The document discusses different types of protection relays used in power systems. It describes relays categorized by their operation mechanism, actuating parameter, application, and logic. Relays are described as mechanical, electromagnetic, or static based on operation mechanism. They are also current, voltage, frequency, or power relays depending on the actuating parameter. Primary and backup relays are differentiated by application. Common unit protection relays are also listed based on their logic, including differential, over/under voltage, over/under frequency, and loss of excitation relays. Electromechanical and solid-state relays are briefly described and compared.

1. BUS
CT
RELAY
PT
OTHER
COMMUNICATIONS
STATION
BATTERY
POWER
LINE
CIRCUIT
BREAKER

2. TYPES OF RELAY
Types of protection relays are mainly based on their
characteristics ,logic, on actuating parameter &
operation mechanism.
 Based on operationof mechanism
1. Mechanical relay
2. Electromagnetic relay
3. Staticrelay
 Based on actuating parameter
1. Currentrelay
2. voltage relay
3. Frequency relay
4. Power relay
 Based on application
1. Primary relay
2. Back uprelay

3.  Based on logic Unit Protection
1. Differential (87 G)
2. Under Voltage (27)
3. Over Voltage (59)
4. Generator CB Failure (50BF)
5. Fuse Failure VT (60)
6. Rotor earth Fault (64R)
7. Stator Earth Fault (64S)
8. Over Frequency (81O)
9. Under Frequency (81U)
10.Over fluxing/Over Excitation V/Hz (24)
11.Reserve power relay (32)
12. Loss of excitation (40)
13. Negative phase sequence relay (46)

4. Inoursimplerelayabove, we havetwosetsof electrically
conductivecontacts. Relays may be “NormallyOpen”,or
“Normally Closed”. One pairof contactsareclassed as Normally
Open,
An example of thisarrangement isgiven below.
ELECTROMECHANICAL RELAY

5. Solid-state Relays (SSRs)
 SSRs usesemiconductor output instead of
mechanical contacts to switch thecircuit.
 Theoutputdevice isoptically-coupled toan LED
light source inside the relay.
 The relay is turned on byenergizing this LED, usually
with low-voltage