Abstract
The insulation degradation of a voltage transformer winding is not easy to find, but it may ultimately cause the transformer to explode, leading to accidents such as phase-to-phase short circuits. At present, power transformers, lightning arresters, and other equipment have on-line methods to detect the insulation state. However, there is no mature method for the on-line monitoring of voltage transformer winding insulation. In this study, a small current disturbance method based on a zero-sequence loop is proposed. The characteristic parameters of the low-frequency oscillation of zero-sequence voltage after a disturbance are used to evaluate the insulation state of the winding and detect faults. Theoretical modeling, simulation tests, and field tests show that when the insulation resistance of the voltage transformer winding is in the range 0–40 kΩ, a low frequency oscillation of about 10 Hz can be detected on the zero-sequence voltage, and its amplitude and duration are proportional to the degree of damage to the insulation. This can hence be used as a criterion for the on-line detection of voltage transformer winding insulation defects.
Highlights
IntroductionThe harmonic elimination device is generally a non-linear silicon carbide resistor
It is generally believed that the ferromagnetic resonance can be eliminated when the ratio of the resistance value R of the primary harmonic elimination device to the excitation reactance Xm of the voltage transformer at the rated line voltage is greater than 0.06
In the field test, when the voltage transformer (VT) insulation is damaged, the third harmonic content of each phase voltage and zero sequence voltage obtained from the VT secondary end is significantly reduced, but the simulation test cannot get this trend
Summary
The harmonic elimination device is generally a non-linear silicon carbide resistor. It is generally believed that the ferromagnetic resonance can be eliminated when the ratio of the resistance value R of the primary harmonic elimination device to the excitation reactance Xm of the voltage transformer at the rated line voltage is greater than 0.06. Insulated electromagnetic voltage transformers and semi-insulated electromagnetic voltage transformers are currentlyused in the distribution network. Insulated VT means that the main insulation between the primary winding and the secondary winding and the ground is subjected to a
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