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p1 ©J.W. Bialek, 2010 Wide-area blackouts: why do they happen and how can modelling help Professor Janusz W. Bialek Durham University
p2 ©J.W. Bialek, 2010 Outline l Modelling of electrical networks l Overview of recent blackouts and their causes l How can modelling help in preventing blackouts
p3 ©J.W. Bialek, 2010 Overview of recent blackouts l Only wide-area blackouts, not local ones –Local ones a majority l Interconnected system blackouts in 2003: US/Canada, Sweden/Denmark, Italy l UCTE “disturbance” 2006 l May 2008 disturbance in the UK
p4 ©J.W. Bialek, 2010 Modelling of electrical networks l A network is a planar graph with nodes (buses, vertices) and branches (lines, edges) l GB high-voltage transmission network is meshed and consists of 810 nodes and 1194 branches l UCTE and US interconnected networks consist of several thousands nodes l For most analyses, the network is described by algebraic equation (Current and Voltage Kirchhoff’s Laws) l Electromechanical stability of rotating generators is described by differential equations
p5 ©J.W. Bialek, 2010 Preventing blackouts l We can’t live without electricity so the power system has to be designed and operated in a robust manner –Should ride through “credible” disturbances –Trade-off between cost of keeping reserves and security l A proxy to probabilistic risk assessment: (N-1) contingency – a deterministic criterion l N-1 contingency: a single disturbance (generation/line outage) should not cause problems –it is unlikely that 2 or more units will be lost simultaneously –generation reserve: the loss of the largest infeed (a nuclear reactor of 1320 MW at Sizewell B) –Transmission reserve: loss of double-circuit line (N-D)
p6 ©J.W. Bialek, 2010 When do blackouts happen? l... when (N-1) contingency analysis has not been done properly (Italy 2003, UCTE 2006) l... or when more than 1 thing went wrong (US/Canada 2003, Sweden 2003, GB 2008) l... or hidden mode of failure (London 2003) l The new world of renewables and Smart Grids may require the use of probabilistic risk assessment –Briefly today, more Thursday 3.30pm “Mathematical modelling of future energy systems”
p7 ©J.W. Bialek, 2010 Classification of blackouts l Transmission inadequacy: a failure in a transmission network causes a cascading overloading of the network (a majority) l Generation inadequacy: failures of power plant(s) cause a deficit of generation (GB 2008 disturbance) l Usually a mixture: an initial network fault causes a separation of the network into parts with deficit/excess of generation
p8 ©J.W. Bialek, 2010 Major transmission failures in late summer/autumn 2003 l 7 blackouts affecting 112 million people in 5 countries l 14 August 2003, USA/Canada l 23 August 2003, Helsinki l 28 August 2003, south London l 5 September 2003, east Birmingham l 23 September 2003, Sweden and Denmark l 28 September 2003, whole Italy except Sardinia l 22 October 2003, Cheltenham and Gloucester
p9 ©J.W. Bialek, 2010 The Oregonian, 24 August 2003, after C. Taylor
p10 ©J.W. Bialek, 2010 NE of USA/Canada: before
p11 ©J.W. Bialek, 2010 NE of USA/Canada: after
p12 ©J.W. Bialek, 2010
p13 ©J.W. Bialek, 2010
p14 ©J.W. Bialek, 2010 Where it all began: Ohio and surrounding areas Source: US/Canada Power System Outage Force
p15 ©J.W. Bialek, 2010 How it all started: tree flashover at 3.05 pm Source: US/Canada Power System Outage Force
p16 ©J.W. Bialek, 2010 Bad luck? l Alarm and logging system in FirstEnergy (FE) control room failed 1 hour before the cascade started l Not only it failed, but control room engineers did not know about it l When lines started to trip they could not take corrective action: the system was not (N-1) secure after first trips
p17 ©J.W. Bialek, 2010 Cascading tripping: an initial line trip casues overloading on other parallel lines Source: US/Canada Power System Outage Force
p18 ©J.W. Bialek, 2010 Effect of line trips on voltages: depressed voltage (Ohm’s Law) Source: US/Canada Power System Outage Force
p19 ©J.W. Bialek, 2010 Source: US/Canada Power System Outage Force
p20 ©J.W. Bialek, 2010 Source: US/Canada Power System Outage Force
p21 ©J.W. Bialek, 2010 Speed of cascading Source: US/Canada Power System Outage Force
p22 ©J.W. Bialek, 2010 Danish/Swedish blackout: 23/09/03, 5 M people Normal load, big margins Denmark self-sufficient, southern Sweden supplied from central/northern 1.2 GW Oskarshamn nuclear plant trips due to a feed-water valve problem 5 min later double busbar fault trips 4 lines at Horred substation (N-5) contingency 1.8 GW Ringhals nuclear plant shuts down Southern Sweden and western Denmark blacks out
p23 ©J.W. Bialek, 2010 Italy
p24 ©J.W. Bialek, 2010 Frequency as real power balance indicator l Power generated must be equal to power consumed l Frequency is the same at any part of interconnected network l If there’s a sudden loss of generation, energy imbalance is made up from kinetic energy of all rotating generators l The speed (frequency) drops triggering all turbine governors to increase generation automatically (feedback control) l If frequency drops too much, automatic load shedding is activated l generation deficit => frequency drops, generation surplus => frequency increases Source: National Grid
p25 ©J.W. Bialek, am: import 6.7 GW, 25% of total demand, 300 MW over agreed CH operated close to (N-1) security limit but Italy didn’t know about it 86% loaded internal Swiss Lukmanier line trips on a tree flashover 3.11 am: ETRANS informs GRTN (disputed, no voice recordings) GRTN reduces imports by 300 MW as requested Source: UCTE
p26 ©J.W. Bialek, 2010 l two more CH lines trip and Italy loses synchronism with UCTE l Island operation: import deficit leads to a frequency drop and load shedding l Until 47.5 Hz, 10.9 GW of load shed but 7.5 GW of generation lost l Frequency drops below 47.5 Hz and remaining units trip l Blackout 2.5 minute after separation: whole Italy, except of Sardinia. Source: UCTE
p27 ©J.W. Bialek, 2010 l UCTE: Union for the Co- ordination of Transmission of Electricity – association of TSOs now renamed ENTSO-E (European Network of Transmission System Operators for Electricity) UCTE disturbance in 2006 Source: UCTE
p28 ©J.W. Bialek, 2010 Flows just before the blackout l Generation 274 GW including 15 GW of wind (5.5%) l Strong east-west power flows, i.e. the West depends on imports l strong wind generation in northern Germany Source: UCTE
p29 ©J.W. Bialek, 2010 Timeline Image: l 18 Sept: a shipyard request EON for a routine disconnection of double circuit 380 kV line Diele-Conneferde in northern Germany on 5 Nov l 3 Nov: the shipyard request to bring forward the disconnection by 3 hours. Late announcement could not change exchange programs l 4 Nov 9.30 pm: EON concludes empirically, without updated (N-1) analysis, that the outage would be secure. Wrong! l 9.38: EON switches off of the line l 10.07: Alarms of high flows. EON decides, without simulations, to couple a busbar to reduce the current l Result: the current increases and the line trips l As the system was not (N-1) secure, cascading line tripping follows l separation of UCTE into 3 regions with different frequencies
p30 ©J.W. Bialek, GW deficit 49.7 Hz 8.9 GW deficit 49 Hz 10 GW surplus 51.4 Hz Source: UCTE
p31 ©J.W. Bialek, 2010 Western Europe: 8.9 GW deficit l Frequency drop to 49 Hz triggered automatic and manual load shedding (17 GW) and automatic tripping of pump storage units (1.6 GW) l However the frequency drop caused also tripping of 10.7 GW of generation – more load had to be shed l DC connection UK-France: continued export from France despite the deficit!
p32 ©J.W. Bialek, 2010 Resynchronisation l A number of uncoordinated unsuccessful attempts made without knowledge of the overall UCTE situation l Full resynchronisation after 38 minutes Source: UCTE
p33 ©J.W. Bialek, 2010 l Cockenzie and Sizewell B were lost within 2 mins: (N-2) event, 1714 MW l Loss of Sizewell B is the largest infeed loss planned for (1320 MW) l Further 279 MW of wind tripped due to frequency drop (total 1993 MW) l Automatic load shedding of 546 MW triggered at 48.8 Hz l Voltage reduction caused reduction of demand by 1200 MW l More generation was connected and supply restored within 1 hour Source: National Grid GB May 2008 event: a near miss
p34 ©J.W. Bialek, 2010 Will there be more blackouts? l People tend to learn from the past l... but generals are usually prepared to the last (rather than future) war l Lessons learned from the blackouts - improvements in communications and coordination in Europe and USA l... but new challenges are looming ahead
p35 ©J.W. Bialek, 2010 Generation adequacy issues l Possible problems after 2015 (Ofgem Discovery report) l Regulatory uncertainty
p36 ©J.W. Bialek, 2010 Increased penetration of renewable generation l Wind already a contributing factor to UCTE 2003 and GB 2008 disturbances l “Any feasible path to a 80% reduction of CO2 emissions by 2050 will require the almost total decarbonisation of electricity generation by 2030” (Climate Change Committee Building a Low Carbon Economy 2008)
p37 ©J.W. Bialek, 2010 Smart Grids l Comms-enabled responsive demand, electric cars etc l Highly stochastic generation and demand: (N-1) contingency criterion may become obsolete soon – new probabilistic risk assessment tolls required l Dependence on comms networks is a new mode of failure
p38 ©J.W. Bialek, 2010 Example of new modelling techniques: preventive network splitting l EPSRC grant started January 2010 (Complexity Science call) l Exciting collaboration between graph theorists from Southampton (Brodzki, Niblo), OR experts from Edinburgh (Gondzio, McKinnon) and power engineers from Durham (Bialek, Taylor) l Split the network in a controlled manner before it partitions itself l Initial main challenge: speaking the same language, mutual education
p39 ©J.W. Bialek, 2010 Conclusions l (N-1) contingency criterion has served us well in the past but there were a number of wide-area blackouts in 2003, 2006 and 2008 l New challenges of increased wind penetration and Smart Grids l New mathematical modelling tools required to prevent future blackouts
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