Electrical Machine 2 assignment

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

Compensating winding


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:


Brake test


Swinburne’s test


Hopkinson’s test


Retardation test


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.


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