8. POWER AND POWER FACTOR MEASUREMENT
FOR SINGLE PHASE LOAD
8.1. Tasks of the measurement
8.1.1. Measure active power, power factor and apparent power consumption of the singlephase load. Use universal clamp digital meter for the measurement. Active power
should be measured also using analogue wattmeter and current instrument transformer
(CT). Evaluate B-type expanded uncertainty (k = 2) of active power measurement for
both cases. Compensate methodical error in case of measurement by means of
analogue meter. Current transformer transformation error is negligible. Find whether
the difference of the measurement results corresponds to their reported accuracy.
8.1.2. Measure the voltage on the secondary winding of the current transformer and check if
the transformer is not overloaded.
Measurement hints
- Use the power supply of 120 V, 50 Hz (voltage between any two terminals of the 3 ×120 V
power line system at the switchboard).
- Since the load current is higher than 5 A at 120 V, a current instrument transformer (CT)
has to be used.
- Do not leave the load connected to the source for more than 2 minutes. It is not designed
for permanent usage.
- The secondary winding of the current transformer cannot be left open if primary winding is
connected to measured current. For connections of primary and secondary windings of the
CT, the thick wires with connection clips are to be used to assure minimal transition
resistance.
8.2. Schematic diagram
120 V/50 Hz
LOAD
I1
KL
V
COM
Fig. 8.1 Active power, power factor and apparent power measurements using universal clamp meter
I
1
K
CT
k
120 V, 50 Hz
L
l
U kl
V3
V1
U1
Z
A
I2
W
Fig. 8.2 Schematic diagram for measurement of active power consumption using analogue wattmeter
8.3. List of the equipment used
KL
A
V1
W
CT
120 V
Z
- universal digital clamp meter PK 430.1;
- iron-vane ammeter, accuracy class. ..., measurement range used ...;
- PMMC voltmeter with rectifier, accuracy class ..., measurement range used ...,
input resistance ...;
- electrodynamic wattmeter, accuracy class ..., voltage measurement range ... V,
current measurement range ... A, voltage coil resistance ... Ω;
- instrument current transformer, transformation ratio ..., accuracy class ...;
- AC power supply - switch board;
- measured load
Theoretical background
See the textbook:
M. Sedláček, J. Holub, D. Hejtmanová: Laboratory Excercises in Electrical Measurements,
CTU Publishing House, Prague, 2005