Abstract: An improved traction apparatus for electrical vehicles that are supplied with energy over a contact line and that utilize a filter capacitor to smooth the input current to a DC convertor that is used to energize a driving motor. The improvement concerns means for avoiding surges of filter capacitor charging current when the line voltage rises after a line voltage drop. A thyristor is used to pass current to the convertor when the line voltage remains within a particular operational range and to block the flow of current to direct the current to a current limiting resistor when the line voltage begins to rise after a short duration or relatively longer duration voltage drop.