REVOLT opposing unnecessary, excessive and intrusive powerline development

opposing unnecessary, excessive
and intrusive powerline development

Revolt FAQs as at 26 February 2008

CAVEAT: These notes are offered in good faith without liability. 

They are not exhaustive but give brief initial guidance. They are drafted by me as Chairman of Revolt for the last 15 years and are not necessarily the opinion of Revolt. I draw on professional and scientific experience and qualifications in certain respects but have no medical or legal qualifications or indemnity. Readers should not rely on these notes alone but should seek indemnified professional advice where necessary. Criticism of government and industry, and grievances from members of the public, are in the nature of Revolt's work, though we try to give credit where it is due. Revolt is strictly non-party-political and regrets any offence which may be inadvertently caused.

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List of questions (not in priority order!):

1. What is Revolt's position on . ?

2. Can you help on masts, wind farms, electro-sensitivity and so on?

3. What can I do about a proposed powerline development near my home?

4. Will it do any good contacting the electricity company proposing a line?

5. What are the key stages and timescale for objectors to a powerline proposal?

6. What are allowable grounds for objection to a powerline proposal?

7. What chance is there of succeeding with objections to a powerline proposal?

8. What chance is there of getting a (proposed or existing) powerline buried?

9. What is a safe distance from powerlines?

10. Do we have to have these pylons / powerlines / poles / substation on our land?

11. Is the powerline / substation near me one I should worry about?

12. How can I find out the electric and magnetic fields (EMFs) in my home and from the powerline or substation near me?

13. How can I reduce EMFs in my home if I want to?

14. How do single-circuit lines compare with double-circuit overhead lines?

15. Is there any evidence of how much a new powerline might devalue my property?

16. How do underground cable options compare with overhead lines?

17. Can high-voltage DC (HVDC) transmission offer advantages?

18. How rapidly do EMFs reduce with distance from powerlines?

19. What about swing and safety clearances from a line close to my house or boundary?

1. What is Revolt's position on . ?

1.1 Revolt maintains a position statement covering many issues related to powerlines. See <http://www.revolt.co.uk>

2. Can you help on masts, wind farms, electro-sensitivity and so on?

2.1 The Revolt web site has links to various umbrella and specialist organisations. We try to prioritise our coverage in relation to power lines and associated works like substations. We do not directly cover related and overlapping topics like masts, mobile phones, Wi Fi, electromagnetic sensitivity (ES), radio-frequency (RF) EMFs, and wind farms, but some of our links do.

3. What can I do about a proposed powerline development near my home?

3.1 The rules vary in different countries, so you would need advice for your country. Revolt maintains some nation links which may help you.

3.2 There is a common framework in the UK though the precise arrangements vary between the home countries. Generally a powerline will be proposed by an electricity company for national approval, with the local planning authority informed as a statutory consultee. Your input can be made to

(1) the company in a consultative stage before the formal proposal is made;

(2) local authorities, both the professional officers and the elected members;

(3) your MP to lobby the decision-making government office; (4) established environmental bodies;

(5) landowners and occupiers whose land the line would cross, as their agreement will be required;

(6) landowners' organisations like the CLA and NFU.

3.3 Objections will be best represented if objectors form an organised group to make the approaches listed above. You may need funds for professional and legal advice. However, a number of individual personal letters can be important in establishing a political issue, and only a modest number are needed to do that although a large number of formal objections can be very helpful.

4. Will it do any good contacting the electricity company which is proposing a line?

4.1 It should always be worth trying. At least you can expect to find out what information is available and some companies have been very helpful. Some may still tend to be defensive and difficult, especially in the formative stages which is precisely when meaningful consultation might potentially best benefit all parties. We have found a culture of secretive and one-sided negotiation with landowners over wayleave and access matters, though this may in part be a product of commercial confidentiality. However, there have been exceptions, and we live in hope of a more enlightened age!

4.2 It may help to make a professional approach, and to understand the objectives and constraints of a major corporation and its employees. There is scope for mutual understanding of the technical needs for and limitations on a project relative to possible alternatives with less impact. Such understanding may help focus objections and avoid chasing lost causes. Cost is a key issue for electricity companies and usually prevents them volunteering alternatives such as burial of high voltage lines. But there may be other feasible alternatives to explore.

5. What are the key stages and timescale for objectors to a powerline proposal?

5.1 First is the consultative stage before the formal proposal is made. The company might consult only authorities, recognised environmental bodies and selected affected people, so you may not get to hear about it, although your parish council should hear and there could be local consultation open meetings run by the company. The press may pick it up, and the company website may have a statement.

5.2 An Environmental Impact Assessment (sometimes called an Environmental Statement) is usually published before, or when, formal application is made. It is produced by consultants working for the electricity company to assess the impact of the proposal under many headings. The formal application is made to Secretary of State for Trade and Industry (or BERR after June 2007) in England and Wales, to the Scottish Executive in Scotland, or to the Department of Environment in Northern Ireland. Then the clock is running with a deadline for formal objections.

5.3 A key objective at this stage is to get the local planning authorities to object. They may include county, district, city and borough councils and national park authorities. If they object, this will normally precipitate a public inquiry, when objections can be heard more thoroughly and transparently. If a public inquiry is held, it becomes a major stage in itself. For a long powerline, there may be firstly a stage for generic issues and then separate stages held locally for site-specific issues. Each inquiry stage can last for months.

5.4 Alongside the public inquiry there may be wayleave hearings for landowners and occupiers who refused to agree voluntary wayleaves or easements.

5.5 After the inquiry, or the deadline for representations if there is no inquiry, there is the decision stage before government announces its verdict. This has taken years in some cases, but nowadays governments are under pressure to speed up the process. The verdict may however not be the end, as it may carry conditions with their own timescales, and parts of the line and some wayleaves may be refused.

5.6 There is then a post-verdict stage, when conditions such as tree planting schemes are to be agreed, and the company considers what to do about refusals. There may be minor diversions of the line to resolve wayleave problems, which may be agreed with the landowners or else come back for further hearings. The company may decide to underground parts of the line where government consent was refused, unless likely options for diversions were identified in the inquiries. Either undergrounding or diversions can lead to more inquiries and decision stages.

5.7 In the UK system where national government decides, there is no facility for appeal, unlike with normal planning decisions. There is the possibility of a legal challenge by judicial review, but that is restricted and expensive. Finally there is the construction stage, with issues of access and local planning permission for verge crossings, monitoring vehicle loads and numbers, and reinstatement after construction has finished.

6. What are allowable grounds for objection to a powerline proposal?

6.1 If there is an inquiry, government usually sets out "relevant matters" which determine the grounds for objection. They naturally include all the usual impacts, such as on visual amenity, health, tourism, agriculture, flora and fauna, in addition to matters of cost and of formal planning policy. Importantly, they also include identifying a better alternative.

6.2 At the strategic level, it is not easy to contest "need" for the development. Increasingly in the UK and elsewhere decision processes are being streamlined, tending to avoid or reduce local objection on questions of national need. The idea is that over-riding national need, whether for powerlines or motorways or airport terminals, would be decided by national government, so that local objections could only be to the detailed location or route or form and not to the existence of the project. However, "need" has been admitted as a consideration in recent major inquiries.

6.3 The strategic context is also important and may warrant a strategic environmental assessment (SEA) covering wider aspects of the need and looking at wider scope for alternative strategic approaches. For example, the present Beauly-Denny powerline proposal is considered only within Scotland by the Scottish Executive and only against local alternatives. On the other hand there is a wider context of UK renewable energy development and UK grid reinforcement including under-sea cables.

6.4 Objections to government policy are not admissible grounds for objecting in a public inquiry to specific proposals. A public inquiry cannot determine matters of law.

7. What chance is there of succeeding with objections to a powerline proposal?

7.1 Based on recent experience, a major powerline project is likely ultimately to go ahead, though perhaps with route variations or in a modified form and perhaps with part underground. There may also be planning conditions, such as tree planting and controls on access and construction.

7.2 A long line (in Donegal) was rejected outright on appeal, mainly on grounds of visual impact near a national park after I showed there was a feasible alternative which had not been assessed. However the proposal is returning in an amended form seven years later (2007). At the latest consultative stage, I assisted one local group and the company in dialogue which led to agreed local changes. This is probably the best way to succeed, though sadly few power companies seem able to take such a constructive approach from the start. There remain other objectors to the Donegal proposal.

7.3 Another (the Northern Ireland interconnector from Scotland) was deferred for six months after I challenged its compliance with the EU EIA Directive. The proposed interconnector siting in a pristine valley was also rejected and it was built instead next to an existing power station. So some rejections have been achieved and some challenges to proposals have been effective.

7.4 The Yorkshire (Lackenby-Picton-Shipton) line went through ten years of inquiries and hearings, contested by Revolt in collaboration with the local authorities, but was eventually built. Parts of the proposed line were rejected on grounds of visual impact and were buried. In that process a sealing end site was also rejected, and a longer section of undergrounding resulted. Another section was rejected and re-routed to avoid an SSSI. Several compulsory wayleave applications were rejected, one leading to local diversions to avoid an avenue of lime trees, another to a pylon site being moved along the line to reduce the visual impact on nearby cottages.

7.5 As things stand health impact alone is not likely to be a successful basis for outright rejection or undergrounding. It might reasonably justify moving a line route at low cost so as to avoid proximity to homes or schools, where there is an alternative at similar cost. Health impact should rather be weighed in conjunction with other concerns in the decision stage. The Beauly-Denny inquiry report and decision, along with government response to the SAGE report, will be an important guide to evolving UK policy.

7.6 News in 2007 from Canada reports the Energy and Utilities Board (EUB) has scrapped scandal-plagued hearings into a proposed 500 kV line between Edmonton and Calgary, setting aside its decision that need had been established, following admissions of eavesdropping on objecting landowners and loss of public confidence. Dirty tricks do happen, and sometimes get found out.

8. What chance is there of getting a (proposed or existing) powerline buried?

8.1 Cost and technical problems make it difficult to get a proposed long high-voltage line completely buried. Experience has shown however that several miles and some 10% undergrounding may be achieved. It is not practical to have many short sections underground, partly because of the need for sealing-end compounds; it is easier to underground fewer longer sections.

8.2 Existing low-voltage lines, for example local lines on wood poles, are sometimes voluntarily buried by power companies at their own cost. This can make sense when refurbishment is due, as the cost difference for low voltage lines is small and there are gains in avoiding bad-weather outages. High-voltage lines may be voluntarily buried when it is commercially viable and paid for by a developer, for example with the 400 kV lines at London Olympics sites.

8.3 Revolt is campaigning for burial of the worst cases of sections of existing high voltage lines in the UK on a priority basis within affordable and proportionate costs. Criteria for judging cases will be posted on the web site (see also Revolt news number 235 item 10).

8.4 Recent developments indicate that the feasible length of underground sections of a 400kV line may be increasing from about 25 km to over 60 km as technology improves. In some cases complete DC underground lines may be feasible. The Irish government is commissioning a study in 2008 (see revolt news252) to assess the latest technological possibilities, in response to strong public demand.

9. What is a safe distance from powerlines?

9.1 This is a difficult question raising matters of definition, uncertainty, judgement and precaution. There is no clear distance at which powerline fields become certainly safe. However, the evidence suggests that living near powerlines may not be a major risk for most healthy adults. For adults and children in general, living more than 100 metres from the highest-voltage lines, or closer still to smaller lines, should be reasonably safe relative to health risks at large generally. Beyond that distance, other exposures are likely to be more important for most people, although both magnetic fields and ionised particles arising from corona ions (and hence potential risk) are detectable at much greater distances. The major Draper study (2005) showed association of childhood leukaemia with proximity of birth address to powerlines up to 600 metres. Further, the potential cumulative impact of low exposure levels on high density housing beyond 100 metres can be a consideration for policy decisions.

9.2 In the UK the SAGE report refers to a distance of 60 metres from a 400 kV line. That was determined on the basis of reducing magnetic field exposure arising from the line to below 0.4 µT for most typical lines. It depends on

(a) a threshold assumption that there is no association with fields below 0.4 µT, although the scientific evidence does not reasonably support such an assumption (as acknowledged by SAGE and by WHO) but rather supports a progressive association in which the risk for exposures above 0.4 µT is double that below 0.1 µT; 

(b) ignoring the addition of fields from the powerline to those from other sources, which will be significant in many cases;

(c) field estimates for typical lines, ignoring more heavily loaded lines. The 60 metres is therefore a rough pragmatic figure in the search for an affordable measure to achieve some significant field reduction, and is not claimed to be a safe distance.

9.3 A longer note on safe distances is maintained on the Revolt web site. There remains much uncertainty, and questions of precaution and also of hypersensitivity in some people continue to be addressed by authorities with different outcomes.

10. Do we have to have these pylons / powerlines / poles / substation on our land?

10.1 The law varies from country to country. The following applies to the UK, with a short note about other countries at the end.

10.2 Where there is a substation on your land, the following notes would apply to the power lines coming from the substation, including their supports and connected apparatus.

10.3 In the UK (with some differences between the home countries) the electricity company needs an agreement (usually a "wayleave") to have the line there. With existing equipment, the landowner should have a written copy of the agreement. With some old installations, no written agreement exists or survives, in which case a wayleave may be deemed to apply by virtue of custom and practice.

10.4 The agreement may be a voluntary wayleave, or a compulsory ("necessary") wayleave, or a permanent easement. Wayleaves may be terminated, usually after 15 years, by the landowner giving six months' formal notice. Then the company could seek compulsory powers.

10.5 If the company can't get the landowner's agreement to a wayleave for a new line, or has notice of termination of an existing wayleave, then the company can seek compulsory powers. If they seek compulsory powers, the landowner is entitled to a hearing and may get the application rejected if there is good reason and if there is an alternative for the company. Rejection has happened, for example in cases of proposals for new lines where the precise siting has been unreasonable and where there was a better alternative.

10.6 A compulsory wayleave cannot be granted for a new line over a "dwelling", which includes a house and its garden. Such lines can be built by agreement with the landowner. A compulsory wayleave may be granted for relocating an existing line with the effect of placing it over a dwelling, though this could generate reasonable objection.

10.7 Although the system may seem to favour the electricity company, the company will generally prefer to avoid the formalities and costs of applying for compulsory powers. Therefore the company may be more amenable to negotiation with the landowner to alleviate the concerns. However, the cost of moving a large powerline or pylon is usually on a higher scale, so the scope of negotiation may be limited. Landowners may then be able to negotiate a permanent easement with compensation reflecting their concerns including the loss of business and property value.

10.8 There is a summary in the supporting paper S16 to the SAGE report, which is on the revolt site and linked to its home site. A fuller discussion on legal aspects is in Brenda Short's recent article at http://www.powerwatch.org.uk 

10.9 By contrast, the position in the Republic of Ireland is as follows, as advised by a contact at ESB. A landowner does not have the right to terminate a wayleave after 15 years. On the other hand where a landowner obtains Planning Permission to build on his land then ESB Networks will move any existing lines in order to facilitate this building if necessary, subject to certain conditions. In cases where the line cannot be moved then a compensation package will normally be agreed.

10.10 In the USA, Christian Science Monitor (Sept 07) reports that under the Energy Policy Act of 2005, the Federal Energy Regulatory Commission (FERC) is allowed to pre-empt local and state zoning laws when it designates a "national interest electric transmission corridor." It also permits the use of federal powers of eminent domain that would require landowners to sell their property.

10.11 Other sources will be needed for advice country by country.

11. Is the powerline / substation near me one I should worry about?

11.1 There are many types of powerlines and substations. They should have an identification plate giving voltage and some other details, and a "danger" warning. Details should be available from the electricity company owning the installation. The local authority should be able to identify the company.

11.2 For a summary of types of powerlines and substations and their associated fields (EMFs), see the powerlines and substations factsheets at http://www.powerwatch.org.uk 

11.3 For an overall information leaflet on EMFs from powerlines and substations from an industry perspective with much useful information, see http://tinyurl.com/2mm3ge 

Note that the leaflet gives a context of much higher natural static fields, without explaining that health concerns relate to oscillating and not static fields; describes powerline fields under the heading "outside the home" whereas magnetic fields penetrate inside homes practically undiminished; says high-voltage underground cables can produce higher magnetic fields directly above them (true for shallow trenched cables) but does not say that deep buried cables can have lower fields above ground.

12. How can I find out the electric and magnetic fields (EMFs) in my home and from the powerline or substation near me?

12.1 The electricity company may provide some details, which should be in line with government guidelines, as advised by the Health Protection Agency. The best way to find out is by actual measurement. This may also reveal sources inside your home due to wiring arrangements and possible faults.

12.2 The UK industry body, the Energy Networks Association (ENA), tel 020 7706 5100, http://www.energynetworks.org , advised us as follows: "Generally all ENA member companies will still carry out free EMF measurements for residents living within their area who have concerns about EMF levels in their own home. Where National Grid equipment is close by, the National Grid will also generally carry out free measurements on the same basis. In all other cases companies will take each case on its merits. Where house purchase is concerned, companies may decide to charge, especially if measurements are being routinely requested on a regular basis. Where a commercial company is having problems with EMF due to internal wiring and wants advice on how to deal with the problem, then companies will usually charge. It is difficult to be precise about the circumstances under which any company will charge for a visit, the best approach is for people to contact their local company and discuss the issue with them. All companies would make it clear to callers whether a visit was free or not before the visit."

12.3 Electricity companies will normally provide you with the actual measurements in writing, which is clearly desirable. Field levels from power lines and other electricity distribution equipment do not normally exceed government and EU guidelines, which protect against proven effects at high exposure levels. However, public concern is at much lower exposure levels where there is a body of scientific evidence giving rational grounds, short of established proof, for suspicion of harm .

12.4 You can purchase an EMF meter from various sources, for example from Powerwatch UK.

13. How can I reduce EMFs in my home if I want to?

13.1 You cannot avoid EMFs completely if you use electricity in your home; even in homes with no wiring faults and not near a power line, there is an unavoidable background level of EMFs from low-voltage wiring and house wiring. Occasionally, the field may be increased because of a fault in the house wiring, which, once identified, can and should be fixed.

13.2 If your home is close to a high voltage line (e.g. 30 metres from a 400 kV line), it would be sensible to have children sleep further from the line rather than closer to it, other things being equal. Some obvious internal field reduction measures include switching electrical equipment off when not in use and especially at night. Further practical advice is given in the SAGE report and there is a booklet available from Powerwatch UK in its subscription section at  http://www.powerwatch.org.uk .

14. How do single-circuit lines compare with double-circuit overhead lines?

14.1 For normal 3-phase lines, the single-circuit lines require only three conductors and therefore less space than double-circuit lines with six conductors. Often the single-circuit lines have the conductors spaced almost horizontally, so they occupy a similar width to the double-circuit lines which have three vertically spaced conductors down each side. Therefore the single-circuit lines are considerably shorter than their double-circuit counterpart, typically for 400 kV lines around 25-35 metres compared with 45-60 metres. Since their lowest conductors are suspended at about the same height, the span lengths (pylon to pylon) tend to be similar for both single- and double-circuit lines, at about a third of a kilometre.

14.2 There is a marked difference in the EMFs. Those from a single-circuit line will spread much further to the side, away from the line, compared with those from a phase-transposed double-circuit line carrying the same total load. This is because of a partial cancelling effect of two properly balanced phase-transposed circuits. However we have no published or reliable data for measured fields from single-circuit lines to check theoretical calculations.

14.3 The National Grid website has a page showing theoretical fields from balanced and unbalanced double-circuit lines carrying a total current of a notional 1,000A. http://www.emfs.info/Source_overhead_balance.asp  The unbalanced line in the example is in effect a single circuit, with all 1,000A on the one circuit. The single-circuit has a nearby field some 60% higher than the double-circuit. The difference in proportion becomes much larger at greater distances, although the graph is only given to 100 metres. A second graph on the same web page shows calculated and measured fields to 500 metres for a double-circuit line. The most realistic calculated graph is the one allowing for most non-ideal effects, but it is still for a phase-transposed double-circuit line. A single-circuit line would have much higher fields, even allowing for it carrying a lower total load. See also FAQ18 below.

14.4 Bearing the above in mind, a double-circuit 275 or 220 kV line may sometimes be preferable to a single-circuit 400 kV line, and could be of similar cost for the same capacity, though the towers would be taller. The double-circuit line would also offer security advantages.

15. Is there any evidence of how much a new powerline might devalue my property?

15.1. Yes, but naturally it depends on many factors: location, location, location and all that. There have been reports of limitations in availability of mortgages and business loans. There seem to be two main reasons: visual impact and health concerns, which affect different properties in different ways.

15.2. Anecdotal cases include devaluation of up to 50% or more in extreme cases. Academic research suggests up to 20% might be expected within 100 metres of a powerline, depending on the type of property and situation, with over 30% for some detached houses. The proximity of a pylon can have a more significant effect than the line alone.

15.3 Revolt maintains a Note on property devaluation on the web site, with references for further details and advice.

16. How do underground cable options compare with overhead lines?

16.1 Stirling Before Pylons Briefing No. 10 gives Europacables answers to key "FAQ", which can be seen at http://www.stirlingbeforepylons.org  Europacables give examples, as at 2006, and cite recent independent academic studies, to show that continental cost ratios for 380/400 kV "can be as low as 2 to 5 times".

16.2 Firm costs of underground cables (UGC) compared with overhead lines (OHL) depend not only on terrain and routes, but also on required capacity and associated works such as transformers and reactive compensation. The whole project cost is more than the cost of the line alone.

16.3 Recent communications with industry suggest a rough guide for 400 kV line capital costs of about 0.5 million per km double-circuit OHL with total capacity over 4,000 MVA (to take a maximum of around 4,000 MW). To match that capacity with UGC, 4 cables per phase would be required, with a cost in UK of about 10 million per km, a ratio of about 20. The 5.7 km of 4 cables/phase 400 kV line buried in Yorkshire in 2001-2 is reported as costing about 100 million Euro (65 million) including end compounds, i.e. about 3 million per km per cable/phase. Where less capacity is needed, the OHL costs do not decrease greatly, whereas the UGC costs can come down to about 3 million per km for one cable per phase. Across Europe they tend to be cheaper, down to 3 million Euro (2 million) per km for one cable per phase, which in UK would give a ratio consistent with the range 2 to 5.

16.4 The impact of underground cables is often exaggerated. There is no sterilised swathe through the countryside, though there is substantial disturbance during construction. Crops grow normally over the cables (see photos on Revolt web site). There are constraints, such as on deep ploughing and deep-rooted plants, but these may be immaterial in many practical situations. Present technology (XLPE) reduces impacts further since oil tanks and pumping are not required. EMFs are greatly reduced and can be effectively eliminated by deep burial instead of shallow trenching.

16.5 The different interests of information sources should be noted: cable companies may give an optimistic, and grid companies a pessimistic, picture of prospects for undergrounding. The 2008 Irish study promises to be helpful. Revolt maintains a Note on underground cables on the web site, with further details and advice. See also FAQ8 above.

17. Can high-voltage DC (HVDC) transmission offer advantages?

17.1 Yes, for very long distances. Undersea cables are DC, which avoids the problems of reactive power. There is an underground DC "Greenconnector" project between Italy and Switzerland. DC transmission lines need expensive (and large) converter stations at each end, so they tend to be for specialised use. There are overhead DC lines (on pylons), e.g. in Australia connecting to the Basslink undersea project, but residents object to them as they do to AC lines.

17.2 HVDC lines would create no AC EMFs, about which there are health concerns. The DC fields are considered more benign.

17.3 Recent communications with industry suggest that costs for HVDC cables depend strongly on the required capacity, as a result of costs for the converter stations which can be over 50 million each for capacity up to about 1,000 MW. For such a capacity, the cost would be around 0.4 million per km for overhead line (HVDC-OHL) or about 1.5 million per km underground (HVDC-UGC), in addition to the converter station costs. On that basis HVDC-OHL would, with converter stations, cost more than ordinary AC OHL, but HVDC-UGC could cost less than ordinary AC UGC for lines longer than about 70 km.

17.4 There are industry claims that a technology HVDC Light for applications up to 550 MW could, on lifetime assessment, cost less than ordinary AC overhead lines. The Murraylink Project in Australia, commissioned in 2002, has 2 HVDC underground cables 180 km long with power rating 220 MW. The company ABB gives example estimated capital cost comparisons:

(a) 1,700 MW over 400 km: HVDC $275-420; AC OHL $130-440 plus $100 indirect costs;

(b) 2,350 MW over 100 km: HVDC $110-150; AC-OHL $40-90 plus unstated indirect costs. See also  www.abb.com 

17.5 Revolt maintains a Note on HVDC cables on the web site, with further details and advice. See also FAQ8 and FAQ16 above.

18. How rapidly do EMFs reduce with distance from powerlines?

18.1 At public inquiries industry bodies have provided data showing rapid fall off based on ideal theory. Under ideal conditions of perfect balance in the three phases of a circuit, and further under perfect balance between two circuits on a phase-transposed double-circuit line, magnetic fields can be shown to tend ultimately (asymptotically) to an inverse-cube relation with distance, but this isn't achieved in practice. The idealised assumptions are clearly broken, with loss of phase- and circuit-balance. That makes a lot of difference at far distances. Nevertheless, there is sufficient balancing, with its partial cancellation of fields, that the theoretical calculations match measured data within the first 100 metres.

18.2 National Grid's EMF expert John Swanson has kindly posted (2008, on www.emfs.info  ) some helpful notes on the rates of fall-off of magnetic fields from powerlines with distance from the lines. The notes confirm that the ideal inverse-cube fall-off is not achieved for real transposed double-circuit lines, partly because of the sloping profile of conductors, and that something nearer to inverse-square would be more typical. See Revolt news247 Appendix B for more.

18.3 Magnetic fields can be significant above background levels even at 500 metres, but then they are smaller than typical internal fields due to sources inside homes. There are few published measured data beyond 100 metres. It would be useful to have "independent replication" in the form of measurements of fields from UK powerlines from other sources. In the end it is measurements which validate the theory and especially validate its application and software.

19. What about swing and safety clearances from a line close to my house or boundary?

19.1 Apart from EMFs, corona ions, noise and visual impact, an overhead line can spread its direct effect in two important recognised ways: swing in the wind and safety clearance regarding electrocution or flashover.

19.2 Swing in the wind would be recognised by government as warranting a wayleave over the affected property. Swing can move the conductors several metres. When the conductor hangs vertically in still air, it curves between the pylons with a fall of several metres at the mid span. In summer the line expands with higher temperatures so there is extra sag. In a side wind, the curve may be considered for safety purposes to swing up to 45 degrees sideways between the pylons. There will not be much movement close to a pylon, but near the mid span this could be over 5 metres on a 400kV line or roughly 4 metres on a 132kV line, though actual configurations will vary. If your land is within these distances, horizontally, of a line on your neighbour's property, then the line may pass over your land and the company should need a wayleave.

19.3 In addition to swing, there are safety clearances constraining building and development and imposing danger of death and extensive liabilities on the landowner. These distances are 5.3 metres from a 400kV conductor and 3.6 metres from a 132kV conductor. The status of these distances is established in industry (ENA) standards which relate to, but are not expressly incorporated in, statutory safety regulations (ESQCR). If a line, with swing and summer sag, passes within these distances of your house or buildings, then it breaches recognised safety guidelines, and you should report it to BERR. Revolt would be interested to hear of such cases. If the power company seeks an easement or wayleave binding you to accept that default, beware; you may wish to seek independent advice before deciding.

19.4 If these safety clearances, with swing and summer sag, would bring a line on your neighbour's land across the boundary on to your land, then there is a case to consider that the power company should have a wayleave over your land. The Finnigan case in Sale, Manchester, is before a court awaiting a ruling as to whether such an intrusion, without a wayleave, should be considered as nuisance or trespass (see Revolt news250 etc.).

19.5 The combination of swing potentially of over 5 metres plus safety clearance 5.6 metres means that any property with a neighbouring 400kV powerline within about 10 metres horizontally of its boundary, or a 132kV line within about 7 metres, could be in this situation, and could warrant a wayleave and/or compensation. Revolt would be interested to hear of such situations.

MJOC 26-02-08

© REVOLT

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