AC Motor Applications 322

AC

Alternating current. Electricity that regularly reverses the direction of its flow. AC switches direction 60 times per second, or 60 hertz (Hz), in the US.

alternating current

AC. Electricity that regularly reverses the direction of its flow. Alternating current switches direction 60 times per second, or 60 hertz (Hz), in the US.

bearing

A friction-reducing device that allows one moving part to glide past or rotate within another moving part. Bearings operate using a sliding or rolling mechanism.

brushes

A sliding electrical contact used to transfer external power to a motor's rotor. Brushes supply power to the slip rings of a wound rotor.

capacitor

An electrical device that stores energy and releases it when needed. A capacitor increases the torque a single-phase motor can provide.

capacitor motor

A single-phase motor that includes a running winding, a starting winding, and a capacitor. Capacitor motors provide more torque than other single-phase motors.

capacitor start-and-run motor

A single-phase motor that uses two capacitors, one for starting and one for operation. A capacitor-start-and-run motor's starting capacitor disconnects along with the starting winding, but its running capacitor remains in the circuit during operation.

capacitor-run motor

A single-phase motor that has a capacitor and starting winding connected in series at all times. A capacitor-run motor has high running torque because the capacitor stays connected during operation.

capacitor-start motor

A single-phase motor that uses a capacitor wired in series with the starting winding to start. A capacitor-start motor also has a centrifugal switch to disconnect the starting winding and capacitor.

centrifugal switch

A control device that uses the force created by the rotating shaft of a motor to open and close. Centrifugal switches are used to disconnect starting windings in single-phase motors.

constant speed motors

A motor that maintains a steady speed from no load to full load. Many constant speed motors have squirrel cage rotors.

DC

Direct current. Electricity that flows in one direction. DC does not reverse the direction of flow.

digital multimeter

DMM. A device that can measure voltage, current, and resistance. A digital multimeter is the most versatile and common meter used today for electrical maintenance.

direct current

DC. Electricity that flows in one direction. Direct current does not reverse the direction of flow.

dual-voltage motor

A three-phase motor that can operate on two different voltage levels. Dual-voltage motors are more expensive than single-voltage motors, but they are also more popular.

eddy current loss

An efficiency loss caused by heat generated by circulating currents. Eddy current loss affects squirrel cage motors because eddy currents form in their metal bars.

eddy currents

Swirling currents induced in solid metals by changes in the magnetic environment. Eddy currents lead to efficiency losses in motors.

efficiency loss

The reduction of energy due to natural effects that cause the energy output to be less than the energy input. Efficiency losses can be minimized with good design, but no system is 100% efficient.

electric motors

A machine that converts electricity into mechanical energy or motion. Electric motors operate on the principle of magnetic induction.

endbell

The cap at the end of an AC motor. The endbell houses the rotor bearing.

grounded

Safely connected to a neutral body that can absorb stray electrical currents. Grounded motors and circuits reduce the risk of injury and damage.

horsepower

hp. A unit used to measure power in large electrical devices such as motors. One horsepower equals 33,000 foot-pounds (ft-lb.) (44,748 joules) of work per minute, or 746 watts.

housing

A protective cover designed to contain or support a component such as an electric motor. The housing of a motor contains the stator, rotor, and windings.

hp

Horsepower. A unit used to measure power in large electrical devices such as motors. One hp equals 33,000 foot-pounds (ft-lb.) (44,748 joules) of work per minute, or 746 watts.

induction motor

An AC motor in which the stator generates a magnetic field that energizes the rotor. Induction motors are self-starting and are the most commonly used AC motors.

laminations

Thin sheets of metal sealed together to form a conductive core. Laminations are stacked together in a cylinder to form a squirrel cage rotor.

lubricant

A substance used to reduce friction between components. Common industrial lubricants include oil and grease.

lubrication

The act of applying lubricant to machines. Lubrication reduces friction and wear in mechanical components such as bearings.

magnetic field

The area in and around a magnet in which a magnetic force exists. Magnetic fields exhibit the powers of attraction and repulsion.

magnetic induction

The use of magnets to cause voltage in a conductor. Magnetic induction occurs whenever a conductor passes through magnetic lines of flux.

motor nameplate

A label attached to a motor that displays important ratings and information, as determined by the manufacturer. Motor nameplates include information like voltage and current ratings.

output shaft

The rotating part of a motor that transmits torque to the load. The output shaft turns loads such as pumps, circular saws, and drill presses.

parallel

An electrical route that has multiple paths. The running and starting windings in a single-phase motor connect in parallel.

phase displacement

The separation of the electrical phases in a motor. Phase displacement creates a rotating magnetic field that causes the rotor to rotate.

pole pieces

A metallic object used to create a magnetic field inside a motor. Pole pieces are used with windings to form electromagnets.

reactance

The resistance to the flow of alternating current due to inductance. Reactance affects the rate of current flow.

resistance

The opposition to current flow. Resistance is measured in ohms (Ω).

rotor

The rotating part of a motor. The rotor connects to an output shaft that drives the load.

running winding

A coil of wire in the stator of single-phase motor that receives the current that allows the motor to operate. Running windings consist of heavy, insulated copper wire.

series

An electrical route that has only one path. Connecting resistance in series with a circuit decreases the current.

series

An electrical route that has only one path. The capacitor connects to the starting winding of a capacitor motor in series.

shaded pole

A stator pole that has a single turn of copper wire wrapped around it. The shaded pole creates phase displacement to start the motor.

shaded-pole motor

A single-phase motor that has a turn of copper wire on one section of each stator pole to create phase displacement and start the motor. Shaded-pole motors produce 1/20 hp or less and are used in devices requiring low torque.

single-phase

1ϕ. Alternating current power that consists of only one voltage. Single-phase power is used for simple residential applications.

single-phase motor

An AC motor that operates on power that has only one voltage. Single-phase motors are often used in residential appliances like washing machines and air conditioners.

single-voltage motor

A three-phase motor that requires a single specific voltage level to operate. Single-voltage motors are less expensive than dual-voltage motors.

slip

The difference between the synchronous speed and the rotor speed of an induction motor. Slip is used to calculate the speed regulation of induction motors.

slip rings

A conductive device attached to the end of a rotor that receives current from an external source. Slips rings receive power from brushes and are used in wound rotor motors.

speed control

The external means of changing a motor's speed. Speed control is easier to accomplish on DC motors than AC motors.

speed regulation

The ability of a motor to maintain its speed when a load is applied. Speed regulation compares a motor's no-load speed to its full-load speed.

split-phase motor

A single-phase motor that includes a running winding, a starting winding, and a centrifugal switch. A split-phase motor uses phase displacement caused by the difference in reactance of the two windings to start.

squirrel cage rotor

A three-phase AC rotor that consists of metal bars connected by rings at each end. Squirrel cage rotors provide constant speed and are the most common AC rotor type.

starting winding

A coil of wire in the stator of a single-phase motor that receives the current used to start the motor. Starting windings consist of fine, insulated copper wire and disconnect after the motor starts.

stator

The stationary part of a motor. The stator houses the motor's rotor and windings.

step down

To decrease the voltage of electrical current with a transformer. Voltages are usually stepped down before entering facilities.

step up

To increase the voltage of electrical current with a transformer. Voltages are usually stepped up before traveling long distances.

synchronous motor

A constant-speed AC motor that requires external DC excitation to energize the rotor. A synchronous motor does not use induction to operate.

synchronous speed

The speed of the rotating magnetic field of an AC induction motor. Synchronous speed is always faster than the speed at which the rotor turns.

thermal switch

A control device that opens or closes a circuit when it detects certain temperatures. Thermal switches are often used to prevent overheating in split-phase motors.

three-phase

3ϕ. Alternating current power that consists of three overlapping voltages. Three-phase power is used for all large AC motors and is the standard power supply that enters homes and factories.

three-phase motor

An AC motor that operates on power with a continuous series of three overlapping AC voltages. Three-phase motors are used for all large AC motor applications.

torque

A force that produces rotation. Torque is measured in pound-feet (lb-ft.) in the English system and Newton-meters (N-m) in the metric system.

transformer

An electromagnetic device that increases and/or decreases the voltage of electrical power. Transformers often increase voltage in power lines and then decrease voltage for the power to enter a facility.

voltage

The electrical pressure or potential that pushes current through a conductor. Voltage is measured in volts (V) and is also called electromotive force.

wear

The gradual removal of material on a surface caused by contact and friction. Wear is typically caused by two or more objects rubbing or sliding against each other.

windings

Wire that is wrapped around a core or into a coil and used to conduct current. Windings connect to pole pieces to form electromagnets and magnetic fields in motors.

wound rotor

A three-phase AC rotor that consists of many windings that connect to slip rings on the shaft. Wound rotors provide high startup torque and variable speed.