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Example of Power System Planning

Wirote Buaklee

ManagerofPowerSystemPlanning

ProvincialElectricityAuthority(PEA)

1)TransmissionPlanning

Existingsystem

 – 20MWload

 – 1Overheadline,20kmwith240/40mm2

(Al/St),impedance0.15+j0.38ohm/km,ratedcurrent:Ir =645A

20 MW-Existing

80 MW-future

Existing Line

Planned Line

230/115 kV

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Newdevelopmentplanforthearea

expectedloadgrowthfrom20MWto

80MW

 Asecondlineshallbeestablished

 – PossibilityA:20kmoverheadline(same

dataasexistingline)cost:5Mil.Baht/km

 – PossibilityB:10kmundergroundcable

500mm2 (Al),impedance0.07+j0.11

ohm/km,ratedcurrent:Ir=540A,cost:

11Mil.Baht/km

1.CalculateforpossibilityAandBfortotalloadof80MW,0.9pf.

1.1totalcurrent

1.2thecurrentoneachline

1.3thelossesonbothlines2.Comparetheinvestmentforboth

possibilities

3.Comparetheannualcostoflossesandthepresentvalueofthesecostsforbothpossibilities

- Specificcostoflosses:5000Baht/kW.yr- Interestrate:7%/yr

- Consideredperiod:20years

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4.Comparethetotalpresentvalues

(investment+losses)

5.Comparethenumberofoutage/yrwith

bothlinesoutofservice-numberoffaultsontheline/year:

overheadline:2/year

cable:0.5/year

- outofserviceformaintenance,repair

orotherwork:

overheadline:2days/year

cable:14days/year

2)SubstationPlanning

Questions:

Whichplanisthebestbetweenbuilding

newsubstationandadditional22kVLine?

2005: 1 MW

2010: 20 MW2020: 40 MW

d = 10 kmSub. A Area B

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 Alternatives  AlternativeA:

1996:- 115/22kVSubstationwith2x40MVAtransformerinareaB

 AlternativeB:

1996:- additional1x40MVAtransformerinexistingsubstationA

- three22kVlines95mm2(AL)fromsubstationAintoareaB

2005:- 115/22kVSubstationwith2x40MVAtransformerinareaB

 Alternatives  AlternativeC:

1996:- additional1x40MVAtransformerin

existingsubstationA- three22kVlines95mm2(AL)from

substationAintoareaB

2005:- Buildforth22kVlines95mm2(AL)

fromsubstationAintoareaB

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Costofconstruction

1x40MVAtransformer 2,500,000Baht

115kVSwitchgear 4,000,000Baht

115kVline 400,000Baht/km

Extension115kVswitchgear 1,000,000Baht

22kVline 180,000Baht/km

Interestrate 7%/year

Transformerresistance 0.03Ohm

115kVlineresistance 0.15Ohm/km

22kVlineresistance 0.31Ohm/km

Costoflosses 300Baht/kW.year

 Assumeallequipmenthavelineardedication