“Voltage Stability Problems in the Power System of Greece ... · June 5-8, 2005 Les Diablerets,...

1June 5June 5--8, 2005 Les 8, 2005 Les DiableretsDiablerets, Switzerland, Switzerland

““Voltage Stability Problems in the Power System of Greece Voltage Stability Problems in the Power System of Greece and Measures taken at System Design Stage, Daily Operation and Measures taken at System Design Stage, Daily Operation

and Real Timeand Real Time””

Thanos Thanos KoronidesKoronidesHellenic Transmission System OperatorHellenic Transmission System Operator


Power System in Power System in HTSOHTSO’’ss ResponsibilityResponsibility

Electric Power Transmission System• 400 kV Bulk Transmission• 150 kV In parallel with 400kV• Interface 400kV/150kV 43 Autotransformers of 250 or 280

MVA

Load of the System• Summer Peak at 9500 MW, last year (estimated)• Load evolution rate about 4% average last 10 years


Μηνιαίες αιχµές για την περίοδο 1997-2010

5,05,56,06,57,07,58,08,59,09,5

10,010,511,011,512,0

Ιαν Φεβ Μαρ Απρ Μάϊος Ιουν Ιουλ Αυγ Σεπτ Οκτ Νοε ∆εκ

µήνας

GW

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

Monthly Peaks and projections 1997-2010


Monthly Peaks since 1997

1997 1998 1999 2000 2001 2002 2003 2004 2005Jan 5768 6202 6212 6874 7076 7537 7408 8075 8102Feb 5875 5967 6288 6661 7055 6820 7832 8012 8393Mar 5658 6007 6131 6507 6736 6996 7488 7639 8016Apr 5614 5550 5684 5984 6343 6703 7145 7160 7445

May 5627 5572 5789 6422 6730 6521 7059 6847

June 6527 6703 6896 7697 7664 8587 8595 8448July 6703 7370 7364 8529 8598 8922 9040 9500*

Aug 6108 6973 7108 7603 7841 7694 8552 8582Sept 5787 6126 6120 6860 7121 6990 8537 8288Oct 5847 5608 5951 6465 6572 6843 6919 7153Nov 5685 6076 6374 6566 7002 7064 7358 8221Dec 6261 6718 6671 7182 7788 7767 8186 8354

Year 6703 7370 7364 8529 8598 8922 9040 9500*


Μοντέλα φορτίου-καιρού ηµερησίων αιχµών για την περίοδο Μαρ 1997 - Φεβ 2005

0

1000

2000

3000

4000

5000

0 5 10 15 20 25 30 35 40 45οC

MW

97-98

98-99

99-00

00-01

01-02

02-03

03-04

04-05

Load Temperature Dependency since 1997

Βασικό φορτίο ηµερησίων αιχµών για την περίοδο Mαρ 1997 - Φεβ 2005

010002000300040005000600070008000

Ιαν Φεβ Μαρ Απρ Μαιος Ιουν Ιουλ Αυγ Σεπτ Οκτ Νοε ∆εκ

1997

1998

1999

2000

2001

2002

2003

2004

2005

Basic Load Since 1997

High load-temperature Dependency

Air Conditioning and Pumping for Irrigation

Lot of MVARs


Main Features of the Power SystemMain Features of the Power System

Existing Production• Most of the Production ( ~68%) in the North• Most of the Load (~45%) in the South• Several Old Units in the South• Lack of 400kV Network in the very South

New Production:• Official Opening of the Market, 2001Zonal UOC pricing System for Generators in 3 zones North-Capital-

South, Most expensive in the North –zero near the Capital• Only one unit (300 MW) built after the opening. This in the North


Transmission System Expansion, very difficult• Licensing very complex and time consuming• Reaction of local communities – even to GIS substations with

cable connections

Voltage Stability Problems

• First incident 1996, at about 6500MW load• Second Incident 2004, 12 July voltage collapse and partial

black out at about 9300 MW


Voltage Collapse as recorded in Generating Stations in the South __

The Center__ and the Capital Area -- --


Measures Taken at the Planning StageMeasures Taken at the Planning Stage

For the Olympics the following was planned• About 500 MVAR of Capacitors mainly at 20 kV including 100

MVAR at 150 kV• Five ATRs (280 MVA each) in the South• New 400/150 kV S/S 10km from the center of Athens• 250 MVA new GTs near Athens

Was available before July 12• About 400 Mvars (capacitors) constructed but ~100Mvars

commissioned, total commissioned few days after• 3 out of 5 ATRs commissioned, 2 commissioned few days after• 100 MVA of new GTs available the rest finished later• 400/150 kV S/S never finished due to local community reaction


During O.G. 2004During O.G. 2004

Before the Olympics the majority of planned enhancements completed, except the new 400/150 kV S/S because of local reaction.

Everything went smooth during the games, it is characteristic that the auxiliary gen sets in Olympic Installations were never used not even for a minute during the games.


Other Measures for the FutureOther Measures for the Future

• Further Compensation of the reactive Load(about 200 MVAR per year)

• Load Management incentives and Load Reduction AutomationFirst Measures Taken Summer 2005

• Provision for Market Splitting into two areas in the new Grid Code (signed in April) in conjunction with a 2 zones UOC pricing for Generators


Measures Taken in Daily OperationMeasures Taken in Daily Operation

Use of OPF

• OPF program available, integrated in the EMS platform• Typically used day ahead for the next day operation and on the

spot with real time data• Use of OPF for tuning taps of 400/150 kV Autotransformers


OPF in the Day Ahead Operation

• Read unconstrained generationschedule from Market Database

• Read from Market Database thesystem load forecast.

• Use expected topology, accordingto the maintenance plan, solve aPower Flow and check for possibleviolations on network branches.

• In case of violations, solve an OPF for generation rescheduling thatcorrects these violations.


OPF and Network Programs in Real Time Operation


Voltages in the south before and after OPF in critical winter day 2003


Change of tap settings


Unit MVar controls


Increase of System Loadability Limits before and after OPF

86008600 9200


Athens area loadability limits before and after OPF


OnOn--Line Voltage Security Assessment in the Line Voltage Security Assessment in the HTSO Control CenterHTSO Control Center


VSA in the NCCVSA in the NCC

VSA implementation in the Control Center of HTSO was developed in the frame of a research project named OMASES partially funded by EU funds.

OMASES-VSA integrates two VSA software packages,Secure Operation Limits (SOL) and contingency filtering which rely on the ASTRE software developed at the University ofLiège.

Computation of Post Contingency Loadability Limits and theproduction of PVcurves rely on the WPSTAB softwaredeveloped at the National Technical University of Athens.


VSA MAIN FUNCTIONSVSA MAIN FUNCTIONS

System Stress: Security margins computed for a pattern of system stress, i.e. a change in load and generation which makes the system weaker by increasing power transfer over long distances.

Loadability Limits: how much the system can be stressed before reaching instability. Pre-contingency loadability limits and Post-contingency Loadability limits (PCLLs) (apply contingency, then stress)

Secure Operation Limits For a given direction of stress, the SOL corresponds to the most stressed operating point such that the system can withstand any contingency of a specified list (stress first, then apply contingencies)

Diagnostic Tools in Expert Mode In case of voltage instability ranking of bus active and reactive power injections, thereby pointing out where generation should be rescheduled, or load shed.

24June 5June 5--8, 2005 Les 8, 2005 Les DiableretsDiablerets, Switzerland, SwitzerlandPackage to be archived

FRONTEND DATABASE

ASTRE

Data Loader Program

WPSTAB

Data Loader

Program

HTTP server

Data files

Results

Log files


One Critical CaseOne Critical Case Summer 2002

no.contingency

namemargin(MW)

329 LINE_CON_ΤΜΟΥ∆ΑΝ-ΜΟΥ∆.1 0296 LINE_CON_ΜΟΥΡΤ-ΜΕΣΟΓ.1 0228 LINE_CON_ΚΘΕΣ-ΣΧΟΛΑΡ.1 0312 LINE_CON_ΜΕΣΟΓΓ-ΚΕΡΚ2.1 0109 LINE_CON_ΑΡΓ2-ΑΡΓ1.1 73347 LINE_CON_ΣΧΗΜ-ΘΗΒΑ.1 9469 GEN_CON_Κ_ΛΑΥΡΙΟ.GFIC.UN 14658 GEN_CON_ΛΑΥΡΙΟ.GFIC.GEN2.UN 16790 LINE_CON_ΑΓΡΑΣ-ΣΚΥ∆ΡΑ.1 292388 LINE_CON_ΦΙΛΙΠ-ΑΜΦΙΠΟ.1 32422 GEN_CON_ΑΓ.ΓΕΩΡΓ.GEN9.UN 470

all other contingencies > 668


National PV curve without Contingency National PV curve without Contingency (500 MW margin)(500 MW margin)

Summer 2002


National PV curve for Contingency 69National PV curve for Contingency 69Summer 2002


LoadabilityLoadability ––Athens Area Load after Contingency 69Athens Area Load after Contingency 69Summer 2002


LoadabilityLoadability ––Central Area Load after Contingency 69Central Area Load after Contingency 69Summer 2002


The PV curve pre BThe PV curve pre B--O Conditions (2004). O Conditions (2004). LoadabilityLoadability limit is 9390 limit is 9390 ΜΜW (400 MW in the South out W (400 MW in the South out

the previous day) and the margin is only 40 MW.the previous day) and the margin is only 40 MW.

0.72

0.74

0.76

0.78

0.8

0.82

0.84

0.86

0.88

0.9

9050 9100 9150 9200 9250 9300 9350 9400

Vol

tage

s (p

.u.)

Area Load (MW)

LONG-TERM SIMULATION

710

2 ATRs and 400 MVARs not commissioned

2 Units went off

Several Lines in maintenance


LoadabilityLoadability after loss of Aliveriafter loss of Aliveri--3 unit. System 3 unit. System collapse due to voltage instability.collapse due to voltage instability.

0.7

0.72

0.74

0.76

0.78

0.8

0.82

0.84

0.86

0.88

0.9

8850 8900 8950 9000 9050 9100 9150 9200 9250 9300 9350 9400

Vol

tage

s (p

.u.)

Area Load (MW)


710


Loss of AliveriLoss of Aliveri--3 unit, but 132 3 unit, but 132 MvarMvar of capacitor banks of capacitor banks available (were commissioned 10 days after). The system available (were commissioned 10 days after). The system could withstand the loss of the unit with a margin of 70 could withstand the loss of the unit with a margin of 70

MW.MW.

0.74

0.76

0.78

0.8

0.82

0.84

0.86

0.88

0.9

0.92

9100 9150 9200 9250 9300 9350 9400 9450

Vol

tage

s (p

.u.)

Area Load (MW)


710


0.74

0.76

0.78

0.8

0.82

0.84

0.86

0.88

0.9

0.92

9150 9200 9250 9300 9350 9400 9450 9500

Vol

tage

s (p

.u.)

Area Load (MW)


710

Capacitors as previous slide and 2 ATRs available, with unit Aliveri-3 out, the system could go up to

9460 ΜW(100 MW of margin), with this unit in up to 9650

(300MW margin)


ConclusionConclusion 1/21/2

• Load Generation inbalance exposes the System in Voltage problems and instability

• Attracting new generation near the load is difficult in the open market environment , unless special measures and market rules are taken. In new grid code in Greece provision exists for market splitting (north-south). Also Generators are charged in two zones for UOC. HTSO is also allowed to procure units under special contracts

• System expansion is becoming more and more difficult. Some communities even react to GIS substations with cable connections.


ConclusionConclusion 2/22/2

• Enhancements within existing substations , more ATRs linking 400kV/150 kV is improving the situation

• Better compensation, capacitors at 20kV, 150 kV and SVCs are effective solutions with no environmental impact

• Tools in the control room are very important for the operator :Provide advice for new tap settings and reactive generation Improve the loadability limits of the systemPin point critical contingenciesPin point areas with most effective load rejectionGive confidence to the operator and Justify operators action


AcknowledgementAcknowledgement

VSA implementation in the NCC of HTSO was developed in the frameof the EU sponsored project named OMASES (Open Market Access and Security Assessment System) with the contribution of the following companiesHTSO,ALSTOM, CESI,TRACTEBELand the UniversitiesNational Technical University of AthensUniversity of LiegeUniversity of GenovaStrathclyde


Main ReferencesMain References

• G.P. Christoforidis D.G. Michos “Operational Experience With Optimal Power Flow At The Hellenic Transmission System Operator” Medpower2004, Cyprus

• C. D. Vournas, G. A. Manos, J. Kabouris, G. Christoforidis, G. Hasse, T. Van Cutsem “On-Line Voltage Security Assessment of the Hellenic Interconnected System”,2003 Bologna Power Tech IEEE

• A. Bihain, G. Burt, F. Casamata, T. Koronides, R. Lopez, S. Massucco, D. Ruiz-Vega, C. Vournas, “Advance Perspectives and Implementation of Dynamic Security Assessment in the Open Market Environment”,paper 39-101, CIGRE 2002.

• Christoforidis G., Kabouris J., Vournas C., and Van Cutsem T., “Investigation of Parameters Affecting Voltage Security of the HellenicInterconnected System”, 15th PSCC, Liege, Belgium, Aug. 2005.

• T. Van Cutsem, J. Kabouris, G. Christoforidis, C. D. Vournas : “Applicationof real-time voltage security assessment to the HellenicInterconnected system”, IEE Proceedings - Generation, Transmission andDistribution,Vol.152, No.1, pp. 123-131, Jan. 2005.

“Voltage Stability Problems in the Power System of Greece ... · June 5-8, 2005 Les Diablerets,...

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