Types of Protective Relays

Protection Relays are mainly classified as:

A. Based on Characteristic:

•Definite time Relays.

•Inverse definite minimum time Relays (IDMT)

•Instantaneous Relays

•IDMT with Instantaneous.

•Stepped Characteristic

•Programmed Switches

•Voltage restraint over current relay .

B. Based on logic:

–- Differential

–- Unbalance

–- Neutral Displacement

–- Directional

–- Restricted Earth Fault

–- Over Fluxing

–- Distance Schemes

–- Bus bar Protection

–- Reverse Power Relays

–- Loss of excitation

–- Negative Phase Sequence Relays etc.

C. Based on Actuating parameter:

–- Current Relays

–- Voltage Relays

–- Frequency Relays

–- Power Relays etc

D. Based on Operation Mechanism:

–1. Electro Magnetic Relay
2. Static Relay
……• Analog Relay
……• Digital Relay
……• Numerical /Microprocessor Relay
3. Mechanical relay

–Thermal
• OT Trip (Oil Temperature Trip)

       • WT Trip (Winding Temperature Trip)
• Bearing Temp Trip etc.

•Float Type
• Buchholz
• OSR
• PRV
• Water level Controls etc.

–- Pressure Switches

–- Mechanical Interlocks

–- Pole discrepancy Relay

E. Based on Applications

–- Primary Relays

–- Backup Relays

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