Over-voltage prevention device and current rectifying circuit

摘要

According to one embodiment, an over-voltage prevention device includes a first short-circuit device (12) provided between a secondary side of a wound-rotor induction machine (1) and a frequency converter (7) configured to excite the secondary side by a three-phase AC current and having a function of shortcircuiting between phases of the three-phase AC current, resistors (13) each connected between the first short-circuit device (12) and the frequency converter (7) for each phase, and second short-circuit devices (14) connected respectively to the resistors (13) in parallel and having a function of shortcircuiting between the frequency converter (7) and the secondary side of the wound-rotor induction machine (1).