Creeping in Energy Meter - Creeping Error & its Prevention

Creeping in Energy Meter :

Generally, the energy meter is designed to measure the energy consumption of load connected to it i.e., the energy meter disc should rotate when there is a flow of load current in the current coil. Whenever there is a current passing through the current coil with the coil excited, the disc of the energy meter rotates and measures the amount of energy consumed.

But sometimes, the disc rotates slowly but continuously even without any current in the current coil. The phenomenon of rotation of disc without any current through the current coil is known as Creeping. Due to this, the meter shows the incorrect reading. In other words, the energy meter records a small amount of energy consumption even when there is no load connected to it. This causes an error in the readings called creeping error.

The main reason for creeping is overcompensation for friction i.e., low load adjustment of energy meter. Under the light load condition, due to friction adjustment using shading loop. The shading loop produces a starting torque on the disc which is irrespective of the load current, thus increases the meter reading. Usually, creeping occurs due to a rise in supply voltage more than the normal value, this increases the torque further.

Adjustment for Prevention of Creeping :

Creeping can be prevented by providing two holes on the disc exactly opposite to each other. Whenever the hole comes under the shunt magnet, the disc stops rotating.

Creeping in Energy Meter - Creeping Error & its Prevention

Whenever the hole comes under the shunt magnet pole, the effective center of the eddy current change hence the eddy current get distorted. Due to the distortion of the eddy currents, there is a force on the disc which moves it in the opposite direction of the rotation. Hence the rotation of the disc is opposed by this force and it will stop.

In some cases, a piece of iron may be attached to the edge of the disc. When the iron piece comes under the braking magnet, the force of attraction between the iron and the brake magnet opposes the rotation of the disc under no-load.

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