Techno-economic aspects of power systems

1. Techno-economic aspects of power systems Ronnie Belmans Stijn Cole Dirk Van Hertem

2. Overview • Lesson 1: Liberalization • Lesson 2: Players, Functions and Tasks • Lesson 3: Markets • Lesson 4: Present generation park • Lesson 5: Future generation park • Lesson 6: Introduction to power systems • Lesson 7: Power system analysis and control • Lesson 8: Power system dynamics and security • Lesson 9: Future grid technologies: FACTS and HVDC • Lesson 10: Distributed generation

3. OutlineIntroduction to power systems • Power systems • Grid structure • Grid elements • New investments in the grid • Tasks of the TSO • Grid operation issues

4. The grid of today • Transmission network • To transport the electric power from the point of generation to the load centers • All above a certain voltage • (Subtransmission) • Distribution network • To distribute the electric power among the consumers • Below a certain voltage

5. Structure of the power gridWhat’s the difference? • Transmission system • Higher voltage (typical at least 110 kV and higher) • Power injection by generation and import, large consumers • Interconnected internationally • Meshed nature-Redundancy • (Subtransmission system) • Between transmission system and distribution system • Connection of large industrial users and cities • Open loop/partly meshed • Distribution system • 400 V to some ten of kV • Industry, commercial and residential areas • Radial

6. Industrial network (Haasrode) • Transformer: 70 kV/10kV, 20 MVA

7. UCTE

8. Example: Map of the Iberian transmission system

9. Transport of electric power • Electric power P [MW] • Alternating current S [MVA] • Two ways to increase the transported power • Increase current I • Larger conductor cross-section • Increase voltage U • More insulation • Two ways to transport electricity • Alternating current (AC) • Direct current (DC) P or S = U * I

10. Problem faced by electricity pioneers AC or DC? • Direct Current DC • Generator built by W. von Siemens and Z.Gramme • Low line voltage, and consequently limitation to size of the system • Alternating current AC • Introduced by Nikola Tesla and Westinghouse • Transformer invented by Tesla allows increasing the line voltage • Allows transmitting large amounts of electricity over long distances

11. Transformer

12. AC transmission system • Frequency of 50 or 60Hz • Current changes direction 100 or 120 times a sec • Active AND reactive power in the same line • 3 phase system • Line voltages can be easily and economically transformed up and down • AC current does not use the whole conductor • Skin effect • AC conductors have larger diameters than adequate DC

13. Switchyard

14. DC transmission system • Only active power • Current flows in one direction • Conductor cross-sections fully used • Low transmission losses • Requires DC-AC converters to control the voltage level • Expensive • Switching of higher voltage DC more difficult

15. AC vs DC • Advantages of AC • Cheaper transformation between voltages • Easy to switch off • Less equipment needed • Known and reliable technology • More economical in general • Rotating field • Advantages of DC • Long distance transmission • Higher investment costs offset by lower losses • on 1000 km line, 5% for DC opposed to 20% for AC • Undersea and underground transmission • No reactive power problem • Connection of separate power systems • With different frequencies (Japan,South-America) • Different control area, i.e. UCTE with Nordel and UK

16. Cost of transmission linefunction of voltage level

17. Lines and cables • Overhead transmission lines • Economical • However, visual pollution • Widely used in transmission over large distances • Underground cables • More expensive than lines • 5 to 25 times higher capital costs for 380kV • Underground, thus invisible to the public • Ground above the cable can be still used • However, maintenance costs are significant • Widely used in urban areas

18. Overhead line

19. Evaluation: different points of view Technical Economical Regulatory Environmental Transmission capacity upgrade • AC overhead • New line • Refurbishing • New conductor types • AC underground • Conventional cables • GILs • HTS

20. Overhead AC transmissionNew line • Advantages • Widely used in transmission over large distances • Most economical (especially in rural areas) • Well-known technology Best choice from techno-economic point of view Classic approach to network reinforcement

21. Overhead AC transmissionNew line • Environmental aspects • Visual impact • Vegetation • Population • Town planning • Cultural heritage • Natural site and landscape

22. Overhead AC transmissionNew line • Social and political issues • Concern about health effects • Not popular → heavy resistance • NIMBY • NIMTO • BANANA • CAVE • NOPE • Regulatory • Permit process up to 15 years

23. Overhead AC transmissionNew line Conclusion • Best from techno-economic point of view • Worst from environmental, social & political point of view • Very difficult to construct new lines in industrialized countries  alternatives needed!

24. Overhead AC transmission Adding/replacing conductors • Increased ampacity • Without supplementary environmental impact • Within existing right-of-way • Equip second circuit • No new towers needed  cost effective • Heavier conductors • Tower and foundation modifications may be needed → very high cost  new conductor types

25. Overhead AC transmissionNew conductor types • Material properties • Composite core • Surrounded by aluminium(-zirconium) • Increased strenght and reduced weight • Increased ampacity • Economics • Significantly higher cost • No tower modifications needed • Regulatory • Outdated standards state maximum conductor temperature independent of conductor type • Other drawbacks • New technology → limited experience e.g.: no data on expected lifetime available • Higher operating temp  losses increase

26. AC cables • AC cables vs. overhead lines • Technical • Almost no maintenance needed • Repair more difficult • Technical difficulties at high voltages • Limited distance • Economical • 5 to 25 times higher capital costs (€/MVA) • Although cost differences have narrowed • Repair costs are significant

27. AC cables • AC cables vs. overhead lines • Environmental • Invisibility • Dangers: oil spill, poisonous SF6 arcing by-products • Social & political • Less right-of-way needed • Permitting takes less time • Less concern for health risks (although electromagnetic fields are higher) • Ground above the cable can still be used • Widely used in urban areas

28. AC cables • Classic • Paper insulated, oil-filled • XLPE • New types • Higher voltages • Lower losses • More expensive

29. AC CablesNew types • Gas Insulated Cables (SF6) • Higher voltages due to better insulation • Suited to bulk transmission • C lower  suitable for long distances • Complex placement (many joints) • Arcing by-products hazardous for environment • Considered for future tunnel connections (e.g. in the Alps) • Temperature protection • Operating very close to limits • Belgium: Tihange - Avernas

30. AC CablesNew types • High Temperature Superconducting • No conduction losses at cryogenic temperatures • Cooling losses • Cooling and cooling equipment expensive • Reduced dimensions • Environmentally friendly • Could prove economic for specific cases • R&D needed

31. AC cables vs DC cables Source: ABB

32. Cables

33. Tasks of the TSO • Transmission System Operator TSO • Operates the grid • Constant monitoring of system conditions • Frequency control (active power) • Voltage management (reactive power) • Administrates the settlement of unbalances • Access Responsible Parties (ARP) need to balance their productions and consumption • TSO takes actions if ARP deviates from the schedule • TSO charges the ARP for the incurred costs “To keep the lights on”

34. ~ ~ ~ ARP Production Import/ Export Grids ARP1 ARPN I/E I/E Consumer

35. Frequency control

36. Tasks of the TSO • Frequency control • Primary frequency control • Compensate for short-term unbalances at local level • Stabilize frequency within acceptable range around set point • Secondary and tertiary frequency control • Control the load-generation balance at the programmed export-import • Contribute to bringing the frequency back to its set point • Relieve the primary control reserve after an incident • Scheduled (set point) frequency (time control) • Laufenburg control centre in Switzerland • To account for the Synchronous Time deviations • 50.01 or 49.99 Hz for the whole day

37. Tasks of the TSO • Reactive power management and voltage control • Primary voltage control • Excitation of generators • Capacitors • SVCs (Static Var Compensators) • Secondary voltage control • Zonal coordination of the voltage and reactive power control • Maintains the required voltage level at a key node • Tertiary voltage control • Optimization of the reactive power distribution • Based on real-time measurements • Device settings adjustment

38. Tasks of the TSO • Constant monitoring of system conditions • State estimation • To get best possible picture of system conditions • Find a best-fit load flow • Based on metered values (imperfect measurements) • Contingency analysis • N-1 security rule • One accident cannot bring the system in danger • Redundancy

39. From national to international grid

40. Synchronous areas in Europe • UCTE • Established in 1951 as UCPTE, 9 control zones, currently 27 • 23 countries, 33 TSOs, 620 GW installed capacity, 295 TWh exchanges • Full synchronous operation of its members in 1958 • absorbed many “smaller” initiatives along the way • CENTREL, SUDEL, COMELEC • 450 mln. people, annual electricity consumption 2500 TWh. • Nordel • F,SWE,NO,DK (part) • UKTSOA • UK • ATSOI • Ireland • UPS/IPS • Ex Commonwealth of Independent States

41. Synchronous areas (1)Why create synchronous areas ? • Increase grid reliability and mutual support • Improved system frequency control to minimize major disturbances • Mutual support in case of emergencies • Sharing reserve capacities • Facilitate functioning of the electricity market • non-discriminatory domestic and cross-border access to the grid • No need for synchronous area as such, also possible with dc links Example of direct benefits • Zone of 15 GW production capacity loses its largest unit 1 GW • Isolated: needs to develop 1 GW in less than 5s to avoid collapse • As a part of UCTE it needs to develop its share of the two largest UCTE unit, and thus x% of 3GW, in 15-30s.

42. Synchronous areas (2)Challenges • Coordination and control of the power flows • Interdependency of power flows • Interconnected systems share benefits and problems • Problems on top of the above • Often different standards applied in control zones

43. Technical standards differences • Exact same line can have different capacities • Different interpretation of frequency control • Different operational standards Source: IAEW

44. Synchronous areas (3) Operational handbook (UCTE) “Stronger interconnections require common and consistent understanding of grid operation and control and security in terms of fixed technical standards and procedures” • Result of discussion between all TSO’s involved • Successor of past technical and organizational rules and recommendations • Unification and formalization of standards • To make the best possible use of benefits of interconnected operation • To keep the quality standards in the market environment Operation handbook: http://www.ucte.org/publications/ophandbook/

45. Cross-border power flowsin European grid • Typical power flow pattern • Countries structurally exporting or importing • However • Unstable production strongly influences the pattern • Wind generation • Restrictions consist typically of several lines • What matters for the grid are individual lines flows! • This differs considerably from the physical “border capacity”

46. UCTE physical energy exchanges 2004 [GWh]

47. Level of congestion between EU Member States Source: DG COMP

48. Franco-Belgian Border 2001 • Unexpected flows not just ONE TIME event • More like a permanent thing

49. Wind power is a problem • Large wind parks problematic for the network • Unstable dispatch within a zone • Will there be wind? Not too much? • Unstable loop flows • Benelux case • Positive correlation between loop flows and wind in Germany • Up to 0.4 • Loop flows almost entirely through BE and NL

50. Phase shifter investments in the Benelux in order allow power flow control • Meeden (Nl) • Gronau (D) • Kinrooi (B) • Kinrooi (B) • Zandvliet (B) • Monceau (B) 1 2 5 3 4 6