Electrical Engineering ⇒ Topic : Classification of Relays
Classification of Relays
A. According to operating characteristics
1. Solenoid type
2. Electrodynamic type
3. Induction type
4.Attracted armature type
5. Moving coil type
6. Directional or reverse current type
7.Directional or reverse power type
8.Under-voltage, under current and under power relay
9.Over voltage, current or over power relay
10. Thermal relay
11. Differential relay
12. Distance relay.
B. According to operation time
2. Definite time lag
3. Inverse time lag
4. Inverse-definite-minimum time lag.
The following points are worth noting about some relays :
Differential-relay responds to vector difference between two or more similar electrical quantities.
Over current relay responds to increase in current ; the relay operates when the current exceeds a preset level.
Impedance relay operates when the impedance between relay point and fault point is below a specified value.
Instantaneous relay is a quick operating relay ; operating time less than 0.2 sec.
Static relay has no moving parts ; the measurement is performed by a stationary circuit.
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