IEEE C62.92.4-1991 pdf free

04-29-2021 comment

IEEE C62.92.4-1991 pdf free.IEEE Guide for the Application of NeutralGrounding in Electrical Utility Systems,Part lV-Distribution.
IEEE C62.92.4 Surge arresters on multigrounded neutral systems are connected directly to earth, and their grounding conductor maybe interconnected directly to the primary neutral conductor and equipment tanks. They may also be interconnectedwith the secondary neutral at transformer installations.
Four-wire unigrounded systems are systems where the primary neutral conductor is insulated at all points except at thesource.The neutral conductor in these systems is connected to the neutral point of the source transformer windings andto ground.Distribution transformers usually are connected between phase and neutral conductors,with the surgearrester connected between phase and ground.Some four-wire unigrounded systems use an arrester between theneutral conductor and ground.A spark gap may also be used at the distribution transformer between its secondaryneutral and arrester ground to provide better surge protection to the transformer windings. The principal advantage offour-wire unigrounded systems is the greater ground relaying sensitivity that can be obtained in comparison tomultigrounded systems (see 3.4).
On three-phase three-wire primary distribution circuits , single-phase distribution transformers are connected phase-to-phase. The connection three single-phase distribution transformers or of three-phase distribution transformers isusually delta-grounded wye or delta-delta.The floating wye-delta or T-T connections also can be used.The groundedwye-delta connection is generally not used because it acts as a grounding transformer. Surge arresters are generallyconnected phase-to-ground. However, the surge arrester rating is higher than those used on multigrounded neutralsystems since the temporary 60 Hz overvoltages expected under fault conditions are also higher.
The feeders from an ungrounded systems may be grounded by the use of a grounding transformer, which may beconnected in zig-zag or in grounded-wye delta.The grounding transformer provides a source for zero sequence currentand will permit the addition of a neutral conductor to an existing ungrounded circuit.
Ungrounded and three-wire unigrounded systems generally result in the least investment when the load is mostlythree-phase. On the other hand, costs favor multigrounded neutral systems when the loads are mostly single phase.Several factors must be given consideration to determine if the system should be grounded or ungrounded.
One factor to consider is the geographical area and the isokeraunic level in which the system will be operating.Thiswill have considerable effect on the type of surge arresters required and the degree of direct-stroke protection that isconsidered necessary. In an area having a high isokeraunic level, it may be advantageous to use a static wire or anoverhead shield wire for direct stroke lightning protection.The primary neutral conductor can very easily be used forthe shield wire and may also function as a common neutral conductor with the secondary system.However, with theuse of aerial cable for secondary circuits, there will be some duplication of neutral conductors that may not beobjectionable compared with the reduced outages and reduction of trips for fuse replacement and repair of lightning-damaged equipment. Also, the number of ground connections on the neutral conductor per mile of line must beconsidered.
Generally, a minimum of four ground connections per mile is considered adequate for a four-wire multigroundedneutral system, but, with the use of a static or overhead shield wire, it may be necessary to install grounds on everypole.IEEE C62.92.4 pdf download.

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