Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

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.
high-voltage DC (HVDC)
transmission transmission of electric power (at typically 500-1500 kV) using DC rather than AC. This can be desirable for several reasons:

1. For economic reasons when a large amount of power is to be transmitted over a long distance, i.e., 300-400 miles, or via
underwater cables;

2. For the connection of asynchronous AC systems; and

3. Improved transient stability and dynamic damping of the electrical system oscillations.
hologram
medium that, when illuminated optically, provides a three-dimensional image of stored information, sometimes called holograph.
holograph

See hologram
holographic data storage
a technique used to store multiple images, or 2-D arrays of digital information, as multiplexed holograms in an optically sensitive material. Multiplexing techniques include angle, frequency, and spatial position. Angle and frequency multiplexing techniques are based on Bragg selectivity where angle multiplexing favors transmission geometries and frequency multiplexing favors reflection geometries.
holographic interconnect
free-space interconnect that uses holograms to control optical paths from sources to detectors. The hologram provides the interconnection by forming the intentionally distorted image of the source array on the detector array. A hologram can be viewed as a combination of gratings. Each grating directs a light beam passing through it to a new direction. The hologram can be displayed by a spatial light modulator to achieve dynamic reconfiguration.
holography
the science of making and reading holograms.
homopolar generator
an electromagnetic generator in which the magnetic flux passes in the same direction from one magnetic member to the other over the whole of a single air gap area. Such generators have been built to supply very large pulsed currents.
homopolar machine

See homopolar generator
homopolar magnetic bearing
a magnetic bearing in which the rotating member always experiences a magnetic field of the same polarity.
horizontal polarization
a term used to identify the position of the electric field vector of a linearly polarized antenna or propagating EM wave relative to a local reference, usually the ground or horizon. A horizontally polarized EM wave is one with its electric field vector aligned parallel to the local horizontal.
horn gap
a V-shaped spark gap which provides a method of extinguishing a power-follow arc by allowing the arc to climb the sides of the V until it is too long to be maintained.
horsepower-rated switch
a manually operated switching device designed for motor circuit applications. It is designed to interrupt the rated overload current at rated voltage of a motor with a horsepower rating that is less than or equal to the horsepower rating of the switch.
hot
an energized conductor.
hot line work
work performed on energized electric power lines. See glove, hot stick, bare-hand.
hot reserve
the state of an idle thermal generating plant whose boilers and turbines are hot and can thus be quickly brought into service.
hot restart
reassumption, without loss, of all operations in the system from the point of detected fault.
hot stick
an insulated pole used by line workers to make connections to and otherwise manipulare energized overhead conductors.
hot tap
a clamp, applied with a hot stick that connects a branch circuit to an existing conductor and typically applied while the system is energized.
hot wire
an energized conductor, particularly as opposed to a neutral or ground wire, both of which are typically maintained at ground potential
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