ELECTRIC TRACTION USING BRUSHLESS MOTORS (INDUCTION MOTORS AND SYNCHRONOUS MOTORS)

The brushless motor, the dream of every railway engineer, was used as a traction machine at a very early stage in the form of an induction motor fed from a fixed-frequency supply. However, this technique failed to find general acceptance because of the costly stationary installations required and the fact that speed control was only possible in coarse steps. The brushless motor has become suitable for traction applications only by the advances in control and power electronics, enabling it to be fed from a variable-voltage, variable-frequency supply. In France, the application of the synchronous motor and induction motor is being tested in parallel. The paper describes the different technical solutions chosen by SNCF for lines operating at 1500 V dc and at 25 kV, 50 Hz single-phase ac. In addition, three motor coaches of the Paris Metro (750 V dc) with inverters and induction, motors are being tested by RATP. In the long run, the commutator motor will, no doubt, be superseded by the new technology, however, no single, universally applicable solution has yet appeared.