Which of the following acts as a protection against high voltage surges due to lightening and switching?

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ALP CBT 2 Electrician Previous Paper: Held on 22 Jan 2019 Shift 1

Answer 1

F1 J.P Madhu 20.02.20 D1

The horn gap acts as a protection device for an electrical power system from high voltage surges.
The horn gap consists of two horn-shaped rods separated by a small distance. One end of this is connected to the line and the other to the earth as shown in the figure with or without a series resistance.
The choke connected between the equipment to be protected and the horn gap serves two purposes:
- The steepness of the wave incident on the equipment to be protected is reduced.
- It reflects the voltage surge back on to the horn.
Whenever a surge voltage exceeds the breakdown value of the gap a discharge takes place and the energy content in the rest part of the wave is by-passed to the ground.
An arc is set up between the gap, which acts as a flexible conductor and rises upwards under the influence of the electromagnetic forces, thus increasing the length of the arc which eventually blows out.
Thermal overload relay works on the heat produced by the excessive overload current. The heat produced by the overload current is utilized to trip the motor circuit.
These are mostly used for the protection of low-voltage squirrel cage induction motors or DC motors of lower output rating.