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?