On resistive grounding of the neutral in networks from 6 to 35 kV

At present the majority of networks from 6 to 35 kV operate with an insulated neutral. In these networks dangerous arc and ferroresonant overvoltages arise at ground faults. The methods developed to protect networks from 6 to 35 kV against single-phase ground faults have not found a wide practical application. One of the ways to improve the operation of medium voltage networks is grounding of the neutral by a means of a resistor. The application of a resistor permits one to construct a selective protection to find a damaged feeder as well as preventing arc and ferroresonant overvoltages dangerous for electrical equipment (especially for voltage transformers) and service personnel. The problem envelops networks of various designs (air and cable), and various purpose (distributive networks, networks of generator voltage of power stations and house networks). The solution of a problem of expediency of resistive grounding application of the neutrals is reduced to solution of the following problems: choice of resistor values; evaluation of their required characteristics from the standpoint of a power and energy; suggestions of organisation of relay protection; analysis of overvoltages in such networks; and development of requirements for zinc-oxide arresters in those networks, where the installation of zinc-oxide arresters is expedient.