Copyright © SEL 2011

Fundamentals and Advancements in Generator Synchronizing Systems

Michael J. Thompson Schweitzer Engineering Laboratories, Inc.

Outline

• Consequences of faulty synchronization

• Components of synchronizing systems

• 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 VIX" X X

+=

+ +G

3PHG

VIX"

=

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-Pole Generators

• 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 close Calculate 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 advanced angle 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 failure Single failure fools multilevel supervision

Advancements

Advanced Synchronizer

• Six VT inputs and programmable I/O eliminate 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 / red indication

Lab Testing

Example A No Local Synchronizing Breaker

Substation Generator Control Room52A Governor

Exciter

Fiber-OpticLink

A25ARIO

Example B Reliability Islanding System

• System includes process steam and electricity cogeneration

• Separation points selected depend on critical load

• All objectives satisfied using only two A25A devices and two RIO modules

• System islands critical loads at 3, 4, 5, or 6

• Resynchronization is performed ♦ By A25A 1 at Sub 27

and Sub 75 ♦ By A25A 2 at Sub 66

Example B Reliability Islanding System

G

1 2

4

3

5

A25A1

Sub 75 34 kV

Sub 274 kV

Sub 66115 kV

6

Utility

7A25A

2

Critical Load

Critical Load

Critical Load

RIO

RIO

Example C Complex 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 C Complex Bus and Multiple Synchronizing Scenarios

• GCS handles frequency control and load sharing

• During synchronizing, GCS performs frequency and voltage matching

• A25A verifies synchronizing criteria and closes breakers

G5

8

U1

4

6

1

23

75

G6U2

A25A-A25A-125A-225A-3 25A-425A-5 25A-6

A25A-B25A-125A-225A-325A-4 25A-525A-6

GCS

Slip

V Diff

Slip

V Diff

1A

2A

1B

2B

Example C Complex Bus and Multiple

Synchronizing 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 as synchrophasors enables remote synchronization and improves operator indications

• Examples illustrate synchronizing systems that were never before possible

Questions?