Fundamentals of
Transmission Operations
System Stability
PJM State & Member Training Dept.
PJM©2013
5/2/2014
Objectives
Following this presentation, the student will be able to:
• Define stable operation
• Define the following stability modes: Steady state,
Transient, Dynamic
• Discuss the actions that may be taken by the System Operator
that will impact the stability of the system
• Discuss how instability threatens the system
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Stable Operation
• Definition
• Generic
• Stability is the condition of equilibrium between opposing forces
• In power system, Mechanical power provided to turbine = electrical
power drawn by the system
• Typical Threats to Stability
•
•
•
•
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Loss of one or more generators
Loss of one or more major pieces of equipment
System faults
Low voltage operation
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Steady State Stability
• Definition of Steady State
•
•
•
•
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Steady loads
Steady generation balanced with load
No disturbances
Small, slow changes are part of steady state
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Steady State Stability
• Relationship of Phase Angle to Steady State Stability
• Review of power flow equation
Generator
Bus
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Equivalent
System
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Steady State Stability
• Relationship of Phase Angle to Steady State Stability
• Magnitude of power flow as a function of angle
Unstable
Area
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Steady State Stability
• Relationship of Phase Angle to Steady State Stability
• Stability Margin
Difference between
operating point and
90 degrees
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Steady State Stability
• Relationship of Phase Angle to Steady State Stability
• Effect of varying MW output
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Steady State Stability
• Relationship of Phase Angle to Steady State Stability
• Effect of removing one line from service
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Steady State Stability
• Relationship of Voltage to Steady State Stability
• Effect of changing machine excitation
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Steady State Stability
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Transient Stability
• Definition
• The ability of a generator or group of generators to remain
in synchronism immediately following a system disturbance
(initial swing)
• Transient stability is typically viewed as first swing stability
• The first swing for a generator takes less than a second
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Transient Stability
• Equal Area Criterion (Area ABC=CDE)
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Transient Stability
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Dynamic Stability
• Definition
• Ability of generators to damp oscillations caused by relatively minor
disturbances through the action of properly tuned control systems
• Mechanisms
• Excitation control
• Governors
• Protective relaying
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Dynamic Stability
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135
130
125
120
115
110
105
100
95
90
85
80
75
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10:20:00
UNIT7
10:19:00
10:18:00
10:17:00
UNIT6
10:16:00
10:15:00
10:14:00
UNIT5
10:13:00
10:12:00
UNIT4
10:11:00
10:10:00
10:09:00
UNIT3
10:08:00
10:07:00
10:06:00
UNIT2
10:05:00
10:04:00
10:03:00
UNIT1
10:02:00
10:01:00
10:00:00
Gen.
Dynamic Stability
Muddy Run - 12/28/99
UNIT8
Time
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Dynamic Stability
Peach Bottom Units - 12/28/99
Peach Bot #3
Muddy Run Tot Gen.
700
600
500
400
Gen.
Peach Bot #2
1150
1140
1130
1120
1110
1100
1090
1080
1070
1060
1050
1040
300
200
Time
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10:11:00
10:12:00
10:13:00
10:14:00
10:15:00
10:16:00
10:17:00
10:18:00
10:19:00
10:20:00
10:00:00
10:01:00
10:02:00
10:03:00
10:04:00
10:05:00
10:06:00
10:07:00
10:08:00
10:09:00
10:10:00
100
0
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Dynamic Stability
Peach Bottom xfmr Switching - 3/23/01
1200
1100
1000
900
800
PB 02 MW
PB 02 MV
MW/MVAR
700
PB 03 MW
PB 03 MV
600
Slm 1 MW
Slm 1 MV
500
Slm 2 MW
Slm 2 MV
400
MR Gen
Cono Gen
300
200
100
9:00
8:56
8:52
8:48
8:44
8:40
8:36
8:32
8:28
8:24
8:20
8:16
8:12
8:08
8:04
8:00
7:56
7:52
7:48
7:44
7:40
7:36
7:32
7:28
7:24
7:20
7:16
7:12
7:08
7:04
7:00
0
Time
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Consequences of Instability
• Loss of synchronization
• Steady state
• phase angle exceeds 90 degrees
• Transient
• excessive rotor angle swings
• units tripped following disturbance
• Dynamic
• continued oscillations over long periods of time
• may damage units before they are tripped
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Consequences of Instability
• Operator Actions Affecting Stability
• Awareness
• Generator MW output
• Decrease MW output to increase stability
• Generator MVAR output
• Increase MVAR output to increase stability
• Lines in service - system strength
• Put more lines in service to increase stability
• Special Relay schemes
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Stability Guides
• Transmission Operations Manual – Section 5
•
•
•
•
•
•
•
•
•
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Calvert Cliffs Voltage Limitations
Indian River #4 “Trip a Unit” Special Protection Scheme
Conemaugh Unit Stability
Conemaugh #2 Unit Stability Trip Scheme - Conemaugh-Juniata
500 kV Outage
PL Northern Generation Stability
PSE&G Artificial Island Stability
Rockport Operating Guide
Quad Cities Stability Operations
Many others…..
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Stability and the PJM Generator Interconnection Process
• What do these guidelines contain?
• Unit restrictions for each outage that affects stability
• Tripping schemes
• Generator MW output restrictions
• Generator MVAR output restrictions
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Stability and the PJM Generator Interconnection Process
• How are these guides developed?
• Guidelines are based on detailed stability studies that consider severe
fault conditions (N-1) that occur under each significant outage
condition (N-2) in the area of concern
• Guidelines are developed under very conservative assumptions of
generation dispatch and load level
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Stability and the PJM Generator Interconnection Process
• When are these guides updated and developed?
• Guides will be updated every time a new generator locates in vicinity
of problem
• Anytime an area becomes concentrated with a large amount of
generation relative to the transmission outlet capability of the area, a
detailed stability study will be performed to see if an operating guide
is needed
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Stability and the PJM Generator Interconnection Process
• Why are these guides so important?
• Guides usually involve several large generators that can easily
be damaged when they are operated out-of-step with the rest
of the system
• A generator that is operated out-of-step will frequently cause
transmission lines to trip before the generator itself trips off-line
• When several large generators are operated out-of-step, cascading
outages and widespread load shedding can result due to the
fluctuations in power flows, voltage and frequency
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Stability and the PJM Generator Interconnection Process
• Conclusion:
• Stability has not yet become the most significant system limitation
• Operators need to be aware of the importance of why stability
operating guides are developed and why they will be updated much
more frequently than in the past
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The ability of a generator to dampen
out oscillations caused by minor
disturbances is called:
1.
2.
3.
4.
Steady State Stability
Transient Stability
Dynamic Stability
Generator Stability
0 of 80
25%
25%
25%
25%
Steady State Stab...
Transient Stability
Dynamic Stability
Generator Stability
The ability of a generator to remain in
synchronism immediately following
a system disturbance is:
1.
2.
3.
4.
Steady State Stability
Transient Stability
Dynamic Stability
Generator Stability
0 of 80
25%
25%
25%
25%
Steady State Stab...
Transient Stability
Dynamic Stability
Generator Stability
Questions?
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5/2/2014
Disclaimer:
PJM has made all efforts possible to accurately document all
information in this presentation. The information seen here
does not supersede the PJM Operating Agreement or the
PJM Tariff both of which can be found by accessing:
http://www.pjm.com/documents/agreements/pjmagreements.aspx
For additional detailed information on any of the topics
discussed, please refer to the appropriate PJM manual
which can be found by accessing:
http://www.pjm.com/documents/manuals.aspx
PJM©2013
5/2/2014