Page 283 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

kWh = rev. travelled by the disc
Meter constant

(250*15) = rev. travelled by the disc
(1000*60 3600
Revolution travelled by the disc=225 rev.
Three phase energy meter
We can use three separate 1ф energy meter for the measurement of 3ф power or a single 3ф energy meter for
the measurement of three phase installation.
3ф energy meter are of two types
1 Three phase three wires E/M

2 Three phase four wires E/M
Three phase three wires e/m
It is a combination of two single phase E/M. The meter is used for three phase balanced load. The deflecting
torque is produced by the resultant reaction between the fluxes of pressure and current coil connected to two
phases.Counting mechanism mounted on the spindle gives the kWh reading. The overall working is identical to
that of a single phase E/M - three element E/M

Three phase four wires e/m
It is a combination of 3 single phase E/M.The meter is capable of measuring energy of 3 phase unbalanced load.
It consist of 3 P.C., 3C.Cand 3 Al discs. All ‘Al’ discs are mounted on same spindle. The counting mechanism
mounted on the spindle gives the kWh reading.

Errors in induction type energy meter
1 Creeping error
The slow but continuous rotation of the disc in energy meter is known as creeping
Causes of creeping
1 When there is no current flow through C.C. i.e. when the P.C. is energized

2 Major cause of creeping is over-compensation of friction.

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CITS : Power - Electrician & Wireman - Lesson 50-53