Electromagnetic processes in transformers during their disconnection by vacuum switches

The influence of the operation of vacuum switches on the electromagnetic processes of transformers of distribution networks has been studied. It is shown that during the disconnection of transformers from the network with the connection scheme of the windings "Wye/Wye, with neutral brought out for grounding" causes significantly higher multiples of overvoltages in the windings than the disconnection of transformers with the connection scheme of windings "Delta/ Wye, with neutral brought out for grounding". It was established that the multiplicity of overvoltages depends on the amount of previously stored magnetic field energy. The value of the magnetic fluxes before disconnecting the transformer for the connection schemes of the windings "Wye/Wye, with neutral brought out for grounding" exceeds the similar ones for the connection schemes "Delta/ Wye, with neutral brought out for grounding". In the process of turning off the transformer with the " Wye/Wye, with neutral brought out for grounding " winding connection scheme, the zero sequence magnetic flux increases compared to the nominal one, and with the "Delta/ Wye, with neutral brought out for grounding " connection scheme, there are no zero sequence magnetic fluxes. When studying the process of turning off the transformer with a vacuum switch, it is important to take into account multiple re-ignition, which occurs if the restored voltage between the contacts of the vacuum switch becomes greater than the electrical strength of the dielectric after opening the contacts. It was established that the occurrence of repeated circuits in the vacuum circuit breaker when the transformer is turned off does not create a dangerous effect on the longitudinal insulation of the windings of the higher voltage of the transformer, but leads to dangerous overvoltages in the windings of the lower voltage of the transformers. The occurrence of dangerous overvoltages in the lower voltage windings of transformers requires forced limitation of overvoltages from the winding side with the help of overvoltage limiters capable of limiting overvoltages on the lower voltage windings caused by repeated multiple ignitions in vacuum switches. New causes of damage and the nature of their appearance in electrical equipment and the possibility of researching electromagnetic processes in equipment with high-voltage windings have been established. The conducted studies and calculations indicate the need for a step-by-step review and adjustment of all regulatory documentation regarding the protection of distribution network equipment (in particular, transformers) against internal overvoltages.