P 505

Statistical Determination of Insulator Performance at Koeberg

Insulator Pollution Test Station

Presented by Dr WL Vosloo (Eskom)

Dr I Gutman (STRI)

Dr JP Holtzhausen (University of Stellenbosch)

Typical Performance Data at KIPTS

Note: E-1 and F are the reference insulators at KIPTS and was not chosen as the optimum solution for this area.

Electrical Performance with Natural Pollution

Natural Ageing Performance

Statistical Approach

S t r e s s f ( ) S t r e n g t h P ( )

R i s k f o r f l a s h o v e r

P o l l u t i o n s e v e r i t y ( )

Str

ess:

den

sity

of o

ccur

renc

e

Str

engt

h: p

roba

bilit

y fo

r fla

shov

er

)()( Pf

S t r e s s f ( ) S t r e n g t h P ( )

R i s k f o r f l a s h o v e r

P o l l u t i o n s e v e r i t y ( )

Str

ess:

den

sity

of o

ccur

renc

e

Str

engt

h: p

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bilit

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)()( Pf

1. Pollution stress at site: probability density function f()

2. Probability for flashover at maximum operating voltage: cumulative distribution function P()

3. Multiplication of f() and P() – the area under this curve defines the risk for flashover

Pollution stress at site:probability density function f()

2

1 fKU

I

where: = conductivity of the pollution layer in μS

I = peak leakage current in A U = peak phase voltage in kV

fK = insulator form factor

L

f sR

dsK

0 )(2 where: S = the distance measured along the profile of the insulator L = creepage path length R(s) = insulator radius at distance ‘s’

The site ESDD in mg/cm2 can be calculated from:

1SiteESDD

where: = 150 (empirically determined factor)

Measured on Insulator at KIPTS

I U

Probability for flashover at maximum operating voltage:

cumulative distribution function P()

2

1 fKU

I

where: = conductivity of the pollution layer in μS

I = peak leakage current in A U = peak phase voltage in kV

fK = insulator form factor

L

f sR

dsK

0 )(2 where: S = the distance measured along the profile of the insulator L = creepage path length R(s) = insulator radius at distance ‘s’

11

1

1%50

n

n

nn

n

f LKAU

where: A = 2.27 (empirically determined factor) n = 0.35 (empirically determined factor)

NCI totally Hydrophilic

Measured on Insulator at KIPTS

Calculated Number of Flashovers per Insulator per year

Determine What Insulation to Use

Predict In Service Insulation Performance

Transmission Line

Calculatedfaults per year

Actualfaults per year

A 0,6 1,0

B 1,0 0,5

C 0,2 0,5

• Further investigate the use of leakage current data measured on all insulators tested at KIPTS so as to determine there statistical performance curves

• Determine statistical performance curves for various standard insulators in the laboratory (ac and dc)

• Establish a methodology where both sets of data can be used so as to help Eskom select insulators for the power network

Future Work

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