An early advantage of AC is that the power-wasting resistors used in DC locomotives for speed control were not needed in an AC locomotive: multiple taps on the transformer can supply a range of voltages. Separate low-voltage transformer windings supply lighting and the motors driving auxiliary machinery. More recently, the development of very high power semiconductors has caused the classic "universal" AC/DC motor to be largely replaced with the three-phase induction motor fed by a variable frequency drive, a special inverter that varies both frequency and voltage to control motor speed. These drives <answer>can run equally well on DC or AC of any frequency</answer>, and many modern electric locomotives are designed to handle different supply voltages and frequencies to simplify cross-border operation.
What is the main advantage of an induction motor?
can run equally well on DC or AC of any frequency