ww governing fundamentals

8/6/2019 WW Governing Fundamentals

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Manual 26260

Governing Fundamentalsand Power Management

This manual replaces manuals 01740 and 25195.

Reference Manual


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Woodward reserves the right to update any portion of this publication at any time. Information provided by Woodward isbelieved to be correct and reliable. However, no responsibility is assumed by Woodward unless otherwise expresslyundertaken.

Woodward 2004All Rights Reserved


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Manual 26260 Governing Fundamentals and Power Management

Woodward i

Contents

CHAPTER 1.INTRODUCTION TO GOVERNING ................................................ 1Introduction ............................................................................................................. 1Other References ................................................................................................... 1What is a Governor? ............................................................................................... 1Governor Components ........................................................................................... 3Development of the Modern Governor System ...................................................... 4CHAPTER 2.HYDRO-MECHANICAL GOVERNORS........................................... 5Basic Hydro-mechanical Governor Components ................................................... 5The Speeder Spring ............................................................................................... 5Thrust Bearing ........................................................................................................ 6Flyweights ............................................................................................................... 6Pilot Valve Plunger and Bushing ............................................................................ 8Oil Pumps ............................................................................................................... 9Direction of Rotation ............................................................................................. 10The Servo (Power) Piston .................................................................................... 11CHAPTER 3.DROOP .................................................................................. 13Introduction ........................................................................................................... 13Why Is Droop Necessary? .................................................................................... 13Speed Droop Operation ........................................................................................ 14Uses Of Droop ...................................................................................................... 15Isolated Systems .................................................................................................. 18CHAPTER 4.LINKAGE................................................................................ 22General ................................................................................................................. 22Governor Travel .................................................................................................... 23Linear Linkage Arrangements .............................................................................. 24Non-Linear Usage ................................................................................................ 25CHAPTER 5.MAGNETIC PICKUPS............................................................... 26Introduction ........................................................................................................... 26CHAPTER 6.LOAD SENSING,LOAD SHARING,BASE LOADING ................... 30Load Sensing ........................................................................................................ 30Load Gain Adjust Potentiometer .......................................................................... 30Balanced Load Bridge .......................................................................................... 31Power Output Sensor ........................................................................................... 34Isochronous Base Load ........................................................................................ 34CHAPTER 7.SYNCHRONIZATION ................................................................ 39What Is Synchronization? ..................................................................................... 39Why Is Synchronization Important? ...................................................................... 42How Is Synchronization Accomplished? .............................................................. 42Prediction of the Worst Case Phase Angle Difference () at the Instant ofBreaker Closure .................................................................................................... 44


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Governing Fundamentals and Power Management Manual 26260

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Contents

CHAPTER 8.MANAGING POWER FOR THE DESIRED RESULT ....................... 46Peaking or Peak Load Control ..............................................................................46Cogeneration ........................................................................................................51Single Engine AGLCBase Load Control .............................................................51Isolated Bus Isochronous Load Sharing System ..................................................57Multiple Engine AGLCBase Load Control ..........................................................60Automatic Paralleling System (2301A) to a Utility Using a Process-Import/ExportControl ..................................................................................................................63Automatic Paralleling System (2301A) to a Utility Using an Automatic PowerTransfer And Load (APTL) Control .......................................................................66

Illustrations and Tables

Figure 1-1. The Driver is the Governor ...................................................................2Figure 1-2. Speed Balance .....................................................................................2Figure 2-1. Speeder Spring ....................................................................................5Figure 2-2. Speeder Spring Deflection ...................................................................6Figure 2-3. Hydraulic Governor Ballhead ............................................................... 6Figure 2-4. Flyweight Action ...................................................................................7Figure 2-5. Flyweights to Minimize Friction ............................................................7Figure 2-6. Pilot Valve Operation Shown On Speed............................................8Figure 2-7. Oil Pumps .............................................................................................9Figure 2-8. Accumulator and Governor Relief Valve ............................................10Figure 2-9. Pump Rotation ...................................................................................10Figure 2-10. Spring Loaded Servo Piston ............................................................11Figure 2-11. Differential Power Piston ..................................................................12Figure 3-1. Response Curves of Governor without Droop or Compensation ...... 13Figure 3-2. Droop Feedback .................................................................................14Figure 3-3. Compensated Governor Schematic ...................................................15Figure 3-4. Comparison of 3% Droop Speed Settings for 50% and 100% Load . 16Figure 3-5. 3% and 5% Droop Curves .................................................................16Figure 3-6. Droop Mode .......................................................................................17Figure 3-7. Swing Machine ...................................................................................18Figure 3-8. Droop Units ........................................................................................19Figure 3-9. Base Load with 5% Droop .................................................................20Figure 3-10. Schematic of Droop Governor .........................................................21Figure 4-1. Linear Fuel Control .............................................................................22Figure 4-2. Non-Linear Fuel Control .....................................................................23Figure 4-3. Correct Use of Governor Travel .........................................................23Figure 4-4. Nonlinear Carburetor Linkage ............................................................25Figure 5-1. Magnetic Pickup .................................................................................26Figure 5-2. Low Reluctance Gear Position ...........................................................27Figure 5-3. High Reluctance Gear Position ..........................................................27Figure 5-4. Magnetic Pickup and Gear Dimensions .............................................28Figure 5-5. Generated Waveforms .......................................................................29Figure 6-1. Generator Load Sensor......................................................................30Figure 6-2. Balanced Load Bridge ........................................................................31


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Illustrations and Tables

Figure 6-3. Basic Load Sensing Block Diagram ................................................... 32Figure 6-4. Load Sharing Diagram ....................................................................... 36Figure 6-5. Load Sharing Block Diagram ............................................................. 37Figure 6-6. Multiple Load Sharing Block Diagram ................................................ 38Figure 7-1. Number of Phases Must Match Number Of Phases .......................... 39Figure 7-2. Phase Rotation Must be the Same Rotation Of Phases .................... 40Figure 7-3. Voltage Difference (Generator to Generator) .................................... 40Figure 7-4. Voltage Difference (Generator to Bus) .............................................. 40Figure 7-5. Frequency Difference ......................................................................... 41Figure 7-6. Phase Difference................................................................................ 41Figure 7-7. Checking Phase Match ...................................................................... 43Figure 7-8. Checking Phase Rotation and Match ................................................ 43Figure 7-9. Phase Angle Relationship .................................................................. 45Figure 8-1. "Peaking" or Peak Load Control ........................................................ 47Figure 8-2. Base Loading ..................................................................................... 48Figure 8-3. Peak Shaving ..................................................................................... 48Figure 8-4. Import Power ...................................................................................... 49Figure 8-5. Import Power (Constant Level) .......................................................... 49Figure 8-6. Export Power ...................................................................................... 49Figure 8-7. Export Power (Constant Level) .......................................................... 50Figure 8-8. Import/Export Control ......................................................................... 50Figure 8-9. Zero Import/Export ............................................................................. 50Figure 8-10. Synchronizing to Utility or Plant Bus ................................................ 53Figure 8-11. Synchronizing Gen Set to Plant Bus or to Utility .............................. 54Figure 8-12. Single Engine AGLC Base Load ...................................................... 55Figure 8-13. Connections for Single Engine AGLC Base Load System .............. 56Figure 8-14. Using AGLC for Soft Load, Soft Unload, and Base Load to an

Isolated Bus for Isochronous Load Sharing .................................... 58Figure 8-15. Connections Used with AGLC for Soft Loading, Unloading, and

Base Loading with Isochronous Load Sharing Against an IsolatedBus ................................................................................................... 59

Figure 8-16. Using the AGLC to Base Load Multiple Engines to a Utility ............ 61Figure 8-17. Connecting an AGLC to Base Load Multiple Engines to a Utility .... 62Figure 8-18. Using Process-Import/Export Control to Automatically Parallel ....... 64Figure 8-19. Connecting Process-Import/Export Control to Paralleling System .. 65Figure 8-20. Using APTL in Automatic Paralleling System .................................. 67Figure 8-21. Connecting APTL in Automatic Paralleling System ......................... 68


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Chapter 1.Introduction to Governing

Introduction

This manual combines former Woodward manuals 25195 (GoverningFundamentals) and 01740 (Power Management). Chapters 15 cover basicgoverning, and chapters 69 cover the principles of power management.

Other References

Other useful references you might find useful can be found on our website(www.woodward.com):

Pub. No. Title25075A Commercial Preservation Packaging for Storage of Mechanical-Hydraulic

Controls

25070D Electronic Control Installation Guide25014C Gas Engine Governing25179C Glossary of Control Names50516 Governor Linkage for Butterfly Throttle Valves82715H Guide for Handling and Protection: Electronic Controls, PCBs, Modules82510M Magnetic Pickups and Proximity Switches for Electronic Controls25071J Oils for Hydraulic Controls83402 PID Control83408 PLCs for Turbine Control Systems50511A Prediction of Phase Angle at Breaker Closure50500D Simplified Unloading Scheme for Electric Governors01302 Speed Droop & Power Generation51214 Work versus Torque

In addition, all product specifications, brochures, catalogs, and application notes

(as well as many technical manuals) can be found on the website.

What is a Governor?

All power sources must be controlled in order to convert the power to usefulwork. The essential device which controls the speed or power output of anengine, turbine, or other source of power is called a governor. For simplicity,well call the source of power a prime mover.

A governor senses the speed (or load) of a prime mover and controls the fuel (orsteam) to the prime mover to maintain its speed (or load) at a desired level. Insome cases the governor controls other factors that determine the speed or load

of the prime mover. In all cases, a governor ends up controlling the energysource to a prime mover to control its power so it can be used for aspecific purpose.


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ExampleIf youve ever driven a car, youve functioned as a governor when youcontrol the cars speed under varying driving conditions.

Figure 1-1. The Driver is the Governor

The driver (governor) adjusts the fuel to maintain a desired speed. If the speedlimit is 100 (this is the desired speed), you check the speedometer (the carsactual speed). If actual speed and desired speed are the same, you hold thethrottle steady. If not equal, you increase or decrease throttle position to makethe desired speed and the actual speed the same (see Figure 1-2).

As the car starts uphill, the load increases and actual speed decreases. Thedriver notes that actual speed is less than desired speed and moves the throttleto increase speed back to the desired speed at the increased load.

As the car goes downhill, the load decreases and actual speed increases. Thedriver notes that actual speed is greater than desired speed and decrease thethrottle to return to the desired speed with the decreased load.

Figure 1-2. Speed Balance


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If your car has a cruise control, the cruise control is a simple governor.

Governor Components

All governors have five fundamental components:

A way to set the desired speed. (The driver sets the desired speedmentally.)

A way to sense actual speed. (The driver refers to the speedometer).

A way to compare the actual speed to the desired speed. (The drivercompares the two items mentally.)

A way for the governor to change the fuel to the prime mover (moving therack or fuel valve). (The driver moves the throttle.)

A way to stabilize the engine after a fuel change has been made.

In the example, when the car went up a hill, the driver saw the actual speeddecrease and moved the throttle to increase the fuel. You will need to increasethe fuel an amount to cause the speed to increase. This will give the engineenough power to make the car return to the desired speed with a bigger load. Asyou see that the actual speed is about to reach the desired speed, you reducethe extra fuel to the exact amount needed to match (balance) the desired speedwith the actual speed. The governor does the same thing, using feedback. Thisfeedback closes the loopin the control system which controls the amount of fuelchange, based on the rate the desired speed is being reached. This preventslarge overshoots or undershoots of speed which is known as hunting, andstabilizes the engine. The opposite is true when the car goes down the hill orload is reduced.

1. Speed SettingSetting the desired speed of a governor is necessary to efficiently controlprime movers. Modern governors have advanced systems of speed settingwhich can compensate for a variety of conditions when determining thedesired speed. Hydro-mechanical governors use what is known as aspeeder spring. The more force applied to this spring, the higher the desired

speed setting is. Electronic controls use an electronic force (voltage andcurrent) to set speed. The more the force is increased, the more the outputto the fuel increases.

Speed setting and the effect on sharing loads between engines will bediscussed in other chapters.

2. Sensing SpeedThe governor must receive a force that is proportional to the speed of aprime mover. In hydro-mechanical governors, it is done by the centrifugalforce of flyweights being rotated from a drive system that is connected to theprime mover, and is directly related to the speed of the prime mover. Inelectronic controls, this force comes from sensing of the frequency of a

magnetic pickup, alternator, or generator which is directly related to thespeed of the prime mover. The frequency is then changed to an electronicforce that the control can use. In both cases, the faster the engine runs, thestronger the speed sensing force becomes.


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3. Comparing the Actual Speed to the Desired SpeedThe force of the desired speed setting and the force of the actual speedare compared or summed together. Desired speed setting is a force inone direction and actual speed is a force in the opposite direction. Whenthese opposing forces are the same value, their sum will be zero and at thatpoint the governor is controlling actual speed at the point of the desiredspeed setting. If the desired speed setting force is stronger than the actualspeed force, the governor will increase fuel. If the actual speed force is

stronger than the desired speed setting force, the governor will decreasefuel. As fuel is increased or decreased, these forces will change until theybalance or sum to zero. In hydro-mechanical governors, these forces aresummed at the thrust bearing. In electronic controls, these forces aresummed at what is known as a summing point. Note that other forces canbe applied along with these forces to allow the governor to be stabilized andperform other functions (some of these are covered in later chapters).Remember that all forces applied to the thrust bearing or summing pointmust algebraically sum up to zero for the governor to control fuel at a steadystate.

4. Ways for the Governor to Change Fuel to the Prime MoverThe hydro-mechanical governor or actuator normally has a rotational or

linear output shaft that is connected to the prime movers fuel system. Whenthe governor needs to make a fuel correction to maintain speed (or load),the output shaft moves in the proper direction to correct the final fuel setting.For electronic controls, an electrical signal is sent to an actuator whichconverts this electrical signal to a mechanical force to move the fuel settingin the same way the hydro-mechanical governors do. Different types ofgovernors and actuators have different amounts of work output to meet thecontrol needs of various prime movers.

5. Ways to Stabilize the Prime MoverStabilization is accomplished through a variety of ways, but all of them use afeedback system to apply a force to the thrust bearing or summingpoint. This feedback is normally in the form of either droop orcompensation, or in a combination of both. Droop or compensation isusually related to the amount the output shaft is told to move (Chapter 3describes the essential principle of droopfeedback).

Note that in many prime mover systems (such as power generation), the speedof the prime mover is fixed. While the governor still controls the prime moversspeed setting mechanism, the end result of changes in the prime movers speedsetting under fixed-speed conditions is that an increase or decrease in the speedsetting causes the prime mover to take on a larger or smaller load.

Development of the Modern Governor System

The first modern governors were applied to controlling the speed and load ofwater wheels (which were used to power many of the early factories during theIndustrial Revolution. Early governors also controlled steam turbines. Thedevelopment of gasoline and diesel internal combustion engines required fasterand more complex governors. Electrical power generation created a muchgreater need for more precise governor control of speed and load.

Hydro-mechanical governors became ever more complex to meet growing needsfor precise control. Since the 1970s, electronic controls have significantlyimproved and expanded the capabilities of governing systems, controlling notonly speed and load, but also electrical loads, exhaust emissions, and manyother parameters.


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Thrust Bearing

The thrust bearing is the part where the force of the speeder spring and the forceof the flyweights sum together. If the speeder spring force and the flyweight forceare equal, there is no load on the thrust bearing.

Figure 2-2. Speeder Spring Deflection

A thrust bearing has a race on the top and a race on the bottom with the bearingin between the races. Since the flyweights rotate and the speeder spring doesnot rotate, the thrust bearing is necessary. The pilot-valve plunger moves withthe thrust bearing either directly or through a linkage. The pilot-valve plungerdoes not rotate.

Flyweights

There are two flyweights in most ballheads. The flyweights are rotated by a drivefrom the engine that is directly related to the speed of the engine.

Figure 2-3. Hydraulic Governor Ballhead


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Pilot Valve Plunger and Bushing

The pilot-valve plunger is positioned by the force on the thrust bearing. It movesup and down inside the rotating pilot-valve bushing (due to the flyweights sensingspeed changes and tipping in or out). The pilot-valve bushing has high pressureoil coming from the oil pump into the bushing above the control land of the pilot-valve plunger.

Figure 2-6. Pilot Valve Operation Shown On Speed

The pilot-valve bushing has ports in it to allow the flow of oil to or from the powercylinder assembly. When the governor and engine are at the desired speedsetting, the pilot-valve-plunger control land is centered over the port in the pilot-valve bushing. This stops oil from flowing to or from the power cylinder assembly.

If the flyweights tip in, due to a change in speed or load, the pilot-valve plungermoves down and let high-pressure oil into the power-cylinder assembly. This willincrease fuel.

If the flyweights tip out, due to a change in speed or load, the pilot-valve plungermoves up to let oil drain from the power-cylinder assembly. This will decrease

fuel.

Pilot-valve-bushing ports have different sizes and shapes for different types ofgovernors to allow more or less oil flow, depending on the application.

The pilot-valve bushing rotates and the pilot-valve plunger does not. Thisminimizes static friction (called sticktion) and allows the pilot-valve plunger tomove with very slight speed changes.


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Oil Pumps

Most hydro-mechanical governors and actuators use the governor drive to rotatea hydraulic pump which provides the pressure oil for the system controlled by thepilot valve. Woodward uses two different types of pumps. Most governors use thetwo- or three-gear positive displacement pump. The 3161 and TG governors andsome actuators use an internal gear oil pump.

Figure 2-7. Oil Pumps

The constant-displacement pump has one drive gear and one or two idler gearsthat rotate in a gear pocket. As the gears turn, oil is drawn from the oil supply andcarried in the space between the gear teeth and the walls of the gear pocket tothe discharge side of the pump. The oil is forced from the space around the gearteeth as the drive and idler gears are rotated and becomes pressurized.

The hydraulic circuits connected to the pumps can be designed to allow eitherone direction of rotation or reversible rotation for use on diesel engines withdrives that run in both directions. Check valves are used to provide pump rotationin either direction. Plugs allow pump rotation in only one direction. Internal gearpumps allow rotation in only one direction. The pump must be removed from thegovernor and rotated 180 to change direction of rotation for internal gear pumps.

The pumps are designed to provide more pressure and flow than needed withinthe governor. The extra flow of oil is returned to sump. Smaller governors use arelief valve. Most larger governors use an accumulator system which provides aspring-compressed reservoir of pressure oil for use during transits whichtemporarily exceed the output of the pump. SG, PSG, and EGB-2 governors userelief valves. A number of hydraulic actuators do not have accumulators.

The relief valve shown in Figure 2-8 is typical of the valves used in SG, PSG,EGB-2 governors and many hydraulic actuators.

Internal operating oil pressures are specified for each governor. Typicalpressures are 100 to 500 psi (690 to 3448 kPa). Different types of governorsoperate at different pressures. Check the specifications for your governorspressure. The higher pressures are created to get more output power from theservo controlled by the governor. Higher pressures may require the addition ofspecial heat exchangers to avoid damage to (break down of) the oil being used inthe governor.


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to a rotarythe oil

iston. Thee fuel.

r decrease

e pistone smallerection.d above

to thewayss of theide (controlel

ishe power

he pilotparticular

otion. Oilon to

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19/76

Manual 2

Woodwar

DrfoDDrful2.Dr

If,shSiorerec

InTreDcospovua

260

d

oop has manrm of droop,

oop is defin

oop is exprell load. The n5% is require

oop is calcul

%

instead of aowing negati

mple hydro-erate in droourns the speovered from

ompensation.

a system wite governorurned to the

e to the comntinue to increed. The goershoot. It widershoot. Thplify until th

Figure 3-1.

y uses and angine-speed

ed as a dec

sed as a perrmal recom

d to maintain

ted with the

roop =No

ecrease in sve droop. Ne

echanical gp. More comed setting toa change in

Why

hout droop, aill respond boriginal spee

bined properease beyondernor againll over-correcis overcorrecengine trips

Response C

overning F

ChapDr

Introd

pplications icontrol woul

ease in spe

centage of tended perc

stability in a

following for

oad Speed Full Loa

peed settinggative droop

vernors havlex governo

its original spspeed or loa

Is Droo

load increasincreasing td.

ties of inertiathe originalill respond t

t the speed ition of speedout on overs

rves of Gov

undamental

ter 3.op

ction

the controld be unstabl

d setting at

e original spnt of droop i

speed-droop

ula:

Full Load RateRated Sped

an increase twill cause in

the droop frs include teeed setting a. The tempo

Necess

e will cause the fuel until t

and power lpeed setting

o decrease sthe other di

in both direcpeed.

rnor without

s and Power

f engines. Win most cas

the load inc

ed setting frs 3% to 5%.governor.

d Speedx 1

akes place, ttability in a g

nction built iporary droofter the engirary droop is

ry?

he engine tohe engine sp

g, the engin, causing anpeed to correrection causitions (instabi

Droop or Co

Manageme

1

ithout somees.

reases.

m no load tminimum o

00

he governorovernor.

and always, whiche hascalled

slow down.eed has

speed willovershoot inct for theg an

lity) will

pensation

t

3

f

is


20/76

Gove

14

This ispeedecresettin

Sim

As lodroopfeedbon thwhich

ComFor ccompaddsspeespeecompknow

rning Funda

nstability prosetting is d

ase causedg. This lower

le Speed

d is appliedfeedback le

ack lever pulspeeder spmaintains th

pensated

mpensatedensation systto the force o

is reached.setting had

ensation systn as tempor

mentals an

lem can becreased. Why the increaspeed settin

Spee

Droop Go

Figur

to the engineer is connec

ls up on the sing, the speee load at a lo

Governor

overnors, wem pushes uf the flyweigThis temporabeen reduceem is reducery droop.

Power Man

liminated wien the govered load, it wiprevents th

Droop

ernor

e 3-2. Droop

, the power ped to the popeeder sprind setting is dwer speed.

en a load isp on the pilotts to close thry force addi. The force t

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agement

h droop. As tnor moves toll be correctie speed from

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Feedback

iston moveser piston an

g to reduce itecreased, ca

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he load incrcorrect for tg to a lowerovershootin

up to increasd speeder sps force. Withusing the dr

emporary fornsation land

before the ethe same waeedle valve oturns to spee

Manual

Woo

ases, thee speedspeed.

e fuel. Thering. Theless forceop action

ce of the. This forceginey as if thef thed. This is

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Manual 2

Woodwar

TDrpofrerpIfnga

IsMdr

260

d

e Droop

oop is a straisition. Normthe referencerence spee

m at full load.

he linkage isload to full lvernor outpujustment.

olated Uniost governoroop operatio

Figure 3-3.

urve

ght line functlly a droop g, from no loa

d of 1236 rp

changed, altad, the droot shaft travel

tare capableis necessar

overning F

Compensat

ion, with a ceovernor lowed to full load

at no load

ering the amp must be reto ensure sta

Uses O

of operatingfor many a

undamental

d Governor

rtain speed rrs the speedThus, a 3%ould have a

unt of goveret. Be sure tbility and all

Droop

in the isochrplications.

s and Power

Schematic

eference forreference froroop governreference sp

nor output sho use a leastw sufficient

nous mode,

Manageme

1

very fuelm 3% to 5%r with a

eed of 1200

aft travel fro2/3 of theroop range

However,

t

5


22/76

Gove

16

FiguSp

IsolatIn sinenginoriginthe sdroop

settin

IsolAn iscomor cosysteWithoisoch

The iany ocapaisochloadtry totwo uenginThe ris sh

rning Funda

re 3-4. Comed Settings

L

ed, single-engle engine aes or the utilial speed afteeed decreasmode, if the

g to return to

ted Syste

lated systeon load. Thibinations of

ms are not c

ut some forronous load

ochronousther engine.ilities, no mo

ronous modeharing contrcarry the entinits to sharee from either

eason for onwn in the foll

mentals an

arison of 3%for 50% andoad

gine applicatiplications, th

ty. In isochror a load hases by a set poriginal spee

the original s

ms

is an applicload could

these and annected to a

of isochronharing contr

ode can alsowever, unlre than one. If two enginls are suppl

ire load and tload, some atrying to take

unit takingowing examp

Power Man

Droop100%

F

ons can opere engine opeous operatieen applied

ercentage aftd is desired,

peed when a

tion where te electrical gy other mec

ny other syst

us load sharl, droop mus

be used oness the govef the engine

es operatinging power tohe other willdditional meall the load,

ll the load ale:

agement

igure 3-5. 3

ate in eitherration is notn, the speedup to 100% ler a load hathe operator

load is appli

o or more eenerators, panical loads

ems or to a u

ing scheme lit be used to

one engine,rnors have isrunning in p

in the isochrthe same lohed all of itsns must beor from moto

d the other u

and 5% Dro

isochronousffected by areturns bac

oad. In droopbeen applie

must raise th

ed.

ngines are drmps, ship pr

. These isolatility.

ke the electrhare these l

unning in paochronous loarallel can bnous moded, one of theload. In ordesed to keepring.

nit dropping

Manual

Woo

op Curves

or droop.ny otherto theoperation,

d. In thee speed

iving aopellers,ed

nicoads.

rallel withad sharingin theithoutunits willr for theeach

all the load

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Woodward 17

If two isochronous units are to be coupled together on the same load and thespeed settings are not the same, the system will become unbalanced whencoupled together. Since there cannot be two different speeds on one systemcoupled together, one engine will have to decrease its actual speed and the otherwill have to increase its actual speed to an average speed between the two. Thegovernor on the engine that decreased speed will move to increase fuel to try tocorrect for the decrease in speed, and the governor on the other unit thatincreased speed will move to decrease fuel to try to correct for the increase in

speed. The result will be that the engine with the higher speed setting willcontinue to take all of the load until it reaches its power limit, and the otherengine will shed all of its load and become motored (driven by the other engine).

As seen by the example, units running in isochronous cannot share loads withoutan isochronous load sharing scheme.

Using Droop to Share Loads

If all engines in a droop system have the same droop setting, they will eachshare load proportionally. The amount of load each carries will depend on theirspeed settings. If the system load changes, the system speed/frequency will also

change. A change in the speed setting will then be required to offset the effect ofdroop and return the system to its original speed/frequency. In order for eachengine in the system to maintain its proportion of the shared load, the operatorwill need to adjust the speed setpoint equally for each engine.

If all engines in a droop system do not have the same droop setting, they will notshare loads proportionally with the same speed settings. If the system loadchanges, the system speed/frequency will also change but the percent of load oneach engine-generator set will not be changed proportionately.

The operator will need to adjust the speed setpoint differently for each engine tomake them carry their proportional share of the load. This could result in runningout of speed setpoint adjustment on an engine before it is fully loaded and

limiting the system load sharing capability. It is best to have the same percent ofdroop set on each engine (3% to 5% is recommended).

Figure 3-6. Droop Mode


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Gove

18

DroDroooperamode

run atspeeof poin the(see

Maxiswingabovsystethe drmachTheswingcapasuchexpe

rning Funda

p/Isochro

/Isochronouted in the dr. It is known

the speed/frsettings ofer. The outload demanigures 3-3 a

um load formachine anthis maxim

m load cannoop machineine can be m

achine withmachine soility. This is

things as effited to chang

mentals an

Is

nous

combines top mode ex

as the swing

equency of tach droop uut power of twhile maint

nd 3-4).

Figu

this type of sthe total set

m will resultt be alloweds. If it does, totorized.

the highest othat the systot a rigid ruliency of diff

e.

Power Man

lated Sy

e first two mept for onemachine. In t

e isochronoit are adjusthe swing maining consta

re 3-7. Swin

stem is limitpower outp

in a decreasto decreasehe system fr

utput capacitm will accep. Selection orent engines

agement

stems

odes. All enghich is oper

his mode, th

s unit. The dd so that it ghine will cha

nt speed/fre

Machine

ed to the cot of the drooin speed/freelow the coquency will i

should nort the largest lf the swingand the amo

ines in the syted in the isdroop mac

roop percentenerates a snge to followuency of the

bined outputmachines.

quency. Thebined outpu

ncrease and

ally be operoad changesachine will dunt the load

Manual

Woo

stem arechronousines will

age andet amountvariationssystem

of theload

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ated as thewithin itsepend onis

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Manual 2

Woodwar

S

Pr(nse

Drrelo

DDrwichg

3-

260

d

stem Tie

eviously theot tied to anot is parallele

The utilityspeed/freunit canno

When an iutility willgovernor sutility busis even frago to full lof a utility

remain at

oop provideserence to ded with the s

roop Base

oop base loall control theange in load.nerator set s

7).

to a Utilit

se of droopther larger sy

with a utility

will basicallyuency for ant be parallele

sochronousetermine thepeed referenill flow to th

ctionally highad in an atte

is a frequenc

ull load.

the solutioncrease as loeed setting

Load

d is the samrequency anThe speed

upplies a fixe

overning F

Figure 3-8.

y Grid

has been disstem such a, there are a

act as an isoy units beingd to the utilit

ngine-generspeed/frequce be less thgenerator a

er than the frmpt to increy which is to

to this probled increases.ince the spe

as droop, wd act as doend droop setd, or base a

undamental

roop Units

cussed for sya utility). W

few things to

chronous uniparalleled to.

ator set is coency of the gan the utilitynd motor theequency of tse the bus sstrong to inf

m. Droop caThis allows t

ed cannot ch

ith the excepthe swing m

tings are adjount, of po

s and Power

stems that wen an enginconsider:

t. The utilityit. A simple i

nected to aenerator. Shfrequency, punit. If the ge utility, theeed. Since t

luence, the e

ses the govhe governor tange.

tion that theachine, absosted so thater to the utili

Manageme

1

ere isolated-generator

ill set theochronous

tility bus, thuld thewer in thevernor spee

governor willhe definitionngine will

rnor speedo vary the

tility or gridrbing anythe engine-y (see Figur

t

9


26/76

Gove

20

Basepowewherengin63 Hzfrequvarieincre

powethe drhighewhich

If thesimplminimIf theopenincredepe

rning Funda

on 5% droor output. Foll

it crosses te-generator, the powerncy line is t, the amountses, the dro

r and producoop will crosr output powit is not.

engine-genedecrease t

um power o

engine gene, separatingse to the spds on where

mentals an

p, increasingwing the droe 60 Hz lineet is at 50%utput will bee amount ofof output pop line will cr

a lower outs the lower utr. This condi

Figure 3-

rator set is toe speed settitput, then op

ator set is ruthe engine ged setting pthe speed s

Power Man

the speed sop line from t(controlled bpower outputat 100%. Whpower output

er will vary iss the highe

ut or power.ility frequenction is often

. Base Load

be unloadedng slowly unen the tie br

nning in a lonerator set fint. The amotting was wh

agement

tting to 61.5he 61.5 Hz sthe utility) it

. If the speedere the drooproduced. If

inversely. If tr utility frequ

If the utility fy line farther

istaken for

with 5% Dro

and disconnil the engineaker.

ded conditiorom the utilitunt the frequen the tie br

Hz will produetting to thecan be seensetting is inline crosses

the utility free utility freqncy line clos

equency decfrom zero, prgovernor pr

op

ected from thgenerator se

and the tie, the frequeency increasaker opened

Manual

Woo

ce 50%ointthat thereased tothe utilityuencyency

er to zero

reases,oducing aoblem,

e utility,t is at

breakercy willes.

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Woodward 21

Figure 3-10. Schematic of Droop Governor


28/76


22 Woodward

Chapter 4.Linkage

General

Linkage between the governor output and the engine fuel control system isresponsible for many unacceptable control conditions that appear to be governorconnected. When acceptable governor control deteriorates or changes, linkage isone of the first areas to troubleshoot. Loose or worn linkage not only can causeunacceptable governor control, but it can also present dangerous conditionsshould it fail completely and leave the engine uncontrolled. Good lockingmethods must be used at all linkage connections.

There must be no lost motion or binding in the linkage attached between thegovernor and the engine. Binding or catches in the linkage can cause speedexcursions and other problems which may appear as being caused by thegovernor. Lost motion in the linkage will cause the governor to have to travel thedistance of the lost motion before any fuel change is made. The governor will

become over-active in fuel control. This overly active governor will provide lessthan optimum control. An overactive governor will also cause excessive wear inlinkage and in the governor. The engine will tend to move up and down in speedor wander.

Governor operation is based on the assumption that linkage is so arranged that agiven movement in the governor output will provide a proportional change in thefuel to the engine.

Many fuel control systems provide a nearly linear response in engine output.(This is usually true of diesel engines.) Other fuel control systems provide anon-linear response to change in the control device position and engine outputs.(This is particularly true of carbureted engines with butterfly valves.) Allgovernors tend to provide nearly linear travel. Differences between the linearity ofgovernor travel and the linearity in the engine fuel control system or valve areaccomplished by the design of the linkage between the governor and the enginefuel system or valve.

Figure 4-1. Linear Fuel Control


29/76


Woodward 23

Figure 4-2. Non-Linear Fuel Control

Governor Travel

Design of the fuel linkage must provide for control of fuel from FUEL OFF toFULL FUEL within the limits of the travel of the governor output shaft. Thedesign must also provide for about 2/3 output shaft travel between NO LOAD

and FULL LOAD. If less than 2/3 travel from no load to full load is not used, itmay not be possible to stabilize the engine. If a lot more than 2/3 travel from noload to full load is used, there may not be enough travel to be sure the fuel isshut off at minimum governor travel, and full fuel may not be reached atmaximum governor travel. This can make the engine appear sluggish. In bothcases, the misadjusted linkage can appear as a governor problem when it reallyis not a governor problem.

Figure 4-3. Correct Use of Governor Travel


30/76


24 Woodward

Linear Linkage Arrangements

This Linkage design provides a large amount of engine fuel motion for a smallamount of governor motion.

This Linkage design provides equal amounts of engine fuel motion and governormotion.

This Linkage design provides a large amount of governor motion for a smallamount of engine fuel motion.

A linear linkage arrangement is used in applications where the governor outputshaft positioning is directly proportional to the torque output of the engine. Alinear linkage is a linkage design which provides as much movement of thegovernor output shaft per increment of engine fuel movement at light loads as atheavy loads.

Using less than the recommended amount of governor travel will providegovernor control which exhibits fast response and is, or tends to be, unstable.Droop load sharing could be impossible if too little governor output shaft travel isbeing used.

Using a lot more than 2/3 of the governor travel may not let the fuel system be

shut off or may not let the fuel system be opened to maximum.

The linkage must be set up to shut fuel completely off and let fuel be opened tofull fuel. Use at least 2/3 of the full governor travel from zero load to 100% load.


31/76


Woodward 25

Non-Linear Usage

Butterfly carburetor valves present extremely non-linear control characteristics.At minimum positions (light load), the valve must move very little to change theamount of fuel flow a large amount. At higher loads, the valve must move a largeamount to have any effect on fuel flow. Since governor output travel is essentiallylinear, special linkage is necessary to make the two conditions compatible. Thisis called non-linear linkage. Non-linear linkage is also required on some dieselinjection systems, although these conditions are not usually as severe as theyare when controlling a butterfly carburetor valve. In all cases the linkage shouldbe designed to provide increased engine output in direct proportion to movementof the governor output.

Figure 4-4. Nonlinear Carburetor Linkage

When installing this linkage, make sure the following conditions are obtainedwhen the governor output is in the min fuel position:

The governor lever and connection link are in line with the governor outputshaft and the point of attachment on the connecting link to the butterflycarburetor lever.

The butterfly carburetor lever is 90 with the connecting link.


32/76


26 Woodward

Chapter 5.Magnetic Pickups

Introduction

Figure 5-1. Magnetic Pickup

A magnetic pickup (see Figure 5-1) is the device most often used to sense thespeed of a prime mover. It is basically a single pole, alternating current, electricgenerator consisting of a single magnet with a multiple-layer coil of copper wirewrapped around one pole piece. The field or flux lines of the magnet exit thenorth pole piece of the magnet, travel through the pole piece and air path tosurround the coil, returning to the south pole of the magnet. When a ferrousmaterial, such as a gear tooth, comes close enough to the pole piece (see Figure5-2) the reluctance path is decreased and the flux lines increase. When theferrous material is far enough away from the pole piece (see Figure 5-3), theoriginal air path is re-established, and the flux lines will decrease to the originallevel. This increase and decrease of flux induces an ac voltage into the coilaround the magnet.


33/76


Woodward 27

Figure 5-2. Low Reluctance Gear Position

Figure 5-3. High Reluctance Gear Position


34/76


28 Woodward

The output of this single pole generator, known as a magnetic pickup (MPU),depends on the surface speed of the gear being monitored, the gap or clearancebetween the pole piece and the gear teeth, the dimensions of the magneticpickup and those of the gear (see Figure 5-4), and the impedance connectedacross the output coil of the magnetic pickup. The voltage wave form of theoutput depends on the shape and size of the gear teeth relative to the shape andsize of the end of the pole piece (see Figure 12-5). Any change in the reluctanceof the flux path, external to the magnetic pickup, caused by the addition or

removal of ferrous material will cause an output voltage to be developed. Gearteeth, projections, or holes, can be used to change the reluctance. Spacingbetween the gear teeth, projections, or holes must be uniform. Differences inspacing will be seen as changes in frequency or speed.

Figure 5-4. Magnetic Pickup and Gear Dimensions

Additional information can be found in manual 82510, Magnetic Pickups andProximity Switches for Electronic Controls.


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Woodward 29

Figure 5-5. Generated Waveforms


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30 Woodward

Chapter 6.Load Sensing, Load Sharing, Base

Loading

Load SensingThe generator load sensor senses the load on a generator. To sense this load,current transformers (CTs) are placed around the power output leads comingfrom the generator. As load is applied to the generator, alternating current flowsthrough the generator lines and induces current into the CTs. The current in theCTs increases proportionally with the load on the generator (see Figure 6-1).

Figure 6-1. Generator Load Sensor

The induced current from the CTs is added vectorially and then is converted to adc voltage in the load sensor. However, since only real power is to be used indetermining the load sensor output, potential transformers are also connected tothe power output leads of the engine-generator. Only CT current which is inphase with the potential transformer voltage is used and converted to a dcvoltage in the load sensor. This dc voltage is proportional to the percent of loadon the generator. The generator load sensor dc voltage is applied across a "LoadGain Adjust" potentiometer (see Figure 6-2).

Load Gain Adjust Potentiometer

The Load Gain Adjust potentiometer provides a means of setting a specificvoltage, selected from the load sensor output, to represent the load on theengine-generator set. This load gain setting is normally at 6 Vdc for 100% of thesets rated load. The output of the generator load sensor is linear so that voltagesfrom 0 to 6 Vdc represent loads from 0% to 100% of the sets rated load. Thisload gain voltage is impressed across a balanced load bridge.


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Woodward 31

Balanced Load Bridge

Isochronous

The balanced load bridge (see R1, R2, R3 and R4, Figure 6-2) is a device similarto a Wheatstone bridge. In our bridge, R1=R2 and R3=R4. As long as the voltagedeveloped across R1 equals the voltage developed across R3, which also means

that the voltage developed across R2 equals that across R4, there is no voltagedifferential across C. The output of the load bridge to the summing point is zero.This is true regardless of the load gain voltage. The control is in isochronous.The load does not affect the speed or frequency.

Figure 6-2. Balanced Load Bridge


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32 Woodward

Droop

The load bridge may be unbalanced by either changing the value of a resistor inone leg of the bridge or by applying an unbalancing voltage across one leg of theload bridge. If you unbalance the load bridge by paralleling R5 with R3, theresulting resistance of (R3, R5) is less than R4. The voltage developedacross.(R3, R5) will be less than that developed across R4. The voltagesdeveloped across R1 and R2 are each still at 1/2 the load gain voltage. A voltage

is now present across C with a value that will be determined by the load gainvoltage and the amount of imbalance caused by R5 in parallel with R3. Thevoltage across C applied to the summing point will be negative with respect tocircuit common. C is not required to make the bridge work. The time to chargeand discharge the capacitor slows down the load bridge action. This is necessaryto ensure that the load bridge is not faster than the speed loop. If it is, oscillationwill result.

At the summing point, the negative signal from the load bridge adds to thenegative signal from the speed sensor. To obtain a summing point balance, theamplifier will act to reduce the speed until the sum of the two negative inputsignals equals the positive input signal from the speed set adjust. The control isin droop. The speed or frequency will decrease proportionally with addition of

load.

To return the system to rated speed, it will be necessary to either increase thespeed set adjust voltage or to re-balance the bridge and return the system toisochronous control.

Figure 6-3. Basic Load Sensing Block Diagram


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Woodward 33

Load Sharing

The action of the load bridge is also used to bring about isochronous loadsharing. Instead of unbalancing the load bridge by changing the resistance ofone leg of the bridge, parallel one leg of a bridge from the control on one engine-generator set with the corresponding bridge leg of the control of a secondengine-generator set (see Figure 6-4). As long as both sets are providing thesame voltage across these connected lines, there will be no imbalance to the

load bridge. The summing point is then returned to zero when the speed set andspeed sensor signals are equal.

Take two engine-generator sets and adjust each sets load gain for 6 Vdc at100% of that sets rated output. The voltage developed across R3 of eachbalanced bridge will be 1/2 of that sets load gain voltage or 3 Vdc at 100% ofrated load. Start one set and load it to 100% of rated load. Start the second setand bring it on line at zero load. Simultaneously, when paralleling the two sets,connect the R3 leg of the balanced bridges of the two sets together by means ofthe load sharing lines (see Figure 6-4).

The voltages across the two R3s are different at the time when set two is broughton line. The R3 of set one is at 3 Vdc, indicating 100% load, and that of set 2 is

zero, indicating no load. These differences will balance out through R6 and R3 toa voltage between zero and 3 volts. Both load bridges will be unbalanced, but inthe opposite sense. The voltage developed across C of the first unit will call forreduced fuel and that of the second for increased fuel. This imbalance willdisappear as the two generator sets approach the same percentage of ratedoutput.

Where both engine-generator sets are of the same output rating, the outputs ofthe two units will both come to 50% of their rated load. The load gains will bothbe at 3 Vdc and the voltages across the R1s and R3s will all be 1.5 Vdc. Thebridges of both sets are balanced. The bridge outputs are zero, and the sets arein isochronous load share at rated speed. Voltage across the load sharing lineswould be 1.5 Vdc.

If the oncoming engine-generator set is rated at only one-half that of the first setsrating (say the first was rated at 100 kW and the second at 50 kW), balancedload would be achieved when each engine-generator set is carrying itsproportional share based on its rated output.

Rated share X =100 KW Load

100 KW + 50 KWor X = 2 / 3 or 66.67percent

Load gain outputs would match at 2/3 of 6 Vdc or 4 Vdc. Voltages across the R1sand R3s would be 2 Vdc. The load bridges would return to balance when the firstmachine was carrying 66.67 kW and the second would be carrying 33.33 kW.The sets are in isochronous load share rated speed. Voltage across the load

sharing lines would be 2 Vdc.

This method of connecting the load bridge between controls of multiple engine-generator sets, which are supplying the same load, can be used to obtain loadsharing between a number of different sets (see Figures 6-5 and 6-6). Themaximum number of sets which can be controlled in this manner has not beendetermined. One known installation has 21.


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34 Woodward

Power Output Sensor

The load sharing of mechanical loads or of mixed electrical and mechanical loadsuses a different type of load sensing. The most desirable method of sensing loadwould be to measure the torque on the engines, but this is difficult and requiresvery special measuring devices. The more common method, based on theassumption that power output is relative to actuator position, is to use a signaldeveloped from the control output (either current or voltage) to the actuator coil.Here, the current is the more desirable since force at the actuator is based onampere turns. If the actuator coil resistance changes with temperature, thechange does not affect the current load signal.

Another signal that can be used is one developed from the fuel valve position.This method makes use of Hall effect devices or of either LVDTs or RVDTs(linear or rotary variable differential transformers). These devices requiremodulators/demodulators to supply an ac voltage to the position sensors and torectify the return signal. A dc signal is developed representing fuel valve position.For load sharing these dc voltages relative to output load do not have to beexactly linearly proportional to the load to be useful for load sharing. They doneed to be equal from each engine in the load sharing system for any particularpercent of each engine's load capability. Again, the sensor output is impressed

on a load gain adjustment potentiometer.

The above load sharing analysis can also be applied to a system using poweroutput sensors to accomplish load sharing. The summing point amplifier in thecontrol of each engine will integrate to a fuel position which brings the loadbridges in each control to balance. This will set the fuel system of each engine tothe same power output whether the load on a particular engine is electric,mechanical, or a combination of electric and mechanical. The actual load sharingwill depend on how closely the fuel systems of the different engines track for thesame percentage of rated load.

Isochronous Base Load

If an engine-generator set is under the control of a load sharing and speed controlor if it is in an isochronous load sharing system, connecting the system to a utilitywill fix the speed sensor input to the summing point. Since the speed set is also ata fixed setpoint and the system is in isochronous, one of two things will happen.Either the system will be motorized or it will go to overload. The summing point,having all inputs fixed, cannot correct what it sees as an imbalance. If the systemwas at a frequency slightly below that of the utility, the speed sensor will send asignal to the summing point in excess of the setpoint input. The amplifier willintegrate in a decreased-fuel direction, cutting fuel to the engine. The utility thenends up driving the system. If the system frequency was slightly higher than theutility, the speed signal to the summing point would be below the setpoint, resultingin increased fuel until the mechanical stops are reached.


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To prevent these two conditions and to set the desired load, an auxiliary biassignal can be applied to the system load sharing lines. This will set a demand onthe generating system to generate a given portion of each engine-generatorsrated output. The action is the same as when load sharing units unbalance thebalanced load bridges. The load bridge outputs to the individual set summingpoints will be either positive or negative based on whether the engines are to pickup load or to shed load. Again, when the output of the engine-generators balancethe voltages on the load bridge, the system will be at the desired load. The

summing point can now function to correct imbalances and the system is underisochronous base load control.

If we now connect such an isochronous load sharing system to a utility, wherethe speed/frequency Is fixed by the utility, and we place a fixed bias signal onthat systems load sharing lines, all units in that system will be forced by loadbridge imbalance to carry the load demanded by the bias signal. This controlmethod opens many possibilities for load management through Isochronousbase loading.


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36 Woodward

Figure 6-4. Load Sharing Diagram


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Woodward 37

Figure 6-5. Load Sharing Block Diagram


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38 Woodward

Figure 6-6. Multiple Load Sharing Block Diagram


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Woodward 39

Chapter 7.Synchronization

What Is Synchronization?

We have talked about synchronizing one generator to another or to a utility, butwhat are we actually describing when we use the word "synchronization"?

Synchronization, as normally applied to the generation of electricity, is thematching of the output voltage wave form of one alternating current electricalgenerator with the voltage wave form of another alternating current electricalsystem. For two systems to be synchronized, five conditions must be matched:

The number of phases in each system

The direction of rotation of these phases

The voltage amplitudes of the two systems

The frequencies of the two systems

The phase angle of the voltage of the two systems

The first two of these conditions are determined when the equipment is specified,installed, and wired. The output voltage of a generator usually is controlledautomatically by a voltage regulator. The two remaining conditions, frequencymatching and phase matching, must be accounted for each time the tie-breakeris closed, paralleling the generator sets or systems.

Number of Phases

Each generator set of the oncoming system must have the same number ofphases as those of the system to which it is to be paralleled (see Figure 7-1).

Figure 7-1. Number of Phases Must Match Number Of Phases

Rotation of Phases

Each generator set or system being paralleled must be connected so that allphases rotate in the same direction. If the phase rotation is not the same, nomore than one phase can be synchronized (see Figure 7-2).


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In this instance, the power factor of the generator will be changed. If thegenerator voltage is much lower than the bus voltage, the generator could bemotored.

An induction generator needs no voltage regulator because its output voltage willautomatically match the voltage of the system supplying its field voltage.

Frequency Match

The frequency of the oncoming generator must be very nearly the same as thatof the system it is being paralleled with, usually within 0.2% (see Figure 7-5).

Figure 7-5. Frequency Difference

If the oncoming generator is a synchronous type, this match is normallyaccomplished by controlling the speed of the prime mover driving the oncominggenerator.

If the oncoming unit is an induction generator, frequency is determinedautomatically by the generator field voltage. Field voltage is supplied by thesystem to which the generator set is being paralleled. However, the field voltageis not applied to the generator until the tie breaker is closed. The generator mustbe kept close to synchronous speed prior to breaker closure. A speed belowsynchronous will cause the oncoming generator to act as a motor, and a speedmuch over 1.5% above synchronous will cause the induction machine to

generate at full capacity.

Phase Angle Match

The phase relationship between the voltages of the systems to be paralleledmust be very close prior to paralleling. This match usually is within plus or minus10 degrees. If the oncoming generator is a synchronous type, phase matching,like frequency matching, is accomplished by controlling the speed of theoncoming generator's prime mover. If the machine to be paralleled with thesystem is an induction generator, the phase match will be automatic, since thesystem is supplying the generator field voltage.

Figure 7-6. Phase Difference


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42 Woodward

For the synchronous generator, voltage, speed/frequency, and phase, must bematched each time before the paralleling breakers are closed. If the oncominggenerator is an induction-type with the armature rotating at synchronous speed,no difficulties will occur when the paralleling breakers are closed. Currently, mostinstallations use synchronous generators. The advantage of synchronousgenerators over induction generators is that synchronous systems allowindependent operation without a utility or other ac power source. Inductiongenerators can not operate without an external ac source.

Why Is Synchronization Important?

When two or more electrical generating sets or systems are paralleled to thesame power distribution system, the power sources must be synchronizedproperly. Without proper synchronization of the oncoming unit or system, powersurges and mechanical or electrical stress will result when the tie breaker isclosed. Under the worst conditions, the voltages between the two systems canbe twice the peak operating voltage of one of the systems, or one system canplace a dead short on the other. Extremely high currents can result from this,which put stress on both systems.

These stresses can result in bent drive shafts, broken couplings, or brokenturbine quill shafts. Under some conditions, power surges can be started whichwill build on each other until both generating systems are disabled.

These conditions are extreme. Stress and damage can occur in varying degrees.The degrading effects depend on the type of generator, the type of driver, theelectrical load, and on how poorly the systems are synchronized when thebreakers are closed.

Modern systems often supply power to sophisticated and sensitive electronicequipment. Accurate synchronization is necessary to prevent expensive downtime and replacement costs.

How Is Synchronization Accomplished?

Normally, one generating system is used to establish the common bus, and theoncoming generator is then synchronized to that bus by changing the speed ofthe prime mover driving the oncoming generator.

Manual Synchronization

Manually synchronized systems rely on monitoring equipment to indicate to theoperator when the two systems are synchronized closely enough for safeparalleling. This equipment may include indicating lights, a synchroscope, asynch-check relay, or a paralleling phase switch.

Figure 7-7 shows one method of using two 115 Vac lamps to check whether twovoltages are in or out of phase. When the voltages are in phase, the lamps willbe extinguished, and when the voltages are out of phase, the lamps willilluminate.

Figure 7-8 shows another method, using four 115 Vac lamps, that will checkphase rotation as well as phase match. As before, when the voltages are inphase, all lamps will be off, and when the voltages are out of phase, all of thelamps will light. If pairs of lamps alternate light and dark (with two lamps darkwhile the other two are light) the phase sequence is not the same.


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This method was later improved upon. The synchronizer would bring theoncoming unit into frequency match with the bus. Once the frequency wasmatched, the speed setting MOP was pulsed, adjusting generator speed to about0.5% above synchronous speed. The speed setting MOP was then run back toabout 0.2% below synchronous speed. This action was repeated untilsynchronization of phase angle occurred and the circuit breaker was then closed.

A modern synchronizer compares the frequency and phase of the two voltages,

and sends a correction signal to the summing point of the governor controllingthe prime mover of the oncoming generator. When the outputs of the twosystems are matched in frequency and phase, the synchronizer issues abreaker-closing signal to the tie-breaker, paralleling the two systems.

These synchronizers may include voltage-matching circuits which send raise andlower signals to the voltage regulator of the oncoming generator. If the voltage ofthe oncoming generator does not match the bus within set limits, thesynchronizer will not allow a circuit breaker closure.

This system is much faster than the earlier models and can even be used toforce an isolated engine-generator to track a utility without actually beingconnected to it.

Prediction of the Worst Case Phase Angle Difference() at the Instant of Breaker Closure

Worst case prediction of phase angle difference assumes there is no generatorspeed correction from the synchronizer after the breaker closure signal is issued(as in the permissive mode). In the run mode, the synchronizer continues toadjust generator speed toward exact phase match during the period the breakeris closing. This provides even better synchronization than the calculationsindicate.

The following calculation can be performed to determine if the speed and phase

match synchronizer will provide adequate synchronization before the breakercontacts engage in the permissive mode.

Each generator system has a worst case or maximum-allowable relative phaseangle (wc) that can be tolerated at the time of breaker closure. If wc and the

breaker time delay (Tb are known, the synchronizer's phase window (w) and

window dwell time may be chosen to ensure that is less than wc when thegenerator breaker contacts engage. The synchronizer will not issue the breakerclosure command unless is within the window (w) and has been there forat least the window dwell time. The drawing (Figure 7-9) shows the relativevalues of and assumes the bus voltage is fixed and pointing straight up.

The relative phase angle, at the instant the main generator breaker contacts

engage, depends on many things. The worst case value would exist when thesynchronizer is in the permissive mode and therefore is not actively correctingthe phase angle during the windo

ww governing fundamentals

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