Ensuring timely repair of power transformers based on data of complex diagnostics Makhsud Sultanov, Elena Zenina, Peter Shamigulov, Valentina Lunenko and Olga Zhelyaskova E3S Web Conf., 288 (2021) 01034 Published online: 14 July 2021 DOI: 10.1051/e3sconf/202128801034