Measurement of the 3phase power by the two watt meter method.

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Aim:- Measurement of the 3phase power by the two watt meter method.
Ammeter (0-5A)- 1no.
Voltmeter (0-600v) –1no
Rheostat (100-5A)-1no
Resister -100K-3nos.
Circuit Diagram-
Here two wattmeter are connected to measure power in 3 phase circuit. Let V1,V2,V3
be rms values of phase voltage and i1,i2,i3 be rms values of line current
Phase voltage=V1=V2=V3=V
Line voltage=V13=V23=V12=Ö3V
Power factor=cos f
Reading of P1 wattmeter =V1Ö3i1cos(30-f)
= Ö3Vphiphcos(30-f)
Reading of P2 wattmeter= V2Ö3i2cos(30+f)
= Ö3Vphiphcos(30+f)
Sum of two wattmeter readings=P=P1+P2
= Ö3Vphiph[cos( 30-f)+cos(30+f)]
Observation Table:-
Sr no Voltage Current Power 3 phase watt
1) Make the arrangement as per the circuit diagram.
2) Adjust supply voltage to 100v take the reading when the wattmeter is connected
between the R and Y phase.
3) Repeat previous for the different reading of the voltage.
4) Also note the corresponding current.
5) Now connect wattmeter between R and B phase .
6) Repeat the previous procedure which will give by the total power consumed by
the load.
Result:- Hence it is found that the calculated power and the measured power by the two
wattmeter method.
Viva Questions:-
1)What do you mean by the 3phase wattmeter?
2)Explain the short how the wattmeter is connected in the circuit to measure
the power delivered to the Load?