OTAHUHU-MANGERE-ROSKILL- HEPBURN ROAD 110 KV CIRCUITS

Transcription

1 NORTH AUCKLAND AND NORTHLAND GRID UPGRADE PROJECT ATTACHMENT J OTAHUHU-MANGERE-ROSKILL- HEPBURN ROAD 110 KV CIRCUITS UPGRADE WITH HIGH TEMPERATURE LOW SAG CONDUCTOR September 2007

2 Contents 1 INTRODUCTION 3 2 METHODOLOGY 4 3 CONDUCTOR BEHAVIOUR Existing Zebra ACSR Existing Wolf ACSR Current Flow Magnetic Field 7 4 VISUAL IMPACT 8 5 FEASIBILITY 8 6 COSTING 9 7 SUMMARY 10 8 CONCLUSIONS 10 September 2007 Transpower 2007 Page 2 of 10

3 1 Introduction The purpose of this document is to summarise the analysis undertaken at a very high level, with respect to re-conductoring the following circuits with High Temperature Low Sag (HTLS) conductors. MNG-OTA 1 & 2 (3.7km) (MNG-OTA A) MNG-ROS 1 & 2 (11.7km) (MNG-ROS A) OTA-ROS 1 & 2 (19.7km) (OTA-PEN B, PEN-ROS A) HEP-ROS 1 & 2 (7.5 & 7.1km) (HEN-ROS A, HEP-ROS A) HEP-HEN 1, 2,3,& 4 (6.7km) (HEN-ROS A, HEN-HEP A) The Northland and North Auckland loads are presently supplied by a two-circuit 220kV line between Otahuhu and Henderson (HEN-OTA A). The (N-1) capacity of these circuits is forecast to be exceeded around Transpower are looking at alternative options for providing a secure supply to these areas beyond The option of having a cross-harbour cable route between Penrose and Albany is presently being investigated. However, alternatives are required to be investigated as part of a complete assessment of the options. This document investigates at a very high level the re-conductoring of the existing 110kV lines between Otahuhu and Henderson as alternative to the cross harbour cables. It is a companion to the similar investigation for the HEN-OTA 220kV line undertaken in August 2007 (see Attachment I). The scope of this study is to investigate the feasibility of using HTLS conductors to achieve maximum possible line ratings without any modification to the existing structures, and whilst maintaining the visual appearance of the lines with respect to sag and conductor diameter, or without increasing conductor sags beyond those presently in place. The existing conductor types are as follows Line Conductor MNG-OTA 1 & 2 Duplex 75 C MNG-ROS 1 & 2 Simplex 75 C OTA-ROS 1 & 2 Simplex 75 C HEP-ROS 1 & 2 Simplex 75 C HEP-HEN 1, 2,3,& 4 Simplex 75 C Table 1-1. Existing 110kV Conductors Costs have been estimated, to an accuracy of +/-50%. This includes costs related to materials and construction and does not include for property costs or consenting costs. September 2007 Transpower 2007 Page 3 of 10

4 2 Methodology Identify one of each of the following High Temperature Low Sag (HTLS) conductor types for investigation. ACSS - Aluminium Conductor Steel Supported ZTACIR - Zirconium Alloy Thermally Resistant Invar Reinforced TACSR/ACS - Thermally Resistant ACSR ACCR - Aluminium Conductor Composite Reinforced ACCC/TW - Aluminium Conductor Composite Core Ensure the chosen conductors satisfy the following general requirements: Overall diameter similar to the existing conductor Conductor maximum horizontal tension not to exceed existing conductor tension (to reduce impact on structures and foundations) Conductor Sag at the maximum operating temperature to be limited to that of the existing conductor Investigate the conductors in PLS-CADD using a representative span. Establish the maximum operating temperature that gives the same or less sag than the existing conductors. Investigate the feasibility of using the chosen conductors on the 5 Lines with particular reference to the following aspects, compared to the existing ACSR conductor: EMF levels Conductor swing Maximum continuous operating temperature without loss of strength and the corresponding MVA rating Estimate the total cost for design, material supply (including conductor, insulators, hardware, connectors etc) and installation, for each conductor option. Note, while similar sized conductors to existing have been analysed, in order to exclude a need to strengthen towers or foundations, it must be considered that some structures may be overloaded in their as-built condition. Detailed analysis may identify a need to strengthen at the time of re-conductoring. No allowance has been made for this. The following conductors were selected for investigation: Type Name Stranding Diameter (mm) Mass (N/m) UTS (kn) Max operating Temperature ( C) ACSR/GZ Zebra 54/ ACSS (54/7) Condor 54/ ZTACIR Drake 26/ Zebra TACSR/ACS (Lumpi) 54/ ACCR 795-T16 26/ ACCC/TW Drake 22/1? September 2007 Transpower 2007 Page 4 of 10

5 ACSR/GZ Wolf 30/ ACSS (54/7) Oriole 30/ ZTACIR Invar160 30/ TACSR/ACS Wolf (Lumpi) 30/ ACCR 336-T16 26/ ACCC/TW Linnet 22/1? Table 2-1. Standard and High Temperature Conductors used in Investigation 3 Conductor Behaviour 3.1 Existing Zebra ACSR Based on the average MNG-OTA A span length of 256m the sag and blowout of the various conductors has been calculated for this line. The crept tension has been matched to the existing tension in the Zebra ACSR/GZ to ensure that the towers will not be overloaded. It can be seen that in all cases the sag and blowout of the chosen conductors is similar or less than that of the existing Zebra. Type Name Stringing Tension (%UTS) Operating Temperature ( C) Max Op. Temp (m) Difference to Existing (m) Blowout from centreline 35 C) Difference to Existing (m) ACSR/GZ Zebra 21% ACSS Condor 37% ZTACIR Drake 20% TACSR/ACS Zebra (Lumpi) 21% ACCR 795-T16 20% ACCC/TW Drake 15% Table 3-1. Physical Parameters for Selected High Temperature Conductors (Zebra Replacements) The initial tensions have been checked against table 6.3 "Overhead conductor safe design tension with respect to aeolian vibrations" Cigre Task Force B , June 2005 to ensure there will be no issues with Aeolian Vibration when the conductor is first installed. 3.2 Existing Wolf ACSR The remaining lines are presently strung with simplex Wolf ACSR ranging in tension from 12.3kN to 15.0kN at 10 C, and average span lengths ranging from 207m to 277m. September 2007 Transpower 2007 Page 5 of 10

6 Based on the average MNG-ROS span length of 277m, and a conductor tension of 15kN (based on ALS survey data) the sag and blowout of the various conductors has been calculated. The crept stringing tension has been matched to the existing tension in the Wolf ACSR/GZ to ensure that the towers will not be overloaded. Type Name Stringing Tension (%UTS) Operating Temperature ( C) Max Op. Temp (m) Difference to Existing (m) Blowout from centreline 35 C) Difference to Existing (m) ACSR/GZ Wolf 22% ACSS Oriole 23% ZTACIR Invar160 24% TACSR/ACS Wolf (Lumpi) 22% ACCR 336-T16 24% ACCC/TW Linnet 21% Table 3-2. Physical Parameters for Selected High Temperature Conductors (Wolf Replacements) The Initial tensions have been checked against table 6.3 "Overhead conductor safe design tension with respect to aeolian vibrations" Cigre Task Force B , June 2005 to ensure there will be no issues with Aeolian Vibration when the conductor is first installed 3.3 Current Flow The possible current flow achievable with the use of high temperature conductors is given below. These are LATTA summer ratings (30 C ambient, 0.6m/s wind) Type Name Operating Temperature ( C) Latta Current Summer Rating (Amps) Latta Power Summer Rating (MVA) ACSR/GZ Zebra ACSS Condor ZTACIR Drake TACSR/ACS Zebra (Lumpi) ACCR 795-T ACCC/TW Drake Rank Type Name Operating Temperature ( C) Latta Current Summer Rating (Amps) Latta Power Summer Rating (MVA) ACSR/GZ Wolf ACSS Oriole ZTACIR Invar TACSR/ACS Wolf (Lumpi) ACCR 336-T ACCC/TW Linnet Rank Table 3-1. Current Ratings of Selected High Temperature Conductors September 2007 Transpower 2007 Page 6 of 10

7 3.4 Magnetic Field The increase in current made possible by the use of high temperature conductors will increase the magnetic field generated by the lines. As there is no change in voltage, there is no change in the electric fields. There are four main tower contract types used on the 5 lines C26, C5532, C460 and C252. The duplex Zebra Line (MNG-OTA A) has C460 towers. The other 3 contract types have been investigated with respect to the Wolf, and it has been found the contract type with the highest magnetic fields is C252 (HEP-ROS and HEP-HEN) due to greater phase spacing The plots below show magnetic field levels at various ratings for the Zebra and the worst case Wolf structures (C252). All are within the ICNIRP levels. These plots are highly conservative as they are based on the mid span sag point and an assumed 100% current in each circuit. In reality the system would be operated at maximum of approximately 50% of capacity and could rise up to 100% only when one circuit is out of service MNG-OTA A reconductoring - Both circuits in service Magnetic Field Profile under 6.5 m clearance Duplex Drake 569 MVA 80 Magnetic Field (µt) PRELIMINARY DRAFT! FOR DISCUSSION ONLY! Please discuss with Pre- Approval engineering before making any conclusions relating to this information. Duplex Condor 490 MVA Existing Duplex 358 MVA Distance from Centre (m) MF - Existing 75 deg C MF A MF A 100µT limit Figure 1 Magnetic Field Profile Comparison of High Temperature and Standard Conductors Zebra Tower Structures September 2007 Transpower 2007 Page 7 of 10

8 Auckland 110 kv HTLS reconductoring C252 - Both circuits in service Magnetic Field Profile under 6.5 m clearance Magnetic Field (µt) PRELIMINARY DRAFT! FOR DISCUSSION ONLY! Please discuss with Pre- Approval engineering before making any conclusions relating to this information Linnet 210 MVA Oriole 185 MVA Invar MVA Existing Simplex 92 MVA Distance from Centre (m) MF - Existing 75 deg C MF - 726A MF - 970A MF- 1103A 100µT limit Figure 2 Magnetic Field Profile Comparison of High Temperature and Standard Conductors Wolf Tower Structures 4 Visual Impact In order to ensure that there is very little change in the visual impact of the line, the conductors assessed have similar diameters to the existing ACSR and the lines have been sagged to match the sag and swing as closely as possible to the existing conductors. 5 Feasibility The stringing of conductors over heavily built up areas and a large number of roads will incur significant hurdling costs and other construction difficulties. In order to maintain safe stringing practices, it may be required that both circuits on the line being restrung are out of service during stringing. If however it is a requirement for one circuit to be continually in service, then a detailed study will be required, including input from the FSO and local maintenance contractors, to determine suitable stringing practices. This is expected to result in additional costs to the stringing works, in the form of special construction practices, as well as increased risk. Sign-off from higher management is likely to be required with respect to the increased risk profile associated with stringing within close proximity of live conductors. September 2007 Transpower 2007 Page 8 of 10

9 The analysis outlined in this document takes into consideration the HTLS technology currently available in use throughout the world. It is in no way to be taken as an endorsement of this technology by PAE (lines), nor a recommendation for its use. Indeed, significant research, testing and study of related aspects (such as constructability techniques, reliability, maintenance, availability of parts etc.) would need to be carried out prior to addition of an HTLS conductor to the Transpower suite of conductors. This in itself may make the use of HTLS conductors in this situation unfeasible, depending on the timeframes involved. 6 Costing For the purposes of this investigation only those conductors of similar size to the existing conductors have been assessed. They have been strung at similar tensions to the existing conductors. As such, the transverse and longitudinal loading is expected to be similar, and it has been assumed no tower or foundation strengthening or replacement would be required. Type Name Total Cost ($M) Rank ACSS Condor ZTACIR Drake TACSR/ACS Zebra (Lumpi) ACCR 795-T ACCC/TW Drake Table 6-1 Costs of High Temperature Conductors for MNG-OTA 1 & 2 Circuits Type Name Total Cost ($M) Rank ACSS Oriole 24 2 ZTACIR Invar TACSR/ACS Wolf (Lumpi) 24 1 ACCR 3m336-T ACCC/TW Linnet 32 4 Table 6-2 Costs of High Temperature Conductors for MNG-ROS 1 & 2,OTA-ROS 1 & 2, HEP-ROS 1 & 2 and HEP-HEN 1,2,3 & 4 Circuits Costs have been estimated, to an accuracy of +/-50%. It must be noted there is significant uncertainty about the cost of stringing, and about the cost of some of the more experimental conductors (ACCR & ACCC). The tabulated values above include costs related to materials and construction. Note that these estimates do not allow for non engineering impacts such as E & P, outages, interest etc, nor are those associated with progressing this technology to a stage where it is accepted as a standard conductor in the Transpower suite. September 2007 Transpower 2007 Page 9 of 10

10 7 Summary Within the constraints of keeping the clearances and tensions similar to the existing line, the advantage of thermally resistant ACSR cannot be utilised. Therefore using TACSR/ACS type conductors offers no advantages over the existing conductor. The ACCC and ACCR composite type of conductors are new on the market, and while they may offer advantages with respect to line rating there have only been a few short line trials worldwide, and the costs are well in excess of the alternatives. ZTACIR type conductors are used in Japan and Korea, and ACSS conductors are becoming more common in the USA. The costs of these types of conductors is less than that of the composite types, and they are considered potentially feasible options. However, significant work would still be required before they could be accepted as standard Transpower conductors. 8 Conclusions This is a very high level investigation and further works will be required before progressing further down this path. The use of HTLS conductor on the Auckland 110kV lines is yet to be determined as feasible from an engineering perspective. All the chosen conductors can be strung with the same or lower sag and blowout, but with higher current flow. The similar diameters ensure the visual impact is minimal. The major difference to the existing line is that the much higher currents result in an increase in the magnetic fields, although a preliminary assessment indicates that all options remain below the ICNIRP limit. The ACCC and the ACCR type conductors are not sufficiently proven at this stage to be considered a reliable option for a core grid lines, and are also the 2 most expensive options. The TACSR does not offer any benefits in this case. It is thought that only ZTACIR and ACSS are suitable for use on the lines investigated. The ZTACIR conductor is approximately 3 times more expensive than the ACSS, although total engineering costs are expected to be within 50%. Of the two, the ACSS conductor has the highest current rating. The overall construction cost is significantly different between the options, ranging in price from approximately $28M for the ACSS to $45M for the ACCR (+/- 50%), excluding E & P, outages, interest etc. The lines are all double circuit lines and could be strung one circuit at a time, with double circuit outages likely to be required. The outage times are difficult to estimate, and would be dependent on the length of the line, which varies from 3.7km to 19.7km, and specific terrain characteristics such as road crossings etc. September 2007 Transpower 2007 Page 10 of 10