Study on simulation and experiments of method of extinction hybrid on-load tap changer in transformers

Arc appears in the switching process of traditional on-load tap changer of transformer significantly, reduces contact life, and accelerates the deterioration of transformer oil. To solve this problem, we developed a procedure of hybrid on-load tap changer, and made a laboratory prototype following the procedure. In the procedure, telescopic movement moving contacts were adopted to ensure switching timing, mechanical components were used for passively triggering of thyristor modules, and the thyristors were used to assist machinery to extinguish arcs. Moreover, we established a numerical model of the arc-eliminating circuit to conduct simulations, and set up a standard low-voltage switching test circuit to conduct experiments. The simulations show that the thyristor gate trigger circuit is simple and reliable, and it is effective in inhibiting the establishment of arc voltage and hence eliminating arcs. The experimental results show that, in one switching process of a thyristor, the thyristor will be triggered by four times: two are natural current zero-crossing off, the other two are off after bypassed by mechanical switch. The simulation and experimental results validate each other, which further proves the proposed hybrid arc-free load tap switching method to be feasible.