The equipment was switched off on March 31, 2018 by the relay protection due to internal winding damages. The autotransformer had already been operating for almost 45 years, so the probability of winding damages, and this is a major component of an autotransformer, was high. This is why it was decided to dismantle the old equipment and replace it with reserve one.
Emergency and restoration works were extremely important and complicated. The substation operated in a heavy regime since, as of the time of emergency repair of autotransformer AT-4, distribution devices 750 and 330 kV were connected only by autotransformer AT-3, which reduced the reliability of capacity delivery from Vuhlehirska TPP and Zaporizhzhya NPP.
All works were performed by transformers repair brigades of Bakhmut regional operation center, lasted for two months and sometimes included quite specific tasks. For example, there was a necessity to restore railway canvas to ensure the possibility of moving an autotransformer weighting 300 tonnes across the substation’s territory.
Thanks to coordinated and professional work of the repair brigade, the reserve autotransformer has been successfully commissioned. The substation is now functioning in a stable and reliable mode.
Technical re-equipment of 750 kV substation “Donbaska” was stipulated by Ukrenergo investment program for 2018 at the expense of depreciation funds. In particular, it also includes the replacement of surge arresters of 750 kV autotransformers and connection reactors of 750 kV substation “Pivdennodonbaska,” used to protect insulators from switching and lightning surges, as well as the replacement of defective gas-insulated 750kV current transformers.