HVDC Technology Phil Sheppard Head of Network Strategy Place your chosen image here. The four corners must just cover the arrow tips. For covers, the three pictures should be the same size and in a straight line.
AC vs DC Power Transmission Alternating Current (AC) Direct Current (DC) Was developed to allow power transfer at higher voltage (to minimise losses) Power flows depending on system impedance (limited control over powerflow) Worldwide choice of power transmission technology (at different frequencies) Power system was initially a DC system! More cost effective for longer power transmission Allows control of power at different routes Allows connection of different synchronised AC zones zones (even at different frequencies) Conventional power generation is AC
HVDC Technologies CSC and VSC Current Source Converter (CSC) Voltage Source Converter (VSC) Thyristors based Line Commutated Converter Lower converter losses IGBT based Voltage Source Operable in AC grids with low short circuit levels Less critical DC line-to-ground faults Independent control of P&Q Filter Switching Required for Different Dispatch Levels Power reversal and Fast Ramp Up/Down Capability Commutation Failure and Operation in Weak Networks Harmonics only seen at Switching Frequency (xkhz) Larger converter station Smaller converter station Can only operate in an energised AC network Can energise an AC network (black start capability)
Worldwide HVDC experience Western Link (UK 2016) LCC 2200MW Inelfe (France Spain 2013) VSC 1000MW Borwin 1 (Germany 2009) VSC 400 MW Skagerrak 4 (Norway 2014) VSC 700MW Jinping Sunan (China 2013) LCC 7200MW KII Channel (Japan 2000) LCC 2800MW Transbay (USA 2010) VSC 400 MW Xiangjiaba - Shanghai (China 2011) LCC 6400MW Basslink (Tasmania 2005) LCC 500MW Caprivi Link (Namibia 2009) VSC 300MW 4 Sapei (Italy 2011) LCC 800MW North East Agra (India 2015) 8000MW
Use of HVDC Technology in GB Present AC interconnector capacity limited by stability constraint 2.2 GW DC Link (subsea) from Scotland to England To further increase the capacity to over 6 GW To enhance system stability (power control, POD) Why not AC? Expensive Option Compared to DC Long Lead Time Visual Impact Two DC links of smaller capacity would be expensive Technology: Line Commutated Current: 2.2 GW and higher HVDC converters are based on proven technology (Current Source Converter) Offer a short-term rating (to 2.4GW) Low losses and no black start requirement favour CSC design DC cables of 600kV rating is a significant benefit (first in the world). 5
Integrated Offshore Windfarms Given the size of the Round 3 windfarms, an integrated solution in comparison to radial offers 25% reduced overall Cost (including the onshore reinforcements required) Fault detection Fault Isolation - Lack of DC Breakers Converter control co-ordination Power reversal 6
Power System Studies for HVDC Projects long list! System Frequency Loss of infeed Low Voltage Ride Through Frequency Control System Stability Voltage Control Power Oscillations Power Reversal Power Quality SSR/SSTI Control Interaction Operating in an islanded network with low system strength (short circuit level) Windfarm/Converter Control DC/AC Faults (detection/isolation/system recovery) Loss of Array Power Sharing (multiple DC Links) Power Quality 7
Innovations in the world of DC Technology Improvements in the design of DC breaker which allows for better meshed DC networks (multiterminal) VSC converter design to reduce the losses Ancillary services from DC links such as Rapid Frequency Response, Power Oscillation Damping Multi-vendor Control platform for multi-terminal development 8
HVDC R&D in National Grid Over 30 live R&D projects on HVDC technology Working closely with UK and International Universities and Manufacturers One of World s leading Transmission companies in HVDC modelling 9
Benefits of East Coast Integration Results from IOTP indicate the overall benefits are in order of 1billion for the current connection programme (2017 onwards) If projects connect after 2020 improved technology should be available and a further benefit up to 2billion can be potentially achieved Results currently present only comparison of capital costs Cost Benefit Analysis, which includes operational cost considerations is underway Current work shows the Integrated offshore concept bring overall benefits Onshore Actions: + QB Opt Onshore Actions: + QB Opt Local Boundary EC7 Tod Point (new s/s) Lackenby (LACK4) Creyke Beck (CREB4) Local Boundary EC1 Killingholme (KILL4) Bootstrap 2.5GW Local Boundary EC3 Walpole (WALP4) 1.8 GW 1 GW 2030 TEC 1 GW 1 GW 1 GW 1GW 1.2GW Local Boundary EC5 Bacton (new s/s) Norwich Main (NORM4) Lowestoft (new s/s) Bramford (BRAM4) 2GW P2 P3 Doggerbank P3 P1 1.8GW * 1.8GW 1.8GW P5 P4 1.8GW* P6 P1 P5a P6a P5b Hornsea (3 x 300MW) (2 x 500MW) P2a P2 P6c P6b P2b Boundary B7 (3500MW) Boundary B7a (3400MW) Boundary B8 (2700MW) Boundary B9 (2800MW) East Anglia P3a P1a P1b Boundary B6 (2500MW) (1 x 200MW) (7 x 300MW) P3b P4 P4b (1GW) (1GW) P4a ONSHORE AREA OFFSHORE AREA
Potential North Sea offshore grid
HVDC Technology Search: national grid high voltage direct current fact sheet 12