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Electrical Machines Practice Test: DC Machines
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Avg score: 100% Most missed: “Swineburne’s test is applicable to those machines in which flux is practically _…”
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. A dc shunt motor is connected to the source through 3-point starter. If the field id kept open and starter handle is moved from off to on position, then __________
2. A dc shunt motor is running at 1000 rpm at the rated load torque. If few of the field windings get shot circuited then the __________
3. A 100KW, 250 V, 400 A, a long shunt compound generator has an armature resistance of 0.025 ohms. There are 1000 shunt fields turns per pole and 3 series field turns per pole. The series field is connected in a such a fashion that positive armature current produces direct-axis MMF which adds to that of the shunt field. Compute the gross MMF at the rated terminal current when shunt field current is 4.7A and speed is 1150 rpm.
4. The brushes of a dc motor, are shifted by 5′, from the main field axis, then __________
5. If a DC shunt generator fails to start, the most primitive action would be __________
6. Maximum torque in dc series motor is limited by __________
7. The quantities needed to complete retardation test are/is _________
8. The brushes should be shifted in _______ direction in generator for the satisfactory operation of commutation.
9. Mark the most incorrect. In dc generator, commutation can be improved by __________
10. The manufacturer has mentioned a medium starting torque and 15% speed regulation. Which is the most appropriate motor for this requirement?
11. The commutation process involves basically reversal of current in armature coil as it crosses MNA.
12. The armature reaction is produced mainly by __________
13. If the electromagnetic torque in a DC shunt-generator is opposite, what can be further concluded?
14. A dc shunt motor is running at 1000 rpm at the rated load torque. If we reverse the supply terminals, then the __________
15. The efficiency in the swineburne’s test can be found.
16. The critical resistance refers to __________
17. Most commercial compound dc generator are normally supplied by manufacturers as ______ compounded machines.
18. The absence of compensating winding lead to __________
19. The flux distortion caused by cross magnetizing armature reaction is more pronounced in a __________
20. If a dc shunt motor is stopped by forcing starter handle back to OFF position, then the __________
21. Interpoles are used to start the dc motor above the base speed.
22. What is the main concern before doing hopkinson’s test for finding efficiency?
23. The armature mmf affects __________
24. Centrifugal pumps, fans-blowers use __________
25. If a self excited DC generator is failed to run, this refers to ________________