Applied Electricity Paper 2 , May/June 2011
 Questions: 1 2 3 4 5 6 Main
Weakness/Remedies
Strength

Question 5
.
1. State the type of d.c. motor required for:(i)large starting torque;(ii)variable load.
2.  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

1.  (i)   Series motor

(ii)  Compound motor

1.  (i)   E = V - IaRa

The voltage drop across the armature is
E – V = IaRa = 200 -179  = 21 V
(ii)   Ia =
Ia =

1. 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.