10EE54 DC Machines & Synchronous Machines B.E Question Bank : sjbit.edu.in
Name of the College : SJB Institute of Technology
Subject Code/Name : 10EE54-DC Machines & Synchronous Machines
Dept : Electrical And Electronics Engineering
Degree : B.E
SEM: : V
Website : sjbit.edu.in
Document Type : Question Bank
Download Model Question Paper : https://www.pdfquestion.in/uploads/sjbit.edu.in/3258-EEE-V-D.C.MACHINES%20%20AND%20SYNCHRONOUS%20MACHINES%20%5b10EE54%5d-QUESTION%20PAPER.pdf
SJB IT DC Machines & Synchronous Machines Question Paper
Question Bank :
UNIT-1
DC Generator
1. Derive the expression for emf induced in a DC generator with usual notations. Dec 2013, Dec 2011
2. Draw the no load characteristic of a DC shunt generator and comment on its shape. Explain how critical resistance can be found out from the no load characteristics. Dec 2013, June 2013
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3. A 6 pole, 148 shunt shunt generator has 480 conductors and is wave wound. Its field current is 2A. Find the magnetizing and cross magnetizing amp turns /pole at full load if i) the brushes are at the geometrical neutral axis (GNA) ii) the brushes are shifted from GNA by 5° elec. iii) The brushes are shifted from GNA by 5° mech. Dec 2013, June2013
4. What is meant by commutation? Briefly explain the steps involved in commutation process. June 2013, Dec 2012, June 2012
5. How would you classifies the types of generators (D.C) and explain them in brief, along with their diagrams. Dec 2012
6. Explain what lap and wave windings arc and where they are preferred in DC machines. June 2012
7. Explain armature reaction with neat figures and derive equations for, i) DC magnetizing ampere tams/pole and ii) Gas magnetizing ampere turns/pole. Dec 2011
8. A long shunt compound generator delivers a load current of 50A at 500V, and has armature, series field resistance of 0.05 ohm and 0.03 ohm, 250 ohm respectively. Calculate the generated voltage and the armature current, allow 1 volt per brush for contact drop. Dec 2012
UNIT-2
DC Motor
1. Classify DC motors according to their field winding connections. Draw the circuit diagrams and write the voltage and current relationships in all the types. Dec 2013
2. With the help of relevant characteristics explain why a series motor should never be started at no load. Dec 2013
3. A 200 V DC shunt motor takes 22 amp at rated voltage and runs at 1000 rpm. Its field resistance is 100 ohm and armature resistance is 0.1 ohm. Compute the value of additional resistance required in the armature circuit to reduce the. Speed to 800 rpm when i) The load torque is proportional to the speed ii) The load torque proportional to the square of the speed. Dec 2013
4. What is meant by back emf? Explain its significance. June 2013, Dec 2011
5. Derive torque equation of a DC motor. June 2013
6. A 440 V, DC shunt motor has a no load speed of 2000 rpm. It is running at 1000 rpm at full load torque, reduced armature voltage and full field. If the load torque is reduced to 50% of rated value, with armature voltage and filed voltage held constant at previous voltages the O speed increases to 1050 rpm. Find the armature voltage drop at full load. Neglect the effect of armature reaction. June 2013
7. What are the different methods of speed control of D.C. shunt motor, explain them in brief. Dec 2012
8. Explain the torque-Armature Current characteristics of shunt and series motors. June 2012, Dec 2011
9. Explain in brief the Ward-Leonard speed control of DC motors. June 2012
10. A series motor whit an unsaturated magnetic circuit and 0.5 0hm total resistance when running at a certain speed takes 60 A at 500V. If the load torque varies as the cube of the speed. Calculate the resistance required to reduce the speed by 25%. June 2012
11. . Write a short notes on Permanent Magnet DC Motors. Dec 2011
UNIT-3&4
Losses, Efficiency and Testing of DC Machines.
1. What are the losses occurring in a DC machine. Explain how do, they vary with the load. Derive the condition for maximum efficiency of a DC generator. Dec 2013, June 2013, June 2013, Dec 2012, June 2012
2. Draw the power flow diagram of a DC long shunt compound generator and explain. Dec 2013
3. Explain, with the help of necessary circuit diagram, how the efficiency of a DC generator and motor can be predetermined by conducting Swinburne’s test. Obtain the efficiency expressions for the motor and generator. Dec 2013, Dec 2012
4. Two identical DC shunt machine, when tested by Hopkinson’s method, gave the following data: Line voltage = 230 V Line current excluding the field current = 30 A Motor armature current = 230 A Field currents 5 A and 4 amp. The armature resistance of each machine is 0.025 ohm. Calculate the efficiency of both the machines. Dec 2013
5. Explain Field’s test as applied to two similar DC series motors. June 2013
6. Explain the power flow diagram in D. C. machine as generator and as motor. Dec 2012
7. The Hopkinson’s test on two shunt machine gave the following results for full load. Line If voltage, 250 V, line current excluding field currents, 5A, and 4.2 A, calculate the efficiency of each machine, armature resistance of each machine is 0.02 0hm. Dec 2012
8. Explain the retardation test on DC machines. June 2012
9. Explain the regenerative test on DC machines. June 2012, Dec 2011
10. Briefly explain the brushless DC motors and their applications. June 2012