Communication Effects Puketoi Wind Farm A Mighty River Power Project Prepared by Rodgers Hulston & White Limited for Chancery Green 22 July 2011 1 1
Table of Contents 1 Table of Contents .................................................................................... 2 2 Executive summary ................................................................................ 4 3 Glossary of technical terms used ...................................................... 6 4 Introduction ............................................................................................. 9 5 Potential Radio Communication Effects from Wind Farms ..... 9 6 Methodology & Assumptions ............................................................ 10 6.1 Electro Magnetic Interference (EMI) ................................................................... 10 6.2 Near‐Field Effects ........................................................................................................ 10 6.3 Diffraction Analysis ..................................................................................................... 10 6.4 Scatter Analysis ............................................................................................................ 11 6.4.1 Calculation Method............................................................................................................. 12 6.4.2 Accuracy of Analysis ........................................................................................................... 12 6.4.3 Summary ................................................................................................................................. 14 6.5 Design assumptions and constraints ................................................................... 14 7 The Existing Environment ................................................................. 14 7.1 Current radio services ............................................................................................... 14 7.2 Radio Site Locations ................................................................................................... 15 7.2.1 Mt Butters ............................................................................................................................... 15 7.2.2 Rising Sun Puketoi Range ................................................................................................ 16 7.2.3 Radio Licence Information .............................................................................................. 16 8 Assessment of Actual and Potential Environmental Effects .. 17 8.1 Electro Magnetic Interference (EMI) ................................................................... 17 8.1.1 Remediation and mitigation .......................................................................................... 18 8.2 Near‐field effects .......................................................................................................... 18 8.2.1 Remediation and mitigation .......................................................................................... 18 8.3 Diffraction Analysis ..................................................................................................... 19 8.3.1 Fixed Links .............................................................................................................................. 19 8.3.2 Area Coverage Services ..................................................................................................... 21 8.3.3 Cranes blocking radio paths during construction ................................................ 22 8.4 Reflection ........................................................................................................................ 22 8.4.1 Area Coverage: Land Mobile Mt Butters ................................................................... 22 8.4.2 Area Coverage: Cellular Mt Butters............................................................................. 23 8.4.3 Area Coverage: TV ............................................................................................................... 23 8.4.4 Area Coverage: FM Radio ................................................................................................ 24 8.4.5 Fixed Links (PTP and PTMP): Mt Butters and PR14 ............................................ 24 8.4.6 Fixed Links (PTP and PTMP): Rising Sun Puketoi Range .................................. 25 9 Section Six – Consent Conditions & Monitoring ......................... 26 2 10 Section Seven – Summary of Effects ............................................... 27 11 Appendices .............................................................................................. 30 11.1 Appendix A Reference List ....................................................................................... 30 11.2 Appendix B Drawings ................................................................................................. 31 3 2
Executive summary Mighty River Power is seeking resource consent to build a wind farm on the Puketoi Range east of Pahiatua. Wind turbines have the potential to cause interference to radio communications in the area surrounding the wind farm. Interference can be caused by four distinct mechanisms: •
Electromagnetic noise (EMI), whereby the wind turbine generator’s electrical and electronic equipment is radiated in a frequency band used by a radio service. •
Modification of an antenna’s radiation pattern where a wind turbine is in close proximity. •
Obstruction of a radio path by a wind turbine, which attenuates the amount of radio signal received. •
Reflection (Scatter) from wind turbine, which can cause echoes of radio signals to be received along with the direct signal. These ‘ghost’ signals can cause distortion and noise. This report analyses the effect of interference caused by these mechanisms on landmobile, cellular, and fixed link radio services that use sites near the wind farm i.e. Mt Butters, Rising Sun Puketoi Range, and PR14. It also analyses the effect of interference on FM Radio and TV reception in the area. To calculate the interference conservative assumptions and models have been used. These are based on methods used for other wind farm proposals both within New Zealand and overseas. The findings of this report are summarised as follows: •
There is no perceptible degradation to radio services caused by EMI (electromagnetic interference) from the wind turbines. •
Antenna radiation patterns are not degraded by the Puketoi wind turbines because they will be located far enough away from any antennas. •
There will be no degradation of digital TV and FM radio reception for households within a defined area surrounding the wind farm. •
Mobile/portable FM radio reception will be degraded within 900m of a wind turbine. There is no practical way to mitigate against this other than to re locate or retune to a “stronger” radio station. •
For Land Mobile services using Mt Butters there is no perceptible loss of coverage caused by turbine obstruction, however reception will be degraded by scatter within 900m of a turbine. Reception may be restored by moving the handset/portable to another location 10 to 30 metres away. •
For cellular services using Mt Butters there will be no perceptible loss of coverage, however reception will be degraded by scatter within 100m of a turbine. 4 •
At Mt Butters and PR14, Point to Point (PTP) and Point to Multipoint (PTMP) fixed links are unaffected by scatter. Such links are also unaffected by turbine obstruction, with the exception of two Powerco links located at Mt Butters. Mighty River Power has committed to replacing these links (PTMP) with PTP links so the antennas can be located where the links are unobstructed. •
For Point to Point (PTP) and Point to Multipoint (PTMP) fixed links services using Rising Sun Puketoi Range there is no obstruction of links by turbine obstruction, however reception will be severely degraded by scatter. To mitigate against this, Mighty River Power has committed to relocating the radio site further northeast. 5 3
Glossary of technical terms used Area Coverage: These are radio services which consist of a central/hub/base radio, like PTMP, which is a fixed location but the other end of the radio link is mobile. Examples of this are Land Mobile and Cellular. These services are designed to provide communication for mobile radios over a large area as opposed to specific locations. Communication is bidirectional and they operate in VHF and UHF bands. Broadcast: This type of radio service is a variation on Area Coverage with the difference being that the communication is uni‐directional from the central/hub/base transmitter to a fixed or portable/mobile receiver. The main types of broadcast service are: AM sound broadcasting (0.5 – 1.6MHz); FM sound broadcasting (88 – 108MHz); Television broadcasting (44 – 68, 174 – 230, 500 – 800MHz). Cellular Mobile: Cellular mobile is the now ubiquitous public mobile telephony service that was introduced into New Zealand in the late 1980s. Cellular mobile networks employ numerous base stations, usually up to around 25 m high, ranging in cell coverage from a few hundred metres to many kilometres, depending on the area to be covered and the anticipated “traffic load” within. The cellular mobile frequency bands in New Zealand are in the UHF range around 900MHz, and also more recently around 2000MHz. C/I (ratio): The ratio of the wanted signal (C) with respect to the unwanted interference (I), usually expressed in decibels. Fresnel Zone: Fresnel zones result from diffraction by a circular aperture. For radio link planning the 1st Fresnel Zone is used to define the region around the radio path where an object (e.g. building, tree, ground) may cause attenuation of the radio signal by diffraction if the objects blocks the 1st Fresnel Zone (or part of it). Fixed Linking: A Fixed Link is where the ends of a radio link are fixed in location i.e. not mobile. Fixed links employ highly directive antennas that are intended to transmit or receive radio signals only 6 in one direction, and operate in the VHF, UHF, and SHF. Interference: The effect of unwanted energy due to one or a combination of emissions, radiations, or inductions upon reception in a radio communication system, or loss of information which could be extracted in the absence of such unwanted energy. (International Telecommunication Union Radio Regulations). ITU: The ITU (International Telecommunications Union) ‐ a UN (United Nations) organisation that sets international rules and recommendations for telecommunications and radio communications. ITU‐R refers to radio communications part of the ITU. Land Mobile Land Mobile services provide personal two‐way wireless voice communications between portable transceiver terminals routed via a “base station” which is usually situated at a high prominent location to provide wide area coverage. Land Mobile services are often used by taxis, emergency services, couriers, etc. and make use of hand portable and vehicular terminals. The Land Mobile frequency bands in New Zealand are in the VHF range at around 80 and 160MHz, UHF from 400 to 500MHz and 800MHz. PTMP: Point to Multipoint ‐ this is a type of fixed linking where two or more fixed points communicate to and from the same central/hub/base site using the same radio equipment at the hub site. A PTMP system can be considered to consist of a number of PTP links. PTP: Point to Point ‐ this is a type of fixed link where the radio equipment only provides communication between two geographical points. Radio Link: A radio link is a communication circuit which consists of a transmitter at one end and a receiver at the other end. The transmitter via an antenna radiates a modulated electromagnetic wave, which is demodulated by a receiver via an antenna. Radio Service: Refers to the purpose of the radio link e.g. FM radio, TV, Cellular, Land Mobile. 7 RCS: Radar Cross Section ‐ it represents how much radio power is reflected off the object in terms of an equivalent area and does not correspond to physical size. RCS is sometimes expressed as dBsm, decibel square metres (10LOG RCS in square metres). RSM: Radio Spectrum Management ‐ the group within the Ministry of Economic Development responsible for managing the radio spectrum in New Zealand. SHF: Super High Frequency – officially defined as the range 3000 MHz to 30000 MHz and often referred to as “Microwaves”. VHF: Very High Frequency – officially defined as the range 30 MHz to 300 MHz. UHF: Ultra High Frequency – officially defined as the range 300 MHz to 3000 MHz and includes part of the region often referred to as “Microwaves”. 8 4
Introduction Mighty River Power is seeking resource consents to build a wind farm on the Puketoi Range east of Pahiatua. The proposed turbine locations are shown on drawing MRP‐PKT‐6701. The purpose of this report is to analyse and summarise the potential effects of the proposed wind turbines on radio communication and recommend ways of mitigating any resulting adverse effects. There are three radio sites in the immediate vicinity of the proposed wind farm; Mt Butters, Rising Sun Puketoi Range, and PR14. Their locations are shown on drawing MRP‐PKT‐6701. Radio services using these sites have the potential to be affected along with other services being used in the area that rely on radio sites located a significant distance from the wind farm (greater than 2km from a turbine). 5
Potential Radio Communication Effects from Wind Farms Wireless communication systems use radio waves to relay information from a transmitter to a receiver. In some circumstances it is possible for wind turbines to cause interference to wireless receivers. There are four distinct mechanisms that can potentially cause interference to a radio service: Electromagnetic Interference (EMI): Occurs when the electrical and electronic equipment inside a wind turbine generator radiates radio frequency energy in a frequency band used by a radio service. Near‐Field Effects: Occurs when a wind turbine is located in close proximity to an existing antenna, such that it modifies the radiation characteristics of the antenna. Diffraction: Occurs when a wind turbine’s location causes radio waves to be partially blocked, causing some signal power loss. Reflection (or Scattering): Occurs when radio waves are reflected from a wind turbine’s surface. 9 6
Methodology & Assumptions 6.1 Electro Magnetic Interference (EMI) The wind turbine consists of an electrical generator and controlling electronics which will generate radio frequency interference as a consequence of its operation. Radio frequency interference can affect radio services over a wide range of frequencies (500kHz to 3000MHz). International and NZ Standards for Electromagnetic Compliance (EMC) deem acceptable limits for interference from wind turbines. The limits are given in terms of the maximum radiated signal strength over a frequency band when measured by an antenna at a specific distance away (10m is the typical measured distance) from the interfering device. These limits are used to calculate the minimum distance away from the wind turbine where the EMI will not adversely affect radio reception. 6.2 Near‐Field Effects This analysis consists of calculating where the radiation characteristic/pattern of an antenna is independent of distance and the influence of other objects. This is given in terms of a minimum distance away from the antenna and is a function of antenna size and operating frequency. 6.3 Diffraction Analysis Diffraction of radio signals occur around obstacles (e.g. building, tree, ground) and results in attenuation of the radio signal. This is undesirable because it may attenuate the receive signal below the minimum working threshold for the link or make it more vulnerable to atmospheric fading. The region around the path where the link is vulnerable to diffraction is called the 1st Fresnel Zone. Any object extending into it will cause diffraction of the radio signal. The region is defined by an ellipsoid with a circular cross section (for example, Figure 1) Figure 1: Fresnel Zone Side Elevation Profile Radio clearance is based on ensuring that the radio path has at least 1st Fresnel zone clearance at K=4/3 (related to the refractive index of the atmosphere) when the signal path passes either over or beside the turbine. This clearance criteria is based on ITU‐R recommendation 10 P.530[2] and ensures there is no additional path loss caused by diffraction. Excess clearance is the difference in height or distance between the perimeter of 1st Fresnel Zone and the perimeter of the circle formed by the rotation of the blades. The clearance is defined as horizontal if the radio path passes beside the turbine and vertical if it passes over the turbine(see Figure 2, below). Figure 2: Fresnel Zone End Elevation diagram showing Clearance 6.4 Scatter Analysis Scattering can cause interference to nearby radio services by two mechanisms: Multi‐path Propagation: Delayed "echo" signals of the wanted signal arrive at a “victim” receiver via reflection (scattering) off the wind turbines causing noise and distortion to the signal received via the direct path. Frequency Reuse: Scattered echoes arrive at a receiver having originated from other transmissions using the same channel frequency in the same geographical area, which causes interference. 11 Figure 3: Scatter from Turbine For both mechanisms, the extent of the impact depends on the strength and delay of the received echoes relative to the direct path signal, the fade margin of the victim radio service, and the countermeasures used in the victim receiver. Strong, long delay echoes are particularly problematic for radio reception. 6.4.1 Calculation Method The analysis of potential scattering effects is undertaken by determining the ratio of wanted signal versus unwanted scattered signal (C/I_scatter ratio) at the input of the victim receiver. For each type of radio service there is a minimum C/I_scatter ratio required to ensure that radio performance is not adversely affected. The ‘Bistatic Radar’ equation is used to estimate the C/I_scatter ratio and it is the most common approach used for wind turbine analysis[6]. The equation depends on: •
total distance from the transmitter to the receiver in metres •
distance from the transmitter to the wind turbine in metres •
frequency of the service (in MHz) •
obstruction loss •
radar cross section (RCS) of the wind turbine in m2 •
receive and transmit antenna gain in the direction of the turbine In general the further away a receiver is from a wind turbine, the higher the C/I_scatter ratio. The results are presented as contour maps which show the regions where a specific ratio is exceeded. 6.4.2 Accuracy of Analysis Antenna Gain To simplify the analysis, this report assumes that all antennas are non‐
directional (isotropic) and hence the benefits that directional antennas give in reducing interference are disregarded. In general, area coverage services use omnidirectional or sectorised antennas and fixed 12 services use directional antennas. Hence the results for fixed services are conservative. Radar Cross Section (RCS) The most uncertain parameter is the RCS of the wind turbine. It is not only dependent on the physical area of the wind turbine presented normal to the transmitter but also depends on the conductivity of the wind turbine materials, the geometry of the wind turbine surfaces and their angles relative to the transmitter. For the purposes of this report a RCS of 35dBsm for a single turbine is used, consistent with similar communication effect studies for NZ wind farms. In this report a RCS of 35dBsm (31622 metres) for a single turbine is used. This value has been selected as being a representative high‐
average value suitable for use in interference co‐ordination studies based on the most recent research presented by authorities in the field. The total scatter interference from a number of turbines is obtained by summing the power from each individual turbine. This is a simple approach as it disregards the fact that scatter from the turbines is coherently related because it originates from the same source and hence involves a complex superposition of scatter field strength. It also ignores the spatial and temporal variability in turbine RCS across the wind farm. However when all these factors are considered and compared, the simple sum gives a conservative yet realistic estimate of the aggregate interference. Minimum Permissible C/I_scatter ratio The minimum C/I_scatters ratio required for each service are given below. With the exception of FM Radio and Digital TV, these figures have been derived from the minimum required C/N ratio for a specific radio service, based on equipment typically used for these services. The C/I_scatter ratio is 6dB higher than this to ensure that the interference contribution is only just perceptible when compared with thermal noise. For FM Radio and Digital TV the ratios are based on test reports [3] and [7] respectively referenced in the Appendix of this report. Service C/I_scatter VHF/UHF FM Land Mobile 26dB GSM Cellular 18dB WCDMA Cellular 13dB (HSPA) 1.5GHz PTMP 22dB FM Radio[3] 27dB DVB‐T[7] (Digital TV) 28dB Broadband wireless access services 24dB Low Capacity DMR (4QAM) 15dB High Capacity DMR (16QAM) 21dB 13 High Capacity DMR (128QAM) 35dB Table 1:C/I_scatter for various radio services Path Obstruction To simplify the analysis, it is assumed that the scattered path (Transmitter‐Wind Turbine‐Receiver) and the direct path (Transmitter–Receiver) are equally affected by obstructions. Given that the turbines and the radio sites are at a similar ground height and relatively close to each other, this is a reasonable assumption for all services except TV and FM radio. These services rely on a site a significant distance from the turbines, and hence the relative obstruction loss between the scattered and direct paths must be considered. 6.4.3 Summary Given the above considerations, the C/I_scatter calculations are conservative for any given location and hence the actual values are likely to be greater than the theoretical value. 6.5 Design assumptions and constraints The analysis relies on external data sources that have a limited accuracy. These accuracies are: • Terrain data: ±10m vertical and ±25m horizontal • GPS locations of Mt Butters and Rising Sun Puketoi Range telecommunication masts ±6m • RSM database: While the RSM database is assumed to contain accurate licence information regarding site placement, transmit/receive height and transmit/receive frequency.,the database does not give the antenna mounting height above ground. Thus an average antenna height of 10m has been assumed. This is a reasonable assumption given a nominal tower height of 30m. Site coordinate accuracy ±50m horizontal • For the turbines a maximum tip height of 160m and a maximum blade length of 65m have been used. 7
The Existing Environment 7.1 Current radio services In the vicinity of the Puketoi wind farm there are three radio sites; two at the north end (PR14 and Rising Sun Puketoi Range) and one at the south (Mt Butter). See drawing MRP‐PKT‐6701. 14 The radio services licensed at these sites are: Site Name Mt Butter Type of Radio Services PTP VHF, UHF, SHF PTMP UHF (400MHz & 1.5GHz) Site Owner Telecom New Zealand Limited Users NZ Police Ambulance New Zealand Ministry of Civil Defence and Emergency Management Area Coverage VHF Landmobile UHF Landmobile Cellular (800MHz) New Zealand Association of Radio Transmitters Inc TeamTalk LTD MR JP McLean Powerco Limited Telecom New Zealand Limited Rising Sun Puketoi Range PTMP‐ VHF PR14 PTMP UHF (1.5GHz) PTP‐UHF Manawatu Wanganui Regional Council Manawatu Wanganui Regional Council Telecom New Zealand Limited Telecom New Zealand Limited Table 2: Type of radio services at affected sites The interference to radio services using these sites had to be analysed along with other radio services used in the area surrounding the wind farm but relying on radio sites outside the area i.e. Wharite TV and FM Radio transmitter site. 7.2 Radio Site Locations 7.2.1 Mt Butters Mt Butters site consists of five antenna mast/towers which for the purpose of the report have been described as: Mt Butters West Mast Powerco Services Mt Butters Mid Mast NZ Police, Ambulance New Zealand, Ministry of Civil Defence and Emergency Management, New Zealand Association of Radio Transmitters Inc, MR JP McLean. Mt Butter Micro Team Talk Microwave link and Telecom fixed links. Mt Butters Cell Telecom cellular and microwave fixed links Mt Butters East Mast Team Talk 15 Mt Butters East Mast
Mt Butters Cell
Mt Butters Micro
Mt Butters Mid Mast
Mt Butters West Mast
Figure 4: Mt Butters Mast Locations Site photographs and information obtained from Powerco was used to determine which service uses each mast. 7.2.2 Rising Sun Puketoi Range Figure 5 below shows the location of the Rising Sun Puketoi Range radio site. It is approximately 60m from WT1. Figure 5: Rising Sun and WT1 Locations 7.2.3 Radio Licence Information Detail regarding licence data is shown on drawing MRP‐PTI‐6716. The RSM database only contains information about radio services with individual licences. As a consequence, individual licence holders have a greater degree of protection from interference than those working under a General User Radio Licence (GURL), which is not registered. In 16 general only licensed radio services can be considered, however Powerco has provided information about links they have in the 5GHz GURL and as such, these have been included in the analysis. 8
Assessment of Actual and Potential Environmental Effects 8.1 Electro Magnetic Interference (EMI) The wind turbines comply with the following EMC standards: • AS/NZS 61000.6.2:2006: “Electromagnetic compatibility (EMC) ‐ General standards ‐ Immunity for industrial environments” • AS/NZS 61000.6.4:2007: “Electromagnetic compatibility (EMC) ‐ Generic standards ‐ Emission standard for industrial environments” In terms of interference to radio signals AS/NZ 61000.6.4:2007 is the relevant one. The maximum radiated signal field strength permissible under AS/NZ 61000.6.4:2007 is outlined in Table 3 below: Frequency (MHz) Field Strength @ at 30m 120kHz Measurement Bandwidth 30 to 230MHz 30dBuV/m 230 to 1000MHz 37dBuV/m Table 3: EMC Emission Spec No specification is given for frequencies higher than 1000MHz. Therefore it is assumed that provided the limits are met at 1000MHz the standard will also be met for higher frequencies. This is a reasonable assumption given that “manmade” noise power typically decreases with frequency at a rate greater than 10dB/decade. Cellular (900MHz) is the most sensitive service in terms of noise. It requires any noise to be at least 10dB below the receiver noise floor (‐
102dBm typically for WCDMA) i.e. ‐112dBm. This equates to a Field Strength of 22dBuV/m for an antenna gain of 0dBi (handset) and a bandwidth of 5MHz. When this is scaled to 120kHz, the bandwidth used in the standard, it becomes 6dBuV/m. This means the receiver must be located at least 180m away from the turbine (based on ground reflection path loss formula) to ensure interference created by the wind turbine will not adversely affect receiver performance. No information is given by the turbine manufacturer about the actual interference level from the turbine other than it complies with the Standard. In practice the interference falls with frequency and hence it will be closer to the limit at the lower frequencies (230MHz) than at the higher frequencies (>900MHz). As a ‘rule of thumb’ it can be assumed that interference at 900MHz will be at least 10 to 20dB below that at 230MHz. This reduces the potential interference and the minimum EMI interference distance from 180m to 60‐100m. This is a 17 conservative estimate as EMI has not been reported as being an adverse effect in the vicinity of other wind farms. 8.1.1 Remediation and mitigation The effect of EMI interference on radio communication is secondary to the interference caused by Reflection/Scatter. It is the latter which will determine how close portable radios/handsets can be used to Wind Turbines. No specific remediation or mitigation is required for EMI interference. 8.2 Near‐field effects If a wind turbine is positioned in close proximity to an antenna, it can modify the radiation characteristics of the antenna. This occurs when the turbine is within the near‐field of the antenna. The near‐field distance is a function of frequency and antenna gain. The calculated near field zones for the various frequencies used at the radio sites is shown in Table 4. For each frequency band where a number of different antennas are used, the worst case value is used. Frequency Band (MHz) Near Field Zone (m) Site Antenna Type 80 2 Mt Butters dipole assumed 1 Mt Butters and Rising Sun Puketoi Range dipole assumed <1 Mobile ¼ wave vertical 6 Mt Butters 8 element yagi 38 Mt Butters 2.5m Panel <1 Mobile Patch antenna 1500 10 Mt Butters and PR14 1m Panel 7000 160 Mt Butters 1.8m parabolic 1300 125 Mt Butters 1.2m parabolic 160 400‐500 900 Table 4: Near Field distances All turbines are outside the near field zone for all antennas located at the radio sites and hence the interference is imperceptible. For mobile radio equipment the antenna performance will only be affected when used next to a turbine. 8.2.1 Remediation and mitigation As the radio reception quality will be degraded by scatter when located immediately next to a turbine, the radio user will be forced to move to a location outside the near field zone to restore communication. This distance is determined by the minimum C/I_scatter for this service (see scatter analysis) and hence no specific remediation or mitigation is required for near field effects. 18 8.3 Diffraction Analysis 8.3.1 Fixed Links Drawing MRP‐PKT‐6702 shows the geographical relationship between existing fixed links (PTP and PTMP) and the proposed wind turbine locations. Further detail regarding the relationship between the turbines in the immediate vicinity of the local radio sites is provided in drawing MRP‐
PKT‐6703 and MRP‐PKT‐6704. This shows there are two Powerco radio links that will pass directly through proposed wind turbines (WT44 and WT46) and hence will be severely obstructed (14 ‐15dB) i.e. Figure 6: Plan View of Obstructed Paths Elevation (m)
The elevation view (path profile) of the obstructed paths are shown in Figure 7 and Figure 8. 900
800
700
600
500
400
300
200
100
0
0
2
4
Mt Butters West Mast
Latitude
40 33 37.29 S
Longitude 176 02 11.84 E
Azimuth
316.64°
Elevation
756 m ASL
Antenna CL 14.0 m AGL
6
8
10
12
14
16
18
Path length (32.36 km)
Frequency (MHz) = 420.0
K = 1.33
%F1 = 100.00
20
22
24
26
28
30
32
TARARUA WIND POWER
Latitude
40 20 53.55 S
Longitude 175 46 30.50 E
Azimuth
136.81°
Elevation
400 m ASL
Antenna CL 7.0 m AGL
Figure 7: Powerco Tararua Wind Power Path Profile 19 800
Elevation (m)
700
600
500
400
300
200
100
0
2
4
6
8
Mt Butters West Mast
Latitude
40 33 37.29 S
Longitude 176 02 11.84 E
Azimuth
280.88°
Elevation
756 m ASL
Antenna CL 12.0 m AGL
10
12
14
Path length (24.61 km)
16
18
20
22
24
MANGAMAIRE
Latitude
40 31 05.41 S
Longitude 175 45 05.23 E
Azimuth
101.07°
Elevation
156 m ASL
Antenna CL 7.0 m AGL
Frequency (MHz) = 420.0
K = 1.33
%F1 = 100.00
Figure 8: Powerco Mangamaire Path Profile The obstruction calculations are: Radio Path Affected Turbine Number Horizontal Distance from Radio Path
Name Length
(km) Nomina
l Freq (MHz) Distance to Turbine (km) 1st Fresnel Radius
(m) (m) WT44 <10 Tararua Wind Power ‐ Mt Butters 32.4 420 1.5 32 WT46 <10 Mangamaire Mt Butters 24.7 420 2.1 37 Excess Horizontal Clearance
(m) ‐22 obstructed ‐27 obstructed Table 5: Fresnel analysis for worst case fixed links Remediation and mitigation The diffraction effects can be overcome by relocating the affected link antennas at Mt Butters to a new location free of path obstructions. However this solution is complicated by the affected links being part of a PTMP service that share a common antenna and frequency with a number of other links. There are a number of ways to overcome this issue. Option 1: Relocate the common antenna to another location The site for relocation must be northeast along the ridge to ensure that other links aren’t obstructed when the antenna is moved. The optimum location is the Telecom Mid Mast and the improvement in clearance is shown in the following table. 20 Turbine Number Radio Path Affected Horizontal Distance from Radio Path Name Length
(km) (m) Distance Nominal to Freq Turbine (MHz) (km) 1st Fresnel Radius (m) Excess Horizontal Clearance
(m) WT44 40 Tararua Wind Power ‐ Mt Butters 32.4 420 1.5 32 8±6 WT46 50 Mangamaire Mt Butters 24.7 420 2.1 37 13±6 Table 6: Clearance improvement with shift to Mid Mast Option 2: Replace each of the affected links with a dedicated PTP radio link This gives more freedom in selecting an obstruction free location for the antennas. One possible location is further southwest along the ridge and at least 100m from the existing Powerco pole. A new pole/mast (8m above ground) would need be installed. Another possible location is mounting the antennas on a wind turbine that is line‐of‐sight to Mt Butters, Mangamaire, and Tararua Wind Power. Suitable locations are WT44 to WT50. For this option new radio equipment and antennas will be needed for both ends of the affected link. If the antennas are mounted on a wind turbine then an additional link will be required between the turbine and Mt Butters. 8.3.2 Area Coverage Services Land Mobile and Cellular radio services use antennas that receive and transmit over a wide angle, 60 to 360 degrees, as the other end of the link is mobile. Therefore these services are more vulnerable to diffraction since there will be instances, depending on the mobile location, where the radio path will be obstructed by a turbine. Diffraction around each wind turbine will cast a narrow signal “shadow” behind it. Simple theoretical calculations indicate that the average signal loss behind a wind turbine 1400 m from a transmitter site is 2 dB and 4 dB for VHF/UHF communications services and 800/900MHz for cellular services, respectively[8]. These levels do not change significantly for various distances behind the wind turbine. At ±1° to ±2° to the side of each wind turbine the signal loss drops to between 0 and 1dB. Of concern is the effect this has on the primary coverage area for Land Mobile and cellular services. Landmobile Mt Butters For Land Mobile, the primary coverage area includes those contiguous areas where the receive signal is greater than ‐95dBm. Any “shadow” loss behind a turbine that reduces the receive signal below ‐95dBm represents a loss of coverage area. The areas where this could occur if 21 a turbine is blocking the path are shown as ‘orange’ in the coverage maps i.e. MRP‐PKT‐6705 and MRP‐PKT‐6706. Cellular Mt Butters XT Cellular coverage is shown in drawing MRP‐PKT‐6707. There will be some minor “shadow loss” in an arc behind proposed turbines west of the site (azimuth 234 to 312 degrees). For mobile locations (vehicle) the reduction will be imperceptible because the vehicle will in general transit through the shadow area quickly. For fixed locations e.g. home and office, the reduction in coverage will also be imperceptible when compared with the normal spatial variability (even within the primary area) as a consequence of multipath. Multipath is the reason why it is necessary to move a short distance from an initial location to restore communications. Remediation and mitigation As the diffraction effects are imperceptible or insignificant no remediation or mitigation is required. 8.3.3 Cranes blocking radio paths during construction There is a possibility during construction that cranes will obstruct radio paths. Given the location of the radio sites and the proposed wind turbines this only needs to be considered for turbine locations south and west of Mt Butters. The worst case obstruction loss occurs when the crane boom lies across the whole 1st Fresnel Zone. The blocking percentage versus frequency is given in Table 7: Frequency Band Worst case Fresnel Zone Radius % of blocking Diffraction Loss <500MHz 81 2% imperceptible 900MHz 34 4% imperceptible 1500MHz 17 7% imperceptible 5 to 7GHz 8 16% <1dB Table 7: Fresnel Blocking by Crane Table 7 shows that the diffraction loss is imperceptible or insignificant for all links at the Mt Butters site that could be potentially affected. Remediation and mitigation No remediation or mitigation is required. 8.4 Reflection 8.4.1 Area Coverage: Land Mobile Mt Butters There are a number of Land Mobile services using Mt Butters. Drawing MRP‐PKT‐6709 shows that the minimum permissible C/N of 26dB is 22 exceeded for all locations including roads except for part of Towai Road between Coonoor and PR14 and in the immediate area surrounding the wind farm (<900m away). Therefore general public use of this service outside the wind farm will be unaffected. For any locations along Towai Rd reception will only be affected for a short time as the vehicle passes through an affected area. Remediation and mitigation Although general public use will be unaffected when the wind farm becomes operational; radio reception will need to be considered within the wind farm when providing emergency communications for maintenance and operational staff. Reception will unreliable in some locations and hence an alternative non ‘wireless’ form of communication will be needed for example a telephone system using fibre optic cables. 8.4.2 Area Coverage: Cellular Mt Butters The minimum permissible C/I is 13dB for 3G Cellular. As shown in drawing MRP‐PKT‐6709, this is exceeded for all locations including roads except in the immediate vicinity of the wind turbines (<100m away). Remediation and mitigation See comments above regarding emergency communication. 8.4.3 Area Coverage: TV The TV coverage for households in the area surrounding the Puketoi project site is provided by transmitters located at Wharite on the Ruahine Ranges. At present both Analogue and Digital TV coverage is available but after September 2013 only Digital TV (DVB_T) will be available. Therefore in the analysis only the impact on Digital TV reception is considered. The predicted coverage from Wharite for Digital TV[4] is shown in drawings MRP‐PKT‐6712/13. It shows that there is no coverage east of the Puketoi Range and hence only households west of the range need to be considered. There are 58 households within 3km of the Wind Turbines. Of these 58 houses only three are considered in this report (Home 38, 104, and 105) as the other houses currently have no coverage. The three locations have obstructed paths to Wharite and are therefore more vulnerable to scatter. The Interference Contour plot for this service (see drawing MRP‐PKT‐
6714) shows the C/I is 35dB or greater for these houses. However, the scatter analysis assumes no differential obstruction loss between the scattered and direct paths and no antenna discrimination. Both of these factors need to be considered for these locations. Obstruction loss will reduce the C/I by 23dB (average obstruction loss), however since a high gain Yagi receive antenna will be needed to 23 receive Digital TV then antenna discrimination will increase the C/I by 18dB. Therefore the overall C/I is 30dB, which exceeds the minimum permissible limit of 28dB. Hence the scatter will have an imperceptible effect on Digital TV reception. Remediation and mitigation No remediation or mitigation is required for Digital TV reception however the impact on Analogue TV reception may have to be considered should the wind farm be operational before the Digital TV changeover occurs. If this is the case and Analogue TV reception is affected then this report recommends installing a DVB_T decoder and UHF antenna at the affected households. 8.4.4 Area Coverage: FM Radio Scatter from the turbines can cause audible distortion to reception in close proximity to a wind farm. Reception of stereophonic programmes is more susceptible than monaural programmes. [3] The FM transmitters for this area are based at Wharite and the indicative coverage and scatter analysis is shown in drawing MRP‐PKT 6715. There is no reliable FM radio reception east of the Puketoi Range and hence like the TV, only those households and portable radios west of Puketoi Range have the potential to be affected. For households in the “likely with high antenna” coverage areas (7 out of 58), the antenna will give sufficient angular discrimination from the turbine scatter signal and reception is unlikely to be affected for the reason given above for Digital TV because the predicted C/I exceeds the minimum permissible C/I (27dB) required for FM Radio. For most of the roads in the area coverage is either unavailable or “uncertain” except for those that cross the Puketoi range. For hand portable radios the only reliable coverage is on the western slopes and main ridge of the Puketoi range where the turbines are located. Mobile/portable applications have to use an omnidirectional antenna which provides no discrimination to the scatter. Therefore in general those areas with good reception will be adversely affected by scatter if less than 1km from a turbine. Remediation and mitigation No remediation or mitigation is required for households in the area because the effect of scatter interference is imperceptible. For mobile/portable radios it is not possible to mitigate against the scatter interference nor is remediation practical because the area surrounding the wind farm, in general, has marginal coverage. The radio user will either have to move further away from a turbine or tune to another radio station with a ‘stronger’ signal. 8.4.5 Fixed Links (PTP and PTMP): Mt Butters and PR14 See drawing MRP‐PKT‐6708/6710. 24 All the ends of these links are outside the 25dB Interference Contour and hence no degradation of these links is expected. There are no Fixed Radio services crossing the path of the turbines so there will be no ‘Frequency Reuse’ problems. Remediation and mitigation Remediation and mitigation is not required because the effect of scatter interference is imperceptible. 8.4.6 Fixed Links (PTP and PTMP): Rising Sun Puketoi Range At Rising Sun Puketoi Range the VHF Land Mobile frequency is being used for a PTMP Telemetry service and hence only fixed locations (i.e. water measuring sites/outstations) are involved instead of the more usual mobile locations. There is also a UHF PTP link from Rising Sun to Mt Ruahine that provides linking back to the telemetry controller in Palmerston North. Turbine WT1 is in close proximity to the Rising Sun Puketoi Range and is likely to cause scatter problems. Drawing MRP‐PKT‐6711 shows the scatter C/I for the Telemetry sites is greater than 10dB but less than 12dB because there are no 12dB contours enclosing the Telemetry sites. Therefore reception will be severely affected when considered against the minimum permissible C/I for this service, 26dB. Remediation and mitigation The most practical way to reduce the interference is to relocate the radio repeater site to another location a greater distance from the turbines e.g. Telecom site at PR14. At this location linking is maintained to the radio sites currently using Rising Sun Puketoi Range. Drawing MRP‐PKT‐6710 shows for PR14 that the C/I outside the windfarm is at least 25dB; similar to the results for scatter from Mt Butters. 25 9
Section Six – Consent Conditions & Monitoring Subject to resource consents being granted, general consent conditions, consistent with the following, are considered appropriate in this case; 1.
2.
3.
Subject to relevant land owner approvals being secured, the consent holder shall relocate the Rising Sun Puketoi Range radio site to mitigate potential degradation of Land Mobile services signal by scatter effects. Subject to relevant land owner approvals being secured, the consent holder shall replace the existing two Powerco links located on Mt Butters with PTP links and locate the antennas so the links are unobstructed by turbines. The consent holder shall ensure that reliable emergency communication is available at all turbine sites during construction. 26 10
Section Seven – Summary of Effects The radio services most likely to suffer interference effects are listed in Table 10 below. The potential interference scenarios and impacts on radio services have been identified using conservative models and assumptions. Type of Service Cause FM Radio Turbines scatter the signal. Effect before Mitigation/Remediation Mitigation Effect after Mitigation/Remediation Fixed Locations Fixed Locations Fixed Locations No perceptible interference for households with FM reception Not required. No perceptible Interference Mobile Locations Mobile Locations Mobile Locations Possible sporadic distortion of sound within 900m of wind turbine. Relocate portable/vehicular receiver. Problem may still persist. May also occur in isolated instances further away if the wanted signal is obstructed. Retune to another radio station Television Turbines scatter the signal. (Digital) No perceptible interference for households with Digital TV reception Not required No perceptible Interference VHF & Turbines scatter UHF Land the signal. Mobile Mt Butters Mt Butters Mt Butters Possible sporadic distortion of sound within 900m of wind farm. Relocate mobile terminal to another location 10 to 30m away from bad location Degradation of reception may still persist depending on flexibility in moving to another location within wind farm. Turbines obstruct the radio path Mt Butters Mt Butters Mt Butters Insignificant reduction in coverage area Not required. Insignificant reduction in coverage area 27 Type of Service UHF Cellular Mobile Cause Turbines scatter the signal. Turbines obstruct the radio path Effect before Mitigation/Remediation Mitigation Effect after Mitigation/Remediation Mt Butters
Mt Butters
Mt Butters
Possible sporadic breaking up of sound within 100m of wind turbine Relocate location of mobile terminal. Interference may be perceptible and annoying within Wind farm depending on flexibility in moving to other location. Minor reduction of coverage area at the edges. Mobile Mobile Vehicles will transit quickly through the affected area. Loss of coverage likely to be imperceptible as multipath will tend to mask any noticeable loss of coverage. Fixed Fixed Relocate to another location within office/ home. Loss of coverage likely to be perceptible but not annoying. Mt Butters Mt Butters Mt Butters Severe obstruction of Powerco radio links to Tararua Wind Power and Mangamaire Relocate UHF PTMP antenna from West Mast to Mid Mast or install dedicated radio radio equipment for affected links and install new antenna on new mast southwest of present one. No perceptible obstruction PR14 and Rising Sun PR14 and Rising Sun PR14 and Rising Sun Fixed Linking: PTP and PTMP Turbines obstruct the path of the signal. No perceptible obstruction Turbines scatter the signal. Mt Butters and PR14 No perceptible interference. Not required Mt Butters and PR14 No perceptible obstruction Mt Butters and PR14 Not required No perceptible interference. Rising Sun Rising Sun Rising Sun Moderate to Severe degradation of communication within the service area of the radio site. Relocate radio site to another location further away from turbines No perceptible Interference 28 Type of Service All radio services All radio services Cause Crane during construction causes obstruction of radio signal Effect before Mitigation/Remediation Frequencies ≤1.5GHz No perceptible obstruction Frequencies >1.5GHz Minor obstruction loss (<1dB). Mitigation Frequencies ≤1.5GHz Not required Frequencies >1.5GHz not required Effect after Mitigation/Remediation Frequencies ≤1.5GHz No perceptible obstruction Frequencies >1.5GHz Minor obstruction loss.(<1dB) Electromagnetic Interference from electrical and electronic components within Wind Turbine Interference to services below 1GHz when within 180m of a Wind Turbine. The effect of EMI interference masked by Scatter Interference within the wind farm and hence no specific remediation or mitigation is required No perceptible interference. Modification of antenna radiation pattern by physical proximity of wind turbine. No perceptible modification Not required No perceptible modification Table 8: Summary of impacts of the wind farm on radio services 29 11
Appendices 11.1 Appendix A Reference List [1] Electromagnetic compatibility (EMC) – Generic emission standard, Part 2: Industrial Environments, Standards Australia/Standards New Zealand, AS/NZS 4251.2:1999, (IEC 611000‐6‐4:1997). [2] Propagation data and prediction methods required for the design of terrestrial line‐of‐sight systems, Recommendation ITU‐R P.530‐
12, Study Group 3 Propagation in Non‐ionised Media, International Telecommunications Union, Geneva, 2007. [3] White Paper on Multi‐path Distortion in FM Radio, B Whiteside, Kordia, October 2001. [4] http://freeviewnz.tv: Digital TV coverage map from Wharite. [5] http://www.telecom.co.nz/mobile/ournetwork/coverage: XT Mobile coverage map. [6] "Fixed‐link wind‐turbine exclusion zone method" Author: D F Bacon Status: released 28 Oct '02 Version: 1.1 [7] ITU‐R Report ITU‐R BT.2142‐1. The effect of the scattering of digital television signals from a wind turbine. [8] Investigation of the impact of wind turbines on the MSSR installations at Dooncarton, Mt Gabriel and Woodcock Hill, Ireland. Final report Sept 04,Sustainable Energy Ireland. 30 11.2 Appendix B Drawings MRP‐PKT‐6701 Puketoi Wind Farm Site Layout MRP‐PKT‐6702 Radio Links Traversing Wind Farm MRP‐PKT‐6703 Radio Link Detail Mt Butters MRP‐PKT‐6704 Radio Link Detail PR14 and Rising Sun MRP‐PKT‐6705 VHF Landmobile Coverage: Mt Butters MRP‐PKT‐6706 UHF Landmobile Coverage: Mt Butters MRP‐PKT‐6707 XT Cellular Coverage MRP‐PKT‐6708 Scatter Analysis Mt Butters MRP‐PKT‐6709 Scatter Analysis Mt Butters: Wideband coverage analysis MRP‐PKT‐6710 Scatter Analysis PR14 MRP‐PKT‐6711 Scatter Analysis Rising Sun MRP‐PKT‐6712 Digital TV Coverage from Wharite: Overview MRP‐PKT‐6713 Digital TV Coverage from Wharite: Detail MRP‐PKT‐6714 Digital TV Scatter MRP‐PKT‐6715 FM Indicative Coverage and Scatter MRP‐PKT‐6716 Abridged RSM Licence Data for Radio Sites 31 32