Deck 19: Motor Maintenance and Troubleshooting

Question 1

If one stator winding in an AC motor is shorted, testing the resistance between all the ____ generally shows one reading to have a higher resistance than the other two.

A) C leads
B) slip rings
C) rotors
D) T leads

Answer 1

D

Question 2

Most of the AC motors in industry are ____-phase.

A) single
B) two
C) three
D) four

Answer 2

C

Question 3

In direct current machines, the segments between commutator bars can become shorted due to a buildup of ____ caused by the wearing of the brushes.

A) copper
B) carbon
C) iron
D) steel

Answer 3

B

Question 4

Slip ring rotors contain ____ slip ring(s), which is(are) used to connect direct current to the rotor winding while the motor is in operation.

A) one
B) two
C) two or three
D) four

Question 5

Periodic maintenance of direct current machines includes testing the insulation on the ____ and the armature with a megohmmeter.

A) brushes
B) coils
C) field windings
D) commutator bars

Question 6

To test a squirrel-cage rotor, it is necessary to access the ____ concealed inside the rotor laminations.

A) copper coils
B) rotor bars
C) slip rings
D) fuses

Question 7

Rotating a rotor ____ by hand will generally reveal a bad bearing.

A) shaft
B) grease fitting
C) brush
D) commutator bar

Question 8

To test an armature for an open winding, connect the leads of an ohmmeter to two adjacent commutator bars.

Question 9

Dual-voltage motors are generally characterized as having more than two T leads. Seven-lead motors are the most common, but some motors have nine leads.

Question 10

Slip ring rotors contain two slip rings, which are used to connect direct current to the rotor winding while the motor is in operation.

Question 11

There is no set standard for determining if a motor winding is good or bad. Some industries use a standard of 1 megohm per 100 volts. Others use 2 megohms per 100 volts. Other industries use a flat standard such as 1.5 to 15 megohms = Poor, 15 to 50 megohms = Fair, and 50 to ____ megohms = Good.

A) 100
B) 150
C) 200
D) 250

Question 12

If periodic preventive maintenance on electric motors is not desired or feasible, vibration sensors on the motor shaft can warn of impending bearing failure before it occurs.

Question 13

When identifying the proper relationship of motor windings, remember that the circuits that exhibit continuity between two leads must be identified as pairs, but do not let the ends of the leads touch anything.

Question 14

It is possible to determine if the motor is connected wye or delta by checking the ____.

A) continuity of the winding
B) resistance values
C) number of slip rings
D) armature

Question 15

A device that is often used to test an armature is called a ____, which is a device constructed by wrapping a coil of wire around a set of V-shaped laminated cores.

A) husker
B) growler
C) coiler
D) corer

Question 16

The rotor of a squirrel-cage motor is easy to test in the field.

Question 17

Testing the field windings of an AC motor is very similar to testing the stator windings in a direct current machine.

Question 18

Brushless synchronous motors contain a separate two-phase winding mounted on the rotor shaft-this winding is used to supply direct current to the main rotor winding-as well as rectifiers and fuses.

Question 19

If a three-phase, wye-connected, dual-voltage motor is connected to a 240-V line, the motor windings are connected in series.

Question 20

A lubrication schedule is the best method of ensuring that motors are not overlubricated in some cases and never lubricated in other cases.