Electrical Terminology

Alternator – A synchronous rotating AC machine used to change mechanical power into electrical power (alternating current – AC).

A.C. – AC Alternating current (AC) is an electric current whose direction reverses cyclically, as opposed to direct current, whose direction remains constant. The usual waveform of an AC power circuit is a sine wave, as this results in the most efficient transmission of energy.

Ambient Temperature – Ambient temperature is the temperature of water, air or surrounding medium where the equipment is used or stored.

Ampere – The standard unit of electrical current. Measure in Amps

Asynchronous speed – The speed of an AC induction motor at full load and full voltage, also defined as the rated speed.

Bearing – A component used to reduce the friction and wear between rotating devices.

By-pass – A by-pass contactor is used to by-pass another device, for example a softstarter to reduce the power loss.

Capacitor – (or condenser) A multi purpose device that can store electrical charge in the form of an electrical field. It is used for example for power factor correction in (inductive) AC circuits. Capacitors are used to buffer electricity (smooth out peaks) and to guard against momentary voltage losses in circuits (see also capacitance).

Capacitor bank – A number of capacitors connected in series or parallel, commonly used in variable speed drives.

Circuit breaker – Devices that interrupt high currents to protect electrical equipment from damage caused by current surges, for example from a short circuit.

CSA – Canadian Standard Association

Current limit – An electronic method to limit the starting current to the motor during start up. It is normally possible to adjust the function so that the motor torque will be high enough to take off.

Cycle – A sequence of operations that is repeated regularly or the time it takes to complete one operation.

DC Direct current – The power supply available from batteries, generators (not alternators), or a rectified source used for special purpose applications

DC Drive – A combination of power and control electronics that connects between electrical supply and DC motor to allow variable speed control.

IP Degree of Protection – Defined and stated as IP (International Protection) class indicating the degree of protection against contact and penetration of solid objects and water.

Delta Connection – A three-phase winding connection in which the phases are connected in series to form a closed circuit.

Derating – When a device has to be operated with reduced ratings (normally the current) due to high ambient temperature or high altitude.

D-end – The end that is normally the drive end of an electrical motor.

D.O.L – Direct-on-line

Duty Cycle – The total cycle from one start to the next, including ramp time for start and stop, operation and pause time, if any.

Dynamic Brake Unit – A control unit generally fitted to an AC inverter that allows excess regenerative energy from the controlled AC motor to be “dumped” on to a resistive element.

ECA – Enhanced Capital Allowances, UK , which allows the full cost of an investment in designated energy-saving plant and machinery to be written off against the taxable profits of the period in which the investment is made. The general rate of capital allowances for spending on plant and machinery is 20% a year on the reducing balance basis.

Efficiency – The ratio between mechanical output and electrical input. The percentage given indicates how effective the motor is at converting electrical energy to mechanical energy.

Energy efficiency – Defined as output energy divided by input energy, and if necessary averaged over time. The electrical efficiency of an appliance is defined as the amount of that energy that is converted into a useful form, divided by the total energy it draws.

EMF – Electromotive Force, another term for voltage or potential difference, for example the voltage generated by a motor.

EPD – Environmental Product Declaration, a description of how a specific product affects the environment.

ESD – Electro Static Discharge.

Fault – Any malfunction that occur and interferes with normal operation.

Flywheel mass – The total mass (mD2 or GD2) of a rotating body normally given in kpm2 or kgm2. The value of the flywheel mass is 4 times the moment of inertia.

Frequency – The number of cycles in a time period (usually one second). Alternating current frequency is expressed in cycles per second, termed Hertz (Hz).

Full-Load Current – The current required for any electrical machine to produce its rated output or perform its rated function.

Gate – The control element of an SCR (thyristor).When giving a small positive voltage to the SCR it will start conducting.

Generator – A device that converts rotating mechanical movement into electric power. The current generated can be either alternating (AC) or direct (DC). In a simple AC generator, a loop of wire is placed between the poles of a permanent magnet. The magnet is then rotated and the electromotive force produced by the movement of the electric field causes a current to flow in the wire. This is the principle of the synchronous motor and big generators in power plants. A DC generator operates on the same principle as the AC generator, but includes a commutator, which effectively prevents the current from alternating.

Harmonic – A multiple of the fundamental electrical frequency. Harmonics are present whenever the electrical power waveforms (voltage and current) are not pure sine waves.

Heat Sink – A component often made of aluminium used to get rid of the heat inside an electrical device generated by the current.

Heavy Duty Start – A start with a load that has a high or very high moment of inertia. A starting time D.O.L. of more then 5 seconds can be defined as a heavy-duty start.

Hertz (HZ) – The preferred terminology for cycles per second (frequency).

High-current transients – Short spikes of high electrical current in a grid, caused by lightning strikes, or rapid switching of electrical devices in the grid, especially capacitors. These transients, or surges, cause cables to overheat, potentially damaging insulation and leading to short circuits. Equipment can be protected from high-current transients by using a surge protector.

High load torque – The braking torque on the motor shaft caused by the load. If the braking torque is equal or nearly equal to the rated motor torque it can be defined as high load torque.

Horsepower – A unit for measuring the power of motors or the rate of doing work. One horsepower equals 33,000 foot-pounds of work per minute (550 ft-lbs per second) or 746 watts.

IEC – International Electro technical Commission which is part of the International Standard Organisation.

Induction motor – An AC motor with a primary winding (usually the stator) connected to the power supply and a secondary winding (usually the rotor) carrying the induced current.

Inertia – A measure of a body’s resistance to change in velocity whether the body is moving at a constant speed or is at rest. The velocity can be rotational or linear.

In-Line connection – A connection type where the devices in the main supply are connected in series with each other.

Inside Delta connection – A connection type where the devices are connected inside the motor delta circuit. The current is reduced to 1/√3 = 58% compared to the line current.

Insulation – Non-conducting materials separating the current-carrying parts of an electric machine from each other or from adjacent conducting material at a different potential.

Insulation Class – A letter or number that designates the temperature rating of an insulation material or system with respect to thermal endurance.

Integrated Circuit (IC) – A small electronic unit that can consist of thousands of transistors usually mounted on a PCB.

Intermitens factor – The relation between how long a machinery is working (ON time) and how long it is resting (OFF time) in a cycle.

Inverter – A combination of power and control electronics that connects between electrical supply and AC motor to allow variable speed control.

IP Code – Ingress Protection code, an alphanumeric code defining the water and or dust withstand ability of a piece of equipment or machine.

ISO 9001 – International standards for quality assurance set by the International Standards Organization.

ISO 14001 – International standards for environmental management systems set by the International Standards Organization.

ISO 18001 – International Safety management systems set by the International Standards Organization.

Jog – Momentary moving of the motor by repetitive closure of a circuit using a contact element or a pushbutton.

Kilowatt – A unit of electrical power. Also, the output rating of motors manufactured and used off the North American continent.

LCA – Life Cycle Assessment, an analysis of how a product affects the environment from ”cradle to grave”.

LCD – Liquid Crystal Display, a readout interface used in digital watches and laptop computers.

LED – Light-emitting diode.

Locked Rotor Current – The current taken from the line when a rotor is at a standstill at rated voltage and frequency.It is the on line current when starting the motor direct.

Maximum Torque – The maximum torque that an AC motor will develop with rated voltage applied at rated frequency without an abrupt drop in speed. Also termed pullout torque.

Locked-Rotor Torque – The minimum torque that a motor will develop at standstill for all angular positions of the rotor, with rated voltage applied at rated frequency.

Megger Test – This is normally measured in megohms using full voltage with low current and is used to measure the resistance in an insulation system. It can be used for checking the thyristors, for example.

Micro processor – A central processing unit utilising large-scale integration technology.

MCCB – Moulded Case Circuit Breaker

MMS – Manual Motor Starter

Motor – A rotating machine that converts electrical power (either alternating current or direct current) into mechanical power.

N-end – The end that is normally the non-drive end of an electrical motor.

NEMA – The National Electrical Manufacturers Association (USA)

Network – A number of nodes connected to each other with some type of communication medium. A network can be of single link type or multiple link type.

Newton-Meter (Nm) – Unit of torque, in the metric system, that is a force of one Newton, applied at a radius of one meter and in a direction perpendicular to the radius arm.

Noise – Unwanted disturbances in a communication medium that tend to obscure the data content.

Normally Closed Contact – A contact or set of contacts that are closed when (NC) the relay or switch is de-energised. The contact(s) open when a relay or switch is energised.

Normally Open Contact – A contact or set of contacts that are open when (NO) the relay or switch is de-energised. The contact(s) close when the relay or switch is energised.

Normal Start – A start with a load that has small or medium high moment of inertia. A starting time D.O.L. of less then 5 seconds can be defined as normal start.

Ohm – Unit of electrical resistance. If a 10-volt source is connected to a wire with a resistance of 10-ohm, then 1-ampere of electrical current will flow.

Overload relay – A device used to avoid overheating of the motor. Can be of electronic or thermal type.

Parallel – Electrical components that are connected in such a way that the flow of electricity can take multiple, or parallel, paths through the circuit are said to be connected “in parallel”. If one of the components in a parallel circuit was to fail, the electricity would continue to flow through an alternative path.

Parallel start – Parallel start of motors is normally when two or more motors are started at the same time with the same starting equipment.

PCB – Printed Circuit Board.

PLC – Programmable Logic Controller, consists of a central processor, input/output interfaces and a memory designed as an industrial control system. A PLC system is used for the storage of instructions, timing, counting, report generation I/O control and more.

Poles – The magnetic poles set up inside an electric machine by the placement and connection of the windings.

Power – Work done per unit of time measured in horsepower (HP) or watt (W).

Power Factor – The ratio of the actual electrical power dissipated by an AC circuit to the product of the r.m.s. values of current and voltage. The difference between the two is caused by reactance in the circuit and represents power that does no useful work.

Power loss – This term generally refers to electrical energy that is lost to inefficiencies in transmission, distribution, or in the use of electricity. As electricity flows through a conductor, individual electrons collide with the atoms of the conductor and transfer energy to them, causing them to heat up. This heat is lost to the atmosphere in the form of thermal radiation. Some power is also lost to electromagnetic radiation. Losses in an electricity distribution system depend on the length of the cable (the longer the cable, the greater the losses) and the conductivity of the material (higher resistance means greater losses).

Protocol – A set of conventions governing the format and timing of data between communication devices.

Rated Temperature Rise – The permissible rise in temperature above ambient for an electric machine operating under load.

Reactive Power – It is a concept that describes the loss of power in a system resulting from the production of electric and magnetic fields in it. Reactive loads in a power system drop voltage and draw current, which creates the impression that they are using up power, when they are not. This “imaginary power” or “Phantom power” is called reactive power, and is measured in Volt-Amps-Reactive (VAR). Reactive power is significant because it must be provided and maintained to ensure continuous, steady voltage on transmission networks. Reactive power is produced for maintenance of the system, and not for end-use consumption. If elements of the power grid cannot get the reactive power they need from nearby sources, they will pull it across transmission lines and destabilize the grid. In this way poor management of reactive power can cause major blackouts.

Resistance – Cables and electrical devices resist the movement of electrons that constitute the current passing through them. This is known as electrical resistance and is measured in Ohms.

Resistor – A resistor is any electrical component that resists the flow of electrical current. Resistors can be used to control current and therefore protect a circuit from overload. Resistors are also an important component in instrumentation and are used together with capacitors in power filters to eliminate unwanted harmonics.

Reversing – Changing of the rotation direction of the rotor or motor armature.

Rotor – The rotating element of any motor or generator.

SCR – Silicon Controlled Rectifier often referred to as athyristor.

SEI – Sustainable Energy Ireland (SEI), formerly the Irish Energy Centre was set up by the government in 2002 as Ireland’s national energy agency. Our mission is to promote and assist the development of sustainable energy. Semi-conductor fuses A special type of high-speed fuse used as thyristor protection since normal (gG/gL or aM) fuses are not fast enough.

Sequential start – Sequential start of motors is normally when two or more motors are started one by one in a sequence with the same starting equipment.

Serial Communication – The way of transmitting data in a network between different nodes, using some type of protocol.

Series – Electrical components that are connected in an un-branched line are said to be “in series” as opposed to “in parallel”. If any one of the components in a series circuit was to fail the circuit would be broken and no electricity would flow.

Service Factor – A multiplier which, when applied to rated power, indicates a permissible power loading that may be carried under the conditions specified for the service factor.

Short circuit – An electrical contact between parts of an electric circuit which causes a very high current, increases in temperature and potentially fire, if the circuit is not properly protected. This can occur if two live wires come into contact with each other perhaps because of worn insulation. The term is also used when defining the safe operating conditions for electrical devices.

Slip – The difference (usually expressed in percentage) between the synchronous speed and the rotor speed of an AC induction motor.

Star-Delta Starting – Star-delta is a connection that is used to reduce the inrush current and torque of a three-phase motor. A star start, delta run motor is one arranged for starting by connecting to the line with the winding initially connected star. The winding is then reconnected to run in delta after a predetermined time.

Star Connection – A three-phase winding connection formed by joining one end of each phase to make a “Y” point. The other ends of each phase are connected to the line.

Starting Torque – The torque produced by a motor at rest when power is applied. For an AC machine, this is the locked-rotor torque.

Stator – The stationary part of a rotating electric machine. Commonly used to describe the stationary part of an AC machine that contains the primary windings.

Surge protection – This is a device used to protect equipment from damage caused by high voltage power surges.

Synchronous speed – The speed of the rotating magnetic field on an AC induction motor determined by the frequency and the number of magnetic poles in each phase of the stator windings. Synchronous speed = Frequency x 120 / Number of motor poles

Thermistor – A resistive device that is used for temperature sensing, generally inserted in the windings of motors and alternators during manufacture.

Thyristor – A solid-state switch that has an anode, cathode anda control element called the gate, which makes it possible to turn it on at will. It can rapidly switch large currents at high voltages.

Three phase power – A form of electricity used to supply heavy loads ( industrial electrical equipment) such as industrial air conditioning units, grinding machines etc.

Torque – The rotating force produced by a motor. The units of torque may be expressed as pound-foot, pound-inch (English system), or Newton-meter (metric system).

Tripping class – The tripping class defines the starting time at a specific current before tripping occurs. Different classes exist, for example 10, 20, 30 etc. where class 30 allows the longest starting time.

Variable Speed Drive – Common term given to AC, DC and servo drives. All used for controlling the speed of motors.

Voltage – The voltage between two points in an electrical circuit is a measure of the potential difference or the force that is pushing electrons between these two points.

Volt drop – A voltage drop is a reduction in the force that “pushes” current through a circuit, which can cause overheating, increased operating costs and the risk of equipment failure.

Voltage rating – The maximum voltage that can be applied to an electrical device.

Watt (W) – Standard unit of electrical power (1 Watt = 1 amp at 1 volt). The Watt is also a general unit of power.

Watt hour (Wh) – Watt hours are a measure of energy transferred ie the product of power (kW) x time (hours).

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