IEEE Std 3003.1-2019 pdf download – IEEE Recommended Practice for System Grounding of Industrial and Commercial Power Systems.
static charge: The electricity generated when two dissimilar substances come into contact. Conveyor belts are active producers of static electricity. switching surge: A transient wave of overvoltage in an electric circuit caused by the operation of a switching device interrupting current. system charging current: The total distributed capacitive charging current (3 VIN/X co) of a three-phase system. three-phase, four-wire system: A system of altermating current supply comprising four conductors, three of which are connected as in a three-phase three-wire system, the fourth being connected to the neutral point of the supply or midpoint of one phase in case of delta- connected transformer secondary for the purpose of conducting load current. three-phase, three-wire system: A system of alternating current supply comprising three conductors, between successive pairs of which are maintained alternating differences of potential successively displaced in phase by one third of a period. touch voltage: The difference in potential between metallic objects or structures within the substation site that may be bridged by direct hand-to-hand or hand-to-feet contact. transient overvoltage: The temporary overvoltage associated with the operation of a switching device, a fault, a lightning stroke, an arcing ground fault on an ungrounded system, or other instigating events. ungrounded system: A system without an intentional connection to ground except through potential indicating or measuring devices or other very high-impedance devices.
Various detection schemes are used to detect the presence of a single line-to-ground fault. The simplest scheme employs three light bulbs rated for line-to-line voltage, each conncted between line voltage and ground. Under normal operation, the three bulbs are iluminated with low equal intensity. When a single line- to-ground fault occurs, that bulb connected to the faulted phase is extinguished. The remaining two bulbs increase in intensity since the voltage on the phases without a fault increases from line-to-neutral to line-to- line. It should be noted that the light bulbs are a high resistance and to some extent provide a ground reference for the ungrounded system. Another scheme frequently used takes the form of three voltage transformers with their primary windings connected in wye and the neutral point grounded. The secondary windings of the transformers are connected in broken delta, with a voltage relay connected in the open corner and used to operate an indication or alarm circuit. Using this scheme, loading resistors may be required either in the primary neutral or secondary circuit to avoid ferroresonance.