Fundamentals and Advancements in
Generator Synchronizing Systems
Michael J. Thompson
Schweitzer Engineering Laboratories, Inc.
Copyright © SEL 2011
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°
Current Can Exceed Three-Phase
(3PH) Short Circuit
I3PH
+
VG
–
VG
=
X"G
3PH Fault
X"G
IOOP
+
VG + VS
=
X"G + XT + XS
Close Breaker Out of Phase
X"G
XT
XS
VG
–
IOOP > I3PH when (XT + XS ) < X"G
–
VS
+
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 CylindricalRotor 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 Room
52A
A25A
Fiber-Optic
Link
Governor
RIO
Exciter
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
Example B
Sub 27
4 kV
Reliability Islanding System
G
2
1
A25A
1
RIO
• System islands critical
loads at 3, 4, 5, or 6
• Resynchronization is
performed
Sub 75
34 kV 3
Critical Load
♦
By A25A 1 at Sub 27
and Sub 75
Critical Load
5
♦
By A25A 2 at Sub 66
4
RIO
Sub 66
115 kV
A25A
2
7
6
Utility
Critical
Load
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
Example C
Complex Bus
and Multiple
Synchronizing
Scenarios
G5
U1
U2
G6
8
6
5
7
1A
1B
1
4
3
2
2A
A25A-A
Slip
25A-1
25A-2
V Diff
25A-3
25A-4
25A-5
25A-6
GCS
2B
A25A-B
Slip 25A-1
25A-2
V Diff 25A-3
25A-4
25A-5
25A-6
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?