Alltec Protection Systems Pvt. Ltd. Becomes the First Company in India to be Certified by Underwriters Laboratories in the Installation of Lightning Protection
The leader which typically initiates each succeeding stroke of a multiple-stroke flash lightning after the first stroke. The first stroke is initiated by a stepped leader. The dart leader derives its name from its appearance on photographs taken with streak cameras. The dart leader’s brightest luminosity is at its tip which is tens of meters in length, propagating downward at about 10^7 m/s. In contrast to stepped leaders, dart leaders do not typically exhibit branching because the pre-established channel’s low gas density and residual ionization provide a more favorable path for this leader than do any alternative ones.
Data Line
A cable carrying information as distinct from power. Examples of data lines are telephone lines, telemetry control and signal lines.
DC Equipment Grounding Conductor (DCEG)
The conductor that bonds an equipment frame, cabinet, or other enclosure to the site grounding system. The DCEG may also bond an equipment unit within a frame, cabinet, or enclosure to the site grounding system.
DC System Grounding Conductor (DCG)
A conductor or conductive path used to provide a connection between one side of a dc source and a point on the site grounding system. The dc source can be a battery plant, a converter plant, or one or more individual dc/dc converters.
Differential-Mode Noise
See: Transverse-Mode Noise
Direct Coupling
The association of two or more circuits by means of self-inductance, capacitance, resistance, or a combination of these that is common to the circuits.
Direct-Reading Ammeters
Ammeters that employ a shunt and are connected in series and carry some of the line current through them for measurement purposes. They are part of the circuit being measured.
Displacement Power Factor
(a) The displacement component of power factor.
(b) The ratio of the active power of the fundamental wave, in watts, to the apparent power of the fundamental wave, in volt-amperes.
Distortion Factor
The ratio of the root square value of the harmonic content to the root square value of the fundamental quantity, expressed as a percent of the fundamental. See also: Total Harmonic Distortion. (IEEE Std 519™)
Doppler Radar
Weather radar that measures direction and speed of a moving object, such as drops of precipitation moving toward or away from the radar. Using the Doppler effect, it measures the speed of particles. It was named for J. Christian Doppler, an Austrian physicist, who in 1842 explained why the whistle of an approaching train had a higher pitch than the same whistle when the train was going away.
Down Conductor
That part of the external LPS which is intended to conduct the lightning current from the air-termination system to the earth-termination system.
Downdraft
A sudden descent of cool or cold air to the ground, usually with precipitation, and associated with a thunderstorm or shower.
Downward Flash
Lightning flash initiated by a downward leader from cloud to earth. A downward flash consists of a first short stroke, which can be followed by subsequent short strokes and may include a long stroke.
Dropout
A loss of equipment operation (discrete data signals) due to noise, voltage sags, or interruption. (IEEE std 1159™)
Dry Lightning
A term in the United States for thunderstorms which produce no precipitation at the surface. This type of lightning is the most common natural cause of wildland fires.
