11. No-load test on a transformer is carried out to determine :
(a) copper loss
(b) magnetising current
(c) magnetising current and no-load loss
(d) efficiency of the transformer
12. The main purpose of performing open-circuit test on a transformer is to measure its :
(a) Cu loss
(b) core loss
(c) total loss
(d) insulation resistance
13. Transformers are rated in kVA instead of kW because :
(a) load power factor is often not known
(b) kVA is fixed whereas kW depends on load p.f.
(c) total transformer loss depends on voltampere
(d) it has become customary
14. At relatively light loads, transformer efficiency is low because :
(a) secondary output is low
(b) transformer losses are high
(c) fixed loss is high in proportion to the output
(d) Cu loss is small
15. The ordinary efficiency of a given transformer is maximum when :
(a) it runs at half full-load
(b) it runs at full-load
(c) its Cu loss equals iron loss
(d) it runs slightly overload
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