p1 ©j.w. bialek, 2010 wide-area blackouts: why do they happen and how can modelling help professor...

p1 ©J.W. Bialek, 2010

Wide-area blackouts: why do they happen and how can modelling help

Professor Janusz W. Bialek

Durham University


Outline

Modelling of electrical networks

Overview of recent blackouts and their causes

How can modelling help in preventing blackouts


Overview of recent blackouts

Only wide-area blackouts, not local ones

– Local ones a majority Interconnected system blackouts in 2003:

US/Canada, Sweden/Denmark, Italy

UCTE “disturbance” 2006

May 2008 disturbance in the UK


Modelling of electrical networks

A network is a planar graph with nodes (buses, vertices) and branches (lines, edges)

GB high-voltage transmission network is meshed and consists of 810 nodes and 1194 branches

UCTE and US interconnected networks consist of several thousands nodes

For most analyses, the network is described by algebraic equation (Current and Voltage Kirchhoff’s Laws)

Electromechanical stability of rotating generators is described by differential equations


Preventing blackouts 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

A proxy to probabilistic risk assessment: (N-1) contingency – a deterministic criterion

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)


When do blackouts happen?

... when (N-1) contingency analysis has not been done properly (Italy 2003, UCTE 2006)

... or when more than 1 thing went wrong (US/Canada 2003, Sweden 2003, GB 2008)

... or hidden mode of failure (London 2003)

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”


Classification of blackouts

Transmission inadequacy: a failure in a transmission network causes a cascading overloading of the network (a majority)

Generation inadequacy: failures of power plant(s) cause a deficit of generation (GB 2008 disturbance)

Usually a mixture: an initial network fault causes a separation of the network into parts with deficit/excess of generation


Major transmission failures in late summer/autumn 2003

7 blackouts affecting 112 million people in 5 countries

14 August 2003, USA/Canada

23 August 2003, Helsinki

28 August 2003, south London

5 September 2003, east Birmingham

23 September 2003, Sweden and Denmark

28 September 2003, whole Italy except Sardinia

22 October 2003, Cheltenham and Gloucester

p9 ©J.W. Bialek, 2010 The Oregonian, 24 August 2003, after C. Taylor


NE of USA/Canada: before


NE of USA/Canada: after


Where it all began: Ohio and surrounding areas

Source: US/Canada Power System Outage Force


How it all started: tree flashover at 3.05 pm



Bad luck?

Alarm and logging system in FirstEnergy (FE) control room failed 1 hour before the cascade started

Not only it failed, but control room engineers did not know about it

When lines started to trip they could not take corrective action: the system was not (N-1) secure after first trips


Cascading tripping: an initial line trip casues overloading on other parallel lines



Effect of line trips on voltages: depressed voltage (Ohm’s Law)


p19 ©J.W. Bialek, 2010 Source: US/Canada Power System Outage Force

p20 ©J.W. Bialek, 2010 Source: US/Canada Power System Outage Force


Speed of cascading



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


Italy


Frequency as real power balance indicator

Power generated must be equal to power consumed

Frequency is the same at any part of interconnected network

If there’s a sudden loss of generation, energy imbalance is made up from kinetic energy of all rotating generators

The speed (frequency) drops triggering all turbine governors to increase generation automatically (feedback control)

If frequency drops too much,automatic load shedding isactivated

generation deficit => frequency drops, generation surplus => frequency increases

Source: National Grid


3 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 requestedSource: UCTE


two more CH lines trip and Italy loses synchronism with UCTE

Island operation: import deficit leads to a frequency drop and load shedding

Until 47.5 Hz, 10.9 GW of load shed but 7.5 GW of generation lost

Frequency drops below 47.5 Hz and remaining units trip

Blackout 2.5 minute after separation: whole Italy, except of Sardinia.

Source: UCTE


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


Flows just before the blackout

Generation 274 GW including 15 GW of wind (5.5%)

Strong east-west power flows, i.e. the West depends on imports

strong wind generation in northern GermanySource: UCTE


Timeline

Image: http://www.cruise-ship-report.com/News/110506.htm

18 Sept: a shipyard request EON for a routine disconnection of double circuit 380 kV line Diele-Conneferde in northern Germany on 5 Nov

3 Nov: the shipyard request to bring forward the disconnection by 3 hours. Late announcement could not change exchange programs

4 Nov 9.30 pm: EON concludes empirically, without updated (N-1) analysis, that the outage would be secure. Wrong!

9.38: EON switches off of the line

10.07: Alarms of high flows. EON decides, without simulations, to couple a busbar to reduce the current

Result: the current increases and the line trips

As the system was not (N-1) secure, cascading line tripping follows

separation of UCTE into 3 regions with different frequencies


0.8 GW deficit49.7 Hz

8.9 GW deficit49 Hz

10 GW surplus51.4 Hz

Source: UCTE


Western Europe: 8.9 GW deficit

Frequency drop to 49 Hz triggered automatic and manual load shedding (17 GW) and automatic tripping of pump storage units (1.6 GW)

However the frequency drop caused also tripping of 10.7 GW of generation – more load had to be shed

DC connection UK-France: continued export from France despite the deficit!


Resynchronisation

A number of uncoordinated unsuccessful attempts made without knowledge of the overall UCTE situation

Full resynchronisation after 38 minutes

Source: UCTE


Cockenzie and Sizewell B were lost within 2 mins: (N-2) event, 1714 MW

Loss of Sizewell B is the largest infeed loss planned for (1320 MW)

Further 279 MW of wind tripped due to frequency drop (total 1993 MW)

Automatic load shedding of 546 MW triggered at 48.8 Hz

Voltage reduction caused reduction of demand by 1200 MW

More generation was connected and supply restored within 1 hour

Source: National Grid

GB May 2008 event: a near miss


Will there be more blackouts?

People tend to learn from the past

... but generals are usually prepared to the last (rather than future) war

Lessons learned from the blackouts - improvements in communications and coordination in Europe and USA

... but new challenges are looming ahead


Generation adequacy issues

Possible problems after 2015 (Ofgem Discovery report)

Regulatory uncertainty


Increased penetration of renewable generation

Wind already a contributing factor to UCTE 2003 and GB 2008 disturbances

“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)


Smart Grids

Comms-enabled responsive demand, electric cars etc

Highly stochastic generation and demand: (N-1) contingency criterion may become obsolete soon – new probabilistic risk assessment tolls required

Dependence on comms networks is a new mode of failure


Example of new modelling techniques: preventive network splitting

EPSRC grant started January 2010 (Complexity Science call)

Exciting collaboration between graph theorists from Southampton (Brodzki, Niblo) , OR experts from Edinburgh (Gondzio, McKinnon) and power engineers from Durham (Bialek, Taylor)

Split the network in a controlled manner before it partitions itself

Initial main challenge: speaking the same language, mutual education


Conclusions

(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

New challenges of increased wind penetration and Smart Grids

New mathematical modelling tools required to prevent future blackouts

p1 ©j.w. bialek, 2010 wide-area blackouts: why do they happen and how can modelling help professor...

Documents

bialek durham university

gloucester slide

classification of blackouts

overview of recent blackouts

widearea blackouts

circuit line nd slide

transmission inadequacy

ucte disturbance