The electric field and ion current environment under HVdc transmission lines is an important design consideration. The flux tracing method (FTM) for calculating the ground-level electric field and ion current density distributions is reviewed and the possible errors caused by the use of Deutsch's assumption in the FTM are estimated. Experimental data obtained under one dc test line and three operating dc transmission lines are compared with calculations made with the FTM. The results show that the most important factor influencing the electric field and ion current distributions is the corona onset gradient of the conductors, or indirectly, the conductor surface roughness factor. The results also show that for practical dc transmission-line configurations, any errors caused by Deutsch's assumption are quite small compared with the observed variations in experimental data.

The objective of this study was to assess the ability of humans to detect the presence of DC electric fields and ion currents. An exposure chamber simulating conditions present in the vicinity of high‐voltage DC (HVDC) lines was designed and built for this purpose. In these experiments, the facility was used to expose observers to DC electric fields up to 50 kV/m and ion current densities up to 120 nA/m2. Forty‐eight volunteers (25 women and 23 men) between the ages of 18 and 57 years served as observers. Perception of DC fields was examined by using two psychophysical methods: an adaptive staircase procedure and a rating method derived from signal‐detection theory. Subjects completed three different series of observations by using each of these methods: one was conducted without ion currents, and the other two involved various combinations of electric fields and ion currents. Overall, subjects were significantly more likely to detect DC fields as the intensity increased. Observers were able to detect the presence of DC fields alone, but only at high intensities; the average threshold was 45 kV/m. Except in the most sensitive individuals, ion current densities up to 60 nA/m2 did not significantly facilitate the detection of DC fields. However, higher ion current densities were associated with a substantial lowering of sensory thresholds in a large majority of observers. Data analysis also revealed large variations in perceptual thresholds among observers. Normative data indicating DC field and ion current intensities that can be detected by 50% of all observers are provided. In addition, for the most sensitive observers, several other detection proportions were derived from the distribution of individual detection capabilities. These data can form the basis for environmental guidelines relating to the design of HVDC lines. © 1996 Wiley‐Liss, Inc.

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