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Electrical Machines Practice Test: DC Machines
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DC Machines topics are: DC machine applications and its circuit models, mmf and flux density waveforms in DC machines, methods of excitation, efficiency and testing of dc machines. DC machines, which can be classified as DC motors and DC generators, convert mechanical energy into electrical energy. They contain AC currents and voltages, but convert AC voltage to DC voltage. DC machines are used in applications where high starting torque and accurate speed control over a wide range are important.  Here are some types of DC machines: DC motors: Use direct current to produce mechanical force.... Show more
Electrical Machines Practice Test: DC Machines
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25 Questions

1. Retardation test on DC shunt motor is used for finding _______
2. Compensating windings are embedded in pole faces and having the same polarity as that of adjoining armature winding.
3. Which is the most appropriate relation to find efficiency of the generator?
4. Inspite of heavy initial investments, dc motors are used due to _____________
5. If the field current and armature current are reversed, then the __________
6. If a self excited DC generator is failed to run, this refers to ________________
7. In the hopkinson’s test on two DC machines. Machine A has field current of 1.4A and B has field current of 1.3A. Which machine acts as motor?
8. Compensating winding has an advantage of __________
9. The voltage drop at brush-commutator contact is variable (1-2V) and dependent of armature current.
10. If the terminal voltage of 220-V dc generator having armature resistance of 1 ohms. The induced emf produced is 200-V. The armature current for the above machine is?
11. The brushes are placed __________
12. A shunt generator has an induced voltage on open circuit of 127 V. When the machine is on load the terminal voltage is 120 V. The load current if the field resistance be 15 ohm and armature resistance be 15 ohm.
13. Which of the following are applied with differential compound motor?
14. What is the main concern before doing hopkinson’s test for finding efficiency?
15. A dc shunt motor is running at 1000 rpm at the rated load torque. If we reverse the supply terminals, then the __________
16. Consider a 200V, 25kW, 30A DC machine lap connected with armature resistance of 0.4 ohms. If the machine is later wave wound, then the developed power is?
17. If the DC machine is held constant at 3000 rpm. The DC voltage is 250V. If the field is held constant with 250V. Is this machine generator or motor?
18. Maximum torque in dc series motor is limited by __________
19. The manufacturer has mentioned a medium starting torque and 15% speed regulation. Which is the most appropriate motor for this requirement?
20. The number of compensating conductors/pole faces is _______ (where Z is the number of active armature conductors/pole; A is number of parallel paths; Ia is the armature current).
21. The conductor EMF and current are in _____ direction and developed torque is in _____ for generating mode.
22. The quantities needed to complete retardation test are/is _________
23. The principle contributors to magneto motive force is/are __________
24. With no commutating poles used the brushes are given backward lead in the dc motor.
25. Hopkinson’s test is also called regenerative test due to ____________