Vocabulary 17

Question 1

Stator

Answer 1

The component within a motor that contains its windings; the stator itself does not turn

Question 2

Rotor

Answer 2

The rotating/moving component of a motor, including the rotor shaft.

Question 3

Bearings

Answer 3

A device surrounding a rotating shaft; reduces wear and tear from the rotating shaft by providing a low-friction contact surface.

Question 4

End bells

Answer 4

A casing located on the end of an electric motor that usually contains bearings and a lubrication system.

Question 5

Housing

Answer 5

Used to describe the entire casing or the protective shell of a motor.

Question 6

Squirrel cage rotor

Answer 6

A cylinder shaped fan assembly used for air flow.

Question 7

Run windings

Answer 7

Electrical windings within a motor that draw current throughout the whole running cycle.

Question 8

Slip

Answer 8

The difference between a motors’ calculated speed and its actual speed.

Question 9

Induction motor

Answer 9

An alternating current motor where the rotor turns due to induced magnetism from its field windings.

Question 10

Torque

Answer 10

A measure of force that can cause an object to rotate about an axis; often applied to the starting power of a motor.

Question 11

Single phase motor

Answer 11

Uses a single-phase power supply to convert electrical energy into mechanical energy; single phase power is a two wire alternating current (AC) circuit. Usually with one power wire or phase wire & one neutral wire, single phase power supplies are most commonly used when the typical loads are heating or lighting.

Question 12

Split phase motor

Answer 12

A type of single phase induction motor with two distinctly different windings, the stator in split phase motor is provided with a start winding & a run winding. Typically used in household appliances such as washing machines, blowers, & small tools.

Question 13

Shaded pole motor

Answer 13

Has a small start windings or shading coils at the corners of each pole that assist the motor by providing an induced current and a rotating field. Used in air conditioners and desk fans/standing fans.

Question 14

Three phase motor

Answer 14

Extremely efficient motors that require no start assist for high-torque applications; they have no start windings or capacitors. Mainly used on commercial equipment, the building’s power supply must have three phase power available.

Question 15

Centrifugal switch

Answer 15

Used to disconnect the start winding from circuit when the motor reaches approximately 75% of the rated speed.

Question 16

Electronic relay

Answer 16

Used with certain motors to open the start windings after the motor has started; a solid-state relay with semiconductors used to stop, start, or modulate power within a circuit.

Question 17

Capacitor start motor

Answer 17

Similar to a split-phase induction motor with two distinctly different windings for starting and running; the capacitor is in series with the start winding which remains in the circuit until the motor reaches up to around 75% of the motor’s rated speed.

Question 18

Capacitor start, capacitor run motor

Answer 18

Similar to a split-phase induction motor, the start capacitor is wired in series with the start windings and disconnects after start-up whilst the run capacitor is wired in parallel with the start windings and stays in the circuit when running.

Question 19

Permanent split capacitor motor (PSC)

Answer 19

A split-phase motor with only a run capacitor. Having very low starting torque, it is the simplest split-phase motor.

Question 20

Leads

Answer 20

Extended surfaces inside a heat exchanger used to enhance the heat transfer qualities of the heat exchanger.

Question 21

Potential relays

Answer 21

A switching device used with single-phase capacitor start, capacitor run motors that need a high starting torque; its main function is to assist in starting the motor.

Question 22

Back electromotive force (BEMF)

Answer 22

Term used for the voltage generating effect of an electric motor’s rotor turning within the motor. BEMF can be measured with a voltmeter across the start winding and opposes line voltage.

Question 23

Pick-up voltage

Answer 23

When the BEMF has generated enough force across the potential relay’s coil in order for the relay’s armature to open the relay contacts between terminal 1 & 2.

Question 24

Drop-out voltage

Answer 24

The voltage at which the relay contacts return to their original closed positions.

Question 25

Continuous coil voltage

Answer 25

The maximum electromotive force that the relay’s coil can withstand “continuously” without overheating and opening the circuit.

Question 26

Current relays

Answer 26

Used on single-phase, fractional horsepower motors that require a low starting torque. An electrical device activated by a change in current flow.

Question 27

Positive temperature coefficient resistor (PTCR)

Answer 27

Compressor starting devices; they are variable resistors that vary their resistance when the surrounding temperature changes. Having a positive temperature coefficient, as their temperature increases so does their resistance & vice versa; as their temperature decreases so does their resistance.

Question 28

Pulse width modulator (PWM)

Answer 28

An electronic device in a motor circuit that is used to control motor speed for variable speed motors. Receives a fixed DC voltage from the converter and then pulses the voltage to the motor. At low speeds, the pulses are short; at high speeds, the pulses are longer.

Question 29

Inverter

Answer 29

The switching or transistor section of the variable frequency drive (VFD) that produces AC voltage at just the right frequency for motor speed control. This section converts the DC voltage back into AC voltage.

Question 30

Switch frequency

Answer 30

The speed at which power devices switch on and off. As switch frequency increases, the resolution and smoothness of the output waveform increases, however, heat in the power device also increases.

Question 31

Carrier frequency

Answer 31

The same as switch frequency.

Question 32

Variable speed motor

Answer 32

A motor controlled by an electronic system to operate and more than one speed.

Question 33

Electronically commutated motor (ECM)

Answer 33

Used for applications involving open-drive fans that are 1 horsepower and smaller. The technology electronically commutes a DC motor, eliminating the need for brushes. Calibrated at the factory in order to suit the piece of equipment.

Question 34

Rectifiers (DC converters)

Answer 34

A special device used to change alternating current (AC) into direct current (DC).

Question 35

Variable frequency drive (VFD)

Answer 35

An electronic device that varies the frequency (hertz) for the purpose of providing a variable speed. Contains three separate sections; their functions and accompanying electronic components are:
*Rectification (diodes) or converter section
*Filtering (capacitors & inductors) or DC bus section
*Switching (transistors) or inverter section