Electromechanical induction type energy meter

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Watt hour meter or energy meter is an instrument which measures

amount of electrical energy used by the consumers.

Energy meters are classified in accordance with several factors such as:

· type of display like analog or digital electric meter;

· type of metering point like grid, secondary transmission, primary and local distribution;

· end applications like domestic, commercial and industrial;

·

technical like three phases, single phase, HT (High Tension), LT (Low Tension) and accuracy class meters.

Electromechanical induction type energy meter

It is the popularly known and most common type of age old watt hour meter. It consists of rotating aluminum disc mounted on a spindle between two electromagnets. Speed of rotation of disc is propor- tional to the power and this power is integrated by the use of counter mechanism and gear trains. It compris- es two silicon steel laminated electromagnets, i.e., se- ries and shunt magnets.

Series magnet carries a coil which is of few turns of thick wire (cur- rent coil) whereas shunt magnet carries a coil with many turns of thin wire (pressure coil).

Braking magnet is a permanent magnet which applies the force op- posite to normal disc rotation to move that disc at balanced position and to stop the disc while power is off.

 

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 force, which is proportional to product of instantaneous voltage, current and phase angle between them.

Vertical spindle or shaft of the aluminum disc is connected to gear arrangement which records a number, proportional to the number of revo- lutions of the disc. This gear arrangement sets the number in a series of di- als and indicates energy consumed over a time. This type of meter is sim- ple in construction and accuracy is somewhat less due to creeping and oth- er external fields. A major problem with these types of meters is their easy prone to tampering, leading to a requirement of an electrical energy moni- toring system. These are very commonly used in domestic and industrial applications.