B CURRENT CABLE PRACTICES IN POWER UTILITIES A report on the recent AORC-CIGRE Panel Regional Workshop in Malaysia

Transcription

1 21, rue d'artois, F Paris B1-101 Session 2004 CIGRÉ CURRENT CABLE PRACTICES IN POWER UTILITIES A report on the recent AORC-CIGRE Panel Regional Workshop in Malaysia AORC Panel BI members. Australia, Hong Kong (SAR China), India, Indonesia, Japan, Korea, Malaysia, New Zealand, Singapore, and Thailand. Ken Barber* Convenor AORC panel B1 1. INTRODUCTION To further CIGRE representation in the Asian Oceania region a workshop was conducted early in 2003 under the sponsorship of the Malaysia National Committee of CIGRE. There was representation from cable experts from 10 countries in the region. The purpose of this paper is to provide a report on the issues raised at that workshop with the objective of sharing the experiences of this region with the broader international community and at the same time, encouraging greater participation in CIGRE by experts in this region. Keywords: Electric Cable Power Practices Projects 2. DESIGN PRACTICES CABLE - ACCESSORIES SYSTEMS 2.1 XLPE cable design. Most countries agreed that due to maintenance problems with fluid filled cables they were adopting XLPE. They agreed that overall there are very few problems relative to the performance of new XLPE cables but some very significant concerns by a number of countries in regards to the remaining life and performance of early XLPE cables, particularly those which did not have fully sealed metallic sheaths. On the other hand, Japan suggested the trend might be to make EHV cable without a metallic sheath or to accept the Moisture Barrier designs. Japan also proposed the introduction of DC XLPE cable up to and including 500kV. 2.2 Cable Protection. Singapore and Australia rely on hard polymeric jackets to protect from termites rather than use chemicals. There was a divergence of views on the performance of aluminium sheathing, with Singapore and Malaysia claiming good performance and Australia, Hong Kong and Thailand having problems with oil leaking from aluminium sheaths on some direct buried oil filled cables Cross bonding. There was also a divergence of views as to the voltage levels for use of cross bonding. Most countries adopted cross bonding on HV circuits to obtain higher ratings but there was concern about the high maintenance cost and security issues relative to link boxes. In India they avoid use of cross bonding where possible and use the next larger size of cable, and in Malaysia they are putting link boxes above ground to make inspection and maintenance easier. In Japan cross bonding is used extensively with a number of arrestors and the length of bonding lead designed by EMTP calculations. In Korea, it has appeared to be the large circulating current, and studies of the reduction method of it, that have led to the development of equipment for measuring the sheath circulating current. * kbarber@olex.com.au

2 The following table provides a summary of the cable types being used by the member countries for transmission and sub-transmission underground networks. Voltages Country kv Australia 33,66,110, 132,220, 275,330 Malaysia 33,132, kV PILC & XLPE. 132 & 275kV OF & 275kV XLPE. New Zealand 11,22,33,66 110, and 350kV DC India 66,110, 132,220, 400 Japan 66,77,110, 132,154, 220,275, 500 Table I - Summary of Cable and System Designs Circuits in New Specific construction and Operation Circuits protection features All cable types. XLPE for all Metallic sheaths for some 33kV, Good experience except and all cables 66kV and higher. with XLPE, poor 330kV. Termite protection Nylon or Brass with extruded tapes-no chemicals. aluminium sheaths. Gas and OF old circuits. New are all XLPE. Submarine DC link. XLPE insulation used exclusively for all HV cables for more than 20 years. XLPE cables to 500kV. OF now only used in special cases eg. Nuclear P/S. Singapore 66,230,400 Significant experience with XLPE at 66kV & recently 230kv. OF at 230kV and 400kV. Korea 66,154,345 and 180kV DC Hong Kong (SAR China) 132,275, kV OF & XLPE 345kV OF & XLPE 3 core OF Compact designs. Indonesia 20,66,150 OF almost exclusively for past 20 years. Now XLPE for reliability. Thailand 69,115,230 PPLP OF Used for past 20 years 69 & 115kV XLPE used for 30 years. XLPE, but also Oil Filled at 275kV. All XLPE except DC cable. New projects with XLPE. Stress level 9-10kV/mm. XLPE Stress levels 15kv/mm XLPE to 230kV with Oil Filled for 230 and 400kV. All XLPE. Oil-filled only used in special cases. XLPE replacing Oil Filled except for 400kV. XLPE to 150kV. XLPE to 115 kv. PPLP & XLPE for 230kV. Aluminium conductor only for 33kV. Copper for. MD/HDPE over-sheath with Alum/foil Moisture Barrier. Optical Fibres included for DTS monitoring. Aluminium and copper conductors. Extruded lead and corrugated alum sheaths. Fire retardant sheaths becoming more popular. Aluminium or Stainless Steel corrugated sheath for EHV cable. Jackets of PVC, PE, or Nylon in special cases. Significant experience with Corrugated aluminium sheath. Standardised cable sizes for the respective voltage levels of 66, 230 and 400kV circuits. Corrugated aluminium metallic sheath, and jacket of PVC (fire retardant) or PE. Copper conductor. Compact designs for limited space. Lead and Corrugated Stainless Steel sheaths. XLPE cables, copper conductors copper wire screen and Aluminium Moisture Barrier with ribbed PE or PVC jacket. 2

3 3. INSTALLATION AND JOINTING PRACTICES 3.1 Direct Buried. Singapore, Australia, India, New Zealand, Hong Kong and Indonesia still adopt direct buried systems wherever possible, as this is the lowest cost solution. This was the practice in other countries but now they install PVC or HDPE pipes during the night to avoid traffic disruption with open trenches. In Japan direct buried is only used in Sub-Stations or private networks e.g. factories. Depth of burial ranged from 750mm for MV circuits to 1.8m for EHV. In Hong Kong, Singapore and Australia, trench walls are fully lined with timber to a depth of 1.5m. Thermal properties of both native soils and trench backfill is a big issue for all, and in New Zealand and Australia, increasing use is being made of specially selected fluidised backfill to avoid labour costs, save installation time and improve ratings. In Singapore they use cement bound sand backfill (stabilised backfill). Korea is also studying improved backfills. This has not found to be cost effective in some other countries where they use river sand for bedding cables and ducts. 3.2 Trench-less technology. Until recently the lack of rural undergrounding throughout the region has not favoured the development of newer forms of trenchless technology. However, there has been a very significant increase in the use of guided horizontal drilling under roads, rivers, railway lines etc. This is particularly the case in many large cities and India and Hong Kong cited many examples of trenchless techniques. In Hong Kong considerable experience has been developed with horizontal drilling techniques on a number of projects up to 1300m and they suggest that this technique can be used for lengths up to 2000m. A number of HDPE pipes are included and in one case due to the depth and pressure, the HDPE pipe was slightly deformed but this was compensated for before installing the cable by pressurising the pipe. Pipe jacking is also used by Australia, Singapore, Hong Kong, Thailand and Japan, to provide multiple ducts for crossings under expressways. In Thailand they have installed some very large diameter pipes using Pipe jacking principles. 3.3 Joint bays. In Singapore as in Australia and New Zealand, most joint bays are constructed with a concrete floor and reinforced concrete walls but they are later filled. In Malaysia for 275kV oil filled cable circuits, the joint bays are left as large reinforced concrete manholes for easy access. 3.4 Tunnels. There was very great interest by all countries on the use of tunnels. In Japan and Korea, tunnels are chosen to avoid external damage during installation and service, they also offer maximum space efficiency, provide ease of maintenance and it is easier to enable diversion. Long span cable installation of up to 2500m using especially wide drums was applied to reduce the construction time and number of joints. Multipurpose tunnels are also widely used in Japan, and undersea tunnels are used in Singapore. New Zealand has just commissioned a 9.2 km tunnel in Auckland and tunnels are currently being built in Sydney, Australia, for 132 and 330kV cables. In Hong Kong tunnels are used for environmentally sensitive and congested areas, with methods of construction ranging from drill and blast to pipe jacking and use of tunnel boring machines. In Thailand a recently constructed tunnel in Bangkok provides for 115kV and 230kV cables, the latter being both PPLP and XLPE. The 230kV cables are shielded with an aluminium cover and water cooling pipes are positioned adjacent to the cables to improve the rating. 3.5 Accessories. All countries indicated that a wide range of medium voltage accessories are used. For HV and EHV there was a trend to premoulded or prefabricated, except in India and Malaysia where tape joints are still used for up to 66kV and respectively due to lower costs. In Malaysia transmission cables are terminated into GIS because of land scarcity. In Malaysia, the aluminium conductors used for distribution cables are jointed using compression with deep indentation type crimping. In Japan the trend is to use premoulded or prefabricated joints at all voltages to 275kV, with EMJ at 275 and 500kV. They also indicated the trend is to use composite insulators in lieu of porcelain for ratings up to 154kV. 3.6 Construction trends. Traditionally, most new project work up to and including was undertaken by the utility with only projects for higher voltage circuits being let as turn-key contracts. In some countries there has been a significant reduction in the overall cost of providing underground transmission compared with increasing cost of building overhead lines. Hong Kong is working with installation contractors on a partnership approach to provide benefits in shortening project duration, and minimising contractual conflict, thus achieve a win-win solution. 3

4 4. FAULT LOCATION / DIAGNOSIS / CONDITION MONITORING All countries agreed that condition assessment and condition monitoring is a significant issue for both old circuits and new installations. 4.1 HV Testing and PD. There was considerable interest in options for partial discharge testing as new equipment and sensors are becoming available. In Malaysia considerable experience has been developed in the use of VLF (0.1 Hz) field testing on 11 and 33kV circuits with both PILC and XLPE cables. They have more than 42,000 MV circuits and over 35% of these have been tested with VLF. Results are excellent and of those tested, 12.5% were shown to have defects and only 3.7% of all faults since have been on circuits that have previously been VLF tested. They have determined that the voltage level, shape of the wave, and time of application of voltage are all very significant factors in determining the diagnosis of the future cable performance. PD mapping is also being carried out on PILC cables and they are using Ultra-Sound on 11 and 33kV terminations. Malaysia is finding water trees on HV XLPE cables installed in the early 80 s. Japan was one of the few countries to have carried out diagnostics on XLPE cables rated at 66kV and above. They are using less current (3 rd harmonic) or residual charge method for the measurement of water-tree deteriorated cables up to 77kV and PD measurement under test voltage is being used as a pre-commissioning test for EHV transmission lines. Singapore was one of the few countries to have variable frequency HV testing facilities for HV cable. India does not have such test equipment and suggested it was doubtful if such equipment would be valuable in some regions because of the difficultly of transportation of such heavy equipment due to poor road conditions. 4.2 Oil filled cables - Dissolved Gas Analysis (DGA). Several countries including Singapore, Malaysia Japan and Korea were using DGA techniques for determination of remaining life performance on oil filled cables. In Japan this is being done by sampling insulating oil from each joint. They have developed an insulated oil sampling connector so that oil sampling can be taken from a live line quickly and at any time. In Singapore DGA results are placed on a computer database for trend analysis. 4.3 X-Ray detection. In New Zealand they have identified core movement within the joints on oil filled cables as a serious problem and have developed a method whereby joints are X-Rayed to establish if core movement has occurred. Any joints which are shown to be defective, can be replaced before failure occurs. The problems seem to be mainly with cables using aluminium conductors and new joints are provided with greater reinforcement. 4.4 Distributed Temperature Sensing (DTS). In Australia, New Zealand, Singapore, Hong Kong and Japan, optical fibres for DTS are being put on new circuits rated at kV, either with fibres in the cable or in a separate cable attached to one power cable at the time of installation. In New Zealand this is even being done on some 22 and 33kV cables. In Singapore and New Zealand analysis of DTS data is providing interesting information on the presence of Hot Spots on a cable route and there was much discussion on how to confirm location and what action to take to reduce the effect. There was also much discussion on what to do with existing circuits. It was agreed that this can only be done at specific point locations typically using thermocouples and Singapore has some significant experience with this technique. In Japan they have developed a technique for installing an optical fibre rod which is stiff enough to be pushed into cable ducts where existing cable is installed. 4.5 Failure statistics. Of particular interest was the cable failure/fault statistics provided by Japan. (Failure statistics of 22kV and above XLPE cables installed in Japanese utilities) Cables installed Cable failure /100 km/year Accessories/100/year 1966 to to In Japan they are using GPS satellite for fault location. In Indonesia, Thailand, Australia, New Zealand and Hong Kong, there are considerable problems with oil leakage on old oil filled cable circuits. The main problem appeared to be corrosion of the aluminium sheath. Thailand provided some very good examples of the problem and repair procedures. Thailand also showed examples of failure on XLPE cables due to insulation contamination. 4

5 Indonesia also maintains very accurate data on fault statistics; recording details of the number of failures for each make of MV joint and termination. All aspects of the network are analysed; performance standards are set for the system and related to the customer s load and revenue. A Service Quality Level has been set in Indonesia and became law in January PROJECTS RECENTLY COMPLETED OR UNDER CONSTRUCTION Table II - Summary of Projects completed or under construction Country Voltage Project Name Australia 120kV DC 110kV 330kV Transgrid Sydney 27 km Single circuit PPL Malaysia New Zealand India Japan Singapore Korea Hong Kong Thailand 275kV 275kV 110kV 22, 33 & 110kV 66kV 66, 33 & 220kV 66kV 500kV XLPE 500kV DC OF 275kV XLPE 275kV XLPE 400kV PPLP OF 400kV PPLP OF 400kV PPLP OF 230kV OF 230kV OF 230kV XLPE 230kV XLPE 230KV OF 230kV OF 345kV XLPE 345kV OF 154kV XLPE 154kV OF 132 & 11kV 275kV 400kV 400kV 230kV XLPE 230kV PPLP 230kV PPLP 69kV XLPE Murray Link -180km link XLPE 200 MVA V.S. Converter CBD Reinforcement EnergyAustralia XLPE with O.F. Brisbane City upgrades Energex XLPE/LAS XLPE Cable, Panglima Malacca OF Cable Pantai Brickfields, Kuala Lumpur XLPE MB design - various circuits K.L. & Penang XLPE Roskill - Liverpool Auckland city Direct buried XLPE cable CBD Reinforcement Project Tunnel XPLE with 1600mm2 cond. Christchurch Delhi Metro Delhi Transco NTPC Rihand Tokyo Electric. Worlds first 40 km Kansai Electric & EDPC 3000mm² - Submarine Chubu Electric - Long Span 2500m Kansai Electric - prefabricated joints Lab. To AR Tuas to AR Tuas to Lab. Seraya to Jurong Island Paya Lebar to Tampines Wafer Paya Lebar to Kampong Jaya Jurong Pier to Jurong Island SNK to Tamp SNK to TW Youngseo S/S~Yeongdeungpo S/S Seoincheon S/S~Sinbupyung S/S Seoincheon S/S and Kyungseo S/S~Youngjong Island Mansu S/S~Juan T/L Kwai Chung Tunnel Chi Ma Wan Tunnel Sham Tseng Crossing Lamma Power Station to Wanchai Substation 14 km of 1000MVA 400kV circuit from TWE to TKE 4 km of 700MVA 400kV circuit from TWE to YME South Thonburi-Tanontok South Thonburi-Tanontok Vibhavadi Vibhavadi 5

6 6. FUTURE PROJECTS IN THE REGION Table III - Summary of future projects in the region Country Voltage Project Name Project Description Australia 460kV DC 110kV Basslink EnergyAustralia Energex DC Cable link from Victoria to Tasmania CBD Tunnel Various projects/upgrades Malaysia 275kV Salak South Sentul K.L. City Transmission Raya Reinforcement Sentul Raya TNB Dist. HQ, K.L. Upgrading of Transmission Cable K.L. City upgrading capacity New Zealand India Japan Singapore Korea Hong Kong 220kV 220kV 220kV 220kV 110kV 220kV 275kV XLPE 275kV XLPE 220kV XLPE 220kV XLPE 66kV XLPE 400kV 400kV 230kV 230kV 66kV 54kV XLPE 154kV XLPE 154kV XLPE 154kV OF XLPE XLPE XLPE submarine cables Manapouri Powerlinks Delhi Transco AP Transco TNEB Shinko-nadahama Kawasaki-takanawa Hiroshima-chuo Kurume Kyusyu Electric- Matsushima-Narao Sinseongnam S/S~Jungwon S/S Siheung S/S~Doksan Song Do New Town~Dongchum S/S Kwang Myung S/S~Oryu T/L Oil-filled cable replacement projects New circuits to reinforce and for new developments Cheung Chau infeed Thailand 115kV Rachadapisak- Paholyothin Replace O.F. cables Hydro P.S. Link from Penrose to Albany 122 km Kansai Electric no metallic sheath Tokyo Electric 2500mm² Y-branch (XLPE-OF-OF) Chugoku Electric 2500mm² Kyusyu Electric 2500mm² 54 km Optical Fibre Composite- Submarine Lab to Seraya PL to AR & Lab Jurong Island Northern region Biopolis 2 circuits, 13 km 2 circuits, 3 km 2 circuits, 5 km 2 circuits, 3 km A number of circuits of various circuit lengths A number of circuits of various lengths 3 x 2.7 km of XLPE 3 core submarine cable circuits 2 Circuits 6 km 6

7 7. MAJOR ISSUES FACING THE TEN COUNTRIES IN THE REGION. 7.1 Diagnostic and condition monitoring of XLPE cables. The insulation deterioration of XLPE cables and accessories due to ageing is of great concern throughout the Asia Pacific region. However, it remains questionable if on-site PD diagnostic methods can be used to detect and monitor defects. PD monitoring at working voltage may be suitable to detect defects in PILC cables, but this may be of questionable value for XLPE cables. Testing and measuring PD with a HV test source may give a better result, but practical experience is presently limited in this field. This is a matter of ongoing interest for both MV and HV cables. 7.2 Field testing of cables. Although on-site commissioning testing with a HV AC resonant test set method is recommended, this is expensive and the apparatus set-up is unwieldy and difficult to transport on poor roads. Delegates at the workshop questioned if 0.1 Hz testing was a possibility. Some countries such as Malaysia have extensive experience with testing at 0.1 Hz on 11kV and 33kV cables, where the frequency and test voltage levels are important criteria. This equipment had not been considered by CIGRE Panel B1 but was of great interest to delegates, particularly for MV cable testing. 7.3 EMF. Workshop delegates agreed that heightened public awareness and concerns need to be addressed. Circuit design with lower levels of EMF for prudent avoidance are being adopted across the Asia Pacific region. Options considered are trefoil configuration, metallic shielding, and shielding cable (opposing current flow). Delegates were keen to access more information about the merits of various systems, for example, the comparative shielding abilities of materials such as aluminium and steel and their practical application. 7.4 Asset rating. The provision of fibres and the use of DTS are recommended for new cable installations. With this method, potential hot spots can be investigated and appropriate action taken. However, it is agreed that is often not feasible to install DTS systems to monitor and assess the rating vis-à-vis assigned/design rating of existing cable assets. One solution is to excavate areas of anticipated hot spots and install thermocouples or short lengths of optical cable. Monitoring soil thermal resistivity also helps identify hot spots and develop techniques to determine changes in soil resistivity to allow dynamic rating of cables. 7.5 Underground installation costs. Workshop discussion focused on the relative cost of cable installations - either direct buried, duct banks, horizontal directional drilling or tunnel construction. This is a serious concern for utilities whether they are operating in a regulated or deregulated market, as projects compete for capital expenditure funding. Some delegates believe that new methods are decreasing the cost of installation but others believe costs are increasing. Delegates agreed that more comparative current day cost data would be valuable to the sector. 7.6 Condition monitoring of oil filled cables. Periodic Dissolved Gas Analysis (DGA) is the oft-quoted condition monitoring method for oil-filled cables and joints. Proper DGA results analysis can prevent incipient faults from developing into catastrophic ones. Manometers, which are used to monitor oil pressure, need to be checked for deterioration when located in humid conditions or areas susceptible or exposed to corroding effects. Delegates believe more reliable systems are worthy of investigation. 7.7 Fault location. The traditional Murray Loop and Wheatstone Bridge techniques are often employed. The pulsing technique used with a surge generator is also used in some instances. Although most delegates were confident of their methods, they were keen to share experiences with fault location techniques. 7.8 Mechanical movement. Movement in oil filled cable joints due to thermal expansion is of great concern to the industry. In particular, there are now serious problems emerging in respect to certain joints and cable types. Delegates are keen to share knowledge and explore the techniques being used by other utilities, such as New Zealand s use of X-ray equipment to inspect joints. 7.9 Tunneling. In densely developed and congested city areas, trenchless techniques like cable tunnel construction become a necessity. There are a number of different design concepts currently being used in the Asia Pacific region. These range from the use of tunnelling machines to prefabricated tunnels and under-road tunnels, some with and some without fire protection systems Co-ordination between utilities. Delegates identified a genuine need to coordinate cable installation works between power utilities and public works, water supply and telecommunication service providers. 7

8 8. CONCLUSION This was the first meeting of the AORC panel B1 and the central CIGRE Study Committee SC B1 Insulated Cables has endorsed the principle. It is now proposed to make the workshop an annual event with the objective of encouraging greater participation in CIGRE by experts in this region and sharing the experiences of this region with the broader international community. For this purpose a close connection between the regional Panel and the central Study Committee will be maintained to ensure the most effective dissemination of information and an optimal co-ordination of future actions with common interest. 9. AORC PANEL B1 MEMBERS Australia Mr. Ken Barber and; Mr. Jim Lyall Hong Kong Mr. Paul Poon and; Mr. H.M. Wong India Mr. Alok Kumar Kulshrestha Indonesia Mr. R. Hutasuhut Japan Mr. Susumu Sakuma and; Mr. Atsushi Toya Korea Mr. Kim, Jae Sung and; Mr. Kim, Yi Kon Malaysia Mr. Leong Whye Hin and; Mr. Zakaria B. Zainal Abidin New Zealand Mr. Ken McDougall and; Mr. David Shipman Singapore Dr. Su Qi and; Mr. Puang Kah Hock Thailand Mr. Pera Yamtong and; Mr. Pongsak Lamoonkit 8