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Fig.
Main protection of a Yyn(d) connected power transformer and control of the HV side circuit breaker using a RET615 with the standard configuration D. Restricted E/F protection with a high impedance scheme is applied on the transformer MV side. A REF615 with the standard configuration C is used as redundant back-up protection on the HV side. In addition, a REF615 with the standard configuration F is used on the MV side to provide, besides O/C and E/F back-up protection, busbar overvoltage and undervoltage protection. Further, the REF615 with the standard configuration F enables local/remote control of the circuit breaker on the MV side.