03

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PILLAR HEAD PRESENTATION

ON 28th Dec 2005

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FAILURE ANALYSIS - 1

Frequent tripping of C18 Breaker at BH-1

Problem

Date & Time: 01.06.05, 06.00PM & 02.06.05, 09.00AM

Failure Category: CMNT

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Introduction

C18 Feeder is one of the two main trunk feeders of 13.2 KV coming from PH-3 to BH-1 and supplies power to the West Plant area such as Blast Furnaces , Blower and Pump Houses , Spares Manufacturing etc.If this feeders trip, there will be load shedding to critical plants. The closing power to the breaker is 250 v DC & trip power is 48v DC.The closing & and trip power is tapped from the same supply.

The Breaker is of FERGUSION & PALIN make OCB and installed in the year 1951.

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C18 FROM PH #3

C23 FROM PH #3

10MVA , 13.2/3.3 KV

10MVA , 13.2/3.3 KV

B/C-1

300/5 B/C

2000/1

Single Line Diagram of BH-1

A FCE WPSSSP#4 A FCE BCP BOILER HOUSE#1RRE

RRW

PH#2TIE

PPH#2TIE

1000KVAT/F#1

GCPMOTORCONV

BLR1CONDENSER

BLR2CONDENSER

BLR3CONDENSER

ERS 1000KVAT/F#2

BCP#3 BCP#2

3.3 KV BUS

BUS PT

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Section area

Date & time of failure

Date & time of

restoration Equipment PartDescription of

problemObserved

byAttended

byCorrective

measure takenBH# 1 01/06/05 ,

06:00PM01/06/05 , 06:30PM

C18 Transformer

Breaker Trip w ithout any fault AKP AKP/BBS Checked the protection relays & Put on the breaker.

BH# 1 02/06/05 , 09:00AM

02/06/05 , 3:30PM

C18 Transformer

Breaker Trip w ithout any fault AKB AKB Put on the stand by source breaker& took the shut dow n of the feeder. .

Incident report

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Sl. No.Parameter Desired Value Actual Value Remarks1 Control Power 250 V DC 250 V DC OK2 Tripping Power 48 V DC 48 V DC OK3 Protection Relays Should not oper. Not operated OK4 Trip mechanism Healthy Healthy OK5 Trip Coil resistance 50 Ohms 52 Ohms OK6 Trip coil to ground resistance in Mega ohms 200 Ohms Not OK

Observation & Check points

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Trip coil ABB

Control Circuit

Closing coil ABB

Closing coil C23

Closing coil C18

Trip coil C18

Trip coil C23

Battery250 V DC

48v DC

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Root Cause1 Inadequate compliance with basic requirement2 Non-compliance with usage requirements3 Neglected deterioration4 Inherent design weaknesses5 Lack of skill

Removed the trip coil ground & Batery -ve ground by changing the cable.

Immediate action taken

Preventive actionInstallation of separate battery and charger Also provided earth leakage indicator.

CauseCable going to the trip coil getting grounded.

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Mr.T.Watanabe’s Comments

No Comments

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Frequent tripping of GHH Axial Blower at BH # 2

Date: 26th NOV’04 & 29TH NOV’04

Failure Category:REPETITIVE (CMNE)

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Tripping of Axial Blower without any

annunciation.

Problem

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AXIAL BLOWER

SILENCER ROOM

BLOWER # 5

IV-1, PNEUMATIC CONTROL VALVE, BACK-UP FROM ‘D’ FURNACE, OPERATING CONDITION COLD BLAST HEADER PR. < 7 PSIg.

IV-2, MOTORIZED CONTROL VALVE, BACK-UP FROM ‘G’ FURNACE, OPERATING CONDITION COLD BLAST HEADER PR. < 7 PSIg. (EITHER ‘F’ OR ‘G’)

BOV

NRV

DISCHARGE VALVE

FLOW MEASUREMENT ORIFICE

SNORT VALVE

STOVES BF

HOT BLAST

COLD BLAST

AXIAL BLOWER AIR BLOWING LAYOUT & CONNECTION OF BACK-UP SYSTEMS

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Incident report

Section area


Date & time of


problemObserved

byAttended

byCorrective

measure takenBH#2 26/11/04 ,

12:30AM26/11/04 , 01:30AM

Axial Blow er Turbine Axial Blow er tripped w ithout any indication.

RK /RSS RK/RSS Checked the system & found steam temp.w ent high. So Restarted the machine .

BH#2 29/11/04 , 07:30PM

30/11/04 , 08:30PM

Axial Blow er Turbine Axial Blow er tripped w ithout any indication.

AK /DCP AK /DCP Restarted the machine for analysis

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The System•The Axial Blower at BH#2 is a steam driven turbo blower and supplies cold blast air to ‘F’ Blast Furnace at a flow 1,50,000 Nm3/hr at a pressure of 2.6 bar gauge for meeting iron. This turbo blower was commissioned in the year 1982 and is of GHH Germany make and the Turbine is supplied by m/s BHEL.The Turbine governing system was originally fitted with Askania regulatorand due to failure of Askania regulator system has been retrofitted with in house developed Electronic Governor..The Electronic Governor speed used to fluctuate occasionally about 200rpm.Due to this problem we have hired the services of M/S Turbo Machinery Hyderabad,for rectification of the problem .They came here and did the modifications in the oil lines and the system has worked satisfactorily for about 2 weeks.•The turbine speed governing mechanism is electro-hydraulic and totally depends on the oil pressure. The minimum oil pressure required for smooth operation of the turbine is 6.5 bar. This oil pressure is developed by means of 3 pumps.one running & 2 standby.

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The System

• Normally, when the machine is in normal operation the shaft driven oil pump supplies the oil pressure. During start up of the machine steam driven pump develops the pressure and it is put off once the shaft driven MOP takes over. Separate steam driven AOP is a stand by pump. The turbine can be tripped electrically as well as mechanically. The electrical trip interlocks are ‘lube oil pressure low low’, ‘Turbine and Compressor Axial shaft low’ and Mechanical trips are ‘trip oil pressure low’ . ‘over speed’ and by operating manual trip gear.•The Turbine speed control is done by sensing the speed of the turbine shaft by means of three speed pickups and is compared against a set point in a controller and the output of the controller is given to a EHC. Control oil pressure is derived from MOP through a pressure regulator is given as input to EHC for developing secondary oil pressure for controlling steam inlet valve position for controlling the speed.

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TURBINE AXIAL BLOWER

T.AOP M.AOP

OIL COOLERS

P.OIL

G.O.P

MOP

OILTANK

MOP SUCTION

EOP

DUPLEXFILTER

LUB.OIL PR. REG.

LUB. OIL HEADER FOR BRG. OILPR.- 3.5 kg/cm²

TO BLOW-OFF VALVES

BOV OIL PR.REG.PR.- 11.5 kg/cm²

DRAIN OIL

BOOSTER PUMPS

BGP OIL PR. - 35 kg/cm²

TO OIL CENTRIFUGE

V.E.FAN

MOP REG.

GOP REG.OIL PR.- 6 kg/cm²

TRIP GEAR & TRIP GEAR TESTER

TO COMMON DRAIN

DRAIN TO OIL TANK

EHC

VARIABLE ORIFICEIN SOP LINE

SOP FROM SR- III GOVERNOR(CONTROL DESK)

TRIP OIL TO CONTROL DESK

PILOT PISTON & SERVO MOTOR

ESV

STEAM CONTROL VALVE

BLOWER SUCTION FILTER

BLOWER DISCHARGE

START- UP OIL (6 kg/cm²) & TRIP OIL (5.5 kg/cm²) FROM CONTROL DESK

MOP OIL REGULATING PR.- 7 kg/cm²

ORIFICE IN MOP LINE

STEAM TO TURBINEPR.- 15 kg/cm², T- 315°C

OIL INJECTOR

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OBSERVATION

.

• All the operating parameters were normal before the trip

• Suddenly the machine tripped.

• Emergency systems such as start up of Auxiliary oil pump and start upof emergency air worked properly.

• The system has not recorded any trip signal provided in the trip logic ofAxial Blower.

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.

Speed controller

CAUSES OF TRIP


MECHANICALMECHANICALELECTRICAL

LUBE OILPRESSURE LOW

LOW

TURBINE AXIALSHIFT HIGH

HIGH

TURBINE OVERSPEED

MANUAL TRIP LEVER

TRIP OIL PRESSURE

LOW

DAS NOT RECORDED

DAS NOTRECORDED

DAS NOTRECORDED

DAS NOT RECORDED

DAS NOTRECORDED DAS RECORDED

BLOWER AXIALSHIFT HIGH

HIGH

DAS:- Data Acquisition System


As the Trip oil pressure can become low due to the following reasons which were checked and rectified.

MSV malfunction Checked and found ok.PLC malfunction Checked and found ok.Cable defective

Over speed mech. Checked and found okManual trip lever

Not responding

Electrical

Pressure regulator Checked and found ok.

Checked and found ok.

MechanicalChecked and found ok.

Oil pressure variation with respect to speed

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Action taken Secondary Oil line has been taken from the main oilpressure line instead of trip oil circuit.

OIL PRESSURE TURBINE SPEED0 40004 4100

4.5 42004.75 4300

5 44005.5 45005.8 4600

Observation on trip oil pressure vs turbine speed

Minimum oil pressure required to hold ESV valve is 4.0 barCause of trip : sudden increase in load use to reduce the turbine speed hence reduction in trip oil pressure due to more consumption of oil in EHCCircuit.

TURBINE SPEED vs OIL PRESSURE

3600

3800

4000

4200

4400

4600

4800

0 4 4.5 4.75 5 5.5 5.8

OIL PRESSURE

TUR

BIN

E S

PEE

D

TURBINE SPEED

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.

Speed controller

Modified line

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Wrong tapping of oil line in the turbine oil governing circuit.

Analysis Correct But Implementation Not CorrectPoor Design Change

Inherent design weakness

Cause

1 Inadequate compliance with basic requirement2 Non-compliance with usage requirements3 Neglected deterioration4 Inherent design weaknesses5 Lack of skill

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Sudden Flow Reduction to the ‘F’ Blast Furnace

Problem

Date & Time13/04/05,6:15AM ; 14/04/05,11:05 ; 16/04/05,08:45

Failure Category: CMNM

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Section area


Date & time of


problemObserved

byAttended

byCorrective

measure takenBH# 3 13/04/05 ,

06:15AM13/04/05 , 06:25AM

Turbo Blow er

Blow ers Flow reduction to the Blast Furnace

SP SP/TkS/SPD Increased the f low set point.

BH# 3 14/04/05 , 11:05PM

14/04/05 , 11:15PM

Turbo Blow er


AKD AKD/ASS/SP Increased the f low set point.

BH# 3 16/04/05 , 08:45AM

16/04/05 , 08:55AM

Turbo Blow er


SP SP/SKD/SPD Increased the f low set point.

Incident report

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The System

•There are two nos of Demag make Turbo Blowers at BH #3 and supplies about 170’000 NM3/Hr. at a pressure of 2.6 Bar to ‘F’ Blast furnace.•These two blowers run in parallel with load sharing control.•The discharged flow of the blowers is controlled by varying the speed of the turbines and inlet guide vanes of the blower.•The speed is varied from 0 to 7900 rpm and the blade angle of the compressor is varied from +40 deg. To -14 deg.•The two Blowers have separate anti surge control ,individual flow control and common flow control.

System BPH

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DEMAG BLOWER 2

DISCHARGE VALVE

SNORT VALVE

STOVES F BLAST FURNACE

HOT BLAST

COLD BLAST (170’000 NM3/Hr. at a pressure of 2.6 Bar )

DEMAG BLOWER 1

BLOWER HOUSE #3

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SYSTEM


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Sl. No.Parameter Desired Value Actual Value Remarks1 Discharge flow at Blower end 1,70,000 NM3/Hr 1,70,000 NM3/Hr OK2 Discharge Pressure at Blowerend 2.6 Bar 2.6 Bar OK3 Flow at 'F' Blast Furnace end 1,70,000 NM3/Hr 1,55,000 NM3/Hr Not OK4 Pressure at 'F' Fce. End 2.6 Bar 2.5 Bar OK5 F' Fce. Snort Valve Position Fully closed Fully closed OK6 Leakage in stoves/CB pipe line Nil Nil OK

OBSERVATION

System BPH

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DEMAG BLOWER 2

DISCHARGE VALVE

SNORT VALVE

STOVES F BLAST FURNACE

HOT BLAST

COLD BLAST (170’000 NM3/Hr. at a pressure of 2.6 Bar )

DEMAG BLOWER 1

BLOWER HOUSE #3

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SYSTEM LAYOUT WITH G BLAST FURNACE


G BLAST FURNACE

M

New G Furnace Blower

PLANNED MAINTENANCE


System

Demag BLOWER

New Blower

DISCHARGE VALVE

SNORT VALVE

STOVES BF

HOT BLAST

COLD BLAST

SNORT VALVE

STOVES BF

HOT BLAST

F

GM

Inter connectionValve

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Then compared the ‘F’ Furnace Flow and pressure with ‘G’ Furnace Flow and pressure on real time basis in the data acquisition system and noticed this problem was happening during ‘G’ Furnace going on low pressure.

Observation

0

50000

100000

150000

200000

250000

300000

1 2 3 4 5 6

Time

Flo

w (

nm

3/h

r)

F-Fce FlowG-Fce Flow

Trends

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0

0.5

1

1.5

2

2.5

3

3.5

4

1 2 3 4 5 6

Time

Pre

ssu

re

(b

ar)

G-Fce Pr.F-Fce Pr.

Trends

From this observation we checked the inter connection valve. Found the valve indication was showing closed . When we rotated the valve manually , it got closed further 4 turns.

From this it was understood that the main cause was “Disturbed Close limit switch position”.

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The valve was manually closed fully and valve open / closelimit switch has been readjusted.

Action Taken

1 Inadequate compliance with basic requirement2 Non-compliance with usage requirements3 Neglected deterioration4 Inherent design weaknesses5 Lack of skill

Root Cause

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TBM Schedule Not Made

Problem is due to:

Preventive Action

Actual valve open / close checking has been introduced in the Turbine Start up check list.Periodic calibration of the valve has been included.

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