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Distribution System Reliability Evaluation

Distribution System Reliability Evaluation. Sree Rama Kumar Yeddanapudi. Overview. Introduction to Distribution systems Distribution Reliability Standard Reliability Metrics Historical Reliability Evaluation Information Required for Predictive Analysis Predictive Reliability Evaluation.

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Distribution System Reliability Evaluation

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  1. Distribution System Reliability Evaluation Sree Rama Kumar Yeddanapudi

  2. Overview • Introduction to Distribution systems • Distribution Reliability • Standard Reliability Metrics • Historical Reliability Evaluation • Information Required for Predictive Analysis • Predictive Reliability Evaluation

  3. Introduction to Distribution Systems • 5kV- 69kV system class, <100 MVA • Layout • Substations • Primary distribution system • Secondary distribution system • Largely a radial system with single, two and three phase lines. • Responsible for the majority (about 80%) of customer interruptions that are either momentary or sustained.

  4. Why do Outages Occur? • Equipment: Thousands of them that can fail • Vegetation/ Trees • Animals • Birds • Squirrels • Snakes • Rodents and pests • Weather • Lightning • Snow storms • Wind • Heavy rains • Human Factors

  5. Distribution Reliability • Motivation/Objective • Determine the system reliability and customer satisfaction: • Number of momentary and sustained interruptions • Duration of interruptions • Number of customers interrupted • Improve system performance • Basis for new or expanded system planning • Satisfy regulatory requirements • Determine performance based rate making • Maintenance scheduling and Resource allocation

  6. Standard Reliability Metrics(IEEE-Std. 1366) • Load point indices • Determine for each customer • The Number of outages (per year) • The Duration of outages (per year) • Unavailability / Availability of service • System wide indices • SAIFI (System Average Interruption Frequency Index) • SAIDI (System Average Interruption Duration Index)

  7. Standard Reliability Metrics Contd. • CAIDI (Customer Average Interruption Duration Index) • MAIFI (Momentary Average Interruption Frequency Index) • CTAIDI (Customer Total Average Interruption Duration Index) • CAIFI (Customer Average Interruption Frequency Index)

  8. Standard Reliability Metrics Contd. • ASAI (Average Service Availability Index) • ASIFI (Average Service Interruption Frequency Index) • ASIDI (Average Service Interruption Duration Index)

  9. Historical Vs Predictive Analysis • Historical Analysis • Use system outage histories to compute indices that reflect past performance of the system • Basis for most short term decision making • Used in the computation of failure rates and repair times required as input to predictive analysis • Predictive Analysis • Combine system topology with a set of techniques to estimate load-point and system indices • Basis for most long term as well as short term decision making

  10. Historical Reliability Evaluation

  11. Historical Reliability Evaluation Contd.

  12. Classification of Outages • Based on geographic/ operational regions • System wide • Region • District • Feeder • Based on cause of outage • Transmission/Substation • Tree Contacts • Equipment Overhead/Underground • Weather • Utility Error • Public • Animal • Unknown/Other • Based on component that failed • Substation Breakers • Transformers • Conductors • Arresters • Fuses • Insulators

  13. SAIFI contributions based on outage cause 0.6000 0.5000 0.4000 1997 0.3000 1998 1999 2000 0.2000 0.1000 0.0000 trees animals OH public UG other subst xyz_err weather transmission

  14. SAIDI contributions based on outage cause 45.0000 40.0000 35.0000 30.0000 1997 25.0000 1998 1999 20.0000 2000 15.0000 10.0000 5.0000 0.0000 OH UG trees other subst public xyz_err animals weather transmission

  15. SAIFI contributions based on component that failed 0.0800 0.0700 0.0600 0.0500 1997 1998 0.0400 1999 2000 0.0300 0.0200 0.0100 0.0000 fuse pole other cable arrestor insulator conductor transformer line hardware subs. Breaker

  16. SAIDI contributions based on the component that failed 10.0000 9.0000 8.0000 7.0000 1997 6.0000 1998 5.0000 1999 4.0000 2000 3.0000 2.0000 1.0000 0.0000 fuse pole other cable arrestor insulator conductor transformer line hardware subs. Breaker

  17. Understanding Failures • An example case: • Loads located at A, B, C; Protective devices: B, F; Switches: S • Fault types: Faults can occur on: —Temporary faults line-segments 1, 2, 3 —Permanent faults laterals a, b , c

  18. How to Predict Reliability? • Analytical Methods • Use system topology along with mathematical expressions to determine reliability indices • Simulation Based Methods • Compute indices by simulating the conditions on the system by generating system states of failure and repair randomly • Assumptions made in Analytical Methods • Temporary and Permanent fault processes are: • Mutually exclusive • Independent • Occurrence of a fault excludes the occurrence of another until the system is restored to normalcy. Can be a reasonable assumption if the system spends a majority of the time in its normal working state • The failure time and the repair time of components are exponentially distributed.

  19. Information Required for Predictive Reliability Evaluation • System topology • Reliability parameters • Over-head and underground line segments • Permanent Failure Rate (lp): Average number of sustained faults/year • Temporary Failure Rate (lt) : Average number of momentary faults/year • Mean Time to Repair (MTTR) : Average repair time/sustained fault. • Protective and Switching Devices (Reclosers, Switches, Fuses, Breakers, etc.) • Probability of Failure (POF): Conditional probability a device/ switch fails to operate when required. • Protection Reliability (PR): Conditional probability a device operates when a fault occurs downstream of it. • Reclose Reliability (RR) : Conditional probability a recloser closes after a fault is cleared. • Mean Time to Repair (MTTR): Average time taken to repair a failed device/switch • Switching Reliability (SR): Conditional probability a switch is operated when required. • Mean Time to Switch (MTTS): Average time taken to operate the switch. • Customer and Load Information

  20. Enumerative Analysis (Failure Modes and Effects Analysis) Switching time = 0.5 hours

  21. Enumerative Analysis (FMEA) contd.

  22. Enumerative Analysis (FMEA) contd.

  23. Fuse Operates (0.95) 0.95*0.2*900= 171 Customers interruptions /Year 0.95* 0.2*3*900= 513 Customer Hours/ Year Fault on L1 (λ=0.2/Year) (1- 0.95)* 0.2*2025=20.25 Customers interruptions /Year (1-0.95)* 0.2*4*2025=81 Customer Hours/ Year Fuse fails (1-0.95) Device Operates (PR) PR*λ*Response 1 Fault (λ) (1-PR)*λ*Response 2 Device fails (1-PR) Accounting for Protection Device Failures • When a protective device fails to operate after a fault occurs downstream of it, the backup protective device operates and clears it causing more number of customers to be interrupted for a longer period of time.

  24. Accounting for Switching Failures • When a switch fails to operate, customers are not restored and experience a duration equal to the MTTR of the fault. • Equivalent outage duration experienced: where • Example: • For an ideal switch S1, Outage on M3 causes 0.5 hours of interruption on Customers C1, C2 and 4 hours to others • For Switch S1 has SR=0.9, Outage on M3 causes 0.9*0.5+ (1-0.9)*4=0.85 hours of interruption at Customers C1, C2 and 4 hours to the others

  25. Other Methods To Evaluate Reliability • Analytical • Zone-Branch Reduction Method • Markov Modeling • Network Reduction • Fault Tree Analysis • Cut-set Analysis • Simulation • Sequential Monte Carlo method • Non-sequential Monte Carlo method

  26. QUESTIONS

  27. References • Muhammed Rahim. “HISTORICAL DISTRIBUTION SYSTEM RELIABILITY ASSESSMENT”, MidAmerican Energy Company, Davenport • S S Venkata, “Distribution System Reliability”, Class presentation for EE 455-Introduction to Energy Distribution Systems. 2001 • IEEE Guide for Electric Power Distribution Reliability Indices, IEEE Standard 1366, 2003 Edition • Richard E Brown, “Electric Power Distribution Reliability”, Marcel Dekker, 2002. • R. Billinton, “Distribution System Reliability Evaluation”, IEEE tutorial course- Power System Reliability Evaluation • Ron Allan, R. Billinton, “Power System Reliability and Its Assessment- Part 3 Distribution Systems and Economic Considerations”. IEEE Tutorial. • Gerd Kjolle, Kjell Sand, “RELRAD- An Analytical Approach For Distribution System Reliability Assessment”, IEEE Transactions on Power Delivery, April 1992. • R. E. Brown, H. V. Nguyen, J. J. Burke, “A Systematic And Cost Effective Method To Improve Distribution System Reliability”, IEEE Power Engineering Society Summer Meeting, 1999. • R. Billinton, Peng Wang, “A generalized method for Distribution system reliability evaluation”; IEEE WESCANEX’95 Proceedings. • IEEE recommended practice for the design of reliable industrial and commercial power systems IEEE Std 493-1997 [IEEE Gold Book] • D.O. Koval, “Zone Branch Reliability Methodology for Analyzing Industrial Power Systems”, IEEE Transactions on Industry Applications, Oct-2000. • R. E. Brown, S. Gupta, R. D. Christie, S S Venkata, R Fletcher, “Distribution System Reliability Assessment Using Hierarchical Markov Modeling”, IEEE Transactions on Power Delivery, October 1996. • R. Billinton, Peng Wang, “Teaching Distribution System Reliability Evaluation Using Monte Carlo Simulation”; IEEE Transactions on Power Systems, May 1999. • A Report of the IEEE/PES Task Force on Impact of Maintenance Strategy on Reliability of the Reliability, Risk and Probability Applications Subcommittee; “The Present Status of Maintenance Strategies and the Impact of Maintenance on Reliability”, IEEE Transactions on Power Systems, Nov 2001 • Ying He, Lennart Soder, Ron N Allan, “Evaluating the effect of protection system on reliability of automated distribution system”, 14th Power system Computation Conference, June 2002. • J. Endrenyi, “Reliability Modeling in Electric Power Systems”, John Wiley & Sons, • Enrico Carpaneto, Alessandra Mosso, Andrea Ponta, Emiliano Roggero, “Comparison of Reliability and Availability Evaluation Techniques for Distribution Network Systems”; IEEE 2002 Proceedings Annual Reliability and Maintainability Symposium. • Papic, M.; Allan, R.N.; “Comparison of Alternative Techniques for the Reliability Assessment of Distribution Systems”, Third International Conference on Probabilistic Methods Applied to Electric Power Systems, 1991. • Theory Manual, “Distribution Reliability Indices for Vegetation- DRIVE version 2.0” • Jim McCalley, Tim Van Voorhis, Yong Jiang, A.P. Meliopoulos, “Risk-Based Maintenance Allocation and Scheduling for Bulk Transmission System Equipment”- PSERC project Final Report • T. Gonen, “Electric Power Distribution System Engineering”, McGraw Hill, 1986.

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