Performance of a long-time unattended station for measuring DC fields and air ions from an operating HVDC line

The authors describe the experience of the Bonneville Power Administration in building and operating a long-term, unattended station to measure electric fields and air ions from the Pacific NW/SW HVDC (northwest/southwest high-voltage direct current) Intertie. The major emphasis is on the performance of the unipolar ion counters, as these have been the most difficult type of instrument to incorporate in an outdoor measurement station. Based on this experience, if heat is properly applied to the ion counter and good procedures are used for regular calibration and maintenance of all the instrumentation, then electric field and air ion instrumentation can be operated unattended in an outdoor environment