Power system protection
Transcript of Power system protection
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Power System Protection
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OUTLINE
System protection-DefinitionNeed for the protection Elements of the protection system
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What is System protection?
System protection is the art and science of detecting problems with power system components and isolating these components.
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Need for the protection
The power system must maintain acceptable operation 24 hours a day
Voltage and frequency must stay within certain limits
Protect the publicImprove system stabilityMinimize damage to equipmentProtect against overloads
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Damage to Main Equipment
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COMPONENTS USED FOR PROTECTION
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Components to be protected
Generators Transformers Lines Buses Capacitors
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GENERATOR PROTECTION
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Generator Protection
What can go wrong? Stator Winding Problems 1. Winding-winding short
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How Do We Protect the Stator? A. Differential Protection (what goes in must
come out) 1. Detects phase-phase faults
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TRANSFORMERPROTECTION
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Transformer Protection
What can go wrong? ● Winding-to-winding faults● Winding-to-ground faults ● Bushing faults
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Transformer Protection
Protection Methods: Fuse Overcurrent Differential
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FUSE
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OVERCURRENT RELAYS
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DIFFERENTIAL METHOD
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TRANSMISSION LINE PROTECTION
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TRANSMISSION LINE PROTECTION
What Can Go Wrong? FAULTS (Short Circuits)
SOME CAUSES OF FAULTS: Trees Lightning Animals (birds, squirrels, snakes) Weather (wind, snow, ice) Natural Disasters (earthquakes, floods) Faulty equipment (switches, insulators, clamps,
etc.)
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TYPES OF FAULTS
Single-Phase-Ground: 70–80%Phase-Phase-Ground: 17–10%Phase-Phase: 10–8%Three-Phase: 3–2%
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How Do We Protect Transmission Lines? Overcurrent BiDirectional Overcurrent Distance (Impedance) Line Current Differential
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OVERCURRET PROTECTION
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DISTANCE PROTECTION
A distance relay measures the impedance of a line using the voltage applied to the relay and the current applied to the relay. When a fault occurs on a line, the current rises significantly and the voltage collapses significantly. The distance relay (also known as impedance relay) determines the impedance by Z = V/I. If the impedance is within the reach setting of the relay, it will operate.
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RELAY PROTECTION
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BUS PROTECTION
Bus Differential: Current into bus must equal current out of
bus
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Capacitor Protection
Purpose of capacitors: Shunt capacitors raise the voltage on a bus or line to a higher level, thus helping keep the voltage at desired level Series capacitors cancel out the inductive reactance of a line, thus making the line appear shorter increasing load flow on the line.
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