ZVEI study investigates the advantages of power electronics in transmission networks

Transcription

1 Guest article in Siemens HVDC-FACTS Highlights ZVEI study investigates the advantages of power electronics in transmission networks by Rüdiger Haake Director of the Power Engineering Division of the ZVEI Zentralverband Elektrotechnik- und Elektronikindustrie e.v. (German Electric and Electronic Manufacturers' Association), Frankfurt am Main December, 2006 ZVEI - Zentralverband Elektrotechnik- und Elektronikindustrie e.v. Stresemannallee Frankfurt am Main Fachverband Energietechnik und Contracting Forum Phone: +49 (0) Fax: +49 (0) Mail: energietechnik@zvei.org

2 ZVEI study investigates the advantages of power electronics in transmission networks In 2005, within the framework of the ZVEI initiative entitled "Modern Power Supply Infrastructures," the Expert Panel of the ZVEI Power Engineering Division began to investigate the topic "Future technologies for power transmission" in terms of suitability for implementation in power transmission networks. In 2006 the Institute for Electrical Installations and Energy Management (IAEW Institut für Elektrische Anlagen und Energiewirtschaft) at the RWTH University of Technology in Aachen was, following intensive preparatory work, commissioned to conduct a study with the title "Potential applications of power-electronics systems in the transmission network". The aim was to develop informed, defensible conclusions on the technological and economic potentials of innovative technologies for transmission networks in Germany and the rest of Europe. This study applied not only to high-voltage DC transmission (HVDCT), but also to flexible AC transmission systems (FACTS). This study was presented at the "Energie im Dialog" (Energy in Dialog) congress on November 7, 2006 in Gelsenkirchen. The application of power-electronics systems in a heavily developed network topology such as that in Europe, and particularly in Germany, has until now been viewed as unnecessary. This opinion was founded on two arguments: the presumed lack of technical necessity, and economic non-viability. Due to the increase in cross-border power trading and power input from wind turbines, especially in regions of low consumption, the number of bottlenecks in the German and European transmission networks has been growing significantly. 2

3 Power plants above 100 MW Black Lignit Fuel Nuclear Hydr Natural Converter Refinery Network Region W Herne 2 Herne-Shamrock 3 DO-Knepper Gross Power in 500 Voerde Voerde-West DU-Walsum Duisburg DU-Huckingen Neurath Frimmersdorf Weisweiler 4 F-Gutleutstraße 5 F-West 6 F-Niederrad Network Region NW GE-Scholven Wilhelmshaven Emsland Münster-Hafen Datteln Lünen Karlsruhe Rheinhafen Iffezheim Huntorf Ibbenbüren Gersteinwerk HB-Hastedt Robert Frank Heyden Kirchlenger Westfalen 3 1 Bergkamen 2 Hagen-Kabel Koepchenwerk D-Lausward Werdohl- W- Elverlingsen Elberfeld W-Barmen Dormagen Rönkhausen Waldeck K-Merkenich K-Niehl Niederaußem Quierschied- Weiher Mainz Biblis Ludwigshafen LU-Süd Ensdorf Bexbach Vöklingen Philippsburg VK-ModellkraftwerkSB-Römerbrücke Wehr H äusern Brunsbüttel Flensburg Kiel-Ost Brokdorf Bützfleth Wedel Unterweser HH-Hafen HB-Farge HB-Hafen Geesthacht Porta Westfalica B-Reuter B-Klingenberg B-Wilmersdorf B-Lichterfelde Eisenhüttenstadt Thyrow Rüsselsheim Walheilm KA-West Pforzheim S-Gaisburg HB-Mittelsbüren H-Herrenhausen Hannover Mehrum H-Linden Staudinger Network Region SW H-Stöcken HH-Tiefstack GrohndeErzhausen Dettingen Obernburg Mannheim Langenprozelten Obrigheim Heilbronn Altbach Salzgitter Neckarwestheim Krümmel WOB-West Goldisthal Grafenrheinfeld Franken Gundremminge WOB-Nord/Süd Buschhaus Staßfurt Bernburg Könnern HRO Marienehe Kirchmöser Rostock B-Charlottenburg B-Mitte B-Reuter-West Zschornewitz Markersbach Schwedt Jänschwalde Ahrensfelde Schwarze Pumpe Bitterfeld-Chemiepark Schkopau Leipzig-NordSchwarzheide Großkayn Boxberg Leuna Lippendorf Leuna Süd Dresden- Mumsdorf Nossener Brücke Niederwartha "Phönix" Jena-Süd Chemnitz-Nord Hohenwarte Ingolstadt M-Nord Happurg Sandreuth Zolling- Leininger Reisach München-Süd Isar 2 Isar 1 Burghausen M-Freimann Network Region NE Network Region E Network Region SE Jochenstein Braunau-Simbach Witznau Rheinfelden Waldshut Säckingen Walchensee Hausham Network Regions Examined In addition, the danger of possible frequency and voltage fluctuations due to concentrated power supply from wind turbines in fringe zones of the networks is also increasing. In combination with a high basic capacity utilization of the tie lines, the need for rapid-control elements for regulation of active-power and reactive-power flows is therefore developing rapidly. The objective of the ZVEI expert panel was therefore to point out potential technological solutions for managing already identifiable, growing, and changing medium-term demands imposed on the electrical power supply system that can in all probability no longer be satisfied with traditional resources and concepts. 1. Parameterization of the synthetic network model To be able to arrive at conclusions that are as universally valid as possible, investigations were conducted not on the basis of actual network topologies, but with 3

4 the aid of a synthetic network model. Technical and economic evaluation of the potential applications was performed for the quasi-stationary system state. OFFSHORE North Sea Network Region NW OFFSHORE Baltic Sea D S D Network Region NE Parameterization of network structure Schematic design N P N Network Region W Network Region E P C F Network Region SW C A Network Region SE A C Note: Electric length of tie lines not identical with diagram Synthetic Network Model Reference Network The network utilization scenarios were derived from realistic prognoses that describe relevant supply and load scenarios for 2015 and In particular, the focus was placed on the year 2025, since it will be approximately at this time we may expect major changes on the supply side of the networks, especially from offshore wind farms. The structure and level of utilization of all network regions were assumed to be identical, since local bottlenecks were not covered by the investigation. The inhomogeneities therefore concentrate on the distribution of offshore wind turbines and on interconnections among the network regions. Another discrepancy between the model and the actual present situation was the assumption that all three-phase AC lines are 380-kV overhead transmission lines. The tie lines inside Germany and those running to neighboring countries were all assumed to accord with the present-day conditions in Germany. In the study, the exchange of power with neighboring countries was simulated by supply and demand at the fringe nodes of the model network. As such, the parameterized, synthetic model of the German transmission network was assumed as reference network for this investigation into the various possibilities of network configuration. 4

5 2. Strategies and scenarios for network expansion The following expansion strategies were investigated: Conventional network expansion in local zones (Conventional Local Zone) Use of power flow-controlling AC resources (Controlled AC) Use of power flow-controlling DC resources (Controlled DC) Vigorously implemented application of power flow-controlling DC resources (Forced DC) For the case of conventional network expansion in local zones, the necessary construction of additional lines was restricted to the most affordable, minimum level. For the scenario in which power flow-controlling resources were used, attempts were made to reduce the degree to which conventional lines are expanded by building new transmission routes between power-supply and consumption centers. Results of conventional network expansion in local zones (Conventional Local Zone) For 2025, the network utilization scenario entitled "Light Load Heavy Wind" with resulting north-south power flow due to concentration of wind turbines in the coastal regions represents the most critical network loading situation. The "Conventional Local Zone" expansion strategy results in the model reference network being expanded by 68 internal circuits, with construction of a length of 2,420 km and a further 15 local zone ties with an overall length of 1,050 km. This means an increase of 12.5 % in the total circuit length required compared with the reference network. The higher loading of the lines is also reflected in the reactivepower requirement, this being provided by capacitors to a total level of 12,100 MVAr. Results of the use of power flow-controlling DC resources (Controlled DC) An HVDCT overhead transmission line with maximum transmission capacity of 2,200 MW carries excess power to a more distant load center; the transmission distance is 590 km long. One important difference in comparison to network expansion using three-phase technology is that HVDCT operates for the most part with neutral effect on reactive power. As a result, reactive-power requirements are reduced significantly, which in turn means a reduced requirement for compensation equipment. 5

6 OFFSHORE North Sea DC long distance transmission 2.2 GW circuits: MVAr circuits: MVAr circuits: MVAr 6 short-distance transmission / 200 km 1 HVDC long-distance transmission / 590 km 1 HVDC long-distance transmission / 320 km OFFSHORE Baltic Sea DC long distance transmisson 3.5 GW circuits: MVAr 4 short-distance transmission / 300 km Controlled DC Forced 41 Internal SK: 1430 km 10 short-distance transmission: 500 km 1 HVDC (3.5 GW): 590 km 1 HVDC (2.2 GW): 320 km MVAr Scenarios 2025 Controlled DC Forced Results of the use of power flow-controlling DC resources (Forced DC) Another alternative investigated was that of aggressively implemented HVDC systems in order to reduce the requirement for conventional expansion of the scenario "Controlled DC". For this scenario, the HVDC system already implemented is upgraded from 2,200 MW to 3,500 MW. An additional HVDC system with a rated power of 2,200 MW and a route length of 320 km increases targeted transfer of windgenerated energy to a different network with greater power demand. Compared with the "Conventional Local Zone" network expansion variant, this configuration enables savings of 990 km circuits and 550 km of local zone ties. In addition, aggressively implemented employment of HVDC systems reduces the reactive-power requirement. 3. Cost assessment To assess the economics of the respective expansion scenarios, their annuity-based expansion costs were compared on the basis of current annual new values. Upon consideration of the investment cost situation for the time horizon of 2025, it becomes clear that the conventional network expansion scenario in local zones no longer affords the significant cost advantage generally assumed until now. 6

7 Annuity-Based Investment Costs for Required Additional Construction Annuity-based costs Conv. local AC remote DC remote Conv. local AC remote current annual DC forced The benefits of conventional expansion strategies are reduced as increasing demand is placed on the power networks Initially: cost equivalence between conventional technology and power electronics Comparison of the Scenarios Annuity-Based Investment Costs for Required Additional Construction Measures This step-by-step investigation of application scenarios for power-electronics systems in transmission networks covers the possible situations of extreme demand placed on networks on which the network utilization scenario for 2025 is based. This study has produced the following results and has led to the following conclusions: using conventional three-phase technology represents a technically and economically satisfactory option for meeting short- to medium-term demand placed on the German transmission network (for a time horizon of 2015). To manage the more extreme demand forecast for the long term involving rapid control of active- and reactive-power flows, and of reliable transport of high levels of power that form the basis of the network utilization scenario for 2025, HVDC long-distance network ties in a synchronous three-phase network represent the scenario of choice for technical reasons. Due to their special characteristics, they cannot be overloaded, and they act as firewalls to contain malfunctions and isolate two interconnected networks in case of malfunction. With respect to costs, it may be summarized by stating that the primary result of the study has led to the following finding for the 2025 expansion scenario: the extensive cost equivalence among the various expansion scenarios a situation not heretofore considered realistic signifies that application of powerelectronics systems in transmission networks in fact represents a viable and genuine alternative, in economic terms as well. 7