Optimum  Design  Return  Period  of  EHV  Lines  Considering  Reliability,  Security  and  Availability

1

CIGRE-­IEC  Colloquium  

Montreal,  May  9-­10,  2016

Optimum  Design  Return  Period  of  EHV  Lines  Considering  Reliability,  Security  and  

Availability

Asim Haldar,  Ph.D,  P.Eng.  CEATI  International

Leon Kempner,  Ph.D,  P.Eng.  Bonneville Power  Administration  

Alex MogilevskyCEATI International

Outline  of  the  Presentation  

Ø Introduction  Ø ScopeØ Historical  Background  of  Line  Failures  Ø Cost  ModelØ Line  Optimization  ModelØ SensitivityØ Summary  and  Conclusions  

A  Typical  Line  Diagram  of    a  230  kV  Power  System  (Network  at  High  Level)

Typical  System  

• Structural  System

• Electrical  System

In  all  these  systems,  load  must  not  exceed  the  capacity  or  demand  must  be  less  than  the  capacity  in  order  for  the  system  to  survive  

Electrical  System

SystemReliability

SystemAdequacy

SystemSecurity

RESILIENCY

Structural  System  

Reliability

Security

Resiliency  Of  The  Power  GridSY

STEM

DES

IGN

LEV

EL

DAMAGE LEVEL

TIMENATURAL HAZARD

EVENT

PRE-HAZARD LEVEL

POST-HAZARD LEVEL

MITIGATIONEFFORT

ΔTIME

ΔDA

MA

GE

RECOVERY TIME

Resilience Index = Area of Triangle

Line  Failures

Serviceability  Limit  State

Ultimate  Limit  State

Reliability  and  Security  Integration  

Ø It   is  well  known  that  two  lines  designed  with  same  reliability  level  can  have  very  different  availabilities  should  the  failure  modes  and  the  extent  of  the  failure  zones  be  different.  

Ø Haldar  et  al  (2007,2008,  2009  and  2010)  have  used  finite  element  models  to  estimate  the  extent  of  the  cascade  zone  of  overhead  lines.  The  model  included  multiple  tower  failures.  The  purpose  was  to  estimate  the  cascade  failure  zone  and  the  expected  number  of  tower  losses  to  link  the  number  of  tower  failures  to  repair  time.  

Ø Although  numerical  model  for  cascade  requires  some  improvement,   these  models  can  be  used  to  explore  the  extent  of  the  line  damage  and  its  effect  on  the  repair  rate  (μ)    and  line  availability.  

Canisius  et  al  ICASP  2007

Scope

Cost

Reliability  (Return  Period)

Initial  Cost Cost  of  Failures

Total  Cost

Least  Cost

Historical  Information-­ Major  Blackouts  in  the  Past  35  Years  (some  examples)

80%  of  FranceBlackout

Sweden  Voltage  Collapse

FranceVoltage  Collapse

SloveniaIce  Storm

1978                          1983                      1987      1996  1998                      2003                                  2005    2007  2008  2012  2014

IndiaBlackout

Northeast  USABlackout

QuebecBlackout

FranceWind  storm

ColumbiaBlackout

LondonBlackout

ItalyMalaysia…

….

MexicoBlackout

MoscowBlackout

ChinaIce  Storm

JapanEarthquake

HurricaneSandy

Historical  Line  Failures

1998  Quebec  Storm  

http://theenergylibrary.com/node/13088

(Electrical)August  2003  

(Structural)  

Line  Cost  Model  -­ Optimum  Cost  Versus  Reliability

Cost

Reliability

Initial  Cost(Cost  of  Maintenance)

Cost  of  Damage(Cost  of  Failures)

Total  Cost

Least  Cost

CT =  CI +  PV(CM +  PfCf +  Outage  Cost)

Design Operation Planning   (Line  Security)

ConsequencesFailure  Probabilities

(Ref:  Robert  Bea)

TCOST

LCOST DCOST

Initial-StructuralDesign System-Model

Line  Cost  Model  – Flow  Chart

Overlap  RegionL R Probability

Density  Functionof  Strength  of

Member

ProbabilityDensity  Functionof  Member  Load

CT =  CI +  PV(CM +  PfCf +  Outage  Cost)

µλµ+

Availability  =  

Unavailability  =   µλλ+

Line  Optimization  Model-­ Reliability  &  Availability  Cost  Components  

DCOST  Determination

ØStructural  SystemPf  =  φ(-­β)=1-­ φ(β)

where  :  Pf  =  failure  probability  

ØElectrical  System

Where:  SI  =  Severity  Index

min60*(MW)LoadPeakhr)(MWEENSSI −

=

Energy  and  Peak

25%

35%

40%Industrial

Commercial

Residential

Example  Problem  -­Optimum  Return  Period  

Sensitivity Summary  &  Conclusions  

A sensitivity analysis also shows that the optimum design return period is less influenced by discount rate and the cost of line replacement and more sensitive to the duration of outage and IEAR value used.

Haldar (2011) has extended the concept to parallel line configuration as well to study the integration of a HVDC line in an existing 230kV power network system by minimizing the total cost and hence, determining the optimum return period.

The study presents a basis for computing the optimum designreturn period of an overhead line considering the initial linecost and the present value of the future failure cost.

The optimization is performed considering the initial line costand the cost of losses due to line failures. The failure costconsists of two components; (1) expected cost of linereplacement and (2) expected cost of energy not supplied.

A mathematical model is developed for a radial lineconfiguration and it is shown clearly that the optimum designreturn period is significantly influenced by the duration of theline repair once it has failed and the cost of energy rate (IEARparameter).

The line should be designed for a higher return period if theduration of repair is expected to be long to ensure that the linecost is balanced against the present value of the failure costs.

The sensitivity analysis also shows that the optimum designreturn period is less influenced by discount rate and the costof line replacement and more sensitive to the duration ofoutage and IEAR value used.

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