Motors

Question 1

Since flux lines repel each other laterally, the stator flux is distorted by the rotor flux. Torque develops and causes the motor to turn clockwise, which is called _____..

Answer 1

Motor action

Question 2

What is the difference between the rotor of a wound rotor motor vs SCIM?

Answer 2

Wound roter has insulated wire wound on poles whereas SCIM is uninsulated and on bars.

Question 3

The closer the rotor voltage and current are to being in phase, the better the _____.

Answer 3

Torque of the motor

Question 4

If the resistance in a wound rotor motor is not removed, the motor will _____ full rated speed at full load.

Answer 4

Not reach

Question 5

Is operating a wound rotor motor at a reduced speed by using secondary resistors efficient? What does it effect?

Answer 5

Not efficient. Increases speed regulation.

Question 6

Motors with higher ______ rotor speeds have lower _____ and higher _____

Answer 6

Full load, % speed regulation, efficiencies.

Question 7

The resistance of a wound rotor motor is adjusted using external resistance connected through ______ and _____

Answer 7

Brushes and slip rings

Question 8

How do induction motors act like transformers?

Answer 8

Rotor current reflected to stator using winding ratios, as motor accelerates stator current also changes magnitude and pf. Basically, transformer action.

Question 9

Current in a motor is not proportional to ______ and _____ even though it increases with them

Answer 9

Power and torque

Question 10

What is used to measure a motor’s range of running speeds?

Answer 10

Tachometer

Question 11

A 3 phase induction motor typically draws about __________ times it’s full load current when started across the line at full voltage.

Answer 11

5 or 6

Question 12

What type of reduced voltage starter doesn’t actually reduce voltage?

Answer 12

Part winding starter & motor

Question 13

Static and rotary phase converters produce different output _____ as the load changes.

Answer 13

Current

Question 14

Which phase converter is better for variable loads?

Answer 14

Rotary

Question 15

In a rotary phase converter, the motor-generator doesn’t start until _____.

Answer 15

The motor-generator accelerates to rated speed

Question 16

Phase converters are used in areas with single phase service such as: (x4)

Answer 16

Farms, small industrial plants, woodworking shops, metal fab shops

Question 17

Single phase motors are not available above __ hp and not common above __ hp

Answer 17

15, 5

Question 18

How does an electronic soft starter work? Once the motor has accelerated, what happens?

Answer 18

Reduce starting current with network of electronic switches and programmable chips on printed circuits.

Once accelerated, a conventional contact closes to bypass the electronic switches and apply full voltage to motor.

Question 19

Kick starting is another term for what?

Answer 19

Initial current surge for loads that require extra torque to overcome interia of load at rest

Question 20

Variable torque loads require __ power and __ torque when at half soeed

Answer 20

1/8, 1/4

Question 21

Constant torque loads require __ power at half speed but _____ torque

Answer 21

Same

Question 22

How do you calculate the line current and torque for reduced stating autotransformers?

Answer 22

Tap setting squared. Ie 2A x 08(sq)

Question 23

Fractional horsepower single phase motors are _____ than fractional horsepower three phase motors.

Answer 23

Cheaper

Question 24

Integral horsepower motors are cheaper when they are three phase or single phase?

Answer 24

Three phase

Question 25

A three phase motor load should be applied _____ the rotary phase converter is started.

Answer 25

As soon as

Question 26

A rotary phase converter can supply only one three phase motor, true or false?

Answer 26

False

Question 27

Nameplate rating of a rotary phase converter is listed in _____.

Answer 27

Running KVA and max starting HP

Question 28

What are two ways to adjust how closely balanced the three phases supplied by a rotary converter?

Answer 28

Adding load, and switching in/out capacitance