Electro mechanical engineering glossary

Glossary

A range of key electro mechanical engineering terms are defined in our electro mechanical engineering glossary of terms and phrases.

A

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: Output speed of drive can be selected from several preset ranges.

 

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

 

Air Gap: Short gap in the magnetic material forming a magnetic circuit.

 

Alternator: Electromechanical device that converts mechanical energy to electrical energy in the form of alternating current.

 

Ambient Temperature: Temperature of the air in the immediate vicinity of the apparatus or component. Commonly known as room temperature.

 

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

 

Ampere (A): 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.

 

B

Baseline: A measurement taken when a motor is in good operating condition that is used as a reference for monitoring and analysis.

Breakdown torque: The maximum torque that a motor will develop with rated voltage applied at rated frequency without an abrupt drop in speed; also termed pull-out torque or maximum torque.

Brush: A sliding electrical contact, usually rotating.

 

C

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: 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.

 

D

Delta Connection: 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: 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.

 

E

 

Eddy Currents: Localised magnetically induced currents in an iron core.

 

Efficiency: The ratio between useful work performed and the energy expended in producing it. Ratio of output power to input power of a device.

 

Electromotive Force: The force induced in a conductor when it is moved across a magnetic field. (e.m.f.)

 

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

 

F

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 pond-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.

 

Full load speed: The speed at which any motor produces its rated output.

 

Full load torque: The torque required to produce rated power at full load speed.

 

G

Generator: Rotating electric machine used to transform mechanical energy into electric energy.

 

H

Harmonic Content: Difference between alternating quantity and its fundamental component.

 

Hermetic Machine: Air-tight machine protected from the environment.

 

Hertz (Hz): The preferred terminology for cycles per second (frequency)

 

Horsepower (hp): Unit of power. 1hp = 746W. Also, the output rating of motors manufactured off the North American continent.

 

I

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: Nonconducting materials that separate the current carrying parts of a motor from each other or from adjacent conducting material at a different potential.

 

Insulation Class: Temperature capability of insulation materials and systems.

 

Inverter: Converter that changes direct electric current to single-phase or poly-phase alternating currents.

 

L

Lap Winding: Armature winding with each coil of 2 conductors placed in slots 90° apart, connections made in adjacent segments of a commutator.

 

Leakage Current: Electric current in an unwanted conductive path.

 

Locked-rotor current: Steady-state current taken from the line with the rotor at a standstill and at a rated voltage and frequency.

 

Locked-rotor torque: The minimum torque that a motor will develop at a standstill for all angular positions on the rotor with rated voltage applied at rated frequency.

 

Loop Test: Test to detect hot spots due to shorted electrical laminations.

 

M

 

Magnetic Flux Density: Strength of a magnetic field.

 

Motor: A machine which converts electrical energy into mechanical energy.

 

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

 

N

 

Newton: Force required to accelerate a mass of one kilogram at a rate of one meter per second per second.

 

P

Part Winding Start: Starting with only part of the winding energised to reduce starting current.

 

Phase Voltage: Voltage between the two terminals of a phase.

 

Poles: Magnetic poles set up inside a motor by the placement and connection of the 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.

 

R

Random Wound Coil: 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): 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: 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.

 

S

 

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

 

Skew: 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: 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.

 

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. Commonly used to describe the stationary part of a motor that contains the power windings.

 

T

Tolerance: Permitted deviation between the declared value of a quantity and the measured value.

 

Torque: The rotational force produced by a motor. The units of torque are expressed as pound-foot, pound-inch or newton-meter.

 

U

Unbalanced Magnetic Pull: Unequal radial pull on a rotor due to magnetic eccentricities in the air gap.

 

V

Variable Speed Drive (VSD): System for altering the rotational speed of an AC motor by controlling the frequency of the electrical supply.

 

Volt (V): Derived SI unit for electromotive force (e.m.f.)

 

 

W

Watt (W): SI unit of power.

 

Wave Winding: Armature winding with each coil of 2 conductors placed in slots 90° apart, connections made in segments approximately 180° apart on the commutator.

 

Winding Factor: The product of the Pitch Factor and the Distribution Factor. (kp x kd)

 

Y

Yoke: Part of a device, composed of magnetic material and intended to complete a magnetic circuit.