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In addition to static electric and magnetic fields (EMF), the electric voltage and current present in a Direct Current (DC) transmission line can produce other electrical effects. This information sheet addresses the potential electrical effects of DC transmission lines on farming operations and communications. For more information on EMF and DC transmission lines, please refer to ATCO Electric’s information sheet entitled “Facts About Direct Current Electric and Magnetic Fields”.
Corona
Under certain conditions, the electric field very close to an energized conductor can be sufficiently concentrated to produce a tiny electric discharge that can ionize air close to the conductors. This partial discharge of energy is called corona.
Because corona contributes to energy losses, transmission lines are designed so that, normally, they do not initiate corona. However, surface irregularities on the conductor i.e. scratches, water droplets, dust and other contaminants, create the conditions that initiate corona. When corona is present on a transmission line, it produces audible noise in the form of a buzzing sound, electromagnetic interference (EMI), sometimes referred to as radio interference, and an increase in the static electric field under the line.
Audible Noise
Transmission facility owners must meet noise limits set by the Alberta Utilities Commission (AUC). These limits must be met when measured at night during fair weather, at the nearest dwelling. If there are no dwellings nearby, the noise limit cannot be exceeded when measured at a distance of 1,500 metres from the transmission facility. In a rural setting, the limit is typically 40 decibels, which is only slightly higher than the typical background level you would expect to find in a rural area.
ATCO Electric’s DC transmission line will be designed so that it meets the AUC noise limit at the edge of the right-of-way, about 30 metres from the center of the line structures. Because existing residences will be at least 150 metres from the right-of-way, this should provide added insurance that audible noise from the line will not be a nuisance to local residents.
Communications Interference
The EMI that results from corona has been known to interfere with AM radio and analog television reception, but usually only if you are directly beneath or very close to the transmission line. Modern communication media such as satellite television, FM radio, cellular telephones, wireless internet, and two way radios operate at much higher frequencies (100 to 1000 times higher) and rarely experience interference from EMI.
ATCO Electric observes all Canadian and Alberta electrical codes with respect to communication interference. Industry Canada stipulates that within six months of the line being energized, radio noise levels are to be measured, and that they must fall within set limits. In the rare event that reception problems occur due to our facilities, ATCO Electric works with Industry Canada to make every reasonable effort to correct the interference.
GPS
The GPS used for navigation by farm equipment also operates at high frequencies and should not experience interference from EMI. The fact that GPS service is provided from numerous satellites in operation at any time also makes signal loss very unlikely.
Livestock/Domesticated Animals and Wildlife
The low static electric and magnetic fields produced by DC transmission lines are similar to the naturally occurring static fields in our environment and are not viewed as a health concern for animals.
Bees
Effects on bees have been shown for alternating current (AC) fields but only for field levels higher than those typically found under AC lines. No research appears to have been conducted on the effects on bees from the static fields found under DC lines but there is no reason to believe that such a study would reach a different conclusion.
However, it would be prudent to relocate hives away from the transmission line so they are not impacted by construction activity. ATCO Electric would assist in the relocation.
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