According to GOST 11677 (Interstate Standard 11677),
IEC – 76 standards

Power down-step three-phase double winding for general purposes oil transformers, power rating from 10 to 4000 kVA for voltage up to 35 kV are intended for national economy needs. Indoor and outdoor installation is possible.

Specification

ТМ-10–4000 power transformers are manufactured with primary winding (HV) voltage rating up to 10 kV and secondary winding (LV) voltage rating up to 0.4 kV, other voltage combinations are possible under agreement with the consumer. Connection scheme and group are Y/Yn -0; D/Yn –11.

Voltage is regulated without excitation. Hence the transformers are equipped with HV tap changers, which are connected to HV winding and allow voltage regulation on LV and HV side by ±2 х 2.5 % steps while the transformer is switched off the system.