CHAPTER 3: BASIC PROTECTION AND SWITCHING EQUIPMENTS

GENERATION

• Generator 
• Turbine
• Transformer

Generator

TRANSMISSION

•  EHV (Extra High Voltage) – 275 kV & 500 kV
•  Subtransmission – 66 kV and 132 kV 

Transmission Line

 DISTRIBUTION
    – 11 kV , 22kV & 33 kV

 LOAD

• Consumer (factory and residency)

CHARACTERISTIC NEEDED FOR SWITCH GEAR

• Realiability
• Selectivity
• High speed
• Sensivity
• Cost

SWITCH GEAR EQUIPMENT

1.) Fuse

• When a fuse blows out, it takes quite sometimes to replace it and restore supply to the customers.
• A fuse cannot successfully interrupt heavy fault currents that result from faults on modern high voltage and large capacity circuits.
• limited to low-voltage and small capacity circuits
• 3 types of fuses; cartridge, rewired, high rate capacitance

2.) Circuit Breaker 

• Suitable for high capacity circuits.
• Can make or break a circuit either manually or automatically under all condition.

ARC PHENOMENON

• When short-circuit occurs, a heavy current flows through the contact of the circuit breaker before they are opened by the protective system. 
• At the instant when the contacts begin to separate, the contact area decrease rapidly and large fault current causes increased current density and hence rise in temperature. 

METHOD OF ARC EXTINCTION

Oil circuit breakers

Air-blast circuit breakers

Sulphur Hexafluoride (SF6) circuit breakers

Vacuum circuit breakers

Short Video