The efficiency of electrical complexes depends directly on the level of power supply system reliability, which comprises extensive and branched distribution networks. A complex of single-phase ground fault (SPGF) relay protection and automation devices (RPA) is used to reduce the economic losses from the failure of the electrical receivers’ distribution networks. This paper presents a study of the protection sensitivity factor, taking into account the influence of the network capacity and the resistance during a fault. The results of this study determined the minimum permissible values of the sensitivity factor that ensures the stable operation of the protection device. This was achieved by taking into account the influence of the transient resistance at the point of short circuit. The practical significance of the study is as follows: the obtained characteristics will allow for the development of new functional logic circuits for SPGF protection. The practical implementation of the obtained results will allow for the following: to increase the sensitivity and selectivity of current non-directional protections in conditions of incomplete short circuits; to ensure the reliable functioning of technological equipment and responsible consumers; to reduce the level of electrical injuries of service personnel; and to reduce economic losses associated with the repair of damaged electrical receivers.

The article proposes a constructive technical solution to increase the contact adaptivity of the mechanical roof support. The developed solution of the mechanized support section is able to adapt to changing mining and geological conditions in the process of excavation of the mining pillar, which increases the efficiency and safety of coal excavation in the longwall.

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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