METHOD AND APPARATUS FOR MEASUREMENT OF CURRENT BY USING PHOTOCURRENT SENSOR

PROBLEM TO BE SOLVED: To obtain a measuring method and a measuring apparatus, which use a photocurrent sensor capable of precisely measuring the difference between the inflow current and the outflow current of a power facility, as an object to be protected, even in a region in which an electrification current is a large current. SOLUTION: A first photocurrent sensor 2 is installed, so as to measure an inflow current i1, and second photocurrent sensor 3 is installed to measure an outflow current i2. A signal processing means 1 comprises a light-emitting means 12, a light-receiving means 16, an AC-signal detection means 17, a DC-signal detection means 18, a division means 19 and a power-supply frequency-component detection means 20. The light- emitting means 12 and the first photocurrent sensor 2, the first photocurrent sensor 2 and the second photocurrent sensor 3 and the second photocurrent sensor 3 and the light-receiving means 16 are connected in series by respective light signal transmission means 4. Regarding a frequency component, which is twice that of the electrification current of a power facility contained in the signal of a difference current measured by the photocurrent sensors, the frequency component which is the same as the energizing current is taken out, and an output which is proportional to the difference current i1-i2 is obtained.