Electrical and Electronics Engineering
Electrical Machines II (Sem Vth)
Assignment 1: Chap 1 – Performance of DC machines
Date: 4th August 4, 2011
Submission Date: on or before 18th August
1. Define the following terms using diagram:
Pole pitch, Coil pitch, Front pitch, Back pitch, Commutator pitch, Dummy coil and
2. Explain the general rules and equations to develop the simplex lap and wave winding.
3. Draw the developed winding diagram with calculations for the given specifications:
4 pole, 12 coil, two layer, lap wound
4 pole, 21 coil, two layer, lap wound
4 pole, 15 coil, two layer, wave wound
4 pole, 21 coil, two layer, wave wound
4. Make a comparison of lap and wave winding.
5. Discuss the process of commutation with diagram.
6. Explain in detail about cause and effects of armature reaction.
7. Discuss the methods to compensate the effects of armature reaction.
8. Discuss in detail about the following tests of DC machine:
1. A 200 V DC shunt motor develops an output of 17.15 kW when taking 20.2 kW. The
field resistance is 50 Ω and armature resistance is 0.06 Ω. What is the efficiency and
power input when the output is 7.46 kW?
2. Two shunt machines connected for Hopkinson’s test take 15A at 200 V from the supply.
The motor current is 100 A and shunt currents are 3 A and 2.5 A. If the armature
resistance of the each machine is 0.05 Ω, calculate the efficiency of each machine for this
particular load condition.
3. The following results were obtained during the Hopkinson’s test on two similar 230V DC
machines: Armature currents 37 A and 30 A. Field currents 0.85 A and 0.8 A. Calculate
the efficiency of each machine if each has an armature resistance of 0.33 Ω
4. A 500 V DC shunt motor takes a total current of 5 A when running unloaded. The
resistance of armature and field is 0.25 Ω and 125 Ω. Calculate efficiency and output
when motor takes 100 A.