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Overhead Lines

High Voltage Direct Current (HVDC)

Page 8:  Overhead Lines (OHL)
Low Impact

Overhead lines (OHL) for HVDC are very low impact, producing much less radiation than AC lines and allowing for agriculture and other plants under the lines.

Figure 8.1  Steel transmission tower for a 2400 km ±600 kV EHVDC line in Brazil.

Figure 8.2  Transmission towers for 2076 km 4 GW ±800 kV UHVDC line in Brazil.

“there is no field inside the body as if the body is protected by a ‘Faraday Cage’, possible leakage currents are negligible. The effect of the electrostatic induction only occurs by entering and escaping the static electrical field, and thus the field is not able to produce permanent body currents.”
— 
Nadine May, “Eco-balance of a Solar Electricity Transmission from North Africa to Europe”, Technical University of Braunschweig, 2005, p. 44–45.
“It is best for the proposed transmission servitude route to follow the existing road networks and settled corridors through the five countries… The land footprint must be kept to an absolute minimum so as to allow for continued land use such as undisturbed natural ground or commercial farming etc. and presence of the line has no effect on normal wild life movements.”
— 
Thomas J. Hammons, Pathmanathan Naidoo, “Africa – Integrated gas and electricity transmission planning in power generation and HVDC engineering in harnessing large-scale hydroelectric sites for interconnected regional power systems”, Energy Systems, (2010) 1: 79–112, p. 102.
“the experimental fact that large machines with rubber tires (such as combine harvesters, automobiles, and some others) are not electrically charged to levels dangerous for a human when the machines are standing under HVDC overhead lines should be considered a significant result of the investigation. The electrical resistance in the tires of these machines (at about 10 MOhm) turns out to be 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, inducted capacitive currents on large machines may be lethal in some cases.”
— 
L. A. Koshcheev, “Environmental Characteristics of HVDC Overhead Transmission Lines”, Third Workshop on Power Grid Interconnection in Northeast Asia, Vladivostok, Russia, St-Petersburg, High Voltage Direct Current Power Transmission Research Institute, 2003, p. 3.

Figure 8.3  Agricultural machinery under bipolar HVDC line in Canada without problem. Three-tier power lines in the distance are AC.

Figure 8.4  HVDC transmission towers may be guyed (left) or self supporting without guy wires (right). Towers with guy wires are called tangent towers and can only be used on sections of transmission lines that do not change direction (referred to as tangent lines). [Manitoba Hydro]

Ultra-high voltage DC (UHVDC) requires more ground clearance for conductors than HVDC. Research is being conducted into possibly hanging ground wires between the conductors and the ground for sections of UHVDC lines that may be lower to the ground.


References for this page:

 1.  Baljit Singh, Gagandeep Sharma, “Power upgrading of Transmission Line by converting EHVAC into EHVDC”, International Journal for Science and Emerging Technologies with Latest Trends, 4(1): 20-24 (2012). pdf


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