Motors Flashcards Preview

Electricity > Motors > Flashcards

Flashcards in Motors Deck (28)
Loading flashcards...
1
Q

Rotor

A

The moving part to which the spinning shaft is attached

2
Q

Stator

A

The stationary part either inside or around the rotor

3
Q

Magnetic Field

A

Created with either permanent magnets or electromagnets

4
Q

Windings

A

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

5
Q

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.

A

brushes, commutator

6
Q

Electronically Commutate Motor (ECM)

A

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.

7
Q

Induction Motor

A

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.

8
Q

Single Phase AC induction motor

A

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

9
Q

3-phase AC induction squirrel cage motors

A

The most widely used industrial motors in the world

10
Q

Nameplate Horsepower (NPHP) of 15-hop means

A

the motor produces 15 hp of work at full load.

11
Q

1 HP =

A

746 Watts

12
Q

Motor efficiency

A

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

13
Q

Load factor =

A

Actual load HP / nameplate HP

14
Q

Ways to measure actual load factor:

A
  • Measure speed of motor in RPM with tachometer and compare to nameplate
  • Use volts, amps, and power factor
15
Q

Actual Electrical Load =

A

NPHP x Load Factor

16
Q

The speed of a synchronous motor is determined by

A

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

17
Q

Motor synchronous speed (RPM) =

A

(120 x frequency) / # of magnetic poles

18
Q

Asynchronous motor

A

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

19
Q

Duty Cycle Rating

A

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

20
Q

Duty is used to…

A

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

21
Q

Duty S1

A

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

22
Q

Duty S2

A

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

23
Q

Duty S3

A

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

24
Q

Variable Frequency Drives (VFD)

A

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

25
Q

VFDs reduce the speed of the motor by adjusting…

A

the frequency of the electrical input

26
Q

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

A

a large reduction of horsepower

27
Q

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

A

20-30%

28
Q

Good candidates for VFDs are…

A

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