ELECTRICAL TERMINOLOGIES



Some of the important Terminologies related to Electrical Engineering are briefly described below:
  • ARC: A disruptive discharge of electricity through an insulator, typically a gas, normally characterized by a voltage drop.  This can be a single event, intermittent or continuous.  Same as Flashover.
  • BREAKDOWN VOLTAGE:  The voltage level which causes insulation failure.  Same as Dielectric Withstand Voltage.
  • CORONA:  A luminous discharge due to the ionization of the gas surrounding a conductor caused by a voltage gradient exceeding a certain critical value.  It does not greatly heat the conductor, and it is limited to the region surrounding the conductor.  While corona is a low energy process, over long periods of time, it can degrade insulators, causing a system to fail due to dielectric breakdown.
  • CORONA EXTINCTION VOLTAGE:  The highest voltage at which continuous corona of specified pulse amplitude no longer occurs as the applied voltage is gradually decreased from above the corona inception value.
  • CORONA INCEPTION VOLTAGE:  The lowest voltage at which continuous corona of specified pulse amplitude occurs as the applied voltage is gradually increased.
  • CREEPAGE:  Current flowing between two conductors along a surface that is in contact with both conductors.  Generally this can be neglected up until the voltage where corona or flashover occurs.
  • CREEPAGE DISTANCE:  The shortest distance separating two conductors as measured along the surface touching both conductors.  Along the surface of most materials, flashover can occur at distances much shorter than the flashover distance in air.  Therefore, it is extremely important in high voltage designs to look for places where creepage can occur.
  • DIELECTRIC:  An insulating material between two conductors.
  • DIELECTRIC WITHSTANDING VOLTAGE or DIELECTRIC WITHSTAND VOLTAGE:  Voltage an insulating material will withstand before flashover (arcing) or puncture.  Same as Breakdown Voltage.  This is a greater value than working voltage.  The difference depends on how much design margin the designer wants between the failure point and the operating point.
  • FLASHOVER:  A disruptive discharge of electricity through an insulator, normally characterized by a voltage drop.  Also, a discharge around or over a liquid or solid material.  This can be a single event, intermittent or continuous.  Same as Arc.
  • HI-POT TEST:  A test performed by applying a dc or ac high voltage for a specified time to determine adequacy of insulating materials in an assembly.  Short for high potential test.
  • HIGH VOLTAGE:  High voltage starts at the point where designers have to consider additional technical issues, and where there are significantly fewer component suppliers to choose from.
  • ISOLATION:  The electrical separation between two conductors or two circuits.
  • ISOLATION VOLTAGE:  The maximum dc or ac voltage that may be continuously applied between two isolated conductors or two circuits.
  • PRIMARY CIRCUIT:  A circuit electrically connected to the input or source of power to the device.  See also Secondary Circuit.
  • SAFETY GROUND:  A conductive path to earth that is designed to protect persons from electrical shock by shunting away any dangerous currents that might occur due to malfunction or accident.
  • SECONDARY CIRCUIT:  A circuit that is electrically isolated from the input or source of power to the device.  See also Primary Circuit.
  • STANDOFF:  A mechanical support insulator used to support a wire or component away from its mounting surface.
  • TRACKING:  Marks made on a surface that experienced flashover.
  • WITHSTAND VOLTAGE:  See Dielectric Withstand Voltage.
  • WORKING VOLTAGE:  The specified or actual operating voltage applied between two conductors, circuits or a component.
  • Space Factor : The ratio ( expressed as a percentage ) of the sum of the effective overall cross sectional area of cable forming a bunch to the internal cross sectional area of the conduit, pipe, duct, trucking or channel in which they are installed. The effective overall cross sectional area of a non circular cable is taken as that of a circle of diameter equal to the major axis of the cable.
  • Spur : A branch cable connected to a ring circuit.
  • Voltage :
1.    Extra Low : Normally not exceeding 50 Volts between conductors, and not exceeding 30 Volts A.C. or 50 Volts D.C. between any conductor and earth.
2.    Low : Normally exceeding extra low voltage but not exceeding 250 Volts, whether between conductors or between any conductor and earth.
3.    Medium : Normally exceeding 250 Volts but not exceeding 650 Volts, whether between conductors or between any conductor and earth.
4.    High : Normally exceeding 650 Volts between phases and earth.
  • Circuit Breaker : A mechanical device for making and breaking a circuit, bothunder normal conditions and under abnormal conditions, such as those of an overload or short circuit being broken automatically.
  • Distribution Board : An assemblage of parts, including one or more circuit breakers, arranged for the distribution of electrical energy.
  • Duct ( For Cables ) : A closed passage way formed underground in a structure and intended to receive one or more cables which may be drawn in.
  • Earth Electrode : A metal rod or rods, a system of underground metal pipes or other conducting object, providing an effective connection with the general mass of the earth.
  • Excess Current Protection Close : Excess current protection which will operate within Four Hours at 1.50 times the designed load current of the circuit which is protects.
  • Fuse : A device for opening a circuit by means of a fuse element designed to melt when an excessive current flows. It normally consists of a fuse base and fuse link. The fuse link may take the form of a cartridge or a carrier supporting a fuse element.
  • Insulation : Suitable non conducting material enclosing, surrounding or supporting a conductor.
  • Isolator : A mechanical device capable of opening or closing a circuit under conditions of no load or negligible current. An off load device. It shall only be operated when Circuit Breaker is open.
  • Resistant Area ( For Earth Electrode Only ) : The area of ground ( around an earth electrode ) within which a voltage gradient measurable with ordinary commercial instruments exists when the electrode is being tested.
  • Switch Linked : A switch, the blades of which are so arranged as to make or break all poles simultaneously or in a define sequence.
  • Switchgear : Apparatus for controlling the distribution of electrical energy, or for controlling or protecting electrical circuits, machines and current using appliances.
  • Bolted Fault : Bolted Short Circuit refers to a worst case scenario of a short circuit where all the conductors in a system are imagined to be bolted together, thus causing the highest possible fault current.  This hypothetical scenario is used to calculate the fault level of an electrical power system.All components of a power system such as switchgear and conductor are designed to withstand this high current. The impedance of the system is assumed to be zero in this kind of condition.



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