The results are given related to the analytical studies of the causes of accidents occurrence and abnormal operating modes of electric receivers in the medium-voltage networks. It is established that the main cause of damage is the single-phase earth fault mode. It is established that the main cause of damage is a single-phase ground fault. It is found that a long single-phase ground fault increases the likelihood of transition to a more severe phase-to-phase short circuit. It is accompanied by immediate shutdown and long downtime of the equipment, large economic losses, as well as the appearance of touch and step voltages that are dangerous for people.
It is identified that the earth fault current in a network with an isolated neutral will decrease in proportion to the decrease in the coefficient of the share of the transient resistance in the total earth fault current.
Analysis of the operability of protection against single-phase earth faults is carried out on the example of a section of 6 kV distribution network of the coal mining enterprise JSC Polosukhinskaya Mine. Experimental studies of the efficiency of the functioning of non-directional current protection against single-phase earth faults were carried out. In the event of an incomplete single-phase earth fault, a drop in the zero-sequence current in the protected line invariably leads to a critical decrease in the sensitivity coefficient. There is a violation of the selectivity of the protection action, as a result of which the probability of electrical injury to the maintenance personnel increases.
Boundary conditions for stable operation of relay protection and automation systems in case of incomplete single-phase earth faults are established. Definition of these conditions allows developing new algorithms for the operation of non-directional current protection in order to improve the electrical safety of the operating personnel.
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