WECC-0071 Common Corridor Issues - Literature Review Drafting Team Meeting, Portland, August 25, 2010

Outline 1. Overview of published sources 2. Common Mode Outages - Basics 3. Common Mode Outage Statistics 4. Common Right-of-Way Issues 5. Composite System Reliability 5. Next Steps

1. Published Literature Theoretical Approaches Papers published by IEEE Committees & Task Forces Outage Data Statistics Standards Common Corridor Issues Must Read References

1. Must Read References Task Force on Common Mode Outages of Bulk Power Supply Facilities of the Application on Probabilistic Methods Subcommittee of the Power System Engineering Committee, IEEE Power Engineering Society, 1976 (B4) R. Billinton, T. K. P. Medicherla, M.S. Sachdev, APPLICATION OF COMMON-CAUSE OUTAGE MODELS IN COMPOSITE SYSTEM RELIABILITY EVALUATION, Vol. PAS-100, No. 7, pp , Dec (A7) W. A. Mittelstadt, S. K. Agarwal Outage Probability Evaluation of Lines Sharing a Common Corridor, PMAPS 2004, Ames, Iowa (E3) Framework for Analyzing Separation Distances between Transmission Lines in Wyoming, Final Report, ICF International, February 2010 (E5)

2. CMO General Definition: A common mode outage is an event having an external cause with multiple failure effects where the effects are not consequences of each other (Unlike, for example, the forced outage of one transmission line due to a lighting stroke followed by an overlapping forced outage of an adjacent line due to protection relay failure). Two types of Common Mode Outages: Controlled common-mode outages (can be identified and possible eliminated – e.g. protection, separation) Un-controlled Common-mode outages (must be accepted and possible minimized – e.g. tornado, lighting etc.)

2. CMO Basics The State-Space Diagram (SSD) The SSD illustrates the possible failure and repair mode for two components 1 and 2 (single down state) 1 U 2 U 1 U 2 D 1 D 2 U 1 D 2 D λ i – component independent failure rate µ i – component repair rate λ c – component common mode failure rate U – Up state, D – Down State µ2µ2 µ1µ1 λ1λ1 λ 2 µ2µ2 µ1 λ1λ1 µc λc

2. CMO Basics (cont..) The State-Space Diagram (SSD) The SSD illustrates the possible failure and repair mode for two components 1 and 2 (separate down states) 1 U 2 U 1 U 2 D 1 D 2 U 1 D 2 D λ i – component independent failure rate µ i – component repair rate λ c – component common mode failure rate U – Up state, D – Down State 1 D 2 D µ2µ2 µ1µ1 λ1λ1 µcλcµcλc λ 2 µ2µ2 µ1µ1 λ1λ1

2. CMO Basics (cont..) Probability of ith component in up state Piu = µi/µi+λi Probability of ith component in down state Pid = λi/µi+λi for µi = 1/ri, the Pid = (λi* ri)/8760 Probability of circuits 1 and 2 on outage is given by: P12 = (λ1* r1)/8760 x (λ2* r2)/8760 The frequency of circuits 1 and 2 on independent outage is given by: λ12 = λ1λ2(r1 + r2) = λ1P2 + λ2P1 The common mode forced outage probability is given as: Pcmo = (λcmo* rcmo)/8760 The total probability Pt for the contingency of circuits 1 and 2 out including effects of common mode outage is given as: Pt = P12 + Pcmo, The frequency and duration are: λ t = λ12 + λcmo r t = (Pt/ λt)*8760

3. CMO Statistics (cont..) CMO Causes Natural Events –Fire in Right-of-Way (forest, brush, tall grasses, agricultural..) –Foundation or Anchor Failure (flood, landslide, ground subsidence) –Severe Environmental Conditions (hurricane, tornado, icing) Interference –Interference with other circuits. HV crossing of lower voltage circuits –Aircraft interference –Rail and road vehicle interference Examples of common-mode outages are: –A lighting stroke causing trip-outs of two circuits on a common tower –An external object causing the outage of two circuits on the same right-of- way –A tornado causing the outage of multiple circuits even if they are not on a common tower or a common right-of-way

3. CMO Statistics (cont..) Use of Transient and Permanent Forced Outage Data Transient outage data should be kept separate from permanent outage data in the study. Since the different durations have different system impacts, and since, often, the location of the outage cause cannot be defined it is recommended to classify transient outages into short duration or restoration by switching, and momentary duration or automatic re-closure.

3. CMO Statistics (cont..) Calculation of Common Mode Outage Indices: The failure rate in outages per 100 right-of-way miles per year The average duration of an outage The probability of more than one line being out simultaneously per 100 right-of-way miles for a common mode failure on system Similar methods can be used to calculate indices for the following categories by sorting the data as required: Transient and permanent faults Voltage classification Tower type Outage cause

3. CMO Statistics Common Mode Outage – Discussion (Ref. B7) There is a need to subdivide common mode outage events into two separate categories: –Simultaneous common mode outages (SCMO) –Overlapping common mode outages (OCMO) SCMO are outages of those components that occur within one second of each other OCMO are outages that occur at a time interval of more than one second, thus allowing time for automatic RAS to operate

3. CMO Statistics (cont..) Clarification of Specific Entries The line length should be expressed as miles of common right-of- way rather than miles of line Specific records should indicate both the number of lines on a right-of-way and the number of lines out. The common mode outage duration is defined as the overlapping time period only, and should be noted in the appropriate unit. Permanent and Transient outages should all be recorded allowing for future sorting. All common mode outages should be recorded, based on commonality of right-of-way.

3. CMO Statistics (cont..) IEEE Survey Conducted in 1974 (Ref. B4) Of 69 requests, 40 replied yielding 18 useful pieces of information The data did strongly suggest that the probability of two lines being forced out on an overlapping outage when they are on the same right-of-way is much larger than the probability of two lines being forced out on an overlapping basis when they are on separate independent rights-of-way. The amount of data is not significant enough to warrant release of figures at this time.

3. CMO Statistics General observations from MAPP Outage Data (Ref. C7) For the purpose of reporting common right-of-way and common tower events, expose of one mile or more are considered Related outage statistics are compiled by the study of outages that occur at the same time The time frame of ten minutes is used as a guideline for classifying independent outages as related outage events. Common right-of-way outages were not reported in MAPP from Common tower outages were reported 5 in the same time period.

3. CMO Statistics (cont..) IEEE Paper 1985 (Ref. C9) Independent Outage Rate 1.356/year Common-mode Outage Rate 0.174/year Dependent Outage* Rate 0.07 /year Total Outage Rate 1.6 /year *Dependent (Related Multiple) Outage Event A multiple outage Event in which one outage is the consequence of another outage Conditionally dependent outages involve two or more lines and are the result of two distinct causes.

3. CMO Statistics (cont..) IEEE Paper 1984 – Common-Mode Outages in MAPP for the time period (Ref. C6) Common Tower: –Number of outages 8 –Average number/100 Miles-Year = 0.20 –Total Duration (Hours) = –Average Duration (Hours/Outage) = –Average Duration (Hours/100miles-Year) = 9.48 Common ROW: –Number of outages 3 –Average number/100 Miles-Year = 0.14 –Total Duration (Hours) = –Average Duration (Hours/Outage) = –Average Duration (Hours/100miles-Year) = 7.79

3. CMO Statistics (cont..) An IEEE Survey of U.S. and Canadian Overhead Transmission Outages at 230 kV and above(1994) (Ref. C18) Common Tower Common-Mode Outages –230 kV …… 5 –345 kV …… 27 –500 kV …… 0 –Total ………. 32 Common ROW Common-Mode Outages –230 kV …… 0 –345 kV …… 9 –500 kV …… 0 –Total ………. 9

3. CMO Statistics (cont..) Con Edison Outage Data (1981) – Frequency of Forced Outages per Year for Average Con. Edison 345 kV Transmission Line (Ref. C5) Line related Cause –Independent …… (0.236)* –Common Mode… (0.171)* –Dependent ……… (0.044)* Terminal related Cause –Independent …… (0.304)* –Common Mode… (0.037)* –Dependent ……… (0.166)* * Momentary outages are excluded