BEE
Assignment-5(D.C. Motors)
4. (A) Draw the power flow diagram of a DC shunt motor and also explain the following terms
i. Electrical Efficiency,
ii. Mechanical Efficiency and
iii. Commercial Efficiency.
(B) A 6 pole DC motor has a wave connected armature with 87 slots, each slot containing 6 conductors. The flux per pole is 20mwb and the armature has a resistance of 0.13ohm when the motor is connected to 240V supply and the armature draws a current of 80A driving a load of15KW.caluculate (i)speed (ii)Armature torque and (iii)shaft torque
Assignment-5(D.C. Motors)
- (A).Explain the principle of operation of DC motors.
(B). the armature of a 6 – pole, 6 circuit DC shunt motor takes 300 A at speed of 400 rpm. The flux per pole 75 mWb. The number of armature turns is 500. The torque lost in windage, friction and iron losses can be assumed as 2.5 %. Calculate
i) The torque developed by the armature
ii) The shaft torque.
2. (A) Derive the torque equation of a DC motor.
(B) A 200V DC shunt motor takes a total current of 100 A and runs at 750 rpm. The resistance of the armature winding and shunt field winding is 0.1 ohms and 40 ohms respectively. Find the torque developed by the armature.
3. (A) what is the significance of back emf generated in a DC machine hence explain the principle of operation of a DC motor. (or)
Explain how back emf makes d.c motor self regulating.
( B) A 100V series motor takes 45 A when running at 750 rpm. Its armature resistance is 0.22 ohms, while the series field resistance is 0.13 ohms. Iron and frictional losses amounts to 750 W.Find the shaft power.4. (A) Draw the power flow diagram of a DC shunt motor and also explain the following terms
i. Electrical Efficiency,
ii. Mechanical Efficiency and
iii. Commercial Efficiency.
(B) A 6 pole DC motor has a wave connected armature with 87 slots, each slot containing 6 conductors. The flux per pole is 20mwb and the armature has a resistance of 0.13ohm when the motor is connected to 240V supply and the armature draws a current of 80A driving a load of15KW.caluculate (i)speed (ii)Armature torque and (iii)shaft torque
5.(A) Write the applications of Dc motors.
(B) A 460V D.C series motor runs at 1000RPM taking a current of 40A.caluculate the speed and percentage change in torque if the load is reduced so that the motor is taking 30A.total resistance of the armature and field circuits is 0.8Ω.Assume ‘Ø’ is proportional to filed current.
6. (A) Explain the losses in D.C. Motor
(b) What happens if D.C series motor is started on no load?
(C) why series motors are applicable for traction applications