Final Report Summary - ECCOFLOW (Development and field test of an efficient YBCO Coated Conductor based Fault Current Limiter for Operation in Electricity Networks)
Executive Summary:
The objective of the FP7-funded project “Development and Field Test of an Efficient YBCO Coated Conductor based Fault Current Limiter for Operation in Electricity Networks” (ECCOFLOW) is to develop a superconducting fault current limiter (SFCL) based on coated conductor YBCO tape (cc-tape) and test it in the medium voltage (MV) power grid (distribution level).
The ECCOFLOW consortium composed of major European electric utilities (Endesa, Vattenfall, Westnetz, A2A and VSE), distinguished academic and research institutions (CNRS, KIT, CSIC, EPFL, RSE, IEE and Tecnalia) as well as AirLiquide and Nexans SuperConductors under the lead of Nexans France carried out research work in the period from 1 January 2010 until 31 December 2013 to design, assemble, simulate the functionality and prepare for field testing of a unique SFCL device. In particular, during the course of the project, the following was accomplished:
SFCL design concept: In a first step a detailed design for the whole ECCOFLOW current limiter system was developed. This included comprehensive specifications, models for AC loss and quench simulation, a conceptual and final design for the HTS components, the HTS modules, the cryostat, the bushings, the cooling system, the air coils and the circuit breakers.
Computational / simulation work: Mathematical models have been developed on different levels to understand various effects from a scientific point of view and to safeguard the design of the SFCL device.
Materials and components characterisation: Several tests of different commercially available superconducting YBCO coated conductor (cc) tapes were undertaken in order to further develop characterization parameters for the materials and components of the ECCOFLOW SFCL.
Manufacturing and integration of SFCL device: The successfully manufactured and tested components have been assembled to modules which were integrated into the cryostat. The SFCL device consists of the cryostat together with terminations, cooling and a control system. Switchgear and air core reactors have been added to achieve the specified limitation time of 1 seconds (s).
Extensive testing of the SFCL device: Reliability tests of the device have been realized at a high power laboratory and simulation studies for an installation in the planned applications have been conducted.
SFCL grid integration and operation: The infrastructure for the grid test was provided including the definition of the SFCL parameters and the test requirements with respect to the integration into the distribution grid. Furthermore, a simulation of the equipment under field conditions was accomplished. The SFCL device is currently installed in Mallorca. Field testing has not taken place in the framework of the ECCOFLOW project.
Socio- and techno-economic aspects: The reliability, marketability and cost reduction potential of the device in the medium term was shown in several studies on socio- and techno-economic aspects of the ECCOFLOW SFCL. The studies have been performed both on existing grids of the DNOs Endesa and VSE as well as on generic grids.
The ECCOFLOW project has yielded a number of scientific and technical results for the further development and usage of SFCL devices. It can be concluded that all scientific and technological objectives have been fulfilled. Furthermore, the results achieved in the ECCOFLOW project are not only purely technical, but also of socio- and techno-economic impact.
The consortium aims at testing the SFCL device after the official end of the project in cooperation with most partners of the consortium. For more information please contact the website www.eccoflow.org or the Project Coordinator Katrin de Tessières (katrin.de_tessieres@nexans.com) and Achim Hobl (achim.hobl@nexans.com).
Project Context and Objectives:
Project context:
As a general trend, electric power networks increasingly face higher levels of fault current due to increasing power demand, the rise in renewable and other forms of distributed electricity generation, changing user patterns (e.g. integration of electric vehicles, micro-grids etc.) as well as due to changes regarding the regulatory framework of energy markets. Higher loading poses challenges on the existing equipment and also constraints on the distribution networks. A higher meshing of distribution networks combined with the rapidly growing integration of renewable energy sources leads to an increase of the fault current level with every new installation. As substations ratings are coming to their limits, network operators have to either decline additional installations to their grids or to upgrade if not rebuild complete substations.
A solution to efficiently and economically reduce the fault current level is not only needed in most EU member states but also in many other countries which are facing a fast growing power demand at a given grid infrastructure. SFCLs could provide a solution to address the increasing incidence and level of fault currents and also contribute to improving the performance, stability and efficiency of electricity grids. SFCL are “self-triggering” devices which are employed in power systems to reduce the actual short circuit current that flows during fault conditions. This operation is achieved by a unique property of the HTS material that is the transition from the superconducting state to the normal conducting state under overload current, called “quench”.
Since the discovery of High Temperature Superconducting (HTS) in 1986 scientists all over the world have been working on understanding and improving superconducting materials and exploring their possible technological applications. Several materials have been further developed and tested for different applications. While low-temperature superconductors (LTS) are facing established markets in the medical sector and in high energy physics research, only few HTS based devices so far have reached the pre-commercial development stage as e.g. in the broadband telecommunication. The prospects for HTS devices are predominantly seen in the energy sector and among the most promising future applications are superconducting fault current limiters, electric power transmission cables, electric motors and magnetic levitation devices. SFCLs are unique devices unparalleled in conventional technology. Among all power applications the SFCL is considered the most promising with a view to near-term commercialization. At the beginning of the project the market introduction of HTS devices was impeded by cost and reliability issues as well as a lacking availability of large quantities of HTS material with reliable properties. However, possibilities for economic applications are seen where the relative efficiency, size and weight advantages of HTS devices outweigh the additional capital costs involved or where the unique physical properties of the material make the HTS device attractive.
Superconducting FCL are estimated to fulfil the requirements for a use in medium grids and were, in 2010, foreseen to be marketable in 5 to 10 years. SFCLs offer conclusive advantages in comparison to conventional techniques to limit fault currents such as rapid and effective current limitation, automatic recovery and negligible impedance during normal operation. Moreover, the device does not intercept the current (which would be an issue for fault detection and selective protection schemes), but limits it to an acceptable level for the grid.
In the case of the resistive type SFCL, the ECCOFLOW partners before entering into the project had intensely tested several HTS material options for their use in fault current limiters. The dominating materials for this purpose had been Bismuth Strontium Calcium Copper Oxide (BSCCO) bulk and Yttrium Barium Copper Oxide (YBCO) thin films on sapphire substrate. Status and prospects of the materials are:
• So far, existing SFCL prototypes based on BSCCO material are exhibiting significant AC losses at higher currents which prevent their commercial introduction.
• SFCLs based on YBCO thin films on sapphire substrate do not provide a commercially viable approach, also due to homogeneity and scalability issues.
• The realisation of YBCO (YBa2Cu3O7) thin films on metal tapes (Y-123 cc-tape or YBCO cc also referred to as 2nd Generation or 2G HTS conductor) with sufficient quality and length now offers advantages over the other HTS material options with respect to reliability and price. This new material is considered to be presently the most suitable with excellent perspectives for current limiting applications also at higher operational voltages and currents. The availability of cc-tape in great lengths at reasonable costs makes a commercial breakthrough of SFCL possible with unique features such as compactness, short recovery-time and low AC losses.
In addition to offering a solution to the increasing level of fault currents, the application of SFCL can make the need to replace or upgrade existing equipment in power systems unnecessary. New options for the effective use of existing grid structures arise and result in cost and energy savings. SFCL further have the potential to support the integration of distributed generation sources into existing grids and could be an enabling technology for other HTS devices such as superconducting cables and transformers, leading to further economic and environmental benefits.
The challenges of efficiently and economically limiting the fault current and at the same time dealing with an increased share of fluctuating renewable energy sources, increased power demand and changing consumption patterns combined with the strong demand of network operators and the technological achievements in the field of material development have led some of the most prominent and experienced industrial and academic institutions from Europe to join forces for this project and to develop a coated conductor SFCL based on second generation YBCO conductor.
Please also refer to Figure 1 of the attachments (Figure 1: Context and innovative dimensions of ECCOFLOW).
Project objectives:
The overall objective of ECCOFLOW was to develop and test a three phase coated conductor fault current limiter based on an improved HTS material: the YBCO cc-tape, and to install it in the medium voltage (MV) power grid (distribution level).
Two different installations at two different sites had been chosen for the field tests to demonstrate the reliability and attractiveness of the device. It was intended that the developed device is also the first SFCL appropriate to stay in the grid in the long-run, thus being a unique showcase in the EU for applied superconductivity.
The following two sites chosen for the applications were:
1. Bus-bar coupling: The device was planned to be installed in the Endesa grid (Mallorca, Spain) in the substation 66/15 kV (“San Juan de Dios”).
2. Installation of the SFCL in the grid of VSE (Košice, Slovakia) on the medium voltage side of HV/MV transformer (110/22 kV transformer) to limit short currents on 22 kV busbar and all outgoing feeders (substation “Es Juh”)
Specific scientific and technologic objectives
• Design a full size 2G HTS coated conductor FCL based on the new tape and test it in a real application scenario.
• Establishment of specifications of projected current limiter
• Assessment of different commercially available superconducting YBCO cc-tapes and knowledge increase on the properties
• Simulation of the SFCL behaviour in the electrical grid
• Development of optimised design of SFCL component, cryostat and cooling system and further models for AC losses and quench simulation in an iterative process
• Design and manufacturing of complete SFCL device
• A guideline how to test MV SFCL devices based on common standards for MV equipment
• Type test of whole SFCL device in a certified lab for MV and HV elements e.g. circuit breakers
• Field test of SFCL which means the integration into two different MV distribution grids
• Techno-economical studies about further MV SFCL device installations based on the grid configuration of ENDESA and VSE
Specific commercial objectives
• Achievement of a break-through in technological as well as commercial terms of HTS device and demonstration of superior functionality over existing conventional solutions
• Analysis of cost and benefit of SFCLs in the grid
• Show reliability, marketability and cost reduction potential of HTS device in the medium term
Project Results:
The ECCOFLOW consortium composed of major European electric utilities (Endesa, Vattenfall, Westnetz, A2A and VSE) and distinguished academic and research institutions (CNRS, KIT, CSIC, EPFL, RSE, IEE and Tecnalia) as well as AirLiquide and Nexans SuperConductors under the lead of Nexans France have successfully specified, designed, built and tested a versatile SFCL for the medium voltage grid. The partners achieved in the period from 1 January 2010 until December 2013 the following results:
SFCL design concept: In a first step a dedicated specification for the SFCL system had to be elaborated. This document had to combine all constraints resulting from the two installation sites and to ensure proper interfacing on all levels of hardware and controls. Since one system only had to fulfil the requirements of both sites, operating at 16 kV and 22 kV, respectively, the more demanding and stringent value had to be selected. This was a particular challenge in the view of 1 s limitation time. The detailed specifications and availability of a common terminology, clear definitions and requirements for the limiter help to further progress the market penetration of the SFCL device and future applications.
Based on these specifications a conceptual design for the whole ECCOFLOW current limiter system was developed. As an economical solution to address the 1 s limitation time it was decided to add a set of air core reactors in parallel to the SFCL, and a circuit breaker to reduce the limitation time requirement for the SFCL. During the conceptual design, models for AC loss and quench simulation, designs for the HTS components, the HTS modules, the cryostat, the bushings, the cooling system, the air coils and the circuit breakers have been developed.
A key development objective of the ECCOFLOW current limiter is the high-temperature superconducting component. Therefore, a general comparison of different geometries has been performed with the result that a non-inductive multifilar coil arrangement of YBCO tapes with 12 mm width fulfils best the ECCOFLOW requirements for the two field tests.
Several concepts have been discussed and evaluated to achieve an optimized electrical insulation within the superconducting component. The final design is based on a specific insulator geometry with polyimide attached to the superconducting tape, and a newly developed spacer to ensure liquid nitrogen in contact with the superconductor.
A considerable number of experimental and theoretical investigations have been performed to identify the most suitable low AC loss configuration. There is experimental evidence, supported by numerical models based on finite-element calculations, that the optimal low-loss arrangement of the tape in the SFCL is a pancake wound from tapes carrying opposite currents (bifilar or multifilar arrangement (pancake)). Furthermore, it also has been shown that the use of twins (two tapes instead of one) does not substantially change the AC loss in units of Joule per meter of the used tape. In addition to the AC loss of the HTS material, the losses of the current lead and the cryostat have been optimized.
The design of the HTS module, i.e. the arrangement of the components, has been optimized with respect to a number of criteria including the use of volume, high voltage (HV) issues in the case of lightning surges, losses in the normal conducting connectors, symmetrisation of currents in parallel tapes, and gas evacuation in the short-circuit case. The influence of electro-mechanical forces as well as manufacturing aspects haven been taken into account.
Three different designs for the current leads and bushings have been evaluated for the ECCOFLOW project. The one found to best adapt to the requirements were encapsulated bushings as they were the most compact in the design and provide the highest level of safety.
For ECCOFLOW, several different cryostat configurations have been investigated in detail with the preference given to the design which showed the best compromise between low losses and ease of assembly and disassembly. The chosen cryostat has the following advantages:
• Easy access to the HTS module
• Only one vacuum vessel is used reducing the cost
• Only grounded parts are located close to the HTS coils
• The cryogenic interconnection pipes are located inside the vacuum vessel. This facilitated the assembly and decreased the manufacturing cost
The ECCOFLOW partners identified a closed loop system with GM cryocoolers as the best solution for the SFCL device cryogenic cooling. At nominal operation, liquid nitrogen evaporates through the heat coming from the HTS module, the cryostat and the bushings, and gaseous nitrogen flows to the cold head. The gaseous nitrogen is liquefied through a heat exchanger and liquid nitrogen flows back to the cryostat by gravity. The main advantages of this solution are:
• The maintenance operations are facilitated by a service flange. This flange allows the access to the heat exchanger of the cold head.
• The design ensures a low temperature difference between the cold head and the HTS module even if the distance is significant.
• The design is modular, therefore, it is possible to connect multiple cold heads to the SFCL cryostat with the same cryocooler module design.
• The cold heads could be located outside the high voltage area in order to realize the maintenance operation even if the SFCL is in operation.
• A redundant cryocooler which is not in operation does not involve any heat inputs thanks to vertically guided pipes.
Computational / simulation work: Mathematical models have been developed on different levels to understand various effects from a scientific point of view and to safeguard the design of the SFCL device:
• The superconducting tape has been simulated with respect to the electro-thermal, electro-mechanical, and the AC-loss properties. This was necessary to achieve an optimized superconducting component design. It was particularly difficult to simulate the quenching behavior, since many physical effects, which influence the propagation of a quench, are highly nonlinear.
• The system behavior has been simulated to ensure fulfillment of the specification, especially with respect to the limitation functionality.
• Several models of integrating the SFCL into the grid have been generated to understand the effects of SFCLs in the electrical network. Special focus was put on the improvement potential regarding stability, reliability, and efficiency of the grid. Furthermore it was shown that a much higher level of distributed generation can be added to the grid when integrating SFCLs.
Materials and components characterisation: Several tests of different commercially available superconducting YBCO cc-tapes were undertaken in order to further develop characterization parameters for the materials and components for the SFCL device. The tests and measurements included:
• Critical current homogeneity of the samples
• Resistance as a function of the temperature
• Quenching behavior under varying prospective currents
• Mechanical testing for stress strain properties
• Thermal expansion
• Mechanical properties of insulation-tape composite
• Effects of wrapped insulation on critical current homogeneity
The level of coated conductor stabilization was one of the main parameters to be fixed before being able to order the tape. Several models were developed and experiments performed to obtain the final level of stabilization, which results in a required silver coating thickness on the conductor. Higher stabilization gives more stable tapes, but results in longer length and therefore in higher costs. The safe and optimum value had been chosen extremely carefully. In this context, critical current and stabilization inhomogenity represent one of the biggest challenges for a highly reliable SFCL.
The profile of the critical current density across the width of the tape is an important factor for the AC losses of the selected conductor. With the help of magnetic field mapping and a dedicated inversion procedure the profile of the critical current density over the width of the tape was found. The influence of tape non-uniformity on AC loss was investigated. The observed reduction of the critical current density was included in the numerical calculations of AC loss in the multifilar pancake configuration. The results showed that a degradation of transport capability at the tape edges could increase the AC loss significantly compared to an ideal tape with constant critical current density across the width.
Manufacturing and integration of SFCL device: A detailed design for realisation of the complete system including all electrical, mechanical, thermal and cryogenic aspects of the limiter, e.g. the terminations, cryostat, cryocooler and limiter module including instrumentation has been developed. Based on the parameters of the single superconducting limiter component, a detailed design of the HTS module has been established regarding all mechanical fixations and electrical connections as well as the dielectric strength with respect to the cryostat on ground potential.
Terminations have been designed and manufactured according to the electrical specifications, norms and regulations for power equipment (lightning impulse tests, partial discharge, etc.) and to the high current of the limiter. In a prior validation step prototypes of these terminations had been successfully tested under cryogenic conditions (77 K / atmospheric pressure) with up to 50 kV AC withstand and up to +/- 125 kV lightning impulse test.
A cryostat was designed and manufactured with a low loss, highly reliable cryogenic system that fulfils all general safety requirements. Boundary conditions for later series productions were also taken into consideration. A vacuum- and multi-layer-insulation was foreseen to reduce thermal losses from radiation and conduction inside the cryostat. The final solution for the cryostat is using only one vacuum vessel, where also the cryogenic interconnection pipes are located. The three cryogenic nitrogen vessels reduce the heat input and can be opened e.g. for assembling or maintenance. A closed cooling system with cold heads was developed. To ensure a re-cooling period of less than 30 s, it was necessary to blow off nitrogen gas after a short-circuit event. Therefore, a refilling valve and reserve volume of LN2 inside the cryostat has been integrated in the system.
Furthermore, all SFCL device elements were manufactured and integrated. A document on the definition of all relevant interfaces of the device had been prepared. Major parts for the electrical integration in a power network are the circuit breaker in line with the superconducting fault current limiter and the air coils in parallel. This arrangement facilitates very long fault durations. All relevant parts of the SFCL are arranged inside a modified 20’ ISO-container, the circuit breakers are inside a small switchgear building. The air core reactors are air insulated and have been connected to all respective other elements using standard medium voltage cabling.
Extensive testing of the SFCL device: At the beginning of the project no comprehensive guideline for testing SFCLs was available. A set of parameters to be used during the device testing has been developed in order to ascertain the current limiting performance of the SFCL device. Finally, guidelines for the testing of MV-class SFCL devices have been developed. The most important test were the current limitation tests under full and partial load, dielectrical test (power-frequency withstand voltage test, partial discharge test, lightning impulse test) to validate the insulation concept, as well as leak and performance tests on the cryogenic system. As a prerequisite to the system limitation tests, the limiter components had individually been tested before assembly. The system has successfully passed all tests.
Guidelines developed during the project can be used as a basis for future SFCL devices as well as for developing and implementing international technical standards to maximize compatibility, interoperability, safety, repeatability, and quality of the systems.
SFCL Grid integration and operation: After identifying the ideal substations for the integration of the SFCL, where an important aspect was a large number of expected short-circuit events, all parameters for the SFCL have been defined. The grids have been analysed in detail to fully understand the performance with and without SFCL. The infrastructure for the grid test was provided including the necessary foundations, connections to the medium voltage grid and to the low voltage grid for the power supply. The data exchange and safety concepts have been specified and realised. Furthermore, a simulation of the equipment under field conditions was accomplished. The SFCL device is now installed in Palma on Mallorca island. Due to delays accumulated during the project, the field testing did not yet take place in the framework of the ECCOFLOW project. The partners are aiming at field testing the device after the official end of the European project.
Socio- and techno-economic aspects: The ECCOFLOW project led to a break-through in technological as well as commercial terms of the HTS device as it developed a ready-to-use system that can easily be integrated into different grid scenarios. An enormous development has in parallel also happened in terms of technology, availability, and cost situation for superconducting tape, partly driven by the demands and dissemination activities of the ECCOFLOW project. Furthermore, the reliability, marketability, and cost reduction potential of SFCL devices in the medium term was shown in several studies on socio-technical aspects based on the grids of VSE and ENDESA.
Potential Impact:
In the long run, the results of the ECCOFLOW project can support the establishment of a market for HTS-based devices in electricity networks, as foreseen as an expected strategic impact in the work programme FP7-Energy-2009-1 related to the grant agreement of this project.
This, in turn, can lead to an improvement of the performance, stability, and efficiency of electricity networks potentially leading to the following socio-economic impacts and wider societal implications:
• Major economic advantages: efficiency gains in existing networks, reduction of capital expenditure for the maintenance or upgrade of grids, less stress and longer lifetime for existing grid components and higher network reliability.
• Important contributions to the efficiency and security of electricity networks in Europe and to achieving strategic objectives of EU policy, such as the goal of the SET plan to improve energy efficiency and the objectives of the EU Energy and Climate Package and the Energy Roadmap.
• Positive environmental effects by reducing CO2 emissions and the achievement of the 20-20-20 goals.
As far as the more direct impacts of the ECCOFLOW project are concerned, its results constitute a crucial cornerstone for the assessment of the optimized technical specifications and market entry strategies at a larger scale for HTS devices.
In the following, the project impacts will be described for the categories of
a) Technological and scientific impacts and
b) Impacts on business opportunities and market commercialization
Technological and scientific impacts – short-term
The ECCOFLOW project has thoroughly prepared the technological basis and scientific advancement for a feasibility assessment regarding the large-scale application of a HTS device in a real MV distribution network. This has been achieved by the proof and assessment of the functionality of the SFCL based on YBCO tape which has not been demonstrated before. In the following, potential impacts are displayed according to the results achieved:
• The optimized technical dimensions and the design (components, modules, SFCL) of a 24 kV, 1 kA three-phased coated conductor resistive fault current limiter have been determined and parameters of HTS materials and components have been defined.
A potential impact of this is an enhanced transferability for similar HTS devices and applications. For example, the results of the test of different YBCO tapes for SFCL and the electrical and thermal characterization of commercial superconducting YBCO tape could be used in the construction of SFCLs, cables, rotating machines, transformers, and other HTS devices.
• The superconducting components, modules, and terminations have been integrated into the cryostat. In total, a complete and successfully tested SFCL system has been provided including control and protection systems.
A related impact will be the facilitation of large-scale production of SFCLs or, in general, HTS devices due to practicable knowledge gained about component integration, manufacturing and assembly as well as system design and integration.
• From a scientific point of view, the lessons learnt about the overall specification and the results of simulations and tests concerning AC loss optimisation, quench and limitation behaviour will most likely lead to an acceleration of related future research activities and enhancement of quality of scientific lectures.
• The results and scaling laws achieved are in many respects applicable also for high voltage SFCLs. Therefore, ECCOFLOW builds a solid base for follow-on development also for larger systems.
Technological and scientific impacts – long-term
The results of the final techno-economic analysis on the introduction of SFCLs for the planning of a new system and economical assessment could lead to a significant advancement regarding an optimal utilisation of the possibilities that HTS-based devices may constitute for the operation of smart electricity networks through enhanced knowledge on:
• Impact of SFCLs in existing distribution network architecture
• Innovative distribution networks planning integrating SFCLs
More specifically, the analysis conducted will impact the future design of SFCLs for operation in electricity networks, particularly in MV power grids, due to the following results:
• Possible equipment cost reductions (for new investments)
• Increase in renewable energy integration potential
• Quality of supply improvement
• Reduction of electricity losses
• Models for current distribution in operating HTS
• Future design perspectives and benefits for smart grids
• Social and environmental benefits
As a specific result of the grid application studies it turned out that meshing the grid is often possible using SFCLs with only low nominal current rating, and, consequently, comparatively low capital and operation costs. Therefore, relatively “cheap” devices at strategic points of the grid can drastically increase the compatibility of the grid with a large fraction of distributed generation and at the same time provide a high reliability of electricity supply.
The results will further impact the design and implementation of future EC energy policy and regulatory issues.
Impact on business opportunities and market commercialization
The achievement of a final break-through in technological as well as commercial terms includes opening
• new market opportunities for the producers of the device and
• new design opportunities for electric network operators.
In the course of the project, more specific information has been gathered on future marketability of such devices and its influence on the planning and design of smart network architecture.
The market potential is significant and the interest of electric utilities across Europe is evident, due to the SFCL being a technological novelty and a unique device offering extensive benefits for the users, such as improved functionalities and numerous potential applications. The interest is underlined by increasing numbers of inquiries from network operators for SFCL systems reaching the industrial partners of the ECCOFLOW consortium.
The reliability tests of the device conducted at the high power laboratory and simulation studies for an installation in the planned applications have shown the functionality for a large scale application. As regards the projections of first applications of the SFCL technology and related market prospects, the following applications are considered as the most promising ones:
• In the short term, an application in distribution substations is foreseen. Currently, there are around 50,000 substations in Europe with a life time of about 40 years.
• The SFCL technology enables coupling of different sub-grids (at same voltage level) within the electricity grid to reduce the number of in-feed transformers.
• Equally, the SFCL can support the coupling of dispersed generation units (e.g. wind power stations and combined heat & power) in the grids.
• The device can be an enabling technology for other superconducting applications such as HTS power cables, transformers, generators, etc. At present, this is demonstrated in a German funded project combining a SFCL with a HTS cable.
• In the long run, there is substantial potential for wider transferability (e. g. positioning of the limiter in other parts of the grids).
Spreading of results and influence of other ongoing activities
The great efforts regarding the spreading of interim and final project results on European and international scale involving the main target groups of electric utilities (Utility Board), other stakeholders in the electricity sector, general industrial operators and the scientific community realized by the project consortium, as described below, greatly contributed to raising awareness of the potential of the SFCL and HTS devices in general and stimulating the demand.
In this project, important contributions to international standardization activities (establishment of international standards, e.g. CENELEC and IEC) on fault current limiting devices related test procedures could be realized through the active participation and membership of various partners in several CIGRE working groups and IEC and IEEE committees.
As the project partners of ECCOFLOW have been acting in a competitive environment and as it is important to be aware of such other activities to avoid any conflicts with IP and in order to learn from each other, these activities have been monitored with the following main results:
During the project also other superconducting fault current limiter technologies have been developed further, e.g. inductive concepts. Since efforts in China and Korea concentrate on high voltage limiters above 110 kV and to some extent on other principles like the DC biased iron core, no influence is given from that area. Notably one larger saturated iron core SFCL system for high voltage had been developed in China, and several publications are available. Compared to the technology developed within the ECCOFLOW project, the limitation of such devices is comparatively weak. Positive influence came from the tape supplier SuperPower, which continuously improved material parameters during the course of the project. The project Hydra in the US involves a current limiting cable and Siemens is a direct competitor to Nexans. This results in naturally low influence from these sides.
Impacts – Summary and outlook
Although not all of the long term impacts could be achieved in the lifetime of the project, in ECCOFLOW the essential basis has been laid to assess how to achieve a successful application of the system in a MV grid and therefore facilitate the final breakthrough in technological as well as commercial terms for the HTS device.
The project results will be further exploited by
• Exploring ways to fund the test of the SFCL outside the official project in order to fully make use of the project results accomplished so far
• In parallel, trying to find an installation site in the MV grid of another European utility
• Further participation in standardization activities as well as ongoing dissemination of the project’s results
• Knowledge sharing activities and evaluation of a possible participation in further related European and national research and demonstration projects
Main dissemination activities and exploitation of results
The results of the ECCOFLOW project were disseminated through the following channels / measures:
• Establishment of the project website
• Organisation of workshops with crucial stakeholders in the fields of [HTS properties simulation, application of SFCL technology]
• Participation in relevant conferences
• Exchange with standardisation bodies in the area of fault current limitation and superconductivity
• Organisation of a standalone event dedicated to the presentation the key project results
The ECCOFLOW consortium plans to further spread the achieved results among the relevant target groups. For this purpose contributions to relevant conferences and publication of scientific (peer reviewed) articles are planned.
List of Websites:
For further information on the ECCOFLOW project please contact the website www.eccoflow.org or the Project Coordinator Katrin de Tessières (katrin.de_tessieres@nexans.com) and Achim Hobl (achim.hobl@nexans.com).
The objective of the FP7-funded project “Development and Field Test of an Efficient YBCO Coated Conductor based Fault Current Limiter for Operation in Electricity Networks” (ECCOFLOW) is to develop a superconducting fault current limiter (SFCL) based on coated conductor YBCO tape (cc-tape) and test it in the medium voltage (MV) power grid (distribution level).
The ECCOFLOW consortium composed of major European electric utilities (Endesa, Vattenfall, Westnetz, A2A and VSE), distinguished academic and research institutions (CNRS, KIT, CSIC, EPFL, RSE, IEE and Tecnalia) as well as AirLiquide and Nexans SuperConductors under the lead of Nexans France carried out research work in the period from 1 January 2010 until 31 December 2013 to design, assemble, simulate the functionality and prepare for field testing of a unique SFCL device. In particular, during the course of the project, the following was accomplished:
SFCL design concept: In a first step a detailed design for the whole ECCOFLOW current limiter system was developed. This included comprehensive specifications, models for AC loss and quench simulation, a conceptual and final design for the HTS components, the HTS modules, the cryostat, the bushings, the cooling system, the air coils and the circuit breakers.
Computational / simulation work: Mathematical models have been developed on different levels to understand various effects from a scientific point of view and to safeguard the design of the SFCL device.
Materials and components characterisation: Several tests of different commercially available superconducting YBCO coated conductor (cc) tapes were undertaken in order to further develop characterization parameters for the materials and components of the ECCOFLOW SFCL.
Manufacturing and integration of SFCL device: The successfully manufactured and tested components have been assembled to modules which were integrated into the cryostat. The SFCL device consists of the cryostat together with terminations, cooling and a control system. Switchgear and air core reactors have been added to achieve the specified limitation time of 1 seconds (s).
Extensive testing of the SFCL device: Reliability tests of the device have been realized at a high power laboratory and simulation studies for an installation in the planned applications have been conducted.
SFCL grid integration and operation: The infrastructure for the grid test was provided including the definition of the SFCL parameters and the test requirements with respect to the integration into the distribution grid. Furthermore, a simulation of the equipment under field conditions was accomplished. The SFCL device is currently installed in Mallorca. Field testing has not taken place in the framework of the ECCOFLOW project.
Socio- and techno-economic aspects: The reliability, marketability and cost reduction potential of the device in the medium term was shown in several studies on socio- and techno-economic aspects of the ECCOFLOW SFCL. The studies have been performed both on existing grids of the DNOs Endesa and VSE as well as on generic grids.
The ECCOFLOW project has yielded a number of scientific and technical results for the further development and usage of SFCL devices. It can be concluded that all scientific and technological objectives have been fulfilled. Furthermore, the results achieved in the ECCOFLOW project are not only purely technical, but also of socio- and techno-economic impact.
The consortium aims at testing the SFCL device after the official end of the project in cooperation with most partners of the consortium. For more information please contact the website www.eccoflow.org or the Project Coordinator Katrin de Tessières (katrin.de_tessieres@nexans.com) and Achim Hobl (achim.hobl@nexans.com).
Project Context and Objectives:
Project context:
As a general trend, electric power networks increasingly face higher levels of fault current due to increasing power demand, the rise in renewable and other forms of distributed electricity generation, changing user patterns (e.g. integration of electric vehicles, micro-grids etc.) as well as due to changes regarding the regulatory framework of energy markets. Higher loading poses challenges on the existing equipment and also constraints on the distribution networks. A higher meshing of distribution networks combined with the rapidly growing integration of renewable energy sources leads to an increase of the fault current level with every new installation. As substations ratings are coming to their limits, network operators have to either decline additional installations to their grids or to upgrade if not rebuild complete substations.
A solution to efficiently and economically reduce the fault current level is not only needed in most EU member states but also in many other countries which are facing a fast growing power demand at a given grid infrastructure. SFCLs could provide a solution to address the increasing incidence and level of fault currents and also contribute to improving the performance, stability and efficiency of electricity grids. SFCL are “self-triggering” devices which are employed in power systems to reduce the actual short circuit current that flows during fault conditions. This operation is achieved by a unique property of the HTS material that is the transition from the superconducting state to the normal conducting state under overload current, called “quench”.
Since the discovery of High Temperature Superconducting (HTS) in 1986 scientists all over the world have been working on understanding and improving superconducting materials and exploring their possible technological applications. Several materials have been further developed and tested for different applications. While low-temperature superconductors (LTS) are facing established markets in the medical sector and in high energy physics research, only few HTS based devices so far have reached the pre-commercial development stage as e.g. in the broadband telecommunication. The prospects for HTS devices are predominantly seen in the energy sector and among the most promising future applications are superconducting fault current limiters, electric power transmission cables, electric motors and magnetic levitation devices. SFCLs are unique devices unparalleled in conventional technology. Among all power applications the SFCL is considered the most promising with a view to near-term commercialization. At the beginning of the project the market introduction of HTS devices was impeded by cost and reliability issues as well as a lacking availability of large quantities of HTS material with reliable properties. However, possibilities for economic applications are seen where the relative efficiency, size and weight advantages of HTS devices outweigh the additional capital costs involved or where the unique physical properties of the material make the HTS device attractive.
Superconducting FCL are estimated to fulfil the requirements for a use in medium grids and were, in 2010, foreseen to be marketable in 5 to 10 years. SFCLs offer conclusive advantages in comparison to conventional techniques to limit fault currents such as rapid and effective current limitation, automatic recovery and negligible impedance during normal operation. Moreover, the device does not intercept the current (which would be an issue for fault detection and selective protection schemes), but limits it to an acceptable level for the grid.
In the case of the resistive type SFCL, the ECCOFLOW partners before entering into the project had intensely tested several HTS material options for their use in fault current limiters. The dominating materials for this purpose had been Bismuth Strontium Calcium Copper Oxide (BSCCO) bulk and Yttrium Barium Copper Oxide (YBCO) thin films on sapphire substrate. Status and prospects of the materials are:
• So far, existing SFCL prototypes based on BSCCO material are exhibiting significant AC losses at higher currents which prevent their commercial introduction.
• SFCLs based on YBCO thin films on sapphire substrate do not provide a commercially viable approach, also due to homogeneity and scalability issues.
• The realisation of YBCO (YBa2Cu3O7) thin films on metal tapes (Y-123 cc-tape or YBCO cc also referred to as 2nd Generation or 2G HTS conductor) with sufficient quality and length now offers advantages over the other HTS material options with respect to reliability and price. This new material is considered to be presently the most suitable with excellent perspectives for current limiting applications also at higher operational voltages and currents. The availability of cc-tape in great lengths at reasonable costs makes a commercial breakthrough of SFCL possible with unique features such as compactness, short recovery-time and low AC losses.
In addition to offering a solution to the increasing level of fault currents, the application of SFCL can make the need to replace or upgrade existing equipment in power systems unnecessary. New options for the effective use of existing grid structures arise and result in cost and energy savings. SFCL further have the potential to support the integration of distributed generation sources into existing grids and could be an enabling technology for other HTS devices such as superconducting cables and transformers, leading to further economic and environmental benefits.
The challenges of efficiently and economically limiting the fault current and at the same time dealing with an increased share of fluctuating renewable energy sources, increased power demand and changing consumption patterns combined with the strong demand of network operators and the technological achievements in the field of material development have led some of the most prominent and experienced industrial and academic institutions from Europe to join forces for this project and to develop a coated conductor SFCL based on second generation YBCO conductor.
Please also refer to Figure 1 of the attachments (Figure 1: Context and innovative dimensions of ECCOFLOW).
Project objectives:
The overall objective of ECCOFLOW was to develop and test a three phase coated conductor fault current limiter based on an improved HTS material: the YBCO cc-tape, and to install it in the medium voltage (MV) power grid (distribution level).
Two different installations at two different sites had been chosen for the field tests to demonstrate the reliability and attractiveness of the device. It was intended that the developed device is also the first SFCL appropriate to stay in the grid in the long-run, thus being a unique showcase in the EU for applied superconductivity.
The following two sites chosen for the applications were:
1. Bus-bar coupling: The device was planned to be installed in the Endesa grid (Mallorca, Spain) in the substation 66/15 kV (“San Juan de Dios”).
2. Installation of the SFCL in the grid of VSE (Košice, Slovakia) on the medium voltage side of HV/MV transformer (110/22 kV transformer) to limit short currents on 22 kV busbar and all outgoing feeders (substation “Es Juh”)
Specific scientific and technologic objectives
• Design a full size 2G HTS coated conductor FCL based on the new tape and test it in a real application scenario.
• Establishment of specifications of projected current limiter
• Assessment of different commercially available superconducting YBCO cc-tapes and knowledge increase on the properties
• Simulation of the SFCL behaviour in the electrical grid
• Development of optimised design of SFCL component, cryostat and cooling system and further models for AC losses and quench simulation in an iterative process
• Design and manufacturing of complete SFCL device
• A guideline how to test MV SFCL devices based on common standards for MV equipment
• Type test of whole SFCL device in a certified lab for MV and HV elements e.g. circuit breakers
• Field test of SFCL which means the integration into two different MV distribution grids
• Techno-economical studies about further MV SFCL device installations based on the grid configuration of ENDESA and VSE
Specific commercial objectives
• Achievement of a break-through in technological as well as commercial terms of HTS device and demonstration of superior functionality over existing conventional solutions
• Analysis of cost and benefit of SFCLs in the grid
• Show reliability, marketability and cost reduction potential of HTS device in the medium term
Project Results:
The ECCOFLOW consortium composed of major European electric utilities (Endesa, Vattenfall, Westnetz, A2A and VSE) and distinguished academic and research institutions (CNRS, KIT, CSIC, EPFL, RSE, IEE and Tecnalia) as well as AirLiquide and Nexans SuperConductors under the lead of Nexans France have successfully specified, designed, built and tested a versatile SFCL for the medium voltage grid. The partners achieved in the period from 1 January 2010 until December 2013 the following results:
SFCL design concept: In a first step a dedicated specification for the SFCL system had to be elaborated. This document had to combine all constraints resulting from the two installation sites and to ensure proper interfacing on all levels of hardware and controls. Since one system only had to fulfil the requirements of both sites, operating at 16 kV and 22 kV, respectively, the more demanding and stringent value had to be selected. This was a particular challenge in the view of 1 s limitation time. The detailed specifications and availability of a common terminology, clear definitions and requirements for the limiter help to further progress the market penetration of the SFCL device and future applications.
Based on these specifications a conceptual design for the whole ECCOFLOW current limiter system was developed. As an economical solution to address the 1 s limitation time it was decided to add a set of air core reactors in parallel to the SFCL, and a circuit breaker to reduce the limitation time requirement for the SFCL. During the conceptual design, models for AC loss and quench simulation, designs for the HTS components, the HTS modules, the cryostat, the bushings, the cooling system, the air coils and the circuit breakers have been developed.
A key development objective of the ECCOFLOW current limiter is the high-temperature superconducting component. Therefore, a general comparison of different geometries has been performed with the result that a non-inductive multifilar coil arrangement of YBCO tapes with 12 mm width fulfils best the ECCOFLOW requirements for the two field tests.
Several concepts have been discussed and evaluated to achieve an optimized electrical insulation within the superconducting component. The final design is based on a specific insulator geometry with polyimide attached to the superconducting tape, and a newly developed spacer to ensure liquid nitrogen in contact with the superconductor.
A considerable number of experimental and theoretical investigations have been performed to identify the most suitable low AC loss configuration. There is experimental evidence, supported by numerical models based on finite-element calculations, that the optimal low-loss arrangement of the tape in the SFCL is a pancake wound from tapes carrying opposite currents (bifilar or multifilar arrangement (pancake)). Furthermore, it also has been shown that the use of twins (two tapes instead of one) does not substantially change the AC loss in units of Joule per meter of the used tape. In addition to the AC loss of the HTS material, the losses of the current lead and the cryostat have been optimized.
The design of the HTS module, i.e. the arrangement of the components, has been optimized with respect to a number of criteria including the use of volume, high voltage (HV) issues in the case of lightning surges, losses in the normal conducting connectors, symmetrisation of currents in parallel tapes, and gas evacuation in the short-circuit case. The influence of electro-mechanical forces as well as manufacturing aspects haven been taken into account.
Three different designs for the current leads and bushings have been evaluated for the ECCOFLOW project. The one found to best adapt to the requirements were encapsulated bushings as they were the most compact in the design and provide the highest level of safety.
For ECCOFLOW, several different cryostat configurations have been investigated in detail with the preference given to the design which showed the best compromise between low losses and ease of assembly and disassembly. The chosen cryostat has the following advantages:
• Easy access to the HTS module
• Only one vacuum vessel is used reducing the cost
• Only grounded parts are located close to the HTS coils
• The cryogenic interconnection pipes are located inside the vacuum vessel. This facilitated the assembly and decreased the manufacturing cost
The ECCOFLOW partners identified a closed loop system with GM cryocoolers as the best solution for the SFCL device cryogenic cooling. At nominal operation, liquid nitrogen evaporates through the heat coming from the HTS module, the cryostat and the bushings, and gaseous nitrogen flows to the cold head. The gaseous nitrogen is liquefied through a heat exchanger and liquid nitrogen flows back to the cryostat by gravity. The main advantages of this solution are:
• The maintenance operations are facilitated by a service flange. This flange allows the access to the heat exchanger of the cold head.
• The design ensures a low temperature difference between the cold head and the HTS module even if the distance is significant.
• The design is modular, therefore, it is possible to connect multiple cold heads to the SFCL cryostat with the same cryocooler module design.
• The cold heads could be located outside the high voltage area in order to realize the maintenance operation even if the SFCL is in operation.
• A redundant cryocooler which is not in operation does not involve any heat inputs thanks to vertically guided pipes.
Computational / simulation work: Mathematical models have been developed on different levels to understand various effects from a scientific point of view and to safeguard the design of the SFCL device:
• The superconducting tape has been simulated with respect to the electro-thermal, electro-mechanical, and the AC-loss properties. This was necessary to achieve an optimized superconducting component design. It was particularly difficult to simulate the quenching behavior, since many physical effects, which influence the propagation of a quench, are highly nonlinear.
• The system behavior has been simulated to ensure fulfillment of the specification, especially with respect to the limitation functionality.
• Several models of integrating the SFCL into the grid have been generated to understand the effects of SFCLs in the electrical network. Special focus was put on the improvement potential regarding stability, reliability, and efficiency of the grid. Furthermore it was shown that a much higher level of distributed generation can be added to the grid when integrating SFCLs.
Materials and components characterisation: Several tests of different commercially available superconducting YBCO cc-tapes were undertaken in order to further develop characterization parameters for the materials and components for the SFCL device. The tests and measurements included:
• Critical current homogeneity of the samples
• Resistance as a function of the temperature
• Quenching behavior under varying prospective currents
• Mechanical testing for stress strain properties
• Thermal expansion
• Mechanical properties of insulation-tape composite
• Effects of wrapped insulation on critical current homogeneity
The level of coated conductor stabilization was one of the main parameters to be fixed before being able to order the tape. Several models were developed and experiments performed to obtain the final level of stabilization, which results in a required silver coating thickness on the conductor. Higher stabilization gives more stable tapes, but results in longer length and therefore in higher costs. The safe and optimum value had been chosen extremely carefully. In this context, critical current and stabilization inhomogenity represent one of the biggest challenges for a highly reliable SFCL.
The profile of the critical current density across the width of the tape is an important factor for the AC losses of the selected conductor. With the help of magnetic field mapping and a dedicated inversion procedure the profile of the critical current density over the width of the tape was found. The influence of tape non-uniformity on AC loss was investigated. The observed reduction of the critical current density was included in the numerical calculations of AC loss in the multifilar pancake configuration. The results showed that a degradation of transport capability at the tape edges could increase the AC loss significantly compared to an ideal tape with constant critical current density across the width.
Manufacturing and integration of SFCL device: A detailed design for realisation of the complete system including all electrical, mechanical, thermal and cryogenic aspects of the limiter, e.g. the terminations, cryostat, cryocooler and limiter module including instrumentation has been developed. Based on the parameters of the single superconducting limiter component, a detailed design of the HTS module has been established regarding all mechanical fixations and electrical connections as well as the dielectric strength with respect to the cryostat on ground potential.
Terminations have been designed and manufactured according to the electrical specifications, norms and regulations for power equipment (lightning impulse tests, partial discharge, etc.) and to the high current of the limiter. In a prior validation step prototypes of these terminations had been successfully tested under cryogenic conditions (77 K / atmospheric pressure) with up to 50 kV AC withstand and up to +/- 125 kV lightning impulse test.
A cryostat was designed and manufactured with a low loss, highly reliable cryogenic system that fulfils all general safety requirements. Boundary conditions for later series productions were also taken into consideration. A vacuum- and multi-layer-insulation was foreseen to reduce thermal losses from radiation and conduction inside the cryostat. The final solution for the cryostat is using only one vacuum vessel, where also the cryogenic interconnection pipes are located. The three cryogenic nitrogen vessels reduce the heat input and can be opened e.g. for assembling or maintenance. A closed cooling system with cold heads was developed. To ensure a re-cooling period of less than 30 s, it was necessary to blow off nitrogen gas after a short-circuit event. Therefore, a refilling valve and reserve volume of LN2 inside the cryostat has been integrated in the system.
Furthermore, all SFCL device elements were manufactured and integrated. A document on the definition of all relevant interfaces of the device had been prepared. Major parts for the electrical integration in a power network are the circuit breaker in line with the superconducting fault current limiter and the air coils in parallel. This arrangement facilitates very long fault durations. All relevant parts of the SFCL are arranged inside a modified 20’ ISO-container, the circuit breakers are inside a small switchgear building. The air core reactors are air insulated and have been connected to all respective other elements using standard medium voltage cabling.
Extensive testing of the SFCL device: At the beginning of the project no comprehensive guideline for testing SFCLs was available. A set of parameters to be used during the device testing has been developed in order to ascertain the current limiting performance of the SFCL device. Finally, guidelines for the testing of MV-class SFCL devices have been developed. The most important test were the current limitation tests under full and partial load, dielectrical test (power-frequency withstand voltage test, partial discharge test, lightning impulse test) to validate the insulation concept, as well as leak and performance tests on the cryogenic system. As a prerequisite to the system limitation tests, the limiter components had individually been tested before assembly. The system has successfully passed all tests.
Guidelines developed during the project can be used as a basis for future SFCL devices as well as for developing and implementing international technical standards to maximize compatibility, interoperability, safety, repeatability, and quality of the systems.
SFCL Grid integration and operation: After identifying the ideal substations for the integration of the SFCL, where an important aspect was a large number of expected short-circuit events, all parameters for the SFCL have been defined. The grids have been analysed in detail to fully understand the performance with and without SFCL. The infrastructure for the grid test was provided including the necessary foundations, connections to the medium voltage grid and to the low voltage grid for the power supply. The data exchange and safety concepts have been specified and realised. Furthermore, a simulation of the equipment under field conditions was accomplished. The SFCL device is now installed in Palma on Mallorca island. Due to delays accumulated during the project, the field testing did not yet take place in the framework of the ECCOFLOW project. The partners are aiming at field testing the device after the official end of the European project.
Socio- and techno-economic aspects: The ECCOFLOW project led to a break-through in technological as well as commercial terms of the HTS device as it developed a ready-to-use system that can easily be integrated into different grid scenarios. An enormous development has in parallel also happened in terms of technology, availability, and cost situation for superconducting tape, partly driven by the demands and dissemination activities of the ECCOFLOW project. Furthermore, the reliability, marketability, and cost reduction potential of SFCL devices in the medium term was shown in several studies on socio-technical aspects based on the grids of VSE and ENDESA.
Potential Impact:
In the long run, the results of the ECCOFLOW project can support the establishment of a market for HTS-based devices in electricity networks, as foreseen as an expected strategic impact in the work programme FP7-Energy-2009-1 related to the grant agreement of this project.
This, in turn, can lead to an improvement of the performance, stability, and efficiency of electricity networks potentially leading to the following socio-economic impacts and wider societal implications:
• Major economic advantages: efficiency gains in existing networks, reduction of capital expenditure for the maintenance or upgrade of grids, less stress and longer lifetime for existing grid components and higher network reliability.
• Important contributions to the efficiency and security of electricity networks in Europe and to achieving strategic objectives of EU policy, such as the goal of the SET plan to improve energy efficiency and the objectives of the EU Energy and Climate Package and the Energy Roadmap.
• Positive environmental effects by reducing CO2 emissions and the achievement of the 20-20-20 goals.
As far as the more direct impacts of the ECCOFLOW project are concerned, its results constitute a crucial cornerstone for the assessment of the optimized technical specifications and market entry strategies at a larger scale for HTS devices.
In the following, the project impacts will be described for the categories of
a) Technological and scientific impacts and
b) Impacts on business opportunities and market commercialization
Technological and scientific impacts – short-term
The ECCOFLOW project has thoroughly prepared the technological basis and scientific advancement for a feasibility assessment regarding the large-scale application of a HTS device in a real MV distribution network. This has been achieved by the proof and assessment of the functionality of the SFCL based on YBCO tape which has not been demonstrated before. In the following, potential impacts are displayed according to the results achieved:
• The optimized technical dimensions and the design (components, modules, SFCL) of a 24 kV, 1 kA three-phased coated conductor resistive fault current limiter have been determined and parameters of HTS materials and components have been defined.
A potential impact of this is an enhanced transferability for similar HTS devices and applications. For example, the results of the test of different YBCO tapes for SFCL and the electrical and thermal characterization of commercial superconducting YBCO tape could be used in the construction of SFCLs, cables, rotating machines, transformers, and other HTS devices.
• The superconducting components, modules, and terminations have been integrated into the cryostat. In total, a complete and successfully tested SFCL system has been provided including control and protection systems.
A related impact will be the facilitation of large-scale production of SFCLs or, in general, HTS devices due to practicable knowledge gained about component integration, manufacturing and assembly as well as system design and integration.
• From a scientific point of view, the lessons learnt about the overall specification and the results of simulations and tests concerning AC loss optimisation, quench and limitation behaviour will most likely lead to an acceleration of related future research activities and enhancement of quality of scientific lectures.
• The results and scaling laws achieved are in many respects applicable also for high voltage SFCLs. Therefore, ECCOFLOW builds a solid base for follow-on development also for larger systems.
Technological and scientific impacts – long-term
The results of the final techno-economic analysis on the introduction of SFCLs for the planning of a new system and economical assessment could lead to a significant advancement regarding an optimal utilisation of the possibilities that HTS-based devices may constitute for the operation of smart electricity networks through enhanced knowledge on:
• Impact of SFCLs in existing distribution network architecture
• Innovative distribution networks planning integrating SFCLs
More specifically, the analysis conducted will impact the future design of SFCLs for operation in electricity networks, particularly in MV power grids, due to the following results:
• Possible equipment cost reductions (for new investments)
• Increase in renewable energy integration potential
• Quality of supply improvement
• Reduction of electricity losses
• Models for current distribution in operating HTS
• Future design perspectives and benefits for smart grids
• Social and environmental benefits
As a specific result of the grid application studies it turned out that meshing the grid is often possible using SFCLs with only low nominal current rating, and, consequently, comparatively low capital and operation costs. Therefore, relatively “cheap” devices at strategic points of the grid can drastically increase the compatibility of the grid with a large fraction of distributed generation and at the same time provide a high reliability of electricity supply.
The results will further impact the design and implementation of future EC energy policy and regulatory issues.
Impact on business opportunities and market commercialization
The achievement of a final break-through in technological as well as commercial terms includes opening
• new market opportunities for the producers of the device and
• new design opportunities for electric network operators.
In the course of the project, more specific information has been gathered on future marketability of such devices and its influence on the planning and design of smart network architecture.
The market potential is significant and the interest of electric utilities across Europe is evident, due to the SFCL being a technological novelty and a unique device offering extensive benefits for the users, such as improved functionalities and numerous potential applications. The interest is underlined by increasing numbers of inquiries from network operators for SFCL systems reaching the industrial partners of the ECCOFLOW consortium.
The reliability tests of the device conducted at the high power laboratory and simulation studies for an installation in the planned applications have shown the functionality for a large scale application. As regards the projections of first applications of the SFCL technology and related market prospects, the following applications are considered as the most promising ones:
• In the short term, an application in distribution substations is foreseen. Currently, there are around 50,000 substations in Europe with a life time of about 40 years.
• The SFCL technology enables coupling of different sub-grids (at same voltage level) within the electricity grid to reduce the number of in-feed transformers.
• Equally, the SFCL can support the coupling of dispersed generation units (e.g. wind power stations and combined heat & power) in the grids.
• The device can be an enabling technology for other superconducting applications such as HTS power cables, transformers, generators, etc. At present, this is demonstrated in a German funded project combining a SFCL with a HTS cable.
• In the long run, there is substantial potential for wider transferability (e. g. positioning of the limiter in other parts of the grids).
Spreading of results and influence of other ongoing activities
The great efforts regarding the spreading of interim and final project results on European and international scale involving the main target groups of electric utilities (Utility Board), other stakeholders in the electricity sector, general industrial operators and the scientific community realized by the project consortium, as described below, greatly contributed to raising awareness of the potential of the SFCL and HTS devices in general and stimulating the demand.
In this project, important contributions to international standardization activities (establishment of international standards, e.g. CENELEC and IEC) on fault current limiting devices related test procedures could be realized through the active participation and membership of various partners in several CIGRE working groups and IEC and IEEE committees.
As the project partners of ECCOFLOW have been acting in a competitive environment and as it is important to be aware of such other activities to avoid any conflicts with IP and in order to learn from each other, these activities have been monitored with the following main results:
During the project also other superconducting fault current limiter technologies have been developed further, e.g. inductive concepts. Since efforts in China and Korea concentrate on high voltage limiters above 110 kV and to some extent on other principles like the DC biased iron core, no influence is given from that area. Notably one larger saturated iron core SFCL system for high voltage had been developed in China, and several publications are available. Compared to the technology developed within the ECCOFLOW project, the limitation of such devices is comparatively weak. Positive influence came from the tape supplier SuperPower, which continuously improved material parameters during the course of the project. The project Hydra in the US involves a current limiting cable and Siemens is a direct competitor to Nexans. This results in naturally low influence from these sides.
Impacts – Summary and outlook
Although not all of the long term impacts could be achieved in the lifetime of the project, in ECCOFLOW the essential basis has been laid to assess how to achieve a successful application of the system in a MV grid and therefore facilitate the final breakthrough in technological as well as commercial terms for the HTS device.
The project results will be further exploited by
• Exploring ways to fund the test of the SFCL outside the official project in order to fully make use of the project results accomplished so far
• In parallel, trying to find an installation site in the MV grid of another European utility
• Further participation in standardization activities as well as ongoing dissemination of the project’s results
• Knowledge sharing activities and evaluation of a possible participation in further related European and national research and demonstration projects
Main dissemination activities and exploitation of results
The results of the ECCOFLOW project were disseminated through the following channels / measures:
• Establishment of the project website
• Organisation of workshops with crucial stakeholders in the fields of [HTS properties simulation, application of SFCL technology]
• Participation in relevant conferences
• Exchange with standardisation bodies in the area of fault current limitation and superconductivity
• Organisation of a standalone event dedicated to the presentation the key project results
The ECCOFLOW consortium plans to further spread the achieved results among the relevant target groups. For this purpose contributions to relevant conferences and publication of scientific (peer reviewed) articles are planned.
List of Websites:
For further information on the ECCOFLOW project please contact the website www.eccoflow.org or the Project Coordinator Katrin de Tessières (katrin.de_tessieres@nexans.com) and Achim Hobl (achim.hobl@nexans.com).