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Draw the constructional diagram of the DC machines. List the various parts stating the
function of each part.
Explain the working principle of DC generator.
Find the flux per pole on no load of a 250V, 6 pole shunt motor having a two circuit
connected armature winding with 220 conductors. At normal temperature, Ra including
brushes is 0.2 ohms. The Ia is 13.3 A at no load speed of 908 rpm.
[ANS = 24.76mWb]
A 4 pole lap wound dc motor has 540 conductors. Its speed is found to be 1000rpm. The flux
per pole is 25mWb. It is connected to 230V dc supply. The armature resistance is 0.8 ohm.
Calculate : i) Induced emf ii) Armature current .
[ANS = Eb0 =225V; Ia0 = 6.25A]
Derive the torque equation of DC motor.
A 200V, 4pole lap wound dc shunt motor has 800conductors on its armature. The resistance
of armature winding is 0.5 ohm & that of shunt field winding is 200 ohm. The motor takes
the current of 21A, the flux per pole is 30 mWb. Find the speed & gross torque developed in
the motor.
[ANS: N=475rpm; Ta = 76.38Nm]
A 250V DC shunt motor has armature resistance of 0.25ohm. It takes an armature current of
50 A while running at 750rpm. Find the speed of motor if the flux is reduced by 10% without
changing the load torque.
[ANS: N = 828.45 rpm]
A 220V DC series motor runs at 800rpm while taking a current of 15 A. The motor has an
armature resistance of 0.3 ohm & series field resistance of 0.2 ohm. Find the resistance to be
connected in series with armature if it has to take same current at same voltage while running
at 600 rpm.
[ANS : 3.541 ohm]
A 4 pole series motor has total number of armature wave wound conductors = 944, flux per
pole = 34.6 mWb, gross torque = 209 Nm, supply voltage = 500 V & motor total resistance
(Ra + Rse) = 3 ohm. Calculate current drawn by motor from supply & speed of operation.
[ANS: Ia = 20.1 A; N = 403.85 rpm]
A 120 V dc shunt motor draws a current of 200 A. The armature resistance is 0.02 ohm &
shunt field resistance is 30 ohm. Find the back emf & speed at which the motor will run, if
the lap wound armature has 90 slots with 4 conductors per slot & flux per pole is 0.04 Wb.
[ANS: N = 483.67 rpm]
Draw & Explain the characteristic of DC Shunt motor.
Draw & Explain the characteristic of DC Series motor.
Why series motor is never started on no load?
State the applications of DC Shunt, Series & compound motor.
Explain the necessity of starter for DC shunt motor.
Explain three point starter with the help of neat diagram.
State the factors affecting speed of DC motor with the help of equation.
State & explain various methods of speed control of dc shunt motor.
A 220V DC shunt motor takes the current of 31 amp. on certain load. Its armature resistance
is 0.8 ohm & field resistance is 220 ohm. Find the resistance to be added in series with the
armature to half the speed if the load torque is proportional to the square of the speed.
[ANS: 15.47 ohm]
State & explain various methods of speed control of dc series motor.