Problems #2

1. A 20 kVA, 2200/220 V, 50 Hz single-phase transformer gave the following test results:

Open-circuit test (on LV side): 220 V, 1.5 A, 102 Watts

Short-circuit test (on HV side): 98 V, 9.1 A, 290 Watts

Compute the parameters of the approximate equivalent circuit referred to the HV and LV sides. Convert the equivalent circuit parameters to per unit (pu) values.

2. A 50 kVA, 6600/400 V, 50 Hz, three-phase, delta-star transformer gave the following test results:

Open-circuit test: 400 V, 4.21 A, 510 Watts

Short-circuit test: 340 V, 4.37 A, 610 Watts

Calculate the per unit circuit parameters.

3. The core loss of a transformer is found to be 60 Watts at 40 Hz and 100 Watts at 60 Hz when operated at the same peak flux density. Calculate the hysteresis and eddy current losses at 50 Hz.

4. A 230 V, 60 Hz single-phase transformer has hysteresis loss of 330 Watts and eddy current loss of 110 Watts. Compute the change in total core loss if the transformer is operated from 220 V, 50 Hz supply. (Assume Steinmetz’s constant=1.6)