Motors

Question 1

Rotor

Answer 1

The moving part to which the spinning shaft is attached

Question 2

Stator

Answer 2

The stationary part either inside or around the rotor

Question 3

Magnetic Field

Answer 3

Created with either permanent magnets or electromagnets

Question 4

Windings

Answer 4

Coils of wire through which the current flows to produce an opposing magnetic field

Question 5

If the windings are on the rotor, the stationary input wires lead to _______ that are held against the spinning ______ which distributes it to the windings.

Answer 5

brushes, commutator

Question 6

Electronically Commutate Motor (ECM)

Answer 6

A small hp brushless (the magnetic field rotates around stationary windings) DC motor that is usually higher efficiency than an AC motor of the same size. Commonly found in HVAC fans.

Question 7

Induction Motor

Answer 7

Most common AC motor.
Has stationary windings around a rotor containing permanent magnets. They’re sealed, self-starting, reliable, rugged, and low cost. No brushes.

Question 8

Single Phase AC induction motor

Answer 8

Extensively used for smaller loads such as appliance fans. Not practical above 5-10 hp

Question 9

3-phase AC induction squirrel cage motors

Answer 9

The most widely used industrial motors in the world

Question 10

Nameplate Horsepower (NPHP) of 15-hop means

Answer 10

the motor produces 15 hp of work at full load.

Question 11

1 HP =

Answer 11

746 Watts

Question 12

Motor efficiency

Answer 12

Measures the effectiveness by which electrical energy is converted to mechanical energy.

Question 13

Load factor =

Answer 13

Actual load HP / nameplate HP

Question 14

Ways to measure actual load factor:

Answer 14

• Measure speed of motor in RPM with tachometer and compare to nameplate
• Use volts, amps, and power factor

Question 15

Actual Electrical Load =

Answer 15

NPHP x Load Factor

Question 16

The speed of a synchronous motor is determined by

Answer 16

the number of magnetic poles within the motor and the frequency of the electricity

Question 17

Motor synchronous speed (RPM) =

Answer 17

(120 x frequency) / # of magnetic poles

Question 18

Asynchronous motor

Answer 18

Always have a difference between its loaded RPM (lower) and its synchronous RPM (higher). This is called slip.

Question 19

Duty Cycle Rating

Answer 19

Indicates its operational profile in terms of starting and stopping, speed variation, and temp. Not used for energy calculations.

Question 20

Duty is used to…

Answer 20

match the correct motor to the correct application, otherwise overheating and premature failure can occur.

Question 21

Duty S1

Answer 21

Continuous duty - runs long enough to reach steady state temperature. Most common motor (compressors)

Question 22

Duty S2

Answer 22

Short term duty - brief operation followed by long rest (appliances)

Question 23

Duty S3

Answer 23

Intermittent periodic duty - consistent on and off (drill press)

Question 24

Variable Frequency Drives (VFD)

Answer 24

Motor controls that vary the speed of a motor to better match the load being put on the motor

Question 25

VFDs reduce the speed of the motor by adjusting...

Answer 25

the frequency of the electrical input

Question 26

A reduction in speed of a fan or pump motor results in...

Answer 26

a large reduction of horsepower

Question 27

VFDs can save between _________ % of the energy used by a typical motor

Answer 27

20-30%

Question 28

Good candidates for VFDs are...

Answer 28

pieces of equipment with variable but consistent loads that will benefit from custom speed control