Introduction to Three-Phase Induction Motors 030302a

Question 1

What is an Electric Motor?

Answer 1

A device that Converts Electrical power (energy) into Mechanical power (energy)

Question 2

What is an Induction Motor?

Answer 2

Is a machine that gets energy into the rotating part by Mutual Induction.

This transfer of energy uses “transformer action”

Question 3

What is another name for Torque?

Answer 3

“The Moment of Force”

Question 4

What basic tool is used to measure Torque?

Answer 4

A “Prony Brake”

Question 5

What is the Formula used to calculate Torque?

Answer 5

T = F • r

F - Force
r - Radius

Question 6

What sophisticated tool do we use to measure Torque?

Answer 6

A Dynamometer

Question 7

What is Torque measured in?

Answer 7

Newton-Metres (Nm)

Question 8

What is Force measured in?

Answer 8

Newtons (N)

Question 9

When referring to the radius in a Torque calculation; which unit do we measure the radius in?

Answer 9

Meters (m)

Question 10

What 3 things make up the formula for Mechanical Power(P)?

Answer 10

1. Rotational Speed (Frequency)
2. Torque
3. A numeric constant (9.55)

Question 11

What formula would you start with to calculate the Torque Output of a 10kW motor?

Answer 11

P=(T•n)/9.55

Question 12

What formula would you start with to calculate the Torque Output of a 10hp motor?

Answer 12

hp=(T•n)/(9.55•746W)

Question 13

What is the formula for Efficiency?

Answer 13

P.out(Mech)

Divided by

P.in(elect)

Question 14

The categories of losses in an induction motor are _________ and __________.

Answer 14

Electrical & Mechanical

Question 15

Name the 2 types of ELECTRICAL losses in an induction motor.

Answer 15

Iron losses (Core losses) and Copper losses

Question 16

What are Iron Losses (Core Losses)?

Answer 16

Losses that occur in the stator and the rotor.

Question 17

Which part of a motor do we see Copper losses?

Answer 17

Copper losses occur in the stator and the rotor.

Question 18

Name the 2 types of Mechanical losses.

Answer 18

Friction and Windage

Question 19

Describe Friction and Windage as they pertain to Mechanical losses.

Answer 19

Friction is the energy loss from creating heat which occurs in the bearings and between brushes and slip rings when they are used.

Windage is the energy lost due to the air movement produced by the rotor.

Question 20

What method is used during rotor construction to prevent “cogging”?

Answer 20

Skewing or Slanting of the rotor bars

Question 21

Name two types of rotors used in induction motors.

Answer 21

• Squirrel-cage Rotors
• Wound Rotors

Question 22

What are the two major components of a stator?

Answer 22

• Stator Core
• Stator Winding

Question 23

What is Windage?

Answer 23

It’s a Mechanical loss of energy due to the air movement produced by the rotor.

Question 24

The Counter-torque produced by a dynamometer or prony brake is the product of what two (2) mechanical quantities?

Answer 24

• Force
• Radius (to the point where the torque is measured)

Question 25

Mechanical power is the product of what two (2) mechanical quantities?

Answer 25

• Torque
• Speed (Rotational Frequency eg. RPM)

Question 26

How many pi’s in a full rotation?

Answer 26

2 (2pi)