Overview of Energy meter

 An energy meter or Watt-hour Meter is a device that measures the amount of electric energy

consumed by a residence, a business, or an electrically powered device. Electric utilities use

electric meters installed at customers' premises to measure electric energy delivered to their

customers for billing purposes. They are typically calibrated in billing units, the most common

one being the kilowatt hour (kWh). They are read once each billing period. These may be

single or three Φ meters depending on the supply utilized by domestic or commercial

installations. For small service measurements like domestic customers, these can be directly

connected between line and load. But for larger loads, step down current transformers must

be placed to isolate energy meters from higher currents. 

Types of Energy Meters:

Electromechanical Type: It is the most conventional type of energy meter. It is made 

up of a rotating aluminum disc placed between two electromagnets. The Series 

electromagnets is powered by the load current and the Shunt electromagnet by a current 

proportional to the load voltage .Series magnet produces the flux which is proportional 

to the current flowing and shunt magnet produces the flux proportional to the voltage. 

These two fluxes lag by 90 degrees due to inductive nature. The interaction of these 

two fields produces eddy current in the disk, exerting a torque, which is proportional to 

product of instantaneous voltage, current and Φ angle between them.

Electronic Type: These are of accurate, high procession and reliable types of

measuring instruments as compared to conventional mechanical meters. It consumes

less power and starts measuring instantaneously when connected to load. These meters

might be analog or digital. In analog meters, power is converted to proportional

frequency or pulse rate and it is integrated by counters placed inside it. In digital electric

meter power is directly measured by high end processor. The power is integrated by

logic circuits to get the energy and also for testing and calibration purpose.