Single-phase intermittent arc discharge, tree-to-bamboo grounding, etc. in the power system cause the system to generate ferromagnetic resonance overvoltage.
Single-phase grounding or inter-turn, inter-layer, and phase-to-phase short-circuit faults occur inside the voltage transformer itself.
A short circuit occurs on the secondary side of the voltage transformer, and the secondary side fuse is not blown, causing the high voltage fuse to blow.
Therefore, when replacing the voltage transformer primary and secondary fuses, be sure to use fuses that meet the specifications.
It should be pointed out that when the high-voltage phase fuse is blown, if the phase C fuses, the voltmeter indication of Ucn should be zero, and the voltmeters of the other two phases Uan and Ubn are still 100V. However, in the actual maintenance work, because the secondary circuit of the voltage transformer passes through the voltage coil of the active and reactive energy meter for metering and the voltage Relay coil in the protection circuit to form a loop, Ucn has a certain voltage indication, but its value Very small.
When the voltage transformer fuse is blown, first check the phase voltage of the input and output terminals of the secondary side fuses with 58V (line voltage 100V) with a multimeter, or take the fuse off and measure the on/off with the multimeter resistance file. Determine if the fuse is blown. If the fuse is intact, the fault occurs on the high pressure side.
The method of treatment is: first open the high voltage side isolation knife of the voltage transformer, remove the low voltage secondary fuse, and after confirming that there is no electricity, do the site safety measures, and then carefully check the voltage transformer once the casing and the end cover Whether there is crack, oil leakage, foreign matter and abnormal smell of insulating oil.
When an abnormality is detected, a megohmmeter is used to measure the insulation resistance. After confirming that the voltage transformer is normal, wear insulated gloves to replace the high-voltage fuses that meet the standard and conduct test transmission.
If it is blown again, the internal fault of the voltage transformer should be considered, and further tests such as DC resistance and ratio should be made to determine whether the voltage transformer is good or bad. Before the voltage transformer is deactivated, the effects on relay protection, automatic devices and metering should be taken into account. After obtaining the dispatch and the permission of the responsible person, the protection device and the automatic device are temporarily deactivated to prevent other devices from malfunctioning. .
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