Three phase power measurement using two wattmeter method

AIM:

To measure the power in 3 -phase balanced star connected load and to determine the power factor.

APPARATUS REQUIRED:

  • Wattmeter  2.50 A, 600V 2 No’s
  • Ammeter 0 – 2.5 A M/I Type 1 No’s
  • Voltmeter 0 – 500 V M/I type 1No’s 
  • Lamp load 
  • Connecting wires.

THEORY:

The following methods are used for the measurement of three phase power.

  1. One Wattmeter Method : For balanced Load
  2. Two Wattmeter Method : For balanced Load / Unbalance Load
  3. Three Wattmeter Method  : For balanced Load / Unbalance Load

PROCEDURE:

  • Connect the circuit as shown in the Figure to measure the power in star connected load. 
  • Check the circuit and switch on 3Φ supply switch. 
  • Take the readings of the ammeters, voltmeters and wattmeter’s connected in the circuit.
  • Total power measured is given by (w1 + w2) watts. 
  • Calculate the power by formula P = √3VLILcosΦ 
  • Compare the two results. 
  • Repeat the experiment for different loads

CIRCUIT DIAGRAM :

OBSERVATION TABLE:


Lamp load per phase

IL  ( A)

VL (V)

W1 (Watts)

W2 (Watts)

P= W1 +  W2
Φ=tan-1 {√3(w2 – w1)] /(w2 + w1)}Power factor =Cos ΦP = √3VLILcos Φ
Star Connection

FORMULA USED:

  • Real power,P = w1 + w2 
  • Reactive power,Q = √3 (w1 – w2 )
  • Tan Φ = √3 (w1 – w2 )/ (w1 + w2)
  • Power factor = cosΦ

RESULT:

Thus the power in 3 -phase balanced star connected load is measured  and determined the power factor

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