TRANSFORMER part-2

1.While testing transformer oil the gap between electrodes is kept at a distance of

(a) 1 mm (b) 2 mm

 (c) 3 mm (d) 4 mm 

Ans: d

2.The short circuit test of a transformer gives

(a) Copper loss at full load

(b) Copper loss at half load

(c) Iron loss at any load

(d) Sum of iron loss and copper load

Ans: a

3.What kVA rating is required for a transformer that must handle a maximum load current of 8 A with a secondary voltage of 2 kV? (a) 4KVA   (b)0.25KVA  (C) 16KVA (d) 8KVA Ans: c 4.Which test is conducted on all transformers in a manufacturing concern  (a) Routine test (b) Type test (c) Special test (d) All above  Ans: a 5.The ratio of kW to kVA is known as  (a) Voltage regulation (b) power factor (c) Transformation ratio (d) None above Ans: b 6.A transformer is plugged into a 120 V rms source and has a primary current of 300 mA rms. The secondary is providing 18 V across a 10  load. What is the efficiency of the transformer? (a) 88%  (b) 90% (c) 92%  (d) 95% Ans: b Pin = 120*0.3=36W. Pout = 18*18/10=32.4. efficiency = Pin/Pout. = (32.4/36)*100. = 90%. 7.The dielectric strength of transformer oil is expected to be a. 1 kV b. 33 kV c. 100 kV d. 330 kV Ans: b 8.A common method of cooling a power transformer is a. natural air cooling b. air blast cooling c. oil cooling d. any of the above  Ans: c 9.The transformer ratings are usually expressed in terms of a. Volts b. amperes c. kW d. kVA  Ans: b 10.The thickness of lamination used in a transformer is usually a. 0.4mm to 0.5 mm b. 4 mm to 5 mm c. 14mm to 15mm d. 25mm to 40 mm  Ans: a