me: JASTINE P. MABUTOL Long Examination in AC Apparatus Date: APRIL 23 Score: Tections: Solve the following problems independently with pride, honor and dignity. Write your complete solution gibly. Express your final answer up to 4 decimal places unless otherwise specified. Any forms of cheating are strictly rohibited and would mean a grade of zero. Enclose your final answer. Equal distribution of points. 1. A 11kV/230V, 150 kVA, single phase, 50 Hz transformer has core loss of 1.4 kW and full load copper loss of 1.6 kW. Determine the kVA load for maximum efficiency and value of maximum efficiency at unity power factor. Determine the efficiency at half load 0.8 p.f. leading. 2. A 200 kVA transformer has an efficiency of 98% at full load. If the maximum efficiency occurs at three quarters of full load, calculate the efficiency at half load. Assume negligible magnetizing current and p.f. 0.8 at all loads. 3. A 4 kVA, 200/400 V single phase transformer has equivalent resistance and reactance referred to low voltage side equal to 0.5 ohm and 1.5 ohms respectively. Find the terminal voltage on the high voltage side when it supplies 3/4th full load at 0.8 power factor, the supply voltage being 220 V. Hence, find the output of the transformer and its efficiency if the core losses are 100 W. 4. The maximum efficiency of a 100 kVA single phase transformer is 98% and occurs at 80% of full load at 0.8 p.f. If the leakage reactance of the transformer is 5%, find the voltage regulation at rated load of 0.8 p.f. lagging. 5. A 300 kVA single phase transformer is designed to have a resistance of 1.5% and maximum efficiency occurs at a load of 173.2 kVA. Find its efficiency when supplying full load at 0.8 p.f. lagging at normal voltage and frequency. 6. Two 100 kW transformers each has a maximum efficiency of 98% but in one the maximum efficiency occurs at full load while in the other, it occurs at half load. Each transformer is on full load for 4 hours, on half load for 6 hours and on one-tenth load for 14 hours per day. Determine the all day efficiency of each transformer.