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GATE 2022 : Electrical Machine Quiz 5

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Question 1

The inrush current of transformer at no-load is maximum if supply voltage is switched on_______.

Question 2

A transformer has iron loss of 90 W at 60 Hz supply and 52 W at 40 Hz supply. Both losses being measured at same peak flux density. The total iron loss in the transformer at 50 Hz supply will be:

Question 3

In a short circuit test with the LV side shorted, a 220/100 V, signal phase transformer required 22 V to allow full load current at φsc = 75°. Calculate voltage regelation at 1.2 times of full load at 0.5 power factor lagging in percentage.

Question 4

A 100 KVA, 11500/2300 V, 1-ϕ transformer having iron loss 2 KW and full load copper loss 16 kW. The transformer is reconnected as autotransformer to maximize its kVA ratings and operating at half load and 0.8 p.f. lagging. Find the % efficiency of autotransformer.

Question 5

The high and low voltage windings of a 6600/250 v, 50 Hz, 1–ϕ transformer have resistance of 0.21 Ω and 2.72 x 10–4 Ω respectively and the value of reactance are 1 Ω and 1.3 x 10–3 Ω. The current and power input, when the voltage Winding is connected to a 400 v, 40 Hz supply with low voltage winding being short circuited are:

Question 6Multiple Correct Options

Consider a single-phase transformer having maximum efficiency of 98%. The condition to occur maximum efficiency is as follows:

i. Power factor = 0.8

ii. 80% of full load

Choose the correct option(s). Take transformer rating 100 KVA and leakage impedance is 5%.

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