Voltage transformer is a transformer with iron core, which is mainly composed of primary and secondary coils, iron core and insulation. In the thunderstorm season, the occurrence of line fall lightning, porcelain vase flashover and other faults, resulting in voltage transformer high-voltage fuse fuse, and even burned voltage transformer. The main causes are the following.
When the 10kV line out of a single-phase grounding, the voltage transformer primary side of the non-fault relative ground voltage for the normal voltage value times. Voltage transformer core soon saturated, the excitation current is sharply enhanced, so that the fuse fuses.
Voltage transformer low-voltage side turns and phase short circuit, low-voltage insurance has not yet fused, due to the rapid increase in the excitation current, so that the high-voltage fuse fuse fuse or burned transformer.
As the power network contains capacitive and inductive parameters of the components, especially the ferromagnetic inductive components with iron core, in the parameters of the combination of unfavorable cause ferromagnetic resonance. Such as non-simultaneous closing of circuit breakers, with transformers, ferromagnetic voltage transformer no-load bus input, distribution transformer high-voltage line volume short circuit to ground, may cause ferromagnetic resonance. In the event of ferromagnetic resonance, the overvoltage multiplier can be more than 2.5 times, which causes insulation breakdown of electrical equipment, burning equipment accidents.
The following measures can be taken to protect the voltage transformer.
Strengthen the substation duty system to eliminate the phenomenon of high-voltage fuses replaced by low-voltage insurance.
Install zero-sequence grounding automatic switch on the primary side of the voltage transformer grounding line to cut off the grounding line; install 3-5A small air switch on the secondary side to avoid short-circuiting and burning by the voltage transformer.
Install detuning device in parallel at the open triangle of 10kV voltage transformer