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.ConditionLoad typeM.F.W1 (W)W2 (W)W = W1+W2 (W)cos ΦΦ
 1.Balanced loadResistive Load 320×2 = 640360×2= 720 1360 0.995 5.817 
2.Balanced loadResistive Load2760×2= 1520720×2= 144029600.9982.68

Calculation:

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

Apparatus used:

Sl. No.Name of ApparatusQuantitySpecificationMakers 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.

Φpf (cosΦ)W1W2
0OunityW=W2W1 = W2
30 O0.866W1 = (W2/2)W2 = (W1/2)
60 O0.5W1 = 0W2 = W
90 O0W1 = +WW1 = -W

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