Deck 25: Summary Review of Units18-24

Question 1

What may result if severe bearing wear occurs in either large or small motors?

Answer 1

Severe bearing wear on either large or small motors may result in actual contact between the rotor and the stator.

Question 2

Briefly describe two methods that are used in lubricating motors.

Answer 2

Methods of lubricating motors include the following:
• Small motors with sleeve bearings have oil holes with spring covers.
• The bearings of larger motors are often provided with an oil ring that fits loosely in a slot in the bearing. The oil ring picks up oil from a reservoir located directly under the ring.
• Many motors are lubricated with grease.

Question 3

The formula Rm = KV + 1 is used as part of a balance test measuring the phase currents under load.

Answer 3

False

Question 4

A(n) ____________________ is used to measure insulation resistance.

Question 5

A(n) ____________________ motor is a self-contained drive made up of a ball-bearing motor and a speed-reducing gear box.

Question 6

A(n) ____________________ is an instrument consisting of an electromagnetic yoke and winding excited from an AC source that can be used to locate short-circuited coils.

Question 7

The bars of a squirrel-cage ____________________ can be broken if the motor is subjected to severe jarring, vibration, or overheating.

Question 8

List two factors that would influence a plant maintenance engineer's decisions for frequency and thoroughness in systematic inspection and servicing of motors.

Question 9

The field coils of alternators can be checked for impedance by applying a low-frequency high voltage to each coil and measuring the current.

Question 10

Briefly describe the repercussions of insufficient oil and excessive oil in a motor.

Question 11

A tachometer is an instrument used to check the speed of a motor.

Question 12

A value of insulation resistance slightly below the recommended approximate value does not necessarily indicate that immediate repair is required. What course of action should be taken by an electrician in this situation?

Question 13

The value of insulation resistance in megohms (1,000,000 ohms) is used as an indication of insulation efficiency.

Question 14

In a good preventive maintenance program with detailed checks, the person in charge should have a history on file for every motor in the plant; entries should include inspection dates, descriptions of repairs, and the costs involved.

Question 15

In a(n) ____________________ test, high but equal current readings in all three phases indicate an overloaded motor.