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 can run equally well on DC or AC of any frequency, and many modern electric locomotives are designed to handle different supply voltages and frequencies to simplify cross-border operation. COUNT 5
QSN1 How can different range of voltages be supplied for AC locomotives? ANS1 multiple taps on the transformer QSN2 What was a disadvantage of DC system? ANS2 power-wasting resistors QSN3 What taps can provide lighting supply? ANS3 low-voltage transformer windings QSN4 What will AC/DC motor be replaced with? ANS4 three-phase induction motor QSN5 What is the main advantage of an induction motor? ANS5 can run equally well on DC or AC of any frequency