# Measurement of 3-Phase Power by 2 Wattmeter Method

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Aim: To measure the total 3-phase power of 3-phase balanced load using 2-wattmeter method and verify the result with its theoretical value.

## Theory

Two wattmeter method can be employed to measure the power in a 3 phase, three wire star and delta connected balanced load.

In two wattmeter method the current coils of the wattmeter are connected in series with two lines, say R and B and the potential coil of each wattmeter are joined to the third line i.e. Y as shown in the figure below.

## Procedure

### a) Star Connection

• Connect the circuit as shown in the circuit diagram 1
• Switch on the 3-phase supply using TPST switch
• Note down the line voltage, line current and readings of the voltmeter
• Compare the total power observed by the two wattmeter method with its theoretical value

### b) Delta Connection

• Connect the circuit as shown in the circuit diagram 2
• Repeat steps 2 to 4 of the star connection procedure

## Tabular Column

Before writing wattmeter reading multiply with wattmeter constant :

wattmeter constant K = VI cosϕ / full scale deflection
where ‘cosϕ‘ is power factor of the wattmeter

## Inference

By conducting the experiment we found out practically that two wattmeters are sufficient to measure the power of 3 phase load.