FIELD: relay protection; automation of electrical networks.
SUBSTANCE: invention is intended to improve the reliability of the operation of an electrical network with an isolated neutral with a single-phase earth fault (SPEF), based on the transfer of a developing or stable separated double earth fault (DEF) into an SPEF. The technical result is to increase the reliability of the operation of an electrical network with an isolated neutral with an SPEF by transferring, developing or stable DEF distributed among different overhead power lines, without disconnecting them in the SPEF of each of the overhead power lines. The technical result is achieved by registering the appearance of a zero-sequence voltage on the low-voltage buses of a power transformer, connecting one of the phases of the low-voltage buses to ground through a low-resistance grounding resistor, and monitoring the appearance of the fault current in the outgoing overhead power line. To switch the power supply of each line from the low-voltage buses of the power transformer, three remotely controlled switching devices are provided, the inputs of each of the three switching devices of the same phase are connected in parallel to the supply network, and their outputs of different phases are connected in parallel to the outgoing overhead power line so that the next remote switching on of any of the three switching devices in the conductors of the outgoing overhead power line changes the order of alternation of all three phases and the order will not be repeated with the next remote switching on of any of the other two switching devices. In normal operating mode, one of the switching devices on each overhead power line ensures the same phase rotation order. When a SPEF appears in an electrically connected network, a signal is generated for alternate short-term switching on to the ground of each of the phases of the low-voltage buses of the power transformer through a low-resistance grounding resistor, while controlling the simultaneous flow of current through it, as well as through the opposite phases of all overhead power lines that have persistent damage and developing insulation defects, the switching device of the overhead power line is left switched on, having a stable SPEF, characterized by a high increase in current in one of its phases at the moment of alternate short-term switching on of one of the phases of the low-voltage buses of the power transformer to the ground through a low-resistance grounding resistor, while promptly switching the corresponding switching devices to others overhead power lines that have developing insulation defects in the other two phases, while the switching devices of all overhead power lines that do not have permanent damage and developing insulation defects are left switched on. The switching devices of the overhead power line are forced to switch when a stable DEF occurs in it, characterized by a high increase in current in one of the phases, occurring simultaneously with an increase in the current in the phases with the SPEF of the overhead power line.
EFFECT: increase the reliability of the operation of an electrical network with an isolated neutral with an SPEF by transferring, developing or stable DEF distributed among different overhead power lines, without disconnecting them in the SPEF of each of the overhead power lines.
1 cl, 1 dwg
