Presentation Overview. HVDC Transmission - Opportunities and Challenges. Characteristics of HVDC. Characteristics of HVDC

Transcription

1 HVDC Transmission - Opportunities and Challenges Presented by Dr Bjarne Andersen Presentation Overview Characteristics of HVDC LCC HVDC VSC Transmission Developments in Energy Policies Developments in Transmission Networks Challenges & Opportunities HVDC System Challenges 28th March th AC/DC Conference, IEE, London 1 28th March th AC/DC Conference, IEE, London 2 Characteristics of HVDC HVDC allows controlled transfer of power between ac networks, independently of the frequency, voltage and phase angle of the ac networks at the two terminals. Power transfer can be controlled very rapidly, and swings and oscillations in either or both networks can be damped. HVDC is the most economic option for long interconnectors, and the only option between asynchronous networks. Characteristics of HVDC LCC HVDC Line Commutated HVDC In commercial service since 1954, maximum scheme rating in service 6300MW, total > 60GW installed VSC Transmission In commercial service since 1999, maximum scheme rating in service 350MW, total >1200MW installed 28th March th AC/DC Conference, IEE, London 3 28th March th AC/DC Conference, IEE, London 4

2 Simplified SLD of LCC HVDC terminal PLC Thyristor Valves Commutation process requires ac voltage HFF Pole 1 DC Filter HVDC OHL Converter Transformer Special Design - Valve Hall harmonics and dc stress AC Harmonic Filters - Absorbs harmonic currents and generates reactive power 28th March th AC/DC Conference, IEE, London 5 Electrode Reactive Power Control - LCC HVDC Reactive Power (Mvar) Var delivered to AC system Convertors Filters Result Var absorbed Transferred from AC Power system (MW) 28th March th AC/DC Conference, IEE, London 6 Simplified Diagram of VSC Transmission IGBT Valves - can switch irrespective of current & voltage DC Cable Reactive Power Control - VSC Transmission Simplified PQ Diagram Rectifier Mode P conv Desired Reactive Power Desired Active Power DC Cable Inductive Q conv Capacitive Interphase transformer - similar to ordinary substation transformer AC harmonic filters - high frequency, and relatively low reactive power Inverter Mode U ac = Max U ac = Nom U ac = Min 28th March th AC/DC Conference, IEE, London 7 28th March th AC/DC Conference, IEE, London 8

3 Energy Policy Trends Competitive energy market low cost, rapid construction generation plant (Gas Turbines) shut down of large conventional generation Higher gas consumption emptying of domestic resources need for more import of gas Siting of generation plant convenient to gas supplies Additional strain on transmission network Rising Political concerns over dependence on Imported Gas Energy Policy Trends Concern over Climate Change Pressure to use renewable power Development of cheap and efficient wind generation Location of generation where the wind resource is most prolific Additional strain on Transmission network 28th March th AC/DC Conference, IEE, London 9 28th March th AC/DC Conference, IEE, London 10 Energy Policy Trends Exploitable wind resource in North Scotland > 8 GW, likely implementation ~ 4 Stornoway 1 GW to 5 GW Minimum load in North Scotland ~ 600 MW N-1 Capacity of Interconnection to Scottish Power is 1.8GW N-1 Capacity of Interconnection to England is 2.2 GW 28th March th AC/DC Conference, IEE, London 11 WESTERN ISLES Tiree Uists Ardmore Coll Skye Harris Islay Broadford Mull Jura Lewis Carradale Fort William Oban Port Ann Bute Ullapool Conon Taynuilt Shin 1 GW Beauly Great Glen Inveraray Killin 400 MW Dunoon Cassley Sloy Foyers Dingwall Fort Augustus Windyhill Alness Errochty Braco Dounreay Nairn Inverness Lambhill 1 GW ORKNEY Brora Pitlochry PERTH Campbeltown Map courtesy of SSE Arran Thurso Mybster Dunbeath Elgin Blackhillock Tealing Keith Kirkwall Kintore Boat of Garten Tarland Scottish Hydro - Electric Transmission 500 MW Bonnybridge Kincardine Longannet Macduff DUNDEE 600 MW Lerwick Arbroath SHETLAND Fraserburgh Persley Fiddes Bridge of Dun Peterhead ABERDEEN 700 km Key : kv circuit kv circuit kv circuit Transmission Network Trends Generally, investment in the transmission network has been less than that in generation since unbundling. Additional capacity has been achieved by re-conductoring, MSCDN, SVCs, Quad Boosters and FACTS. Strong and Growing public resistance to new OHLs Potential impact of Electric and Magnetic fields Amenity impacts (Visual, Audible, Wildlife) Long Public Enquiries - delays of up to 10 years before new lines can be constructed! 28th March th AC/DC Conference, IEE, London 12

4 Transmission Network Trends Rising gas and oil prices, results in large increases in energy costs. Renewable energy is becoming attractive and competitive!! The Transmission Network will need enhancement to cope with different power flows. Interconnectors between networks can help minimise overall energy costs. We need new Transmission Lines!!! HVDC to the Rescue! Under-grounding of new Transmission Lines could drastically reduce delays. Delays cost money! A cable may be lower cost than OHL Series2 Other Series1 Capital 28th March th AC/DC Conference, IEE, London th March th AC/DC Conference, IEE, London 14 HVDC to the Rescue! HVDC is cheaper and has lower power loss when a certain distance is exceeded. Converting AC Lines to DC operation could increase capacity and reduce the impact of electric and magnetic fields. HVDC embedded in an ac network can increase the capacity of the network by more than the capacity of the dc link. Let s make HVDC even more attractive! We need to face some Issues: Cost & Value of HVDC Power Loss Complexity, Dispatch & Control Integration in AC network Multi-terminal HVDC Harmonics Multi-Infeed of HVDC 28th March th AC/DC Conference, IEE, London 15 28th March th AC/DC Conference, IEE, London 16

5 Cost & Value of HVDC Today What HVDC Market is a volume niche product would relatively be released low volume if prices high were cost Higher reduced volume by results another in lower 30% cost!? Marketing Campaign Increase awareness of the technical advantages: full and fast control, ac network benefits, limited short circuit contribution, ac voltage control R & D cost reductions through development & design further performance improvements 28th March th AC/DC Conference, IEE, London 17 Power Loss The Efficiency of HVDC converter stations is very high, but lower than for an ac substation: 99.7% for typical ac transformer substation 99.3% efficiency per terminal for LCC HVDC 98.2% efficiency per terminal for VSC 110 Transmission AC 1 LCC 2 VSC 3 28th March th AC/DC Conference, IEE, London 18 Power Loss - Future reductions LCC HVDC Mature and Efficient Technology New and Better materials? Transformer steel New Semi-conductors, Silicon Carbide?? Super Conductivity? Energy recovery? Reducing power loss will be a significant challenge for LCC HVDC Is targeting 99.5% efficiency realistic? 28th March th AC/DC Conference, IEE, London 19 Power Loss - Future reductions VSC Transmission New and Developing Technology More scope for Loss reduction through R&D Now Developing 3rd Generation technology New and Better materials? Similar possibilities as for LCC HVDC New Topologies and new control algorithms. Is a target efficiency of 99% realistic? 28th March th AC/DC Conference, IEE, London 20

6 Complexity Of HVDC schemes HVDC systems are slightly more complex than conventional ac substation. Experienced HVDC users manage their system without problems. Documentation and Training In the early years technical backup from the supplier is essential Sharing of experience with other HVDC Users Service Contracts Dispatch An HVDC scheme can be dispatched like a controlled load and generator. VSC Transmission gives smooth Q control. LCC HVDC gives stepped Q control Need small Q steps for weak networks Could add a SVC or TCSC for smooth Q control Would additional costs be significant? Is smooth control essential? 28th March th AC/DC Conference, IEE, London 21 28th March th AC/DC Conference, IEE, London 22 Control Control is typically automatic - various modes Normal control Power control / Frequency control ac voltage control / Reactive Power Control Other control Damping Control, Emergency run back/run up automatic start up & shut down Education and Training is needed to ensure the advanced performance of HVDC is understood and advantage taken of it. Integration in AC Network Large ac harmonic filters can cause temporary ac overvoltages, particularly in weak networks! Performance could be improved by adding dynamic reactive power control at ac terminals. Should this be an optional add on? Is improvement needed for all HVDC schemes? Does the unfamiliarity with HVDC cause Network owners to reject HVDC? Education!! 28th March th AC/DC Conference, IEE, London 23 28th March th AC/DC Conference, IEE, London 24

7 Multi-Terminal HVDC Sometimes HVDC is rejected because it is perceived as purely point to point. Multi-terminal HVDC is successfully in operation! Performance issues, e.g. commutation failures Limited number of terminals Need R & D to improve performance and cost, particularly for small taps Advances in telecommunication and converter technology should increase performance and costs. 28th March th AC/DC Conference, IEE, London 25 Harmonics Harmonic Pollution is generally increasing in networks, because of more power electronics. tighter harmonic limits more difficult filtering filters can magnify background harmonics! Problems tends to be worse for LCC HVDC than VSC Transmission, due to frequency range. Need R&D to reduce harmonics at source, improve passive filtering and/or commercialise active filters. 28th March th AC/DC Conference, IEE, London 26 Multi-Infeed HVDC Two or more inverters in close proximity may interact with each other. VSC Transmission not subject to interaction LCC HVDC schemes can suffer commutation failures Many examples of successful multi-infeeds. Solution lies in controls and co-ordination, and strengthening of ac connection by Sync Comps and STATCOM in extreme cases. Conclusions HVDC is a good technology for enhancement of ac networks. The HVDC market may be poised for significant growth, because of energy policy and environmental trends. Tackling some of the issues mentioned could result in more application for HVDC. Interaction between Manufacturers and Network Operators needed to identify priorities. 28th March th AC/DC Conference, IEE, London 27 28th March th AC/DC Conference, IEE, London 28

8 Thank you for your Attention! Any Questions? 28th March th AC/DC Conference, IEE, London 29