AC = alternating current

ANSI = American National Standards Institute

ASD = adjustable speed drive

BHP = brakehorsepower

CFM = cubic feet per minute

CSA = Canadian Standards Association

CSI = current source inverter

DC = direct current

DSP = digital signal processor

ECC = eddy current coupling

FPM = feet per minute

GPM = gallon per minute

GTO = gate turnoff (thyristor)

HDF = harmonic distortion factor

IGBT = insulated gate bi-thermal thyristor

IEEE = Institute of Electrical and Electronics Engineers

LCI = load-commutated inverter

NEMA = National Electrical Manufacturers Association

NPV = net present value

PAM = pulse amplitude modulation

PLC = programmable logic controller

PWM = pulse width modulated (inverter)

SCR = silicon-controlled rectifier

SR = switched reluctance

THD = total harmonic distortion

V = voltage

VSI = variable source inverter

VVI = variable voltage inverter

**Alternating Current: **The flow of electricity which changes direction on a regular continuous cycle reaching a maximum in one direction, decreasing to zero, then reversing to reach a maximum in the opposite direction.

**Air Gap: **The space between the rotating and stationary part of an electric motor. Magnetic energy is transferred across this gap.

**Ambient: **The air which surrounds a motor for air cooled machines.

**Ampere: **A unit of current which is a measure of the rate of electron flow. It is often abbreviated as Amp. The unit of current flow is the amp.

**Breakdown Torque: **The maximum torque that a motor can develop at rated voltage without stalling or an abrupt drop in speed.

**Brush: **A current carrying material which is in contact with an armature or slip ring assembly to provide an electrical connection between rotating and stationary components of a motor.

**Capacitor: **A device which can store electrical charge. In an AC circuit, a capacitor causes the voltage to lead the current. The unit of capacitance is the Farad.

**Commutator: **An assembly which is mounted on the shaft of a DC motor to provide the switching functions between the armature coils and the power supply.

**Conductor: **Any material which offers little resistance to the flow of electricity such as copper.

**Duty Cycle: **The relationship between the operating time and the resting time of an electric motor.

**Eddy Current: **Localized currents in electrical steels that are caused by alternating magnetic flux resulting in losses and heating.

**Efficiency: **The ratio of mechanical output to the electrical input power of a motor.

**Electromotive Force (emf): **A synonym for voltage usually used to describe induced or generated voltages in an electric circuit.

**Field: **The term used to describe the stationary part of a DC machine. The field provides the magnetic flux which interacts with the armature.

**Flux: **The magnetic field which is established around a current carrying conductor or a permanent magnet.

**Frequency: **The rate at which alternating current reverses its direction of flow. The unit of frequency is either Hertz or cycles per second.

**Full Load Current: **The current that a motor draws at rated voltage, frequency and load.

**Full Load Slip: **The difference between the synchronous speed of a motor and full load speed. It is often expressed as a ratio of the synchronous speed to full load speed in percent.

**Full Load Speed: **The speed of the motor at rated voltage, frequency and load.

**Full Load Torque: **The torque that is necessary to produce rated horsepower at full load speed.

**Horsepower: **A measurement of power used to rate electric motors. The unit of power rating in motors is either horsepower or kilowatts. One horsepower is equal to 746 watts.

**Impedance: **The total opposition a circuit offers to the flow of alternating current. It is the vector sum of resistance and reactance.

**Inductance: **The property of an electrical circuit which opposes a change in current due to the magnetic field induced by that current.

**Inertia: **Inertia is the resistance an object has to a change in its state of motion. It is determined by the weight of the object multiplied by the square of the radius of gyration (k). Rotating parts do not operate at the same speed, therefore calculating the inertia for each moving part allows rotating parts to be considered as a single unit working together.

**Line Voltage: **The voltage supplied to the input terminals of an electric device.

**Magnetomotive Force (mmf): **The magnetic energy supplied in the establishment of magnetic flux. It is analogous to the electromotive force in an electric circuit.

**Phase: **A term used to describe the spatial relationship of windings in an electric motor or voltages and currents in an electric circuit.

**Power Factor: **A measurement of the difference in phase between voltage and current in an electric circuit. Most electrical devices cause the current to lag the voltage because of inductance. The voltage leads the current in capacitive circuits.

**Reactance (inductive): **The property of a magnetic circuit which causes the voltage to lag the current.

**Resistance: **The property of an electrical conductor which impedes the flow of electricity. The unit of resistance is the ohm.

**Rotor: **The rotating member of an electric motor.

**Service Factor: **The service factor of an AC motor is a multiplier which when applied to the rated horsepower indicates the permissible loading which may be carried under the conditions specified for the service factor.

**Slip: **The ratio between the synchronous speed and the operating speed of an induction motor, often expressed as a percent.

**Stator: **The stationary part of an AC motor housing the steel laminations and the windings.

**Temperature Rise: **The difference between the temperature of the windings of an operating motor and the ambient temperature.

**Torque: **The turning force applied to a shaft, usually expressed as pound-feet (English) or Newton-meters (metric).

**Voltage: **The standard unit of electromotive force which produces a flow of current in a conductor. The unit of electromotive force is the volt.

**Watt: **A measurement of power in an electrical circuit which is equal to one joule of energy being expended in one second.