IEEE 3003.1-2019 pdf free download

IEEE 3003.1-2019 pdf free download.Recommended Practice for System Grounding of Industrial and Commercial Power Systems.
In an ungrounded system, it is possible t’or destructive transient overvoltages to occur throughout the system during restriking ground faults. These overvoltages, which can he several times normal in magnitude. result from a resonant condition being established between the inductive reactance of’ the system and the distributed capacitance to ground. Experience has proven that these overvoltages may cause failure of insulation at mukiple locations in (he system. particularly at motors. Transient overvoltages from restriking ground faults are the main reason why ungrounded systems are no longer recommended and grounded systems of’ some form are the predominant choice. To reduce transient overvoltages during restriking ground faults, one should ground the system using either solid or impedance grounding as indicated in Figure 10.
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 connected between line voltage and ground. Under normal operation, the three bulbs are illuminated with low equal intensity. Vhen 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 he 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 ot’ 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 he required either in the primary neutral or secondary circuit to avoid terroresonance.
Locating a single line-to-ground fault on an ungrounded system can he lime consuming. Usually. the first step is to open the secondary feeders, one at a time, to determine which feeder on which the fault is located. This is verified by observing the three lights to determine when the ground fault has been cleared. This process is repeated downstream until the faulted device is detected,
It’ a ground cannot he located before a second line—to—ground fault occurs on a different phase. a line-to— line fault will result The current must he carried either by the protective conductor, metallic raceways. or by the earth. This will be contrasted later to a grounded system that develops enough fault current to clear. automatically and selectively, each faulted circuit.IEEE 3003.1-2019 pdf free download.