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GATE 2019: Electrical Machines Quiz 2

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Question 1

The internal and external characteristics of a separately excited dc generator is shown below.

Analysing the characteristics, determine the figure that depicts the armature voltage drop.

Question 2

The parallel paths of a 4-pole dc machine armature with lap winding, are symmetrical, and each has a resistance of 0.6 Ω. Determine the armature resistance.

Question 3

An emf of 236.8 V is induced in a dc generator, with armature resistance 0.25 Ω. When the generator enters the motoring mode, a back emf of 223.2 V is induced at the same terminal voltage and the same armature current. Determine the value of the armature current.

Question 4

A 230V, 15 kW ,1000rpm shunt motor with armature resistance of 0.50 Ω, has a rated line current of 72 A and a rated field current of 2.2 A. The change in field flux (in %) required to obtain a speed of 1800 rpm while drawing a line current of 54.6 A and a field current of 1.8 A is

Question 5

A DC machine running at 800 rpm induced voltage is 220V. What will be percentage increase in field flux if the induced emf is 240V at 600 rpm?

Question 6

A 25 kVA, 1- φ transformer, 2200 V to 220 V has a primary resistance of 1 Ω and a secondary resistance of 0.01 Ω. Find the full-load efficiency in Percentage, at 0.8 p.f. if the iron loss of the transformer is 80% of the full-load copper loss.

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Jun 21ESE & GATE EE