B1-00. SPECIAL REPORT FOR SC B1 (Insulated Cables) Walter Zenger. Special Reporter

Transcription

1 CIGRE 2016 B1-00 SPECIAL REPORT FOR SC B1 (Insulated Cables) Walter Zenger Special Reporter 1. General Study Committee (SC) B1 is responsible for all aspects regarding land and submarine insulated cable systems. The scope of work of SC B1 is theory, design, applications, manufacture, installation, testing, operation, maintenance and diagnostic techniques for AC and DC cable systems. The four strategic directions given by the Cigre Technical Committee serve as a basis for the performed work. These are preparation of the electrical power system of the future, to make the best use of existing systems, focus on environment and sustainability and communication on power system issues for decision makers. For the 2016 Group Discussion Session, three preferential subjects were proposed to stimulate discussion in the light of the strategic directions. The total number of published papers is Preferential Subject No. 1 The title for PS1 is Feedback from newly installed or up graded cable systems. The subject covers all four strategic directions and involves the following sub-items: Design, qualification, installation techniques, operation Environmental issues This preferential subject attracted 9 contributions. wzenger@usi-power.com 1

2 2.1 Papers for Preferential Subject No. 1 B1-101: This paper describes activities to underground two 40 year old overhead lines in a now very dense urban area in Brazil. The utility had to deal with a narrow right-of-way that in addition had experienced several ROW encroachments. The work needed to satisfy necessary information requests from authorities such as environmental studies, EMF mitigation measures, traffic plans and special demands regarding the civil work. The authors showed that undergrounding of overhead lines is not a simple process even when utilizing existing ROW. The permitting process is still in progress. B1-102: Due to the Great East Japan Earthquake a new underground power line was necessary to be commissioned in a very short time. To reduce the installation time by 50%, pre-molded joints for 275kV were used in Japan for the first time. New test procedures needed to be developed to prove the reliability of the new connections including determination of the maximum permissible contamination size, visual detectability of contaminations by splicers and long duration verification tests including partial discharge measurements. The new high voltage withstand test combined with PD measurements successfully confirmed the validity of the existing process control methods. In addition the installation faced challenges of a long tunnel and a steep slope section. The circuit went into operation in B1-103: This contribution presents a project to reinforce transmission capacity in New Zealand. It covers cable design of a 220kV XLPE cable system, installation along a 1.4km bridge and inside manholes. The challenges include the mitigation of thermo-mechanical forces in joint bays, cable attachment and clamping within the bridge structure including evaluation and full scale testing of its thermo-mechanical, seismic and vibration stresses. Design of snaking arrangements to greatly restrain the cable thrust into manholes has been verified by tests. Modelling and tests of a dilation mechanism at the bridge showed that supports allow for horizontal and vertical bridge movements and aimed to simulate 80 years of TMB activity. B1-104: Maintaining underground cable network in Mumbai City is a challenging task. Some cables were installed more than 100 years ago. Since the System Operator has Gas Filled, Oil Filled and XLPE cables, maintenance practices are different and adapted to each type of cable. The report presents various techniques and methods to monitor and upgrade the Underground Cable Network of Mumbai City. B1-105: Multiple parallel cable systems can exhibit a complex network of conductors, metallic shields and grounding conductors. Modelling of mutual inductive and ohmic interference of a multi-phase conductor 400kV cable system is presented in this paper. Starting with a definition of modelling parameters an impedance matrix is computed using self impedances and coupling impedances. Together with earthing resistances a chain model is formed to calculate voltage and current distributions on all accessible sites along the circuit. Measurements at an existing 400kV cable system were performed at low load operations. The results show good correlation with the model. B1-106: This paper describes the development, design, installation, commissioning and field testing of a novel, gravitational water cooling system for cables. After the installation of a new 230kV XLPE cable system, fiber optic temperature measurements revealed that an existing hot spot mitigation around a steam pipe was insufficient, forcing a derating of the 2

3 EHV system by about 20%. Rating studies and mathematical models showed that a gravitational closed-loop water cooling system should be sufficient. This largely maintenance free cooling, would accommodate the required heat transfer away from the hot spot resulting in a reduction of the ambient backfill temperature. Initial tests show a good agreement between model and actual measurements. B1-107: HVAC submarine connections are increasing in numbers due to interconnections, offshore windfarms and connections to oil & gas platforms. This contribution reports on the designing and testing of a 400kV HVAC submarine cable system in Korea. The system includes the cable, factory and repair joints, and terminations. Based on Cigre recommendations a program of development, type and pre-qualification tests, both electrical and mechanical, was established. In addition a test for long-term accelerated aging was devised. The development and type tests were successfully completed. The pre-qualification test is scheduled to be completed in October B1-108: Transient overvoltages in cross-bonded systems induced by lightning have been dealt with in Cigre TB 283. This Spanish paper presents how the Cigre analytical equations are deduced to model unconventional grounding of cross-bonding joints as well as outdoor and GIS terminations protected by sheath voltage limiters (SVL). The authors also show the impact mixed coaxial and unipolar grounding leads can have on the protective margin of the system. Similar important is the consideration for the length of the grounding lead. The resulting overvoltages can by far exceed the withstand level of the outer sheath or the accessories. The new equations were applied to 150 circuits of 220 and 400kV in the Spanish network leading to the proper protection level for a total of 392km of EHV cable systems. B1-109: This paper describes the qualification process for the Italy France 320kV HVDC intertie across the Alps. Since international standards are currently unavailable, the specifications and testing requirements were based on present Cigre recommendations of TB 496. The two TSO s requested additional tests beyond the Cigre TB 496 to make sure the cable system withstands the specific environmental conditions of this particular installation. The tests included space charge measurements on full size cables and a superimposed impulse voltage tests at very cold temperatures down to -25C. Challenges for the installation were long viaduct crossings and long pulling length to reduce the number of joints and the necessary use of large drums. The successful completion of the qualification tests has given confidence to users and suppliers. 2.2 Discussion of Preferential Subject No. 1 The papers submitted for Preferential Subject No.1 show the wide range of topics related to newly installed or up-graded cable systems worldwide. The papers cover three overarching subjects Increase of transmission capability Improvement of reliability New and novel designs or installation methods Transmission capability is increased by installing new systems such as in New Zealand or by replacing overhead lines in existing right-of-way as done in Brazil. Emergencies such as the large Japanese earthquake necessitate a quick system reinforcement challenging existing selection of accessories and installation procedures. A novel gravitational water cooling 3

4 system is now mitigating an existing hot spot thus preventing a derating of an EHV system in Canada. System performance and reliability can be improved by verification of design parameters. This has been shown by a full scale mechanical testing for new types of installations on bridges and in manholes, determining and testing the criticality of contaminations in accessory interfaces, confirming the voltage and current distribution along a cross-bonded system, and rating audits on installed systems. Transient overvoltages that exceed the insulation level of cable sheaths or accessories can be hazardous. Thus modelling, testing and implementing a design to limit these transients improve reliability of the system. New cable system designs require development, type, pre-qualification and commissioning tests. Several papers address these requirements for EHV/HV AC and HVDC cable systems. Test specifications are based on Cigre recommendations, IEC standards, and customer needs. Utilities now specify additional project specific requirements, some of these might later be included in industry standards. In addition new types of installation techniques are presented such as attachments to long bridges or viaducts, cable installation on steep slopes or placement of a closed-loop gravitational cooling system next to a new EHV system. 2.3 Questions from Preferential Subject No. 1 The review of the papers and the discussion implied the following questions for Preferential Subject No. 1 (Feedback from newly installed or up graded cable systems): Question PS1 Q1: Several papers address the modelling of cable and system parameters. Are there other methods available that confirm these findings? How do they relate to voltage and current distribution in cables, to overvoltages in shields, to cable ratings or to thermomechanical properties? Question PS1 Q2: Quality control and testing during commissioning is crucial for reliability. Both can be performed separate or combined. What is the advantage of either approach? Are users inclined to verify process control through testing or is the combined QC and test beneficial. What could be the future process? Question PS1 Q3: Qualification test procedures for AC EHV cables are well established. Additional requirements are stipulated for submarine cables. What test requirements for HVAC cable systems are missing as users still require additional testing? Is there a need for additional long-term aging tests? Is there a need to update TB 303? Question PS1 Q4: HVDC cable systems are growing in numbers and are now increasingly used for land based systems. What environmental conditions do they have to withstand? What is the optimal laying length for such cables? Are current Cigre recommendations for HVDC cables sufficient? Is it time to prepare recommendations for Extension of Qualification of HVDC Cable Systems? 4

5 3. Preferential Subject No. 2 The title for PS2 is Best use of existing cable systems. The subject addresses the second strategic direction. The subject covers: Condition assessment and diagnostic testing of cable systems Trends in monitoring cables and accessories Upgrading methodologies and related experiences Trends in maintenance strategies This preferential subject attracted 16 contributions. 3.1 Papers for Preferential Subject No. 2 B1-201: This paper describes the development of a new maintenance plan for EHV XLPE cable systems in Latin America. The specification is based on Cigre TB 279 and TB 379 and selected a Reliability Centered Maintenance (RCM) approach. Experience has shown that physical location and condition of the maintenance access points is of high importance. Manholes and link boxes need to be accessible and free of water for PD or sheath current measurements and thermographic inspections. The specifications for manholes and link boxes have been revised to aid the new maintenance procedures. B1-202: The condition assessment method for HV and EHV transmission cable systems at a US utility is shown in this paper. The practice covers both extruded dielectric and pipe-type cable systems. Extensive evaluations and repeated field examinations are needed to ensure early identification for reliable operation over the expected design life of 40 years and more. The authors list the key inspection items including possible degradations and remediation possibilities. Corrosion even for new circuits can be an important factor. It is also shown that different cable manufacturer apply different techniques for maintenance concerns. B1-203: This contribution presents the selection process of an optimal field test system for 115kV extruded dielectric cables in Thailand. The utility experienced frequent follow-on failures after DC commissioning tests. The selection process was focused on the local needs such as portability and power consumption but also included test effectiveness, cable length and adoptability to PD measurements; although PD measurements proved to be challenging in a field environment. The selection process that also included multi-criteria decision making led the utility to select a Damped AC test system. B1-204: Cancelled B1-205: Online PD monitoring for medium voltage cable systems is increasingly applied to detect weak spots prior to a failure. This new technology incorporates two sensors at both ends of a circuit enabling the detection and location of PD sources. The measurement is aided by injecting a time synchronization pulse. The system can be applied not only to radial systems but also to distribution networks. Online PD detection can be advantageous since PD occurrence can be sporadic and changing in magnitude over time. The authors report that PD can last months to years prior to failure. Dutch utilities have demonstrated that the application can improve their reliability indices such as SAIDI and SAIFI. 5

6 B1-206: This contribution is focusing on armor losses of three conductor submarine cables. Cigre TB 640 has reported that armor losses calculated with IEC standards result in higher than actual losses and thus resulting in lower ratings. The authors developed a measurement system and a FEA simulation model for armor losses on actual cables. Several different types of cables were tested and modeled. Measurements were conducted at room and operating temperature. The tests showed armor losses up to 60% lower than the IEC values. The FEM, correlated with the measurements, can be used for cables with other conductors and armors types. B1-207: Dissolved Gas Analysis (DGA) has been a useful tool for fluid filled cable systems to inspect abnormalities or for regular maintenance procedures. The issue is what level of detected gases is critical and needs to be addressed by corrective maintenance. Improved precision in prediction is necessary to be able to repair prior to failure. This paper Japanese presents a new updated criterion matrix for SCLF cables with highly accurate diagnosis based on pattern analysis. A second part of the paper describes how gas analysis (GA) for fluid filled XLPE HV terminations can be used to diagnose tracking degradation between the cable and stress cone due to solidification of silicone oil. B1-208: The paper describes the development of a robot maintenance system for a long cable tunnel across the Pyrenees between France and Spain. The 8.5km long tunnel with a diameter of 3.5m contains two HVDC circuits. Due to environmental constraints the tunnel is only accessible at its ends. Regulatory restrictions define the tunnel as accessible but not visitable, requiring the development of an automated maintenance robot vehicle. This vehicle can carry out preventive maintenance tasks without the need of workers but also is able to transport workers into the tunnel for corrective maintenance work. Sensors and cameras ensure a safe and reliable operation of the train. B1-209: This contribution presents efforts by a Spanish utility to analyse sheath currents to detect abnormal conditions such as damage to the oversheath, performance of surge voltage limiters whether during faults or their possible malfunction, incorrect sheath bonding during installation or removal of earthing leads by theft. The utility develops systems that monitor sheath bonding systems, basically an easy measurement but not typically employed, to optimize the maintenance process. Theoretical studies have been conducted regarding sheath currents in normal and abnormal conditions. Research is continuing to develop automatic interpretation of monitored currents to estimate the probable nature of defects. B1-210: Connections to off-shore windfarms in Germany face a special requirement where the temperature difference between the sea ground and cable surface must be less than 2K. Thus cable losses can limit the transfer capacity of the submarine cables below their maximum operating temperature. As an interim solution parallel cables provide necessary reserves. The final solution is a predictive feed forward dynamic rating strategy explained in this paper. The algorithm is based on metaheuristic optimization and takes into account predicted low wind conditions. With the presented solution 22% more energy can be transmitted. B1-211: This paper describes condition monitoring approaches by UK operators of medium and high voltage submarine cable networks for renewable off-shore generation. While historically time based maintenance (TBM) had been applied, users now move to condition based maintenance (CBM). Cigre TB379 and TB398 contain strategies for land based systems. It is argued in this paper that submarine cables have a shorter service life and thus 6

7 need to have a different maintenance approach compared to land cables. The paper explains applications of electrical detection diagnostic methods such as online PD, sheath current and power quality monitoring. Two case studies show that 90% of electrical issues would be identified by the diagnostics. B1-212: This contribution focuses on the Life Cycle Assessment (LCA) of a 380kV HVAC double circuit in Italy. LCA evaluates the environmental burdens of a product, a process or an activity, quantifies the needed resources and pollution emissions and assesses opportunities for improvement. The work was based on ISO standards and used existing software packages. The interpretation of the results showed that the operational phase is dominant with cable losses and land occupation over a 40 year life span. Next highest importance was assigned to the realization phase and impacts due to mining and production of copper. B1-213: Renewable energy systems pose new challenges to TSO s. In the past, new cable systems rarely were loaded up to the maximum design ratings. The Belgian TSO decided to use a real time thermal rating (RTTR) system to better control load flow in a strategic 150kV circuit. This includes a safe and controlled overloading of the cable with help of distributed temperature sensing (DTS) and RTTR. The paper explains the TSO s experience with installation, typical problems and final recommendations for integration and overload capabilities. Critical actions are early involvement between cable experts and IT, and focus on follow-up actions after installation that are listed in the paper. B1-214: The tracking of combustion test standards for cables is the focus of this Chinese paper. It addresses Chinese and international standards based on the relevance and development track, applied combustion tests for new and aged cables as well as the toxicity of the combustion gases. Cables have been the cause of many fire accidents in power grids. In China two thirds of all fires in cities are caused by cables. The authors present a test framework for cable combustion tests in the laboratory based on international and local standards. It is also proposed to include toxicity tests in standards including the laboratory emissions during these tests. B1-215: This paper describes new technology developments for the location of submarine cables. Determining the correct position of submarine cable is essential for installation, maintenance and repair. For protection against damage, many of these cables have been buried thereby increasing the difficulty of location. New 3 axis magnetometers improve the efficiency of reliable location for both AC and HVDC submarine cables. The new technologies are also complemented by sophisticated signal processing and filtering techniques. Applications on installed links are presented. The authors also present a new, remote controlled tone generator to locate and identify multiple cables in a narrow corridor. B1-216: Breakdown of HVDC mass impregnated non-draining (MIND) cables can be caused by large cavities in the laminated paper dielectric. These voids can be created by excessive load cycling. MIND cables, for a long time, have been the dominate dielectric for the highest DC voltages. Operators now increasingly demand a faster change of the load flow to better adapt to renewable generation. This paper presents mechanisms that can lead to excessive voids near the conductor. It shows how conductor temperature, the temperature across the insulation and external pressure are driving cavity formation. Parameters of existing systems are presented. 7

8 B1-217: This contribution from Bahrain presents the application of PD diagnostics to EHV GIS terminations for the early detection of incipient failures. It describes the importance of PD measurements and outlines a case study for the periodic monitoring with the timely detection of PD in a 220kV wet type GIS termination. It explains the application of high frequency current transformers (HFCT) with focus on practical problems and the challenges experienced during the PD measurements. The paper also recommends an online silicone oil level measurement for oil inside the terminations. 3.2 Discussion of Preferential Subject No. 2 Papers submitted for Preferential Subject No.2 Best Use of Existing Cable Systems illustrate a large scope of topics targeting the operation and maintenance of existing assets. Maintenance plans for land and submarine cables show different approaches on how to select plans for specific needs whether they focus on time based, condition based or reliability based parameters. Access to the infrastructure can be an issue that can be addressed by either new specifications or development of robotic equipment. Cable condition monitoring needs to provide essential information for necessary corrective actions. Corrosion of infrastructure components has been shown to be an issue even for fairly new installations and needs attention. Electrical measurements such as sheath currents can provide helpful feedback for the asset owner and research effort point to an automated interpretation of results in the future. New test techniques are discussed in four papers. Some point to difficulties of testing in the field. A key question for users is how new techniques can improve system reliability and the ways to quantify the benefits. Location of submarine cables can be improved with two new test systems and a paper recommends toxicity of combustion testing to be included in international standards. Renewable generation is growing rapidly and with it is challenging cable technology with new requirements. Overall it needs to be discussed whether many of the condition and monitoring parameters established for land cables are also applicable for submarine cables. With regards to cable losses, there can be impacts on the marine environment. There can be also a desire for a safe and controlled overload of cables connecting to renewable generation. Cigre TB 640 indicated that the actual losses in 3 conductor armoured cables are less than calculated and thus the ampacity for such cables could be higher. A test procedure to verify the losses of armoured cable is presented. Are there other parameters where specifications are too limiting? MIND cables are susceptible to void formation during load cycles and are challenged with requests of faster load changes. A better understanding of the mechanism can increase the possible transfer capacity. 3.3 Questions from Preferential Subject No. 2 The review of the papers and the discussion implied the following questions for Preferential Subject No. 2 (Best use of existing cable systems): Question PS2 Q1: New renewable generation presents a number of challenges for cable system operators. For submarine cable connections is there a need to change condition 8

9 monitoring compared to land cable? What is the environmental impact of such cables and how can it be mitigated? For land cables, is there a need for RTTR and temporary overload? Question PS2 Q2: Selection of maintenance approaches for cables is discussed in a number of papers. What is the selection criteria for time based, condition based or reliability based plans? Will maintenance robots be used in the future for not readily accessible spaces? Question PS2 Q3: Correct and in-time knowledge of the cable condition is paramount for reliable cable operation. Will there be automated interpretation of results. Can DGA or other cumulative tests replace spontaneous measurements such as PD to detect degradation and how? Question PS2 Q4: Losses are an important consideration for cable operations. Do present loss calculations reflect the true conditions? How can system operation be modified for MIND cables? What impact have losses on the environment and how can they be reduced to an optimal value? How can LCA be a helpful tool for losses in the planning process? Question PS2 Q5: New test techniques are presented in several papers. What are the challenges for testing the condition of cables in the field? Can an impact on system reliability through periodic or online testing be quantified and by what method? What tests can best locate submarine cables? Question PS2 Q6: Corrosion has been mentioned as an important non electrical condition, should Cigre engage in this? Is there a need to include toxicity in combustion tests in our standards? 4. Preferential Subject No. 3 The title for PS3 is Insulated cables in the power system of the future. The subject addresses the first strategic direction. The subject covers: Higher voltage level for AC and DC cables New functionalities expected from cable systems Integration of cables and accessories in the network Innovative cable types This preferential subject attracted 14 contributions. 4.1 Papers for Preferential Subject No. 3 B1-301: HVDC cable systems with ever higher voltages and transmitted power are becoming essential components for renewable energy delivery. This Swedish paper describes the successful development of an extruded XLPE HVDC cable system for 525kV including an oil and porcelain-free termination, a land joint and a flexible sea joint. The new system can transmit 50% more power compared to the present 320kV voltage level. Development steps are outlined showing use of a new insulation material for cables but also relying on new and existing technologies for stress control in accessories. Extensive modelling and testing procedures have been applied in the development process aided by Cigre TB 496. B1-302: As off-shore wind farms are growing, some countries need to rely on floating wind generator platforms due to marine conditions. This Japanese contribution shows the 9

10 development of a dynamic cable system for 22kV and 66kV, suitable for the connection to floating generators and substations. Starting with an analytic simulation the system was designed for a 20 year service life. This included fatigue analysis as well as experimental tests on actual cables. A connection via a lazy-wave arrangement with intermediate buoys was selected. The cable system to a 7MW wind turbine, as part of a demonstration project, has been successfully installed and is in operation. B1-303: The cost of cables contributes significantly to the overall cost of off-shore generation. Increased attention is given to improve the transfer capabilities of inter-array and export cables. This Danish analysis shows that these cables rarely reach the designed service temperature. The paper suggests a new systematic method where load profiles, a load step function and thermal properties of the surroundings provide data for the cable rating. FEM together with methods outlined in Cigre TB 610 can model installation conditions. The authors propose to apply a Thermoelectric Equivalent (TEE) model as an analytical numerical solution to quickly calculate daily temperature response based on several years of data. B1-304: Three core armored submarine cables are the cables of choice for both array and transmission cables for off-shore wind farms. Ampacities calculated in accordance with IEC have shown to underestimate cable ampacity. This Danish paper investigates the impact of different parts of the cable with regards to the total losses even though hysteresis losses are not incorporated. It is suggested that the loss inaccuracy is based more on the screen loss factor than on the armor loss factor. Estimation of shield losses is determined by the shield currents. New research is proposed to improve shield current calculation and to use EMTP simulations for pipe-type cables even though the magnetic parameters are currently not accessible for calculation. B1-305: This paper describes the development of a transition joint between XLPE and selfcontained oil filled cables for the 132kV grid in Argentina. The drivers for the development were reduced delivery lead times, speed of installation, use of local splicers and the application of a pluggable design. The development was initiated by a local utility. The design successfully passed the tests in accordance with IEEE 404. The authors present the installation process of the new joint together with a comparison of the installation of a conventional transition joint. B1-306: Selection of the optimal material for conductors and screens has always been key to efficient cable design. Considerations are given to weight, conductivity, volume, ease of installation, health and environmental aspects. Materials of choice for conductors are Aluminium or Copper while the choice for screens can be Aluminium, Copper or Lead. The authors present their design considerations and two case studies for a 380kV and a 150kV application that resulted in the selection of Aluminium for both conductor and screens as the best solution. Test programs for the cable designs are included in the contribution. B1-307: This contribution presents what effect ultraviolet (UV) radiation and sandstorms have on the flashover voltage of silicone rubber cable terminations. These types of terminations are increasingly applied in Egyptian distribution networks. UV exposure of the test samples was followed by flash over and leakage current tests with water of varying conductivity. There was a decrease in flash over voltage based on the severity and duration of exposure to UV and simulated sand storms. The impact of sand storm damage has shown to be more severe than UV radiation. 10

11 B1-308: High Temperature Superconducting (HTS) cable systems have been long associated with future solutions for power transmission. This European paper presents a concept for a 400kV HTS cable system to partially underground major HVAC overhead transmission lines near urban areas. The designed system will have operating currents in range of 4kA. Thus only a single cable system will be able to carry the current of an overhead circuit. Cables can be placed closer together, a double circuit requires a trench width of 2m versus 20m compared to a traditional XLPE cable system. The losses of a HTS system at 4kA are over 50% lower than for a XLPE system. Suitable joint and termination designs are presented. Testing of a 220kV prototype has been completed successfully. B1-309: This French paper describes commissioning tests for long HV AC (up to 400kV) and HV DC cable systems up to 320kV as well as alternative tests and future trends. It also addresses cable system design with special consideration to safety and cost efficiency. Alternatives to the traditional testing can be resonant AC, partial discharge or DTS systems. The adequacy of DC vs AC tests on long HVDC cables is discussed. The paper reviews the French practices, shows the experiences while testing a number of recent large scale projects and discusses test parameter with proposed test levels and durations. B1-310: This contribution presents the planning, design, testing, installation and commissioning of a 4.6km long double circuit 400kV submarine cable crossing of the Dardanelles strait in Turkey. This project consists of 6 parallel submarine cable plus one spare. Justification of the project from a systems operations point of view, cable design criteria, installation and testing are discussed. Cable plowing had been selected as a protection against external damage. Planning also needed to address switching and temporary overvoltages. The system has been commissioned in April B1-311: An optimizing strategy for the armor design of submarine cables is the focus of this Chinese paper. An EMTP model is used to analyze the impact of cable components on ampacity. The analysis for this application found that at optimum sheath and armor currents should be about equal. The optimal armor design calls for 53 galvanized steel armor wires with two added copper wires. A cross-section of the cable is presented. The optimized configuration results in ampacity increase of 20%. Due to the higher voltage between sheath and armor a semiconducting sheath is required. B1-312: This paper describes the design and type testing of a new deep water 420kV HVAC submarine cable to be installed across two Norwegian fjords and having a combined length of about 32km. The development and system test include factory and repair joints. Due to an record installation depth of 390m special tests such as radial water penetration tests of joints, longitudinal and radial water penetration tests on the cable have been devised. The test program was developed based on Cigre TB 303 and TB 490 recommendations. The challenges of manufacturing in long length and of future developments are outlined. B1-313: For protection submarine cables are mostly installed in trenches. The knowledge of the thermal properties of the sediment surrounding these cables is therefore important. As part of the HVDC NordLink connector between Norway and Germany traditional geotechnical surveys were conducted to characterize soils and identify thermal bottlenecks. Inconsistent Thermal Conductivity (TC) measurement results raised questions about instruments, methods and sample handling. This European paper describes new in-situ measurements during a resurvey. In situ measurements need to be careful evaluated but when interpreted correctly can be an important addition to traditional techniques. 11

12 B1-314: This contribution presents a case study to assess the thermal effect water mains can have on the ampacity of cables. A 380kV HVAC cable in Saudi Arabia is installed part of the route parallel along a water main. An improved implementation of the well-known FEM method shows different dependencies of installation, soil and backfill as well as thermal resistivity. The most influential parameter is the temperature of the water pipe. 4.2 Discussion of Preferential Subject No. 3 A large number of papers have been submitted for this subject about Insulated Cables in the Power System of the Future. As with many other papers this year, focus is on submarine cables for renewable energies. Cost and efficiencies are another key topic for this year s Cigre session. The main aim is how to install new systems quicker and at less cost. The optimum selection of conductor material is one of the addressed options. New extruded HVDC cables systems with improved materials and higher operating voltage can increase the transmitted power significantly. New developments for HTS cables aim at the highest transmission voltages and transfer of power one for one with overhead lines. Submarine cable armouring design is optimized to increase power transfer by partially replacing steel wires with copper wires. While wind generators anchored in the sea floor are now commonplace, new developments aim at areas in the sea where only floating units can be installed thus challenging reliable cable connection technologies. The cost reduction of submarine cables and application of submarine cables for connectors, array or transmission cables is subject of four papers. Another group of papers deals with application of existing cable systems for new applications such as submarine cables for great depth, crossing of busy water ways, and new transition joints. Testing and system modelling will provide new solutions and systems for the future be it commissioning testing for long HVAC and HVDC systems or the thermal environment in submarine or land installations. 4.3 Questions from Preferential Subject No. 3 The review of the papers and the discussion implied the following questions for Preferential Subject No. 3 (Insulated cables in the power system of the future): Question PS3 Q1: Extruded HVDC cable systems are proposed with ever higher voltage levels. What is the driving force for higher voltages? What will be the future for extruded HVDC cables and is there still a future place for laminar (lapped) HVDC systems? Question PS3 Q2: EHV HTS cable systems are now in development. Are there limits on the magnitude of transmission capacity for a single circuit so that it is manageable from a view point of cable technology, system operation or short circuit forces? What other applications can be seen for EHV HTS systems? 12

13 Question PS3 Q3: Higher ratings and cost efficiency for submarine cables are of concern to current designers and users. What key questions need to be addressed and solved in the future? Do we see an increasing demand for floating wind farm installations? What additional specific testing is necessary? Question PS3 Q4: Commissioning testing of installed systems can impact the future reliability. How can we make sure that the type of test, the voltage level and duration is appropriate to detect defects while not damaging sound cable? In the future, do we need to make adjustments to the cable or accessory design to better accommodate commissioning testing? Question PS3 Q5: Armour loss calculation has been a major concern of cable engineers over the past years but also losses in conductors and screens are being discussed. What future actions do we need to take and what type of modelling will be necessary? How can we correctly assess permeability of carbon steel? Is there a better way to assess the overall cost of losses and how can cable design be adjusted for this in the future? IMPORTANT NOTE: it is expected that above questions relevant to the three Preferential Subjects will attract a number of prepared contributions. The timing of the B1 session usually allows a maximum of 45 prepared contributions. Contributors are invited to comply with Cigre rules i.e. to send their contributions two weeks in advance to the Session and to be ready to discuss contents and allocated speaking time on Wednesday 24 th of August in room 361, the day before the Group Meeting. Contributions shall be prepared on the basis of the templates that can be found on the Cigre website. These templates will be also posted on Cigre B1 website together with the latest information regarding SC B1. The SC B1 session held on Thursday August 25 th will start at 8h45 in Salle Bleue and the lunch time will be from 12h30 to 14h00 (sharp). A questionnaire prepared by the Customer Advisory Group of SC B1 will be circulated to better understand the expectations of Insulated Cables community. 13