|Environmental Handbook Volume II: Agriculture, Mining/Energy, Trade/Industry (GTZ, 1995, 736 p.)|
|Mining and energy|
|42. Power transmission and distribution|
Adequate power supply systems constitute an essential part of any country's technical infrastructure. Such systems comprise facilities for the generation, transmission and distribution of electricity.
This brief deals with the planning, construction and operation of all technical facilities required for transmitting and distributing electric power.
Transmission is understood as the conveyance of electrical energy from its place of generation to its place of use. Power transmission is characterized by the conveyance of electric power over comparatively long distances with the aid of high-voltage and medium-voltage systems. Depending on the relative locations of the power generating facilities and the power consumers, many different forms of landscape and vegetation can be affected.
Distribution is understood as the delivery of electric power from the bulk power source to the consumer. As a rule, this involves relatively short distances within populated areas by way of medium-voltage and low-voltage systems.
The technical facilities required for transmitting and distributing electric power comprise mainly:
- overhead power lines
- transformer and switching stations.
Direct effects on the environment result from the erection and operation of such facilities, with the extent and intensity of the impacts depending substantially on the physical circumstances and the project planning.
This section describes and illuminates the direct and indirect effects of power transmitting equipment on the natural environment, i.e.:
- resources (water, soil, air) and
- ecological systems (flora and fauna, interlinked biotopes)
as well as on humans, i.e.:
- their health and safety, occupational and otherwise,
- their socioeconomic and sociocultural circumstances, as well as
- their visual perceptions.
2.1 Consequences for the natural environment
· Soil, water and air
In wooded areas, the erection and safe operation of overhead power lines necessitate the maintenance of unobstructed lanes, the widths of which vary between 25 and 100 meters, depending on the size of the transmission line. Paved or unpaved access roads may be needed for installing and inspecting the lines and towers. That, in turn, entails the permanent destruction of forest; due to the loss of its original vegetation, the disturbed soil is at least temporarily unprotected and exposed to the climatic effects of heat, frost and rain, all of which promote erosion. Soil compaction resulting from project-site motor vehicle traffic intensifies the soil's susceptibility to erosion. Afterward, the affected area is only conditionally suitable for other forms of utilization. Any strip of land that cannot be used for forestry purposes due to its being located along a right of way (danger of grounding) should be greenbelted in order to combat erosion. The use of space-saving components helps reduce the space requirement quite substantially.
The erection of towers and tower footings on steep slopes demands detailed knowledge of the subsoil situation. Any mistake made in planning and executing the work can seriously impair the stability of the slope and lead to slip erosion.
The construction of switching and transforming stations permanently occupies certain areas and jeopardizes the soil and groundwater through the potential leakage of coolants and insulants (mineral oil or other liquids possibly containing toxic polychlorinated biphenyls - PCB) in large quantities from such components as transformers, capacitors, ground-fault neutralizers and underground cables.
Suitable collecting troughs/separators must be provided to prevent contamination of the groundwater and soil.
· Flora and fauna
Due to the machines involved, the erection phase of power transmission lines and switch plant imposes stress on - and causes potentially permanent damage to - the surrounding flora and fauna.
The clearing of lanes in wooded areas modifies the microclimate by admitting more insolation and wind, thus altering the temperature distribution. Such changes can disrupt the local ecosystem.
Depending on the attitude of the transmission route, such lanes can seriously enhance the windslash incidence in the adjacent woods.
Frequently, fire and herbicides are used to create lanes and keep them clear of vegetation. Since such practices are very damaging to both flora and fauna, they should be dispensed with to the greatest possible extent.
Due consideration should also be given to the danger of dissecting biotopes into small "islands" that are not likely to survive beyond the medium term.
Overhead power lines are a fourfold hazard for birds:
- they debase breeding grounds;
- birds (particularly night-flying species) can fly into the wires;
- birds can be killed by simultaneously contacting two wires or a wire and the tower (medium-voltage lines);
- the "magnetic compass" effect can interfere with their navigating system.
In Germany, the populations of several species of large birds have been substantially decimated; some 70 % of all white storks are lost to electrocution.
In extremely rare cases, a short circuit or other defect in a transformer or switchgear has been known to cause a fire with resultant destruction of the surrounding flora and fauna.
The roads and lanes established to enable the erection and maintenance of overhead power lines can have the same environmental consequences as other traffic routes, in particular opening-up effects (cf. environmental briefs Transport and Traffic Planning, Road Building).
· Minimization and avoidance measures
The aforementioned impacts can be minimized or avoided by heeding the following points in connection with the planning and erection of overhead power lines:
- consider possible alternatives to new construction,
e.g., conversion or more efficient/multiple utilization of existing lines;
- adjoin overhead lines to existing traffic routes and pipelines;
- adapt the right of way to existing landscape structures, i.e., avoid such exposed locations as hilltops and domes, ridges, razorbacks, etc.;
- significantly reduce the consumption of landscape and forest by installing high towers to permit greater spans between towers, thus traversing larger areas;
- avoid nature preserves and other protected areas, biologically and/or ecologically significant regions and recreation areas;
- use insulation sleeving, shrouding covers, perching and nesting platforms on towers for MV and LV lines as protection for birds;
- allow for the future installation of additional lines, i.e., for multiple use of the transmission route (multiple-circuit lines);
- significantly reduce space requirements by choosing suitable tower types (latticed steel, steel-pipe/concrete/wood) and configurations (size and arrangement of line-supporting cross-arms) and by using trefoil insulated LV and MV conductors;
- reduce the ground-area-requirement by using cables instead of overhead lines, even though the cable route also has to be kept free of tree growth (The use of cables can be problematic, however, for economic and technical reasons attributable to the high cost of investment and the need for highly qualified maintenance personnel.);
- minimize the danger of soil and groundwater pollution by performing routine safety inspections of pole impregnating facilities and by either replacing tar-base impregnants with more environmentally appropriate (salt-base) agents or opting for vacuum- or high-pressure impregnated wood;
- prevent soil erosion by mulching and greenbelting to cover all exposed ground. In climate zones with rainy seasons, this should be done at the beginning of the rainy season in order to prevent sheet erosion;
- modify and strengthen existing lines to save energy and additional cables;
- restock working areas under forest-traversing spans.
2.2 Human health, occupational safety and accident prevention
The primary cause of accidents imperiling human life and limb (electrocution, serious burns) is inadvertent contact with live components, possibly in inadequately protected facilities, and the secondary cause is fire resulting from short circuits.
The danger of accidents is most acute when:
- technical specifications relevant to safety measures are
disregarded in the planning and erection of plant and equipment (use of
low-quality components, inadequate sizing, negligent execution, nonobservance of
safety clearances), so that the finished facilities are inherently unsafe;
- the operating personnel has not received sufficient training in connection with safety measures and their observance;
- the local populace has not been properly educated with regard to electrical hazards, which can lead to such misbehavior as climbing up on towers, trespassing on switching stations, lack of lightning conductors, illegal tapping of electricity, etc.
In the past, and to a certain extent even today, the use of polychlorinated biphenyls (PCB, askarel/chlophen) as flame-retarding dielectric liquids in transformers and capacitors has constituted a health hazard in its own right. PCBs are very toxic. They accumulate in the food chain, cause chronic disorders and are carcinogenic. Moreover, their incineration (due to, say, exposure to an accidental fire) produces highly toxic dioxins and furans.
With but few exceptions (e.g., for electric plants in underground mines), the use of PCB in electrical plants is now generally prohibited in many countries.
Tar-base impregnants for wooden poles constitute a health hazard in that they can cause skin ailments.
Such risks can be substantially reduced or even completely avoided by:
- choosing plant components of the proper type and size,
- precluding unauthorized access to electrical plant and installing anti-climbing guards on high-voltage towers,
- reducing the danger of fire by using noncombustible dielectric liquids or dry transformers and refractory partitions,
- avoiding the use of dielectric liquids containing PCBs and of coolants in new installations; ensuring proper disposal and replacement of old transformers and the like,
- providing the operating personnel with appropriate safety clothing and suitable tools and test instruments,
- ensuring that the operating personnel receives the proper, duly qualified training,
- educating the local populace about the dangers of electrical installations.
· Effects of electric and magnetic fields on human health
According to information derived from prolonged observations and experiments in numerous countries, the electric and magnetic fields around power transmission and distribution facilities (exhibiting frequencies between 50 and 60 Hz) have no harmful effects on human health.
According to a WHO publication dealing with the effects of magnetic fields on human health, field strengths below 0.4 mT at 50 - 60 Hz induce no detectable biological reaction. The magnetic fields acting on the ground below overhead lines develop a maximum field strength of 0.055 mT for the above frequencies.
· Noise nuisance
Substation and distribution-system transformers generate a monotonous buzzing sound that can be annoying in residential areas. The use of quiet-running transformers and/or appropriate structural measures (incl. adequate distances) can avoid such problems.
2.3 Optical impairment of the landscape
Overhead power lines amount to an optical disturbance. The extent of disturbance depends on:
- the size, type and general configuration of the lines and
- the concentration of overhead lines within a given area,
- the transmission route and/or visibility of the lines, i.e., how well the right of way has been accommodated to the landscape (color, "low profile"),
- the location (undeveloped/developed land, population density, industrial/residential areas, etc.).
The recreational value of landscapes and affected areas is diminished by the optical impairment.
The aforementioned preventive measures apply in equal measure to the avoidance of optical impairment.
2.4 Socioeconomic and sociocultural impacts
Any direct consequences the installation and operation of power transmission and distribution facilities may have on the socioeconomic and sociocultural environment are of minor significance. Radio and television reception, for example, can be substantially disturbed by corona discharges [luminous discharge along undersized and/or improperly arranged conductors (bundle-conductor lines)].
Indirect consequences derive from the purpose of such facilities, namely to improve living conditions by supplying electricity to a region or center. Access to electricity increases comfort and convenience in private life (e.g., time saved and work facilitated) and in the public domain. In combination with other technical infrastructural measures, it can initiate or stimulate economic activities aimed at creating new jobs (i.e., reducing unemployment) or rationalizing production processes6).
6) The negative environmental effects of power generation can be aggravated by excessive demand resulting from artificially low (submarginal) supply tariffs.
On the other hand, past experience has shown that electrification and other forms of regional development can lead to a loss of traditional ways of life, modes of behavior, cultural peculiarities and sociocultural ties and structures. Moreover, it can have a whirlpool effect on neighboring regions, giving rise to emigration and new congested areas.
Numerous different authorities, associations, public and private bodies both corporate and individual must be involved in defining the rights of way and the locations of substations. The process must include appropriate consideration of environmental interests.
Suitable structural measures (e.g., to prevent erosion) and technical measures (e.g., to prevent the escape of transformer oil) must be taken to avoid pollution of the soil and/or water.
Optical impairment of the landscape is unavoidable but should be minimized. The extent of impairment depends both on how the land is used (work - recreation) and on its optical complexity. The right of way can be visually assessed with the aid of a computer.
Detriment to flora and fauna must be appraised with a view to the protection of endangered species and in consideration of local, national and international standards and regulations. Determination of the local and regional significance of biotopes must be based on a large-scale survey in which suitable measures for the protection of birds are included.
Internationally recognized and harmonized, detailed standards on safety clearances, protective measures against contact with and entry to, in addition to working on, live systems [e.g., the German Standards DIN 0800, DIN 0848, DIN 57106, Association of German Electrical Engineers' VDE guideline 0106, accident prevention provisions and implementing instructions for electrical equipment and operating equipment issued by the Verband gewerblicher Berufsgenossenschaften ("Elektrische Anlagen und Betriebsmittel" - VBG 4)] should be consulted in connection with the planning of power transmission and distribution facilities.
The use of PCB in closed systems (transformers, capacitors, etc.) has been prohibited in the EC since 1985, although the continued operation of existing PCB-filled equipment is permitted for the duration of its service life. In the interest of environmental protection, however, such equipment should be replaced and properly disposed of (sodium-base dechlorination of the oil). Its incineration would produce dioxins!
The planning and installation of power transmission and distribution systems depend on decisions deriving from higher-level (national, regional) planning processes devoted to regional development, general energy development, town and country planning, general power supply measures, etc. (cf. corresponding environmental briefs).
There is a direct connection to the power generating sector (cf. environmental brief Thermal Power Stations). As soon as power transmission is correlated to a particular power source, the environmental impacts of the latter, i.e., of power generation, demand consideration; high transmission losses also have environmental consequences in that they necessitate the generation of additional power.
The rights of way for transmission lines are extensively determined by the relative locations of the power plant and the power consumers. Particularly valuable biotopes and landscapes must be protected by routing such rights of way around them.
Coordination with existing or still-to-be-installed technical infrastructure (roads, railways, waterways, other supply lines, etc.) is not only possible but even necessary for, say, crossing airports, waterways, roads, etc. and for the parallel routing of power transmission and telecommunication lines - all in order to ensure the safe, reliable operation of all facilities concerned.
With regard to the reprocessing and disposal of transformer oil (with or without PCB content), please refer to the environmental brief Disposal of Hazardous Waste.
The aforementioned environmental impacts and their consequences are evaluated below, and potential means of minimization and avoidance are proposed.
Landscape consumption in the form of pressure on natural resources (soil, vegetation) and destruction of landscape is generally unavoidable, though adequate attention to environmental concerns at the planning stage can at least diminish its consequences.
Appropriate structural measures can be adopted to reduce, but not eliminate, the hazard for birds posed by overhead power lines.
The danger of accidents for humans emanating from transmission and distribution installations can be reduced by strict adherence to existing, recognized rules, regulations and standards. Relevant training and sensitization are crucial in this area.
The emissions (noise, corona conduction) of power transmission and distribution installations can be reduced to negligible levels by appropriate technical means. The use of liquids containing PCBs in transformer substations still constitutes a substantial hazard potential in that such liquids are liable to escape to the environment as a result of equipment malfunction or accident (leakage, fire). Consequently, the use of components and equipment containing PCBs should be globally prohibited, and existing equipment should be replaced.
Compared to other means of energy conveyance (road, rail, water, pipeline) the transmission of electricity involves a modest, though by no means negligible, risk. Whenever new facilities for transmitting and distributing electric power are deemed absolutely necessary (e.g., if there is no possibility of opting for noncentralized power generation), appropriate low-impact approaches should be sought out.
The easiest and most effective way to minimize or completely avoid harmful environmental impacts is to conscientiously allow for environmental concerns from the planning stage on.
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