| 摘要 |
PURPOSE:To prevent an earth detection device from being subjected to insulation breakdown and to improve reliability, by connecting a line shortcircuit detection resistance of a line shortcircuit detection device to the earth side of a limiting resistance of the earth detection device. CONSTITUTION:A line shortcircuit detection device 40 connects series circuits of a voltage dividing resistance R1 and a line shortcircuit detection resistance r1, which is a variable resistance, respectively to a three-phase circuit of an AC excitation circuit 37. These series circuits are formed into a three-phase bridge in a Y-connection. An earth side of a limiting resistance R2 is connected to the neutral point of this three-phase bridge to complete the constitution. Both terminals of the line shortcircuit detection resistance r1 and the earth detection circuit resistance r2 are introduced to a detection section 6 respectively. Since the line shortcircuit detection resistance r1 is connected to the earth side of the limiting resistance R2, no potential of an isolation amplifier of the line shortcircuit detection device 40 will be so high against the earth as before that the occurrence of shortcircuit there can be prevented. |
