Substation1
Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

earth electrode system
a network of electrically interconnected rods, plates, mats, or grids installed for the purpose of establishing a low-resistance contact with earth. The design objective for resistance to earth of this subsystem should not exceed 10 Ω.
earth wire
an overhead wire which is maintained at ground potential for purposes of lightning shielding and system grounding.
earthing

See grounding
economic dispatch
a generation scheme in which units are utilized such that the greatest profit is generated for the utility.
economic interchange
an arrangement between interconnected electrical power systems whereby a system can meet its load demand by buying power from one or more of the other systems in the interconnection group.
eddy current
a circulating current in magnetic materials that is produced as a result of time-varying flux passing through a metallic magnetic material.
eddy current brake
a braking device in which energy is dissipated as heat by generating eddy currents.
eddy current drive
a magnetic drive coupled by eddy currents induced in an electrically conducting member by a rotating permanent magnet, resulting in a torque that is linearly proportional to the slip speed.
eddy current loss
the energy wasted in sustaining undesirable eddy currents in an electrical conductor.
efficiency
(1) the ratio of the input power to the output power. It is a figure of merit for the energy cost effectiveness of a device.
(2) in antennas, the ratio of the power radiated to the input power. This term is sometimes defined with the mismatch loss (1-γ2) included in the total efficiency of the antenna; other times, it is omitted from the calculation.
electric charge
a basic physical quantity that is a source of electromagnetic fields. The units of electric charge are coulombs.
electric charge density
the fundamental, macroscopic source of the electromagnetic field that quantifies the average number of discrete electric charges per unit volume. SI units are coulombs per cubic meter.
electric current density
a source vector in electromagnetics that quantifies the amount of electric charge crossing some cross-sectional area per unit time. The direction of the electric current density is in the direction of electric charge motion. SI units are amperes per square meter.
electric field
in a region of space, if a test charge q experiences a force F then the region is said to be characterized by an electric field of intensity E given by

E = F / q
electric field intensity
a force field that is a measure of the magnitude and direction of the force imparted upon a discrete charge normalized to the discrete charge's value. Depends on material characteristics. The units are volts per meter.

electric flux density
basic electromagnetic field quantity used to describe the effects of permeable matter to the electric field; it is expressed in SI units of coulombs per square meter.
electric furnace
a method of smelting metals and applying high heat for industrial processes which makes use of the heat from an electric arc struck between (typically) carbon electrodes.
electric permittivity
tensor relationship between the electric field vector and the electric displacement vector in a medium with no hysteresis; displacement divided by the electric field in scalar media.
electric polarization vector
an auxiliary vector in electromagnetics that accounts for the creation of atomic dipoles in a dielectric material due to an applied electric field. Macroscopically, the electric polarization vector is equal to the average number of electric dipole moments per unit volume. Mathematically, P = D - Є0E, where D is the electric flux density, E is the electric field intensity, and Є0 is the free space permittivity. SI units are coulombs per square meter.
electric susceptibility
tensor relationship between the electric field vector and the electric polarization vector in a medium with no hysteresis. It is the polarization divided by the permittivity of free space and the electric
field in scalar media.