This question is about d.c. machines a)Explain briefly why the terminal voltage of a d.c. machine is not equal to thegenerated or back emf except at no load when V = E. b)Hence, state the relationship between V, E, the armature current and resistance thatapplies at normal loads for a generator. c)A 250 V shunt motor has an armature resistance of 0.4 Ω and runs at a speed of 750 rev min –1 when taking a full load current of 25 A. i)Estimate the speed of the motor at no load when the armature current is 3 A, assuming that the flux per pole remains constant. ii)Derive the relationship between speed, emf, and flux. iii)Calculate the field current for a field resistance of 110 Ω, if the load torque remains constant; iv)calculate the new armature current if the speed is increased to 1000 rev min –1 v)Hence, find the value of the additional resistance required in the field circuit to maintain this current d)If the field current of a shunt wound d.c. motor is halved, what effect will thishave on the speed?
This question is about d.c. machines
a)Explain briefly why the terminal voltage of a d.c. machine is not equal to thegenerated or back emf except at no load when V = E.
b)Hence, state the relationship between V, E, the armature current and resistance thatapplies at normal loads for a generator.
c)A 250 V shunt motor has an armature resistance of 0.4 Ω and runs at a speed of 750 rev min –1 when taking a full load current of 25 A.
i)Estimate the speed of the motor at no load when the armature current is 3 A, assuming that the flux per pole remains constant.
ii)Derive the relationship between speed, emf, and flux.
iii)Calculate the field current for a field resistance of 110 Ω, if the load torque remains constant;
iv)calculate the new armature current if the speed is increased to 1000 rev min –1
v)Hence, find the value of the additional resistance required in the field circuit to maintain this current
d)If the field current of a shunt wound d.c. motor is halved, what effect will thishave on the speed?
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