分布式发电的高覆盖率对电力系统设计和运行的影响分析(英文).pdf

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1、第 33 卷 第 15 期 电 网 技 术 Vol.33 No.15 2009 年 8 月 Power System Technology Aug.2009 文章编号1000-3673200915-0037-10 中图分类号TM7 文献标志码A 学科代码4704051 分布式发电的高覆盖率 对电力系统设计和运行的影响分析 Bartosz Wojszczyk1Omar Al-Juburi2王靖3 1埃森哲公司美国 罗利市 276012埃森哲公司美国 旧金山市 94105 3埃森哲公司中国 上海市 200020 Impact of High Penetration of Distributed G

2、eneration on System Design and Operations Bartosz Wojszczyk1Omar Al-Juburi2Joy Wang3 1AccentureRaleigh 27601U.S.2AccentureSan Francisco 94105U.S.3AccentureShanghai 200020China ABSTRACT:This paper addresses the topic of massive utility-oriented deployment of Distributed Generation(DG)in power systems

3、.High penetration of DG presents significant challenges to design/engineering practices as well as to the reliable operation of the power system.This paper examines the impact of large-scale DER implementation on system design,reliable operation and performance and includes practical examples from u

4、tility demonstration projects.It also presents a vision for the utility of the future and describes DG technologies being implemented by utilities.KEY WORDS:distributed energy resources distributed generationpower system design and operation 摘要 文章探讨了电力公用事业大规模实施分布式发电的问题。分布式发电的日益普及将对电力系统的设计、工程实施以及运行的可

5、靠性提出很高的要求。作者考察了分布能源(DER)的大规模应用对电力系统设计、安全运行与绩效的影响并引用电力示范项目例举说明。同时论文也展望了未来的电力公用事业发展远景 描述了应用于电力公用事业的分布式发电技术。关键词分布式能源分布式发电电力系统设计和运行 0 Introduction Distributed generation(DG)or decentralized generation is not a new industry concept.In 1882,Thomas Edison built his first commercial electric plant“Pearl Str

6、eet”.This power station provided 110V DC electricity to 59 customers in lower Manhattan.In 1887,there were 121 Edison power stations in the United States delivering DC electricity to customers.These first power plants were run on water or coal.Centralized power generation became possible when it was

7、 recognized that alternating current power could be transported at relatively low costs and reduce power losses across great distances by taking advantage of the ability to raise the voltage at the generation station and lower the voltage near customer loads.In addition,the concepts of improved syst

8、em performance(system stability)and more effective generation asset utilization provided a platform for wide-area/global grid integration.In recent years,there has been a rapidly growing interest in wide deployment of DG.Commercially available technologies for DG are based on combustion engines,micr

9、o-and mini-gas turbines,wind turbines,fuel-cells,various photovoltaic(PV)solutions,low-head hydro units and geothermal systems.Deregulation of the electric utility industry(in some countries),environmental concerns associated with traditional fossil fuel generation power plants,volatility of electri

10、c energy costs,Federal and State regulatory support of“green”energy and rapid technological developments all support the proliferation of DG units in electric utility systems.The growing rate of DG deployment suggests that alternative energy-based solutions play an increasingly important role in the

11、 smart grid and modern utility.Large-scale implementation of DG can lead to situations in which the distribution/medium voltage network evolves from a“passive”(local/limited automation,monitoring and control)system to one that actively(global/integrated,self-monitoring,semi-automated)responds to the

12、 various dynamics of 38 Bartosz Wojszczyk等分布式发电的高覆盖率对电力系统设计和运行的影响分析 Vol.33 No.15 the electric grid.This poses a challenge for design,operation and management of the power grid as the network no longer behaves as it once did.Consequently,the planning and operation of new systems must be approached so

13、mewhat differently with a greater amount of attention paid to global system challenges.The principal goal of this paper is to address the topic of high penetration of distributed generation and its impact on grid design and operations.The following sections describe a vision for the modern utility,D

14、G technology landscape,and DG design/engineering challenges and highlights some of the utility DG demonstration projects.1 Vision for modern utilities 1.1 Centralized vs.distributed The bulk of electric power used worldwide is produced at central power plants,most of which utilize large fossil fuel

15、combustion,hydro or nuclear reactors.A majority of these central stations have an output between 30MW(industrial plant)and 1.7GW.This makes them relatively large in terms of both physical size and facility requirements as compared with DG alternatives.In contrast,DG is:1Installed at various location

16、s(closer to the load)throughout the power system and mostly operated by independent power producers or consumers.2 Not centrally dispatched(although the development of“virtual”power plants,where many decentralized DG units operate as one single unit,may be an exception to this definition).3Defined b

17、y power rating in a wide range from a few kW to tens of MW(in some countries MW limitation is defined by standards,e.g.US,IEEE 1547 defines DG up to 10MW either as a single unit or aggregate capacity).4Connected to the distribution/medium voltage network-which generally refers to the part of the net

18、work that has an operating voltage of 600V up to 110kV(depends on the utility/country).The main reasons why central,rather than distributed,generation still dominates current electricity production include economy of scale,fuel cost and availability,and lifetime.Increasing the size of a production u

19、nit decreases the cost per MW;however,the advantage of economy of scale is decreasingtechnological advances in fuel conversion have improved the economy of small units.Fuel cost and availability is still another reason to keep building large power plants.Additionally,with a lifetime of 2550 years,la

20、rge power plants will continue to remain the prime source of electricity for many years to come 1.The benefits of distributed generation include:higher efficiency;improved security of supply;improved demand-response capabilities;avoidance of overcapacity;better peak load management;reduction of grid

21、 losses;network infrastructure cost deferral;power quality support;reliability improvement;and environmental and aesthetic concerns(offers a wide range of alternatives to traditional power system design).DG offers extraordinary value because it provides a flexible range of combinations between cost

22、and reliability.In addition,DG may eventually become a more desirable generation asset because it is“closer”to the customer and is more economical than central station generation and its associated transmission infrastructure 2.The disadvantages of DG are ownership and operation,fuel delivery(machin

23、e-based DG,remote locations),cost of connection,dispatchability and controllability(wind and solar).1.2 Development of“smart grid”In recent years,there has been a rapidly growing interest in what is called“Smart Grid Digitized Grid Grid of the Future”.The main drivers behind this market trend are gr

24、id performance,technology enhancement and stakeholders attention(Fig.1).The main vision behind this market trend is the use of enhanced power equipment/technologies,monitoring devices(sensors),digital and fully integrated communications,and embedded digital processing to make the power grid observab

25、le(able to measure the states of critical grid elements),controllable(able to affect the state of any critical grid element),automated(able to adapt and self-heal),and user-friendly(bi-directional utility customer interaction).The Smart Grid concept should be viewed through the modern utility perspe

26、ctive of remaining profitable(good value to shareholders),continuing to grow revenue streams,providing superior customer service,investing in technologies,making product offerings cost effective and pain free for customers to participate and partnering with new players in the industry to provide mor

27、e value to society.It is important to recognize that there is merit in the Smart Grid concept and should be viewed in light of it 第 33 卷 第 15 期 电 网 技 术 39 Market Trend Drivers Performance Areas Technologies Energy Efficiency Renewable Energy Power Quality/Reliability Distributed Resources Communicat

28、ion Stakeholders Customer Choice Corporate Branding Maintainability and Cost of Ownership Advances Protection and Control Advances Monitoring and Metering Advances MaterialsEnvironmentalistsUtility ExecutivesFederal/State Lawmakers/Regulators 图 1 智能电网市场发展驱动力 Fig.1 Smart grid market trend drivers bri

29、nging evolutionary rather than revolutionary changes in the industry.In general,this market trend requires a new approach to system design,re-design and network integration and implementation needs.In addition,utilities will have to develop well-defined engineering and construction standards and ope

30、ration and maintenance practices addressing high penetration levels of DG.2 DG technology landscape DG systems can utilize either well-established conventional power generation technologies such as low/high temperature fuel cells,diesel,combustion turbines,combined cycle turbines,low-head hydro or o

31、ther rotating machines,renewable energy technologies including PV,concentrated PV(CPV),solar concentrators,thin-film,solar thermal and wind/mini-wind turbines(Tab.1)or technologies that are emerging on the market(e.g.tidal/wave,etc.).Each of the DG technologies has its own advantages and disadvantag

32、es which need to be taken into consideration during the selection process(Tab.2).表 1 DG 技术概况 Tab.1 DG technology overview Technology Reciprocating Engine Microturbine Combustion Turbine Fuel Cells PV/CPV/Concentrators Wind DG Size Range 5kW6+MW(3)25500kW 0.530+MW(3)500W10 MW 1kW1+MW(3)2kW5MWFuel Nat

33、ural gas,diesel,landfill gas,digester gas Natural gas,hydrogen,propane,diesel Natural gas,liquid fuels Natural gas,landfill,digester gas,propane,hydrogen,fuel oil Sunlight Wind Efficiency 25%45%20%30%(Recuperated)20%45%36%60%(up to 85%with cogeneration)10%35%40%Estimated Equipment Cost/($/kW)(1)5007

34、00 7001200 7001100 20005000 25005000 600 O&M/($/kW)0.01 0.0050.016 0.0040.010 0.002(2)0.0020.004 0.01 Environmental Emission controls required for NOx and CO Low(1000kWor 20%feeder load Disconnect Switch yes yes yes yes Protective Relays:Islanding Prevention&Synchronization yes yes yes yes Other Pro

35、tective Relays(e.g.unbalance)Optional Optional yes yes Dedicated Transformer Optional Optional yes yes Grounding Impedance(due to ground fault contribution current)no no OptionalOften Special Monitoring&Control Requirements no Optional yes yes Telecommunication&Transfer Trip no Optional Optionalyes

36、4Interaction with other DG(s)or load(s).5Location in the system and the characteristics of the grid such as:Network,auto-looped,radial,etc.System impedance at connection point.Voltage control equipment types,locations and settings.Grounding design.Protection equipment types,locations,and settings.An

37、d other.DR system impact is also dependent on the“penetration”level of the DG connected to the grid.There are a number of factors that should be considered when evaluating the penetration level of DG in the system.Examples of DG penetration level factors include:1 DG as a percent of feeder or local

38、interconnection point peak load(varies with location on the feeder).2DG as a percent of substation peak load or substation capacity.3 DG as a percent of voltage drop capacity at the interconnection point(varies with location on the feeder).4DG source fault current contribution as a percent of the ut

39、ility source fault current(at various locations).4.1 DG impact on voltage regulation Voltage regulation,and in particular voltage rise effect,is a key factor that limits the amount 第 33 卷 第 15 期 电 网 技 术 41(penetration level)of DG that can be connected to the system.Fig.2 shows the first example of t

40、he network with a relatively large(MW size)DG interconnected at close proximity to the utility substation.Large DG(many MW)Distance Voltage Heavy Load No DG Heavy Load with DG ANSI C84.1 Lower Limit(114 v)Light Load No DGDG Supports most of feeder load Substation LTC CT Line drop compensator LTC Con

41、troller End 图 2 临近电力企业变电站的 DG 连接 Fig.2 DG connection close to the utility substation Careful investigation of the voltage profile indicates that during heavy load conditions,with connected DG,voltage levels may drop below the acceptable/permissible by standards.The reason for this condition is that

42、relatively large DG reduces the circuit current value seen by the Load Tap Changer(LTC)in the substation(DG current contribution).Since the LTC sees“less”current(representing a light load)than the actual value,it will lower the tap setting to avoid a“light load,high voltage”condition.This action mak

43、es the actual“heavy load,low voltage”condition even worse.As a general rule,if the DG contributes less than 20%of the load current,then the DG current contribution effect will be minor and can probably be ignored in most cases.Fig.3 and Fig.43 show the second example of the network with DG connected

44、 downstream from the bi-directional line voltage regulator(VR).During“normal”power flow conditions(Fig.3),the VR detects the real power(P)flow condition from the source(substation)toward the end of the circuit.The VR will operate in“forward”mode(secondary DGVR Load centerwith DG Voltage profile Regu

45、lationDirectionP(kW)Q(kvar)图 3 VR 双流向模式(正向流向)Fig.3 VR bi-directional mode(normal flow)DGVRVoltage profileRegulationDirectionP(kW)Q(kvar)Substation10%图 4 VR 双流向模式(逆向流向)Fig.4 VR bi-directional mode(reverse flow)control).This operation is as planned,even though the“load center”has shifted toward the VR

46、.However,if the real power(P)flow direction reverses,toward the substation(Fig.4),the VR will operate in the reverse mode(primary control).Since the voltage at the substation is a stronger source than the voltage at the DG(cannot be lowered by VR),the VR will increase the number of taps on the secon

47、dary side;therefore,voltage on the secondary side increases dramatically.Bi-directional voltage regulators have several control modes for coordination with DG operation.Bi-directionality can be defined based on real(P)and/or reactive(Q)power flow.However,reactive power support(Q)from DG is generally

48、 prohibited by standards in many countries.Therefore,VR bi-directionality is set for co-generation modes(real current)(Tab.4)3.Tab.5 gives examples of voltage change due to various DG sizes.表 4 无功电压控制模式 Tab.4 Voltage regulator control modes 7654321Neutral idleReverse idleReactive currentReactive bid

49、irectionalReal currentCo-generationReal currentBi-directionalReal currentLocked reverseNo Locked forwardControl ModesMost common modesFor system with DG installationCareful considerationflow direction Detection of power No No 表 5 因不同 DG 容量导致的电压变化示例 Tab.5 Examples of voltage change due to various DG

50、sizes DG Size(kW)Feeder Portion of V(DG 2 miles away from the substation)Substation V Total VoltageChange(vector sum)1000.102%0.075%0.157%1 0001.020%0.750%1.567%5 0005.080%3.740%7.840%10 00010.200%7.490%15.7%Notes:DG connected 2 miles from the substation on 12.47kV feederwith 336kcmil conductor;12.4