What is creeping into the energy meter?
In the energy meter, an aluminium disc is placed between the air gap of the shunt electromagnet and the series electromagnet. The Seris electromagnet consists of a current coil that is connected in series with the load and the shunt electromagnet consists of a voltage coil or pressure coil which is directly connected to the supply voltage.
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| Creeping In Energy Meter |
The shunt and series electromagnet produces a magnetic flux and induces the eddy current in the aluminium disc. Due to the interaction of both electromagnet magnetic flux and disc eddy current deflecting torque produced in the disc and disc rotates.
When load consume power, the disc rotates and a number of rotation of the disc are recorded in the recording instrument.
The aluminium disc continuously rotates when the voltage coil is only connected to the supply voltage and current is not flowing through the current coil or the current coil is not connected to the load. this phenomenon is called creeping in the energy meter. The necessary condition for creeping error is voltage coil must be energised.
The creeping is one type of recording error. In creeping error, the energy meter consumes a small amount of energy even when the load is not conned to the energy meter. Due to creeping energy meter record incorrect reading. The creeping in energy meter increase the speed of rotation of aluminium disc under low or light load condition and increase the energy meter reading.
The energy meter consists of rotating parts like a disc which is made from aluminium. So friction losses are takes place in the energy meter. The main reason for creeping is friction. The vibration in the energy meter, stray magnetic field-a magnetic field which appears around the energy meter and extra voltages across the voltage coil(Voltage surges) are also responsible for creeping errors in the energy meter.
Reduction of creeping in energy meter
The creeping in energy meter is reduced by providing the two-hole in the aluminium disc in opposite direction. When the disc rotates and holes come under the shunt electromagnet, the aluminium stops rotating. This hole in the disc reduced the rotation of the disc.
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| Construction of Energy Meter |
When the aluminium disc rotates and a hole on the disc come under the shunt electromagnet, the circular path of the eddy current is disturbed. Due to distortion of eddy current, torque is produced on the disc which moves the disc in opposite direction. The rotation of the aluminium disc is opposed by this torque and the aluminium disc stop rotating.
The aluminium disc rotates under no-load conditions until the hole on the disc does not reach under the shunt electromagnet.
In some energy meters, small iron pieces are used to prevent creeping errors. The iron pieces are attached to the edge of the aluminium disc. When these pieces of iron come under the shunt electromagnet, the force of attraction takes place between the iron piece and the electromagnet. This force of attraction opposes the rotation of the aluminium disc under the no-load condition.