Power System Protection

Electrical Energy is

• Generated at few kV and stepped up.

• Transmitted through AC and HVDC lines.

• Stepped down and distributed at load centers.

Its natural mode of synchronous operation knits the systemtogether.

Why do we need protection?

Electrical apparatus operates at various voltage levels and may be enclosed or placed in open. Under abnormal operating conditions protection is necessary for

• Safety of electrical equipments.

• Safety of human personnel. 

Types of Protection

• Apparatus Protection

• System Protection 

Types of Protection

• Apparatus Protection

• Transmission Line Protection

• Transformer Protection

• Generator Protection

• Motor Protection

• Busbar Protection

• System Protection

• Out-of-Step Protection

• Under-frequency Relays

• Islanding Systems

• Rate of Change of Frequency Relays 

What is a Relay?
A relay is a logical element which process the inputs (mostly voltages and currents) from the system and issues a trip decision if a fault within its jurisdiction is detected. Inputs to a relay are

• Current from a current transformer.

• Voltage from a voltage transformer