PJM State & Member Training Dept.
Fundamentals of Transmission Operations
System Stability
5/2/2014 PJM©2013
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
5/2/2014 PJM©2013
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 • Loss of one or more generators
• Loss of one or more major pieces of equipment
• System faults
• Low voltage operation
PJM©2013 5/2/2014
Steady State Stability
• Definition of Steady State • Steady loads
• Steady generation balanced with load
• No disturbances
• Small, slow changes are part of steady state
PJM©2013 5/2/2014
Steady State Stability
• Relationship of Phase Angle to Steady State Stability
• Review of power flow equation
PJM©2013 5/2/2014
Generator Bus
Equivalent System
Steady State Stability
• Relationship of Phase Angle to Steady State Stability
• Magnitude of power flow as a function of angle
PJM©2013 5/2/2014
Unstable Area
Steady State Stability
• Relationship of Phase Angle to Steady State Stability
• Stability Margin
PJM©2013 5/2/2014
Difference between operating point and 90 degrees
Steady State Stability
• Relationship of Phase Angle to Steady State Stability
• Effect of varying MW output
PJM©2013 5/2/2014
Steady State Stability
• Relationship of Phase Angle to Steady State Stability
• Effect of removing one line from service
PJM©2013 5/2/2014
Steady State Stability
• Relationship of Voltage to Steady State Stability
• Effect of changing machine excitation
PJM©2013 5/2/2014
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
PJM©2013 5/2/2014
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
PJM©2013 5/2/2014
Dynamic Stability
PJM©2013 5/2/2014
Muddy Run - 12/28/99
7580859095
100105110115120125130135
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
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
Time
Gen.
UNIT1 UNIT2 UNIT3 UNIT4 UNIT5 UNIT6 UNIT7 UNIT8
Dynamic Stability
PJM©2013 5/2/2014
Peach Bottom Units - 12/28/99
1040
1050
1060
1070
1080
1090
1100
1110
1120
1130
1140
1150
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
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
Time
Gen.
0
100
200
300
400
500
600
700
Peach Bot #2 Peach Bot #3 Muddy Run Tot Gen.
Peach Bottom xfmr Switching - 3/23/01
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
7:0
0
7:0
4
7:0
8
7:1
2
7:1
6
7:2
0
7:2
4
7:2
8
7:3
2
7:3
6
7:4
0
7:4
4
7:4
8
7:5
2
7:5
6
8:0
0
8:0
4
8:0
8
8:1
2
8:1
6
8:2
0
8:2
4
8:2
8
8:3
2
8:3
6
8:4
0
8:4
4
8:4
8
8:5
2
8:5
6
9:0
0
Time
MW
/MV
AR
PB 02 MW
PB 02 MV
PB 03 MW
PB 03 MV
Slm 1 MW
Slm 1 MV
Slm 2 MW
Slm 2 MV
MR Gen
Cono Gen
Dynamic Stability
PJM©2013 5/2/2014
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
PJM©2013 5/2/2014
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
PJM©2013 5/2/2014
Stability Guides
• Transmission Operations Manual – Section 5 • 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…..
PJM©2013 5/2/2014
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
PJM©2013 5/2/2014
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
PJM©2013 5/2/2014
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
PJM©2013 5/2/2014
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
PJM©2013 5/2/2014
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
PJM©2013 5/2/2014
The ability of a generator to dampen out oscillations caused by minor
disturbances is called:
1. Steady State Stability
2. Transient Stability
3. Dynamic Stability
4. 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. Steady State Stability
2. Transient Stability
3. Dynamic Stability
4. Generator Stability 25%
25%25%
25%
Steady State Stab... Transient Stability
Dynamic Stability Generator Stability0 of 80
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/pjm-agreements.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
5/2/2014 PJM©2013