ACTIVE NETWORK MANAGEMENT (ANM) TECHNOLOGY Current Technology Issues and Identification of Technical Opportunities for Active Network Management

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1 ACTIVE NETWORK MANAGEMENT (ANM) TECHNOLOGY Current Technology Issues and Identification of Technical Opportunities for Active Network Management CONTRACT NUMBER: DG/CG/00104/00/00

2 CURRENT TECHNOLOGY ISSUES I AND IDENTIFICATION OF TECHNICAL OPPORTUNITIES ORTUNITIES FOR ACTIVE NETWORK MANAGEMENT (ANM) ( CONTRACT NUMBER: DG/CG/00104/00/00 URN NUMBER: 08/621 Contractor Sinclair Knight Merz The work described in this report was carried out under contract as part of the BERR Emerging Energy Technologies Programme, which is managed by AEA Energy & Environment. The views and judgements expressed in this report are those of the contractor and do not necessarily reflect those of the BERR or AEA Energy & Environment. First published 2008 Crown Copyright 2008

3 EXECUTIVE SUMMARY This project was sponsored by the Distribution Working Group (DWG), an industry group seeking to prepare distribution networks in Great Britain for a low carbon future. The project has considered current technology issues and opportunities with regards to active network management (ANM), and produced a practical set of recommendations aimed at enabling a near term increase in ANM. A separate DWG project underway at time of writing will consider non-technical ANM barriers and opportunities. It is found that there are currently no significant technical barriers to ANM. Generally, new technologies follow a path from academic research, through to desktop simulation, development, pilot projects, large scale trials and then eventually to full implementation. A literature review found that a large body of work exists on the subject of ANM technologies, and that many new technologies are nearing the latter stages of development in the UK. Various industry working groups and regulated incentive schemes, in particular the IFI and RPZ 1 mechanisms have been reasonably effective in encouraging Distribution Network Operators (DNOs) and manufacturers to bring forward ANM pilot projects. However, ANM appears to remain a somewhat niche area of development for DNOs. Several promising technologies for facilitating ANM were considered for detailed assessment. Particular emphasis was made on the operational robustness of different technologies, ie the impact of integrating a new technology into the existing network. For this project, a technology was defined as a new device, an existing device that could be used in a different way or a new system, method or practice that might enable ANM. The chosen technologies were: Inline voltage regulators SVCs and STATCOMs Active voltage controllers Dynamic line rating systems Each of these new technologies or new applications of an existing technology has or is currently undergoing a trial phase somewhere on the network. They are each therefore available commercially now or expected to be in full commercial mode within the next 5 years. It should be noted that this is not an exhaustive list of such technologies. An overview was given of each technology, and then they were assessed against the following factors: Technical functionality and barriers Operational impact Planning impact 1 Innovation Funding Initiative (IFI) designed to encourage research and development, and the Registered Power Zone (RPZ), also to encourage research and development but specifically in relation to connecting distributed generation ii

4 Other issues, including eligibility for IFI/RPZ funding It is found that each of the four technologies could be an appropriate solution to certain network problems in particular circumstances. It is therefore recommended that DNOs make the necessary changes throughout their organisations to incorporate these technologies into their standard kit of solutions when considering options for network investment. This will provide the DNOs with greater flexibility to meet network needs, particularly DG connections. However, greater flexibility might also represent a new challenge for DNOs who have traditionally been used to dealing with a more limited set of options. It is recommended that manufacturers seek to work closely with DNOs across all areas of their businesses to help fully implement new technologies. Particular attention needs to be paid to the planning department of a DNO business where many of the investment decisions are made, and where new tools and a fuller understanding of the impact of the new technologies might be required. The importance of full demonstration of a project to DNOs (who are driven in large part by security, reliability and safety) is also emphasised, as is the need to reduce the cost and complexity to implement, operate and maintain products that are new to the organisation. It is recommended that the RPZ and IFI schemes be revised to provide an incentive for DNOs to take up the best technologies trialled by other DNOs, thus propagating best practice throughout the industry. DNOs should conduct regular reviews of their network to determine if there are any opportunities to gain benefit from implementing new technologies under these schemes. In addition, the DWG might be able to play a role in coordinating DG developers and DNOs to find suitable areas of the network to implement an RPZ. Such areas must have particular network conditions and be attractive to developers. Existing Electricity Networks Association (ENA) guidelines, ETR 124 and 126, on implementing ANM technologies were originally a useful summary of possible solutions but now appear lacking in detail. Ideally, these will be updated following successful completion of the various trial programmes currently underway on the network. In addition, the existing technical standard defining network voltage limits might benefit from a review to cater for the changing network conditions, particularly increasing amounts of distributed generation and ANM. Finally, it is recommended that all future projects sponsored by the DWG include an update of the ANM pilots and trials register developed under a previous DWG project. iii

5 CONTENTS Executive Summary... ii 1 Introduction Aim of the Project Definition of ANM and ANM Technologies Methodology Summary of Issues Driving ANM Technical Regulatory and Commercial Drivers Literature Review Existing ANM Outcome of the Existing Practices Report Results of the IFI and RPZ Mechanisms Innovation Funding Initiative (IFI) Registered Power Zones (RPZ) Effectiveness of the RPZ/IFI Mechanisms Literature Review New and Emerging Technologies Common Themes New Technologies Report ANM Register Other Projects of Interest from the ANM Register ENA Reports Dynamic Equipment Rating Control DGFACTS Selection of Technologies for Appraisal Primary Plant Secondary Plant Rejected Technologies Technology Appraisal Assessment Methodology General Technical Operational Planning Other Detailed Analysis Inline Voltage Regulators Overview Technical Issues Operational Issues Planning Issues Other Issues Synchronous Compensators: SVCs and STATCOMs Overview iv

6 6.2.2 Technical Operational Planning Voltage Control by Active Controllers Overview Technical Operational Planning Other Dynamic Line Rating Overview Technical Operational Planning Other Summary of Results Recommendations Introduction Manufacturers General Inline Voltage Regulators SVCs and STATCOMs Active Voltage Controllers Dynamic Rating Systems DNOs Integration of New Technologies and Practices Regular Network Reviews Specific RPZ Opportunity Asset Replacement DG Developers IFI/RPZ Schemes Technical Standards for Voltage ENA Guidelines DWG Conclusions Appendix A Project P01 Active Network Management Definitions... 1 Appendix B Glossary... 1 Appendix C Sample Questionnaire... 2 v

7 1 INTRODUCTION The Electricity Networks Strategy Group (ENSG) is an electricity industry group sponsored by the Department of Trade and Industry (now the Department of Business Enterprise and Regulatory Reform, BERR) and Ofgem. It seeks to identify, and co-ordinate work to address the technical, commercial, regulatory and other issues that affect the transition of electricity transmission and distribution networks to a low-carbon future 2, and builds upon previous similar programmes. The Distribution Working Group (DWG) is a subgroup of ENSG, coordinating a number of projects in various work streams specifically aimed at distribution networks. One of these streams, Work Programme Three, Enabling Active Network Management, considers the ways in which Distribution Network Operators (DNOs) can actively manage their network to better facilitate low carbon power systems with efficient use of investment. Sinclair Knight Merz (SKM) was commissioned to support Work Programme Three - Project Six: Current Technology Issues & Identification of Technical Opportunities for Active Network Management (ANM). 1.1 Aim of the Project The aim of this project is to summarise the current known technology issues and identify potential technical opportunities in undertaking active distribution network management 3. In particular, the aim is to produce a practical set of recommendations that might lead to some immediate action, whether by DNOs, manufacturers, the regulator or other stakeholders. Particular emphasis was made by the DWG Project Team on assessing the operational robustness of different technologies, ie the impact of integrating a new technology into the existing network. A separate DWG project, Work Programme Three, Project Five: Addressing Current and Emerging Commercial, Legislative and Regulatory Barriers, underway at the time of writing this report, will consider non-technical issues. The scope of this project was limited to technologies intended to apply in the voltage range of 11 kv to 132 kv and either available now or expected to be in full commercial mode within the next 5 years. 1.2 Definition of ANM and ANM Technologies Programme 3 Project 1 produced a definition of Active Network Management (ANM), which is included in Appendix A. This can be summarised as: ANM means devices, systems and practices that operate pre-emptively to maintain networks within accepted operating parameters. ANM may be compatible with automation of the network to speed supply restoration following an abnormal event, and increased visibility and control of the network to facilitate management practices 4. For this project, a technology is defined as: From the project brief 4 Modified from A Technical Review and Assessment of Active Network Management Infrastructures and Practices, EA Technology,

8 a new device; an existing device that could be used in a different way; or a new system, method or practice, that might enable ANM. 1.3 Methodology The methodology was as follows: 1. A review of the recent relevant Work Programme reports. a) Work Programme 3, Project 3 (the Existing Practices Report ), completed by EA Technologies Ltd 5 ; b) Work Programme 3, Project 4 (the ANM Register ), completed by University of Strathclyde 6 (and a review of the reports referenced in the register); and c) Distributed Generation Coordinating Group Workstream 5, Project 10 (the New Technologies Report ), completed by PB Power A review and summary of current ANM initiatives undertaken by DNOs. 3. A number of technologies were selected for further appraisal from the New Technologies Report and the ANM Register, taking into account how they would fit into the distribution networks as identified in the Existing ANM Practices report. The DWG project team were provided with an interim report at this stage and hence consulted before finalising the selection. 4. A set of criteria for evaluating the technologies was developed and also discussed with the project team, and this is presented in this report. The criteria were based on the priorities of the DNOs in the areas of operability and key parameters such as safety, the environment, operating and maintenance costs and reliability of supply. 5. Questionnaires were sent to manufacturers of the chosen technologies where there was not sufficient data available from the literature review (Areva, GE Energy and ABB). The format of the questionnaires is given in Appendix C. 6. The technologies were then considered against the evaluation criteria. 7. Recommendations were made based on the resultant findings. 5 A Technical Review and Assessment of Active Network Management Infrastructure and Practices, EA Technology, 2006 [Existing Practices Report] 6 Register of Active Management Pilots, Trials, Research, Development and Demonstration Activities, University of Strathclyde, 2006 [ANM Register] 7 New Technologies to Facilitate Increased Levels of Distributed Generation, PB Power, 2006 [New Technologies Report] 2

9 1.4 Summary of Issues Driving ANM Technical One of the most significant recent changes to distribution networks that are driving closer examination of the potential benefits of ANM in Great Britain are increasing levels of Distributed Generation (DG), particularly wind generation. The impacts of increasing levels of DG on traditionally passive distribution networks have been well documented, and consist primarily of: Increased fault levels, potentially exceeding equipment fault level ratings; Increased power flows, potentially exceeding equipment thermal ratings; and Changing power flows, potentially causing voltages at various places on the network to deviate from acceptable levels. It is expected that carbon polices, energy prices and other factors will drive not only DG but also increased levels of Demand Side Participation (DSP) from customers or their suppliers. This might also place additional technical demands on the network, primarily in the form of a need for greater levels of status information. Although load growth in Great Britain is relatively low, pockets of the networks are experiencing significant load growth. The increased power flows can cause problems with exceeding equipment thermal ratings, and/or causing excessive volt drop. In heavily urbanised areas (such as inner-cities), access to some DNO assets can be difficult due to transport, infrastructure density (such as other services in the same location) and other logistical difficulties. This might provide incentives to increase levels of automation to avoid delays sending personnel to the site, which is turn relates to regulatory penalties and incentives to improve reliability. Finally, the age of the UK networks means that a significant amount of the equipment installed in the post war period of network expansion is reaching the end of its lifetime, triggering large asset replacement programmes. This provides both a problem to be resolved and funded but also an opportunity for DNOs to introduce new technologies Regulatory and Commercial Drivers DNOs, like any business, have a commercial imperative to meet both current and future customer (end consumer, load and generation developers) needs and expectations. Improving the quality and reliability of electricity supplied to end customers has driven some of the major changes in distribution networks since privatisation, and safety for staff, the public and the environment is a key concern. In addition, there are regulatory drivers on DNOs, including those resulting from the price control process. Active networks might help reduce or defer capital expenditure in some situations, but until recently the facilitating technologies have often been seen as new and unproven, and it is not always easy to compare the lifetime costs of active networks with traditional reinforcement schemes. There is some doubt about whether the price control mechanism gives appropriate signals with regards to a lower capex but higher opex and shorter lifetime active network solution. 3

10 Active network design and planning to date has proved to be far more time consuming than traditional reinforcement methods. Ofgem and the DNOs are already considering how the balance between opex and capex drivers might change in the next price control period, which will potentially strengthen the drivers for ANM. These matters are being further considered in Project Five. In 2005, Ofgem created two new incentive schemes to encourage DNOs to explore novel methods, known as the Innovation Funding Initiative (IFI) and Registered Power Zones (RPZ). IFI provides a level of funding to DNOs for research and development projects aimed at delivering value to end consumers. The RPZ mechanism builds upon the existing DG mechanism which encourages DNOs to reduce the cost of deep reinforcements. The RPZ specifically provides an additional incentive to DNOs to connect generation in an innovative way. For the RPZ and IFI schemes, innovation is measured by Ofgem in accordance with published criteria 8. In assessing ANM technologies, this report considers whether they meet the criteria for funding under these two schemes. Another regulatory driver is the security standard P2/6 and the related key performance indicators of Customer Minutes Lost (CML) and Customer Interruptions (CI) and their associated financial penalties and incentives. The benefits of technologies that can make an impact on CML and CI can be readily quantified, and hence make the decision making process of whether to implement a new technology simpler and faster than if the benefits are less tangible. 8 ENA Engineering Recommendation G85, Electricity Networks Association, 2005 [ER G85] 4

11 2 LITERATURE REVIEW EXISTING ANM 2.1 Outcome of the Existing Practices Report The aim of Programme 3 Project 3 project was to review and document the current approaches and infrastructures for network monitoring and active operation control across the DNOs. The authors surveyed the DNOs to determine what control and communications equipment was employed across the network at the time of the survey, as well as more specifically what ANM practices were being used. The report also considered new technologies and potential barriers to their implementation. One of the key findings from this report was that DNOs currently and increasingly have large numbers of intelligent electronic devices (IED), such as programmable protection relays, embedded in their system which could be used as key components in a system to provide greater levels of active control over parts of the network but whose functionality potential is largely untapped. 2.2 Results of the IFI and RPZ Mechanisms Innovation Funding Initiative (IFI) The DNOs have initiated a number of projects under the IFI mechanism, including projects considering ways to allow more generation onto the network with less capital cost than traditional solutions. A small selection of ANM projects relevant to the technologies being considered in this report is given below. More information is found in each of the DNOs annual IFI reports. DNO Collaborative Aura-NMS project Collaborative Strategic Technology Programme Collaborative EDF EDF E.ON Central Networks E.ON Central Networks E.ON Central Networks Project Description Development of an integrated and repeatable active controller Several projects aimed at enabling connection of DG Investigation of superconducting fault current limiters Development of state estimation algorithms for the whole distribution system Electricity storage and DSP technologies Integrated sensor and monitoring system for advanced distribution automation Research and development for a solid state power transformer Investigation of magnetic fault current limiters Scottish Power North Wales inline voltage regulator to facilitate DG connection 9 Scottish Power Scottish Power Development of a battery system for energy storage Trial of a new voltage control relay using measurements from DG feeder current transformers to refine overall Automatic Voltage Control (AVC) relay response 9 Modelling the Interaction Between an In-Line Voltage Regulator and a Doubly-Fed Induction Generator, Tegni Cymru Cyf, EA Technology, SP Power Systems, UMIST,

12 Scottish Power Scottish and Southern Energy Scottish and Southern Energy United Utilities Thermal modelling and development of a dynamic ratings system Study to determine if energy storage will allow more renewable generation to connect on the isolated Shetland Island network Development of a distribution power electronics voltage regulator for the 11 kv and 33 kv networks Development of a software tool for fair allocation of distribution losses to DG Registered Power Zones (RPZ) The RPZ mechanism has triggered three projects to be registered with Ofgem to date, namely: Orkney Islands active network management (33 kv) Scottish Hydro Electric Power Distribution Skegness & Fens dynamic line ratings (132 kv) Central Networks (E.ON) Martham Primary GenAVC voltage control in Norfolk (11 kv) EDF Energy The existing RPZ projects are of particular relevance to this study as they provide some of the only real demonstrations of the use of ANM in the UK. Scottish Hydro Orkney Islands RPZ The Orkney Islands has recently seen a rapid expansion of connected DG due to its significant renewable energy resources 10. Changing from being a net importer to a net exporter of electricity caused a number of problems. The first was significant voltage rise on the island s 33 kv network as well as the two main subsea cables connecting the island to the mainland and radial feeders out to smaller islands with connected generation. These voltage problems were resolved by installing a dynamic VAr compensator (DVAr) and shunt reactors for the more localised voltage problems on the radial feeders. The DVAr had the added advantage of providing a local controllable source of reactive power to address what would have otherwise been short term voltage excursions on changing demand and supply patterns. The authors of the report on the scheme considered the introduction of the DVAr onto the network a success. The second problem encountered on Orkney with increasing amounts of connected DG was that of exceeding thermal limits. This problem was solved primarily through commercial means, enabled by standard and communication technologies (although using quite novel logic sequences). Extensive power simulation studies were done to create a range of scenarios which were then converted into ladder logic for the controllers. Generator maximum outputs were then controlled on the basis of last on, first off to keep the system within the theoretical limits determined by the studies. As the maximum transfer capacity of the subsea cables has already been reached by existing generation, new generation must fit into the gaps created by the intermittency of existing generation and increasing load, which is managed by the ANM scheme. 10 Facilitate Generation Connections on Orkney by Automatic Distribution Management, Scottish and Southern Energy,

13 An interesting feature of the ANM is that the decision was made to set the generation limit based on thermal limit of both subsea cables in operation. A more conservative, traditional approach might have been to set the limit at the limit of the lower rated cable, which would have effectively halved the total allowable generation. The report on the scheme notes that these cables have never experienced a fault. In the event of one of the cables tripping, the ANM scheme trips sufficient generation to remain within the thermal limit of the remaining cable. This intertripping scheme operates before the overcurrent protection on the second cable, which has sufficient time delays to allow this to occur. The ANM on Orkney Island also incorporates dynamic load switching, which has been in place since before the increase of DG beyond capacity of the main feeders, using publicly broadcast radio signals. A key ongoing concern regarding this ANM scheme will be logic complexity. Each new DG and each change in configuration of the network is likely to require changes to the logic controlling the scheme. Although the cost of actually making the changes for each new scheme might be capitalised, it is likely that the scheme will also impact on the operational expenditure of the DNO with additional switching complexity, resources, training, contract administration with the DGs and so on. The result of this scheme will be to allow generation to connect to the network up to the economic levels determined by the amount of time that generation is likely to be constrained. Without this scheme, an expensive new subsea cable would be required before additional DG could be connected. It should be noted also that this scheme exploits the intermittent nature of wind generation. E.ON Central Networks Skegness RPZ The trigger for the Central Networks RPZ was a series of generator connection requests near a line that did not have sufficient thermal capacity when determined using traditional rating methods. Traditional line rating methods in accordance with Engineering Recommendation P17 make conservative assumptions regarding ambient temperature, which results in a reduced allowable power flow than theoretically possible for most of the time. Calculations by E.ON 11 showed at best a doubling of line capacity between the best case predicted by traditional methods (ie the winter rating) and the best case likely to occur with real time dynamic rating. This scheme will be implemented by using two weather stations to feed back data to the existing central control system (using the ENMAC SCADA system), which will then dynamically calculate the ratings to the lines. After determining the ratings, the modified control system will take action to constrain the generators if necessary. As an additional safeguard, the scheme will use a device to measure (rather than calculate) actual line temperature and sag. This will be used to verify the dynamic rating calculations and the location of the weather stations. Without this scheme, as with the Orkney scheme, an expensive new line with new wayleaves would be required before the new DG could be connected. Again, this scheme exploits the particular characteristics of wind generation, but this time to use the high 11 An Introduction to Central Networks RPZ, Martin Orme, E.ON, presented at the IET Active Networks Workshop

14 coincidence of high power output with high wind speed leading to lower conductor temperatures and associated higher line ratings. A final similarity with the Orkney project is that it relies on contractual arrangements with the generators to constrain them down on a last on, first off basis. The cost of this scheme has been estimated at 270,000 to connect 90 MW of additional generation capacity 12. It should be noted that EDF have also implemented a dynamic ratings scheme using weather stations and the Power Donut on 132 kv lines to avoid reinforcement costs following connection applications from wind generators. EDF Energy GenAVC Martham Primary RPZ The Martham Primary RPZ is one of the test sites for the GenAVC product being developed by Econnect and has been registered as the third RPZ. Under previous programmes of the DGCG and the DWG and other such activities, a considerable amount of research has been directed towards developing algorithms to actively control the AVC relay setpoint at primary substations so that voltages are maintained within limits at all parts of the downstream network even when DG is connected. The GenAVC is one of the results of that research effort. It has successfully been actively controlling the voltage for the Martham 11 kv network since late As a further part of this project, an assessment tool is being developed 13 to allow planners to determine whether GenAVC was appropriate in any given place. EDF are now planning to trial a commercial version of GenAVC at another site at Steyning where a DG is experiencing trips at times of low load. Before making this decision, EDF supplied network data to Econnect, who verified the output of the assessment tool using system studies. It should be noted that the GenAVC has also been installed at a location on the United Utilities network. In addition, EDF and Scottish Power are involved in a similar project being developed by ABB, the AuRA NMS. Other RPZ Studies Although other DNOs besides those mentioned above have undertaken various studies to determine if they can also take advantage of the RPZ scheme, no others have been registered. In particular, CE Electric UK commissioned a study by Econnect to examine the feasibility of setting up RPZs in two areas using energy storage technologies to avoid other forms of network reinforcement. 14 The studies concluded that such an approach was not economically feasible at that time. 12 New Power Zones will Connect More Renewable Generators to the Electricity Network, Ofgem Press Release, EDF Energy Networks Ltd IFI/RPZ Report for EPN/LPN/SPN, EDF Energy, Registered Power Zones, Assessing the Feasibility of Establishing Power Zones on Northern/Yorkshire Electricity Networks, Econnect,

15 2.3 Effectiveness of the RPZ/IFI Mechanisms The RPZ and IFI schemes have successfully triggered greater levels of ANM activity than was occurring previously, and several ANM technologies are now entering the full demonstration mode because of these initiatives. It remains to be seen if these demonstration projects will lead to widespread adoption of the technologies. An important feature of the RPZ mechanism is that the innovative technology or use of a technology must not have been used before in the UK. This might encourage a broad spectrum of new technologies and approaches and do nothing to ensure the most successful are propagated amongst the companies. 9

16 3 LITERATURE REVIEW NEW AND EMERGING TECHNOLOGIES 3.1 Common Themes The literature review found reasonable correlation between the technologies identified and discussed. One notable feature that emerges from the documentation on ANM and the related topics of increasing distributed generation and load management is that despite this considerable research effort, there is little evidence world-wide of a major shift towards implementing ANM. ANM appears to remain a somewhat niche area of development for DNOs. In general, the most mature efforts in the UK appear to have been in the area of voltage control, followed by overcoming thermal limits. This is probably in part because these two factors are often the first limits when connecting DG. The literature review found that the DNOs have several intelligent devices that could facilitate greater ANM, but that they have largely not used the functionality of these devices or adopted the necessary systems and processes to do so. Some reasons for this have been suggested, and this issue is examined in more detail later in this report. 3.2 New Technologies Report The DG Coordinating Group (DGCG) preceded the DWG. Workstream 5 Project 10 project, of which the New Technologies Report was the outcome, was designed to address the following principle objectives: To identify what new technologies are available or emerging (in UK and world-wide) to facilitate increased levels of DG in the time frame to 2010; and To provide a summary of the status of emerging technologies to help inform decisions about what further work might be appropriate in this area. The New Technologies Report recommends a number of technologies for further study where the technology development is sufficiently advanced and of sufficient benefit in terms of allowed increased levels of DG to connect to the networks. These recommendations have been the basis for some of the technologies chosen for consideration in this report. The recommended technologies from the New Technologies Report are: Inline voltage regulators Inline voltage regulators are an established technology; however they were included in that report due to their current limited use in the UK despite potentially offering advantages in the area of voltage control. They are referenced in the ENA guidelines on voltage control with connected DG. FACTs Devices SVCs and STATCOMs have traditionally been used on transmission systems to provide reactive power and other forms of network support, and they are proven technologies. Their use at the distribution level has been virtually non-existent due to their cost, perceived complexity and possibly some apprehensions about the state of 10

17 development of the technology. However a number of manufacturers have been developing smaller scale systems specifically aimed at the distribution network market. Micro-grid controllers Several reports commissioned as part of DGCG or DWG workstreams 15 and a number of studies referenced in the ANM Register have suggested means of actively controlling voltage and power flow using new control algorithms, without requiring significant capital investment and using hardware that effectively exists now. Of particular interest will be the availability of Plug and Play devices that can avoid the problem of an excessive customisation burden on DNOs. Two micro-grid controllers in the UK are known to be currently under development. Super-conducting fault current limiters Of the four recommended technologies, superconducting fault current limiters seem to be furthest from commercial application in the UK. However, the authors concluded that manufacturers are close to providing fully tested solutions, and would do so within 5 years. Given the issues of high cost and long lead time of traditional network reinforcement and the increasing frequency of fault level problems, it seems reasonable to suppose that market pull might be a factor with this technology. Their ability to gain acceptance in other markets, particularly North American markets, provides hope that any perceived safety and reliability issues in the UK can be resolved. The DWG Work Programme 2, Project 9 is specifically aimed at investigating fault current limiting technologies to determine if they can be used in the UK. Therefore, to avoid overlap they will not be considered further in this project. 3.3 ANM Register The aim of Programme 3 Project 4 was to provide a clear statement of the status of recently completed, ongoing and planned active network management field pilot and trial activities, international developments in related areas, and research, development and demonstration activities. The project resulted in a comprehensive register of ongoing ANM Pilots, Trials, Research, Development and Demonstration Activities, demonstrating extensive body of literature being generated world wide regarding ANM and related topics. The register provides information on 105 novel ANM techniques and devices, as well as a variety of overarching programmes being run by different organisations world-wide. The majority of the activities identified were in the theoretical, research and development stages, with the remainder describing systems or devices in various stages from desktop studies through to full commercialisation. A large number of projects concentrated on control and communication issues. The ANM Register has been a valuable resource for sourcing information regarding the technologies chosen for review. The authors of the ANM Register recommend that the register is regularly updated, and this recommendation is reiterated here. 15 For example, EA Technology, Identification of Outline Solutions for the Connection and operation of Distributed Generation,

18 3.4 Other Projects of Interest from the ANM Register ENA Reports The Electricity Networks Association (ENA) has produced several Engineering Technical Reports related to the connection of DG and identified in the ANM Register, in particular: ETR 124 Guidelines for Actively Managing Power Flows Associated with the Connection of a Single Distributed Generation Plant ETR 126 Guidelines for Actively Managing Voltage Levels Associated with the Connection of a Single Distributed Generation Plant ETR 130 Application Guide for Assessing the Capacity of Networks Containing Distributed Generation ETR 131 Analysis Package for Assessing Generation Security Capability The first two reports in particular are designed to be planning guides for DNOs addressing an application for connection from DG which cannot easily be accommodated in the normal unconstrained manner. However, it is unclear whether they are being used, given that many of their recommendations are related to the technologies identified in this report which have not been widely implemented Dynamic Equipment Rating One potential means of increasing the amount of export from DG without upgrading lines that are currently operating at close to their thermal capacity is through the use of dynamic line ratings. This can ensure that the limits imposed on connected DG are reasonably linked to the real time conditions of the lines. Generally, safety margins are set so that ratings will not be exceeded even under the worst case conditions, resulting in capacity being available but unused. The Skegness Boston RPZ will encompass dynamic line rating using a device called the Power Donut2, from USi-Power to measure the actual sag of the lines and thus provide feed into calculations to determine what the additional line loading could be. The ANM Register also lists other condition monitoring technologies for transformers and cables Control Besides micro grid controllers, other methods have been proposed using, for example, various state estimation techniques, and some existing commercial control systems such as ENMAC can incorporate such functionality to provide similar levels of active voltage control as it is described in ETR DGFACTS The aim of the European research project known as DGFACTS was to research quality problems on the distribution networks and to develop FACTs devices suitable for solving these problems. The programme was designed to develop both stand alone (such as the D-STATCOM) FACTs devices as well as integrated devices. Integrated devices will expand the capability of standard inverter connected DG from merely meeting Distribution Code requirements at the point of connection to actively providing DNOs with power 12

19 quality support. DGFACTS resulted in a large body of literature describing the state of power quality on the distribution networks throughout Europe, as well as functional specifications for FACTS devices and for quality standards and regulations as well as for test procedures. It found that quality standards throughout Europe vary considerably, as do actual performances. 13

20 4 SELECTION OF TECHNOLOGIES FOR APPRAISAL The following technologies were identified from the literature review, and after consultation with the project team, as suitable for further study. In effect, technologies that are largely available now but for various reasons are not being widely used by the DNOs have been selected, rather than brand new technologies. 4.1 Primary Plant Inline Voltage Regulators (IVRs) Static VAr Compensators (SVCs and STATCOMs) Both of the above relate to voltage control, with other power quality and stability benefits from the use of the FACTs devices. 4.2 Secondary Plant Active Voltage Controllers (new and existing) with state estimation modules (not currently employed for ANM purposes) At least two micro-grid controllers are being developed in UK to specifically provide ANM of small sections of the distribution network where it is most needed. In addition, at least one major SCADA manufacturer has developed a module that can provide real time state estimation on the distribution network and is building upon this to add ANM control functions. Dynamic Line Rating 4.3 Rejected Technologies There are a number of other technologies being developed that were not selected for this study for reasons such as: They will not be available in the required timeframe (eg solid state tap changers) They have been designed to overcome a short-term problem (eg devices aimed at overcoming the reverse power limitations of existing, reactor based tap changers as such transformers are undergoing ongoing upgrade and replacement) They fall outside the scope of this project (eg protection based technologies) A judgement of the cost benefit analysis suggests they are less likely to be economically viable in the required timeframe than those chosen (eg some energy storage solutions 16 ) They are significant safety concerns (eg sequential switching for fault level limiting) The main issues for the technology are regulatory, commercial and contractual rather than technical (eg use of DG to provide reactive support and DSP) 16 For example, Assessing the feasibility of establishing power zones on Northern/Yorkshire Electricity, Econnect, 2006 and the Technology Report 14

21 5 TECHNOLOGY APPRAISAL ASSESSMENT METHODOLOGY The following questions were considered when assessing each of the technologies. 5.1 General Overview of the technology what problem is this technology designed to overcome and how does it achieve this? State of development is the technology likely to be commercially available within the next 5 years? 5.2 Technical Safety and environment does the equipment introduce any unacceptable safety or environmental risks? Is it failsafe? Are there adequate failsafe backup systems? What is the consequence of failure? Functionality what issue/opportunity is the technology designed to overcome/enhance? How well does the functionality of the technology meet its particular objective? How much benefit does the technology provide (quantified where possible)? Is the technology unnecessarily gold plated? What other advantages does this technology give to DNOs and other stakeholders? Technical barriers are there any particular technical barriers to the adoption of this technology? Specific communications and SCADA issues what speed of operation and bandwidth is required? What reliability is required? Can this be achieved using existing systems? Are there any issues with communication standards? Application engineering - How complex is the application engineering? How modular is it? How well has the software/logic been tested compared to the hardware platform? 5.3 Operational Impact on existing network how well does the technology integrate with existing systems, equipment, and operations (particularly with respect to safety and reliability)? Operational robustness what is the technology s availability, and on failure, how long to repair/replace compared to traditional solutions? How often does it need to be maintained? Design robustness how modular is the technology? Must each installation be significantly customised? Impact on operational staff what changes to operating and maintenance practices will be required? What additional training might be required? Legacy issues will the technology result in scattered bespoke solutions, each requiring considerable knowledge transfer as development staff leave? Impact on key operational measures eg CML, CI, etc 15

22 5.4 Planning Risk identification and analysis, including failure rates where that information is available. What are the consequences of failure? P2/6 requirements will the technology make it easier or harder to assess compliance than traditional solutions, such as installing new lines? What happens when the technology is not in service? Expected life of technology compared to traditional solutions Future proofing will the technology integrate well with likely future network architectures identified in Work Programme 1 Project 2 or will it impede their development? How adaptable is the technology to meet changing requirements? How difficult will new hardware or software upgrades be in the future? Integration with existing planning systems will training and new systems be required for planners and consultants? Notes on cost, where that information is available 5.5 Other Appraisal against the criteria of Engineering Recommendation G85 (regarding innovation in electrical distribution network systems), and thus suitability for funding from the Innovation Funding Initiative (IFI) and Registered Power Zone (RPZ) Ofgem incentive mechanisms. To be eligible for these programmes, the project must meet the following criteria 17 : Technical Development is the project of a technical nature and related to enhancing the technical performance of a DNO s network Degree of Innovation is the project sufficiently innovative? Is it an applied invention that has, so far as can be reasonably demonstrated, not previously been adopted by a UK DNO? Customer Value will sufficient value delivered to end consumers if the project is successful? Final commentary on any other issues that appear during the review. 17 From Engineering Recommendation G85, Innovation in Electrical Distribution Network Systems; A Good Practice Guide, ENA,

23 6 DETAILED ANALYSIS 6.1 Inline Voltage Regulators Overview Inline Voltage Regulators (IVRs) are effectively 1:1 ratio transformers with on load tap changers (OLTC). They are most frequently used by DNOs to boost the voltage at the end of long radial feeders (often with several spurs) that experiences substantial volt drop towards the end of the lines, and where this cannot be alleviated by boosting the voltage at the substation without causing the voltage for near in customers to exceed limits. However they also have potential to control the voltage on feeders containing DG 18, leaving the voltage on the rest of the system to be managed by the AVC at the main substation. Figure 1 below provides a generic example of a conventional use of an IVR. A radial feeder experiences increasing voltage drop with increasing distance from the substation. When an IVR is introduced, the voltage at the end of the feeder is restored. In Figure 2, DG connected at some distance from the substation causes the voltage to rise. When an IVR is connected, voltage near the DG is reduced. Figure 1: Conventional network, with and without an IVR 18 For example, as described in Optimisation of the Application of Sustainable Energy Systems, Chapter 4, Grid Connection of Wind and Solar Sources (1) Optimising Generation Levels, University of Western Sydney,

24 Figure 2: Network with DG, with and without an IVR The IVR is a well established technology, and uses both power and control components that have been used in the field for many years with several suppliers. The majority of the experience to date has been to use IVRs as a voltage booster, ie to increase voltage unidirectionally and often using fixed or seasonal tapping. Nonetheless, there examples around the world of the bi-directional use of IVR, including in South Africa, the United States, Australia, New Zealand, Greece 19 and one identified example in the UK. This latter was installed by Scottish Power on a trial basis in North Wales in relation to connecting DG. A considerable body of literature is available concerning IVRs, including datasheets from various manufacturers, which were reviewed for this report. The project in North Wales used a Cooper Power Systems 20 IVR. Other manufacturers identified include Siemens 21 and GE Energy 22. Each of these manufacturers offer single and three phase IVRs with the capabilities discussed in this report Technical Issues Safety and Environment Safety and environmental risks for IVR are similar to that for transformers and other oil cooled equipment, and revolve around the risk of fire, explosion or general oil release. Oil tanks are generally of sealed construction, however as with any OLTC, there is some risk associated with the moving parts of the tap changer. Such risks are managed using pressure relief devices, oil level gauges and oil sampling and temperature alarms 23. These alarm devices could be used to trip an upstream circuit breaker, thereby appearing to present no greater risk than any equivalent ground mounted or pole mounted transformer and less risk than the majority of transformers without such protection. 19 Report on Steady State and Dynamic Analysis of MicroGrids, MicroGrids Consortium, For example, the VR-32 model, accessed October For example the JFR model, accessed October For example, the VR-1 model, accessed October Quantified in manufacturers data sheets, such as those from Cooper Power Systems, Siemens, et al 18

25 Functionality If a connecting distributed generator is considered to present unacceptable risk of voltage rise on the local feeder even after adjusting local AVR settings, then the traditional solution might have been to construct a dedicated circuit from the substation, often at the primary rather than secondary voltage. Various previous DWG and DCDG reports have suggested a hierarchy of voltage control solutions depending on the extent and nature of the problem. For example, it might be possible to adequately control the voltage using the tap changers on the main transformers as the only controlled element, with various modification of the existing AVC schemes such as by using line drop compensation, cancellation CTs or others techniques to modify the measured variables or the control philosophy 24. If it is not possible to keep the voltage of supplied customers within range for all parts of the network using the transformer OLTCs (usually because the variance on different feeders is too wide, as is the classic case with DG), then IVRs might be considered. At this stage, the DNO would have several decisions to make to ensure that an appropriate balance is reached between adequately addressing the voltage issue and avoiding unnecessary cost and complexity. Typically, IVR provide around ±10 to15% voltage regulation using in the order of 32 steps. The actual benefit provided must be determined by system studies on a case by case basis; however the example in North Wales reportedly provided an increase in network capacity for generation connection on an 11 kv feeder from 600 kw to 2.3 MW in this particular instance, with significant avoided costs for a new line 9. System studies must determine on a case by case basis whether it will be appropriate to use an IVR in any given situation. In addition, consideration must be given to what control functions will be used and how much interface with other network devices and the DG will be required. Sample studies reviewed for this report show that an outage of a single connected DG might be a concern. If the IVR is on a low tap to correct a voltage rise problem at a time of low load and high generation, and then that DG trips, it is possible that customers downstream of the IVR will experience low voltage until the IVR can tap back up to restore the voltage. This might take up to 15 seconds, although manufacturers advertise faster tap changing times than this 25. Engineering Recommendation P28 ( Planning limits for voltage fluctuations ) will apply in such circumstances. Studies will be needed to determine whether the settings for the IVR can be selected to manage this issue. It should be noted that in some cases, voltage problems on distribution networks are accompanied by a lack of thermal capacity. The IVR usually does not provide any assistance with thermal limitations, or might worsen existing issues as upstream currents are increased. Given that the majority of UK distribution circuits have been optimised in terms of distributing voltage and length, appropriate locations for IVR installations are likely to be limited to long rural feeders with connected DG. 24 Methods to Accommodate Embedded Generation Without Degrading Network Voltage Regulation, EA Technology, Datasheets from Cooper Power Systems state that the Cooper Quik-Drive Tap Changer can achieve 32 tap steps in 9 seconds. 19