| 摘要 |
<p>PURPOSE:To securely detect a zero-phase current by providing an overvoltage absorber in parallel to the resistance of secondary winding and connecting an optical voltage sensor to a tertiary winding circuit. CONSTITUTION:When electric power is supplied normally to a power transmission line connected to opening/closing electrodes 7a, 7b, and 7c of a switch 7, the sum of secondary currents induced at secondary coils 8b, 9b, and 10b of current transformers 8, 9, and 10 is zero and no voltage is developed across the resistance 11, so that none of the tertiary coils 8c, 9c, and 10c generate a voltage. Continuous light which is sent from an optical transmitter 1 to an optical transmission line 2 is therefore transmitted through the optical voltage sensor 12 which is applied with no voltage and outputted to a signal processing circuit 5 through an optical reception path 3 and an optical receiver 4. Here, if one phase of the line has a ground fault and a large zero-phase current flows, a large current and a high voltage generated at a secondary winding circuit are suppressed by the overvoltage absorber 18 to prevent a dielectric breakdown. Then the detected voltages of the tertiary coils 8c, 9c, and 10c are summed up and applied to the electrode of the sensor 12 and the light which is transmitted through the sensor 12 is polarized to display the flowing of the zero-phase current.</p> |
