IEEE 142-1982 pdf free.IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems.
IEEE 142 problem of groundfaultprotection devices typically installed inlow-voltage main circuit breakers, servicebreakers,etc, is that a ground fault in acable or equipment of a small subfeederor branch of the system is likely to tripthe large main circuit breaker,shuttingdown the entire installation. Nonselectivetripping can be a problem unless coordinated ground-fault protection devices areinstalled at each feeder，subfeeder，andat each load branch of the system. Whereisolation of only the faulted portion of asystem is important, much care must beused in applying ground-fault protectionequipment.
Thus the solidly and lowresistancegrounded-neutral systems provide a basisfor easily securing protection againstruinousphase-to-ground arcing faultburndowns. (Unfortunately , no compar-ably reliable and universally applicablemeans of protection against lowlevelline-to-line arcing fault burndowns hasbeen devised.)
Location of Faults. On an ungrounded system,a ground fault doesnot open the circuit.Some means of detecting the presence of a ground fault onthe system should be installed. Lampsconnected to indicate the potential fromeach phase to ground will show the presence of a ground fault and which phaseis involved,but will not show on which feeder the fault has occurred. Locatinga ground fault on one of the several feeders may require removing from serviceone feeder at a time until the ground detector indicates that the faulted feederhas been removed from the system.Should it happen that the same phase oftwo different feeders becomes faulted toground at the same time,the faultedfeeders cannot be located by removingthem from the system one at a time. Itmay be necessary to remove all feedersand restore them to service one at a time,checking the ground detector as eachfeeder is restored.
The location of a grounded feeder onan ungrounded system may be facilitatedby the use of various types of locatingapparatus [13]. For example，an interrupted direct voltage or superimposedaudio signal may be applied to the feederbus and the tracing current detected inthe grounded feeders. Some operatorshave reported success using locating ap-paratus not requiring deenergizing system feeders [14]. This，of course，hasthe advantage of permitting the locationof ground faultswithout waiting forlight load periods on the system.
An accidentalground faulton agrounded system is both indicated and atleast partially located by an automaticinterruption of the accidentally groundedcircuit or piece of equipment.IEEE 142 pdf download.