| 摘要 |
PURPOSE:To remove a malfunction due to a noise, etc., by detecting an arc by a digital operation element in accordance with a voltage time area value of voltage generated between zero crossing of voltage and ignition of a thyristor. CONSTITUTION:When a digital operation element 18 detects a zero crossing signal detected by a zero crossing detector 13, it immediately counts a pulse train corresponding to magnitude of voltage sent from a voltage frequency converter 17. This operation is executed until a thyristor 2 or 3 is ignited, that is to say, until a voltage detector 12 detects a fall of voltage across the thyristor 1 or 2 and outputs a detecting signal Fi. A voltage time area value is calculated at every half-cycle, and in case when its mean value exceeds a reference value set in advance, the digital operation element 18 decides that an arc has been generated, and sends an alarm signal to an alarm device 6. In this way, since an arc is detected by the voltage time area value instead of a voltage level, it is detected with high accuracy. |
