Use Two Watt-meters for Measuring Active Power of Three-phase Balanced Load

Experiment No.: 3

Experiment Name:

Use two watt-meters for measuring active power of three-phase balanced load.

Objective:

To use two watt-meters for measuring active power of three-phase balanced load.

Theory:

For Balance Load Condition:

The above equation shows that the sum of the two wattmeter readings gives the total power consumed in the three-phase balanced system. We can also calculate the load power factor angle from the measurement of W₁ and W₂.

Circuit Diagram:

Procedure:

1. Make the connections as per the circuit diagram.
2.  Switch on A.C supply.
3. For balanced load condition measured the values of wattmeters, ammeters and voltmeter.
4. Switch off all the loads and supply.

Observation Table:

Sl. No.	Condition	Load type	M.F.	W1 (W)	W2 (W)	W = W1+W2 (W)	cos Φ	Φ
1.	Balanced load	Resistive Load	2	320×2 = 640	360×2= 720	1360	0.995	5.817
2.	Balanced load	Resistive Load	2	760×2= 1520	720×2= 1440	2960	0.998	2.68

Calculation:

cos Φ = cos (tan^-1 √3. (W₂-W₁)/(W₂+W₁)) = 0.995

Apparatus used:

Sl. No.	Name of Apparatus	Quantity	Specification	Makers name
1.	Single phase wattmeter	2	0-750-1500-3000 W 150-300-600 V 5-10 A, Electrodynamometer type	MECO-G
2.	Three phase load box	1	Resistive Load

Remarks: Effect of power factor variation on wattmeter reading.

Φ	pf (cosΦ)	W1	W2
0O	unity	W1  =W2	W1 = W2
30 O	0.866	W1 = (W2/2)	W2 = (W1/2)
60 O	0.5	W1 = 0	W2 = W
90 O	0	W1 = +W	W1 = -W