| 摘要 |
PROBLEM TO BE SOLVED: To surely detect the failure of a linkage/parallel-off semiconductor switch such as a thyristor switch, etc. SOLUTION: An instrument current transformer 21 which measures a current applied to a linkage/parallel-off semiconductor switch (thyistor switch 13), and a failure detection circuit 22 are provided. The circuit 22 has a means which judges whether the semiconductor switch is in a control state or not in accordance with a control state signal; a means which judges whether a current is applied to the semiconductor switch or not in accordance with the measurement signal of the current transformer 21; and a means which processes the judgement results of both the judging means through a logic gate, and judges that the failure of the semiconductor switch exists if it is judged that the current is not applied to the semiconductor switch while the semiconductor switch is in an on-control state, or that the current is applied to the semiconductor switch while the semiconductor switch is in an off-control state. |
