A method for performing diagnostics on a target transformer, the method comprising: applying, by switch circuitry, a voltage output of a voltage generator to a winding or phase of the target transformer; and controlling, by a processor (120, 505), the voltage generator to output an AC voltage at a first frequency; a) measuring, by the processor (120, 505), a first excitation current flowing into the target transformer associated with the first frequency; b) controlling, by the processor (120, 505), the voltage generator to output an AC voltage at a second frequency; c) measuring, by the processor (120, 505), a second excitation current flowing into the target transformer associated with the second frequency; d) determining, by the processor (120, 505), an actual excitation current of the target transformer as a function of both first and second excitation currents; e) comparing, by the processor (120, 505), the determined actual excitation current of the target transformer to excitation currents associated with one or more benchmark transformers having known electrical characteristics; and when the actual excitation current of the target transformer matches an excitation current of one of benchmark transformers, determining the electrical characteristics of the target transformer to match electrical characteristics of the one benchmark transformer. applying, by switch circuitry, a voltage output of a voltage generator to a winding or phase of the target transformer; and controlling, by a processor (120, 505), the voltage generator to output an AC voltage at a first frequency; a) measuring, by the processor (120, 505), a first excitation current flowing into the target transformer associated with the first frequency; b) controlling, by the processor (120, 505), the voltage generator to output an AC voltage at a second frequency; c) measuring, by the processor (120, 505), a second excitation current flowing into the target transformer associated with the second frequency; d) determining, by the processor (120, 505), an actual excitation current of the target transformer as a function of both first and second excitation currents; e) comparing, by the processor (120, 505), the determined actual excitation current of the target transformer to excitation currents associated with one or more benchmark transformers having known electrical characteristics; and a) measuring, by the processor (120, 505), a first excitation current flowing into the target transformer associated with the first frequency; b) controlling, by the processor (120, 505), the voltage generator to output an AC voltage at a second frequency; c) measuring, by the processor (120, 505), a second excitation current flowing into the target transformer associated with the second frequency; d) determining, by the processor (120, 505), an actual excitation current of the target transformer as a function of both first and second excitation currents; e) comparing, by the processor (120, 505), the determined actual excitation current of the target transformer to excitation currents associated with one or more benchmark transformers having known electrical characteristics; and when the actual excitation current of the target transformer matches an excitation current of one of benchmark transformers, determining the electrical characteristics of the target transformer to match electrical characteristics of the one benchmark transformer.