# Assignment-I-Subject-Electrical Machines

Saturday, February 8, 2020

**Edit****Assignment-I**

**SET-A(Div-SY-1)**

**DC Machines**

**Subject_ Electrical Machines**

1.Derive
the torque equation of DC motor

**.****2.**Explain the construction of DC machine.

3.
What is back e.m.f. ? Explain the significance of back e.m.f.

4.
Draw and explain the Torque-Armature Current, Speed-Current and
Torque-Speed characteristics of (a)DC series motor and (b) DC shunt motor.

5.
Explain construction and working of brushless DC motor. State its advantages,
disadvantages and applications.

6.Explain working of Servo Motor motor. State its advantages,
disadvantages and applications.

7. A 200 V, d.c shunt machine has an armature resistance of 0.5 Ω and field resistance of 200 Ω. The machine is running at 1000 rpm as a motor drawing 31 A from the availability mains. Calculate the speed at which the machine must be driven to realize this as generator.

8.
A 4-pole series motor has Z = 944, wave wound, flux/pole= 34.6 mWb. Gross
torque 209 N-m, supply voltage = 500 V and R = 3 W. Calculate line current and
speed.

9.A 220 V shunt motor has armature and field resistances of 0.2 Ω and 220 Ω respectively. The motor is driving load torque, load torque is directly proportional to square of speed and running at 1000 rpm drawing 10 A current from the supply. Find the new speed and armature current if an external armature resistance of value 5 Ω is inserted in the armature circuit. Neglect armature reaction and saturation.

9.A 220 V shunt motor has armature and field resistances of 0.2 Ω and 220 Ω respectively. The motor is driving load torque, load torque is directly proportional to square of speed and running at 1000 rpm drawing 10 A current from the supply. Find the new speed and armature current if an external armature resistance of value 5 Ω is inserted in the armature circuit. Neglect armature reaction and saturation.

**SET-B(SY-2 and 3)**

**Assignment-I**

**Subject_ Electrical Machines**

1.Derive
from first principle , the e.m.f. generated of DC generator.

**2.**Explain the construction of DC machine.

3.
What is back e.m.f. ? Explain the significance of back e.m.f.

4.
Draw and explain different characteristics of
(a)DC series motor and (b) DC shunt motor.

5.Compare
lap winding and wave winding with neat diagram.

6.Explain construction and working of stepper
motor(permanent magnet type). Draw and explain briefly its performance characteristics.

7.Explain
construction and working of Universal motor. State its advantages,
disadvantages and applications.

8. A 200 V, d.c shunt machine has an armature resistance of 0.5 Ω and field resistance of 200 Ω. The machine is running at 1000 rpm as a motor drawing 31 A from the availability mains. Calculate the speed at which the machine must be driven to realize this as generator.

9.A
220 V d.c series motor has armature and field resistances of 0.15 Ω and 0.10 Ω
respectively. It takes a current of 30 A from the mains while running at 1000
rpm. If an external resistance of 1 Ω is inserted in series with the motor,
find the new steady state armature current and the speed. Assume T

_{L }∝ n^{2}.