Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

AC-DC integrated system
a power system containing both AC and DC transmission lines.
asynchronous AC systems
AC systems either with different operating frequencies or that are not in synchronism.
asynchronous system
a (computer, circuit, device) system in which events are not executed in a regular time relationship, that is, they are timing-independent. Each event or operation is performed upon receipt of a signal generated by the completion of a previous event or operation, or upon availability of the system resources required by the event or operation.
basic input-output system (BIOS)
part of a low-level operating system that directly controls input and output devices.
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.
equivalent system dynamics
a dynamical system model resulting from substituting the equivalent control into the plant's modeling equation. The equivalent system's trajectory is confined to a surface that is parallel to the sliding surface if the system's initial condition is off the sliding surface. If the initial condition is on the sliding surface, then the equivalent system's trajectory will stay on the sliding surface.
excitation system
the DC voltage source and its accompanying control and protection systems connected to the synchronous generator rotor.
fault-tolerant control system
a system that exhibits stability and acceptable performance in the presence of component faults (failures) or large changes in the system that resemble failures.
flexible AC transmission system
a transmission scheme in which each power line is maintained at its optimal impedance, generally by means of thyristor-controlled series compensators.
forced system
a dynamic system is said to be forced if it is excited by a nonzero external source.
global positioning system (GPS)
system of 18 primary satellites in medium earth orbit, distributed so that at least four are simultaneously visible from each point on the globe; typically used in timing and positioning applications.
Global System for Mobile Communications (GSM)
a set of systems specifications that describe the Pan European digital mobile cellular radio system. This set of 13 recommendations describe service, synchronization, hardware, operating and maintenance characteristics for the system.
high-resistance grounded system
an electrical distribution system in which the neutral is intentionally grounded through a high resistance. The high-resistance grounded wye system is an alternative to solidly grounded and ungrounded systems.

High-resistance grounding will limit ground fault current to a few amperes, thus removing the potential for arcing damage inherent in solidly grounded systems.
illumination system
the light source and optical system designed to illuminate the mask for the purpose of forming an image on the wafer.
lighting system
any scheme used for illuminating a scene, usually for acquisition by a digital system. Illumination is crucial to digital images, since even illumination gradients that cannot be perceived by the eye can have an influence on the results of digital processing. For inspection tasks and document digitization, a uniform, reproducable, high level of lighting is usually required. Other applications have other requirements for uniformity, frequency, and intensity.

Structured lighting schemes are used to collect multiple images of a scene each having different illumination .

Strobe lights can be used to effectively freeze motion, and are useful for many visual inspection tasks.
See structured light
National Television System Committee (NTSC)
a body that recommended the standard for colored television broadcasts in the U.S. in 1953. NTSC video contains 525 lines, a field rate of 59.94 fields/second, a horizontal frequency of 15,734.264 Hz, and an interlaced color subcarrier frequency of 3.579545 MHz. The NTSC format is also in use by many countries other than the U.S.
per-unit system
a dimensionless system for expressing each quantity in terms of a fractional part of a "base" value, often the nominal or rated value of the system. Typical electrical calculations require four base quantities (voltage, current, impedance, and apparent power), any two of which may be chosen arbitrarily. The per-unit system greatly simplifies calculations in electrical systems containing transformers with non-unity turns ratios, making the voltage differences transparent.
percent system
a variation of the per-unit system in which the ratios expressing system quantities are expressed as a percentage of the base quantity.
polyphase system
electrical system that has more than one phase, which are separated by angles of 360=n, where n is the number of phases. For example, three phase systems are polyphase systems where the three phases are separated by 120 electrical degrees from each other. A six-phase system is a polyphase system where each successive phase is separated by 60 electrical degrees from the other.
power system stabilizer
a control device that provides an additional input signal to the AVR to damp power system oscillations.
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