Direct current on the DC transmission pole line of the high voltage direct current（HVDC） project is one of the most critical technical data for supervising the operating conditions and system control.Harmonic currents

which caused by the converter in HVDC

superimpose on the direct current

and this will interfere the telephone & communication lines.In recent years

the possible interference has been more and more heavily restricted in the specifications of HVDC-schemes

which requires the current sensor to offer the accurate harmonic current signal to active DC filter to suppress interference effectively.For this reason

a new optical fiber current sensor suitable for high-voltage environment is designed to measure currents of HVDC pole line accurately.This paper describes its principle

construction and key technologies adopted in detail.