Foto Lesson6 Stability - PJM

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

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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 • 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 • Steady loads

• Steady generation balanced with load

• No disturbances

• Small, slow changes are part of steady state

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• Relationship of Phase Angle to Steady State Stability

• Review of power flow equation

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Generator Bus

Equivalent System



• Magnitude of power flow as a function of angle

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Unstable Area



• Stability Margin

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Difference between operating point and 90 degrees



• Effect of varying MW output

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• Effect of removing one line from service

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• Relationship of Voltage to Steady State Stability

• Effect of changing machine excitation

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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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Dynamic Stability

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Muddy Run - 12/28/99

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Time

Gen.

UNIT1 UNIT2 UNIT3 UNIT4 UNIT5 UNIT6 UNIT7 UNIT8

Dynamic Stability

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Peach Bottom Units - 12/28/99

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Peach Bot #2 Peach Bot #3 Muddy Run Tot Gen.

Peach Bottom xfmr Switching - 3/23/01

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PB 02 MW

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PB 03 MW

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MR Gen

Cono Gen

Dynamic Stability

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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 • 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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• 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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• 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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• 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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• 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. 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

Questions?

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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

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Foto Lesson6 Stability - PJM