Provided is a relay dualization apparatus, in a substation automation system including at least one or more upper units and at least one or more lower units, the apparatus including a plurality of first relays receiving a power data from the lower unit using a predetermined communication method, and transmitting the power data to the upper unit, and receiving a control command from the upper unit and transmitting the control command to the lower unit, and a second relay performing communications with the plurality of first relays using the communication method to replace a relay that has generated an error in the plurality of relays.