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HVDC TRANSMISSION

HVDC TRANSMISSION. F. M. Gatta, A. Geri, S. Lauria, M. Maccioni, G. M. Veca Università degli Studi di Roma “La Sapienza” Dipartimento di Ingegneria Elettrica Via Eudossiana n° 18, 00184 Roma, Italia Presented by Prof. Stefano Lauria. 28/03/08 @ 14.30.00. INTRODUCTION.

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HVDC TRANSMISSION

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  1. HVDC TRANSMISSION F. M. Gatta, A. Geri, S. Lauria, M. Maccioni, G. M. Veca Università degli Studi di Roma “La Sapienza” Dipartimento di Ingegneria Elettrica Via Eudossiana n° 18, 00184 Roma, Italia Presented by Prof. Stefano Lauria 28/03/08 @ 14.30.00

  2. INTRODUCTION • In the past ... • Today ... • In Europe ... Introduction Applications Integration NAIG links At the beginning of 20th century, DC (Direct Current) was superseded by AC (Alternating Current) for large-scale electrification. DC power did nevertheless survive, in applications like electric traction and drives. Today, bulk power systems are 3-phase AC, while utilization is either 1-phase or 3-phase AC. Continental Europe is actually a single AC power system, running synchronously at 50 Hz, spanning from Portugal to Poland and Greece! 2 HVDC BERLIN '08 Prof.Giuseppe Veca 28/03/08 @ 14.30.00

  3. UCTE • Introduction • UCTE • History • Applications • Integration • NAIG links 3 HVDC BERLIN '08 Prof.Giuseppe Veca 28/03/08 @ 14.30.00

  4. History of events • 1930s • 1940s • 1954 • 1970s • Today ... • Introduction • UCTE • History • Applications • Integration • NAIG links Efficient static AC/DC conversion (mercury arc valves) was made possible. High Voltage DC (HVDC) bulk power transmission was studied in Germany. First commercial application in Sweden: submarine link bet-ween mainland and Gotland island (100 kV-20 MW-90 km). Thyristors (SCRs) took over; today, HVDC operation voltages attain 600 kV, transmitted power over 3000 MW. 4 DC made its way back into bulk power systems! HVDC BERLIN '08 Prof.Giuseppe Veca 28/03/08 @ 14.30.00

  5. TYPICAL HVDC APPLICATIONS • There are three typical HVDC applications: Introduction Applications Integration NAIG links • 1.Interconnection of non-synchronous AC power systems, even at different frequencies. • 2. Power transmission over long undersea cable links, if the AC solution requires intermediate compensation. • 3.Point-to-point, long-distance transmission of large blocks of power. • For entries 1. and 2., HVDC is the only practical solution. • For entry 3. the choice of DC or AC transmission is a matter of technical-economic convenience. 5 HVDC BERLIN '08 Prof.Giuseppe Veca 28/03/08 @ 14.30.00

  6. Submarine transmission 1 • For a 380 kV-50 Hz AC submarine cable • A bipolar HVDC submarine link can transmit 1000 MW over several hundreds of km, with 2 cables • Several HVDC links in operation or planned in Italy • Introduction • Applications • Submarine 1 • Submarine 2 • Submarine 3 • Long-dist.1 • Long-dist.2 • Long-dist.3 • Integration • NAIG links • maximum practical length is around 100 km • transmissible power over a single circuit (3 cables) is around 1000 MW • Sa.Pe.I., (Sardinia-Italy, under construction). 420 km, 500 kV, 1000 MW. • NorNed (Norway-Netherlands) 580 km, 450 kV, 700 MW 6 HVDC BERLIN '08 Prof.Giuseppe Veca 28/03/08 @ 14.30.00

  7. SACOI – Three-terminals monopolar link, 200 kV – 300 MW (Sardinia – Corsica – Tuscany)‏ SAPEI – Bipolar link, ±500 kV – 1000 MW (Sardinia – Latium)‏ GRITA – Monopolar link 400 kV – 500 MW (Italy – Greece)‏ Submarine transmission 2 • Introduction • Applications • Submarine 1 • Submarine 2 • Submarine 3 • Long-dist.1 • Long-dist.2 • Long-dist.3 • Integration • NAIG links 7 HVDC BERLIN '08 Prof.Giuseppe Veca 28/03/08 @ 14.30.00

  8. 4 Francia Italia Croazia 5 SACOI (300 MW)‏ 6 Albania SAPEI (500+500 MW)‏ 1 GRITA (500MW)‏ 500÷1000 MW 3 2 500÷1000 MW 500 ÷ 1000 MW Algeria Tunisia Libia Submarine transmission 3 • Introduction • Applications • Submarine 1 • Submarine 2 • Submarine 3 • Long-dist.1 • Long-dist.2 • Long-dist.3 • Integration • NAIG links There are also other feasibility studies by TERNA Preliminary studies 1 - completed 2 - completed 3 - underway 4 - underway 5 - to be performed 6 - to be performed 8 HVDC BERLIN '08 Prof.Giuseppe Veca 28/03/08 @ 14.30.00

  9. Long-distance transmission 1 • HVDC overland links are usually bipolar, on overhead lines. Compared to AC, DC transmission has several advantages • As a consequence, less DC lines than AC lines are actually needed to transmit the same power • Introduction • Applications • Submarine 1 • Submarine 2 • Submarine 3 • Long-dist.1 • Long-dist.2 • Long-dist.3 • Integration • NAIG links • HVDC overhead lines are less expensive and require narrower right-of-ways. • Line losses (Joule and corona) are also smaller. • Angular stability and reactive power balance are not a concern: there is no need of intermediate switching/compensating stations. 9 HVDC BERLIN '08 Prof.Giuseppe Veca 28/03/08 @ 14.30.00

  10. Long-distance transmission 2 • The main shortcomings lies in the AC/DC conversion stations due to their cost, large footprint and additional energy losses • The comparison between all the above factors, dictates the convenience of AC or DC • Introduction • Applications • Submarine 1 • Submarine 2 • Submarine 3 • Long-dist.1 • Long-dist.2 • Long-dist.3 • Integration • NAIG links 10 HVDC BERLIN '08 Prof.Giuseppe Veca © Siemens 28/03/08 @ 14.30.00

  11. Long-distance transmission 3 • The AC vs. DC break-even distance can be loosely estimated at 600-800 km for a 3000 MW power transfer • Some existing links • The current industry “standard” is 500 kV, 3000 MW for a single bipolar link • In the midterm, operation of 800 kV links is expected, trasmitting 5-6000 MW on a single line • Introduction • Applications • Submarine 1 • Submarine 2 • Submarine 3 • Long-dist.1 • Long-dist.2 • Long-dist.3 • Integration • NAIG links • Itaipu (Brazil): 600 kV, 2×3150 MW, 785 km. • ‘Three Gorges’ (China, 2001-4): 2 links, 500 kV, 3000 MW each, 890 and 940 km 11 HVDC BERLIN '08 Prof.Giuseppe Veca 28/03/08 @ 14.30.00

  12. INTEGRATION IN AC NETWORK • There are severalconditions to satisfy: Introduction Applications Integration NAIG links • 1.The AC nodes at the HVDC line terminals must be able to supply/evacuate the rated power of the DC link. • 2.The rated power of the DC link must be compatible with the TSO’s operation rules: f.i. UCTE takes at 3000 MW the largest single loss of generation in the European system. • 3.AC short-circuit power at the conversion stations must be sufficiently larger than DC rated power (say, ESCR>3; depends on adopted technology). 12 HVDC BERLIN '08 Prof.Giuseppe Veca 28/03/08 @ 14.30.00

  13. North Africa to Italy 1 • There are no particular shortcomings aside from the cost of submarine cables: in the first stage (say, 3000 MW power transfer) up to 3 cables per pole are needed • Other key points are: • Introduction • Applications • Integration • NAIG links • NA to Italy1 • NA to Italy2 • Italy to G 1 • Italy to G 2 • Individuation and survey of cable routes in deep sea (see f.i. studies conducted for Sa.Pe.I. link)‏ • Identification of suitable EHV terminals in the Italian network (several powerful nodes on the Tyrrhenian coast, from Naples to Suvereto)‏ 13 HVDC BERLIN '08 Prof.Giuseppe Veca 28/03/08 @ 14.30.00

  14. North Africa to Italy 2 • SAPEI cable route attains 1600 m depth and required extensive surveys by means of Remotely Operated Vehicles (ROVs)‏ • Introduction • Applications • Integration • NAIG links • NA to Italy1 • NA to Italy2 • Italy to G 1 • Italy to G 2 14 HVDC BERLIN '08 Prof.Giuseppe Veca 28/03/08 @ 14.30.00

  15. Italy to Germany 1 • At an initial stage (e.g. 2-3000 MW) the existing 380 kV AC network could be used. • Italy permanently imports 6000 to 7000 MW through the alpine interconnections, mainly from France and Germany; the new, northbound flow would be mainly virtual. • This solution, however, potentially interferes with the Italian energy market, capping the transfer capability between network zones “Center”, “Center-North” and “North”. Network expansion could be required. • Dedicated HVDC lines would solve Italian network problems. The key issue here, however, is the strong NIMBY attitude in Italy. • Introduction • Applications • Integration • NAIG links • NA to Italy1 • NA to Italy2 • Italy to G 1 • Italy to G 2 15 HVDC BERLIN '08 Prof.Giuseppe Veca 28/03/08 @ 14.30.00

  16. Italy to Germany 2 • The best long-term choice is probably represented by 800 kV overhead lines, despite their visual obtrusiveness. Routing is undoubtedly a problem. • At a significant cost, HVDC underground cables could solve the public acceptance problem. • If the auxiliary galleries of new railway tunnels are made available, cables would greatly simplify crossing the Alps. • Introduction • Applications • Integration • NAIG links • NA to Italy1 • NA to Italy2 • Italy to G 1 • Italy to G 2 16 HVDC BERLIN '08 Prof.Giuseppe Veca 28/03/08 @ 14.30.00

  17. E-MAIL ADDRESSES • Prof. Fabio Massimo GATTA • fabiomassimo.gatta@uniroma1.it • Prof. Alberto GERI • alberto.geri@uniroma1.it • Prof. Stefano LAURIA • stefano.lauria@uniroma1.it • Marco MACCIONI • marco.maccioni@uniroma1.it • Prof. Giuseppe Maria VECA • giuseppe.veca@uniroma1.it 17 HVDC BERLIN '08 Prof.Giuseppe Veca 28/03/08 @ 14.30.00

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