9. Fill in the blanks with proper words and phrases:

1. A new dc motor should be tested before it is_____. 2. Test for_____ in the fields, armature, brush holders.

3. Test for_____ in the field circuit, in the armature circuit. 4. Test to identify the six_____ of a compound motor. 5. Test for cumulative or differential_____. 6. Test for correct interpole______. 7. Rest for correct position of the brush_____ . 8. If the motor fails to run when the switch is turned on, the_____may be:

Symptom: the motor runs faster than______ speed. 9. Testing dc generators is similar to testing______.

10. If the field poles loose residual magnetism, it is impossible for the armature to_____ , and therefore no current can be generated. 11. To remedy this condition, the shunt field is connected to a source of ______foe a few seconds. 12. Because the building-up process of a generator depends on the continued increase in the strength of the field, it is obvious that the_____ can­not build up if a high resistance in the field circuit prevents sufficient______from flowing in the field coils to increase the flux. 13. The residual magnetism in a generator produces lines of force from a _____ to a _____. 14. If the current in the field coils is in the wrong direction, lines of force will be produced______ to the residual lines. 15. If completely shorted, the voltage will not increase, and the armature will_____.

10. Speak about:

a) Testing of a dc motor.

b) Common symptoms in defective dc motors and their remedies.

c) Testing of a dc generator.

d) Common symptoms in defective dc generators and their remedies.

11. Below you will find multiple choice questions on the troubleshooting and repair. By answering them you will be able to check your knowledge on the topic.

1. What is the probable fault for motor overheating?

a. insulation resistance broken down

b. ground fault

c. mechanical overload

d. a and b

e. b and с

2. What is the probable fault for hot bearings?

a. bearing lubrication failure

b. drive belts overtensioned

c. bearings worn

d. a,b,c.

3. Why might a generator not start?

a. low battery voltage

c. starter motor fault

d. air in the fuel system

4. Why might.a generator not hold load?

a. air cleaner clogged

b. injector pump fault

c. fuel filter clogged

d. a,b,c

5. Why could exhaust smoke be black?

a. air cleaner clogged

b. low compression

c. cold start

d. a and b

e. b and с

6. Why could exhaust smoke be white?

a. air cleaner clogged

b. engine cold

c. low compression

d. fuel filter clogged

7. Why would a generator start and stop?

a. fuel filter clogged

b. air in fuel system

c. fuel supply valve closed

d. a,b,c

8. When would you test a motor?

a. immediately after installation

b. before it is installed

c. at the engine builder

d. a,b,c

9. If the motor fails to run when the switch is turned on, the trouble may be:

a. wrong voltage

b. poor, brush contact on the commutator

c. burned out fuses d dirty commutator

10. If the motor runs slowly, the trouble may be:

a. shorted armature or commutator

b. dirty or clogged brushes

c. open field circuit

d. burned out fuses

11. If the motor runs faster than name-plate speed, the trouble may be:

a. wrong voltage

b. shorted or grounded field

c. open circuit in the armature

d. a,b,c

12. If the motor sparks, the trouble may be:

a. worn bearing

b. poor brush contact on the commutator

c. rough commutator

d. a,b,c

13. If the motor is noisy in operation, the trouble may be:

a. worn bearing

b. high or low bars

c. rough commutator

d. a,b,c

14. If the motor runs hot, the trouble may be:

a. worn bearing

b. overload

c. tight bearing

d. a and b

e. b and с

15. If a generator does not generate the trouble may be:

a. differential connection

b. overload

c. loss of residual magnetism

d. resistance in the field circuit

16. If the voltage drops considerably as the load is placed on the generator, trouble may be:

a. differential connection

b. shorted armature

c. overload

d. a,b,c

17. If the voltage does not build up to a maximum the trouble may be:

a. wrong field connection

b. wrong rotation

c. differential connection

d. speed of generator too low

Grammar exercises.

Read, translate the sentences and define the types of subordinate clauses.

1. A property of a conservative system is that its energy is a function of its state only and is described by the same independent variables that describe the state. 2. Since core losses are usually small, they may be neglected, or their effect may be included in the lossy portion of the electrical system. 3. The study of electric machines from the coupled-circuit viewpoint is based on the fundamental consideration that machines can be viewed in terms of sets of linear lumped circuits in relative motion. 4. Relative motion exists be­tween the two magnetic members of the electric machine, namely, the stator, which is the stationary member, and the rotor, which is the rotating member. 5. The radial length of the air gap is always kept very small compared to the radial dimension of the outer surface of the rotor in order to produce a large magnetic field for a given current. 6. The two windings in relative motion are known as the field winding, which produces the flux density, and the armature wind­ing in which the working emf is induced. 7. The iron core forming magnetic structure is laminated in order to reduce the field iron losses if the field current is alternating or contains an alternating component. 8. Losses are on inevitable part of any energy-transforming device, even though they pity essentially no basic role in the energy-conversion process. 9. No-load (or open-circuit) core losses consist of the hysteresis and eddy-current losses, which occur because of the periodic magnetic reversals in the ferromagnetic parts of the machine. 10. The brushes are held in contact with the commutator by a combination of rectangular brush holders and springs whose tension may be adjusted. 11. The holder is so located that the brush always makes contact with a commutator segment connected to a coil in which no voltage is induced. 12. Since the separately generator requires a separate dc field supply, its use is limited to applications where a wide range of controlled voltage is essential. 13. A force is exerted on the conductor because it is carrying current and it is located in a magnetic field. 14. The length of the conductor is also a factor that determines the magni­tude of the force on the conductor. 15. With generators the only part of the conductor that was effective in generating a voltage was the part in the magnetic field. 16. Because the shunt field is connected across the line, the flux in the ma­chine will remain essentially constant. 17. Since the torque is proportional to the flux and the armature current, the flux in the compound motor is greater than in the shunt because of the additional flux pro­duced by the series winding. 18. In a series motor the flux depends upon the current in the series field, which is the same current that flows through the armature. 19. As long as the magnetic material is not saturated, the torque is proportion­al to the square of the armature current. 20. If three slip rings are connected to points which are several electrical degrees apart, the result is a three-phase gen­erator. 21. If a four-pole rotor is used, the two conductors of each coil must lie under adjacent poles. 22. The salient-pole construction is required when there are many poles on the rotor and is used for medium- and slow-speed machines. 23. Summarizing, we can say that cylindrical rotors will most likely be on alternators located where steam power is readily available. 24. It may be noted here that the terms high-speed and low-speed rotors are sometimes used synonymously with cylindrical- and salient-pole rotors, respectively.