Distribution Network Review - OSTI.GOV

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Transcript of Distribution Network Review - OSTI.GOV

Distribution Network ReviewPREPARED BY R J Fairbairn D Maunder P Kenyon
The work described in this report was carried out under contract as part of the New and Renewable Energy Programme, managed by the Energy Technology Support Unit (ETSU) on behalf of the Department of Trade and Industry. The views and judgements expressed in this report are those of the contractor and do not necessarily reflect those of ETSU or the Department of Trade and Industry.__________
First published 1999 © Crown copyright 1999
Page iii
1. EXECUTIVE SUMMARY.........................................................................................................................1.1
3.1 Description of the existing electricity supply system in England, Scotland and Wales ...3.1 3.2 Summary of PES Licence conditions relating to the connection of embedded generation3.5 3.3 Summary of conditions required to be met by an embedded generator.................................3.10 3.4 The effect of the Review of Electricity Trading Arrangements (RETA)..............................3.11
4. THE ABILITY OF THE UK DISTRIBUTION NETWORKS TO ACCEPT EMBEDDED GENERATION...................................................................................................................................................4.1
4.1 The ability of distribution systems to accept embedded generation........................................ 4.1 4.2 Northern Scotland - Scottish and Southern Energy...................................................................4.4 4.3 Central and Southern Scotland - Scottish Power...................................................................... 4.12 4.4 North East England - Northern Electric...................................................................................... 4.16 4.5 North West England - Norweb...........................................................................................................4.20 4.6 Merseyside and North Wales - Manweb..........................................................................................4.24 4.7 Yorkshire and Humberside - Yorkshire Electricity.................................................................... 4.29 4.8 West Midlands - Midlands Electricity............................................................................................4.33 4.9 East Midlands - East Midlands Electricity................................................................................... 4.36 4.10 Norfolk and East Anglia - Eastern Electricity............................................................................4.40 4.11 Central London - London Electricity.............................................................................................4.43 4.12 South East England - SEEBOARD..................................................................................................... 4.45 4.13 Southern England - Southern Electric...........................................................................................4.49 4.14 South Wales - SWALEC.........................................................................................................................4.51 4.15 South West England - SWEB............................................................................................................... 4.55
5.1 Utilisation of distribution network assets...................................................................................... 5.1 5.2 Distribution System Losses and Overall System Efficiency....................................................... 5.2 5.3 Security and quality of supply............................................................................................................. 5.5 5.4 Need for distribution reinforcement................................................................................................. 5.7 5.5 Avoidance or deferment of distribution reinforcement..............................................................5.8 5.6 System control, load balance and safety........................................................................................5.8 5.7 Implications forNGC............................................................................................................................... 5.9
6. POTENTIAL FOR UPTAKE OF EMBEDDED GENERATION TECHNOLOGIES........................6.1
6.1 The Projected Near-term Uptake of Renewable Energy Projects in England, Scotland and Wales6.1 6.2 The Projected Near-term Uptake of Embedded Fossil-fuelled Projects in England
Scotland and Wales...........................................................................................................................................6.14
7. COMPARISON OF DISTRIBUTION NETWORK CAPACITY WITH POTENTIAL UPTAKE ...7.1
8. POSSIBLE SOLUTIONS TO OVERCOME OBSTACLES.................................................................. 8.1
8.1 Voltage regulation 8.1
Appendix A Scope of work
Appendix B Assessment of capability of PES networks to accept new embedded generation
Appendix C Questionnaire responses from Industry Stakeholders
Page 1.1
1. EXECUTIVE SUMMARY
This report covers the work undertaken by PB Power, Merz and McLellan Division, on behalf of ETSU, as part of the United Kingdom’s Department of Trade and Industry (DTI) New and Renewable Energy Programme. The objective of the study is to review the distribution network in England, Wales and Scotland to examine its ability now and in the near future to accommodate more embedded generation, taking account of both renewable and conventional types of generation. For the basis of these studies we have considered generators with a registered capacity of less than 100 MW.
The studies described in this report were performed in late 1998 and early 1999 and they involved soliciting the views of numerous organisations, including the 14 Public Electricity Supply companies, the Electricity Regulator (OFFER), key policy makers and industry stakeholders.
As a background to the studies we have included a general description of the existing transmission and distribution systems in the United Kingdom. This description includes a brief history of how the networks were developed from discrete, isolated power systems with localised generators that served a number of specific consumers, to an interconnected network that enabled generation to supply demands in other parts of the country. As part of this background information we include a summary of the conditions stipulated in the Public Electricity Supply licences granted under the Electricity Act 1989 that are relevant to the developers of embedded generation schemes. We also include a summary of the agreements and consents that an embedded generator must obtain in order to connect to, and operate on, a distribution system. This background information is included in Section 3 of this report where we also include a brief description and commentary on the Review of Electricity Trading Arrangements that are presently being performed by OFFER.
In Section 4 we present the results of our discussions with the Public Electricity Supply companies together with some analysis based on these discussions. The aim of this analysis is to identify on a regional basis the existing levels of embedded generation, the capacity for new embedded generation to be connected and the factors that impose limits to the connection of new embedded generation. In this section we also include responses from the Public Electricity Supply companies regarding their experiences of operating distribution systems with embedded generation connected. Table 1.1 below summarises the existing level of generation that is presently thought to be embedded within each of the PES companies distribution systems.
The operational experience advised by the PES companies is considered in more detail in Section 5 of this report, where we attempt to identify the technical and non-technical benefits and drawbacks that may accrue from the presence of embedded generation on a distribution network. We have performed some simplified analysis based on our understanding of the different types of typical distribution networks to compare the responses obtained from the PESs and common beliefs regarding embedded generation with the performance of idealised models. Our analysis indicates that an embedded generator of a modest capacity will tend to reduce distribution system losses, both in terms of peak power losses and annual energy losses. However, such a generator would generally be rated to meet the minimum demand of other consumers that are connected to the same part of the distribution system. In practice the capacity of generators tend to be maximised for economic reasons and are rated to meet the capability of the system to accept the generation, rather than to meet local demand. In such circumstances, depending on the capacity of the generator and the nature of the
Page 1.2
variations in local demand, the generator will tend to increase losses compared with the case where the generator is matched to minimum local demand. In the extreme it may be expected that both peak power losses and the overall annual energy losses could increase above existing levels. This analysis supports the operational experience related by several PES companies. Other considerations include the increase in administration effort required for the PES to operate their system with embedded generation in service, increased load forecasting uncertainties and increased numbers of nuisance trips that may affect quality of supply issues.
Table 1.1 Existing levels of embedded generation by PES company
PES Approximate level of existing embedded generation (MW)
Eastern 493 East Midlands Electricity 748 London Electricity 268 MANWEB 712 Midlands Electricity 224 Northern Electric 266 NORWEB 986 SEEBOARD 250 Southern Electric 482 SWALEC 342 SWEB 145 Yorkshire Electricity 650 Scottish Power 522 Scottish Hydro-electric 1251.6 Total 7339.6
The connection of embedded generation should, in theory, allow distribution companies to defer system reinforcement and allow the generation output to improve the security of supply to their customers. However, the theoretical benefits can only be realised in practice if there are suitable commercial agreements in place to ensure that the PES company can meet its obligations under the terms of its PES licence. Concerns about the availability of embedded generation and the reluctance of generators to offer a firm capacity that the PES can rely upon if required has tended to prevent the full theoretical benefits that could arise from embedded generation being realised in practice. The PES companies are obliged under their PES Licences to meet minimum security of supply conditions and as such there may be a disincentive to defer distribution system reinforcement if they can not rely on the availability of the generation when required. It is therefore likely that until there are strong commercial incentives for either developers of embedded generation projects to offer a firm generation capacity to PES companies, or for the PES to defer system reinforcement, that embedded generation will not be preferred to system reinforcement.
We have assessed the potential uptake of embedded generation in the next 5 years by polling the opinions of key policy makers and industry stakeholders. Based on our investigations we have derived estimates for the potential uptake of renewable energy, CHP and fossil fuel embedded generation schemes.
Page 1.3
The uptake of renewable energy projects in England, Scotland and Wales in the next five years is expected to be dominated by the contracted NFFO and SRO projects, although not all of these projects are expected to be constructed. We would, however, expect there to be some limited uptake of renewable energy projects outside of the NFFO/SRO mechanism, dominated by wind energy, some landfill gas, and with perhaps a very few municipal and/or industrial waste projects
In total we would expect that an estimated 1.8 GW of installed capacity of renewable energy projects would be built within the next five years. It is anticipated that there will be a considerable spread of capacities distributed amongst the various PES regions. About half of the PES regions are expected to have an above average capacity. The five PES regions in which the highest capacities are to be expected are Eastern, Norweb, Scottish Power, Scottish Hydro-Electric and Northern Electric. A total installed capacity for these five regions is about 1.1 GW. The main obstacles to the uptake of non­ wind renewable energy projects are the availability and cost of the fuel supply, the uncertainty associated with obtaining planing consents and the problems with raising private venture capital for such projects. The NFFO and SRO initiatives are having a substantial impact on the levels of uptake of renewable energy projects and the continuance of these initiatives will obviously be expected to maintain the stimulus required to achieve a considerable penetration of renewable projects.
Predicting the near-term uptake of fossil-fuelled embedded generation plant (both CHP and non-CHP) in England, Scotland and Wales is extremely difficult, particularly at this time of substantial uncertainty and change in the Electricity Supply Industry. Nevertheless, our investigations suggest that between 1,500 and 2,750 MWe of fossil-fuelled embedded generation plant could be developed in the next five years.
Should there be strong government policy in the form of inducements or other short term measures, developers may find more projects become viable. It should be noted that there would be an 18 months to 2 year lead time to develop, engineer and construct such plants which rules out significant increases in the short term. This will require an even greater rate of take up in year 2001 and beyond to meet the Government’s 2010 objectives.
Whatever the rate of development, we expect that most of this capacity will be in the form of gas fired CHP plant with power export. We do not anticipate significant growth in District Heating in cities, based on CHP and power export. Furthermore, most of these CHP projects will be developed in the traditional industrial areas England, Scotland and Wales. It is in these regions that the impact on the local distribution systems will be highest.
Table 1.2 compares our predicted uptake of embedded generation with our expectation of what generation could be accepted by the PES networks. It is important to recognise that our expectation of the capacity that could be connected to the PES networks is an indication of the maximum total capacity from a large number of small capacity generators connected at suitable locations on the distribution systems. The best locations to connect embedded generation are generally close to primary substations at 11 kV, close to 33 kV bulk supply points or at 132 kV. The information in this report should not be interpreted as meaning that a particular PES network should be able to accept a small number of large capacity generation schemes with a total capacity equal to that indicated in Table 1.2.
Page 1.4
Table 1.2 Comparison of network capability to accept new generation with potential uptake over the next 5 years
Likely uptake of PES Region Indicative renewable CHP non-CHP Total generation
network energy Capacity capacity capacity capacity MW (MWe) (MWe) MWe
Eastern 910 264 10-150 3-40 277-454 East Midlands Electricity 920 82 10-100 5-40 97-222 London Electricity 390 23 10-100 5-100 38-223 MANWEB 460 153 35-400 2-30 190-583 Midlands Electricity 330 43 25-300 5-40 73-383 Northern Electric 250 174 25-100 2-30 201-304 NORWEB 620 275 10-300 2-40 287-615 SEEBOARD 710 75 25-100 25-50 125-225 Southern Electric 1270 61 10-100 25-100 96-261 SWALEC 210 110 10-400 10-20 130-530 SWEB 430 63 20-50 10-40 93-153 Yorkshire Electricity 650 143 35-200 2-40 180-383 Scottish Powerf 810* 217 35-200 2-40 254-457 Scottish Hydro-electricf 110* 193 5-50 2-10 200-253
f These indicative capacities assume that there will be no transmission constraints imposed by the capacity of the Scotland-
England interconnector. In practice it is possible that access to the interconnector may limit the capacity of new generation that
can be connected in Scotland
* This includes the capacity of contracted SRO generators that have not already connected
We have identified a number of possible solutions to difficulties that limit the opportunities for connecting embedded generation. The major difficulties that can be presented to the connection of embedded generation are normally those related to voltage regulation, thermal loading and fault levels. The solutions may be found through technical solutions, commercial solutions and regulatory solutions. It is not intended that the order in which they are listed signifies any sense of importance or priority, which will need to be determined from further analysis. The technical solutions may include the following:
• Impose limits on generator operating power factors • Install reactive power compensation equipment • Reinforce existing circuits back to source substation • Make direct connection to source substation • Use power electronic interface to accurately control generator output to control voltage at
point of common coupling within specified range • Connect to a higher voltage system • Design connection and generator to maximise the impedance between the generator and
the PES system, minimising fault contribution. • Reconfigure the existing PES network to reduce the fault contribution from the rest of the
system.
Page 1.5
• increase the network short-circuit rating, by replacing switchgear etc. • Use a direct current link between the generator and the PES system to effectively eliminate
a fault current contribution from the generator.
commercial solutions may include the following:- • Restrict periods of the year when the generator can operate • Allow generator to indemnify PES against any claims or losses arising from voltage levels
outside permitted range
and regulatory solutions may include • Allow PES to schedule generation and allow NFFO/SRO generation to be constrained, as
appropriate to the local network • Allow principals within Distribution Price Control to implement appropriate technical
solutions without penalty • Examine the existing arrangements to minimise any single generator developers exposure
to system reinforcement costs.
In order to encourage increased levels of penetration of embedded generation that will be required to reach the Government’s targets for electricity production from renewable and energy efficient sources we make to the following recommendations;
• Formally separate the supply and Distribution businesses of PES companies. • Enable PES companies to charge for the transport or electricity from a generation site in a similar
way to how it charges for the transport of electricity to demand customers. • Develop commercial measures that encourage PES companies to make the best use of embedded
generation on their system. • Increase the incentives to PES companies to reduce distribution loss levels. • Review and update where appropriate Engineering Recommendation P2/5 • Replace the “must take” nature of future NFFO and SRO orders (or their equivalent) with a more
flexible obligation that allows generation to be constrained under extreme system conditions • Review the requirements of G59 and in particular encourage both PES companies and developers
to consider alternatives to Rate of Change of Frequency relays for loss of mains protection. • Allow PES companies to install higher fault rating equipment when upgrading their system
Although many of the PES companies felt that embedded generators contributed very little to the performance of the distribution system whilst taking an inordinate share of engineering and administrative resources, this has not appeared to adversely affect the service they offer to potential developers. The growth of embedded generation is being managed competently by the PES companies and the development of procedures to deal with connection applications and general enquiries indicate the generally co-operative attitude that exists within the distribution companies.
In summary our investigations have indicated that there is approximately 5.5 GW of embedded generation connected to the distribution networks in England and Wales and 1.8 GW connected in Scotland. We estimate that there is the potential for between 6.4 and 9.6 GW of additional generation capacity to be connected in England and Wales and between 0.9 and 1.6 GW in Scotland without significant reinforcement to the existing systems.
Page 2.1
2. INTRODUCTION
This report covers the work undertaken by PB Power, Merz and McLellan Division (M&M), on behalf of ETSU as part of the United Kingdom’s Department of Trade and Industry (DTI) New and Renewable Energy Programme. The overall aim of this report is to review the distribution network in England, Wales and Scotland to examine its ability now and in the near future to accommodate more embedded generation, taking account of both renewable and conventional types of generation. However, for the basis of these studies we have considered generators with a registered capacity of less than 100 MW.
This draft report has been prepared to allow comments from ETSU and other parties that have contributed to the studies presented prior to formal submission to the DTI which is expected to lead to public circulation. Since the final report will be available in the public domain, it is the intention that this draft report will enable those organisations referred to in this report to verify the information contained and the opinions expressed.
The studies described in this report were performed by M&M during the later months of 1998 and early 1999. The studies required that the information be obtained from numerous organisations including the 14 Public Electricity Supply Companies (PESs), the National Grid Company (NGC), key policy makers and industry stakeholders. We used telephone conversations, questionnaires and face to face meetings in order to elicit the appropriate information from the appropriate organisation. The scope of the studies is included as Appendix A of this report.
In Section 3 we include background information to provide the reader with a description of the existing transmission and distribution network in the UK including a commentary on regional variations. As part of this background information we have included a summary of the PES licence conditions that relate directly to the connection of embedded generation, as these are inevitably crucial to the analysis of the ability of the distribution systems to accept increased levels of embedded generation.
In Section 4 we assess the ability of the UK distribution networks to accept embedded generation by considering, on a regional basis, the existing levels of embedded generation, the capacity for more embedded generation, network planning strategies and the factors which impose a limit to the connection of new embedded generation. This information is based on the results of our discussions with the PES companies.
The technical benefits and the drawbacks that may arise from the connection of embedded generation are considered in more detail in Section 5. In that section we have combined the experiences reported by the PES companies together with our own analysis on issues such as asset utilisation, power losses, security of supply, system reinforcement and protection.
In Section…