HART 1341 Chapter 15 Study Guide

Common Single-Phase Motors (5)

1) Split phase 2) Capacitor-start, induction-run (CSIR) 3) Capacitor-start, capacitor-run (CSCR) 4) Permanent split-capacitor (PSC) 5) Shaded pole motor

Two types of Stator Windings

1) Start windings 2) Run windings

Motor Speed Variables (2)

1) The alternating current's frequency (measured in Hz) 2) Number of magnetic field poles in the stator.

Variable Frequency Drive (VFD)

A control circuit that modifies the signal produced to the desired level of oscillation. Controls the speed of a motor by using inverter and rectifier circuits to change the frequency of the current supplied to the motor.

Hermetic Compressor

A motor and compressor that are totally sealed by being welded in a container.

Locked Rotors

A motor can quickly burn out when the rotor cannot turn or is locked. This may occur due to a motor having to start under heavy load or mechanical interference.

Dual-Voltage Motor

A motor that has its stator windings arranged in pairs so that it can be used with two different voltages.

Single-Phase Motor

An AC motor that runs on a single phase of alternating current. Most rated at 120V, 208V, or 240V. For many of these motors, the rotation direction can be changed by reversing the connections to the start wiring.

Centrifugal Switch

An electrical device mounted on the end of a motor shaft that disconnects the start windings from the circuit.

Three-Phase Motor

An induction motor that has three sets of stator windings energized by a three-phase power signal.

Constant Speed Relationship

Applied voltage Counter EMF Current

Field Poles

Are electromagnets whose polarities change as the flow of current alternates in the field windings.

Field Windings

Are the wires wrapped around the field poles of the Stator.

Motors not 100% efficient (Why?)

Because of clearances, bearing friction, and imperfect windings. While larger motors operating at a certain voltage may be up to 97% efficient, the efficiency of smaller motors at the same voltage is often only 50% to 60%.

Capacitors

Cause capacitive reactance in a circuit, which is the opposition to the flow of current that causes voltage to lag behind current in an AC cycle.

Motor Induction

Causes inductive reactance, which is the opposition to the flow of current that causes current to lag behind voltage in an AC cycle.

Single-Phase Motor Terminals

Common Terminal (C) Starting Terminal (S) Running Terminal (R)

Rated Full Load Amperage (FLA)

Current level at which full load torque and horsepower are reached.

Slip

Difference between synchronous speed and rated full load speed, generally, motor slip is between 4% and 5% of synchronous speed.

Problems of Motors Starting under heavy load

Examples include motors connected to fans with worn bearings, which cause excessive strain on the motor, and compressors pumping against excessively high head pressure.

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Frequency

Motors Differ

From each other by the amount of starting torque and running torque that they generate.

AC Motor

HVACR motors that runs on alternating current.

Open Drive Compressor

Has a motor that drives its crankcase by using a belt that connects the motor to the compressor.

Squirrel Cage

Has metal bars mounted on an iron core and connected at each end of the rotor to form a complete circuit.

Three-Phase Power

Has three separate voltage signals alternating in three separate phases.

Motors with More Poles

Have less RPM's and vice versa

Phase-Splitting

How single-phase motors are started, which create a rotating magnetic field in the stator, causing the rotor to start turning.

Time Rating

Indicates whether or not a motor is designed for continuous duty.

Unloader

Is a device that can be used to reduce a compressor's load on start-up or for capacity control.

Capacitor-Start, Capacitor-Run (CSCR) Motor

Is a single-phase induction motor that has a start capacitor and a run capacitor wired in series with the start winding, but the run capacitor is wired in parallel with the start capacitor. The current through the run winding is out of phase with the current in the start winding due to the start and run capacitors. Thus produces a high starting torque.

Capacitor-Start, Induction Run (CSIR) Motor

Is a single-phase induction motor that has a start capacitor wired in series with the start windings. The start capacitor puts the current in the start winding out of phase with the current in the run winding. Usually used in hermetic compressors and refrigeration units.

Permanent Split-Capacitor (PSC) Motor

Is a single-phase induction motor that uses a single run capacitor in series with the start winding for the motor's entire operation.

Stator (Windings)

Is the stationary part of the motor that is attached to the inside of the motor housing. ( Field poles and field windings, wrapped around stator)

Torque

Is the work performed by a twisting or turning action, such as a rotating motor shaft.

Run Capacitor (oil filled)

It remains in the circuit while the motor is running. Provides a signal that is out of phase for added torque.

Frame Size

Letter and number designation for the physical dimensions of the motor.

NEMA Design Letter

Letter designation based on LRA, torque and slip.

Locked Rotor Amperage (LRA)

Locked rotor amperage (LRA) current that the motor draws as power is first applied to start turning the motor.

Shaded-Pole Motor

Low-torque single-phase motor that uses shaded field poles, instead of a start winding, to produce starting torque. Popular small motor, especially for small fans.

Rated Ambient Temperature

Maximum ambient temperature at which the motor can operate

Insulation Class

Maximum temperature that the insulation of the windings can withstand before they breakdown.

Motor Efficiency

Mechanical energy produced by the motor shaft divided by the power input to the motor.

Less Static Pressure

More air flow

Rated Full Load Speed

Motor operating speed at full load.

Motor Terminal Box

Mounted on the outside of the frame where electrical connections are made to control and power the motor.

Motor Nameplate

Mounted on the outside of the frame, which displays essential motor information.

Manufactures Name

Name, address to order parts

NEMA

National Electrical Manufacturers Association

P

Number of poles

Common Terminal

On a hermetic compressor connects to a single line that joins one end of the start winding to one end of the run winding.

Run Terminal

On a hermetic compressor connects to the end of the run winding, opposite the end connected to the common terminal.

Start Terminal

On a hermetic compressor connects to the end of the start winding, opposite the end connected to the common terminal.

Induction Motor

Operate by using the magnetic field generated in the stator to induce current in the rotor.

HVAC Motor Applications

Operating compressors, fans, pumps and dampers.

End Bells

Or Plates, close the openings of either end of the motor frame. They hold the bearings and support the rotor.

HVAC Fan Motors Used In

Outdoor unit (condenser) Indoor unit air handler (evaporator)

Service Factor

Overload capacity or overload horsepower, at which a motor can operate without overheating or being damaged. (HP X Service factor= Motor overload horsepower.

Electronically Commutated Motors (ECM)

Programmable, brushless DC motor that uses an electronic control module to control voltage to the stator windings. Rotor made of permanent magnets instead of coils of wire or metal bars. Include quiet operation, variable speeds, compact design, efficient performance,and durability.

Standard Motor Data Specifications

Rated Voltage Manufacturers Name Rated Volts Full-Load Amperage (FLA) Frequency (Hz) Phase Rated Full-Load Speed (RPM) Rated Horsepower (Hp) Insulation Class Rated Ambient Temperature Time Rating (Continuous or Intermittent) Locked Rotor Letter (LRA) NEMA Design Letter Inherent Motor Protection Condensation Prevention Heater Specifications Service Factor Frame Size Full-Load Efficiency Guaranteed Minimum Efficiency Power Factor

Rated Volts

Recommended voltage supply

Inductive and Capacitive Reactance

Resists the flow of alternating current in a circuit, causing an alternating current and its voltage to cycle out of phase

Electric Motor Components

Rotor and Stator

Split-phase Motor

Single-phase induction motor in which the power is split between the start and run windings of the motor. Operate in a fractional horsepower range, such as fans and compressors in capillary tube systems.

Synchronous Speed

Speed of the rotating magnetic field in the stator.

Rated Full-Load Speed (RPM)

Speed under full-load when both the rated voltage and frequency are supplied.

Two types of capacitors

Start and run

Start Windings

Stator windings that are used for motor starting and additional torque. Smaller diameter wire and has more turns, more resistance.

Rotor "Catch Up"

The attraction of unlike poles and repulsion of like poles causes the rotor to rotate as it tries to "catch up" to the changing magnetic polarities of the stator.

Rotor

The axle mounted unit that rotates as the polarities of the stator's field position change. The rotor can also be called the armature.

Squirrel Cage Rotor

The bars that connect at each end of the rotor to form a complete circuit.

Locked Rotor Code

The letter that indicates a motor's locked rotor amperage (LRA)

Counter Electromotive Force (CEMF)

The oppositely polarized voltage induced by the rotor's magnetic field.

Motor Operation Based On

The principles of electricity and magnetism.

Induction

The process of generating electromotive force using a magnetic field.

Built-up Terminals

These bolt to the compressor dome.

Inherent Motor Protection

This is provided by internal protection such as snap-disc or a thermistor. Thermally protected and impedance protected.

Full-Load Efficiency

This percentage represents how efficiently a motor converts electrical power into mechanical power.

Power Factor

This the ratio of apparent power to true power under full load conditions.

Start Capacitor (dry electrolytic)

Used only during motor start up, provides additional phase shift to the start winding and are designed to be in the circuit for only a few seconds.

Rated Horsepower (hp)

Value indicating the amount of mechanical work that a motor can perform based on both motor speed and torque.

Rated Voltage

Voltage to which OPERATING and PERFORMANCE characteristics are referred

Electromagnetic Field

When current from a power source flows through the field windings, it creates an electromagnetic field around the poles.

Run Windings

Windings that are energized during the entire operation of the motor. They provide the bulk of the magnetic force for driving the rotor. Larger diameter wire and has less turns, less resistance.