Definitions
Alternator
A synchronous rotating AC machine used to change mechanical power into electrical power (alternating current - AC).
Alternating Current
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
The surrounding temperature of any cooling medium. Generally called room temperature, when the air is the cooling medium in contact with a piece of equipment.
Ampere
The standard unit of electrical current.
Brownout
A dip in the voltage level of a power system, which can damage electrical equipment or cause it to under perform.
Busbar
An electrical conductor that makes a common connection between several circuits. Sometimes electrical wire is not big enough to accommodate high-current applications, and electricity must be conducted using a bus bar- a thick bar of solid metal (usually copper or aluminium). Busbars are un-insulated, but are physically supported by insulators. They are used in industry to feed large amounts of electricity to a number of machines.
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).
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.
Closed loop system.
This is a system used to regulate a process using feedback control (as opposed to an open control system, which has no feedback). A closed loop system responds to actual system conditions via an encoder and can react with a range of responses.
Code Letter
A letter, which appears on the nameplates of AC motors to show their locked-rotor kilovolt-amperes per horsepower at, rated voltage and frequency.
Constant Horsepower Motor
A term used to describe a multi-speed motor in which the rated horsepower is the same for all operating speeds. When applied to a solid-state drive unit, it refers to the ability to deliver constant horsepower over a predetermined speed range.
Constant Torque Motor
A multi-speed motor for which the rated horsepower varies in direct ratio to the synchronous speeds. The output torque is essentially the sa
A combination of power and control electronics that connects between electrical supply and DC motor to allow variable speed control.
Delta Connection
A three-phase winding connection in which the phases are connected in series to form a closed circuit.
Design
NEMA design letters A, B and C define certain starting and running characteristics of three phase squirrel cage induction motors. These characteristics include locked-rotor torque, locked-rotor current, pull-up torque, breakdown torque, slip at rated load, and the ability to withstand full-voltage starting.
Duty
A continuous or short time rating of a machine. Continuous-duty machines reach an equilibrium temperature within the temperature limits of the insulation system. Machines, which do not, or cannot, reach an equilibrium temperature, have a short time or intermittent-duty rating. Short-time ratings are usually one hour or less for motors.
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.
Efficiency
The ratio between useful work performed and the energy expended in producing it. It is the ratio of output power divided by the input power.
Emissions
The release or discharge of substances, effluents or pollutants into the environment.
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.
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.
Full-Load Speed
The speed at which any rotating machine produces its rated output.
Full-Load Torque
The torque required to produce rated power at full-load speed.
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.
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.
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.
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.
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 9000
International standards for quality assurance set by the International Standards Organization.
ISO 14000
International standards for environmental management systems set by the International Standards Organization.
Kilowatt
A unit of electrical power. Also, the output rating of motors manufactured and used off the North American continent.
Locked-Rotor Current
Steady-state current taken from the line with the rotor of a motor at standstill and at rated voltage and frequency.
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.
Mega (Insulation Tester)
An instrument for measuring insulation resistance.
Motor
A rotating machine that converts electrical power (either alternating current or direct current) into mechanical power.
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.
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.
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.
Poles
The magnetic poles set up inside an electric machine by the placement and connection of the windings.
Power factor correction
Depending on the type of equipment a consumer connects to the electricity supply power factor varies. Unless this variation is corrected, higher currents are drawn from the grid, leading to grid instability, higher costs and reduced transmission capacity. Most utilities impose penalties on consumers who fail to correct errant power factors.
Power Factor
The ratio of watts to Volt-Amperes of an AC electric circuit.
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).
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.
Rotor
The rotating element of any motor or generator.
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 between synchronous and operating speeds, compared to synchronous speed, expressed as a percentage. Also the difference between synchronous and operating speeds, expressed in rpm.
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 created by the primary winding of a rotating electric machine. When the speed of the rotating element matches the speed of the rotating magnetic field, it is said to be rotating at synchronous speed.
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.
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).
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).
