R05, 1007, PH

14. Master channel is running. When Slave is paralleled

to Master, current in Slave is not same as in Master.

Further Slave channel sometimes trips on Load

Commutation failure.

When currents are steady in both Master and Slave,

CRSTART values were checked with Laptop PC and found

to be different. Further in Master Channel, other channel

running signal IOMA TB5/09,10 was TRUE. Also, the

current reference from Master channel IOMA TB7/10,11

was positive which is OK for motoring. Therefore, fault

was in Slave (Ch-2). Changed NLCB card as this is the first

card in the signal path for current reference. Paralleled

Slave Ch-2 to Master. Problem solved.


Page 13 of 95

Category Sl.no. Problem Solution MISC 1. During Start-up operation, ID Fan has tripped on

“Source Overcurrent” on channel Ch-1 and Load

Overcurrent” on channel Ch-2. Overcurrent relays

operated on load breaker switch.

Restarted the drive but again tripped on the same

fault. LMODE on HHT not changed from ‘0’.

1. Conducted all tests-found OK. Run in Local mode and

motor in uncoupled condition. OK.

Motor coupled back and started drive with slightly

higher CRSTART & FRSTART. Motor start and run was

OK from both channels. Normalised CRSTART &

FRSTART to original values.

This phenomenon happens after long shut down, when

oil film under fan bearing not built-up or inlet damper,

inlet and outlet gates not properly closed during start.

Customer has been asked to check these points.

MISC 2. Channel tripping several times due to various faults. Customer feels that mother board is not giving proper

contact to SEM modules which causes frequent trips. Has

requested to change all mother boards or provide

alternative modified female connectors in mother board.

BHEL-EDN sent SEM lock bars to customer and the same

was installed on all SEM modules. Problem solved.


Page 14 of 95

Category Sl.no. Problem Solution MISC 1. ID Fan 6A suddenly got unloaded even though motor

contactors are ON. ID Fan 6A currents suddenly

dropped to zero.

FD Fan 6A did not trip on interlock ID Fan 6A

Speed<Min.

Both fans were hand tripped, restarted.

ID Fan 6A hand tripped and FD Fan 6A tripped on

“ID Fan Speed <Min”.

220 VDC supply from distribution board failed and

therefore contactor did not trip. Further STOP command

was issued from I&C to both channels as 220V DC supply

had failed.

Further customer asked to check in I&C system whether

MAMS has been taken for MFT1, MFT2, MFT3 in FSSS

for ID Fan OFF. Customer confirmed that same has been

done.

PLL FAULT 2. Channel tripping frequently on “PLL Fault”. After

manual reset, channel comes into service.

SEM not earthed properly. SEM earthing done as per SEM

Earthing document. Problem solved.

GROUND FAULT 3. Slave channel tripped on Ground Fault.

Flex leads at motor terminal box had got melted and

neutral point on bushing was burnt out. Motor stopped,

rectification done by putting HT Insulation tape.

MISC 4. Fan started from standstill and did not start. Fan

did not pick up speed and was rotating very slowly in

the wrong direction..

Suspected No flux build up possibly because of melting of

field lead connections inside motor rotor exciter.

STIM, FRSTART, CRSTART increased. Motor Started.

Parameters changed to old values and start trials taken

were successful. Old parameters retained.

Reason- High breakaway torque. Subsequent starts were

OK because oil film was formed between bearing metal &

shaft, causing lower breakaway torque.

LOAD

COMMUTATION

FAILURE

5. 5A2 channel tripped on ”Load Commutation failure Found thyristor in leg module LTM3 defective. Both

thyristors were shorted out. Replaced leg module. Problem

solved.

FAILURE TO

START

6. 6A Ch-1 started, LMODE did not increase from ‘1’

many times in spite of changing parameters like

MTRFMIN, FLUXS, STIM, CRSTART, FRSTART

etc. Suspected motor winding may be faulty.

Found that snubber in STM6 was faulty. Capacitor was

shorted. Replaced snubber. Problem solved.

Customer asked to check bearing alignment on Fan bearing

in next shutdown.


Page 15 of 95

Connected Ch-2 winding of motor to Ch-1 of LCI.

Problem persists.

LOAD

COMMUTATION

FAILURE

7. Channel tripping on “Load Commutation Failure” in

5B1 and “PLL Fault” in 6A1.

HPTF cards changed in both channels after doing crowbar.

SEM earthing done as per SEM Earthing document.

Problem solved.

MISC 8. There was a heavy jerk on grid and due to that

almost all 210MW units tripped out. When starting

and taking ID Fans on load, found that Fan B was not

taking load, but Fan A was getting loaded. Currents

and voltages in both channels equal in Fan B. This

phenomenon was present even when Fan B was run at

700 rpm.

Changed Slave to Master and vice versa. Problem persists.

This confirmed no problem in VFD. Found problem was in

Inlet damper to ID Fan. Damper was almost in closed

condition and would not open. Corrected damper problem.

Problem solved. OK.

MISC 9. When Ch-2 is individually started, Load contactor

closes, Field contactor closes but no current in

motor. But Ch-2 (Slave) can be paralleled with Ch-

1(Master) and is OK. If Ch-1 is tripped, then Ch-2

does not take the load and its current stays at zero.

FLDCN (Field Contactor close) was not true in Ch-2 when

running alone. Aux. contact of Field contactor was not OK.

Rectified. Problem solved.

MISC 10. Top mounted blower (one of the two) on the

synchronous motor was giving lot of sound and

needed replacement.

Load was reduced to 150MW by lowering the speed and

also the channel currents. The temperature of windings

dropped by 10 deg.C. Blower replaced and then vent load

raised. No rise in temperature of windings during change

of blowers. Problem solved.

Caution: It was advised to keep monitoring the winding

temperatures during the change and trip the motor if

winding temperature exceeded 120 deg.C. It must be

noted that there is no part load rating of the motor with

one blower of the two out of service. This is due to the

inherent construction of the heat exchanger and mounting

of blowers in the heat exchanger.


Page 16 of 95

MISC

R05, 1006, PH

11. Drive end bearing problem. Excessive vibration. Decision taken to change motor. Motor replaced and

following tests conducted on both channels:

a. Exciter test

b. Uncoupled run

c. Coupled run

The readings compared with those recorded during

commissioning/annual overhaul, especially observing the

readings of exciter voltage and exciter current for Sl.b

and c. All readings found in order. Fan taken into service

with new motor.

Formatted: Bullets and Numbering


Page 17 of 95

Category Sl.no. Problem Solution MISC 1. 1. Channel B2 tripped on “Motor Isolator not

closed.”

2. Second time tripped.

1. Breaker closing link was not latching and breaker was

tripping immediately after closing (Mechanical

problem). Breaker truck replaced and channel started.

Found that latching mechanism was faulty. Faulty part

replaced and CB truck tested and kept ready for


2. Fault resetted and started.

LOAD

COMMUTATION

FAILURE

2. Channel B1 tripped on “Load Commutation Failure” 1. Checked load bridge capacitances for charging

currents with megger – OK..

2. Checked MOVs of load bridge for Insulation

resistance.- OK.

3. Checked gate pulses on HPTK card in gate test mode.

One HPTK card pulse not OK. Replaced card. Problem

solved.

MISC 3. “Bus hog “ error on HMPG card. Inserted HMPG card properly.

Put lock bars on SEM rack.

Also checked whether EPROMS are inserted properly on

HMPG/DMPB. Problem solved.

SOURCE

UNDERVOLTAGE

4. Tripping on “Source Undervoltage when BFP started

and during fast bus changeover from unit to station.

Source Undervoltage alarm appears immediately but

“Source Low line” fault appears after sometime.

It was observed that source voltage dips below u/v set

value whenever MDBFP starts. This is because of very high

Inrush current in MDBFP. Changed source u/v setting to a

lower value as per site requirement. Problem solved.

MISC 5. Abnormal sound of blower in panel. Due to damaged bearing of fan.

Bearing changed and fan replaced. Problem solved.

MISC 6. 2 nos. temp. scanners are malfunctioning. Hence

tripping removed. However, winding temp. and

bearing temp. tripping from I/C panel is in service.

BHEL agreed to repair the faulty scanners. Scanners sent

to BHEL-EDN for repair.


Page 18 of 95

MISC 7. Speed indicating at VFD panel and actual speed are

matching. Speed at PMS not matching.

BHEL has requested to adjust the mA reading as per

procedure given in VFD O&M manual, Vol1-Book1-Chapter

Clause 6.15.4 & 5.

EDN reply-The speed signal o/p from VFD to Plant C&I is

only for Indication Purpose & not for regulation/control.

Speed feedback on all channels adjusted. Speed reading on

PMS and actual speed are matching.

COOLING

BLOWER LOSS

8. Alarm “Cooling blower loss on Ch-1 and tripped on

“Loss of cooling fan”. But blowers running normal.

Fault resetted and drive started.

Cooling blower contactor dropped. 415V UV has occurred

for a time greater than normal leading to this trip.

MISC

9. Fan tripped without any indication.

Tripped due to failure of SEM supply.

Fan tripped without any indication.

Fan tripped without any indication.

MCB of PSFF had tripped. MCB reset and made ‘ON’. PSFF

was malfunctioning in this channel.

Site concerned about momentary malfunctioning of

electronic cards since on next starts, card behaves normal.

Sometimes, no alarm is annunciated.

EDN replies that tripping of VFD channel & becoming OK

after MP reset could be due to:

a. Dust accumulation on PCBs

b. Loose connection between card & backplane connector.

All cards, Power modules, Power supplies cleaned with

blower. Problem solved.

Failure of HRIA card. Failure due to RUNX relay failure.

HRIA replaced and channel restarted.

Processor found hanged. Control supply made ON/OFF.

Processor normalised and restarted.

GROUND FAULT 10. Channel tripped on ground fault. Fault resetted and channel started smoothly. Problem may

be due to :

a. Loose connection in load side connections (busbars,


Page 19 of 95

connector, earthing lug on HPTK, SEM Earthing.)

b. Loose connection on star point of load side filter

capacitor circuit.

c. Check voltage setting.

Site says all connections above have been found normal.

Suspected transient ground fault as there were no failures

of components to detect the same.

SOURCE

COMMUTATION

FAILURE

11. Tripped with following indication on printouts:

a. Source O/C b. Load Commutation failure c. Load

O/C d. Source commutation failure.

b. Channel could not be restarted, tripping on same

faults and hunting in currents.

1. UPS voltage at panel checked and found OK.

2. Source side thyristor STM4 found failed. Replaced

module STM4 and channel taken into service. OK.

MISC 12. ID Fan B-1 speed was locked at in running condition. HMPG found hanged. HMPG resetted and fan started.

Could be due to loose connection of HMPG.

Site advised to put lock bars on SEM. Problem solved.

SHORTED MOTOR

WINDING & LOAD

COMMUTATION

FAILURE

13. Fan B1 tripped once on a) Load commutation failure

b) Bridge filter fuse c) Shorted motor winding

Second time on a) Load Commutation Failure

Third time on a) Load Commutation Failure b)

Shorted motor winding

1. HPTK card found faulty after checking waveforms in

gate test mode. Replaced card.

2. Y ph thyristor in field exciter module had failed.

Calibration of field current feedback was wrong. Same

corrected. (in A1)

I/O PROBLEM 14. Tripped on indications:

a) Motor Isolator not closed. b) RUNP missing c)

Bridge filter fuse

Fault indications were false. Fault reset and drive

restarted. Suspected UPS feeder supply problem.

I/O PROBLEM 15. C1 tripped on

a. Source PLL Fault

b. STARTP/RUNP missing.

Fault resetted and channel restarted.

Suspected UPS feeder supply problem.

MISC 16. Channel tripped. 11kV Source breaker tripped on

IDMT O/C protection relay. No indication on VFD

before tripping.

Relay resetted and channel restarted.

Malfunctioning of IDMT relay suspected.

MISC 17. HD of 5th harmonic of VFD system is 30%. To be

confirmed.

30% HD for 5th harmonic current is acceptable as it is in

the case of all thyristor bridges. Voltage distortion is <5%


Page 20 of 95

on 11kV VFD bus due to VFD operation which satisfies

requirement as per IEEE 519.

MISC 18. Channel tripped on “Circuit Breaker protection”

indication.

Investigation reveals all the thyristors in one power

module failed. Cause of the failure was that stud got

sheared. Replaced studs in all power modules wherever

failure suspected. OK.

LOAD PLL FAULT 19. Channel tripped on “Load PLL Fault Balanced Voltages at NLIB(1D) by back charging from

master channel and made voltages at FAB,FBC and FCA

equal with offset zero below 30mV DC. Channel taken into

service. OK.

MISC 20. Channel tripped with Bushog Led on HMPG Same not

resetting.

Replaced HMPGDMPB. Checked that the 6 nos. of

EPROMs are installed correctly. Problem solved.

SHORTED MOTOR

WINDING

21. Channel tripped on “Shorted Motor winding”. 1. Check thyristor healthiness.-OK.

2. Reset and restarted - tripped.

3. Dry solder in voltage attenuator circuit on XPTN

card. Attended dry solder, Self test halted at 29 &

gate test also halted. LVSH on NPSJ card in PSFF

module was not present. NPSJ replaced and restarted.

Check to be done on Berg jumper position in XPTN during

card replacement. Channel taken into service. OK.

I/O PROBLEM 22. Channel tripping on blower loss. Blower selection contact “Bottom blower selected” not

wired to IOMA card. Same done. Problem solved.

MISC 23. HMPG card did not pass Self Test. Hangs midway. Replace HMPG Put EPROMs U22, U23, U24, U25, U02, U03

and EEPROMs U04,U05 from old card in respective slots

in the new card. Lock bar to be put in SEM Rack. Problem

solved.

GATING SUPPLY

UNDERVOLTAGE

24. Tripped on Gate supply u/v. 1. In gate test mode, HPTK card in LTM1, 1A fuse blown

Replaced and started. OK.

2. MCB ‘CB2’ feeding electronic modules found tripped.

“NTRF” card in PS7 module found faulty. Replaced.

Problem solved.


Page 21 of 95

Category Sl.no. Problem Solution SOURCE

OVERCURRENT &

LOAD

OVERCURRENT

1. Speed not raising beyond 140rpm (Rated =

700rpm). Current hunting in 2 channels.

Channel tripped on “Source and Load Suppression

Fault”

Source side attenuation voltage feedback not

available.

1. 1st channel –Current hunting due to improper voltage

feedback from source bridge due to failure of

attenuator in HPTF card. Replaced HPTF. Problem

solved.

2. 2nd channel – Wrong polarity of current feedbacks

from motor side CTs.

3. Changed NLCB card. No change observed. Original

card put back in rack.

4. Checked ribbon cable from IOMA is properly seated

on the SEM header. 4-20mA not reaching SEM.

Pressed connector & became OK.

5. Conducted crowbar test. Crowbar test OK.

Motor with both channels taken into service. OK.

MISC 2. Self test not going through. Each time test failed in

different steps.(2 racks)

0PAR signal was pulled down by defective NLIB cards.

Replaced NLIB cards in the 2 racks. Problem solved.

MISC 3. HMPG did not recognise status of running blowers

even when blowers were run. Hence Source breaker

close permissive was not available.

HMPG found defective. Replaced the 6 EPROMs from the

defective card. Ensured that they are put in the correct

position with correct polarity. Channel started. OK.

GROUND FAULT 4. Tripping on ground fault whenever speed raised

beyond 500rpm and motor volts is 500V without

any fault in motor or cable.

1. Replaced HLCB card. No change observed. Original

card put back in SEM rack.

2. 3 MOVs MOV1, MOV2 and MOV4 failed at a much

less voltage than designed.

Checked wiring in panel. Found wrong wiring. Corrected

the same. Drive taken into service. OK.

MISC 5. Cleared crowbar test. But motor not starting

smoothly. Current going to inversion.

1. Check whether CT feedback polarity is reversed on the

load side. Corrected polarity of load side CT.


Page 22 of 95

2. One leg of load thyristor bridge conducting. Changed

HPTF. OK.

Drive taken into service.

MISC 6. During crowbar test, one thyristor cell found not

conducting.

One thyristor found not conducting. Gate resistance found

abnormally high. Replaced thyristor cell. OK.

LOAD

COMMUTATION

FAILURE

7. Unit tripped frequently on “Load Commutation

failure causing Unit trip out.

1. UPS voltage found low, changed transformer tap to

raise the input voltage.

2. Conducted crowbar test. OK. Drive taken into service.

LOAD PLL FAULT 8. Channel tripping on Load PLL Fault. 1. Conducted crowbar test. Test was not OK.

2. Shorted DC buses on load side with DC Link Reactor in

circuit. Conducted crowbar test. Test OK.

3. Changed NSFC load and conducted crowbar test. Test

not OK.

4. Checked all thyristors and snubbers on load side

bridge. All OK.

5. Checked pulses to gate of all load side thyristors, with

current probe. OK.

6. Removed individual thyristor module on load side. Found

that tightening studs on LTM1 was loose. Tightened

the same.

7. Conducted crowbar test after removing DC bus short

on load side. Crowbar test OK.

8. Channel taken into service. OK.

NOTE: When putting back power module, pulse ribbon

cable and attenuator connector must be put in the correct

direction.

MISC 9. Channel tripped without any ‘fault’ indication and

“Bushog” LED on HMPG came ON.

Lock bar at SEM centre installed.

Checked SEM fan direction of rotation. OK.

Channel taken into service.

MISC 10. Sparking on contactor MISOL. MISOL found Cleaned contact with sandpaper and CTC and drive taken


Page 23 of 95

damaged.

into service. OK.

MISC 11. VFD trips on u/v condition of control supply. VFD trf. 110V/110V given for rectification sent to site.

Customer was told to check UPS feeder voltage. Changed

tap on trf. in VFD panel C & EXE cubicle feeding

electronics. OK.

MISC 12. Reference voltage keeps varying even with constant

demand signal. Causes Drive hunting.

Motor speed and current changing at I&C, even

though steady at panel.

SPD test point gives 14V even when speed is zero.

Motor Speed and current indication at both local &

remote are erratic.

Replaced NLCB. Problem solved.

Replaced NLCB. Problem solved.

Replaced DLCB. Problem solved.

Replaced NLCB Problem solved.

MISC 13. Printer works OK in test mode, but does not print

Status/Fault from SEM

Replaced Printer. Printer sent for repair to BHEL-EDN.

I/O PROBLEM 14. HRDD does not give output LEDs and voltages

corresponding to existing status.

Replaced HRDD. Problem solved. Card sent for repair to

BHEL-EDN.

FAILURE TO

START

15. Motor crawling during starting and did not pick up

speed.

Changed parameters FRSTART, MTRFMIN and CRSTART

to slightly higher values.

Inlet and outlet gates on ID Fan duct not closed properly.

OK.

MISC 16. Channels getting unloaded with all operating

conditions normal.

Suspected due to dust accumulation on firing cards.

Firing cards cleaned by air blowing. OK.

MISC 17. Drives could not go to current limit and increase the

fan speed due to clamp on speed reference from

I&C system (Auto clamping).

Investigation to be done by customer during shutdown at

I&C system.


Page 24 of 95

LOAD

COMMUTATION

FAILURE

18. Channel tripping due to Load Commutation failure

Running normal after fault reset.

Loose connections in the CT feedback.

Improper earthing of SEM Rack.

SEM Rack earthed as per SEM Earthing document. Drive

taken into service. OK.

I/O PROBLEM 19. Channel tripping on Bridge Differential Pressure

fault when taken into service.

Channel started, after crossing min. speed, current

started hunting and tripped on Load Commutation

failure. Crowbar test was done for power ckt. check,

one hump missing in current waveform.

Current hunting when channel taken into service.

IOMA found faulty. Replaced IOMA.

HPTF card in source bridge found failed. Replaced and

became OK.

Load side cards not firing correctly or in sequence. One

HPTF card, both neons did not switch On/Off together.

HPTF card faulty. Replaced and Problem solved.

I/O PROBLEM 20. When RUN relay energised, BDIFSW (IOMA TB6-

08) goes high, HMPG senses this as Bridge

Differential Pressure Fault & drive trips.

To be checked in test jig of repair cell at BHEL-EDN.

Energise RUN relay in IOMA. Check if TP8 in HRIA(2A)

goes high, JJ pin 22 on SEM header goes high, flicker of

LED I15 on HISA 1B.

IOMA checked in repair cell but no fault found. Replaced

the two mother boards on IOMA. Retested and

despatched to site. Suspected tracking problem on mother

board.

MISC 21. Slave channel and Master channel can individually

start and run. But Slave channel cannot be paralleled

with Master. If paralleling is done, current in slave

remains at zero.

Backcharge Slave with Master running and adjust FAB,

FBC, FCA on NLIB Load of Slave same as Master. Use the

same multimeter.

Found Slave adjustment was not OK. Adjusted. Problem

solved.

SOURCE

UNDERVOLTAGE

22. Source Undervoltage fault even though Source

voltage is OK.

Asked to check voltage feedback circuit from HPTF

attenuator to NSFC and also line voltages on NSFC

backplane. Found Y phase Source attenuator not OK.

Replaced. Problem solved.


Page 25 of 95

Site was also asked to check whether the ground pillar on

HPTF is not loose (dry solder) before sending HPTF card

for repair.

MISC 23. Ch-1 and Ch-2 speed meters not matching. Speed meter does not have pot.

Customer advised to adjust LCI door 10V DC speed meter

after seeing counts 1024=60Hz=900rpm. Told to adjust

SPM pot only.

Problem solved.

MISC 24. Channel trips without any fault or alarm message.

RUN light is ON but channel gets unloaded

current=0.

All SEM voltages O.K.

Gate test not O.K. Self test done. Failed in test 06:

NSFC-2C. Replaced NSFC –2C. Problem solved.

MOTOR OVER

TEMPERATURE

25. System trouble annunciation appeared and Motor

Overtemperature Alarm appeared on Local panel.

Temperature scanner displayed 89 to 91 deg.C.

Similar readings found in I&C CRTs leading to

conclusion that there is an actual rise in Stator

winding temperature.

Load on channel reduced to half for about an hour and

normalised. Temperatures came down and alarm got

cleared.

Cooling blower motor found to be rotating in the reverse

direction. Direction of rotation restored to normalcy.

Temperature of motor reached a max. of 74 deg.C.

LOAD

COMMUTATION

FAILURE

R05, 1206, PH

26. Slave channel trips on Load Commutation Failure as

soon as it is paralleled with MASTER at minimum

speed. This is the first time after annual shutdown.

Back-charged Slave (Ch-2) with Ch-1 running. Found

unbalance in voltage on NSFC load. Found that attenuator

resistor LTM2 on HPTF open and 10 pin connector not

inserted properly. Changed HPTF card. Channel taken into


LCI CHANNELS FOR VFD – COMPENDIUM OF FAULTS

Page 26 of 95

Category Sl.no. Problem Solution MISC 1. Channel starts but gives loss of speed reference

though 4mA reference is present.

Customer asked to check I&C reference. Must be 4mA

minimum.

FIELD

OVERCURRENT

2. VFD Field Overcurrent problem. Adjusted Field current feedback at SEM card. Problem

solved.

LOAD PLL FAULT 3. During starting, VFD trips on “Load PLL Fault”.

Firing pulses not getting released in Gate Test

mode even though Self test passes.

1. Variable components on NLIB-1C and 1D not as per

scheme.

2. Pin-72 of HAIA had got dislodged. Not making proper

contact on the backplane.

3. Rectified sl.no.1&2 above. Problem solved.

FIELD

OVERCURRENT

4. Channel tripping on Field Overcurrent. Checked cable of AC Input Exciter, was getting heated.

Power termination inside the module found loose.

Tightened and became OK. Drive taken into service.

I/O PROBLEM 5. HROA found malfunctioning. MAMX and ALARMX

relays remain latched even if fan is in stopped

condition & there is no alarm in the system.

HROA replaced. Drive taken into service. OK. Card sent

for repair to BHEL-EDN.

I/O PROBLEM 6. Self test Crowbar test excitation power test done

in Channel 1 & 2 of 3A.

1. 1 no. HROA card found defective in 3A1. Replaced.

2. 1 no. NSFC card replaced in 3A2.

3. Drive taken into service.

4. Cards sent for repair to BHEL-EDN.

MISC 7. Channel taking more time to start and come to

minimum speed.

This behaviour was not observed during

commissioning.

BHEL stated this may happen due to additional loading of

the fan during starting.

This happens if inlet damper at ID Fan is not closed

properly.

MISC 8. FD Fan trips when MAMSX and ALAMX relays drop

due to momentary voltage dips or voltage jerk

condition.

Suggested to introduce time delay (off delay) of 1.5secs.

for FD Fan tripping when MAMSX drops. Problem solved.


Page 27 of 95

MISC 9. Unbalanced field currents when channel is taken

into service.

Due to irregular firing of thyristors in NHVL card.

Replaced NHVL Problem solved.

MISC 10. When 220V DC fails, VFD motor contactor will not

trip even though power to motor is cut-off.

No harm to VFD system due to 220V DC supply failure.

I&C system will issue STOP to both channels. Load side

contactor will trip when 220V DC is re-established. Hence

no modification required.

MISC 11. ID fan tripping was provided through temp.

scanners in addition to direct C&I trippings. Any

malfunctioning of temp. scanner caused ID Fan

tripping.

Temp. scanners replaced. Temp. scanners used for Alarm

purpose only. Bearing and Winding temp. tripping is kept

through C&I only.

MISC 12. Malfunctioning of Door interlock switches provided

in ID Fan panel door (to trip the channel if door is

opened during channel running.) causing channel

tripping.

Door switch bypassed and ensured that door is always in

locked condition during channel running. Interlock switch

will be replaced during next shutdown.

MISC 13. When Ch-1 is running at 400A and Ch-2 is started,

Ch-2 current shot upto 600A for 1 minute and

slowly came down to 400A.

It seems that the flux in Ch-2 was much higher than in Ch-

1. Therefore Ch-2 which is the Slave channel tries to

correct the flux by increasing its armature current and

thus trying to de-magnetise the flux. Flux closed loop in

the slave is also in operation.

NLIB Load fluxes FAB, FBC, FCA in Ch-2 adjusted to the

same values as in Ch-1 by backcharging Ch-2. Tune up

values relating to flux in Ch-2 checked to be the same as

that of Ch-1. Problem solved.

LOAD

COMMUTATION

FAILURE

REV.04

14. Master channel tripping on Load Commutation

failure. Slave channel current remains at minimum

when working with Master, but OK when run

independently.

Channel trips again on Load Commutation failure.

Found in Master channel that the ripple was very high in

28Volts DC when compared to healthy channel. PSFF

replaced. Found Electrolytic capacitor in PSFF faulty in

28V DC circuit. Channel taken into service.

Crowbar test conducted. Found one HPTK card on Load

side faulty. Changed. Master Channel taken into service.

OK. But Slave channel current goes to minimum when

Master is taken into service. Found Analog 0-10V current


Page 28 of 95

signal from Master not OK in Slave. Loose connection of

wire at IOMA TB. Rectified. Problem solved.

LOAD

COMMUTATION

FAILURE

R04

14. Master channel tripping on Load Commutation

failure. Slave channel current remains at minimum

when working with Master,but OK when running

independently.

Channel trips again on Load Commutation failure.

Found in Master channel that the ripple was very high in

28Volts DC when compared to healthy channel. PSFF

replaced. Found Electrolytic capacitor in PSFF faulty in

28V DC circuit. Channel taken into service.

Crowbar test conducted. Found one HPTK card on Load

side faulty. Changed. Master Channel taken into service.

OK. But Slave channel current goes to minimum when

Master is taken into service. Found analog 0-10V signal

from Master not OK in Slave. Loose connection of wire at

IOMA TB. Rectified. Problem solved.

FIELD LOSS

R05, 1206, PH

15. Master channel trips on Field loss. ID Fan continues

to run on Slave channel. Due to grid conditions, ID

Fan cannot be taken out of service.

Connections on IOMA TBs removed as per list given in

Annexure-4 for Crowbar test. Incoming wires to

excitation contactor R,Y,B disconnected. Dummy load of

Halogen lamps connected. Conducted exciter test. Found no

current in one phase. Problem traced to bad connection to

one of the thyristor gate in Exciter box in 4 pin white

molex conector Rectified the same.

Conducted exciter test again and found current is

balanced. Normalised all connections and took MASTER

channel into service. Problem solved.

FIELD LOSS

R05, 0407, PH

16. Master Channel trips on Field loss. Due to

constraints, shutdown of fan not given. Exciter test

to be conducted on Master with Slave channel

running.

Connections on MASTER channel IOMA TBs removed as

given in Annexure for conducting Exciter test with other

channel running. Removed cable at output of field exciter

R,Y,B and isolated the same. Connected dummy load at field

exciter output(halogen and incandescent lamps). Performed

field exciter test. Found that one phase current was very

low compared to other. On investigation, found that 4 pin

white Molex connector carrying firing pulses to one

thyristor pin was loose and not mating properly with

connector on NHVL board. Rectified the same. Conducted


Page 29 of 95

Field exciter test. Currents balanced. OK. Restored R,Y,B

field of exciter connections and IOMA connections.


NOTE: CARE TO BE TAKEN WHEN DOING THE

ABOVE. CONFIRM THAT R,Y,B POWER CABLES ARE

ISOLATED AND TAPED PROPERLY.


Page 30 of 95

Category Sl.no. Problem Solution MISC 1. Tripping on undervoltage. 1. Changed C17 on DLIB to 0.47µF from 0.047µF. Did not

solve the problem.

2. LT supply to Control panel changed to Unit LT Bus

instead of Station LT bus.(voltage will not be steady

because external grid disturbances will get reflected

to this).

3. Found that timers in Control Panel were ON delay

instead of OFF delay. Changed timers to OFF delay

type.

4. Problem solved.

MISC 2. One no. thyristor module on load side failed in BFP

10C. All 3 nos. series thyristors got shorted.

Module replaced with healthy power module. Faulty module

sent to BHEL-EDN for repair.

MISC 3. System tripped without any annunciation.

HMPG hanged and test led is glowing.

1. Check if all EPROMs and EEPROMS on HMPG/DMPB

are properly seated. Found OK.

2. Check SEM Lock bar is put and all card top and bottom

locks are firm. Found OK.

3. Check if SEM frame is locked to the panel using the L-

angle provided. Found OK.

4. Found out that even though SEM locking bar is put,

there is clearance between lock bar foam and card.

5. EDN sent lock bars with thicker foam for all SEM

modules so that bars are in contact with all the cards.

Problem solved.

MISC 4. Problem of crowbar test.

Channel current is found hunting for a load beyond

350A.

Malfunctioning of HAIA card.

1. C1-Exciter output found abnormal. One thyristor of

EVC was not conducting. Replaced & OK.

2. C2-NHVL card of EVC found defective. Replaced and


Page 31 of 95

No hunting observed.

3. Replace NLIB –Source card.

4. NHVL – only 2 lamps found glowing. Channel manually

tripped. HMPG thoroughly cleaned and restarted. No

hunting observed.

5 . FCLIM values increased. Speed meters for all 4

channels calibrated.

6. Speed regulator gain changed from 35 to 25.

EDN suggested checking of exciter feedbacks during

calibration.

FIELD LOSS 5. Feedback of NHVL card is not coming.

Only 2 Leds on NHVL card are glowing.

Replaced NHVL card.

HMPG, HLCB & NSFE replaced. Cards sent for repair to

BHEL-EDN.

MISC 6. Field current saturates above certain load. ID Fan was getting overloaded. Customer requested to

check whether the loading is as per the load points given in

Motor data sheet in O&M Manual. Also inlet damper

position to be checked. Problem solved.

SOURCE PLL

FAULT

7. Channel tripped on Source PLL Fault. 1. Ribbon cables are tightened.

2. If trips again, recommended to replace HLCB card.

MISC 8. Channel tripping frequently on SEM power supply

(PSFF) failure.

BHEL recommended to decrease AC temperature in VFD

Room for better cooling and provide internal fan for

channel. If not solved, Replace PSFF.

Recommended temperature in AC VFD room is 25°C.

Replaced MCB in PSFF. Problem solved.

MISC 9. Unequal field current in 10A & 10B. 10A taking 20A

more current than 10B.

Load on 10A is more than 10B, at same speed. Hence

higher stator current and also field current.

MISC 10. Motors not attaining full speed of 740rpm for 100%

demand.

Motor does not have sufficient reserve torque to

accelerate beyond a certain speed and excitation current

limit is being reached.

LOAD PLL FAULT 11. PLL Fault and Motor shorted winding Fault. Load side thyristor electrical connections tightened.


Page 32 of 95

& SHORTED

MOTOR WINDING

Loose connection of Load attenuator wire from Local AC

Busbar found. Problem solved.

FAILURE TO

START

12. Motor rotates in the correct direction very slowly,

when run either from Ch-1 or Ch-2.

Motor was in service earlier from both channels. Individual

channel running was also proved. Therefore suspected

motor.

Found that DC cable in motor from output of exciter

diode bridge to main field had melted at lug point.

BHEL-BHOPAL representatives called to site. Changed

cable. Problem solved.

MISC 13. Output Contactor was not holding after close

command was given. Contactor is M/s.

Telemachanique make Magnetic latch type

CR1BL33M21. Magnet face OK.

Adjusted cam that actuates the contacts for the coil

control circuit on the contactor. Channel taken into

service. OK. Problem solved.

LOAD

COMMUTATION

FAILURE

14. Slave channel of BFP trips on Load Commutation

failure randomly.

SEM grounding, panel grounding checked and found OK.

Changed HLCB card. Problem solved.

SHORTED MOTOR

WINDING

15. Master channel tripping on Shorted Motor Winding. Changed Slave to Master and vice versa. Backcharged

Slave from Master. Adjusted Slave NLIB load fluxes to

same as Master. Problem solved.

LOAD

COMMUTATION

FAILURE

R05, 0107, VI

16. Slave channel of Boiler Feed Pump trips

intermittently on Load Commutation Failure. This is

accompanied by failure of one thyristor device in

Load side bridge.

Checked Earthing of SEM and all other connections

including panel Earth Bus earthing. Found pulse height in

gate test mode on one load side module not OK. Replaced

HPTK card. Suspected track problem in NTDA on one

thyristor during gate test mode. Replaced NTDA.

Added extra wraps to DCOM from NSFC and NSFE pin

37. Replaced NSFE card as this was not passing Selftest.

Pump taken into service with both channels.


Page 33 of 95


Page 34 of 95

Category Sl.no. Problem Solution MISC 1. Flickering of LEDs on HPTK cards both in

rectifier and Inverter in Gate Test Mode.

Problem solved by changing HPTK cards.

BRIDGE

DIFFERENTIAL

PRESSURE

2. “Bridge Differential Pressure” message appearing

in the printer in spite of blowers running.

1. Check cable connection from AFM to IO module. OK.

2. Replaced Air Flow monitor. Problem solved.

LOAD PLL FAULT 3. At rated speed, fluctuations observed in main power

supply to motor, accompanied by unbalanced

excitation parameters.

Voltage sensed by VFD was higher.

Motor speed could not be increased beyond 400rpm

and VFD tripping on “LOAD PLL FAULT”.

1. Jumper setting in HPTK Voltage attenuator circuit

corrected.

2. Exciter phase sequence wrong.

Problem solved.

EDN insisted that VFD room should be maintained dust

free.

FAILURE TO

START

4. Channel tripped on Microprocessor alarm.

Hunting observed. Crowbar and EVC test found OK.

CRSTART modified from 0.3 to 0.5 and started.

Hunting persists.

Snubber bar assembly LTM2 and LTM5 were found open.

Replaced Snubber Bar Assembly & started.

Load current CT feedback cable(10 pin) on SEM header

found reversed. Inserted in correct direction. Problem

solved.

MISC 5. Run light always ON. Backplane wire wrapping problem. Corrected. Problem

solved.

P105

UNDERVOLTAGE

6. Channel tripping due to P105 u/v. Changed DPSA card.

Changed DPSA power supply.

Mounting of power supply found loose(no screw). Also, AC

input to the card has been reduced to 110V by adjusting

tap position to the input transformer. Problem solved.


Page 35 of 95

MISC 7. Self Test fails at 2001. EDN says problem is in Self test circuits only. Site asked

to go ahead with motor running. This circuit does not have

any function when drive is in service.

MISC 8. Could not go to Gate Test mode. Corrected offset zero on NLIB Load and NLIB Source

FAB, FBC & FCA with test oscillator ON by slightly

adjusting BAL1 and BAL2 potentiometers on NLCB Then

changed MTRFMIN and FLUXS to 0.2 and 0.1 respectively.

Problem solved.

MISC 9. “MAMS relay not getting reset even after VFD is

stopped (Speed is zero).

HRDA card found faulty. Replaced. Problem solved.

MISC 10. Speed suddenly reached 500rpm and unit tripped on

furnace pressure very low.

Due to sudden high set point from I&C 4-20mA signal.

Corrected problem at I&C. Problem solved.

MISC 11. ID Fan Auto control is not working properly. Hunting

in current when Furnace pressure controller is put in

Auto mode.

Customer asked to change P & I values in PI furnace draft

controller in I&C system. Problem solved.

MISC 12. Controller very slow. May damage VFD/motor.

Clearance asked to make controller fast.

Customer asked to time furnace draft PI controller at I&C

system for optimum performance to suit system

requirement. Problem solved.

MISC 13. VFD did not stop with Stop command from DCS,

Filed stop PB. Finally stopped with Emergency Stop

PB from 6.6kV.

Speed does not vary with input signal and

communication to HRDA card fails.

Due to Bushog problem in HMPG Suspected loose

connection between HMPG and mother board on SEM rack.

HMPG cleaned and inserted in rack. Lock bar put. Problem

solved.

MISC 14. Drives reached rated currents at less than rated

speed.

Current drawn at 705 rpm (max.) is exceeding

rated current in 3 motors.

Current limit to be raised by raising the value of SRCLSC

by 10% to increase the speed further. This can be done as

there is margin in motor and VFD. Problem solved.

MISC 15. HMPG IMOK Led was going OFF resulting in tripping

of 6.6kV breaker.

Problem temporarily removed after tightening of

SEM front bar plates. Problem persists & repeats

after 2 days.

Due to vibration of SEM Rack.

Source of vibration-SEM Rack cooling fan. Fan replaced.

Problem solved.


Page 36 of 95

MISC 16. During starting, Stop command was being given by

C&I system.

Due to higher time taken to achieve minimum speed of

145rpm from standstill. Timing in C&I increased from 30

secs to 60 secs. Problem solved.

MISC 17. One no. Neon lamp of XPTN card on load side

thyristor module is not glowing.

Corresponding thyristor found failed. Replaced thyristor

module and sent faulty thyristor module to BHEL-EDN for

repair.

MISC 18. Current and voltage at motor isolator switch is not

matching with the corresponding values at control

and excitation panel.

There will be difference in indication upto 25Hz. Over this

the indications will be nearly same. This is due to

saturation in the metering core of CT at low frequency.

Indications in VFD panel to be taken as actual.

MISC 19. The maximum speed at 100% demand from control

room is below rated speed. i.e. 725rpm in all 3

motors.

Current drawn at 705rpm is exceeding the rated

current of all 3 motors.

Since VFD is a current limited drive, speed can increase

only upto the current limit set. Customer asked to check

inlet damper position and verify whether it is as per

recommendation.

MISC 20. Microprocessor alarm appears. IMOK of HMPG and

NLCB disappears and subsequent tripping of 6.6kV

breaker occurs.

Frequent tripping of Fan on various faults.

1. Observe whether the fault appears under the conditions:

a. Only Auxiliaries ON, HT supply OFF to VFD

b. With HT & auxiliaries ON, drive not running

c. With drive running.

2. Check voltage levels of P5, P15, N15 & P28 supplies.

3. Check the status of Alarm Word.

4. Replace all 6 EPROMS (4 on HMPG & 2 on DMPB).

5. Check if SEM earthing is as per SEM Earthing

document.

6. Since sl.1 to 5 did not lead to any definite reason,

SEM rack was changed. The original cards were

returned. Lock bar of SEM put.

7. Problem was solved.

MISC 21. Fan tripped with Motor Overtemperature Alarm and

Overtemperature Trip. Found MCBs CB1, CB2, CB4

and CB13 in control panel tripped without actual

1. Could have been only due to fault in the circuit

connected to CB1 breaker. Checked all auxiliary

circuits including 110V contactors connected to CB1


Page 37 of 95

temp. rise in motor.

Subsequently motor did not start and “Rotor

position start alarm” was observed.

breaker for healthiness.

2. Motor opened and inspected. Found exciter wiring had

soot covering at some spots.

Exciter stator winding round carbonised. Motor

needs to be repaired/replaced with new one. Motor

sent to Bhopal for rectification of exciter rotor.

Received back at site.

LOAD

COMMUTATION

FAILURE

22. Channel tripping intermittently on Load Commutation

failure.

Channel tripped again after few hours.

Self test conducted. Speed feedback circuit found

malfunctioning in NLCB/DLCB.

Crowbar test conducted. Current feedbacks O/C

protection circuits checked, adjusted and started.

Channel tripped on “Load Commutation failure” again

after few hours.

HMPG, 5 nos. of NTDA cards changed.

Load side bridge thyristors, snubber ckt., CT circuit,

gating circuits checked. All terminations on HPTK and

NTDA cards checked for loose connections and

soldered/tightened/replaced wherever required.

DLCB replaced.

Firing pulses and load side HPTK cards, NSFC, related

cables checked. 2 HPTK cards on load side, reference for

detection of UV of gating supply was 1.3VDC while in

others it was 1.8VDC. This reference adjusted to 1.8V in all

HPTK cards.

Gating power supply voltage was low. Corrected this to

required level. Self test and Gate test passed. Channel

taken into service.

MISC 23. HMPG and NLCB IMOK going OFF. SEM cards to be thoroughly cleaned by blowing over SEM

with blower.

Check SEM lock bar is installed correctly and firmly. SEM

module is anchored properly. Drive taken into service.

GATING SUPPLY 24. UV chattering of relay in PS7 power supply. NTRF card in PS7 changed. Problem solved.


Page 38 of 95

UNDERVOLTAGE

FAULT

Card sent for repair to BHEL-EDN.

MISC 25. Drive tripping on Microprocessor Alarm and Stack

fault.

This type of problem is due to spurious interrupts which is

normally attributable to grounding.

Found that earth bus at rear of panel was sheared off at

panel end and also earthing bus was not continuous.

Incorporated jumper cables on earth bus and tightened

connections. Incorporated extra connections between

2A/34, 2B/34, 2C/34 to DCOM. Drive taken into service.

MISC 26. Channel LM100 Breaker from 110V UPS tripping

because current taken is too high (14 Amps). When

only SEM and IOMA are ON (drive stopped), the

current is 4 Amps. When drive is started, then

current jumps to 14 Amps. Normally, it should be

about 11 Amps.

PS70 output voltage was 84Volts DC on load. Voltage

lowered to 80 Volts DC by adjustment of pot. on NTRF.

Current came down to 11 Amps. Breaker did not trip.

Problem solved.

MISC

REV.04

27. Source breaker trips on Microprocessor Alarm

through SWGR relay on IOMA even when drive not

running.

Found that P28 fuse on PSFF was not properly put in

holder. Same tightened. NLIB Source changed and offset

adjusted to zero on FABR, FBCR, FCAR with Source

breaker closed. Drive taken into service. Problem solved.

SOURCE

UNDERVOLTAGE

R05, 1206, PH

28. ID FAN is 6 pulse drive. Drive starts and goes to

minimum speed but does not increase beyond this

either in LOCAL or REMOTE reference. Source

Undervoltage alarm comes frequently and MAMS

relay chatters. Motor currents unbalanced.

NLIB and NSFC load cards changed. Problem persisted.

Found that wire had got cut in the lug and was giving loose

connection at IOMA TB input LBKRS. The same was re-

lugged and tightened. Problem solved.


Page 39 of 95

Category Sl.no. Problem Solution MISC 1. Unbalance motor Currents upto 1.5A in blowers. Vendor has informed that unbalanced current of the motor

cannot cause any damage or reduce overall life expectancy

of blowers.

MISC 2. Failure of cards and intermittent failure of VFDs. Failure rate of cards could be high during commissioning

but extremely low after stabilisation.

Analysis-Most of the component failures attributed to

voltage mix-up and wrong cabling during pre-commissioning,

handling, dust accumulation during commissioning.

LOSS OF

COLLING FAN

3. Channels tripped on Blower loss. Due to tripping of blower supply to ID Fan because of

flashover in ESP LT switchgear.

Customer requested to provide individual channel’s blower

AC supply from 2 separate sources.

Customer was advised that the same is not required, as

such problem has not occurred at any other site. Reason

for flashover in ESP switchgears to be analysed and

corrective action to be taken.

MISC 4. PSFF power supply MCB trips frequently even

though load is normal.

Replaced MCB of PSFF. Problem solved.

MMI FOR VFD 5. 1 no. Line driver found defective.

On executing VFD MMI S/w, after 2 minutes,

program came out of main exe. File. “Drive status

had also not got updated.”

1. Replaced. Defective line driver sent for repair to

BHEL-EDN.

2. Check if Serial intelligent card & Reed relay card are

available.

3. Check 24V DC Jyothi Relay in C&EXE panel is getting

energised on program execution. If OK, Connect 25 pin

connector to door mounted printer. Check that

messages are printed on printer.

4. Check MMI system connections as per scheme.

If all connections/hardware are OK, Pink window –


Page 40 of 95

Drive Status should appear on MMI screen, else Blue

window – Link Failure appears on MMI screen.

MISC 6. Com Port of one Laptop supplied for VFD is not

working.

1 computer of VFD-MMI not working.

Repaired by BHEL-site through laptop vendor.

Mother board replaced by computer vendor at site.

LOAD

COMMUTATION

FAILURE & LOAD

PLL FAULT

7. Channel tripping on Load Commutation Failure.

Channel tripping intermittently on faults “Load PLL

Fault Load Commutation Failure, Motor Winding

Shorted & Power Supply PSFF failure.”

SEM earthing found not proper. Same rectified.

3 nos. HPTK modules and 1 no. PSFF changed.

MISC 8. 3 MOVs of 440V 1A,2A & 3A found burnt during

inspection and maintenance work. Found incorrect

connections,

Fuses feeding MOVs – No failure observed. Found MOVs

burnt. Found wrong connection in panel.

Advised to change all 9 MOVs 1A to 1C, 2A to 2C, 3A to 3C.

MOVs changed. Problem solved.

LOAD

COMMUTATION

FAILURE

9. Slave Channel tripping on Load Commutation failure. Channel back-charged with Source breaker open and Load

breaker closed. FAB, FBC, FCA in NLIB load found with

large DC offset.

Changed NLIB card and adjusted DC offsets to less than

30mV and balanced AC voltages of FAB, FBC, FCA. Channel

taken into service. OK. Problem solved.

MISC 10. Both Master and Slave channel of one ID Fan

tripped out. In Master channel, Source and Load

breaker tripped. In Slave channel, only Load breaker

tripped.

Flashover in Source side of Master channel. Master

channel isolated and Slave channel taken into service.

Found source side AC and DC filter fuses blown and also

cable tapping from busbar to filter fuses burnt. MOVs on

Source side OK. Fuses and wires replaced. All clearances

are more than adequate. Cause of flashover not known.

Channel taken into service. OK.

MISC 11. Fan-B Ch-2 tripped. Following were noticed: 1.

Source breaker tripped. 2. FT1 indication observed

at VFD end. 3. HMPG IMOK LED was not glowing.

Crowbar test done – Found O.K.

Gate Test done - Found O.K.

Self Test done – Found O.K.


Page 41 of 95

4. There was huge current hunting only in this

channel before tripping.

Primary injection tests in all 4 CTs done. Found O.K.

Finally problem was traced to improper earthing in

electronic earth pit. Salt added. Drive started and found

O.K.

GATING SUPPLY

UNDERVOLTAGE

R05, 0207, PH

12. Channel trips on Gating Supply Undervoltage. Output voltage of 70Volts Power supply measured under

Gate test mode. Showed OK 82 Volts DC. Checked voltage

of Power supply healthy signal from each of the HPTK

cards going to XTFH diode circuits. All 12 voltages OK.

Changed XTFH card and Channel taken into service.

MISC

R05, 0407, PH

13. Channel tripped on Fault. Found that all LEDs on

HRDD are ON. FT1, FT2 and RST LEDs on NLCB

ON. 6 Amps 28V fuse on PSFF adjacent to circuit

breaker blown.

From the problem it was inferred that the problem could

be in IOMA module. Isolated by removing 28 Volts Power

supply from PSFF connector feeding IOMA. Replaced

PSFF 6Amps fuse. Swithched ON PSFF. 28Volts fuse did

not blow. But all LEDs were glowing as before.

Switched OFF PSFF power supply. Removed all 4 cards in

IOMA module. Put back IOMA power supply connector on

PSFF. Switched ON PSFF. 28Volts fuse on PSFF did not

blow. Inserted one card after another in IOMA switching

OFF PSFF everytime. Found that 28Volts 6Amps fuse

blew when HRIA/2A card was inserted. Changed HRIA

card. Problem solved. Channel taken into service. OK.


Page 42 of 95

Category Sl.no. Problem Solution MISC 1. Incoming MCCB to IOMA PSFF tripping due to

inrush currents.

Breaker setting adjusted according to site conditions.

Problem Solved.

MISC 2. Channel did not start smoothly. Found load C.T polarity reversed after examination of Load

current waveform w.r.t. load firing pulses. Corrected

polarity. Problem solved.

MISC 3. Hunting observed in current & speed. Parameter SRGAIN tuned.

Problem solved.

MISC 4. During exciter test on channel, resistors R70, R71

replaced from 56 Ohms to 46 Ohms to adjust

burden of CT

Feedback as required adjusted with potentiometer on

NHVL.

Problem solved.

MISC 5. Self test not passing because offset value was not

within the range.

DC offset on source & load NLIB FAB,FBC and FCA could

not be adjusted within 30mV with test oscillator ON by

adjusting BAL1, BAL2 pot’s on NLCB. NLCB replaced.


Page 43 of 95

Problem solved.

MISC 6. HMPG IMOK not coming. Replaced HMPG with EPROM sets of tested card (6

EPROMS). Card sent for repair.

MISC 7. Pulses not getting distributed to thyristor stack

individually in gate test mode.

Card XTFX in source side found defective. Replaced.

Problem solved.

MISC 8. ID Fan ‘ON’ check back derived from its speed

being above a certain value

(MAMS). During starting MAMS chatters as speed

hunts slightly resulting in ID Fan ON/OFF toggle.

This gives auto start to shutdown sequence.

Automatic initiation of shutdown sequence due to ID fan

‘OFF’ status will be delayed. Introduced time delay OFF

logic for MAMS input at I&C. Problem solved.

MISC 9. VFD demand goes to max. when both ID Fans are

OFF. This prevents reducing the VFD demand to

min, when taking the first ID Fan into service.

This command is removed in I&C system as it is not

necessary.

Problem solved.

MISC 10. ID Fan VFD given a protection trip from Source

Breaker OFF condition but also source breaker is

given trip on VFD OFF condition, thus creating a

logical problem.

Source breaker trip due to VFD OFF condition will be

removed and instead will be given a trip command on its

‘Electrical protection acted’ input being true. This is

implemented at I & C. Problem solved.

LOAD

COMMUTATION

FAILURE

11. Channel tripping on Load Commutation failure LMARG was changed from 25° to 30°.

Found P28 was 21.5Volts. Site asked to change this to

minimum 24V level during gate test mode. Problem solved.

Changed back to 25° after channel was normalized.

MISC 12. Any electrical supply system jerk causes drive to

trip.

Presently UPS feeding VFD is not fully commissioned and

UPS is running on By-pass. Problem will not occur if UPS is

commissioned.

MISC 13. Customer expressed that ‘Auto fault Reset’ facility

is not available.

EDN informed that facility will not be given. It is

required that the maintenance engineer has to come to the

VFD panel to find out the fault and take corrective action

before re-setting.

MISC 14. Coil for OEN make relay found burnt in IOMA Suspected quality problem. Relay changed. OK.


Page 44 of 95

Reason unknown.

MISC 15. NLCB gives IMOK indication but fails

during self test of NCLB card.

DLCB card components R1 & C1 not matching as per

scheme. Changed from other card. Problem solved.

MISC 16. NLIB gives IMOK indication but fails in Self Test. Daughter board components R22, R31, R40, R23, R32, R41,

R60, R68, R72 not matching as per scheme.

Changed the components as required and also adjusted the

gains of FAB, FBC, FCA as per commissioning procedure.

Problem solved.

SOURCE

COMMUTATION

FAILURE &

SOURCE

OVERCURRENT

17. Drive tripped on “Source Commutation Failure”.

Drive restarted and motor tripped without picking

speed on “Source Backup Overcurrent Operated”

tripping Source breaker also.

Gate test and Crowbar tests passed.

Advised to conduct EVC test and crow bar test. Also

inspection of output contactor contacts advised.

Found that one of the thyristor cells in the load side

bridge had got shorted. Replaced thyristor module & sent

the faulty module for repair to BHEL-EDN.

Problem solved.

I/O PROBLEM 18. Both channels commissioned but not able to take

both into service simultaneously because of a

missing feedback due to HROA card.

Current hunting after that.

HROA card replaced. Simultaneous operation possible.

Problem solved.

HROA card sent for repair to BHEL-EDN.

MISC 19. Current sharing problem between channels. Actual currents were balanced. Meter on LCI channel not

showing correctly. Meter adjusted OK with pot. IM on

NLIB.

FAILURE TO

START

20. VFD failed to start and Rotor failed to start (Bit 1

of ALARM WORD) displayed on printer.

Problem in DC field and exciter on synchronous motor.

Motor changed in presence of BHEL-Bhopal person and it

is running OK.

MISC 21. Laptop battery back up not working. Customer has asked to send 2 battery back ups.

EDN says that Laptop PC can be fed from UPS supply

available in VFD panel. As such battery back up is not

required in laptop PC for VFD maintenance.


Page 45 of 95

MISC 22. Unit tripped on received AUTO OFF commands.

WSPOSE relevant alarm display was “Auxiliary

Supply failure”

Customer requires that 24V DC and 220V DC

supply failure be separated.

Site : Logic built in VFD such that a time-delayed timer 0-

35secs. (set to 3secs.) drops when either of 24V or

220V DC supply fails. Contacts of this timer used for

Source drive breaker Start Perm. and its inverted status

used for generating AUTO OFF commands to source

breaker cards simultaneously.

EDN does not recommend separate logics for 24V & 220V

DC monitoring, as both 24V DC and 220V DC failures

should trip the drive.

MISC 23. High vibration noticed in fans at speed above

650rpm (Speed at unit F.L.condition is <600rpm)

Resonance is being observed from foundation at

speed>650rpm. However, vibration is in good zone.

BHEL-Ranipet recommends that status of spring

compression can be checked during annual maintenance

shut down.

MISC 24. VFD trips when small system jerks occur. Time delay of 2 secs. already incorporated to tide over

the problem. Customer has been asked to look into the

source of the swing/jerk and take appropriate action.

LOAD

COMMUTATION

FAILURE

25. When Ch-2 is started with Ch-1 running normally,

Load sharing is equal, but Ch-2 tripped after 5-10

hrs

28Volts DC of SEM power supply checked and found to be

atleast 24V. Also its waveform did not have any ripple.

LMARG increased by one degree. Problem solved.

MISC

REV.04

26. Heavy hunting in Slave channel when paralleled with

Master. Also Master current hunting when running

alone, but oscillations are not of large magnitude as

in Slave. Slave runs OK when run alone.

Shutdown of Master channel taken and isolated it from

Slave by removing connections on IOMA TBs for Rotor

Position/other channel running and Torque reference input

and Torque reference output.

Crowbar test conducted on Master with Slave in service.

Found LTM2 on Slave defective. Replaced card. Master

taken into service. Found OK. But heavy hunting in Slave

continued. Found that wires were loose on IOMA TB 12

pulse Input signal 2BF IOMA TB7/16,17. Wires on TB

tightened. Slave taken into service. Problem solved.


Page 46 of 95

Category Sl.no. Problem Solution MISC

1. When individually run, both channels run OK. When

both channels put on parallel for equal sharing of

current, it could not work. Current in Ch-2 became

0.

Ch-1 Tripped due to MP module power supply failure.

Ch-2 tripped due to Stack failure.

Only once, channels could run in parallel operation,

but local stop PB did not respond, tripping could be

done by operating local/remote selector switch.

Problem seems to be due to 240V supply fed to electronics

or malfunctioning of circuit breaker in PSFF module. EDN

has asked site to carry our the following & give feedback.:

a. Put both channels in Gate Test mode at the same time

by changing MTRFMIN to 0.2 and FLUXS to 0.1 &

putting NLCB switch up. DO NOT SAVE. It may take

about 5 minutes for pulses to be released.

b. Check input supply at sheet 1BB of scheme. Change tap

of trf. to get 110V on sec. of T1.

Check 28, +5, +15, -15 volts on SEM rack OK.

Check 70V DC from gating power supply OK. Should be

atleast 75V DC during gate test.

c. Quit gate test by putting NLCB switch down and

resetting MP.

d. Check 220V DC supply to VCBs OK.

e. Run up Ch-1(master) to minimum speed. Check

LMODE=3.

f. Run Ch-2(slave). Check LMODE goes to 3 in slave. If it

does not, slightly lower MTRFMIN and FLUXS in Ch-2.


Page 47 of 95

g. Power supply tripping problem in Ch-1 sorted out.

MISC 2. Following problems during parallel running of 2

channels:

a. Individual load breakers do not trip with remote

trip command/local stop PB. Only Run relay

drops & MP does not issue a trip command via

RUN relay.

However process trip commands trip load side

breakers at a time for both channels as

expected.

b. During loading, fan speed rises upto 35% speed

ref. Command. And beyond that speed does not

rise. Stator current hunts from min. to max.,

but speed does not rise.

a. Monitor 105V DC level on IOMA TB3-9,10 when RUN1

& RUN2 relays in control panel drop. Check operation

of load breakers, independently by removing plug-in

type RUN relay in IOMA and simulate Load Breaker

operation. Source breakers must be OFF when doing

this test.

Mistake in wiring chart of Ch-2. This was the cause of

Ch-2 not switching OFF when STOP command given

from C&I. Problem solved.

b. Observe INVLIM during normal running and when

hunting happens by continuous display of INVLIM.

The value of INVLIM displayed will tell the type of

fault. Please do the following:

1. Increase LMARG to 0.3 from present 0.16. Run

drive and see if hunting persists. Hunting

persisted.

2. If it persists, Change LMARG back to 0.16. Change

resistor R60,R68, R76 in NLIB to 100K from 180K.

Run & see if hunting persists, Changed resistors.

Hunting persisted.

3. If it persists, change above resistors from 100K to


Page 48 of 95

56K. While changing resistors, NLIB to DLIB

Ribbon cable connection is to be removed.

Hunting remains.

Inadequate excitation caused dip in Armature voltage

leading to hunting of speed and armature current.

ALPHFLD was reaching 255. Exciter current was

reaching 63A LRMS-too high for the load. Reversed

exciter stator cable thereby changing the phase

sequence. Problem solved.

MISC 3. Motor current calibration on VFD C&EXE panel. Run both channels at min. speed. Check LMODE=3 in both

channels. Measure trf. sec. winding current with clip-on

meter. Since trf. current = motor current, adjust

NLIB/DLIB pot. IM so that panel meter reads correctly.

Note that at minimum speed current will be minimum &

steady.

MISC 4. Running VFD when ID Fan handles air instead of flue

gas. Speed does not go to Maximum.

Since density of air is much higher than flue gas, it will not

be possible to run the drive to 540rpm as current will

reach the limit values before this speed.

LOAD

COMMUTATION

FAILURE

5. Channel tripped giving Commutation failure.

Both channels tripped due to fan vibration very

high-process trip.

1. Changed XL compensation resistors in NLIB load R60,

R68, R76 from 180K to 67K. Tripping continues.

Resistors changed back to original value.

2. P70 Volts output changed to 80 Volts during gate test

mode. Problem solved.

3. Vibration problem attended by mechanical

maintenance group.


Page 49 of 95

MISC 6. Channel does not start. On excitation board, only 2

LEDs glowing on Start command.

Power supply unit failed.

Printer not receiving data from the MP.

1. NHVL excitation board failed in Field Exciter.

Replaced. OK. Failed board sent for repair.

2. PSFF module replaced. OK. Failed PSFF sent for repair.

3. Printer replaced.

I/O PROBLEM 7. Motor decoupled smooth in both channels. While

starting the fan on Ch-1, ammeter reading does not

go beyond 400A whereas in running it goes upto

600A and comes back for any speed increase

command.

When fan started through ch1, fan did not start,

rotor oscillating and stator current hunting. Ch-1

stopped and ch-2 started. Ch-1 paralleled. Found

OK. Ch-1 OK even ch-2 stopped. Ch-1 started

independently before rotor came to rest. Ch-1 does

not start from rest position.

11 nos. Modules found defective. Replaced.

Ch-1-Polarity of CT inside excitation board was changed as

IFB waveform not found OK. During power-up, before

restarting, MAMX in picked-up condition though HROA-R2

LED not glowing. Load breaker closed without any

command. Self test failed in 230D. HRDD, NLCB

suspected defective, Replaced & power On. MAMX picking

up. HROA in 1B failed. Spark observed in K3 relay body.

FU-6 blown in HROA. In MAMX, suppressor block (R-C

net) changed as lugging was not OK. IOMA changed. HROA

connector found burnt. HRDD found defective.

All replaced. Self test passed. Fan started.

4-20mA for remote indication was not there. NLCB

changed. OSP and SPM setting was done. Fan run and

paralleled.

Ch-1 fault and not starting. All LEDs on HRDD glowing.

HRDD replaced. Remote speed indication and local speed

indication became zero. NLCB changed and ID fan started.

Problem repeated again.

Problem maybe in exciter module or NSFF card. Check

waveform during field exciter test at TP IFBK in NSFE.

Compared with healthy channel. Also, checked exciter

pulses SIG1 to SIG6 at NSFE.

One of the thyristor pulses was missing, Pulse trf. on

NHVL exciter board failed.


Page 50 of 95

When motor started through VFD Ch-2, did not start and

tripped on Source & load OverCurrent & ground faults.

During meggering on motor insulation , IR value found very

low. Problem related to Motor insulation, BHEL-Bhopal

contacted. Motor end covers opened & 1 conductor was

observed to have turned black. This was due to insulation

failure which resulted in high earth fault. Motor

replaced. Same problems observed. Also spurious

trippings/startings observed in Ch-1.

IOMA modules replaced in Ch-1 & 2. PSFF replaced in Ch-2.

Fan Run OK.

MISC

LOAD

COMMUTATION

FAILURE &

SOURCE

COMMUTATION

FAILURE

8. Ch-2 self test not passing. DC Offset not getting

adjusted to zero volts.

During trial run, Ch-1 “Commutation failure fault

appeared.

Additional earthing provided. NLIB card replaced. Offset

voltage made zero in NLIB Source & NLIB Load FAB, FBC,

FCA by adjusting BAL1, BAL2 pot’s in NLCB. Self test

passed OK.

NTDA card on thyristor modules resoldered wherever it

was suspected dry solder present. Fans run OK.

I/O PROBLEM 9. Failure of IOMA modules. Seems to be a chance of voltage mix-up in P105 and IOMA

output contactor circuit. Mix-up could be from inside the

panel or from outside IOMA.

Found that there was no voltage mix-up in panel side.

IOMA modules suspected.

Sent to BHEL-EDN for repair. Found problem of open PCB

tracks on IOMA module backplane and also tracking

between PCB tracks. Backplane PCB’s on I/O module

changed. Vender de-listed. Quality problem. Problem

solved.

FAILURE TO

START

10. Ch-1 of ID fan-starting and running

OK.

Found in Ch-2 that the load side CT polarity is reversed

after observing the waveforms of load side firing pulses


Page 51 of 95

Ch-2 (slave) of ID fan- Does not start. But runs OK

after paralleling with Ch-1.

Tune-up parameters are same in Ch-1 & Ch-2.

w.r.t. Load side CTs. Corrected CT polarity.

Problem solved.

LOAD PLL FAULT 11. On starting, Load breaker trips. Load PLL Fault or

Load Overcurrent or Shorted Motor Winding

message appears. SUPP Led not glowing.

Found that NSFC load card was loose and not properly

inserted in rack.

Inserted card in rack and put SEM lock bar. Drive started

and found OK.

GROUND FAULT 12. Ch-2 tripping on ground fault intermittently and

thereafter as soon as channel was paralleled to Ch-

1.

Action taken:

Checked tightness of all power connections including earth

bus. Found OK.

Checked SEM earthing. Found OK.

Checked gate pulses and any loose connections etc. Found

OK. Backcharged Ch-2 and checked load fluxes on NLIB

load. Found OK.

Crowbar was conducted with all doors and backcovers

open with CRSTART=0.

Found sparking on one of the load side capacitors in Fan &

filter panel. It was seen that the discharge resistor

connected across capacitor terminals was very close to

capacitor body leading to the sparking and hence ground

fault.

Corrected position of resistor and its leads for adequate

clearance from capacitor body.

Problem solved.

I/O PROBLEM

REV.04

13. Channel tripping on I/O address problem. HMPG

Bushog LED comes ON.

HLCB and HAIA cards changed. Problem persisted and

Bushog LED on HMPG coming ON after 2 minutes. HMPG

card changed retaining old DMPB. Channel taken into



Page 52 of 95

LOAD PLL FAULT

R05, 1007, PH

14. Master channel trips on Load PLL Fault. Backcharged from Slave channel. Found that NLIB load

FBC AC voltage was oscillating. Changed NLIB Load card

and set the values of FAB,FBC,FCA as in Schematic drg.

Sht. 1DA. Channel taken into service. OK. It is inferred

that OPAMPS in NLIB load may have drifting problem in

FBC circuit. Sent card to BHEL-EDN for repair.

Formatted Table


Page 53 of 95

Category Sl.no. Problem Solution MISC 1. Door mounted printer not

printing messages.

Found one wire wrap wire carrying printer signal was cut on

SEM. Re-wrapped wire. Problem solved.

FAILURE TO

START

2. Drive not picking up speed. Runs at a speed below

minimum speed continuously.

One load side thyristor module not firing properly.

Problem traced to loose connection on wire lug carrying

firing pulses. Re-crimped wire. Problem solved.

FIELD

OVERCURRENT

3. Drive trips on Field Overcurrent or Field loss

during start.

415V auxiliary supply for VFD was fed from DG set. The

main 11KV supply was fed from Electricity board feeder.

Since the Source Thyristor bridge and Excitation

Thyristor bridge work on the some PLL (Phase Locked

Loop), both bridges must be fed with electrical power

derived from the same power source.

Changed auxiliary power 415V source feeder. Problem

solved.

FAILURE TO

START

4. Motor not starting in uncoupled

condition.

Found that parameters in software were parameters for

coupled condition. Changed to uncoupled condition

parameters. Motor Run. OK.

MISC 5. Motor starts and heavy vibration observed in Motor

and fan.

Found that no firing pulses to STM3. Also source 11kV

current unbalanced.

Changed HPTK card on STM3. Problem solved.


Page 54 of 95

Category Sl.no. Problem Solution MISC 1. Channel tripped. Found that DMPB IMOK was not

‘ON’. LVSH from PSFF power supply was giving ‘high’.

Also HMPG was not communicating properly with

Laptop PC.

See DMPB IMOKP15, N15 at PSFF. IMOK LED of DMPB lit

up. Channel taken into service. OK. Problem solved.

MISC 2. Frequent tripping of VFD transformers on process

trippings.

EDN did not recommend introduction of any extra

breaker/contactor/switch giving the following explanation:

1. LCI decides to open the Load or Source breaker or

both depending on the type of fault.

2. Emergency stop conditions are rare as this represents

emergency conditions.

3. Once unit starts generating, the no. of operations of

the source breaker becomes extremely low.

4. Similar interlocks for source breaker existing in

earlier drives already supplied and in service. No

transformer failures encountered to date.

MMI FOR VFD 3. VFD MMI:

1. While carrying additional tests for Line drivers

mounted in C&EXE panel, R+ and T+ led are glowing

but key pressed in not getting printed on VT100

screen.

2. Link fail is coming in window during Integrated

test for MMI system.

Check all cabling is as per document.

1. Check that cable connection that has been made

between the VT100 terminal and the line drivers is a

one-to-one connection, i.e. Connect the wires to the

respective as follows: 2-2, 3-3, 7-7 (and connect 7

to ground) , check that individual line drivers are OK

and then conduct Loop-Back test.

2. Check if the software is reading the MPCC card and

the Reed-relay card. For this, take out the above

cards from their respective slots inside the PC. Run

the MMI.exe file. The following should happen:

a. A message will be printed out: MPCC/Reed-relay

card not in place.


Page 55 of 95

3. Error no. 13 is also appearing in editor mode.

4. In O&M panel, while switching on ‘PON’ and ‘TL’

both LEDs glow, whereas in C&EXE panel, ‘R+’

and ‘PON’ LEDs glow and when wire is looped by

shorting T+ to R+ and T- to R- then ‘TL’ LED

glows.

b. The MMI window will not appear.

If the message dos not appear and MMI window

appears-contact BHEL-EDN.

If the above is OK, put back the 2 cards and re-

execute the MMI.exe file and then perform the

Integrated test. While conducting the test, start

with conducting it only on a single C&EXE panel i.e.

switch off all the other line-drivers in the O&M panel

and the other C&EXE panels. Switch on only the line-

driver in one C&EXE panel and the line driver

corresponding to this channel in the O&M panel. It is

very important that the other line-drivers be

switched off since the open connection at the D-

connectors can give rise to link failure.

3. After the above tests have passed, check whether

this error message still appears.

4. Do this test first on the O&M panel Line-driver:

While switching on this line driver, switch off &

remove the connection between the C&EXE panel line

driver & the O&M panel. i.e. do this check with this

line driver totally isolated. Remove the shorting

between T+ & R+,T- & R- if present. The TL Led

should not glow. Then short T+ & R+,T- & R-. Now the

TL Led should glow.

Perform the same test on C&EXE panel line driver and

check that the same is OK. Of problem persists, swap

the line drivers and check. If the above is not

happening, the individual Line Driver buffer may have

got spoilt and the same needs to be replaced.

RS232 interface adaptor found defective. Replaced.

Problem solved.


Page 56 of 95

MISC 4. Current hunting problem during loading of drive

motor accompanied by voltage collapse.

Phase sequence at motor exciter terminal box changed.

Problem solved.

MISC 5. Loading of RPM meter and current meter. BHEL-EDN suggested to put a resistance of 200 Ohms

across the respective IOMA TBs after disconnecting

external cables. EDN to revert back after receiving the

reading on the door module meters and the mA current

through the 200 Ohms resistance.

Problem traced to higher loading in C&I. Problem at C&I

sorted out. OK.

LOAD

COMMUTATION

FAILURE

6. Ch-2 tripped on “Load Commutation Failure”. NSFC Load card found defective. Replaced. Problem

solved.

GATING SUPPLY

DIP

7. 1. Ch-2 tripping on “Gating Supply dip”.

2. After 12 hours running, irregular firing and no

LED indication on leg STM3 reported by

customer. Machine did not start after stopping.

3. During starting current going to 580A then

coming to zero and then going to 500Amps, then

stabilizes around 100-150 Amps.

1. HPTK card of STM3 found defective. Card replaced.

OK.

2. One HPTK card of STM3 & one NSFC card found

defective. Replaced and Machine started.

BRIDGE

DIFFERENTIAL

PRESSURE

8. Channel Tripping on Bridge Differential Pressure. Lowered the differential pressure setting in Air Flow

monitor. Problem solved.

SOURCE

COMMUTATION

FAILURE

9. Channel tripped on “Source Commutation failure”

when running on no-load.

One no. SCR in STM2, all three SCRs in LTM1 and 2 SCRs

in LTM3 showing zero resistance. Problem cause is the

loose connection of T2 control trf. in LCI panel.

Connection tightened. Problem solved.


Page 57 of 95

MISC 10. Current hunting problem in channels. One no. thyristor leg found defective. Replaced and

problem solved.

LOAD

COMMUTATION

FAILURE

11. Channel tripped on “Load Commutation Failure”. Following tests were carried out:

1. Resistance across all the thyristors checked. Found

satisfactory.

2. Fuses in all HPTK cards checked. Found OK.

3. Self test failed in 2901 during testing of HRDA(1A),

HISA(1B) & I/O module.

Replaced HRIA (I/O 2A), HROA (I/O 2B), HISA (1B).

Fuse & 105V supply checked. Continuity of ribbon cables

from I/O module to SEM checked.

Problem persists.

Dust ingress on SEM Electronic rack cards & HPTK

thyristor pulse trf. card found to be the problem. Dust

removed by air blowing.

Problem solved. Channel taken into service.

GATING SUPPLY

DIP

12. Problem of Gating supply dip & LED not glowing in

STM3 NTDA card.

One thyristor of STM3 found short. Replaced. Gating

supply UV problem persists.

MISC 13. Failure of as many as six thyristor legs in one unit

and 2 thyristors in another unit.

Customer asked for an expert thorough analysis at site.

Dust level on the cards in the electronic rack & in the

thyristor power modules found high. This found to be the

possible cause of failure after thyristor failure analysis

done at BHEL-EDN.

LOAD

COMMUTATION

FAILURE,

SOURCE

OVERCURRENT &

FIELD LOSS

14. 1. “Load commutation failure” leading to tripping

of the fan.

2. “Source Overcurrent” fault

leading to tripping of the fan.

3. “Field loss” fault on start-up and unable to start

the fan.

Excitation circuit thoroughly checked up. Found

terminations in ‘C’ phase and the current feedback CTs

were loose. Terminations tightened and ‘EVC Power test’

conducted.

Problem solved.


Page 58 of 95

MISC 15. 2x500MW plant not able to generate more than

480MW when only 3 channels of ID Fan are

available.

Damper position increased to 85% as per BHEL-Trichy

recommendation. Problem solved.

MISC 16. Motor currents in 2 channels of ID FAN A suddenly

shot-up from 476.95A/466.8A to

741.02A/749.22A, whereas speed varied from

462.89/488.89 to 470.95/504.64 rpm. Sudden

increase in speed and current lasted only for a few

seconds and the values came back to their original

level.

BHEL-EDN rep. Has explained to customer that this

problem is related to reference from I&C. Not a VFD

problem.

MISC 17. Ch-2 not taking over when ch-1 tripped due to any

fault. Ch-2 not starting individually.

Problem traced to failure of fuse in HROA-1B card. Same

replaced.

Ch-2 started individually and in dual mode and operation

found normal.

Changeover and taking over of either channel in case the

other trips has also been found in order.

MMI FOR VFD 18. MMI of ch-2 not working. Circuits of door mounted printer port of VFD, line drivers

(VFD), line drivers (O&M), Multiplexer, Demultiplexer,

Junction base, MPCC card checked and found in order.

Data transfer and communication from SEM suspected.

Door mounted printer of VFD replaced. Problem solved.

FIELD LOSS 19. Tripping of ID Fan on field loss.

Self test failed.

Excitation system thoroughly checked. Found that in ch-2

the exciter output current was less due to non-conduction

of one thyristor. NHVL card changed. Channel cleared for

service after EVC power test and calibration.

One of the zener diode in IOMA Mother Board had

failed. Replaced and self test was passed.


Page 59 of 95

MISC 20. Vibration of motor current on ID Fan (sometimes in

the order of 80A). Output voltage waveform was

found distorted.

Output feedback CTs were found loose at the mounting.

Same tightened. NHVL card replaced.

Motor current vibrations still present.

Adjustment of speed regulator gain did not reduce the

variations. SFE of ch-1 to be replaced when shutdown

available.

Ch-2 configured as Master and ch-1 as Slave and Fan put

into service. Variations not observed.

Defective card brought to BHEL-EDN for repair.

MISC 21. Unbalance of 50A in the motor current between the

two channels of VFD.

Ch-1 current indication at the remote(UCB) was showing

less where as in the local, the current was showing

balanced because of problem with the V/I converter in

NLCB card. Same replaced.

Problem solved. Current for both channels were balanced

at the remote. Defective card brought to BHEL-EDN for

repair.

GROUND FAULT 22. When ID Fan started after cleaning for annual

maintenance, Ch-1 & ch-2 tripping on Ground fault at

a motor voltage of about 800VAC (300rpm). This

was observed on trials in single channel operation or

in dual channel mode.

During cleaning of the panels, customer has broken

connection at the lug points of the HV cables connecting to

the load side filter ckts. Cables recrimped. Problem solved.

LOAD

COMMUTATION

FAILURE

23. Channel tripped on Load Commutation Failure. 1. Check SEM earthing as per SEM Earthing document.

2. Change X(reactance) compensation resistors in

NLIB(1D) i.e. change R60, R68, R76 from 180K to

100K Ohms & check the 3 flux reconstructed

waveforms on NLIB(1D). Change resistors to lower

values (upto 33K Ohms) till the reconstructed

waveforms are sinusoidal.

3. Change LIMARG.

All the above done but problem not solved.

Intermittent tripping of channel between period of 4 hrs

to 48hrs observed.


Page 60 of 95

1. The load side thyristors, snubber ckt, CT ckt, gating

ckts thoroughly checked. All terminations on HPTK

and NTDA cards checked for loose connections and

soldered/tightened/replaced wherever required.

2. Self test & gate test conducted. Speed feedback

ckt found malfunctioning in NLCB /DLCB. DLCB

changed. Speed fdbk ckt calibrated.

3. Gating power supply changed from 89V to 91V.

4. Crowbar test s conducted. Current feedbacks O/C

protection ckt checked and adjusted wherever

required.

5. Channel put into service, Voltage and checked

waveforms checked and found normal.

Channel tripped again on “Load Commutation Failure”.

1. Firing pulses and the associated ckts of HPTK , XTFU

and the related ribbon cables checked.

2. In 2 of the HPTK cards on the load side, the

reference for detection of ‘undervoltage of gating

supply’ was 1.3V DC while in others it was 1.8V DC.

Reference adjusted to 1.8V DC in all HPTK cards.

Self test and gating tests conducted and all

parameters found normal.

Problem solved.

MISC 24. Ch-2 tripped. SEM Power supply PSFF found OFF. PSFF replaced.

Problem solved.

MISC 25. Ch-2 tripped. HMPG not getting reset. HMPG Bushog problem. HMPG replaced. Problem solved.

BRIDGE

DIFFERENTIAL

PRESSURE

26. Ch-1 tripped on ‘Bridge Differential Pressure’.

‘RSFM’ resistance found dry soldered. And

disconnected from ‘Tag board resistance card’.

Dry solder problem in Tag board. Soldering done properly.

Problem solved.


Page 61 of 95

MISC 27. Ch-2 Current suddenly reduced to 220A. Berg Jumper J2 on DMPB defective. Replaced. OK.

GATING SUPPLY

DIP & LOAD

COMMUTATION

FAILURE

28. Ch-2 tripped on “gating supply dip, load commutation

failure, gating power supply loss”.

HPTK card of LTM4 burnt. HPTK card replaced.

HLCB card found failed. Replaced.

Problem solved.

SOURCE PLL

FAULT

29. Ch-2 tripped on ‘Source PLL Fault ’ Loose attenuation card connection in STM1.

LOAD

COMMUTATION

FAILURE

30. Ch-2 tripped on ‘Load Commutation failure’. Dry solder problem in NTDA card. Card replaced.

2 nos. HPTK card changed. HMPG found failed. HMPG

replaced. Problem solved.

GATING SUPPLY

UNDERVOLTAGE

31. Ch-1 alarm ‘Gating supply undervoltage’. NTRF card changed & channel started and channel tripped

on ‘Field loss’ problem.

Field exciter board NHVL changed. Problem solved.

Channel taken into service.

GATING SUPPLY

DIP

32. Ch-2 tripped on ‘Gating supply dip’. NTRF card failure on 70V power supply. NTRF changed.

Problem solved.

LOAD

COMMUTATION

FAILURE

33. Ch-2 tripped on “Load Commutation Failure”. 24V DC in PSFF found dipped. HROA(1B) having Motor

above minimum speed changed. Problem solved.

MISC 34. Source Breaker trips but no Alarm or Fault lamp or

any message on printer. Channel taken into service

after taking out the wires on IOMA Elmex TB

connecting to SWGR relay aux. contact.

Advised to change HROA relay card in IOMA module

which energises SWGR relay. This module will have

SWGRX relay on it.


Page 62 of 95

MISC 35. Gating tests and Exciter Power tests not passing in

Fan-B Ch-1.

HMPG card found to be the problem. U10 IC on the HMPG

cards found of Harris make.

HMPG cards replaced and Problem solved.

LOAD

COMMUTATION

FAILURE

36. Ch-2 randomly tripping on Load Commutation Failure. SEM Rack cleaned by blowing air. Channel taken into

service. OK.

GROUND FAULT,

LOAD

COMMUTATION

FAILURE

REV.04

37. Channel tripping on Ground Fault and Load

Commutation failure.

Channel Tripping on Ground Fault. Observed that neon

lamps across Load Bridge Thyristors also glow when Source

breaker is switched ON. Found ground fault in cable

connecting transformer secondary and Source bridge. This

was done after isolating cable at both ends using HV

megger and Hi-pot. Cable changed and Channel taken into

service.

Thereafter Channel tripping on Load Commutation failure

intermittently. Since all waveforms were OK, it was

inferred that the problem can be attributed to spurious

malfunction in electronic cards. NLIB(load) ,HLCB, HAIA

and Pulse distribution card XTFH changed. Problem

persisted. Grounding system of entire channel thoroughly

checked and re-inforced with additional cables from panel

earth strip to station earthing mat. Channel taken into


MISC

R05, 1107, PH

38. Field Contactor chatters when Ch-1 (Master) is

paralleled to Ch-2 (Slave), with motor running

through Ch-2. No Fault or Alarm annunciation.

Since field contactor closes after Load Breaker closes,

aux. contact problem in Load breaker was suspected i.e.

MISOL input in IOMA changing from True to False to true

to false, even though breaker is closed.

Found contact resistance in aux. contact of Output Ckt.

Breaker not OK. Shifted wires to another contact.

Problem solved.

Formatted Table


Page 63 of 95

LOAD

COMMUTATION

FAILURE

R05, 1107, PH

39. Slave (Ch-2) trips immediately after paralleling to

Ch-1.

Back-charged Ch-2. Found that voltages on NSFC Load

Unbalanced. Further found that one attenuator resistor in

R Phase load XTFH was open. Changed card. Ch-2 taken

into service. Problem solved.


Page 64 of 95

Category Sl.no. Problem Solution MISC 1. Ch-1 had problem of not starting. Gate pulses for Source and Load were checked and found

OK.

SEM cards were removed, cleaned and inserted in its

position.

2 lug connections at HPTK card were found to be loose and

were corrected.

Customer requested BHEL-EDN to supply spare lugs and

snubber mounting screws for fixing.

Trial run of Ch-1 was taken from Local control and

starting of fan was smooth. This was checked again for

repeatability and found OK.

MISC 2. Ch-2 not taking load when paralleled with Ch-1. Checked 12P11P and 12P11N connections on sheet 2BF.

Found OK.

Changed NLCB in Ch-2.

Paralleled OK and took load.

Cleaned original NLCB and replaced. Load taken.

Problem was due to dust on NLCB/DLCB.

MISC 3. Drive speed dipped below minimum and came to

MODE 2 when speed is lowered to minimum speed.

Changed SRGAIN in steps of 0.1 upwards and multiple

trials taken till satisfactory performance was observed.

Problem solved.


Page 65 of 95

LOAD PLL FAULT 4. Ch-1 tripped on “Load PLL Fault”. Surge protective

arrestors of CT1,CT3,CT4 and CT6 which are

connected at TB3-01&02 got burnt and damaged the

CT wiring of CT1 & CT3.

1. Fan & Filter panel thoroughly cleaned.

2. Blowing done at C&EXE, Bridge panels.

3. Wiring checked at C&EXE, Bridge,Fan & Filter panels.

4. CT circuit checked for tightness.

5. Surge arrestors SD1, SD3, SD4, SD6 replaced. After

replacement, CT circuit checked for continuity and

links closing. Self test done and passed. Problem

solved.


Page 66 of 95

Category Sl.no. Problem Solution MISC 1. Some sounds and vibrations observed in the DC

reactor link between Converter and Inverter and

hunting in speed found. Tripping of Fan-B Ch-2

when voltage reached above 500 Volts.

XLPE Power Cable screen not earthed. Screen earthed.

Problem solved.

GROUND FAULT 2. Ground fault in both channels of Fan-B. Load side capacitors found faulty and neutral grounding of

R-C circuit was not O.K. Problem resolved.

GROUND FAULT 3. Ground Fault problem in Ch-2. Cable from contactor to motor was found faulty during hi-

pot test to earth. Faulty part of cable removed and joint

put. Problem resolved.

MISC 4. With Ch-1 tripped, Ch-2 not responding to speed

Raise command. Current and speed of ID Fan not

responding.

Parameter SRCLSC found to be 0.7 instead of 1.0.

SRCLSC changed to 1.0. Problem solved.

LOAD

COMMUTATION

FAILURE/SHORTED

MOTOR WINDING

5. Channel tripping with fault message “Load

Commutation Failure and Shorted Motor Winding.”

Firing pulse LED on one card in Source bridge

missing.

NSFC card changed and checking of all connectors and RC

Filters carried out. Power bridge on load side checked.

HPTF card on load side changed. Problem solved.

LOAD

COMMUTATION

FAILURE

6. Load Commutation Failure message received on

channel and thyristors produced hissing sound

during dry firing.

Voltage on the P70 module was measured and found to be

73 volts instead of 80 volts by adjusting the

corresponding pot. Problem solved.

SOURCE

OVERCURRENT

7. Source Overcurrent message received on channel.

Sparking found at the gland end of R phase at the

back side of the bridge panel.

Earthing of XLPE cable not found either on bridge end or

the transformer end. Earthing done on the transformer

end. Problem solved.

GROUND FAULT 8. Ground Fault message received on channel. Voltage at NTL port of NLCB card was measured and

found to be 0.51V instead of 0V. The cause was found to

be unbalance of current in the three phases. On

performing the megger and hi-pot test, it was found that

Formatted: Indent: Left: -0.13 cm,Right: -0.13 cm

Formatted Table


Page 67 of 95

the ‘Y’ phase insulation had failed. The cable for ‘Y” phase

was replaced. Problem solved.

LOAD

COMMUTATION

FAILURE,

GROUND FAULT

REV.04

9. Slave channel trips during running, on Load

Commutation failure and Ground Fault.

Crowbar test conducted and found OK. Therefore Ground

fault suspected on load side. MOV and PT on Load

breaker checked, found OK. With Output breaker drawn

out, Motor AC voltage measured with respect to earth by

Motwane multimeter in High voltage range. Great care was

taken when doing this. Voltage unbalance found. Motor

stopped. Cable fault found between Motor and Output

breaker after Hi-pot test. Note that Megger value of

failed cable was OK. Fresh joint made. Channel taken into


SOURCE

COMMUTATION

FAILURE

REV.04

10. Source Commutation failure occurs when channel is

taken into service.

Crowbar test conducted, but channel tripped on Source

Commutation failure. AC side line filter capacitor checked

and found OK. Attenuated voltages on Source NSFC and

FAB,FBC,FCA on Source NLIB found OK. HLCB changed.

Problem persisted.

Cable connections from transformer secondary to panel

removed. Meggered transformer and found OK. Meggered

cable and found OK. Finally, XLPE HT cable earthing braid

from transformer to panel was found loose. Connection

tightened. Problem solved.

LOAD PLL FAULT

R05, 1106, VI

11. Drive trips on Load PLL Fault once in a while but

period of tripping is regular.

Found that panel was not earthed. Earthed the panel from

ground bus at rear at both ends. Completely cleaned the

panel by air blowing. Checked all connections in Load side

filter RC circuit and MOV. Some of the bleeder resistors

across filter Capacitor leads were very close to the

capacitor case. Made these resistors lead vertical.



Page 68 of 95

Category Sl.no. Problem Solution MISC 1. Source breaker getting tripped immediately after

closing. Overvoltage lamp on NLIB card found

glowing.

Overvoltage setting in NLIB card changed as per scheme.

Problem solved.

MISC 2. Speed and voltage not increasing at 35 Hz and

current swinging. Pump not attaining full speed.

INVLIM getting set at 2304 & 288.

DC Offset voltages at NLIB FAB, FBA & FCA was

1.0Volts DC, when no voltage was present on Source

bridge or Load Bridge. Adjusted NLIB (L) Offsets to

zero. Problem solved.


Page 69 of 95


Page 70 of 95


R05, 0906, PH

1. Cannot parallel Slave channel with Master at min.

speed. Current in slave does not rise. Tune-up

parameters in both channels OK. Running of motors

in individual channels OK.

Master channel run at minimum speed. Back-charged slave

channel and adjusted offset zero on Load NLIB FABR,

FBCR, FCAR. Also adjusted values of FAB, FBC,FCA on

Load NLIB same as in Master, taking master as reference.

Put slave channel into service. Problem solved.

MISC

R05, 0207, PH

2. Channel-1 Master running. But when Slave channel is

paralleled with Master and speed is raised, Slave

channel current remains at minimum.

12PII (Torque Reference) +/-10 Volts analog from IOMA

Ch-1 to IOMA Ch-2 not connected correctly. It should be

noted that this connection is polarity sensitive.

Wires connected correctly.Channel taken into service. OK.


Page 71 of 95


R05, 1206, PH

1. Communication with Laptop PC stops. Originally OK. Changed HMPG card. Problem remained. Changed HLCB

card. Problem solved.

GROUND FAULT

R05, 1206, PH

2. Motor starts and runs upto minimum speed. As soon

as it reaches LMODE=3, channel trips on Ground

Fault. Motor voltage at this instance approx. 400V.

Other channel was not available to check this fault by

backcharging.

Connected a 415V Source to Inverter Output. Found Line

to Neutral voltages unbalanced. Isolated Load side RC and

MOV circuits. Found Line to Neutral voltages balanced. On

further investigation, it was found that brazing on one of

the load side RC filter resistor had opened. Resistor

replaced. 415V applied. All line to neutral voltages found

balanced. Channel taken into service. No ground fault trip

observed. Problem solved.

GROUND FAULT

R05, 0507, PH

3. Channel trips on Ground Fault when speed reaches

over minimum speed. Other channel not

commissioned. Therefore, back-charging not

possible.

Fed 415V 3ph 50Hz from Auto-transformer to Load side

busbars R,Y,B in channel, with output VCB in OFF

condition. Found unbalance in FAB, FBC, FCA in NLIB-

Load. Removed cable from DC Reactor to Load side

negative and also P1-P2 jumper busbar connecting Load

and Source side bridges. Unbalance on FAB,FBC,FCA

remains. Isolated Load side MOVs. Unbalance remains.

Found that connection to Y ph R-C circuit resistor

terminal wire cut-off. Replaced the wire wound resistor.

Problem solved.


Page 72 of 95


R05, 1006, VI

1. All 4 channels of the 2 ID Fans give problems during

starting. Starting not smooth. Heavy oscillations of

current/source and load overcurrent during

starting.

During crowbar in all channels, high overshoot was

observed in IFB source current. There was no change in

overshoot by changing CRALPH1 & CRALPH2. Peak of

overshoot was reduced if SMARG was increased.

By Load NSFC SIG waveform it was ascertained that the

Load thyristor module gave the overshoot. Corresponding

module swapped from Source bridge. Conducted crowbar

test. No overshoot observed. Trials were taken and

starting was found to be smooth. Problem solved.

LOAD PLL FAULT

R05, 0207, VI

2. Slave channel current oscillates at higher load and

this happens whenever the current demand is

greater than 50%. Sometimes the channel trips on

Load PLL fault. INVLIM sets to 4096 sometimes

during the period when current oscillations occur.

During this time the Master channel current is

steady.

Found that NLIB Source and Load cards were

interchanged. This was done after all the checks referred

as given in Annexure for this fault.

Interchanged the cards. Problem solved.


Page 73 of 95


COMMUTATION

FAILURE

R05, 1106, VI

1. Slave channel FanB Ch-2 trips on Load Commutation

Failure after certain speed.

Observed that below tripping speed Load side feedback

0IA was missing. Found that links on CT shorting

terminals were loose on CATDM4 TBs. Tightened the

same. Problem solved.

MISC

R05, 1106, VI

2. After certain speed, slave channel current oscillates

but master channel current remains steady.

INVLIM does not set during this time in slave

channel.

Found Load side CT phasing of 0IC is not OK. Corrected

the same by reversing the Secondary terminal

connections. Problem solved.

I/O ADDRESSING

PROBLEM

R05, 0407, PH

3. Channel running normally. Trips sometimes on I/O

Addressing problem. With this, other IOMA Input

faults like Fan Compartment door open are also

displayed. BUSHOG LED on HMPG does not come

ON.

Changed all ’H’ cards in SEM HAIA, HLCB, HRDA one by

one. No change observed. Changed HMPG but retained

DMPB. Problem solved.


Page 74 of 95

Category Sl.no. Problem Solution GROUND FAULT

R05, 0207, PH

1. Slave channel trips on Ground Fault when paralleled

with Master.

Backcharged Ch-2(Slave). Found that one load side

feedback voltage at Load NSFC 2B was not OK. Found

one resistor of the attenuator resistor network was open

in LTM2 HPTK. Changed HPTK. Problem solved.

MISC

R05, 0707, PH

2. During exciter test current is unbalanced. But when

exciter output is connected to a dummy load, the

R,Y,B currents are balanced.

The Stator resistance of the exciter (each phase) was

equal. But when measuring the inductance of each stator

phase of exciter, the values were different. Found that

the start and end of one phase of exciter rotor star

winding was connected wrongly. Changed the connection.

Conducted exciter test. Currents balanced. Problem

solved.

It is inferred that during exciter test, if the shaft of the

motor was moved to different positions, the exciter

current imbalance would have shifted from one phase to

another.

MISC

R05, 1107, PH

3. Source breaker trips without any alarm or fault

annunciation. Trip is from IOMA SWGR relay. Trips

occur spuriously. No pattern i.e random.

Changed HRDA and HROA. But problem persisted.

Observed that in HRIA inputs low level DC voltages are

present even though input contacts to HRIA open –

Suspected backplane board problem. Complete IOMA

module changed. Channel taken into service. Problem

solved.

MISC

R05, 1107, PH

4. Output circuit breaker trips without any alarm or

fault being annunciated. Trip is from IOMA RUN

relay. Trips occur spuriously. No pattern i.e random.

Checked the auxiliary contact of Load side circuit

breaker. Operation and change of MISOL input is OK.

Observed that in HRIA inputs low level DC voltages are

present, even though input contacts to HRIA open.

Suspected backplane board problem. Complete IOMA

module changed. Channel taken into service. Problem

solved.


Page 75 of 95


R05, 0907, PH

1. Channel was in service and running OK. After

shutdown while starting, Fan speed reaches minimum

speed but LMODE remains at 1. Also does not

parallel with other channel over minimum speed.

Gate test mode OK. Crowbar test OK. Back-charged over

minimum speed. Load FAB, FBC, FCA values were same as

other channel.

MTRFMIN and FLUXS Lowered by 0.1. LMODE=1

changed to LMODE=3. Problem solved.


Page 76 of 95


COMMUTATION

FAILURE

R05, 0107, PH

1. When channel is run individually, speed does not

raise. Current hunting is observed and channel trips

on Load commutation failure.

During current hunting INVLIM was being set to 1.

(Source-load differential). Found CT phasing on Load side

was not OK. Corrected the same.

Drive started and found that IFB Source and IFB Load

DC Volts on NLIB Source and Load not equal. Adjusted

XTFX CT burden resistor potentiometers to make CT

burden on load side equal to that of the source. Channel

started and resumed trials. Problem solved.


Page 77 of 95


R05, 0307, VI

1. Motor takes very longtime to start. During starting period, it was observed that firing pulses

to STM1 were not present as LED on HPTK STM1 not

glowing. Replaced HPTK on STM1. Problem solved.

MISC

R05, 1007, PH

2. When START command is given from Remote,

Output CB closes but opens after 3 to 4 seconds.

Checked whether RUN command from Common Control

panel was ON. Found OK. Put clip on 220V Jyothi relay in

VCB. No change. Suspected HRIA card RUNX relay 1BH49

not working. Swapped HRIA card 2A & 2B. Problem solved.

MISC

R05, 0607, VI

3. Master and Slave do not share equal current when

paralleled. When speed is raised, heavy oscillations

occur in Slave (Ch-2).

Found that in IOMA TB07/10,11, the polarity of current

reference going to Slave (Ch-2) was negative instead of

positive (Motoring condition). Changed NLCB card in

Master. Problem solved.

LOAD

COMMUTATION

FAILURE

R05, 1107, VI

4. When drive runs on single channel and higher speed

and load, Load commutation failure occurs after

three hours approximately.

All tests as given in Annexure of Compendium already

done, but problem persists. The 180K resistors on NLIB

load R60, R68, R76 for XL compensation of motor

changed from 180K to 100K. Channel taken into service.

Problem solved.


Page 78 of 95


R05, 0707, PH

1. When channel is run individually, current hunting

takes place. INVLIM does not set to any value and

remains at zero continuously. There was light

hammering sound in the motor.

Since INVLIM does not set to any value, it was inferred

that the problem would be in the excitation circuit. Did

exciter test. Excitation currents balanced. Motor was

thoroughly inspected. Condition found OK. It was thought

that the sound in the motor could be due to sudden

change in the magnetic centre during running. Excitation

IFB waveform on NSFE checked when running. Found

that sometimes the waveform was getting disturbed.

Changed NSFE card slot 2E. Problem solved.

GROUND FAULT

R05, 1207, PH

2. Channel gives Ground fault during crowbar. But,

when back-charged from other channel, ground fault

does not occur. Channel is 2.3kV LCI.

Checked MOV, RC circuits on Load & Source side and also

DC Link Source/Load. All found OK. All earthing checked

and found OK.

Crowbar was performed with 415Volts (earthed supply) on

Load & Source bridge separately, by swapping NSFC

connectors on Source/load and current feedback ribbon

cables on SEM header, when during Load side crowbar,

only 3 resistors in XPTN put in circuit. Ground fault

occurred in both instances of Source & Load crowbar.

While doing this test with isolated 415Volts supply,

Ground fault did not occur. It was suspected that the

problem could be only on Source side circuit between

Transformer and Source bridge. When cables were hi-

potted, Y phase cable gave fault w.r.t ground after 2.5kV

AC. Examined cable and found at one location insulation

was slightly damaged. Cable changed to new. Conducted

crowbar test. OK. Channel taken into service. Problem

solved.


Page 79 of 95

Category Sl.no. Problem Solution GROUND FAULT

R05, 1207, PH

1. Channel gives Ground Fault during Crowbar test. No

ground fault when back-charged with 415V 3ph from

Load side and with only 3 resistors shorted on load

and source HPTF. Channel is 1.2kV LCI. Other

channels not available for back-charging.

It was inferred from the 415V back-charging that the

ground fault will be on the source side. Checked RC circuit

and MOV circuit on Source side. Found that star point of

Source MOV was earthed, instead of the earth being

done from the fourth MOV. Changed the connection as

per scheme. Crowbar performed OK. Problem solved.


Page 80 of 95

GENERAL CHECKS:

1. Check thyristor gate pulses in Gate test mode.

2. Check thyristor and snubber healthiness.

3. Check healthiness of load, source and DC circuit capacitors, MOVs.

4. Check passing of Self test .

5. Conduct crowbar test and get OK results. During crowbar the voltmeter on C&EXE panel should show zero volts and must be

steady at that value. Also Source phase currents must be clean without any spikes.

6. Conduct Megger test on complete power circuits from transformer upto motor. 7. Remove motor inspection cover. Check healthiness of windings w.r.t. earth, between windings.

8. Check CT /PT feedback circuits.

9. Ensure proper earthing of SEM Rack by removing paint at various points.

10. All connections including busbars, connectors, wires, crimped terminals are to be checked for tightness. Ensure SEM Lock bar is firmly in place.

11. All electronic cards, thyristor power modules, air filters are to be blown with clean air to remove dust.


Page 81 of 95

CHECKS FOR GROUND FAULT , LOAD COMMUTATION FAILURE, LOAD PLL FAULT :

1. Check SEM earthing OK.

2. Back charge Ch-1 from Ch-2 by tripping Ch-1 source breaker and locking it out. Then close output contactor by shorting IOMA

TB8 after removing RUN relay from IOMA plug-in base. Check the waveform of attenuated voltages at NSFC Load and Flux

waveforms at NLIB-load. Check the waveform at NTL on NLCB . Ground fault occurs if NTL > 0.55V DC.

3. Check capacitors on load side by meggering with 1000V or 500V megger across its terminals & also w.r.t ground. Discharge

capacitors by using the 20M, 2W resistor on the DC capacitors or any suitable rheostat. Check capacitance values of Load side

capacitors by LCR bridge. 4. Remove end covers on the panels and check that the earth bus is continuous from C & EXE. Panel to ACOP panel. If earth bus is

broken in between the panels, bridge this connection with 25sq.mm Cu cable. Also check the JL solder stud on XTFL-Load is firmly

soldered and the wire from this point firmly connected to the earth bus running on the rear of the panels. Ensure that SEM

ground gives proper continuity with this stud. 5. Hi-pot to earth cables from motor to Output Contactor /Breaker after removing both ends of cable. Hi–pot voltage can be

restricted to the voltage, at which ground fault occurs.

6. Check load connection in load side MOV and load side RC filter circuit. Check healthiness of fuses on this circuit.

7. Check values of variable components in SEM cards as per Schematic diagram. Formatted: Bullets and Numbering


Page 82 of 95

Annexure-1: EARTHING FOR SEM RACK

S S S N

S

CARD N Aluminium

SLOTS Extrusion

Aluminium

N Extrusion Z

CARDS GND

SLOTS N

SEM FRONT Y

VIEW Cu. Braid

Remove only one Nut/Bolt at a time. Check Spring/Plate washer present

1.Remove paint on both sides of Nut/Bolts marked ‘N’.

2.Remove paint on Nut side of ‘S’ and lacquer on PCB board track(if lacquered) on Head side of ‘S’.

Test with mulimeter if in doubt. Generally this mother board will not be lacquered.

3.GND is tinned copper ground bus in C & Exe Panel (Regulation panel in high current rectifier) .

Make connection ‘Y’ at site(if not already present) with 25-sq. mm. Aluminium or copper cable with lugs on

both sides. Check if ‘Z’ cable copper/PVC already exists. If not make connection ‘Z’. Cable ‘Z’ is 16 sq.mm.

Copper braid/PVC cable, connection may already done at BHEL/EDN in Panel.

Front Back Front Back

CCC

SEM SIDE SEM SIDE SEM BACK

VIEW VIEW COVER

4.Scrape paint on both sides on plate of nut/bolt ‘A’ and ‘B’. Exercise caution as the motherboard

pins may get bent accidentally when doing this.

5 Scrape paint on back cover on head side of screws’C’.

6.The objective of these points 1 to 5 is to ensure that PCB(mother board) ground track mentioned in

point 2 is perfectly connected to tinned copper earth bus in C & Exe, panel(Regulation

Panel in high current rectifier).

7. All Nut Bolts to have spring and plate washers. Only plated washers to be in contact with paint

scraped surfaces only. Replace if biting/toothed washers are present. Replace one at a time.

8. Check that the PCB motherboard pins have not been bent.

9. Re-check all points 1 to 8 above have been done. Check for continuity between ‘S’ and ground

copper flat.

10.Install SEM back cover carefully.

A

A

A

B

B

B

C C

C C

C C


Page 83 of 95

Annexure-2: DETAILS OF FT1 AND FT2 INDICATION ON LED BAR

IN NLCB CARD

FT1

UNLATCH

ISTLINHB FT1

RESET

SUPP(S)

OSFT1

FT2

10SP FT2

SUPP(L)

OVA(L) FLT(SWRE)

FT1 AND FT2 are the first two LED’s seen from the top on the BAR LED of NLCB with

inscriptions of FT1 and FT2 respectively.

1. Description of FT1:-

The logic for the LED FT1 being ON is as given in the diagram above.

When the FT1 LED turns ON it also closes the SWGR relay in the IOMA to trip the source

breaker, if it is closed or if the source breaker is closed the permissive to close is lost.

FT1 is turned ON in case of major faults. They are the Hardware Source over-current,

Microprocessor stall (µP stall) and System Fault (Not(NSFLT)) as detailed below.

a) Hardware Source over-current (SUPP(S)) :- The currents from the 3-phase of the

source side obtained through CT’s are rectified in the analog boards to obtain a DC

current feedback IFB which is compared in the source NLIB board with the SUPP

settings to initiate source over current after 25ms.A source over current has occurred

and it persists for a period of more than 25ms. The message in case of this condition

is “Source back up over current fault”.

STALL

INHIBIT

OR

RD

OR

RD


Page 84 of 95

b) Microprocessor stall (µP stall): To detect software malfunctioning and Software code

runaway a hardware circuit is built consisting of a tickle timer in Monoshot mode. In

the event the software does not regularly reset this timer as the software has run away

or in the case of malfunction this timer generates a stall signal.

c) System Fault (Not (NSFLT)): - Please see the Ladder logic in sheet 1FE of the LCI

scheme. This is declared under any of the following conditions: -

a. Source current imbalance. (Series 12 pulse only)

b. Source over-current.

c. Loss of cooling fan.

2. Description of FT2: -

The logic for FT2 led to turn ON is as given in the diagram in previous page. When the FT2

turns ON the fault relay IOMA also closes. Thus a fault is annunciated.

FT1 is turned ON in case of Over-speed (1OSP), Load Over current (SUPP (L)), Load over

voltage (OVA (L)) and Channel fault (NOT (NCFLT)) as detailed below.

a) Over speed (1OSP):- The speed feedback is obtained by the hardware circuit on the

NLCB from the voltage waveform of the load side. When this speed signal exceeds

the setting of OSP on the NLCB then this is actuated.

b) Load Over current (SUPP (L)): (Load backup over current fault) The currents from

the 3phases of the load side obtained from CT’s are rectified in the analog boards to

obtain a DC current feedback LIFB which is compared with the SUPP setting on the

load NLIB board to initiate load over current after 25ms. The message in this

condition is the “Load backup over current fault”.

c) Load over voltage (OVA (L))( Load AC over voltage): - The 3∅ voltages of the load

side are attenuated and available at the input of the load NLIB boards. The analog

board has a rectifier circuit converting these AC voltages to DC. This DC voltage is

compared with the OVR setting of the load NLIB board and when greater initiates a

load over voltage fault.

d) Channel fault (NOT (NCFLT)): -The NCFLT is as per ladder logic on sheet 1FE of

LCI schematic diagram. The Channel fault is declared when a hardware or software

fault occurs in the drive as per the logic in sheet 1FE.


Page 85 of 95

Annexure-3: Details of Fault and Alarm Messages in the LCI Drive

FAULT MESSAGES: -

1. LOSS OF COOLING FAN : -

Please refer ladder logic sheet no 1FK

LOGIC = NOT (NBLF)

2. SOURCE LOW LINE


LOGIC = SUVFLT

3. FIELD LOSS


LOGIC = FLD_LOSS_FLT

4. SOURCE BACKUP OVERCURRENT FAULT Please refer ladder logic sheet no 1FK

LOGIC = SRC_SUPP

INPUT = PORT 900C BIT 2

5.LOAD BACKUP OVERCURRENT FAULT Please refer ladder logic sheet no 1FK

LOGIC = LD_SUPP


6.SOURCE OVERVOLTAGE FAULT Please refer ladder logic sheet no 1FK

LOGIC = SRC_OV


7.GATING SUPPLY UNDERVOLTAGE FAULT Please refer ladder logic sheet no 1FK

LOGIC = GSUV

8.P105 SUPPLY UNDERVOLTAGE Please refer ladder logic sheet no 1FK

LOGIC = NOT (NPSUV)

9.LOAD OVERVOLTAGE FAULT Please refer ladder logic sheet no 1FK

LOGIC = LD_OV


10. OVERSPEED


LOGIC = OS


11.GROUND FAULT


LOGIC = GNDF


Page 86 of 95

INPUT = PORT 8010 BIT 0

12. FAN COMPARTMENT DOOR OPEN Please refer ladder logic sheet no 1FK

LOGIC = NOT(BFNDR)

13 .BRIDGE DIFF PRESSURE


LOGIC = BFDIFSW

14. FIELD CURRENT IMBALANCE: - FLTWD BIT 0

Field current imbalance check is for AC exciter only.

If a field current imbalance is detected by the NSFE card and persists for more than 0.5 sec then a fault is declared.

15. FIELD OVERCURRENT :- FLTWD BIT 1

If field current exceeds “FCLIM” for the no of attempts given by “ FCFTIME” then the fault is declared. A penalty

function is implemented such that 6 good firings following a failure will cancel a fault firing. This allows recovery from

non repetitive faults.

16. SHORTED MOTOR WINDING :- FLTWD BIT 2

During a start up from standstill, when the motor speed has exceeded the value set by “TRSPD” and the Load PLL is

locked. Then the peak flux reading taken at every 60 deg electrical from the machine (obtained from integration of load

voltages from NLIB Load card) exceeds its previous value set by “SWINDTOL”(approx 10%). Then a Shorted Motor

Winding Fault is declared. The shorted phase can be obtained from the variable Shorted winding in ENGG mode.

17.SOURCE OVERCURRENT: - FLTWD BIT 3

If source current exceeds “LKLIMS” for the no of attempts set by “LKOCTIM” then the fault is declared. A penalty

function is implemented such that 6 good firings following a failure will cancel a fault firing. This allows recovery from

non-repetitive faults.

18.LOAD OVERCURRENT : - FLTWD BIT 4

If source current exceeds the limit set by “LKLIML” for the no of attempts given by “LKOCTIM” then the fault is

declared. A penalty function is implemented such that 6 good firings following a failure will cancel a fault firing. This

allows recovery from non-repetitive faults.

19. SOURCE COMMUTATION FAILURE : - FLTWD BIT 5

During normal running of the drive, if the difference between the source and load current (read in synchronous with load

frequency cycle) exceeds the limit set by “LKLIMD” for the no of times set by “STHRUTIM” then a fault is declared.

A penalty function is implemented such that 6 good firings following a failure will cancel a fault firing. This allows

recovery from non-repetitive faults.

20.LOAD COMMUTATION FAILURE :- FLTWD BIT 6

During normal running of the drive, if the difference between the source and load current (read in synchronous with

Source frequency cycle) exceeds the limit set by “LKLIMD” for the no of times set by “STHRUTIM” then a fault is

declared. A penalty function is implemented such that 6 good firings following a failure will cancel a fault firing. This

allows recovery from non-repetitive faults.


Page 87 of 95

21.SOURCE PLL FAULT:- FLTWD BIT 8 The Source voltages are attenuated thro attenuator boards , conditioned in the firing card NSFC and then integrated in the

NLIB boards. These integrated signals are used for synchronization to fire the source bridge thyristors.

Software/Hardware Phase Locked Loop (PLL) does the synchronization.

If this synchronization is lost and remains as such for a period set by “SPLLTIM” then a fault is declared.

22.LOAD PLL FAULT:- FLTWD BIT 9

The Load voltages are attenuated thro attenuator boards , conditioned in the firing card NSFC and then integrated in the

NLIB boards. These integrated signals are used for synchronization to fire the source bridge thyristors.

Software/Hardware Phase Locked Loop (PLL) does the synchronization.

If this synchronization is lost and remains as such for a period set by “LPLLTIM” then a fault is declared.

26. FIELD OVERVOLTAGE FAULT:- FLTWD BIT 10

In Case The Exciter is DC. The field DC voltage is obtained through attenuators and the NSFF circuit. The NSFF circuit

has a over voltage detector (OOV) with fixed set point. When the field DC Voltage exceeds the limit the OOV sends a

signal and the Fault is annunciated.

23. STACK FAULT :- FLTWD BIT 11

The processor because of extraneous reasons may run away and may do unintended tasks very frequently In such cases

the STACK builds up. It is necessary to declare a fault in such cases.

24. FAILURE TO START :- FLTWD BIT 12

During start the speed regulator is open looped and the current command is fixed. The current command is ramped from

minimum current to a value required until motion is detected. Current reference ramps until the drive position has

changed 120 electrical degrees to maximum value of CUR_REG_REG_STRT_E. Motion is detected by looking for a

two cell pair change in the load side firings. If motion is not detected even after 5 secs then a fault is declared.

25. EEPROM TRANSFER FAILURE:- FLTWD BIT 13

The tunes up constants are stored in the EPROM of HMPG the Processor Board, during running of the drive these

constants are loaded in to the EEPROM for operation. If there is a problem in this operation during initialization then this

fault is declared.

26. MOTOR ISOLATOR NOT CLOSED Please refer ladder logic sheet no 1FK

LOGIC = MISOL_STATUS_FLT

27. TACH FEEDBACK OR HTCA PROBLEM

This fault is only in Drives using Tacho feedback with HTCA card. When the HTCA card or the tacho malfunctions then

this fault is declared.

28.SOURCE MASTER/SLAVE CURRENT UNBALANCE

29. SLAVE HARDWARE OVERCURRENT

The above two faults are declared in case of series 12 Pulse.


Page 88 of 95

ALARM MESSAGES: -

1.MOTOR OVERTEMPERATURE Please refer ladder logic sheet no 1FK

LOGIC = NOT(MOVTEMP)

2.TRANSFORMER ALARM


LOGIC = NOT(TTRBLE)

3.LINK REACTOR OVERTEMPERATURE


LOGIC = NOT(LTRBLE)

4.PCR OVERTEMPERATURE Please refer ladder logic sheet no 1FK

LOGIC = NOT(PCROT)

5.USER DEFINED ALARM Please refer ladder logic sheet no 1FK

LOGIC = NOT(USERA)

6.COOLING BLOWER LOSS Please refer ladder logic sheet no 1FK

LOGIC = NOT(NBLA)

7.BRIDGE FILTER FUSE BLOWN


LOGIC = NOT(BFILF)

8.RUN PERM OR START PERM MISSING


LOGIC = RUNPM, STRTPM

9.GATING SUPPLY DIP

Please refer ladder logic sheet no 1FE

LOGIC = GSUV_ALM

10.FIELD EXCITER VOLTAGE LOSS:- ALA BIT 0 01H

During start when the field is energized and the field voltage is built and present but its value is lower than required then

this alarm is declared.

11.ROTOR POSITION START ALARM ALA BIT 1 02H

During run If the motor fails to start within 1 sec from start, then this alarm is declared. The rotor position is determined

from relative flux amplitudes.

12.I/O ADDRESSING PROBLEM ALA BIT 2 04H


Page 89 of 95

The Processor is sending and receiving data from various boards within the SEM Rack. If the response of the Board

exceeds a given time then this alarm is activated.

13.MICROPROCESSOR ALARM ALA BIT 3,4, 5,6,7.8.9.10

The Processor switches tasks by means of interrupts. This alarm is activated when the processor receives unintended

interrupts.

14.SOURCE UNDERVOLTS ALA BIT 12 02H

If the Source breaker is energized, and the source NLIB indicates a Source under voltage condition then this alarm is

declared.

15.FIELD THERMAL OVERLOAD ALA BIT 13 02H

The field thermal model when enabled, checks the field current with time and declares an alarm if the current has

exceeded its time limit.

16.LOSS OF SPEED REFERENCE ALA BIT 14 02H

The drive remote reference will have value between 4 to 20 mA. If the reference falls below a value of 4 mA then this

alarm is activated.

17.LOSS OF SPEED CONTROL

During the drive operation in Self-commutation mode, if the difference between the Speed reference and the Speed

feedback to the Speed regulator exceeds the set parameter “SRETOL” for a time settable by “SQTMR5” then an alarm is

declared.

18.FIELD GROUND ALARM DC Exciter only.

A ground fault detector circuit is part of the NSFF Card on the SEM rack. This circuit detects grounds, which may occur

at the output of the Excitation module. This alarm is annunciated whenever this circuit is activated.

19. TACH FEEDBACK/HTCA PROBLEM

This Alarm is only in Drives using Tacho-feedback with HTCA card. When the HTCA card or the tacho malfunctions

then this alarm is declared.

STATUS MESSAGES: -

To accommodate drives which run multiple motors of different ratings a tune up variable “MOTSEL” is

available. (a set of drive constants for every motor is stored separately ).

1. MOTOR TABLE 0 SELECTED

This Message is annunciated when the first motor is selected.

2. MOTOR TABLE 1 SELECTED This Message is annunciated when the Second motor is selected.


Page 90 of 95

Rev.04

Annexure-4: Procedure for conducting Crowbar test with other channel in

service in 12 Pulse drives

Crowbar test can be conducted on either Master or Slave channel with the other channel running.

On the channel on which crowbar test is to be done remove the following wires:

a. IOMA TB5/09 Other channel running

IOMA TB5/10 Sht 1BD/2BD grid 61

b. IOMA TB7/10 Current reference to other channel

IOMA TB7/11 Sht 1BF/2BF grid 55

c. IOMA TB2/15 This channel running/RTPOS

IOMA TB2/02 16 Sht 1BG/2BG grid 5161

d. IOMA TB7/16 Current reference into this channel


e. Remove and put insulation tape on wires. Connect wires back in the same TB after

finishing Crowbar test.

f. Ensure Load side Breaker/Contactor does not close by switching OFF supply in

Breaker/Contactor. Short MISOL input at IOMA TB4/05 and TB4/06 Sht 1BD/2BD

grid 21. Remove this short after Crowbar test.


Page 91 of 95

Rev.04

Annexure-5: Procedure for Backcharging of one channel in 12 Pulse drives with

the other channel of the same motor in service

a) Rack out the Source 6.6kV/11kV breaker for the channel which is to be back-charged.

b) Remove RUN relay from its base on IOMA module.

c) Short IOMA TB8/05 & TB8/06 Sht 1BJ/2BJ grid 23 momentarily. The load side

Breaker/Contactor closes and stays closed.

d) Motor voltage feedback is now available on NSFC load and Motor flux on NLIB Load.

e) Trip Output Breaker/Contactor by momentarily shorting IOMA TB8/07 and TB8/08 Sht

1BJ/2BJ grid 29.

The load side Breaker/Contactor opens.

f) Put RUN relay back on its base in IOMA module.

g) Rack in Source breaker 6.6/11kV.


Page 92 of 95

R05

Annexure-6: Procedure for Conducting Exciter test on one channel in 12 Pulse

drives with the other channel in service

Exciter Test can be conducted on either MASTER or SLAVE channel with the other channel

running by connecting a dummy load consisting of Lamps and Resistors at the output of Exciter

bridge.

In the channel on which Exciter test is to be done, remove the following wires:

a. IOMA TB5/09 Other channel running

IOMA TB5/10 Sht 1BD/2BD grid 61

b. IOMA TB7/10 Current reference to other channel


c. IOMA TB2/01 This channel running

IOMA TB2/02 Sht 1BG/2BG grid 51

d. IOMA TB7/16 Current reference into this channel


e. Remove and put insulation tape on cables R,Y,B at the output of field exciter

and also in wires (a) to (d) above.

Connect the dummy load to Exciter bridge output. Perform Exciter test.

Connect the cables on the Exciter and wires on the IOMA TBs back in the same positions

before removal. Extreme care to be exercised while doing this test. Switch OFF circuit breakers and

power supplies whenever required.

Formatted: Indent: First line: 0 cm,Outline numbered + Level: 2 +

Numbering Style: a, b, c, … + Start at:1 + Alignment: Left + Aligned at: 1.27cm + Tab after: 1.9 cm + Indent at:

1.9 cm

Formatted: Indent: First line: 0 cm,

Outline numbered + Level: 2 +Numbering Style: a, b, c, … + Start at:1 + Alignment: Left + Aligned at: 1.27cm + Tab after: 1.9 cm + Indent at:

1.9 cm

Formatted: Indent: First line: 0 cm,

Outline numbered + Level: 2 +Numbering Style: a, b, c, … + Start at:1 + Alignment: Left + Aligned at: 1.27cm + Tab after: 1.9 cm + Indent at:

1.9 cm

Formatted: Indent: First line: 0 cm,Outline numbered + Level: 2 +Numbering Style: a, b, c, … + Start at:1 + Alignment: Left + Aligned at: 1.27

cm + Tab after: 1.9 cm + Indent at: 1.9 cm


Page 93 of 95


Page 94 of 95


Page 95 of 95

Date post:	21-Nov-2014
Category:	Documents
Upload:	vurumuu
View:	508 times
Download:	53 times

vfd

Documents