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2 November 2011
2Lecture 15a Power Engineering - Egill Benedikt Hreinsson
HVDC TransmissionHigh Voltage Direct Current Transmission
2 November 2011
3Lecture 15a Power Engineering - Egill Benedikt Hreinsson
AC to DC Comparison
•Originally the power systems were DC•An historical struggle between Edison and
Westinghouse was called: “War of Currents”– http://en.wikipedia.org/wiki/War_of_Currents
•The AC won over DC, at least for the time being?
2 November 2011
4Lecture 15a Power Engineering - Egill Benedikt Hreinsson
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
2 November 2011
5Lecture 15a Power Engineering - Egill Benedikt Hreinsson
•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.
Why has HVDC taken off?
2 November 2011
6Lecture 15a Power Engineering - Egill Benedikt Hreinsson
• 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
Increased Benefits of Long-Distance Transmission
2 November 2011
7Lecture 15a Power Engineering - Egill Benedikt Hreinsson
• 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.
Relative Cost of AC versus DC
2 November 2011
8Lecture 15a Power Engineering - Egill Benedikt Hreinsson
2-Nov-11
• 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.
AC versus DC (continued)
2 November 2011
9Lecture 15a Power Engineering - Egill Benedikt Hreinsson
•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.
AC versus DC (continued)
2 November 2011
10Lecture 15a Power Engineering - Egill Benedikt Hreinsson
• 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.
AC versus DC (continued)
2 November 2011
11Lecture 15a Power Engineering - Egill Benedikt Hreinsson
• 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.
Special Applications of HVDC
2 November 2011
12Lecture 15a Power Engineering - Egill Benedikt Hreinsson
HVDC projects around the world
Source: http://www.spectrum.ieee.org/
2 November 2011
13Lecture 15a Power Engineering - Egill Benedikt Hreinsson
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
2 November 2011
14Lecture 15a Power Engineering - Egill Benedikt Hreinsson
International HVDC projects
An interestning link on HVDC : HVDC Transmission:Part of the Energy Solution? http://cohesion.rice.edu/CentersAndInst/CNST/emplibrary/Hartley%2004May03%20NanoTechConf.ppt
2 November 2011
15Lecture 15a Power Engineering - Egill Benedikt Hreinsson
15Different types of HVDC linksa) Monopolar with
earth/sea returnb) 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
DCAC AC
2 November 2011
16Lecture 15a Power Engineering - Egill Benedikt Hreinsson
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
2 November 2011
17Lecture 15a Power Engineering - Egill Benedikt HreinssonThe functioning of the 12 pulse Graetzbridge
2 November 2011
18Lecture 15a Power Engineering - Egill Benedikt Hreinsson
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
2 November 2011
19Lecture 15a Power Engineering - Egill Benedikt Hreinsson
The firing angle for thyristors
The DC voltage converter for different angle.
2 November 2011
20Lecture 15a Power Engineering - Egill Benedikt HreinssonChange of power flow in a HVDC system
Source: http://www.spectrum.ieee.org/
2 November 2011
21Lecture 15a Power Engineering - Egill Benedikt HreinssonSymbols and the composition of semiconductor parts
• Light triggered thyristor
Gate
2 November 2011
22Lecture 15a Power Engineering - Egill Benedikt Hreinsson
The Cross Section of aHigh Voltage Thyristor
• The valve is the basic power-switching element of a converter. It consists of series-connected, fully protected thyristorlevels, each having high power thyristors of up to 125mm diameter, 8.5kV rating
2 November 2011
23Lecture 15a Power Engineering - Egill Benedikt Hreinsson
Thyristor characteristics
• Anode current as a function of voltage for a thyristor
Anode current
Anode voltage
Characteristic curve for forward cutoff current
A characteristic line for forward current
Characteristic curve for current break-through backwards
2 November 2011
24Lecture 15a Power Engineering - Egill Benedikt Hreinsson
A Thyristor unit
•A thyristor unit with 7 water cooled thyristors
LTT=light triggered thyristor
2 November 2011
26Lecture 15a Power Engineering - Egill Benedikt Hreinsson
Dannebo converter station(Fennoskan)
2 November 2011
27Lecture 15a Power Engineering - Egill Benedikt Hreinsson
Baltic Cable converter station
2 November 2011
28Lecture 15a Power Engineering - Egill Benedikt Hreinsson
Baltic Cable converter station
Q comp
AC filter
ActiveDC filter
Transformer building
Valve hall
DC line
Smoothing reactor
AC switchyardAC line
2 November 2011
29Lecture 15a Power Engineering - Egill Benedikt Hreinsson
Valve cooling system diagram
HVDC : ThyristorValve Technology
2 November 2011
30Lecture 15a Power Engineering - Egill Benedikt Hreinsson
The evolution of a thyristor’s current and voltage capacity 1970-1995
01
23456
1970 1975 1980 1985 1990
Nominal currentthrough thyristor
Maximum cut offvoltage for thyristor
Current (kA)
2
4
6
8Voltage (kV)
2 November 2011
31Lecture 15a Power Engineering - Egill Benedikt Hreinsson
HVDC link between Norway and Denmark (Skagerak)
AC transmissionlines
Reactive power generation
Back-up generation
Harmonics filters
High passfilters
Thyristor valves
Thyristor valves Harmonics filters
High passfilters
Reactive power generation
Back-up generation
AC transmissionlines
2 November 2011
32Lecture 15a Power Engineering - Egill Benedikt HreinssonThe submarine cable between Sweden and Finland (Fennoskan)
• 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
A SINTEF employee with a cable sample
Heimild: http://www.energy.sintef.no
2 November 2011
33Lecture 15a Power Engineering - Egill Benedikt Hreinsson
A plan for submarine cable project in Malaysia
2 November 2011
34Lecture 15a Power Engineering - Egill Benedikt Hreinsson
HVDC cable cross
section
Source: Vattenfall, Stockholm, Sweden
Fennoskan(Sweden-Finland)
2 November 2011
35Lecture 15a Power Engineering - Egill Benedikt Hreinsson
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
2 November 2011
36Lecture 15a Power Engineering - Egill Benedikt Hreinsson
Typical HVDC Break-Even Distances
Source: Arrillaga (1998)Source: Arrillaga (1998)
An interesting link : HVDC Transmission:Part of the Energy Solution? http://cohesion.rice.edu/CentersAndInst/CNST/emplibrary/Hartley%2004May03%20NanoTechConf.ppt
2 November 2011
37Lecture 15a Power Engineering - Egill Benedikt Hreinsson
Cost of HVDC converter stations
The cost of the DC/AC converters shows a significant economies of scale
2 November 2011
38Lecture 15a Power Engineering - Egill Benedikt Hreinsson 38From a HVDC submarine cable factory
The cable is wound on a horizontal roll and is then delivered to the ship
2 November 2011
39Lecture 15a Power Engineering - Egill Benedikt Hreinsson
Submarine cable and cable laying vessel
Slide 14 of 21
Left: submarine cable with all layers shown- Top right: cable laying vessel and the crew at work
2 November 2011
40Lecture 15a Power Engineering - Egill Benedikt Hreinsson
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.
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)Source: Arrillaga (1998)
2 November 2011
41Lecture 15a Power Engineering - Egill Benedikt Hreinsson
• 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.
Neptune Project
2 November 2011
42Lecture 15a Power Engineering - Egill Benedikt Hreinsson
HVDC Energy delivery in the North Sea
Valhall
Hod
UlaTambar
2 November 2011
43Lecture 15a Power Engineering - Egill Benedikt Hreinsson
Valhalla Norwegian oil project
Flank South
Flank NorthEkofisk
Lista
Valhall Complex
New PH
Pipeline from HOD
HVDCCable
Oil Pipeline to Ekofisk
2 November 2011
44Lecture 15a Power Engineering - Egill Benedikt Hreinsson
~
=
ACFilter
Transformer Phasereactor
Converter
Åna-SiraConverter Station
300
kV
0 kV
-150 kV
DCFilter
DCFilter
~=
Phasereactor
Transformer
ACFilter
Converter
11 k
V
ValhallConverter Station
Lista
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)
Norwegian oil platforms, 290 km
2 November 2011
45Lecture 15a Power Engineering - Egill Benedikt Hreinsson
Norned45
700 MW , 580 km link available 2008 between Norway and thNetherlands.Transmission capacity auctioned 1 day ahead. Price differences in the APX and Nordpool
2 November 2011
46Lecture 15a Power Engineering - Egill Benedikt Hreinsson
Britned
1000 MW, 280 km link to take into operation 2010 between the UK and Netherlands
2 November 2011
47Lecture 15a Power Engineering - Egill Benedikt Hreinsson
China
http://www.ptd.siemens.de/artikel0707_low.pdf
Several DVDC links in China
2 November 2011
48Lecture 15a Power Engineering - Egill Benedikt Hreinsson
History repeats itself!!
• Back to Edison !• Use DC power !
2 November 2011
49Lecture 15a Power Engineering - Egill Benedikt Hreinsson
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) http://www.spectrum.ieee.org/