What are the different types of electric meters used in power and energy reading?
An electric meter is a device that measures and registers the integral of an electrical quantity with respect to time. The term “meter” is also used in a general sense to designate any type of measuring device including all types of electrical measuring instruments. Use of “meter” as a suffix to a compound word (e.g., voltmeter, ammeter, frequency meter) is universally accepted. However, in this chapter the narrow meaning of “electric meter” is used.
Types of Electric Meters
The most common types of electric meters are watt-hour meter, VAR-hour meter, and ampere-hour meter.
The most common types of electric meters are watt-hour meter, VAR-hour meter, and ampere-hour meter.
Watt-Hour Meter:
The watt-hour meter is an electric meter that measures and registers electric energy in watthours or kilowatt-hours (1,000 watt-hours).
EXAMPLE 13-2: If the active electric power of a circuit is 15 kW and is consumed at a uniform rate for
3 hours, the watt-hour meter will register 3 x 15 = 45 kWh.
3 hours, the watt-hour meter will register 3 x 15 = 45 kWh.
VAR-Hour Meter:
A VAR-hour meter is an electric meter that measures and registers reactive power in reactive volt-ampere-hours (or reactive kilovolt-ampere-hours).
Ampere-Hour Meter:
An ampere-hour meter is an electric meter that registers the quantity of electricity in ampere-hours.
Demand Meter
A demand meter is a device that indicates or records the maximum average load over any specified time interval (usually one hour or less) or the average load over a number of equal time intervals. It is a special form of electric meter indicating or recording the measured load for a given time interval and then resetting.
A demand meter is a device that indicates or records the maximum average load over any specified time interval (usually one hour or less) or the average load over a number of equal time intervals. It is a special form of electric meter indicating or recording the measured load for a given time interval and then resetting.
Combination Watt-Hour and Demand Meters
These meters measure and register load and also indicate or record maximum demand.
EXAMPLE 13-3: If the active electric power in a circuit at the beginning of the measuring period is 20 kW and is uniformly decreasing until it reaches 10 kW at the end of 1 hour and then continues at the same uniform rate of 10 kW for 2 more hours, the watt-hour meter will read 35 kWh at the end of the third hour, and the demand meter will read a maximum 1-hour demand of 15 kW.
These meters measure and register load and also indicate or record maximum demand.
EXAMPLE 13-3: If the active electric power in a circuit at the beginning of the measuring period is 20 kW and is uniformly decreasing until it reaches 10 kW at the end of 1 hour and then continues at the same uniform rate of 10 kW for 2 more hours, the watt-hour meter will read 35 kWh at the end of the third hour, and the demand meter will read a maximum 1-hour demand of 15 kW.
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