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ENGINE

GOVERNING SYSTEMSIN E R N A TIO N A L

LS 671A SECTION EG 70-10

PRECISE LOAD SHARINGMODULE

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ENGINE

GOVERNING SYSTEMSir-_ T E R N A T IO N A L

LS 671A SECTION EG 70-10

INTRODUCTION

The LS671A Precise Load Sharing Module is an accessory outputs, a multiple arrangement of generator sets can be

device used in conjunction with the AMBAC International connected in parallel to share load equally. The module

Engine Governing system. It measures the true power can also be used to control the power output of one or

output of an AC generator and converts this output to a more generator sets delivering power to an infinite bus.

proportional DC voltage. By proper connections of the

SPECIFICATIONS

LS 671A PRECISE LOAD SHARING MODULE PERFORMANCE CHARACTERISTICS

--Load Sharing .................................................... Adjustable to within +2% between sets

--Performance .... .. .. ... .. .. ... .. .. ... .. .. ... .. .. ... .. .. Isochronous or droop paralleling and power control

POWER INPUT

--AC Signal ........................................... 208 or 416 volt (nominal) line-to-line, 5 amp., CTS,with minimum 12.5 VA rating (internal 0.5 ohm

burden resistors).

--Supply ......................................... 10 VDC from terminal K of "C" series speed control unit

--Line-to-Line Voltage ..................................... HZ LOW RANGE ItIGIt RANGE

Min Max Min Max

*50 70 104 140 208

*60 85 130 170 260

50 140 208 280 417

60 170 260 340 500

400 170 260 340 500

*Low range input voltages can be accepted as long as CT

secondary current is limited to 3 amps at maximum rated

load. If higher voltages must be used, external PT's can be

added. The transformer burden capability is insignificant.

ENVIRONMENTAL

--Temperature Range ................................................. -550 to + 85C (-650 to + 185F)

--Relative Humidity ....................................................................... up to 100%--Case .............................................................. Fungus proof and corrosion resistant

PHYSICAL

--Dimensions ............................................................................ See Figure 1

--Weight ............................................................................ 1.5 kgs (3.3 lbs)

--Mounting ........................................................ Any position (See Installation Page 6)

RELIABILITY--Tested ...................................................................................... 100%

--Vibration ................................... All printed circuit boards are conformally coated on both sides.

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ENGINE

GOVERNING SYSTEMSET'_T E R N A T I O N A L

LS 671A SECTION EG 70-10

TEST

185mm 10ram ,ql-- 52mm _[I'_ 7.2812" O.375" 2.0625"

I 13mm lI 0.5"

F

LOAD SHARING

SENSITIVITY

DROOP

O LOAD ANTIC('_ADJUSTADJUST

PARALLEL

416 JUMP FOR CABLE TO

I I 2osl oRooP r-] OVE..O.CT CT CT _ I R H K

1 2 3 1 2 3 4- - 152mm

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 6"

t-'11" _ I" "_I" pu--|_' "t'l--i_ _T J -I't TI--I 1- ,'-I -r I_'-_JT ,-1 Tl--i'-I-r'l--I _ _ I

m

P'__ F-,_F,_ _q P_F_I F'_Pq F:,,_-;IFq P_P-,,p_0p_ rr_ P_r_

LJL IL L IJ JL UJ LIJ J__I.L LI J.L U U jL. IJ. J. L LI -I1

8mm "_

0.3125" TYP.

207mm8.1562"

7mm

0.2056" DIA. -4 HOLES

Figure 1. LS 671A precise load sharing module dimensions

DESCRIPTION

A single engine generator set operating on an isolated load If each of the two engines in parallel was controlled by an

may run well isochronously. Thus, under all load condi- isochronous governor each would try to force its speed to be

tions, the steady state frequency of the generator is the the sameas its reference. Although two isochronous gover-

same. The only deviations fromthis steady state frequency nors could be set to nearly the same frequency, it is not

are caused momentarily by sudden load changes or tran- possible for their references to be exactly the same. Under

sients. However, if two engine generator sets are used to these circumstances the two engines must run at some average

supply power in parallel to a single load, the two generators speed. The first engine whose governor reference is at a

are forced to run at exactly the same speed and in phase slightly higher frequency will try to increase its power

with each other. When two generators are connected in generation. On the other hand, the second engine with its

parallel and supplying a common load, any tendency of one governor set slightly below the average speed, will keep

unit to get out of phase with the other is resisted by the decreasing throttle in order to slow down. The net result is

magnetic forces (synchronizing torques) within the that in a short time, the first engine will be taking all the load

generators as if they were connected together with a chain it can and the second engine will be dropping off as much as it

drive, can until its generator begins acting as a motor which will

drive the second engine.

Pnnted*nU S A Page 2 IssuedAugust, 1989

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ENGINE

GOVERNING SYSTEMS

[ I N T E R N A T I O N A LLS 671A SECTION EG 70-10

To force the engine s t o carry equal loads, true power Line current inputs are usually from existing CT's which

measuring devices, called Precise Load Sharing Modules (LS may be part of the ammeter circuits. Accurate instrument671A or LS 672A), are used (see Figure 2). CT's with secondary ratings of 5 amps and a minimum volt-

amp rating of 12.5 VA should be used. Due to wire

This module takes the voltage and current of each of the resistance in the CT lines to the load sharing unit, the volt-

three phases of the generator and develops a DC voltage amp rating of the CT must be increased accordingly. Output

proportional to true power. The voltages of the several sets of the load sharing unit is a DC voltage proportional to real

are averaged and the voltage difference between the average load. This voltage can be measured at terminals 14 and 15

power and the actual power of each set is sent to the (15 negative) or test points shown in Figure l and ranges

reference point of each speed control unit. Thus, if a given from 0 to about 8 volts depending on engine load and CTengine generator set tends to generate at a power level dif- ratios.

ferent from its proportionate share, a correction voltage is

sent to its governor reference to correct its power. Since Maximum voltage measurement will be obtained when the

there is as much positive as negative correction, the overall sensitivity control is full CW. All the load sharing units are

system remains isochronous. This system is very accurate connected in parallel via the parallel cable (terminals 14and is independent o f actuator and throttle characteristics, and 15). If any voltage difference between paralleled units

However, it can be applied only where each set has as its exists, a small DC current will flow in the parallel cable.

principal load, a single generator. This current will cause the respective speed control unitsreferences to be set to a slightly different speed; some

Load Sharing raised, some lowered. Since the increases in reference speeds

The load sharing unit is an electronic equivalent of the watt- are balanced by the decreases, the system speed remains un-

meter (see Figure 3). The inputs to the load sharing unit are changed. Only the load will change in the direction to

line to line voltage, line currents and battery supply, reduce the paralleling cable current to a minimum. TheNominal voltages of 208 volts or 416 volts (measured from sensitivity control can be used to match the generator

line to line) can be used. Lower voltages can be accepted by power output of each unit to others.adjusting the CT ratios (See specifications on page 1). If

higher voltages must be used, external PT's will be required.

Battery supply is for operation of the relay circuits.

FLYWHEEL _ FLYWHEEL

THROTTLE /GEAR _ GEAR \ THROTTLE

/..... / , CIRCUIT f C IR CU IT , _ I.... ,I

/, =]I I I _"*RENT I BREAKER [ BREAKER I CURRENT I .... I_ : I ...... ;I", PRIME , !-J MAIN ' SENSING ,_x / 0/-', I SENSING -- "_=" "_-I Mr;VER II

MOVER f= GENERATOR I GENERATOR I C ._O.t h-ITRANSFORMER:b ': TRANSFORMER77 ri ."ir =l/ J[ I I i i I , I t l= -_---,_

I..... _ -I MAGN ET-I C " [ " I 3e | I 31 I ! MAGNETIC._'_ 1, LJ"SPEED | I CURRENT | _ CURRENT I | SPEED t_J I

' _- - - -ITSENSOR| I SENSING : = SENSINGI-_ / SENSOR/r "----_.,4 _ / ]3e l I I ue / /I "

....... _._ i/ IVOLTAG_-I _ I IVOLTAq L_ l A ',TUATOR ILRt_/uPt/ )111 I I -- -- --

---/ 7 ., , ! NSING / [

/ I I LOAD o----o LOADi ISPEED_--_ SHAR,NG_ PARALLELCAD'E _ SHAR,_r--_ SPEED

CONTROLI I COmOLI-----O_'% C_O_____ICONTROLI I coNTRLUNIT I t (TRUEPOWERt / (TRUEPOWER)I I UNIT

J [ MEASUREMENT) 1 1MEASUREMENT)I I

Figure 2. Functional schematic of two engines in parallel

Printed in U S A Page 3 IssuedAugusl 1989

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ENGINE

GOVERNING SYSTEMSI_ T E RN A TIO N A L

LS 671A SECTION EG 70-10 _'_

TERMINALS

IDROOP

I / I JUMPER

SENSITIVITY _1 FOR

30VOLTAGE _ +! ADJUST IOK _ _.__ j DROOP

CW l 15 I CABLE

3, CURRENT -= I" ) :'-i--18 I. _J + 10V FROM

II REF (TERMI NAL "K")WATTMETER

/ __,_, OUTPUT (TO TERMINAL "R") OF "C" SERIESSPEED CONTRO1__ J.

DIFFERENTI--_ _ I UNITAMPLIFIER

'1 17 _1 GROUND (FROM TERMINAL "H")

I

I

Figure 3. Power measuring circuit

Load Anticipation unit will be reset back to synchronous speed, thus limiting the

A load anticipation signal is included in the module to load. The engine load level can be adjusted by using the

minimize speed transients. An internal control is provided to power bias control to any level from zero to full load.

adjust the sensitivity of the load anticipation signal. CW

rotation of the adjustment increases sensitivity. POWER & LOAD TRANSFER CONTROL FORSEVERAL GENERATORS

Droop A single power and load transfer control for severalWhen paralleing with an infinite bus, droop is often used. generators paralleled to the utility main can be added by

An internal control is provided for droop adjustment and is following the connections and circuits shown in Figure 5.The circuit depicts load sharing connections for twolocated under the dot plug on the cover.generators but additional generators may be added with

POWER CONTROL -- SINGLE GENERATOR more respective connections of 30K resistors to terminal

Control of the power output from a generator that is "R" of the speed control units and terminals 14 and 15 of

operated in parallel with an infinite bus can be accomplished all LS 67 IA load sharing modules connected in parallel. Ter-

by using the load sharing unit to provide power control to minal 16 of the additional LS 671A load sharing modules

the speed control unit. An engine generator system which should also be connected to terminal "R" of their cor-

will operate under isochronous speed control in standby responding speed control units. The load transfer control

operation and under load control when in parallel with a including the 100K droop resistor remains unchaged asmain bus automatically is shown in Figure 4. Many varia- additional units are added. The power level accepted by all

tions of the power control circuit can be constructed, but the generators can be set by closing the load transfer switch and

principle is usually the same. The load sharing is connected manually adjusting the load transfer control. The power

to the generator as shown in Figure 4. The generator is syn- transferred from the utility mains will be shared by the

chronized and connected in parallel to the main with no generators to the proportion previously set for each LS

load on the generator. As soon as the auxiliary contacts are 671A load sharing module. Refer to "Adjustments, l.oad

closed, the load sharing unit's output voltage is zero (units Sharing". Full load from the utility main can be transferred

sensing no load). The speed control units speed setting will by moving the adjustment of the load transfer control

automatically be set higher than the synchronous speed. The toward the maximum position until the utility main is carry-

engine load will quickly rise along with the voltage output of ing no load. The utility main can be disconnected tom the

the parallel cables. When the parallel cable voltage has generators once full load is transferred with minimum elec-

reached the power control bias voltage, the speed control trical disturbance. Once separated, the unloading swilch

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ENGINE

GO VERNING SYSTEMS

[INTERNATIONAL

LS 671A SECTION EG 70-10

should be turned off to eliminate any droop. The separation engine/generator sets are synchronized to the utility mains

of the utility main from the generators allows the load by using the load transfer control to match the generatortransfer control to be used as a frequency control for all the frequency by changing engine speed. The main breakers can

engine/generator sets. Speed changes can be made now be closed and the load transfer control moved toward

simultaneously without affecting load sharing adjustment, the minimum position until the generators are carrying no

Load can be transferred manually to the utility main from load. When the engine/generator sets are delivering nothe generators by closing the unloading switch. The power, they can be removed from service.

LS 671A

I,f I01'J',J,I,0r,ll;J+r,J1, cs--CON,OI II I [ . R (JON-23)

_. K + 1 0.2 VDCI I I z REF IN

208 VOLTS J_ I_ i._ I _ 5K POWER

LINE T O LINE Iv i I [ _ .e"T"e 25K_'_ -IcONTROLUSE 2, 4 & 6 [ [ v BIAS

I I = SKt[ ] I CLOSES WITH JI H - (GROUND)

416LINEUSEVOLTS1,3TO LINE& 5 -- -' --"=ll IIII = III = Ill I _ MAIN BREAKER ] [ -=.-_,_-Till,__--_J

I I ' I [ i BREAKER I I '

I i i , I

I 4 "i L

I_._

/_U_uv 1 PHASECURRENT _ GENERATOR

TRANSFORMERS L

Figure 4. Wiring for single generator power control bias adjustment circuit

.L

MIN _

SPEED MAXSPEED

CONTROL UNIT LOAD CONTROL UNIT

r'K _ H--I -J ITRANSFE R

Ic"'"LI

I "_' I _ _. .

4

UNLOADING [SWITCH

_PARALLEL

ISOLATED

LS 671A 100K LS671A

14 PARALLEL +

15 CABLE

Figure 5. Load transfer schematic

Prr_tF,; ; ' '*' Page 5 Issued AuousI 1989

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ENGINE

GOVERNING SYSTEMSENTE RNATIONAL

LS 671A SECTION EG 70-10

INSTALLATION

The LS 671A Precise Load Sharing Module is wired to the ing have 0.1 ohms resistance, this will raise the demand on

generator and to the speed control u nit as per wiring the CT's by 2 0%, based on 0.5 ohm burden resistors. Thus

diagram (see Figure 6). The module is typically found in the it is recommended that the resistance of each wire be heldcontrol cabinet with the instrumentation and controls. The below 0.1 ohm. The parallel cable operates with low voltage

power resistors will dissipate up to 40 watts, so the natural and low current so almost any cable typically used on

flow of cooling air must not be obstructed, engines will suf fice. It is recommended that some care betaken not to allow leakage currents between the parallel

The wiring to the generator must be of appropriate size to cables or from the parallel cables to ground or other cir-

carry the voltage and current to the load sharing units. The cuits. Such leakage can cause unwanted droop.

voltage sensing connections 1 thru 6 require low currentsThe output (terminal 16) which connects to the speed con-

(less than 200 mA), so wire size and quality consistenttrol unit terminal "R", may require a shielded cable if this is

with good mechanical installation is recommended. not a direct connection of short length. The speed control

Terminals 7 thru 12 are part of the CT circuits and require unit connection (terminal "R") is quite sensitive, so care

currents up to 5 amps to operate the load sharing. If the must be taken on leads attached to terminal "R" that stray

resistance of the cables connecting the CT's to the load shar- fields of leakage to other terminals are not present.

_'_TO"R" (TO "J" ON-23) _) OF "C" SERIES

FOR -__FROM"K" (+10V REF) UNIT

DROOP lLS 671A \ + -

II1=13141'.].,, l_J 1. l j" ,,II,I-H

I _ _ : PARALLELCABLE2(_8VOLTS .=

LINE TO LINE I ]_,_ "- _ _ COMMON TO ALL

[ " I "- "- LOAD SHARING ASSYSUSE 2.4 & 6 I OPEN FOR SINGLE _ AUXILIARY

UNIT OPERATION CONTACTS

I CLOSES WITHI

, , __ USE 1, 3 & 5 [ II II I [ MAIN CIRCUIT ]II j I

MAIN

,-- I 3 PHASECURRENT/_ - I GENERATOR

TRANSFORMERS

Figure 6. Wiring to LS 671A precise load sharing module

Printed _n U S A Page 6 issued August, 1989

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ENGINE

GOVERNING SYSTEMS_ATIONAL

LS 671A SECTION EG 70-10

ADJUSTMENTS

CAUTION: With the system at no load, adjust each generator set forzero real power output reading on the generator set watt-

THE ENGINE SHOULD BE EQUIPPED WITH ANmeter using the speed trim adjustment. Then adjust theINDEPENDENT OVERSPEED SHUTDOWN

MECHANISM TO PREVENT RUNAWAY WHICH voltage regulators to trim the reactive current on the

CAN CAUSE EQUIPMENT DAMAGE OR generator set ammeter to zero. Load can now be applied tothe system. If instability occurs, see "Troubleshooting".PERSONNEL INJURY.

Load Sharing

CAUTION: Once the system has load applied, it is important that each

HIGH VOLTAGE PRESENT ON TERMINALS 1-6. engine share the system load proportionally. Check the

DO NOT power output of each generator set that is reflected by each

OPEN CIRCUIT CT's AS HIGH VOLTAGE generator set wattmeter. Turn the Load Sharing Sensitivity

WILL BE PRESENT. Adjustment CCW. The generator set carrying least load canbe adjusted by turning the engine's Load Sharing Sensitivity

Adjustment CCW until its shareof the loadhas been picked

Preset the sensitivity control on each load sharing unit to the up.

full CW position. Set the load anticipation adjustment full Changing the speed trim adjustment of any individual unit

CW. All the engine-generator set speed control units should will have the effect of adding or subtracting power from

be adjusted to the desired speed before load sharing is that particular unit and raising or lowering the system

attempted. Use the speed trim to accomplish this. With a DC frequency slightly.voltmeter, measure the voltages across terminals 14 (+) and

15 (-) with a load applied to the generator. A voltage of Load Anticipation

about + 8 volts will represent full load with 5 amps CT The load sharing units have a load anticipation circuit to

input. Instrument polarity must beobserved. Momentarily, improve transient response. The load anticipation adjustment

shor

t the i

ndiv

idu

al CT's (

7 to 8

, 9

to

10

, 11 to

12)o

ne at a is facto

ry set at zero

sensitivity (full CW). T

he lo

ad anticipa-time with an insulated lead. The voltage read on the tion should be adjusted while the engines are in parallel.

voltmeter will fall by about 1/3for each individual shorting Carefully advance the control CCW while occasionally pok-

of a CT. If these voltage drops do not occur, it indicates ing the throttle or changing load. Instability or overshoot

improper phasing of the CT's and/or voltage connections may result if t h e control is advanced too far.which must be corrected. Make sure power is off before

making corrections. During CT phasing, voltage Droop

measurements, while individual CT's are being shorted, can After disconnecting the parallel cable, 5 % adjustable droop

be conveniently made at test points shown in Figure 1 with with load is obtainable by adding a jumper from terminal

right hand test point being (+) positive. 13 to 14. The jumper applies a direct short circuit to

the parallel cable connection. Adjust the droop control to

Once the proper CT phasing has been verified, the generator the desired droop level. It is linear and may be set at anysets may then by synchronized manually with the speed trim load.control or with the AMBAC automatic phasing synchronizer.

Once synchronized, the generator sets can be paralleled.

TROUBLESHOOTING

Instability, when the units are paralleled, may occasinally If instability i s stillpresent, the gain adjustmenton the speed

result. The instability can be caused by the sensitivity of the control unit may be reduced slightly or it is possible that the

load sharing being too high. Turn all thesensitivity controls voltage regulator is marginally stable and adjustment of the

CCW proportionately until stability is restored. The system voltage regulator is required. Refer to the voltage regulator

should stabilize with the controls no more than 75% CCW. manufacturer's instructions for adjusting the regulator forparallel operation.

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ENGINE

GOVERNING SYSTEMSINTERNATIONAL

LS 671A SECTION EG 70-10 "-"

TROUBLESHOOTING

If the load sharing function does not operate properly, the fault may be found by performing the following tests.

STEP TERMINALS NORMAL VALUE PROBABLE CAUSE OF ABNORMAL READING

1 18,17 10.2 _+ 0.5 VDC 1. Speed Control Unit not turned on.

(reference input) 2. Error in wiring to speed control unit.

(6.2 VDC with ECQ series 3. Defective speed control unit.

speed control.)

2 14,15 8 VDC at full load with 1. Improper relative phasing at A.C. inputs.

the sensitivity control CW. 2. Used thehigh voltage range inputs(terminals 1,3, 5)

(Parallel Cable) instead of low range (terminals 2, 4, 6).

3. Execessive resistance (>0.1 ohm) in wiring tocurrent transformers (C.T.).

4. Improper C.T. ratios.

SYMPTOM PROBABLE TROUBLE

NEGATIVE DROOP 1. Improper relative phasing at A.C. inputs.

2. Wiring to current transformers reversed.

UNEQUAL or ERRATIC LOAD SHARING 1. Improper adjustment of Load Sharing Sensitivity Control.2. Excessive (>0.1 ohm) or unequal resistance in connections

to current transformers.

3. Excessive noise on A.C. line.

4. Adjustment required at generator set's voltage regulator.

Pr,nled *nU S A Page 8 issued AugHs; 1989