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 © 1996-2009 Operation Technology, Inc.  Workshop Notes: Reliability Assessment Reliability Assessment

24 - Reliability Assesment

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  • 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Reliability Assessment

  • Slide 2 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Power System Reliability

    Analysis

    Reliability

    The probability of a system performing its function adequately for the period of time and operation conditions intended

    Adequacy

    Sufficient facilities within the system to satisfy customer demand

    Security

    Ability of the system to respond favorably to disturbances arising within that system

  • Slide 3 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Power System Reliability

    Analysis

    Used in system planning and operation

    Reliability Assessment for:

    Generation station and generation capacity

    Composite generation and transmission system

    Distribution system

    Substation and switching stations

    Protection system

  • Slide 4 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Power System Reliability

    Analysis

    Various Indices to Measure Reliability

    Customer Interruption Frequency

    Customer Interruption Duration

    Customer Curtailment Power/Energy Not Served

    Reliability Worth Study

    Minimize Total Cost: Reliability Cost and Consumer Interruption Cost

  • Slide 5 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Distribution System Reliability

    Analysis

    Concerned with availability and quality of power

    supply at each customers service entrance

    Adequacy Analysis

    Statistics show that failures in distribution systems

    contribute as much as 90% towards the

    unavailability of supply to a load as compared with

    other parts of electric power systems

  • Slide 6 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Reliability Analysis Using ETAP

    Assesses distribution system reliability level for radial and looped systems with a very efficient

    algorithm

    Considers single and double contingencies

    Assesses reliability level for system and each load point based on component failure model and

    system configuration

    Performs sensitivity analysis to identify the optimal location to make greatest improvement on system

    reliability at minimum cost

  • Slide 7 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Single & Double Contingencies

    Consider a system with two or more parallel branches.

    In case of Single Contingency Analysis failure of only one branch at a time is considered.

    In case of Double Contingency Analysis simultaneous failure of two branches at a time is also considered in addition to failure of one branch at a time.

  • Slide 8 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Single & Double Contingency

    Example

    Single Contingency:

    Failure of T5 or T6 at a time is considered.

    Double Contingency

    Simultaneous failure of T5 & T6 and failure of T5 or T6 at a time is considered.

  • Slide 9 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Component Model

    A - Active Failure Rate (No of Failures/Year)

    Causes the operation of the protection devices aroundthe failed component, i.e. a short-circuit fault

    Failed component itself (and those components that aredirectly connected to this failed component) restores to

    service after repair or replacement

    P- Passive Failure Rate (No of Failures/Year)

    Does not cause the operation of protection around thefailed component, i.e. an open circuit fault

    Failed component itself restores to service after repairor replacement

  • Slide 10 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Component Model

    Mean Time To Repair in hours (MTTR)

    Time required to repair a component outage

    and/or restore the system to its normal operating

    state

    Mean Repair Rate (No of repairs per year) ( )

    = 8760/MTTR

    Mean Time To Failure (years) (MTTF):

    MTTF = 1.0/( A+ P)

  • Slide 11 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Component Model

    Mean Time Between Failure (Year) (MTBF)

    MTBF = MTTF + MTTR/8760

    Forced Outage Rate (Unavailability) (FOR)

    FOR = MTTR/(MTBF*8760)

    Switching Time

    Time in hours for isolating a fault occurred at the component

    Assume that CB/Fuse trip a fault instantaneously

    Time for replacing a failed element by a spare one,in hours rP

  • Slide 12 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Single-Component Concepts

    Two-State Model

    A two-state up/down representation is used for the operation/repair cycle of a component (such

    as lines, cables, transformers, breakers, fuses,

    switches, loads and busbars)

    DOWN

    = ( A+ P)Up

    Down

    MTTF

    ..

    ..

    MTTF

    MTTR MTTR

    UP

  • Slide 13 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Model for Components in

    Series/Parallel

    Two Components in Series

    sys

    rr

    sys

    rrrrsysr

    2211)

    22)(

    11(

    2211

    1, r1

    Component 1 Component 2

    21sys

    2, r2

  • Slide 14 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Model for Components in

    Series/Parallel

    Two Components in Parallel

    1, r1

    Component 1

    Component 2

    2, r2

    )21

    (21

    22111

    )21

    (21 rr

    rr

    rrsys

    21

    21rr

    rr

    sysr

  • Slide 15 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    System Modeling

    Fault Current Interruption

    Only overcurrent protection devices (CB and fuse) can interrupt fault current

    Fault current interruption is assumed to be instantaneous

    Assumed to have no effect on components with multiple source connection and isolated from

    fault by CB/fuses

  • Slide 16 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    System Modeling

    Fault Isolation

    All switching devices can isolate faults. CBs and fuses isolate fault instantaneously

    Switches isolate fault at switching time of the faulted component

    Switching time for a load is equal to that of the closest component

  • Slide 17 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    System Modeling

    Normally Open Tie: Open tie PD can be closed

    (switching time) to provide back up power

    Two terminal buses should be energized

    Can have several PDs connected in series and with one or more open

  • Slide 18 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Library for Reliability Analysis

    Component Reliability

    Data for each type of component - transformer, bus, line, etc.

    Active Failure Rate

    Passive Failure Rate

    Repair Time

    Switching Time

    Replacement Time

    Typical data from IEEE Standard

  • Slide 19 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Library for Reliability Analysis

    Sector Customer Interruption Cost

    Standard Industrial Classification (SIC) is used to divide customers into seven categories of

    large user, industrial, commercial, agriculture,

    residential, government & institutions and office

    & buildings.

    Sector Customer Damage Functions (SCDF) are interruption costs for several discrete outage

    durations.

  • Slide 20 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Library for Reliability Analysis

    A log-log interpolation of the cost data is used where the interruption duration lies between two

    separate times.

    If fault duration is outside the range, a linear extrapolation with the same slope as that

    between the two largest durations are used to

    calculate the interruption cost.

  • Slide 21 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Distribution System Reliability

    Indices

    Nejjei ,

    Average Failure Rate at Load Point i, i(f/yr)

    e,j - The average failure rate of element j (or element

    combination j, such as double contingency).

    Ne - The total number of the elements whose faults will

    interrupt load point i.

    Annual Outage Duration at Load Point i, Ui(hr/yr)

    Nejijrjei

    U,

    rij --Failure duration at load point i due to a failed element j.

  • Slide 22 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Distribution System Reliability

    Indices Average Outage Duration at Load Point, ri(hr)

    iiU

    ir /

    Expected Energy Not Supplied Index at Load Point, EENSi (MWhr/yr)

    iUiP

    iEENS Pi - the average load of load point i.

    Expected Interruption Cost Index at Load Point, ECOSTi(k$/yr)

    Nejjeij

    rfiP

    iECOST

    ,)(

    The EENS and ECOST for a bus are calculated based on loads that

    are directly connected to that bus due to the outage of that bus.

    Where f(rij) is the SCDF.

  • Slide 23 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Distribution System Reliability

    Indices Interrupted Energy Assessment Rate Index at Load Point,

    IEARi ($/kWhr)

    System Average Interruption Frequency Index, SAIFI

    (f/customer.yr)

    System Average Interruption Duration Index, SAIDI

    (hr/customer.yr)

    iEENS

    iECOST

    iIEAR

    iN

    iNiSAIFI

    servedcustomer ofnumber Total onsinterrupticustomer ofnumber Total

    Where N is the number of customers at load point i

    iN

    iNi

    USAIDI

    servedcustomer ofnumber Totaldurationson interrupticustomer of Sum

  • Slide 24 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Distribution System Reliability

    Indices Customer Average Interruption Duration Index,

    CAIDI(hr/customer interruption)

    Average Service Availability Index, ASAI(pu)

    iiN

    iNi

    UCAIDI

    onsinterrupticustomerofnumberTotalsdurationoninterrupticustomerofSum

    8760

    8760

    demanded hoursCustomer service available ofhoursCustomer

    iN

    iUi

    Ni

    N

    ASAI

    Where 8760 is the number of hours in a calendar year

  • Slide 25 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Distribution System Reliability

    Indices

    Average Service Unavailability Index, ASUI(pu)

    System Expected Energy Not Supplied Index, EENS (MWhr/yr)

    ASAIASUI 1

    EENS = Total energy not supplied by the system = EENSi

    System Expected Interruption Cost Index, ECOST(k$/yr)

    ECOST = ECOSTi

  • Slide 26 1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment

    Distribution System Reliability

    Indices

    Average Energy Not Supplied Index, AENS

    (MWhr/customer.yr)

    System Interrupted Energy Assessment Rate Index,

    IEAR($/kWhr)

    iN

    iEENS

    AENSservedcustomer ofnumber Total

    system by the suppliednot energy Total

    EENSECOSTIEAR

  • RA Example 1 Using ETAP

    1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment Slide 27

  • RA Example 1 Using ETAP

    Data:

    Active failure rate for breakers: a = 0.003 failure/year

    Passive failure rate for breakers: p = 0.002

    failure/year

    Failure rate for Bus, Utility: = 0.001 failure/year

    MTTR for breakers: 30 hours

    MTTR for buses, utility: 2 hours

    1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment Slide 28

  • RA Example 1 Using ETAP

    Reliability Indices at LP1:

    Failure rate for the main bus:

    CB1 fails actively OR passively CB2 and CB3 fail actively Utility fails Main bus itself fails

    yearfailure

    BusMainUtilityCBaCBaCBpaLP

    /013.0

    001.0001.0003.0003.0005.0

    3211

    The main bus would be de-energized if:

    1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment Slide 29

  • RA Example 1 Using ETAP

    Annual unavailability for the main bus:

    yearhour

    MTTR

    MTTRMTTR

    MTTRMTTRU

    BusMainBusMain

    UtilityUtilityCBaCB

    CBaCBCBpaCBLP

    /334.0

    001.02001.02003.030003.030005.030

    33

    22111

    Time to replace the main bus:

    hoursU

    rLP 692.25013.0

    334.01

    1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment Slide 30

  • RA Example 2 Using ETAP

    Results for the Single Contingency case

    1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment Slide 31

  • RA Example 2 Using ETAP

    Results for the Double Contingency case

    1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment Slide 32

  • RA Example 2 Using ETAP

    Calculations for the Double Contingency case:

    For simplicity for hand calculations:

    Failure rates for the breakers connecting the transformers to the buses are taken to be zero

    Failure rates of the two transformers are taken to be 1; MTTR = 200 hr.

    Therefore the failure rate at Bus 2 due to double contingency:

    yearfailuresrr

    rr

    double /0436681.0

    8760

    200120011

    8760

    )200200(11

    87601

    8760

    )(

    2211

    2121

    1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment Slide 33

  • RA Example 2 Using ETAP

    Calculations for the Double Contingency case:

    Failure rate for the single contingency case:

    Therefore total failure rate at Bus 2 :

    yearfailures

    gledoubleBus

    /0546681.0011.00436681.0

    sin2

    yearfailures

    A

    CBBusMainBus

    P

    CB

    A

    CBUgle

    /011.0

    62111sin

    1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment Slide 34

  • RA Example 3 Using ETAP

    1996-2009 Operation Technology, Inc. Workshop Notes: Reliability Assessment Slide 35