I4 Learning Task 1 thru 4

Question 1

Define: Stator

Answer 1

the stationary part of the motor that consist of a hollow, cylindrical, laminated steel core.

Question 2

List the purposes for the slots in the stator core.

Answer 2

support the stator coil windings

provide a low-reluctance path for the magnetic circuit

Question 3

Three-phase stator windings is made up of three-single phase windings placed

Answer 3

120 electrical degrees apart

Question 4

Define: rotor

Answer 4

the portion of the motor that rotates and consists of a cylindrical laminated steel core with evenly spaced holes from one end to the other.

Question 5

Describe: Squirrel cage

Answer 5

the actual rotor winding and it consists of copper or aluminum bars.

Question 6

Why are the bars of the squirrel cage rotor windings slightly skewed?

Answer 6

produces a smoother and quieter motor operation.

Question 7

List the two types of motor enclosures

Answer 7

Open machine

Totally enclosed machine

Question 8

List the two types of winding enclosures for severe environmental conditions

Answer 8

encapsulated windings

sealed windings

Question 9

Frame designations

Answer 9

a set of NEMA standards that all motor frames are manufactured to.

Question 10

Describe Service factor (SF)

Answer 10

when the SF is multiplied by the rated horsepower, the product is the max HP the motor can supply continuously at rated voltage and frequency without damage to the motor

Question 11

What does a motor with a rating of “Continuous” mean?

Answer 11

the motor can go on supplying its full-load HP rating without interruption or change.

Question 12

What does a motor with a rating of “short time” mean?

Answer 12

Short-time ratings are 5, 15, 30 or 60 min. Can only supply rated HP for the time designated in the rating.

Question 13

Define: Ambient temperature

Answer 13

the temperature of the surrounding cooling medium that comes in contact with the heated parts of the motor.

Question 14

List the four Insulation system classifications

Answer 14

Class A
Class B
Class F
Class H

Question 15

How much can the frequency vary for normal operation of a motor

Answer 15

not more than 5%

Question 16

How much can the voltage vary for normal operation of a motor

Answer 16

not more than 10%

Question 17

Define: FLC

Answer 17

is the current the motor draws when it operates at the rated voltage and supplies the rated HP

Question 18

Describe: Code letter for locked-rotor kVA

Answer 18

this letter may be looked up in a table to determine the ratio of the locked-rotor kVA to the HP rating

Question 19

Decribe: Design Letter

Answer 19

designates the relationship between the torque and the speed of the motor. There are four design-letter ratings: A, B, C and D

Question 20

Describe Linear-induction motor

Answer 20

is a motor that, instead of rotating, moves in a line.

Question 21

What part of a linear-induction motor moves?

Answer 21

stator

Question 22

What effect does the increasing the Hz of the supply have on the speed of the rotating magnetic field?

Answer 22

increases

Question 23

Define: Slip Speed

Answer 23

Sync speed - rotor speed

Question 24

Define: full-load torque

Answer 24

torque necessary to produce rated HP at rated full-load speed

Question 25

Define: breakdown torque

Answer 25

max torque a motor will produce and if exceeded the motor will quickly slow down and stall

Question 26

Define: locked rotor torque

Answer 26

the amount of torque produced the moment that power is applied to the stator and the rotor is not moving

Question 27

At what rotor speed will the stator current be the highest?

Answer 27

O rpm or 100% slip

Question 28

in what units is the synchronous speed of a linear-induction motor measured?

Answer 28

meters per second

m/s

Question 29

What value of resistance is acceptable for a megger test on a low voltage motor?

Answer 29

1 megaohm or larger