Fictitious Loading

Aim of the Experiment: Testing of single phase Energy meter at different power factors.

Apparatus Required: Serial no.

Apparatus name

1

Energy meter

2

Variac

3 4 5 6

Voltmeter Ammeter Rheostat Connecting wires

Circuit diagram:

Theory:

Type Single phase,

Specification 600 rev/KWh,

Induction type, Single phase Three phase MI type MI type Cylindrical PVC

230 V, (10-20) A (0-270) V ,8 A (0-440) V,12 A (0-300) V (0-10) A , 200 ohm , 5 A SWG

Quantity One Two One One One One As reqd.

This method of testing is fictitious loading process. No actual loading is done while the testing is performed. The pressure coil (P.C.) and current coil (C.C.) are Separately excited. The PC is fed by single-phase supply whose voltage is used as reference voltage. The CC is supplied by two single phase variacs as shown in the circuit diagram through the resistive load. Input supply to the 1-phase variacs are taken from the phases R and Y of a 3-phase variac. Again the PC is also fed by phase-R. Now, varying the different tappings of two 1-phase variacs while keeping the 3-phase supply constant, the test can be performed.

Procedure: 1. Connect the circuit as shown in the figure. 2. Adjust the 3-phase variac to a constant output voltage, so the PC is supplied with a constant voltage. 3. Apply full resistance by moving the rheostat knob. 4. Increase variac1 to full voltage and hold variac2 at zero. So the current through CC will make an angle of zero degree with the reference PC voltage, which acts as unity power factor load. 5. Keep the variac1 voltage constant and vary the voltage output of variac2 to full voltage. The resultant current due to this arrangement will make an angle 60 degree with the reference voltage, which will act as power factor of 0.5. 6. Now move the knob of variac2 keeping variac1 at constant voltage as before. The resultant current through CC will make an angle of 30 degree with the reference voltage, consequently a power factor 0.866. 7. For achieving lagging and leading power factor the above two steps(5 & 6) have to repeat by interchanging R and Y.

Precautions: •

All connections should be neat and tight.

•

Intensive care should be taken while separating the current coil and pressure coil of the Energy meter.

•

High resistance must be provided in the passage of current to the current coil.

•

Voltage variations of two 1-phase variacs should be done by removing the supply.

Case analysis: An experiment has been performed by applying 400 V. at the output of 3-phase variac. So, constant voltage of 230 V. at the PC is obtained. Now the steps 4,5,6,7 have to be followed and the result is shown in figure below. Voltage output of variac 1 230 V. 230 V. 230 V.

Voltage output of variac 2 0 V. 230 V. 115 V.

Power factor 1 .5 .866

The power factor is lagging when variac1 is connected to R and variac2 with Y. Leading power factor is obtained by inter changing this connection.

Conclusion: Single phase energy meters are used for measuring the active power only. By performing this experiment it can be concluded whether the meter is rotating for unity, lagging and leading power factor.