Cascading simulation techniques in Europe: the PRACTICE experience

1. Cascading simulation techniques in Europe: the PRACTICE experience E. Ciapessoni, D. Cirio, A. Pitto 2013 IEEE PES General Meeting Vancouver, British Columbia, Canada July 21-25, 2013

2. PRACTICE • Tool for probabilisticassessment of operationalriskin powersystems • Based on riskconcept • Combination of probability and severity of a disturbance (contingency) • Assessingcascadingevolution … • important task • Cascadingenginehastwooperationmodes: • Single path • Multi path

3. Cascading engine: general features • Robust power flow program enhanced with steady-state models of: • frequency regulation (5% default droop) • main protection and defence systems, • e.g. line and transformer overcurrent, minimum impedance for lines, minimum and maximum voltage for generators and loads, under-frequency load-shedding (pumps and loads). • Able to assess an “impact” for the contingencies which cause load-flow divergence • adopting suitable load reduction techniques

4. “Single path” mode • Uncertainty only related to initiating event • Check violations of currents/voltages • One element trippedat a time • The element with highest violation • Does not take into account the uncertainty on protection systems response • Fast algorithm

5. “Multi-path” mode • Considersalsouncertainty in protectionsystemsresponse • Probabilistic models are defined for: • Hidden failures (HF) of protections exposed by the initial contingency or by overloads • Correct operation of the overcurrent relays

6. Benchmark for cascading engine • Italian EHV transmission grid with foreign equivalents: • 1400 electrical nodes • 1000 lines • 700 transformers • 300 generators • Peak and off peak load early 2000’s • Goal: comparing time sequence of events given by T-D simulator with the sequence of trippings by the single path cascading

7. Benchmarking • Dynamic model: • Prime movers & AVRs • Automatic load shedding • Overcurrent protections for branches (120% Imax) • No secondary frequency control • Standard model for loads (50% dyn 50% static) • Quasi static model (in PRACTICE): • Primary control • Automatic load shedding for power deficits • Overcurrent protections for branches (set to 120% Imax) • Constant power model for loads • Under/over voltage for loads and generators

8. Benchmarking results (I) Loss of an important 400 kV line in the North East Tripping of BUIV-UDNV 220 kV line Tripping of SOVV-LNZO 220 kV line at 42 s eliminatesviolation on this line!

9. Benchmarking results (I) Loss of an important 400 kV line in the North East Tripping of BUIV-UDNV 220 kV line Mutualreliefmechanismstakeninto account in quasi staticapproach Tripping of SOVV-LNZO 220 kV line at 42 s eliminatesviolation on this line!

10. Benchmarking results (II) Three most probable cascading paths identified by multi-path cascading engine (future time interval=5 minutes) Loss of the first line BUIV211-UDNV211 implies a very high overloading (140%) on branch SOVV212-LNZO211 Prob. of tripping of both lines (path # 1) >> prob. of tripping only of the first line (path # 3)

11. Benchmarking results (III) Loss of a large thermalpowerplant Cascading trippings well caught by PRACTICE

12. Benchmarking results (III) Loss of a large thermalpowerplant Cascading trippings well caught by PRACTICE (angle, voltage) instability mechanisms

13. Remarks • Proposed a benchmark for cascadingtools • A model of the Italian EHV transmissionsystem with foreignequivalents (early 2000’s) • Quasi static «single path» cascadingenginetestedagainst time domain simulator • Verygoodmatching with the sequence of events by time domain simulationatleast in the earlystages of cascading • Multi-pathcascadingengineprovidesprobability of differentsequences of trippings • Takinginto account hiddenfailuresand uncertainties on protectionrelaysettings Contact: Dr. Andrea Pitto, PhD e-mail: andrea.pitto@rse-web.it