Increasing the Sensitivity of Current Protection of Distribution Networks 6–10 K v Based on Linear Voltage Measurements

There is a problem of ensuring sufficient sensitivity of current relay protection in distribution networks 6–10 kV. Features of overhead distribution networks 6–10 kV are the reasons for the insufficient sensitivity of current protection: the use of steel and steel-aluminum wires of small sections, the long length of overhead lines of distribution networks, the remoteness of small power supplies. All these factors affect the magnitude of the short circuit current at the most remote point of the line of the main zone, while the short circuit currents are close in magnitude to the currents of the maximum mode, which leads to an overestimation of the relay operation current and, as a result, insufficient sensitivity not only in the zone protection redundancy, but also in the main protection zone. The article considers a device that has increased sensitivity during two-phase short circuits, compared with devices that respond both to a decrease in the mains voltage and to a change in the negative sequence voltage. The device consists of a number of blocks that perform the following functions: signal inversion, signal multiplication of two input line-to-line voltages, a direct current component extraction unit, a minimum value extraction unit from three input signals. The simulation results showed the advantage of the proposed method for increasing the sensitivity of current protection.