Testing of single phase Wattmeter.

Experiment No.: 03

Aim of the Experiment: –

Testing of single phase Wattmeter.

Apparatus Required: –

Sl. No.NameSpecificationQuantity
1Single-phase Auto-transformer(0-270) V, 10A2 nos.
2Ammeter(0-5) A, MI1 no.
3Voltmeter(0-250) V, MI1 no.
4Wattmeter(0-1500) W, 1 no.
5Rheostat(0-80) Ω, 5A1 no.
6Connecting wirePVC Insulated copperAs per required.
Table No. 3.1

Circuit Diagram: –

fig. 3.1

Theory: –

Wattmeter are instruments which indicate power consumed in electrical circuits. Power consumed by electrical circuit at any instant of time is the product of the voltage across and current through the circuit. Wattmeter shows the average power. In case of AC circuit instantaneous power is given by:

\[\color\red{p=v*i}\] \[\color\green{Where,}\]
\[\color\red{v = V_mSin (wt)}\] \[\color\red{ i = I_m Sin(wt-\theta)}\] \[\color\red{p = V_mI_m Sin (wt) * Sin(wt-\theta)}\]
\[\color\red{p = [(V_mI_m)/2][2Sin wt * Sin(wt-\theta)]}\] \[\color\green{Average \;Power}\] \[ \color\red{p = V_rms I_rms Cos\theta}\] \[\color\green{W_A= Reading \;of \;wattmeter/measured \;power}\] \[\color\green{W_T= \;True power = \;V_rms \;I_rms;*Cosθ }\] \[\color\green{(Assumed \;to\; be\; true\; power)}\] \[\color\green{Cosθ = \;1 \;for\; resistive \;load.}\]

Procedure: –

  1. Connect all the apparatus as per circuit diagram.
  2. The Voltage across Pressure coil PC of wattmeter is to be kept fixed at certain voltage says 200V.
  3. Fix the load resistance to a certain value.
  4. The voltage across current coil CC is increased with the help of auto-transformer.
  5. Note the different readings of Wattmeter, Voltmeter and Ammeter and calculate the percentage error of each readings.

Observation Table: –

Sl. No.Voltage (V) in volts.Current (I) in amps.Power (WT=VI) in watt.Wattmeter reading (WR)Multiplying Factor(MF)Power (WA= WR*MF) % Error= {(WT-WA)/WT}*100
1
2
3
4
5
6
7
Table No. 3.2

Conclusion: –

To be written by student.

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