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.

Accepted Answer

When one stator winding in an AC motor is shorted, testing the resistance between all the T leads (terminals) will generally show one reading to have a higher resistance than the other two because the shorted winding affects the resistance measurement, making it different from the readings of the unshorted windings.

Question 2

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

Accepted Answer

Three-phase AC motors are the most commonly used type of AC motor in industry because they provide efficient and reliable power for industrial applications. Single-phase motors are typically used in residential and small commercial applications, while two-phase and four-phase motors are less common and usually only used in specialized applications.

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.

Accepted Answer

In direct current machines, the commutator bars are made of copper and the brushes are made of carbon. Over time, as the brushes wear down, carbon dust can collect between the commutator bars and cause a short circuit.

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.

Accepted Answer

Slip ring rotors typically contain two slip rings, which are used to transfer DC voltage to the rotor winding.

Question 5

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

Accepted Answer

Periodic maintenance of direct current machines involves testing the insulation on the field windings and the armature to ensure they are not breaking down or shorting out, which is crucial for the machine's performance and safety.

Question 6

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

Accepted Answer

The squirrel-cage rotor consists of rotor bars concealed inside the rotor laminations. These bars are integral with the rotor and are used to conduct current throughout the rotor. Testing the rotor bars is essential to identify any faults or damages in the rotor.

Question 7

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

Accepted Answer

Rotating a rotor by hand and feeling for any roughness or resistance can indicate a bad bearing. Checking the other options (grease fitting, brush, commutator bar) may also be necessary in diagnosing issues with the motor, but they would not necessarily reveal a bad bearing.

Question 8

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

Accepted Answer

To test for open windings in an armature, an ohmmeter should be used to measure the resistance between two adjacent commutator bars. If the resistance is infinite, then there is an open circuit in the winding.

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.

Accepted Answer

The answer of Dual-voltage motors are generally characterized as having...

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.

Accepted Answer

Slip ring rotors do contain slip rings that 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.

Accepted Answer

The given standards are not consistent and vary across industries. However, the flat standard of 1.5 to 15 megohms = Poor, 15 to 50 megohms = Fair, and 50 to 200 megohms = Good seems like the most practical choice as it provides clear categories and covers a broad range. Option C is the value that fits in the range of "Good" category.

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.

Accepted Answer

Vibration sensors can detect changes in vibration patterns and can alert maintenance personnel to the need for bearing replacement or other maintenance before a failure occurs. This technology allows for predictive maintenance, which can save time and money compared to waiting for a failure to occur and conducting unplanned repairs.

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.

Accepted Answer

It is important to identify continuity between two winding leads as pairs, but it is also important to avoid letting the ends of the leads touch anything to prevent damage to the motor or injury to the person testing it.

Question 14

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

Accepted Answer

The answer of It is possible to determine if the...

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.

Accepted Answer

A growler is used to test an armature by creating a magnetic field around the armature, causing any defects or inconsistencies to become apparent as vibrations in the armature.

Question 16

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

Accepted Answer

Testing the rotor in the field requires removing the motor from the machinery and dismantling the stator, which is a complex and time-consuming process that requires specialized tools and knowledge. Therefore, it is not easy to test the rotor 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.

Accepted Answer

The answer of Testing the field windings of an AC...

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.

Accepted Answer

Brushless synchronous motors do not contain a separate two-phase winding on the rotor shaft. They have permanent magnets on the rotor and use electronic controllers to provide the necessary current to the stator windings.

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.

Accepted Answer

When a three-phase, wye-connected, dual-voltage motor is connected to a 240-V line, the motor windings can be connected in either series or parallel depending on the desired voltage and current requirements.

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.

Accepted Answer

A lubrication schedule outlines the appropriate amount and frequency of lubrication needed for a motor, therefore preventing over or under lubrication.

Quiz 19: Motor Maintenance and Troubleshooting