Engineering vocabulary

A comprehensive vocabulary list of 102 terms related to electrical machines, AC/DC circuits, and magnetic systems.

Actuator

A device that creates mechanical motion by converting various forms of energy to rotating or linear mechanical energy.

Active power ($P$)

Real power in an AC circuit measured in Watts ($W$).

Adjustable Speed Drive

A drive where the output speed can be selected from several preset ranges.

Aging

The reduction of insulation life due to thermal, voltage and other stress.

Air Gap

A short gap in the magnetic material forming a magnetic circuit.

Alternator

An electromechanical device that converts mechanical energy to electrical energy in the form of alternating current.

Ambient Temperature

The temperature of the air in the immediate vicinity of the apparatus or component.

Amortisseur Winding

Embedded windings in the field poles of synchronous machines to aid starting and / or dampen rotor oscillations.

Ampere ($A$)

The SI base unit of electric current.

Apparent Power ($S$)

Measured in volt-amperes ($VA$) in an AC circuit.

Armature

The part of a machine which receives or delivers active power to the external electrical system.

Asynchronous Machine

An AC machine in which the speed on load and the frequency of the system to which it is connected are not in a constant ratio.

American Wire Gauge

A standardised wire gauge system used predominantly in the USA.

Brush

A sliding electrical contact, usually rotating.

Capacitance

The amount of electrical energy stored for a given electric potential.

Chord or Pitch Factor ($kp$)

The factor by which short pitching a coil reduces the back e.m.f.

Cogging Torque

Magnetic interaction between stator and rotor resulting in undesired machine operation such as jerkiness.

Coil

A set of series connected turns.

Coil Pitch or Span

The number of tooth pitches which separate the slots in which the two sides of a coil are placed.

Commutation

Change-over switching in a periodic and automatic manner without interruption of the electric current.

Commutator

An assembly of insulated conducting segments connected to the rotating armature winding.

Concentric Winding

A distributed winding in which the individual coils of each phase group per pole are concentric and have different coil spans.

Conductor

A material which contains movable electrical charges.

Core Loss

The electrical losses in a machine caused by the magnetisation of the core iron.

Critical Speed

The rotating speed at which resonance occurs.

Delta Connection

Connection where the 3 phases are connected in series to form a closed circuit.

Direct Current Machine

A machine incorporating an armature winding connected via a commutator to a direct current system.

Distribution Factor ($kd$)

Ratio of the actual voltage of a phase band to the arithmetic sum of the individual coil voltages.

Dhalander Connection

A pole-changing winding giving a rotational speed ratio of $2:1$.

Duplex winding

An armature winding in which the coil ends are connected to alternate commutator segments.

Duty Cycle

A specified sequence of operating conditions.

Eddy Currents

Localised magnetically induced currents in an iron core.

Efficiency

The ratio of output power to input power of a device.

Electromotive Force (e.m.f.)

The force induced in a conductor when it is moved across a magnetic field.

Exciter

A source of the power to the field winding of an electrical machine.

Foot-Pound (energy)

The energy transferred on applying a force of $1$ pound-force ($lbf$) through a displacement of $1$ foot.

Foot-Pound (torque)

The torque created by one pound-force ($lbf$) acting at a perpendicular distance of one foot from a pivot point.

Form Wound Coil

Coil of square or rectangular insulated magnet wire preformed to fit into winding slots.

Form Factor

Ratio of the root-mean-square value of an alternating quantity to its rectified value.

Generator

A rotating electric machine used to transform mechanical energy into electric energy.

Harmonic Content

The difference between an alternating quantity and its fundamental component.

Hermetic Machine

An air-tight machine protected from the environment.

Hertz ($Hz$)

SI derived unit for frequency defined as the number of cycles per second of a periodic function.

Horsepower ($hp$)

A unit of power where $1hp = 746W$.

Impedance

The ratio of the voltage to the electric current; a measure of opposition to time-varying electric current in an electric circuit.

Inductance

Property in an electric circuit where a change in the current induces an electromotive force that opposes the change in current.

Induction Motor

An AC motor where power is supplied to the rotor by magnetic induction.

Induction Generator

An induction machine, connected to a reactive power source, working as a generator.

Insulation

The materials and parts used to insulate conductive elements of a machine.

Insulation Class

The temperature capability of insulation materials and systems.

Inverter

A converter that changes direct electric current to single-phase or poly-phase alternating currents.

Lap Winding

Armature winding with each coil of 2 conductors placed in slots $90^{\circ}$ apart, with connections made in adjacent segments of a commutator.

Leakage Current

Electric current in an unwanted conductive path.

Loop Test

A test to detect hot spots due to shorted electrical laminations.

Magnetic Flux Density

The strength of a magnetic field.

Magnetomotive Force (m.m.f.)

The physical force that produces magnetic flux.

Motor

A machine which converts electrical energy into mechanical energy.

Mush Coil

A wound coil where the conductors occupy random positions in the slot.

Newton

The force required to accelerate a mass of one kilogram at a rate of $1\,m/s^2$.

PAM winding

Pole Amplitude Modulation winding with connections giving speed combinations other than $2:1$.

Part Winding Start

Starting with only part of the winding energised to reduce starting current.

Phase Voltage

The voltage between the two terminals of a phase.

Poles

Magnetic poles created in a machine by windings.

Pole Pitch

The distance between two consecutive poles, usually expressed as a number of tooth pitches.

Power

The rate at which work is performed.

Power Factor

Ratio of the absolute value of the active power $P$ to the apparent power $S$.

Random Wound Coil

A coil where the conductors occupy random positions in the slot.

Rated Temperature Rise

The permitted rise in operating temperature above ambient when running on load.

Reactance

The resistance to AC current due to capacitance or inductance.

Reactive Power ($Q$)

Power measured in var in an AC circuit.

Regeneration

Operation of a motor in a generator mode to feed energy back into the power supply.

Regulation

The amount of speed or voltage change due to load variations.

Reluctance

The 'resistance' of a magnetic circuit.

Resistance

Defined as the ratio of voltage to current.

Rotor

The rotating part of an electrical machine.

Salient Pole

A field pole which projects from the yoke or hub towards the air-gap.

Secondary Winding

A winding in an electrical machine which is not connected to the external electrical system.

Series Excitation

A DC machine with field coils connected in series with the armature.

Service Factor

The factor by which the rated power can be increased under specified conditions of service.

Shaft Currents

Induced circulating currents due to machine asymmetries or supply voltage effects.

Shunt Excitation

A DC machine with field coils connected in parallel with the armature.

Skew

The non-parallel stator and rotor slot alignment.

Slip

The difference between the synchronous speed and the actual speed of a rotor expressed as per unit or as a percentage of the synchronous speed.

Slot

A recess in a core in which the conductors of a winding may be placed.

Squirrel Cage

A rotor winding consisting of a number of conducting bars with their ends connected by conducting rings.

Space Factor

The ratio of the area of bare insulated copper conductors to the available slot area.

Star Delta Starting

A delta wound motor connected in star during starting to reduce inrush current.

Synchronous Machine

An AC machine in which the frequency of the generated voltages and the speed of the machine are in a constant ratio.

Full load Speed

The machine speed at rated load.

Synchronous Speed

The speed of magnetic field rotation determined by the supply frequency and the number of poles.

Stator

The stationary portion of a machine.

Tolerance

The permitted deviation between the declared value of a quantity and the measured value.

Torque

The rotational force produced by a motor.

Breakdown Torque

The maximum torque an AC motor will develop.

Full Load Torque

The torque the rated load demands on the shaft end of a motor.

Unbalanced Magnetic Pull

Unequal radial pull on a rotor due to magnetic eccentricities in the air gap.

Variable Speed Drive (VSD)

A system for altering the rotational speed of an AC motor by controlling the frequency of the electrical supply.

Volt ($V$)

The derived SI unit for electromotive force (e.m.f.).

Watt ($W$)

The SI unit of power.

Wave Winding

Armature winding with each coil of 2 conductors placed in slots $90^{\circ}$ apart, with connections made in segments approximately $180^{\circ}$ apart on the commutator.