Page 851 - Basic Electrical Engineering

T ∝ [VIcosϕ + VIcos ϕ]
d

or,

T ∝ VIcosϕ
d

Thus, the deflecting torque is proportional to the power consumed. For a

particular period of time, if power consumed is recorded, the recorded value
will give the measure of energy consumed.

The brake magnet produces a braking torque, T . When the aluminum disc
b
revolves due to T , the magnetic flux of the brake magnet induces eddy
d
current in the disc. The more the speed of the disc the more is the magnitude
of the induced eddy current. By Lenz’s law, EMF a opposite torque T is
b
developed which controls the speed of the disc due to T . At a steady speed,
d
T = T b
d

and

T α N
b

This shows that the revolutions of the disc is the measure of power consumed

and = Energy consumed.

The revolution made by the aluminium disc per hour when the load is 1kW
is called the meter constant. When we say meter constant is 1200, it means

1200 revolutions of the aluminium disc will indicate the consumption of 1
unit of electricity, i.e., 1 kWh of electricity.
One defect in energy meters, known as creeping, show that aluminium disc

rotates even when there is no load connected and only the voltage coil is
excited.

To prevent any creeping, two small holes on two opposite sides of the
spindle is made on the aluminium disc.