A Research of Digital Directional Current Protection Devices Operation Stability in Transient Modes During Single Phase to Earth Faults in 6-10 KV Networks With Isolated Neutral Point

Single phase to earth fault is the prevailing type of damage in 6-10 kV medium voltage networks. The most dangerous of single phase to earth faults is intermittent arc earth faults, which are accompanied by significant overvoltage in electrically connected network. In 6-10 kV distribution networks in the function of earth fault protection device during the impossibility of simple and sustainable zero sequence current protection devices, directional zero sequence current protection devices are commonly used. According to the data from operating experience the main disadvantage of some directional zero sequence current protection devices is refusal-to-operate possibility during internal faults and unnecessary operation during external intermittent arc faults. That is why, the research and substantiation of directional zero sequence current protection devices realization principles, which can provide high dynamic stability of protection operation is the relevant objective. The main tendency of development of relay protection equipment, including single phase to earth protection devices is associated with introduction of microprocessor technologies and digital signal processing methods. Thus, in this work the research of functioning of protection devices during transient modes is made for digital-based performance of zero sequence current protection devices.