| 摘要 |
PURPOSE:To judge a service interruption with a high speed and high reliability by a method wherein the service interruption is judged in accordance with the decline of a power supply frequency and a power supply voltage. CONSTITUTION:A first detecting means 8 has two detection characteristics with which a decline not less than 0.5Hz of a power supply frequency for 10-20sec. or longer and a decline not less than 0.25Hz of the power supply frequency for 10-20sec. or longer are detected respectively. A second detecting means 9 has two detection characteristics with which a decline not less than 10% of a power supply voltage for 10msec. or longer and a decline not less than 6% of the power supply voltage for 10msec. or longer are detected respectively. A judging means 10 judges a service interruption in accordance with the combinations of the four detection characteristics. For instance, the output of a fourth AND gate 23 corresponding to the decline of 0.25Hz of the power supply frequency and the decline of 6% of the power supply voltage is given to an output circuit 15 which disconnects phase advancing capacitors to accelerate the attenuation of a residual voltage and the other respective output circuits 11, 12, 13 and 14 corresponding to the outputs of the other AND gates 20, 21 and 22 judge a service interruption to switch the power supply and to disconnect the other loads. |
