In this article we will discuss about the disadvantages of ampere-hour meters.
Ampere-hour meter actually measures electrical energy in ampere-hour. It is equal to current in ampere flowing through the current coil of the meter multiplied by the time in hour during which the current flows. But as the B.O.T. unit of electrical energy is kilowatt-hour, the scale of the instrument is graduated in that unit.
Kilowatt-hour is calculated as follows:
Ampere-hour = Current in ampere flowing through the coil x time in hour during which the current flows.
ADVERTISEMENTS:
Kilowatt-hour = [(ampere-hour) x (supply voltage)]/1000
Supply voltage is assumed to be constant when kilowatt-hour is calculated. This rated voltage of the meter is to be mentioned (engraved) clearly on the plate fixed on the outer, cover of the meter. Now, if the supply voltage varies, i.e. it becomes higher or lower than the rated voltage of the meter, the actual amount of energy consumed by the load circuit will not be recorded on the scale of the instrument.
When the meter is used as a house- service meter in a consumer’s house, the meter will read more than the actual amount of energy consumed by the load circuit if the supply voltage is less than the rated voltage. As a result the consumer will suffer a loss, since he will have to pay more than the actual cost of energy consumed by his load circuit.
For recording actual consumption of energy, a kilowatt-hour meter is to be connected in the circuit in place of an ampere-hour meter. A kilowatt-hour meter has two coils, one current coil and the other potential coil. Current coil is connected is series with the live line, while potential coil is connected across the supply lines.
ADVERTISEMENTS:
The energy in kilowatt-hour recorded on the dial of the instrument is given by the product of voltage across the potential coil, current in ampere flowing through the current coil and the time in hour during which the current flows divided by one thousand. If V-volt be the potential difference across the potential coil, I-ampere be the current flowing through the current coil and t be the time in hour during which the current flows, then, energy recorded by the meter = (VI t)/1000 Kilowatt-hour.
Here a constant supply voltage is not assumed. The reading of the meter varies with the variation of supply voltage and a consumer can pay the correct amount for the energy actually consumed by his load circuit. But the cost of a kilowatt-hour meter is much higher than that of an ampere-hour meter. Therefore, in most cases, an ampere-hour meter is usually used as a house-service meter in those localities where supply is available in d.c.