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Effects of Electric Fields

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The electric field produced by a HVDC transmission line is a combination of the electrostatic field created by the line voltage and the space charge field due to the charge produced by the line’s corona. Investigations of the environmental influence of electric fields around HVDC transmission lines performed in Canada and Russia have shown that the discomfort to humans that is typically felt under HVAC transmission lines is not observed under HVDC lines.

This discomfort arises from spark discharges from humans to bushes, grass, and other vegetation.

While discharges also occur under the influence of the HVDC transmission line electric fields, these discharges are quite infrequent in contrast to the discharges caused by HVAC transmission line fields, which can amount to 100 discharges per second.

Subjectively, the sensation perceived by a human standing under a HVDC overhead line does not usually go beyond the electrostatic stimulation of hair movement on the head. Such results suggest that electrostatic fields below HVDC transmission lines are limited and generally are not hazardous to humans.

You can see from the photos that the AC lines generated much stronger magnetic and electric fieldshttp://electrical-engineering-portal.com/wp-content/uploads/2016/06/hvdc-hvac-electric-field-120x84.jpg 120w, http://electrical-engineering-portal.com/wp-content/uploads/2016/06/hvdc-hvac-electric-field-280x195.jpg 280w, http://electrical-engineering-portal.com/wp-content/uploads/2016/06/hvdc-hvac-electric-field-360x250.jpg 360w" sizes="(max-width: 728px) 100vw, 728px">
HVDC line running along side a traditional AC line. The lines carry 500 kV DC each. You can see from the photos that the AC lines generated much stronger magnetic and electric fields. The electric field meter was pegged under the AC lines. (photo credit: michael1111.blogspot.rs)

A study done in Canada found that large machines with rubber tires (such as combine harvesters, automobiles, and someothers) are not electrically charged to dangerous levels when the machines are standing under HVDC overhead lines.

The electrical resistance in the tires of these machines, while high (at about 10 megaohms), turns out to be low enough to prevent the accumulation of a dangerous charge (via charge leakage) even when the machine is standing on dry asphalt. In the case of HVAC overhead lines, induced capacitive currents on large machines may reach dangerous levels.

In addition to a static electric field, the space charge around a DC line produces a flux of ions away from the line.

Measurements show that in good weather the ion current existing under an HVDC overhead line (corona) can lead to an increase in the concentration of positive ions in the air from normal 103 – 104 levels to 106 – 107 per cubic inch. During precipitation events, however, this value can rise several times higher. Positive ion concentrations higher than 105 per cubic inchare considered detrimental to health due to prolonged exposure of the human respiratory tract.

The level of corona-induced space charge from HVDC lines is variable, as it depends on weather conditions. Thus, the total electric field and ion current flux near a transmission line must be described statistically. Guidelines designed to limit the health impact of electrical fields from transmission lines typically include separate limits on the total electric field of a DC line including space charge, the electrostatic field, and the ion current density.

Local codes and regulations limiting the electrical field impact exert a large influence on the design of overhead line construction, and on the resulting technical and economic performance of the HVDC transmission lines ultimately built.


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