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MEASUREMENT OF POWER IN 3•PHASE CIRCUIT

• The power in 3-phase load can be measured by using the following methods:
1. Three wattmeters method.
2. Two wattmeters method.
3. One wattmeter method.
• A wattmeter consists of two Coils: Refer Fig.25
1. Current coil-possesses a low resistance.
2. Pressure or potential coil-possesses high resistance.
Fig.25

The ‘current coil’ is connected in series with the line carrying the current and the ‘pressure coil’ is connected across the two points whole potential difference is to be measured. A wattmeter shows a reading which is proportional to the product of the current through its current coil, the potential difference across its pressure coil and cosine of the angle between this voltage and current.