Q: Relay and its types?
Relay:
Relay are electrical switches that open or close another circuit under certain conditions.
Types of relay:
Electromagnetic relay
Solid state relay
Numerical relay
Q: Overcurrent relay, types, application?
Overcurrent relay:
The overcurrent relay is defined as the relay, which operates only when the value of the current
is greater than the relay setting time.
Types of Overcurrent relay:
Instantaneous Overcurrent relay
Inverse time Overcurrent Relay
Definite Time Overcurrent Relay
Inverse Definite Time Overcurrent Relay
Very Inverse Definite Time Overcurrent Relay
Extremely Inverse Definite Time Overcurrent Relay
Instantaneous Overcurrent relay
Application of Overcurrent relay:
1.Motor Protection:
Used against overloads and short-circuits in stator windings of motor.
Inverse time and instantaneous overcurrent phase and ground
Overcurrent relays used for motors above 1000 kW.
2.Transformer Protection:
Used only when the cost of overcurrent relays are not justified.
Extensively also at power-transformer locations for external-fault back-up protection.
3.Line Protection:
On some sub transmission lines where the cost of distance relaying cannot be justified.
primary ground-fault protection on most transmission lines where distance relays are
used for phase faults.
For ground back-up protection on most lines having pilot relaying for primary
protection.
4.Distribution Protection:
Overcurrent relaying is very well suited to distribution system protection for the following
reasons:
It is basically simple and inexpensive.
