JKLU Jaipur
Engineering Measurements and Machine (ES1107)
Assignment-2: Transformer
1. Describe the direct load testing to determine efficiency and voltage regulation of a single phase
transformer.
2. What are the no load losses that occur in a two winding transformer and state the reasons for such
losses.
3. What happens when a DC supply is applied to a transformer?
4. Why does the OC test on a transformer performed on the low voltage side?
5. Why does the SC test on a transformer performed on the high voltage side?
6. What will happen if a power transformer designed for operation on 50 Hz is connected to a 500 Hz
source of same voltage?
7. A 200 kVA, 2400/240 V, 50 Hz, single phase transformer has 80 turns on the secondary winding.
Assuming ideal transformer; determine: (i) The number of primary turns (ii) Transformer turn ratio, a
(iii) Primary and secondary currents (iv) The maximum value of the flux.
8. A 20 kVA single phase transformer 4800/480V has primary resistance and reactance of 5 and 15
respectively, while the resistance and reactance of secondary winding is 0.1 and 0.15  respectively.
Calculate: (i) The parameter referred to primary side of transformer and draw the equivalent circuit
(ii) The approximate value of secondary voltage at full load power factor of 0.8 lagging if 4.8kV primary
supply.
9. A 50kVA, 2200/220V, 50Hz transformer when tested gave the following results.
OC test, measurements in LV side:
405W,
5A,
220V
SC test, measurements on HV side:
805W,
20.0A,
95V
Draw the circuit model of the transformer referred to the HV and LV sides. Label all the parameters.
Calculate the parameters of the transformers input referred to the HV and LV sides.
10. The result of open circuit and short circuit test on a 25kVA, 440V/220V, 60 Hz transformer are as
follow: OC: Primary open-circuited. V=220V, I=9.6A, P = 710W SC: Secondary short circuited. V=42V,
I= 57A, P=1030W. Obtain the parameters of the equivalent circuit (R1, R2, X1, X2, X0 and R0).
11. A 100 kVA, 6.6kV/415V, single phase transformer has an effective impedance of (3+8j) Ώ referred to
HV side. Estimate the full load voltage regulation at 0.8 pf lagging and 0.8 leading pf.
12. A 20 KVA, 2400/240V, 50Hz two winding transformer has an efficiency of 97.5% at full load, 0.8 Pf. It
is connected as a 2400/2640 V auto transformer. (i) What are the other different possible connections
as an auto transformer? (ii) For the auto transformer mentioned above, at full load calculate the kVA
output. , kVA transformered & kVA conduted. Find also the efficiency at full load, unity power factor.
(iii) Ratio of weight of auto transformer conductors to weight of conductors in two winding
transformer.