Motors

Question 1

What are the positives and negatives of a series motor

Answer 1

High-speed
High starting torque
Compact size and lightweight

Negatives
High noise pollution

Question 2

What are the positives and negatives of a three phase induction motor

Answer 2

Mechanically strong and robust
Fairly cheap
More efficient
Self starting

Negatives
Speed not easily changed
Always operate under lagging power factor
Worst power factor occurs at low load
Poor starting torque

Question 3

Where are three phase induction motors used?

Answer 3

Lathes
Drilling machines
Industrial pumps
Industrial drives

Question 4

What are the negatives and applications of a single phase motor

Answer 4

Low staring torque

Used for:
Low starting conditions
Washing machines
Tumble dryers

Question 5

Capacitor-start induction motor
Positives and applications

Answer 5

Good starting torque
Quiet running

Applications:
Compressors
Refrigerators
Hard starting loads

Question 6

Capacitor start and run motors
Positives and applications

Answer 6

Quiet and smooth running
Higher efficiency than motors that run on the main windings only

Applications
Loads requiring frequent starts
High pressure water pumps
Air compressors

Question 7

Three phase synchronous motor
Positives, negatives, and applications

Answer 7

High efficency
Ability to control the PF
High torque low starting current
Low operating and maintenance costs

Negatives:
Can’t be started on load due to starting torque being 0
Can’t be used for variable speed
Need a DC supply
Can’t be used if frequent starting is needed

Applications
Timers
Clocks
Crushers
Belt conveyors
Rolling Mills
Compressors

Question 8

How do you calculate line current?

Answer 8

I = P / √3 X Vl X PF X Eff

Question 9

How do you convert horse power to watts

Answer 9

HP X 750