(1) When the high-voltage fuse of the voltage transformer gives out the grounding signal in one phase, if the relative ground voltage of the fault decreases while the voltage of the other two phases increases and the line voltage remains unchanged, it is a single-phase grounding fault.
(2) asymmetrical arrangement of bus or overhead wires in substation; Drop type fuse in the line one phase fuse; The use of RW type drop switch control long line switching operation is not the same period, will cause three relative capacitance imbalance, so that the neutral point voltage rise and give out grounding signal, this situation occurs in the operation, and the line did not actually occur grounding.
(3) When the empty bus is closed, the ferromagnetic resonance overvoltage is generated due to the adverse combination of excitation inductive reactance and ground reactance, and the grounding signal will be reported. This situation mostly occurs in the single phase disconnection, intermittent arc grounding caused by resonant overvoltage, and the system has not occurred grounding fault.
(4) When the 10kV line is struck by lightning and arc light is grounded, the voltage of the sound phase voltage transformer increases suddenly, and the coil flows through a large inrush current, which saturates the core magnetic of the transformer and leads to reduced inductance and inductive reactance. When the inductive reactance is less than the capacitive reactance, after the core magnetic saturation of the sound phase transformer, the neutral point voltage will rise, and the insulation monitoring will also report the grounding signal. In fact, the power grid has not been grounded.
(5) During the operation of 10kV power grid, the single-phase wire is broken; Artificial "lack of phase operation" when avoiding falling and adjusting load; The operation of high-power single-phase equipment will cause serious imbalance of three-phase load, which will lead to the rise of neutral voltage. At this time, insulation monitoring also gives out grounding signal, but the power grid has not been grounded.
(6) When the 10kV line is struck by lightning, due to the mutation of the electric field, the bound charge on the wire becomes free charge and moves to both sides of the wire at approximately the speed of light, forming overvoltage wave and generating induced overvoltage. When the surge wave reaches the line arrester, the gap breakdown discharge voltage is limited when the shock voltage is greater than the arrester discharge voltage. But as a result of lightning arrester discharge gap volt-ampere characteristic, nonlinear coefficient of different valve plates and the influence of the manufacturing process, etc., make each phase arrester discharge voltage, the residual pressure, arcing voltage range, leading to a slow and fast appear unbalanced three-phase voltage, so that the neutral point voltage rise, quote us ground signal, however did not happen grounding grid fault.
Wuhan Xinshengneng Technology Co., LTD
