Distribution System Reliability Evaluation

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,
• 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

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
xyz_err
subst
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
weather
animals
transmission
15
(No Transcript)
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
cable
other
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
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 SR0.9, Outage on M3 causes
• 0.90.5 (1-0.9)40.85 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 WESCANEX95 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