Development of DC Optical Current Transformer for Cable Protective Relay in Hokkaido-Honshu HVDC Link

摘要

We have developed an optical current transformer (OCT) based on the Faraday effect using a reflection Sagnac interferometer for DC current measurement, and we have been performing a field test on the Hokkaido-Honshu HVDC Link in Japan since Feb. 2008 in order to confirm its stability over time and under severe environment conditions. The developed OCT was designed to be installed under the cable head bushing without disassembling it. Therefore, the diameter of the sensor head is comparatively large: about 2m. The rated current is DC±1200A. For about one year of the field test, the variation of ambient temperature around the sensor head was from -15°C to 27°C, and we confirmed that the accuracy of our developed OCT conformed to the Japanese Electrotechnical Committee (JEC)- 1201 class 1PS requirements. This is the standard of AC current transformers, but the required error is lower than the full scale error generally used for DC current measurement. Therefore, in order to ensure the accuracy of our developed OCT in the small current region, the OCT is estimated by this standard. About one year of field data shows that the performance of our developed OCT is stable with no significant change.