| 摘要 |
PURPOSE:To prevent a resistor for rheostatic braking from overheating and burning by varying the conductive ratio of a chopper for rheostatic braking based on the current detection signals from a stringing current detector. CONSTITUTION:A conductive ratio arithmetic circuit 12 operates the conductive ratio of a chopper 7 for rheostatic braking so that the voltage between terminals of a filter condenser 5 may become the predetermined value. On the other hand, in case the power running current flows into the main circuit from a stringing power source 1, a stringing current detector 10 outputs a current detection signals to the conductive ratio arithmetic circuit 12. Thus the conductive ratio arithmetic circuit 12 sends out output signals of proper operational value to a phase shifter circuit 13 and narrows down the conductive ratio of chopper 7 for rheostatic braking. The current flowing to a resistor 6 for rheostatic braking is therefore limited and its over-heating and burning prevented.
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