A megger has _ current coil(s) and _ potential coil(s).

Question

Question

This question was previously asked in

MPPGCL JE Electrical 28 April 2023 Shift 3 Official Paper

Answer 1

Megger

A Megger (Megohmmeter) measures high insulation resistance in electrical circuits. It consists of:

Current Coil (1 Coil): Produces torque proportional to the current flowing.
Potential Coils (2 Coils): Produces torque proportional to the applied voltage.

The interaction between these coils ensures accurate insulation resistance measurement.

Construction of Megger

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The Megger has one current coil and two voltage coils V₁ and V₂.
The voltage coil V₁ is passed over the magnet connected to the generator.
When the pointer of the PMMC instrument deflects towards infinity, it means that the voltage coil remains in the weak magnetic field and thus experienced very little torque.
The torque experienced by the coil increases when it moves inside the strong magnetic field.
The coil experiences the maximum torque under the pole faces and the pointer is set at the zero ends of the resistance scale.
To improve the torque, the voltage coil V₂ is used.
The coil V₂ is so allocated that when the pointer deflects from infinity to zero, the coil moves into a stronger magnetic field.
In Megger, the combined action of both the voltage coils V₁ and V₂ are considered.
The coil comprises a spring of variable stiffness. It is stiff near the zero ends of the coil and becomes very weak near the infinity end of the spring.