Correct Answer - Option 1 : Mho relay
Distance Relay:
- A distance protection relay is a name given to the protection, whose action depends on the distance of the feeding point to the fault.
- The time of operation of such protection is a function of the ratio of voltage and current, i.e., impedance.
- This impedance between the relay and the fault depends on the electrical distance between them.
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Types of distance relay are impedance relay, reactance relay, and the mho relay.
Mho Realy:
- A Mho relay or admittance relay measures a component of admittance |Y| ∠ θ. But it's characteristic when plotted on the impedance diagram is a circle passing through the origin.
- The relay is called the Admittance relay because its characteristic is a straight line when plotted on an admittance diagram.
- It is inherently a directional relay as it detects the fault only in the forward direction.
- The operation of the Mho relay is most affected due to arc resistance.
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A reactance relay is an overcurrent relay with directional restraint.
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Mho relay is a voltage restrained directional relay.
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A reactance relay is suitable for the protection of a short transmission line because its operation is independent of arc resistance.
- The relay which is selected for a long transmission line should be less affected due to power swings. Hence Mho relay is preferred.
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Impedance relay is suitable for medium transmission lines.
Synchronizing power surge effect:
Reactance relay > Impedance relay > Mho relay
Arc fault effect:
Mho relay > Imedance relay > Reactance relay > over current relay