Chapter 11: Noise and electronic interference
Introduction
1218. In this chapter, a variety of potential sources of other adverse effects on the environment are addressed: audible noise, electronic interference with radio and television reception; potential third-party telecommunications; earth potential rise and transferred and induced voltages and current; ground heating (from underground cables); electric and magnetic fields around underground cables and substations; and induced voltages associated with underground cables.
Audible noise
1219. The Board addresses separately audible noise from construction activities, and from routine operation of the overhead line and substations: corona discharge noise; wind-induced noise; and noise from transformers and circuit-breakers.
Construction noise
1220. Some submitters (for instance, Ms L Bilby, Mr A Loveridge, Mr R McKenzie, Mr C Riddell and Mr M Spring) raised their concerns about the noise that would be generated by construction of the overhead line: especially by numerous heavy-truck movements, and by helicopter movements, which they considered would disturb and frighten livestock and spoil a quiet way of life. Messrs R McKenzie and M Spring explained their concern that noise of construction activities in the Brownhill Road catchment would be amplified due to adjacent hillsides, and asserted that there is very little background noise in that environment.
1221. Transpower responded that it proposed conditions requiring that the noise from construction activities comply with the New Zealand Standard on Construction Noise NZS 6803:1999 (and with the Standard DIN4150 in respect of structural vibration). Further, amendments to the proposed condition suggested by the Manukau City Council had also been accepted by Transpower, and are incorporated in the proposed consolidated conditions.
1222. An independent acoustical consultant, Mr Warren, acknowledged that most district plans refer to New Zealand Standard 6803:1999 (Acoustics – Construction Noise) to control construction noise; and gave his opinion that it would be appropriate to control noise from construction of the Grid Upgrade Project.
1223. He observed that although construction activity for the project would be likely to be spread over 2 years, each site is likely to experience construction noise of less than one month over three specific working periods (foundations, tower construction, and stringing); and the preparation stages would be of a scale normally anticipated in a rural working environment.
1224. Mr Warren acknowledged that implosive jointing of conductors may occur in some locations; and that night-time construction activities could sometimes be necessary to avoid unacceptable disruption to essential services such as major roads. In those events, noise would be controlled by construction noise management plans.
1225. On construction of the Brownhill transition station and substation, Mr Warren stated that each of the stages is anticipated to take about 12 to 18 months; and that night work after 8 pm and before 6:30 am is not generally anticipated. All earthworks would take place during Stage 1; and an all-weather service road within the site is to be constructed in Stage 1 or Stage 2. Upgrading Brownhill Road would be carried out progressively so that it could take transformers up to 300 tonnes in Stage 3.
1226. Mr Warren gave his opinion that noise associated with construction and earthworks would be consistent with noise associated with residential development and forestry clearance being undertaken in the vicinity. He predicted that the noise effects of constructing the transition station and substation would be minor, except during heavy-vehicle movements and major earthworks.
1227. Cross-examination of Mr Warren raised no doubt about the acceptability of the witness’s evidence.
1228. Another independent acoustics consultant, Mr N R Lloyd, recommended refinements to the proposed conditions which have subsequently been incorporated. Mr Lloyd was not cross-examined.
1229. No other expert evidence was given about noise that would be generated by construction of the overhead line.
1230. On the basis that the construction would be controlled by the proposed conditions (incorporating the Standard for Construction Noise) and by the amendments suggested by the Manukau City Council and by Mr Lloyd, the Board finds that the noise would be appropriately constrained, and no significant adverse effect on the environment would result.
Noise from operation of overhead line
1231. Several submitters (among them Mrs F Aldridge, Ms L Bilby, Mr M Chitty, Ms S Hall, Mr P Hexter, Ms A Jones, Mr R McKenzie, Ms W Parker, Mr E J Smith, Mr C Riddell, and Mr M Spring) raised their concerns about noise that would be generated when the Grid Upgrade is in operation, particularly corona noise, and noise of wind. They contended that these noises would be unpleasant for humans working nearby, and would also have detrimental effects on wild animals, farmed animals, birds and insect life.
1232. Mr Chitty also raised a perception that increased noise in wet weather would frighten horses and affect market confidence in Haunui Farm’s horse stud business.1 Mr Hexter described the corona noise from an existing transmission line as crackling, and an eerie sound;2 and Mr E J Smith described it as a loud constant noise, audible for a considerable distance in wet conditions.3 Messrs R McKenzie and M Spring stated their concerns that a noise consultant engaged by Transpower had measured the background noise in winter when most mornings, due to the low-lying nature of the landscape, the valley is covered in a blanket of fog which would increase the corona noise.
1233. In his evidence, Mr Warren identified the sources of audible noise associated with the Grid Upgrade Project as wind-induced noise in the overhead conductors and towers; corona discharge noise from overhead conductors; and noise from substation transformers and circuit-breakers. Potential noise from those sources is now addressed.
Corona discharge noise
1234. Mr Warren explained that corona discharge noise is due to ionisation of the air surrounding a conductor, caused by a voltage difference applied across a column of air. He stated that corona discharge noise is wideband noise (hiss, crackle etc) generally only audible in wet conditions such as rain or fog, together with a much lower level of steady 100-Hz hum.
1235. Mr Warren gave evidence, based on empirically derived formulae and measurements, that at 400 kV at the 65-metre designation edge, the broadband noise level would be 35 dB; that the average level of the 100-Hz hum would be in the order of 25 dB; and that there would be no cumulative increase above the level of the broadband noise when both are present.
1236. This witness also stated that when the line is operated at 220 kV, the noise levels would be considerably lower.
1237. Mr Warren had considered the extent of time the Waikato is affected by rain or heavy fog, and explained his assumptions that wet conductor conditions would occur for 11 per cent of the time in the northern part of the line, and 12 per cent of the time in the southern part.
1238. He gave his opinions that, even in wet-conductor conditions, the corona discharge noise level of 35 dBA at the designation boundary would comply with the noise limits of all the applicable district plans; and that at the initial 220 kV, it would be lower still. Mr Warren recommended an LAeq 40-dB noise limit to control corona discharge noise, applied at the designation boundary. He also stated that the lower predicted corona discharge noise level of 35 dBA at the edge of the designation would be well below a level likely to cause sleep disturbance; that it would meet the AS/NZS 2107:2000 Standard; and that the predicted noise effects from operation of the line at the maximum voltage of 400 kV would be minor.
1239. On disturbance of animals by noise, Mr Warren described his experience that farm animals habituate to noise readily without any detrimental impact; he referred to horses and, in particular, cattle and sheep grazing right beside a busy road.4
1240. Mr K M Rooney, a veterinarian, disputed this. He contended that the noise generated by the proposed transmission line could have adverse effects on equine health at Haunui Farms. In addition the safety of workers could be jeopardized if horses were startled by the noise from the line. The witness stated in rebuttal evidence that the impact on horses or donkeys on other properties would be less, due to the generally quieter nature of these farms and the quiet nature of donkeys; by comparison, Haunui Farms are thoroughbred breeding farms.
1241. In supplementary evidence, Mr Khot stated that the audible corona discharge noise increases in rain, fog or mist; it is highest in heavy rain, but then the noise of the rainfall itself tends to mask the noise from the conductors. In moderate rain audible noise could be higher than in heavier rain). The tolerance between 35 dBA and 40 dBA allows for this and for noise due to spots on the surface of conductors resulting from broken strands or bird droppings.
Wind-induced noise
1242. Mr Warren described two sources of wind-induced noise: wideband turbulent noise and Aeolian noise (tones and whistles that vary in frequency with wind speed) caused by air fluctuations across a conductor. He explained that the surface profiles of the proposed conductors would be similar to those used elsewhere, and are known not to cause Aeolian noise problems.
1243. This witness estimated that in a stiff breeze (about 10 metres per second), the Aeolian noise level would be less than 25 dBA at the designation edge, and would have a low tone at a frequency of about 150 Hz. The tone would be likely to be masked by other wind noise effects (such as vegetation), and would not increase the overall ambient noise level. He added that insulators of the type proposed would not produce tonal noise. He also told the Board that he had never come across a noise problem generated by a transmission tower itself, or by current tracking across insulators.5
Noise from transformers and circuit-breakers
1244. Mr R McKenzie and Mr M Spring stated concern about noise from the proposed substation at Brownhill Road.
1245. Mr Warren described modelling and assessment of noise from activities at each of the substations. The Brownhill Substation is to be developed in stages. The first stage is a transition station, which would have no transformers or circuit-breakers. The second stage is to be a 220-kV gas-insulated switching station with several circuit-breakers and an emergency standby generator. The circuit-breakers would be inside the building and the generator is to be sound-attenuated. The third stage (anticipated to be constructed in about 2033) is to include seven 400/220-kV transformers (including one spare unit) and a 400-kV gas-insulated switching station enclosed in another building. The generator would also be sound-attenuated. Mr Warren gave his opinion that, in practice, there would only be significant noise emissions from Stage 3.
1246. The witness explained that transformer noise is relatively constant, and most likely to be noticed at night when noise from other sources is at lowest levels.
1247. Assuming six transformers operating, noise screening from site earthworks and three-sided firewalls around the transformers, and a westerly wind of 2.5 metres per second, Mr Warren predicted noise levels slightly in excess of 30 dBA for existing residences to the west, and in excess of 50 dBA at the north-eastern boundary, but capable of being considerably reduced by four-sided enclosures around the transformers.
1248. With four-sided enclosures for the transformers, the witness predicted that in ‘worst-case’ downwind conditions at all existing residences and realistic future residential locations, the noise level would be less than 30 dBA; and at the most affected boundary of the Transpower property, 45 dBA.
1249. Mr Warren accepted that it would be reasonable to aim for noise control design that achieves an L10 of 35 dBA at existing and realistic future notional boundaries, and considered that this could be achieved by setting a night-time limit at the designation boundary of 45 dBA. To provide a high standard of protection against intrusive noise for existing dwellings, he proposed limits at the designation boundary of 55 dBA L10 daytime, 45 dBA L10 night time, and 75 dBA Lmax; and 45/35 dBA L10 and 75 dBA Lmax at the notional boundaries of existing dwellings.
1250. The witness explained that the notional boundary control would provide a high standard of protection for existing dwelling, and would be readily complied with at stages 1 and 2. The designation boundary limits would be relevant in Stage 3, when the 400-kV transformer equipment is installed. It would protect future dwellings, and provide long-term certainty for Transpower.
1251. Referring to the noise of the circuit-breakers (which are to be enclosed in buildings), Mr Warren considered that they would readily be able to meet the Lmax limit of 75 dBA at the designation boundary, and 65 dBA at the notional boundary of any existing or future dwelling.
1252. No concern was raised about audible noise effects from transformers or circuit-breakers at other substations. The noise from the long-established Otahuhu Substation would be reduced by installation of newer quieter transformers; and the noise environment there is significantly elevated by noise from industrial activity and noise of traffic on the Southern Motorway, so the substation noise alone could not be measured effectively.6 The noise from the Pakuranga Substation is exceeded by the ambient noise environment; with enclosure of the new transformers, it can comply with the district plan limits. Noise from new transformers at Whakamaru North is predicted to comply with the Taupo District Plan.
1253. Mr Lloyd also contributed to the conditions proposed in these respects.
1254. Mr Warren’s evidence was not shown by cross-examination to be unacceptable, and Mr Lloyd was not cross-examined, nor was Mr Rooney. No other expert evidence was given on noise from operation of the overhead line or the associated Brownhill Substation.
1255. The Board accepts the evidence of Messrs Warren, Lloyd and Rooney and finds that, if operated in compliance with the proposed conditions, any noise from the overhead line and substation would be limited so as not to amount to a significant adverse effect on the environment.
Radio, television, and other electronic interference
1256. Mr J Sexton (Sexton Farms) stated that he had been a licensed radio amateur operator since 1961, and his father since 1957; that they operate on all high-frequency and very high-frequency radio bands, and have aerials on 15-metre and 13-metre steel towers respectively; and wire aerials for the lower high-frequency bands extend 80 metres from the house and 15 metres high. Mr Sexton stated his concern that the proposed 400-kV line closer than 150 metres would make high-frequency radio communication almost impossible.
1257. Messrs W Jamieson and K Willoughby, presenting submissions on behalf of Orini Downs Station, stated that they are unsure whether communications on the farm (mobile phone or hand-held radio-frequency radios) would be affected by the transmission line. Mr E J Smith (Greenhaven Farm) stated his concern that the electromagnetic radiation emanating from the line would have substantial adverse effect on wireless transmission affecting television, mobile phone and internet communications. Mr H K Ruffell expressed similar concern.
1258. Mr A Loveridge stated his concern that the overhead lines would have an effect on the electronics of his new million-dollar milking shed, as they would be only 250 metres away.7 Ms L Bilby stated her concern that electric-fence controllers may be blown out; and also referred to an ‘incredible light’ seen on foggy nights in the vicinity of an existing high-voltage transmission line.8 Mr E J Smith stated his concern that electromagnetic radiation emanating from the new line could damage computer hardware. Lichfield Farms expressed similar concern. Ms S Hall stated her concern that the electromagnetic fields from the proposed line could cause interference with the large antennae on Mount Ruru.9
1259. Mr P and Mrs D Dombroski expressed concern that energy fields from the transmission line would have serious effects on farm vehicles, causing them to malfunction; and that this could be a costly, inconvenient and ongoing problem.
1260. Mr R D Cooper is an independent consultant professional engineer with specialist expertise on effects of electric and magnetic fields from transmission lines on electrical equipment and appliances. In his evidence he referred to the standards applicable to the design and building of transmission lines (emission standards and immunity standards), and described the effect of magnetic fields on electric and electronic equipment.
1261. Mr Khot had calculated the magnetic field strengths from the proposed overhead line. Based on his evidence, Mr Cooper concluded that there should be no issue with magnetic fields affecting cathode-ray tube monitors on computers and television sets beyond the edge of the designation until 2015. After that year, with expected increase of maximum winter loading conditions of the line, the magnetic field strength at the designation edge may increase to 1.25 microtesla (µT) but he stated that there is unlikely to be any issue with cathode-ray tube monitors on computers, as by then they would have been replaced by liquid-crystal display equivalents. He assessed the probability of specific effects on cathode-ray tube television sets as probably very small, perhaps only once per year.
1262. This witness stated that disruption to radio and television reception can be affected by electric corona noise (having a bandwidth of about 1–1500 MHz), reflections (such as aircraft nearby, glass-covered buildings, or water), and shadowing effects (such as a tower, transmission line or hill blocking radio or television signals). Corona noise and shadow effect are the most likely to arise from the new 400-kV-capable transmission line; in most cases shifting the affected antenna would solve the issue.
1263. Mr Cooper also advised that telephones, computers, printers, fax machines, cordless and DECT phones, stereos, and digital clocks and similar appliances are generally immune to magnetic fields of at least 50 µT, and the maximum magnetic field likely to be experienced underneath the line is 28.4 µT (during maximum winter loading after 2042). If users of hearing aids with telecoils, or assisted listening systems were to experience interference, then remedial solutions could be implemented. Pacemakers are immune to mains frequency magnetic fields of at least 400 µT.
1264. Cross-examination of Mr Cooper did not leave question in the Board’s minds about the acceptability of his evidence; and there was no expert evidence to the contrary of his. The Board accepts it.
1265. In reliance on Mr Cooper’s evidence, the Board finds that the overhead line would not have any significant adverse effect on radio communications, television reception, electric-fence controllers, computer equipment, or on other electronic devices.
Third-party telecommunications
1266. Although the topic does not appear to have been addressed by counsel for Carter Holt Harvey, in his evidence Mr Parrish raised concern that the telecommunication line to be strung on the overhead line structures might be used for conveying third-party telecommunications for added value.
1267. In rebuttal evidence, Ms Allan responded that she had no experience of designations expressly excluding activities that are not ancillary to the purpose of the designation.
1268. The Board sees no need to depart from the provisions of section 176(2) by which activities on designated land for a purpose other than the designated purpose are subject to the district plan. The Board adds that it is not aware that there would be any adverse effect on the environment of the telecommunication line being used for third-party communications; and that there may be a positive benefit of avoiding an extra structure to carry the third-party communications.
Earth potential rise and transferred voltages associated with overhead line
1269. Earth potential rise can occur for a short time when current arising from an earth fault on a transmission tower flows through the ground. Step and touch voltages can arise where a human or animal contacts two different voltages simultaneously. Depending on the magnitude of the current, this may be felt as an electric shock. Voltages and currents may be induced in conductive objects (such as unearthed wire fences, cables and pipelines) near the transmission line.
1270. Mr Mitton gave evidence of systematic analyses he had made of risks from these phenomena in respect of the proposed overhead line, based on New Zealand Standards for risk AS/NZS 4360:2004 and HB 436. The basis for his opinions that the risks would be low, was that appropriate mitigation can be implemented to minimise them so that the line would not introduce any significant risk to people or to third-party infrastructure.
1271. None of the submitters cross-examined Mr Mitton, nor called contradictory expert evidence.
1272. In reliance on Mr Mitton’s evidence the Board finds that the overhead line, constructed and operated in compliance with the proposed conditions, would not have any significant adverse effect on the environment by earth potential rise, step and touch voltages, or induced currents.
Ground heating from underground cables
1273. The proposed underground cables from the Brownhill Substation to the Otahuhu and Pakuranga Substations are designed to operate at a nominal voltage of 220 kV; they would generate heat that would be dissipated through the sheathing and serving into the surrounding ground and then to the atmosphere. After about 2032, Transpower intends to install forced water cooling to increase the rating of the cables by circulating water through polyethylene pipes laid about 50 mm from the cables. Water would be pumped through the pipes, and the heat discharged to the atmosphere.
1274. Mr Wildash, an electrical engineer having considerable professional experience with underground power cables, gave evidence that under normal conditions the cable serving would have a maximum surface temperature of about 50º to 60º C, and that special thermally stable backfill would be placed under and around the cables during installation.
1275. There was no evidence to the contrary, and the Board finds no basis for any adverse effect on the environment from dissipation of heat from the proposed underground cables.
Electric and magnetic fields around underground cables and substations
1276. In paragraphs [766] and [767] of Chapter 9, the Board summarised the evidence given by Mr Mitton, on the electric fields around underground cables and substations. He also gave evidence that modelling had shown that during steady-state operation in normal and peak loading, the levels of electric and magnetic fields around the underground cables and substations, at ground level and at 1 metre above ground, would not exceed reference levels recommended by the National Radiation Laboratory. In particular, he produced details showing that the magnetic fields above the cables are below the ICNIRP Guideline of 100 µT for public exposure. (For further discussion see Chapter 9, para [777].)
1277. Mr Mitton was not cross-examined by submitters, nor was contradictory evidence given or called by any of them. The Board finds that the proposed underground cables and substations would not have adverse effects on the environment in terms of electric or magnetic fields around them during steady-state operation under normal and peak loading.
Induced voltages associated with underground cables
1278. Mr Mitton also gave evidence about induced voltages associated with the proposed underground cables. He had calculated maximum acceptable lengths of metallic structures or services parallel and 1 metre from the cables and induced voltages in steady-state and fault conditions. For fault conditions, the maxima are 2.1 kilometres for fences, 0.9 kilometre for communications cables and 1.4 kilometres for water or gas pipelines.
1279. Mr Mitton gave his opinion that specific analysis and mitigation should be considered in respect of metallic structures that are closer or longer than the maximum lengths used in his calculations.
1280. Mr Mitton’s evidence was not called in question, and the Board finds that potential induced currents associated with the underground cables would not be likely to have any significant adverse effect on the environment.
Conclusions
1281. In summary, the Board finds that if the Grid Upgrade is constructed and operated in compliance with the proposed conditions, it would not have significant adverse effects on the environment in terms of: audible noise; interference with radio, television or other electronic equipment; earth potential rise or transferred, step, touch, or induced voltages or current; ground heating or electric or magnetic fields; or induced currents associated with underground cables.
Endnotes
