Long distance bulk transmission Dr. Yanny Fu, KEMA Consulting 6 October 2010 Experience you can trust.
2 Contents Transmission technologies AC and DC Overhead lines and underground/submarine cables Transmission economic aspects Investments Losses Land occupation Transmission of bulk sustainable energy from long distances China s solution European solution Technical innovations needed
3 Long distance transmission: AC or DC? Situations where DC transmission is typically used as an alternative to AC transmission are: Bulk power transmission over long distances Power transfer over long distance cable connections Power exchange between two asynchronous networks Economic aspects
4 Long distance cable connections Capacitance of an AC high-voltage cable gives rise to charging current. This charging current effectively reduces the amount of power a cable is able to transport. The charging current is proportional to the length of the cable and thus the longer the cable, the less power it is able to transport. An AC high-voltage cable has a maximum length of approximately 60 to 100 kilometers. For DC the capacitive reactance of the cable is infinite so no charging currents exist. This makes the transmission distance virtually unlimited.
5 Economic aspects (1) The total costs for a electrical power system are mainly determined by the station cost and line cost. For AC the line cost exceeds the station cost. For DC the station cost exceeds the line cost. There is a break-even distance where DC transmission is more economical than AC transmission. This distance is about 700km.
6 Economic aspects (2) The line cost for AC systems is higher since there are more conductors involved then for DC systems and leading to higher material costs. Secondly, and the right-of-way is less leading to lower costs for land acquisition and permits.
China s solution: UHVDC and UHVAC transmission 7 Coal Mining Long transport distances from source to consumers Large volumes of electricity Many consumers concentrated in city s near the east coast Experience from China applicable in other regions (e.g. Europe, US and Brazil) Consumers Hydro Power KEMA s Involvement in China Three Gorges Shanghai HVDC (±500kV, 3000MW, 1000km, 1999-2004) Three Gorges Guangdong HVDC (±500kV, 3000MW, 1000km, 2003-2005) North-West 750kV grid (2000MVA, 100km, 2006-2007) Central China 1000kV UHVAC (3000MVA, 600km, 2006-2008) Ningxia-Shangdong HVDC (±660kV, 4000MW, 1500km, 2008-2010) Yunnan-Guangdong UHVDC (±800kV, 5000 MW, 1400km, 2007-2010) Xiangjiaba Shanghai UHVDC (±800kV, 6400MW, 2100km, 2008-2010)
DESERTEC Concentrated Solar Power 8
Desertec Indicators 9
European solution: VSC HVDC transmission grid 10 Solar energy from Africa and Southern Europe Hydro power from Scandinavia Wind power from North Sea region Geothermal Power from Iceland Grid extension to sea Transition from overhead lines to underground cable grids Transition to smart super European transmission grid based on new VSC HVDC technology
Possible power flow 11
12 VSC compared with LCC HVDC LCC HVDC uses thyristors. VSC HVDC uses fully controllable switches (IGBT s) making the converter self-commutating. Advantages: Can be connected to weak AC grids Full and fast control of active and reactive power flow No or little filter capacity required: smaller footprint Voltage has always the same polarity regardless the direction of the power flow: usage of extruded cables is possible Disadvantages: Higher switching losses Limited capability for bulk power transport
13 Future DC hub.. DC bus 1 DC bus 2 Converter 1 DC breakers DC cable 1 Converter 2 DC cable 2 Converter n DC cable n
Simplified single line diagram of HVDC Light 14
Submodule (HVDC Plus ) 15
Hybride VSC-HVDC topology 16
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18 VSC HVDC cables Since for VSC-HVDC no polarity reversal is required for reversing the power flow, extruded cables can be used which reduces the cable cost of HVDC connections. So far, only VSC-HVDC connections in combination with cables are in commercial operation.
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HVDC land Cable laying 20
21 500 kv AC XLPE Cable Nexans 500kV XLPE 3x 17km Shanghai 100 joints
400 kv AC Cable Quatar 22
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End sheet Thank you for your attention. Experience you can trust.