Power Engineering - Egill Benedikt Hreinsson. Lecture 15a. HVDC Transmission. 2 November 2011

Transcription

1 1 HVDC Transmission

2 2 HVDC Transmission High Voltage Direct Current Transmission

3 3 AC to DC Comparison Originally the power systems were DC An historical struggle between Edison and Westinghouse was called: War of Currents The AC won over DC, at least for the time being?

4 4 HVDC Transmission Point to point (from A to B ) rather than meshed network. No commercially available DC circuit breakers Used exclusively for long underground/submarine cable transmission Flexible Computer or Electronic control of power flow Transmission over long distances by HVDC overhead line Recently HVDC light. Lower cost of AC/DC converters

5 5 Why has HVDC taken off? HV is needed to transmit DC a long distance. Semiconductor thyristors able to handle high currents (4,000 A) and block high voltages (up to 10 kv) were needed for the widespread adoption of HVDC. Newer semiconductor VSC (voltage source converters), with transistors that can rapidly switch between two voltages, has allowed lower power DC. VSC converter stations also are smaller and can be constructed as self-contained modules, reducing construction times and costs.

6 Increased Benefits of Long-Distance 6 Transmission Long distance transmission increases competition in new wholesale electricity markets. Long distance electricity trade, including across nations, allows arbitrage of price differences. Contractual provision of transmission services demands more stable networks. Bi-directional power transfers, often needed in new electricity markets, can be accommodated at lower cost using HVDC

7 7 Relative Cost of AC versus DC For equivalent transmission capacity, a DC line has lower construction costs than an AC line: A double HVAC three-phase circuit with 6 conductors is needed to get the reliability of a two-pole DC link. DC requires less insulation ceteris paribus. For the same conductor, DC losses are less, so other costs, and generally final losses too, can be reduced. An optimized DC link has smaller towers than an optimized AC link of equal capacity.

8 8 AC versus DC (continued) Right-of-way for an AC Line designed to carry 2,000 MW is more than 70% wider than the right-of-way for a DC line of equivalent capacity. This is particularly important where land is expensive or permitting is a problem. HVDC light is now also transmitted via underground cable the recently commissioned Murray-Link in Australia is 200 MW over 177 km. Can reduce land and environmental costs, but is more expensive per km than overhead line. 22-Nov-11 November 2011

9 9 AC versus DC (continued) Above costs are on a per km basis. The remaining costs also differ: The need to convert to and from AC implies the terminal stations for a DC line cost more. There are extra losses in DC/AC conversion relative to AC voltage transformation. Operation and maintenance costs are lower for an optimized HVDC than for an equal capacity optimized AC system.

10 10 AC versus DC (continued) The cost advantage of HVDC increases with the length, but decreases with the capacity, of a link. For both AC and DC, design characteristics trade-off fixed and variable costs, but losses are lower on the optimized DC link. The time profile of use of the link affects the cost of losses, since the MC of electricity fluctuates. Interest rates also affect the trade-off between capital and operating costs.

11 11 Special Applications of HVDC HVDC is particularly suited to undersea transmission, where the losses from AC are large. First commercial HVDC link (Gotland 1 Sweden, in 1954) was an undersea one. Back-to-back converters are used to connect two AC systems with different frequencies as in Japan or two regions where AC is not synchronized as in the US.

12 12 HVDC projects around the world Source:

13 13 HVDC submarine projects in Scandinavia Gemmell, B.; Loughran, J. HVDC offers the key to untapped hydro potential, IEEE Power Engineering Review, Volume: 22 Issue: 5, May 2002 Page(s): 8-11

14 14 International HVDC projects An interestning link on HVDC : HVDC Transmission:Part of the Energy Solution? st/cnst/emplibrary/hartley%2004may 03%20NanoTechConf.ppt

15 Different types of HVDC links a) Monopolar with earth/sea return AC DC AC b) Bipolar link e.g. +/- 400 kv. Earth return in the case of a single pole failure c) Unipolar link e.g. with 2 * -400 kv and earth/sea return

16 16 HVDC applications HVDC links can be used to connect 2 AC power systems with different frequencies and/or phase HVDC is and asynchronous connecting link

17 The functioning of the 12 Power pulse Engineering - Egill Benedikt Graetz Hreinsson 17 bridge

18 18 HVDC terminal station The design of the terminal station with: a YY transformer a YD transformer A thyristor stack as a 12 pulse Gaetz bridge

19 19 The firing angle for thyristors The DC voltage converter for different angle.

20 Change of power Power flow Engineering - Egill Benedikt Hreinsson 20 in a HVDC system Source:

21 Symbols and the composition Power Engineering - Egill Benedikt of Hreinsson 21 semiconductor parts Light triggered thyristor Gate

22 The Cross Section of a 22 High Voltage Thyristor The valve is the basic power-switching element of a converter. It consists of seriesconnected, fully protected thyristor levels, each having high power thyristors of up to 125mm diameter, 8.5kV rating

23 23 Thyristor characteristics Anode current as a function of voltage for a thyristor Anode current A characteristic line for forward current Anode voltage Characteristic curve for forward cutoff current Characteristic curve for current break-through backwards

24 24 A Thyristor unit A thyristor unit with 7 water cooled thyristors LTT=light triggered thyristor

25 25 The thyristor valve hall

26 Dannebo converter station (Fennoskan) 26

27 27 Baltic Cable converter station

28 28 Baltic Cable converter station Q comp AC line AC switchyard Valve hall AC filter DC line Transformer building Active DC filter Smoothing reactor

29 29 HVDC : Thyristor Valve Technology Valve cooling system diagram

30 The evolution of a thyristor s current and voltage capacity Current (ka) Maximum cut off voltage for thyristor Voltage (kv) Nominal current through thyristor

31 HVDC link between Norway and Denmark 31 (Skagerak) AC transmission lines Reactive power generation Back-up generation Harmonics filters High pass filters Thyristor valves Thyristor valves AC transmission lines Back-up generation Reactive power generation Harmonics filters High pass filters

32 The submarine cable between Power Engineering - Egill Sweden Benedikt Hreinsson 32 The copper conductor is 1200 mm2 The cable weights 54 kg/m Double armouring Transmission capacity 500 MW Voltage 400 kv DC Length 200 km Commissioning 1989 and Finland (Fennoskan) A SINTEF employee with a cable sample Heimild:

33 33 A plan for submarine cable project in Malaysia

34 34 HVDC cable cross section Fennoskan (Sweden- Finland) Source: Vattenfall, Stockholm, Sweden

35 35 The Break-even Distance for HVDC Gemmell, B.; Loughran, J. HVDC offers the key to untapped hydro potential, IEEE Power Engineering Review, Volume: 22 Issue: 5, May 2002 Page(s): 8-11

36 36 Typical HVDC Break-Even Distances An interesting link : HVDC Transmission:Part of the Energy Solution? May03%20NanoTechConf.ppt Source: Arrillaga (1998)

37 37 Cost of HVDC converter stations The cost of the DC/AC converters shows a significant economies of scale

38 From a HVDC 38 submarine cable factory The cable is wound on a horizontal roll and is then delivered to the ship

39 39 Submarine cable and cable laying vessel Left: submarine cable with all layers shown- Top right: cable laying vessel and the crew at work Slide 14 of 21

40 40 N. American Transmission Regions Four major independent asynchronous networks, tied together only by DC interconnections: 1. Eastern Interconnected Network all regions east of the Rockies except ERCOT and Quebec portion of the NPCC reliability council. 2. Quebec part of the NPCC reliability council. 3. Texas the ERCOT reliability council. 4. Western Interconnected Network the WSCC reliability council. Source: Arrillaga (1998)

41 41 Neptune Project Proposed Neptune Project: 1,000 km 1,200 MW submarine cable from Nova Scotia to Boston, New York city and NJ. Take natural gas energy to NY with less visual impact, while avoiding a NIMBY problem in NY and allowing old oil-fired plant in NY to be retired. Help improve network stability and reliability. The southern end has a summer peak demand, the northern end a winter one, so a bi-directional link allows savings from electricity trade.

42 42 HVDC Energy delivery in the North Sea Valhall Hod Tambar Ula

43 43 Valhalla Norwegian oil project Flank North Ekofisk Lista Oil Pipeline to Ekofisk Valhall Complex HVDC Cable New PH Pipeline from HOD Flank South

44 44 Norwegian oil platforms, 290 km System 78 MW is needed to deliver 150mbd / 175mmscf/d, offshore The main components: Power delivered form the shore HVDC converter stations on land and offshore (ABB) HVDC cable includes a fibre optic cable (Nexans) Lista Åna-Sira Converter Station Valhall Converter Station 300 kv Transformer AC Filter Phase reactor Converter ~ = DC Filter 0 kv -150 kv DC Filter Converter = ~ Phase reactor Transformer AC Filter 11 kv

45 45 Norned 700 MW, 580 km link available 2008 between Norway and th Netherlands. Transmission capacity auctioned 1 day ahead. Price differences in the APX and Nordpool

46 46 Britned 1000 MW, 280 km link to take into operation 2010 between the UK and Netherlands

47 47 China Several DVDC links in China ikel0707_low.pdf

48 48 History repeats itself!! Back to Edison! Use DC power!

49 49 References Gemmell, B.; Loughran, J. HVDC offers the key to untapped hydro potential, IEEE Power Engineering Review, Volume: 22 Issue: 5, May 2002 Page(s): 8 11 The rise of high-voltage, direct-current systems by Narain G. Hingorani, Consultant (1996)