How To Improve The Power Distribution System

Transcription

1 The distribution network of the future: challenges and business opportunities The reasons of a revolution trasp. 1

2 The liberalised market The unbundling of the distribution service The society is concerned about the environment Customers are much more interested in quality of service than in the past The cost of energy is continuously increasing The information and communication technology is making it possible to enhance the operation of distribution networks. Key drivers for the innovation trasp. 2

3 The liberalized energy market Open access of infrastructures to many subjects Networks available for private producers Regulator agencies Changing from costs to prices Many private investors consider the opportunity of producing at the distribution level EU directive 54/2003 gives to the distribution system a new role and requires that all customers buy energy in the energy market by 2007 trasp. 3

4 The distribution service The DSO has the duty to operate and develop the network in the area where it has the monopoly; DSO suppliers to sell energy to customers with a prefixed level of service quality; EU requires the unbundling of network operation (DSO) and energy selling (Suppliers) Suppliers may find convenient to buy energy produced at the distribution level and make a lot of pressure to facilitate the diffusion of DG trasp. 4

5 The distribution service The distribution system is a monopoly business regulated by Regulator Bodies; Revenues are related to The number of customers served The asset used The investments made The performance level Regulators adopt price controls to protect consumers from poor service and to encourage efficiency DNO revenues are in many cases performance based and not only asset based trasp. 5

6 Greater attention to the environment; Kyoto agreement and EU directives oblige to reduce polluting emissions (CO 2 ) All countries strive to harness renewable energy sources (RES) Subsidies for RES (e.g. green certificates, white certificates) RES are normally connected to distribution networks RES have poor dispatchability and are characterized by (randomly) fluctuating power production Environmental issues trasp. 6

7 Power Quality Customers are becoming much more sensitive to voltage and current disturbances Regulators require DSO reach a prefixed level of service continuity (in Italy a mechanism based on penalties and prizes has been established) DG can help to improve service continuity (intentional islanding, back-up generators) and may contribute to increase PQ (e g. it reduces the effect of voltage dips) DG not properly positioned or chosen may make worse the situation trasp. 7

8 The distribution network of the future: challenges and business opportunities Innovative distribution schemes trasp. 8

9 Innovative distribution schemes Distribution networks have been designed and operated in the same manner since 50s; Automation and communication are exploited at a very basic level; ICT allows managing networks more efficiently and achieving significant economic benefits ICT will also facilitate the introduction of generation and demand response (DR) policies New technologies will permit the integration of DG (RES) and DR policies and the deferment of network investments trasp. 9

10 Traditional Distribution Networks Passive Designed to accept bulk power from transmission system and distribute to customers Generally with unidirectional flows, although some are interconnected Control at planning stage Ad hoc approach with existing practise ( connect and forget ) No control on DG Worst case scenarios condition for connection (maximum generation minimum load) Limited capacity of DG to be absorbed by the existing networks trasp. 10

11 Innovation to overcome barriers to DG Distribution networks have not been designed and operated to accommodate generation: new schemes and operational practice are necessary Distribution networks are radially operated: distribution may have many advantages from interconnection Protection coordination is based on the uni-directionality of flows: very difficult use with DG; Automation is still at a low level of implementation, even if many improvements have been made: network automation is essential for DER exploitation Present practice is based on 1950s technology: with ICT generators and loads could be controlled Liberalized energy market and distribution unbundling require load and generators at the distribution level must have open access to market trasp. 11

12 Distribution System is the most insurmountable barrier Fuel Cells DR Interconnection Old Grid EPRI trasp. 12

13 Active Networks Limiting Factors for connecting DG Urban areas: Fault levels Rural areas: Voltage rise effect Connection cost is related to voltage level at which DG is connected Conflicting objectives Distribution network operator - as high voltage level as possible Distributed Generation - as low voltage level as possible Active distribution networks Integration of DG within network operation Active control of voltage/flow profiles trasp. 13

14 Active networks S P, ±Q P, -Q DMS WT CHP P, Q, V P, Q, V P, Q, V P, ±Q = PV Full Distribution Management Systems with additional facilities to deal with Distributed Generation Closed Loop Network or Weakly Meshed Networks are important for an active management trasp. 14

15 Distribution Management System Controller trasp. 15

16 Energy (MWh) Generation curtailed Generation curtailed Net generation Net generation p.f = p.f =0.95 Energy (MWh) Example Embedded wind generation penetration (MW) Embedded wind generation penetration (MW) Energy (MWh) Generation curtailed Net generation OLTC Energy (MWh) Generation curtailed Net generation OLTC+VR Embedded wind generation penetration (MW) Embedded wind generation penetration (MW) trasp. 16

17 Active networks as DG facilitators The network of the future does supply connectivity (it provides connectivity between points of supply and consumption); Active Networks The infinite network no longer exists, it does not remain unaffected whatever loads and generators are doing Structural Solution Proposed Interconnection as opposed to dominantly radial networks Local control areas ( cells ) System services are specified attributes of a connection Active networks of this type are taking place in Denmark (ELTRA experience) trasp. 17

18 Active Networks: the ultimate form Energy transport is not dependent on a single path; If some paths run a risk of being overstressed, power can be re-routed Engineering caveats: Domino-effect: faults could propagate in a very large area. New protection system and coordination Fault levels Power Quality: in an automated interconnected distribution network we can have frequent short interruptions and deeper voltage dips trasp. 18

19 The economic benefit of Active Networks All the changes ask for few physical reinforcement Reinforcements are unavoidable for massive amounts of DG Only a few new lines No new transformers thanks to interconnection More switchgear (sectionalizers) More control systems and actuators trasp. 19

20 Meshed Networks: the first step towards active networks Changing from radial to meshed network is an essential condition for a massive diffusion of DG; Distribution networks are mostly weakly meshed and radially operated, thus only a few new lines should be built; Distribution networks with DG are till now no longer radial; First step of the research is to investigating on the benefits achievable with meshed networks for the: Reduction of Energy Losses Deferment of network investments Short circuit level Reliability Dynamic stability trasp. 20

21 Case study: a portion of the Italian distribution network S 1-2 V T 1-2 P The network is mainly constituted by overhead lines with a small number of buried cables (10% of the total extension). 4 Primary Substations 999 MV/LV nodes 1005 Edges 18 Trunk Feeders DG in 4 feeders trasp. 21

22 Steady state analysis A deep analysis of radial and meshed network has been performed for different level of DG penetration and load demand T S1 S P Open loop network Closed loop network Meshed 1 Meshed 2 Meshed 3 Load Scenario [MVA] Minimum Load Actual Load Medium Term Load Long Term Load For each load scenario 5 different level of DG, 0%, 10%, 30%, 70%, and 120% have been considered trasp. 22

23 Impact on Power Losses and Investments DG has the potentiality to reduce losses in radial and meshed networks; Excessive or bad positioned DG may cause an increasing in losses; Meshed network may accommodate more DG before losses increase; Changing to closed-loop networks is generally useful to reduce losses for a given load and a given generation level; Transformers DG has a positive effect on transformers that are less loaded (for a given net and a given load); Changing from open-loop to closed-loop networks allows a better exploitation of transformers; Lines Closing the open-loop networks has the potentiality to reduce the number of lines heavy loaded in case of high DG; The number of lines exploited for more than 50% of its capacity reduces; trasp. 23

24 Voltage profile and short circuit current The voltage profile in a feeder with DG is more uniform; The problem is the HV/LV transformer tap-changer; Meshed networks can only help to regulate voltage in the network but not much more. The meshing of a network gives the strongest contribute to increase the short circuit level; The incremental percentage variation due to network meshing or DG in some nodes is comparable; A meshed network does not suffer the effect of adding more DG; Switchgears have to be changed or short circuit current limiters have to be used. trasp. 24

25 Dynamic behaviour of DG connected to meshed and radial Radial Meshed There is no need to disconnect slow Synchronous Generators (SG) (on faulty or healthy lines) for three phase short circuits cleared within 300ms; Faster SGs must be disconnected in a shorter time (CCT=220ms) for faults close to the generator. SGs connected to healthy lines could remain in service during 3 phase s.c. cleared by a high-speed reclosure. SGs (slow or fast) connected to faulty lines must be disconnected. Self-extinguished faults Temporary faults: Slow SGs connected to healthy lines could remain in service, fast SGs if not close to the fault. SGs connected to faulty lines must be disconnected to avoid re-energization of SGs out of synchronism. Permanent faults: SGs must be disconnected for 3phase s.c. not cleared by a high-speed reclosure trasp. 25

26 Microgrids Interconnection of small, modular generation to low voltage distribution systems forms a new type of power system, the MicroGrid. MicroGrids can be connected to the main power network or be operated autonomously, similar to power systems of physical islands Courtesy of R.H.Lasseter trasp. 26

27 Grid Redesign - Enhanced Reliability with DR R Smart switches/ Electricity routers Customer nodes DR to Base Power DR DR DR generation (fuel cells, etc) Micro Ring DR R Micro Ring DR DR R DR R DR DR R R DR to Base Power DR Micro Ring DR R DR Micro Ring DR R DR Micro Ring DR to Base Power to Base Power trasp. 27

28 Technical, economic and environmental benefits Energy efficiency Minimization of the overall energy consumption Improved environmental impact Improvement of energy system reliability and resilience Network benefits Cost efficient electricity infrastructure replacement strategies Cost benefit assessment trasp. 28

29 Technical Challenges for Microgrids Relatively large imbalances between load and generation to be managed (significant load participation required, need for new technologies, review of the boundaries of microgrids) Specific network characteristics (strong interaction between active and reactive power, control and market implications) Small size (challenging management) Use of different generation technologies (prime movers) Presence of power electronic interfaces Protection and Safety trasp. 29

30 Market and Regulatory Challenges Coordinated but decentralised energy trading and management; Market mechanisms to ensure efficient, fair and secure supply and demand balancing; Development of open and closed loop price-based energy and ancillary services arrangements for congestion management; Secure and open access to the network and efficient allocation of network costs; Alternative ownership structures, energy service providers; New roles and responsibilities of supply company, distribution company, and consumer/customer. trasp. 30

31 Self-healing networks Physical and information assets that are protected from manmade and natural threats, and a power delivery infrastructure that can be quickly restored in the event of attack or a disruption: a self healing grid ; Extremely reliable delivery of the high quality digital grade power needed by a growing number of critical electricity end uses; Availability of a wide range of always on, price smart electricity related consumer and business services; Minimized environmental and societal impact by improving use of the existing infrastructure; Promoting equipment and systems and the use of clean distributed energy resources and efficient combined heat and power technologies; Improved productivity growth rates, increased economic growth rates, and decreased electricity intensity (ratio of electricity use to gross domestic product, GDP). trasp. 31

32 Self-healing networks (EPRI-EDF) Courtesy of CIRED trasp. 32

33 Self-healing networks (EPRI-EDF) trasp. 33

34 Advanced Distribution Automation (ADA) ADA is fundamental in order to allow DER to be completely exploited Traditional distribution systems were conceived to perform one function: distributing power to end-users. ADA will transform traditional systems into multifunctional systems that take fully advantage of new capabilities in power-electronics, information technology, and system simulation. Stages of ADA implementation The major components of ADA will be: Flexible electrical system integration (including Intelligent Electronic Devices, Distributed Resources, etc.) Communication and control systems based on an open architecture Real time state estimation tools for predictive simulations and for the on-line system optimisation (energy, demand management, efficiency, reliability and power quality). trasp. 34

35 Conclusions 1 Many pressures on DSO to radically change distribution system DG and load growth are the most important factors of innovation EU 53/2004 states that DG and DSM should be considered by DSOs to solve network capacity problems Some leading countries have implemented some innovative schemes yet New business opportunities for DSO Tools to manage the transformation and planning the future trasp. 35

36 The dream Wind Energy Long Distance Transmission Energy Management via Satellite Hydro Power Solar Energy Central Power Stations fossil fired and nuclear Combined Cycle Power Plant Biomass Power Plant Superconductive transmission & Distribution Fuel Cells trasp. 36

37 The nightmare trasp. 37

38 The distribution network of the future: challenges and business opportunities Technologies for DG trasp. 38

39 Technologies for DG Traditional technologies for CHP applications Reciprocating engines Industrial gas turbines Innovative technologies for CHP applications Fuel cells Micro-turbines Technologies for DG/RES exploitation Photovoltaic conversion Solar thermal Wind turbines Mini-hydro Additional technologies for DG application Storage ICT trasp. 39

40 Traditional technologies for CHP applications Reciprocating engines Range : up to 20 MW Pro: solid technologies, high efficiencies high reliability, high partial load efficiency, low installation costs Contra : noise, pollution, maintenance programmable but heavy, only part of the heat is of good quality CHP capability : exhaust flue gases C stream, also good quality steam cooling 90 C in case of atm. pressure, more with pressurized cooling circuits low quality steam (hot water) thermal efficiency (ratio heat to primary): 40-45% about equally divided between exhaust and cooling system trasp. 40

41 Traditional technologies for CHP applications Industrial gas turbines Range : 5-30 MW Pro: compact, light, quick to be installed, low emissions, limited vibrations and noise (with carefull operation), quick start, easy remote Contra: low efficiencies, bad partial load efficiency (constant RPM), only fuelled with refined fuel (gas, gas oil or gasified fuels), small sizes very expensive CHP capability : high quality and high heat availability trasp. 41

42 Innovative technologies for CHP applications Micro turbines Range : kw Pro: high efficiency at low load, low emissions, quick start, easy remote, low maintenace cost Contro: low efficiency at nominal load, high installation cost, noise, refined fuel CHP capability : high quality and high heat availability size appropriate for applications in the tertiary or small industry sector trasp. 42

43 Innovative technologies for CHP applications Low temp. fuel cells: PEM kw, suitable for stationary or vehicle application High temp. fuel cells: SOFC, MCFC 100-2MW high global efficiency (>70%) if integrated with microtg (innovative combined cycle) trasp. 43

44 Technologies for DG/RES exploitation Photovoltaic conversion Range : 10-3MW Roof top Grid support Stand alone trasp. 44

45 Technologies for DG/RES exploitation Solar thermal CESI Eurodish: Dish Stirling solar generator system based on the SOLO 161 Stirling motor parabolic concentrator, 8.5 m diameter, 56 m² 2000 suns, 800 C, net efficiency 15%, Two axis tracking: azimuth & elevation 10 kwe 400 V ac 3 p. Asynchronous alternator grid connected trasp. 45

46 Technologies for DG/RES exploitation Wind turbines Range : 10 kw- 5MW 40 GW installed by end 2003 (28 GW in EU) Expected 75 GW in EU - 15 by 2010 Very high penetration in some country: 5% in Spain and in Germany (15 GW in the N and NW regions) 20 % in Denmark some drawbacks in the power system operation are now already mentioned by the grid operators Wind turbines Wind farm Off-shore trasp. 46

47 Technologies for DG/RES exploitation Mini - hydro In EU - 15 mini hydro are plants <10 MW In 1998 the total installed capacity was about 10 GW, the total production was 38.4 TWh trasp. 47

48 Additional technologies for DG applications Energy storage Pb battery REDOX 45 kw Flow battery Flywheels trasp. 48

49 Additional technologies for DG applications Information and communication systems Field DDPI DDPI DDPI DDPI DDPI LAN CDCS Internet RHFS RHFS trasp. 49

50 The distribution network of the future: challenges and business opportunities Distribution Planning University of Cagliari trasp. 50

51 Distribution System Planning Classical approach to distribution planning Load Forecast SubstationLocation location and capacity Feeder routing and design Academics developed many sophisticated techniques but: distribution planners are looking for flexible, simple and best practice oriented methodologies; the distribution business goes faster than the research; too much sophisticated methodologies become obsolete before the planner can utilise them. trasp. 51

52 Requirements for the distribution planning 1. Deterministic approach can be no longer used Deterministic algorithms hide the potential benefit of DG due to the worst case approach. 2. Risks have to be explicitly considered in planning Each time a decision has to be taken in an uncertain scenario the risk comes. The future distribution system will be affected by many uncertainties and tools to deal with are necessary. 3. Planning tools should be multi-objective oriented Planners have to face with contrasting objectives multi-objective programming and decision theory can help to find a good solution among different planning alternatives. 4. Planning should explicitly consider system operation The concept of active network strongly impacts the network expansion planning since it may allow withstanding load and DG growth postponing network investments. trasp. 52

53 The Italian experience: SPREAD Network optimization Green field/brown field planning Optimal expansion plans Network reconfiguration Comparison of different strategic choices Service quality DG allocation Loss reduction Investment minimization Improve reliability Network services Risk Analysis and MO-Programming trasp. 53

54 The structure of SPREAD CANDIDATE LINKS Generation and Manipulation External Data Base USER INTERFACE Radial / meshed Voltage DIPS Daily CURVES Q DG optimization Alternative Sizing Costs / O.F. assessment Radial Optimization Algorithm Module PREDA Nodal Voltages Icc Meshed Optimization Algorithm Technical Constraints Imax Long Interruptions Module TEODORA Automatic Construction of the Alternatives/Scenarios Table DT method Results Module ACTIVNET Riconfiguration Generation Curtailment DSM Actions Results Enviromental Constraint Output Files Intentional Islanding Active Network Operation GA Optimization Algorithm Module PROLOCOGD OPTIMAL SOLUTION Graphical Results Multiobjective trasp. 54

55 Conclusions 2 Distribution planning needs new methodologies The deterministic approach should be abandoned A novel planning software has been developed by CESI and UNICA: SPREAD SPREAD can be applied in long term strategic planning studies as well as in the medium term analysis Details on the methodologies implemented can be found in IEEE and IEE transaction papers and CIRED proceedings trasp. 55