Applied Electricity Paper 2 , May/June 2011

Questions:		1	2	3	4	5	6		Main

General Comments
Weakness/Remedies
Strength

Question 5
. State the type of d.c. motor required for:(i)large starting torque;(ii)variable load. The armature resistance of a shunt motor is 0.07 Ω. When the motor is connected across 200 V supply, it develops a back e.m.f. of 179 V. Calculate the: (i) voltage drop across the armature circuit; (ii) armature current; (iii) armature current at standstill.
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Observation
The expected answers were: (i) Series motor (ii) Compound motor (i) E = V - IaRa The voltage drop across the armature is E – V = IaRa = 200 -179 = 21 V (ii) Ia = Ia = Armature current at standstill, Ia = = = 2857.14 A The question was on D.C. Electrical Machines. The question was popular with the candidate. The performance of the candidates was average. Many of the candidates could not provide answers to part (a) of the question. However, almost all the candidates got the calculation part correct, though some did not understand the implication of standstill.