Field test of DC optical current transformer for HVDC Link

For DC current measurement, we have developed optical current transformer (OCT) based on Faraday effect using reflection Sagnac interferometer and performed the field test in Hokkaido-Honshu HVDC Link in Japan from Feb. 2008 in order to confirm its stability over time, and through environment condition. The developed OCT was designed to be installed at the bottom of the cable head bushing without disassembling it. Therefore the diameter of sensor head is comparatively large, about 2m. The rated current is DC ± 1200A. During about one year field test, the variation of ambient temperature around the sensor head was from -15°C to 27°C, and we have confirmed that our developed OCT is conformed to the Japanese Electrotechnical Committee (JEC)-1201 class 1PS. This is the standard for AC current transformer, however, in order to ensure the accuracy in the small current region, we apply it for our developed OCT. About one year data at the field shows that the performance of our developed OCT is stable with no significant characteristics changing.