Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

foot-candle
the unit of illuminance when the foot is taken as the unit of length. It is the illuminance on a surface one square foot in area on which there is a uniformly distributed flux of one lumen.
footing impedance
the electrical impedance between a steel tower and distant earth.
forced commutation
the use of external circuitry to artificially force a current zero, thus allowing a diode or thryistor to turn off.
forced interruption
an interruption in electric supply caused by human error, inappropriate equipment operation, or resulting from situations in which a device is quickly taken out of service by automatic or manual switching operations.
forced outage
the unscheduled interruption of electric power to a portion of a power system due to equipment failure, weather conditions, or other mishaps.
forced outage rate
a measure of performance usually applied to generation units. It is the ratio of equipment down-time vs. the total time that the unit is available for operation.
forced system
a dynamic system is said to be forced if it is excited by a nonzero external source.
forward converter
an isolated version of a buck converter. The primary and the secondary of the transformer conduct at the same time. The transformer does not store energy. An additional winding with a diode is often used to reset the magnetizing energy when the transistor is off.
four-point starter
a manual motor starter that requires a fourth terminal for the holding coil. Because of its independent holding coil circuit, it is possible to vary the current in the field circuit independently of the holding coil
circuit. The disadvantage is that the motor starter holding relay will not drop out with loss of the field; however, proper overcurrent protection should shut down the motor in the event of field loss.
four-quadrant operation
(1) a signed representation of electrical or mechanical variables in the phase plane in order to situate the different modes for energy transfer. This term can be used both for power electronics and electrical machines. For electrical variables, the four-quadrant operation is defined by the voltage-current (or current-voltage) characteristic with the two variables expressed as instantaneous or mean values. For mechanical variables, the term is defined by the torque-speed (or speed-torque) characteristic with the same time-domain representation as previously explained. The energy transfer is defined with electrical power in the voltage-current curve and with mechanical power in the torque-speed curve. The four-quadrant operation is related to reversible power in electromechanical systems.
For example, in the case of power electronics, the four-quadrant operation is defined only with electrical variables to visualize the way of energy transfer in a static converter. For electrical machines, the same operation can
be defined with electrical variables at the input (motor) or at the output (generator) and also with mechanical variables at the output (motor) or at the input (generator).

(2) the four combinations of forward/reverse rotation and forward/reverse torque of which a regenerative drive is capable. These are: motoring: forward rotation/forward torque; regeneration: forward rotation/reverse torque; motor: reverse rotation/reverse torque; and regeneration: reverse rotation/forward torque. four-wave mixing a nonlinear optical
phenomenon in which four optical beams interact inside nonlinear media or photorefractive crystals. When four beams of coherent electromagnetic radiation intersect inside a nonlinear or photorefractive medium, they will, in general, form six interference patterns and induce six volume refractive index gratings in the medium. The presence of the index gratings will affect the propagation of these four beams. This may lead to energy coupling. The coupling of the four optical
beams is referred to as four-wave mixing. In one of the most useful four-wave mixing configurations, the four beams form two pairs of counterpropagating beams. In this particular configuration, some of the refractive index gratings are identical in their grating wavevectors. This leads to the generation of phase conjugate waves. Four-wave mixing
is a convenient method for the generation of phase conjugated waves.
fractional horsepower
National Electrical Manufacturers Association (NEMA) classification describing any "motor built in a frame smaller than that having a continuous rating of 1 horsepower, open type, at 1700 to 1800 rpm."
frequency
the repetition rate of a periodic signal used to represent or process a communication signal. Frequency is expressed in units of hertz (Hz). 1 Hz represents one cycle per second, 1 MHz represents one million cycles per second, and 1 GHz represents one billion cycles per second.
frequency converter
an equipment or circuit that converts an RF signal to an intermediate (IF) signal in receivers. It converts an IF signal to an RF signal in transmitters.
frequency regulation
the change in the frequency of an unloaded generator with respect to its frequency in a fully-loaded state. Typically applied to small, isolated power systems such as emergency power units.
frequency relay
a protective relay which monitors the frequency of the electric power system.
frequency resolution
a measure of the ability of a system to resolve different frequencies in a signal. As the frequency resolution increases, more finely-spaced frequency components can be resolved. The time resolution of a system is roughly inversely proportional to the frequency resolution; the uncertainty principle places a lower bound on the time-frequency resolution product.
frequency variation
a change in the electric supply frequency.
frog
the top of a tower.
front end
(1) an initial processing unit that provides a user interface and/or reformats input data for subsequent computations on a special-purpose or high-performance back end processor.

(2) the portion of the compiler that does machine-independent analysis. front of a motor the end of a motor that
is opposite to the major coupling or driving pulley.
fuel cell
an electrochemical device in which the chemical energy of a conventional fuel converted directly and efficiently into low voltage, direct current electrical energy.
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