Page 282 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

In AC induction type energy meter is universally used in domestic as well as industrial uses.
It is an example of integrating instrument. These types of instruments keep a record of the total quantity of energy
consumed from the time they are connected to the supply, to the time of reading. Energy meter (watt-hour meter)
measure the quantity of electricity in kwh
Parts and function of energy meter

Iron core-is specially shaped to direct the magnetic field in the desired path
Pressure coil (P.C)-is connected across the supply carry current proportional to the supply voltage (coil have
many turns of thin wire).
Current coil (C.C) - is connected series with the supply and carry full load current (coil have few turns of thick
wire).
Disc- is the rotating element in the meter. The disc is made of aluminum and is positioned between the air gap
between the two coils (PC & CC)
Spindle- the disc is mounted on a vertical spindle whose ends have hardened steel pivots. The pivot is supported
by a jewel bearing. There is a worm gear at one end of spindle. As the gear turns the dial they indicate the amount
of energy passes through the meter.
Break magnet-as the name implies it produce necessary controlling torque on disc.

Working
When energy meter connected to supply,

• Two fluxes produced by C.C & P.C act on ‘Al’ disc
• The changing flux induces eddy currents in the disc which intern produce rotating torque on the disc
• Hence the disc rotates due to the interaction of the two fluxes

• The speed of the disc is proportional to the product of voltage, current and time i.e. the energy consumed by
the load
• The no. of revolution completed by the disc for 1kwh is called meter constant

• Energy consumed = Rev. travelled by the disc
Meter constant
Calculate the no. of revolutions, which would be completed by the disc of 1 ф E/M in 15 minute when the load on
it is 250W.Meter constant, is 3600 revolution /kWh

ANS - We know that

269

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