Page 281 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Operation of this instrument in both AC and DC is possible due to the fact that whenever the current reverses in
AC , the direction of flux in the fixed coil as well as the direction of flux produced by moving coil reverses at the
same time resulting in the same direction of torque
In this type of instrument, the main magnetic field is produced by an electro magnet named as fixed coil.
The fixed coil is treated as current coil and the moving coil is made as pressure coil with necessary multiplier
resistance. The deflection torque is proportional to the load current. This type of watt meter have uniform scale

Advantage
• This instrument can be used both in AC and DC.
• As this is an air cored instrument, the hysteresis and eddy current losses are eliminated.

• When used as wattmeter, the scale is uniform.
Disadvantage
• It is more expensive than PMMC instruments.
• It consumes more power than PMMC meters.

• Sensitive for over loads and mechanical impact. Hence careful handling is necessary.
Energy meter

Necessity
The electrical energy supplied by the EB should be billed, based on the actual amount of energy consumed.
Electrical energy is measured in KWH in practice. The meter used for this purpose is known as energy meter

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