电力系统失步保护概述

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Philosophy of Power-Swing Protection
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Separate the system at locations that provide good balance of load/generation in the resulting system islands Trip only at pre-selected network locations and block tripping at all other locations Trip only under controlled transient recovery voltages or with low current
Degrees
200 0 -200 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Seconds
Relay Elements Prone to Operate During Power Swings
Transient Stability Concepts
VS
1
Line 1
2
VR
3
Line 2
4
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Prefault state (Both lines in service) Fault state Fault state with breaker 3 open Post-fault state (Line 2 out)
Introduction
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The aim of this presentation is to explain

The fundamentals of out-of-step (OOS) protection Discuss which relays and relay systems are prone to operate during power swings Share experiences and lessons learnt from the past to avoid making the same mistakes

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Equipment damage Widespread outages in the power system
Philosophy of Power-Swing Protection
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Detect both stable and unstable power swings Block tripping of relay elements prone to operate during power swings Differentiate between stable and unstable power swings Separate the system into islands during out-of-step conditions

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In many cases they prevent further propagation of the disturbance In some cases undesired relay operations have contributed to cascading blackouts

Outline
Out-Of-Step Protection Fundamentals
Demetrios Tziouvaras Schweitzer Engineering Laboratories, Inc. IEEE PES San Francisco Chapter December 13, 2007
Copyright © SEL 2007
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Large voltage variations Large power oscillations Loss of synchronism Zero voltage at the electrical center Frequency excursions
Angular Instability

System faults Line switching Major load switching Loss of large generation Major system disturbances
Stable and Unstable Power Swings Definitions
Need for Out-of-Step Protection
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Generators operating asynchronously with the rest of the power system cannot regain stability as a result of any excitation or regulator action Asynchronous power system areas must be separated in a controlled fashion to avoid:
Power Flow Two-Machine System
Line 1 VS
1 2
VR
3
Line 2
4
X
VS δ VR
P=
VS ⋅ VR X
sin δ
Effect of Fault Type on Power Transfer
VS
1
Line 1
2
VR
3
Line 2
4
Normal System P Single-Line-Ground Fault Phase-Phase Fault Phase-Phase-Ground Fault Three-Phase Fault δ
Seconds
Angular Instability
V1 and Angle of V1 / I1
Positive-Sequence Voltage Magnitude Per Unit
0.6 0.4 0.2 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
400
Seconds Angle of (V1 / I1)
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Out of step (OOS) protection fundamentals Relay performance during OOS conditions

Transmission lines Generators
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System design and protection improvements Conclusions
Unstable System
P Prefault Post-Fault
Fault
δ
Stable and Unstable Power Swings
Rotor Angle
δ Unstable System δ1 δ0 Stable System
t
Angular Instability
Distinguishing Features
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A power swing is considered stable if the generators do not slip poles and the system reaches a new state of equilibrium, i.e. an acceptable operating condition An unstable power swing results in a generator or group of generators experiencing pole slipping or loss-ofsynchronism for which some corrective action must be taken.


Introduction
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Interconnected systems experienced an increased number of large disturbances in the last 15 years Protective relay systems are often involved during major disturbances
Large Voltage Variations
Voltage Magnitude Per unit
1 0 -1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Seconds
1.5
Per Unit
1 0.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Seconds
Equal-Area Criterion
VS
1
Line 1
2
VR
P
3
Line 2
4
Prefault
6 0 5 Area 1 3 1 2 4 Area 2
Post-Fault
P0
Fault (one breaker open) Fault
180°
δ
E
What Is a Power Swing?
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Variation of power flow which occurs when generator rotor angles are advancing or retarding relative to each other in response to:

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Out-of-step is the same as an unstable power swing.
Power Swings can Cause Undesired Protective Relay Operation