A wattmeter is a combination of an ammeter and a voltmeter and, therefore consists of two coils known as current coil and pressure coil. The operating torque is produced due to interaction of fluxes on account of currents in current and pressure coils.
There are following three types of wattmeters:
- Dynamometer wattmeter
- Induction wattmeter
- Electrostatic wattmeter.
We shall discuss here only the first and second type.