12kV Single-Phase Recloser, DNP3.0 Communication Reclosing Device, 11kV Pole-Mounted High-Voltage Recloser

Single phase reclosing is an automatic reclosing method used in power engineering for transmission line protection. Its operation mode is as follows: in case of a single-phase fault, only the faulty phase is disconnected and then reclosed; in case of an inter-phase fault, all three phases are tripped, and whether to perform three-phase reclosing is decided according to the situation; if reclosing is performed on a permanent fault, all three phases are disconnected. This method is mainly applied in large grounding current systems of 220kV and above, and can improve power supply reliability and system transient stability. Since the secondary arc current generated by the coupling of sound phases through capacitance and mutual inductance will affect the arc extinction at the fault point, measures such as grounding the neutral point of a high-voltage reactor or temporarily closing the grounding switch are required to extinguish the arc. Its phase selection elements include distance phase selection, phase current difference mutation phase selection, and phase current instantaneous overcurrent, etc. Internationally, single phase reclosing is mostly adopted for UHV lines above 1000kV, while phase-segregated reclosing is adopted for double-circuit lines on the same tower.

Power system operation experience proves that most faults on overhead lines are temporary, such as insulator surface flashover caused by lightning overvoltage, temporary line contact caused by strong wind, discharge through birds, and short circuit caused by branches falling on conductors. When the faulty line is quickly disconnected, the arc is extinguished, and the insulation strength at the fault point is restored. Therefore, performing a reclosing after the line is disconnected can greatly improve the reliability of power supply. Most lines of 110kV and below adopt three-phase one-time reclosing. According to operation experience, more than 70% of short-circuit faults in high-voltage overhead lines of large grounding current systems above 110kV are single-phase ground faults, especially for overhead lines above 220kV, the proportion of single-phase ground faults is even up to about 90% due to the large distance between phases. In this case, if only the faulty phase is disconnected and then single phase reclosing is performed, while the two sound phases continue to operate during the reclosing cycle, the power supply reliability and the stability of system parallel operation can be greatly improved. Therefore, single phase reclosing is widely adopted in large grounding current systems above 220kV. When the instantaneous single-phase ground protection trips one phase of the line, the sound phases supply capacitive current to the fault point through the inter-phase and phase-to-ground capacitances. At the same time, the load current of the sound phases generates induced potential on the faulty phase through the coupling of inter-phase current transformers, and supplies inductive current to the fault point through the inter-phase and phase-to-ground capacitances. These two parts of current together constitute the secondary arc current. The magnitude of the secondary arc current is related to line parameters. Generally, the higher the line voltage and the larger the load current, the larger the secondary arc current. Due to the existence of the secondary arc current, the arc at the fault point is not easy to extinguish, which delays the single phase reclosing. When fast single phase reclosing is adopted, it may cause the failure of single phase reclosing and lead to tripping of all three phases.

The time of single phase reclosing (the time from power supply disconnection at the fault point to re-application of operating voltage) must be longer than the time required for arc extinction at the fault point and line insulation recovery. Different from three-phase reclosing, during single phase reclosing when only the faulty phase is disconnected, before the arc at the fault point is extinguished, the fault point is still connected to the inter-phase capacitance, and current is supplied by the power sources of the other two phases that remain in operation to maintain the arc. After the arc is extinguished, the fault point mainly bears the distribution voltage formed by the two operating phase power sources through the phase-to-ground capacitance of the faulty phase. When the arc is stretched and disconnected due to current passing through zero, if the insulation recovery speed at the fault point is lower than the rising speed of the voltage wave across it, near the peak of the voltage wave, the insulation at the fault point will break down again. At this time, in addition to the arc current supplied by the non-faulty two phases, the electrical energy stored in the fault capacitance will also be released to the fault point, forming a re-ignition current whose peak is much larger than the previous steady-state arc current. This phenomenon repeats every half power frequency cycle, thus affecting the final arc extinction time. The higher the line operating voltage and the longer the line length, the longer the final arc extinction time. Artificial short-circuit tests and actual operation records have confirmed this conclusion. In order to shorten the single phase reclosing time to a reasonable value, for example, not more than about 1 second, to meet requirements such as system stability (reclosing time) and coordination of relay protection, while not reducing the success rate of reclosing, auxiliary arc extinguishing measures are widely adopted on medium and long lines with voltage of 500kV and above. There are mainly two types: ① At the neutral point of the high-voltage reactor connected to the line for line capacitance compensation, grounding is performed through a reactance of an appropriate value, which is equivalent to having a resonant inductor connected in parallel with it, thereby significantly reducing the follow current through the fault point and the recovery voltage across the fault point, providing a prerequisite for the fast and smooth final arc extinction of the fault arc. This method has been successfully and widely adopted in power systems. ② During the single phase reclosing process, the grounding switch is temporarily closed on both sides of the disconnected faulty phase line, making the fault point at a basically zero potential to achieve the purpose of fast arc extinction. For special important heavy-load lines (double-circuit lines on the same tower), if phase-segregated reclosing is successfully implemented considering the case of different-phase faults (such as fault on phase A of line A and phase B of line B), the grounding switch is a feasible method.