| 摘要 |
<p>PURPOSE:To sense a current or voltage value of 3-phase AC by a signal value inputted from an optical fiber sensor still after a ground-fault by providing the optical fiber sensor, an LED and a CPU. CONSTITUTION:According to zero-phase current/voltage sensor LED control circuits 4-6, when 3-phase AC is normal, a CPU 22 derives an average value being equivalent to a DC component of an input signal from optical fiber sensors 1-3. Subsequently, by a command value being proportional thereto, a command is given to D/A converters 26-28, a current which is allowed to flow to the LEDs 4-6 is controlled, and the generation quantity of the LEDs 4-6 is kept constant. In this state, when the CPU 22 has decided that the input signal from the sensors 1-3 is a ground-fault accident of 3-phase AC, the CPU 22 fixes the command value to the converters 26-28 by a value immediately before the ground-fault accident has occurred. In such a way, still after the ground-fault accident, a current or voltage value of 3-phase AC can be sensed by input signal data from the sensors 1-3.</p> |
