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在中性点非直接性接地电网(又称小电流接地系统)中发生单相接地时,由于故障电流很小,而且三相之间的线电压仍然保持对称,对负荷的供电没有影响,因此,在一般情况下都允许继续运行1～2h,而不必立即跳闸。但是在单相接地后,其他两相的对地电压要升高3~(1/2)倍,为了防止故障进一步扩大形成相间短路,要求及时发出信号,以便运行人员采取措施予以消除。 通常情况下,对单相接地故障的保护是采用绝缘监视装置,利用单相接地时电压互感器开口三角形绕组出现的3U_0发出信号,但是不能指出是哪一条线路
When a single-phase ground occurs in a neutral indirect non-earthed network (also referred to as a small current grounding system), since the fault current is small and the line voltage between the three phases remains symmetrical and has no effect on the power supply to the load, , In normal circumstances are allowed to continue running 1 ~ 2h, without having to immediately trip. However, after single-phase grounding, the voltage of the other two phases should be increased by 3 ~ (1/2) times. In order to prevent the further expansion of the fault to form a short circuit between phases, it is required to send a signal in time so that the operators can take measures to eliminate them. Normally, the protection of single-phase to ground fault is the use of insulation monitoring device, the use of single-phase voltage transformer opening triangular winding appears 3U_0 signal, but can not indicate which line