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Fundamentals and Advancements inGenerator Synchronizing Systems

Michael J. ThompsonSchweitzer Engineering Laboratories, Inc.



Outline

• Consequences offaulty synchronization

• Components of

synchronizingsystems

• Fundamentals of

system design

• Advances



Consequences of Faulty

Synchronization

• Damage to generator and prime mover

♦ Mechanical (rapid acceleration / deceleration)

♦ Damaged windings (due to high current)

• Standards for generators

♦ Slip, ±0.067 Hz

♦ Voltage, +5%

♦ Angle, ±10°



OOP 3PH T S GI > I when (X + X ) < X"

G SOOP

G T S

V VI

X" X X

+=

+ +

G3PH

G

VI

X"=

VG

X"G

3PH Fault

+

–

VS

X"G

VG

XT XS

Close Breaker Out of Phase

+

– +

–

Current Can Exceed Three-Phase

(3PH) Short Circuit



Consequences of Faulty

Synchronization

• System disturbances

♦ Power oscillations

♦ Voltage depression

• Relay operation

♦ Reverse power

♦ Loss of field



IEEE Standards and Guides

• IEEE C50.12, Standard for Salient-PoleGenerators

• IEEE C50.13, Standard for Cylindrical-

Rotor Generators

• IEEE 67, Guide for Operation and

Maintenance of Turbine Generators

• No guide for prime mover



Synchronizing System Components

• Control functions♦ Control governor to match frequency

♦ Control exciter to match voltage

♦ Cause breaker to close at 0°

• Automatic and / or manual controls?

♦ All functions automatic or manual♦ Mix of both

♦ Both available and used as required



Permissive Devices

• Synchronism check

• Voltage elements

• Operator control



Manual Systems

• Require an operator in the control loop• Operator indications typically include

♦ Two light bulbs (composite measurement of all

three parameters)

♦ Synchroscope (angle, rpm gives slip)

♦ Voltmeters (voltage difference)

Incoming (generator)

Running (bus)



Automatic Systems

• Slip-compensated advanced angle closeCalculate angle using measured slip multiplied

by mechanism delay

• More precise and consistent than operator



Automatic Systems

• Generator control♦ Raise and lower pulses

♦ Proportional pulse width characteristic

• Islanding systems with multiple generators

♦ Synchronizer sends slip and voltage difference

to automatic generation control (AGC)

♦ AGC matches

♦ Synchronizer does slip-compensated

advanced angle close



Visualization

• Critical for manual systems

• Optional for automatic systems



Synchronism-Check Relays

• Traditional♦ Window and delay surrogate for slip

♦ Late close possible in slipping applications

• Microprocessor-based

♦ Directly measures slip and voltage difference

♦ May include slip-compensated advancedangle close

♦ Is superior for slipping applications



System Design

• Design for fault tolerance

• Include redundancy

Single point of failure makes generator unavailable

• Include multilevel control and supervision

Single failure causes faulty synchronization

• Eliminate common-mode failureSingle failure fools multilevel supervision



Advancements



Advanced Synchronizer

• Six VT inputs and programmable I/Oeliminate sensing and control signal switching

• Peer-to-peer synchrophasors allow systems

never before possible

• Fiber-optic remote I/O allows remote control



Synchrophasor Synchroscope

• Improved operator indications

• Independent of automatic synchronizer

• No required physical signal switching

• Part of existing synchrophasor installation



Direct Indication of

Synchronizing Criteria

• Angle

• Slip

• Voltage

difference

• Green / redindication



Lab Testing



Example ANo Local Synchronizing Breaker

Substation Generator Control Room

52AGovernor

Exciter

Fiber-OpticLink A25A

RIO



Example BReliability Islanding System

• System includes process steam and

electricity cogeneration

• Separation points selected depend oncritical load

• All objectives satisfied using only two

A25A devices and two RIO modules



• System islands critical

loads at 3, 4, 5, or 6

• Resynchronization isperformed

♦ By A25A 1 at Sub 27

and Sub 75

♦ By A25A 2 at Sub 66

Example BReliability Islanding System

G

1 2

4

3

5

A25A

1

Sub 75

34 kV

Sub 27

4 kV

Sub 66

115 kV

6

Utility

7 A25A

2

Critical Load

Critical Load

Critical

Load

RIO

RIO



Example CComplex Bus and Multiple

Synchronizing Scenarios

• Alumina processing plant has

double-bus / single-breaker

• Generation control system (GCS)

synchronizes across all breakers

except generator breakers

• Two A25A devices connect to all

six VTs for redundancy



Example CComplex Bus and Multiple

Synchronizing Scenarios

• GCS handles frequency control

and load sharing

• During synchronizing, GCS performs

frequency and voltage matching

• A25A verifies synchronizing criteriaand closes breakers



G5

8

U1

4

6

1

2

3

75

G6U2

A25A-A

25A-1

25A-2

25A-3

25A-4

25A-5

25A-6

A25A-B

25A-1

25A-2

25A-3

25A-4

25A-5

25A-6

GCS

Slip

V Diff

Slip

V Diff

1A

2A

1B

2B

Example CComplex Bus

and MultipleSynchronizing

Scenarios



Summary and Conclusions

• Synchronize generators carefully• Build synchronizing systems for

fault tolerance

• Use multilevel supervision (recommended)

• Simplify synchronizing systems with

microprocessor-based technology



Summary and Conclusions

• New developments improve performance –reducing costs and possibilities of hidden

failures and improving reliability

• Advanced technology such assynchrophasors enables remote

synchronization and improves operator

indications• Examples illustrate synchronizing systems

that were never before possible



Questions?