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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
Electrical Performance with Natural Pollution
Natural Ageing Performance
Note: E-1 and F are the reference insulators at KIPTS and was not chosen as the optimum solution for this area.
Strength P()
Stress f()
f ( )  P( )
Risk for flashover
Strength: probability for flashover
Stress: density of occurrence
Statistical Approach
Pollution severity()
1.
2.
3.
Pollution stress at site: probability density function f()
Probability for flashover at maximum operating voltage: cumulative distribution function P()
Multiplication of f() and P() – the area under this curve defines the risk for flashover
Pollution stress at site:
probability density function f()
The site ESDD in mg/cm2 can be calculated from:
ESDDSite     
1
where:

 
=
I
U
150 (empirically determined factor)
I
1
Kf 
U
2
where:

=
=
=
=
I
U
Kf
Kf  
L
0
conductivity of the pollution layer in μS
peak leakage current in A
peak phase voltage in kV
insulator form factor
Measured on Insulator at KIPTS
ds
2    R( s)
where:
S
L
R(s)
=
=
=
the distance measured along the profile of the insulator
creepage path length
insulator radius at distance ‘s’
Probability for flashover at maximum operating voltage:
cumulative distribution function P()
U 50%  A  K f
n
n 1
1
n 1
L


n
n 1
where:
A
n
 
=
=
2.27 (empirically determined factor)
0.35 (empirically determined factor)
I
1
Kf 
U
2
NCI totally Hydrophilic
where:

I
U
Kf
=
=
=
=
Kf  
L
0
conductivity of the pollution layer in μS
peak leakage current in A
peak phase voltage in kV
insulator form factor
Measured on Insulator at KIPTS
ds
2    R( s)
where:
S
L
R(s)
=
=
=
the distance measured along the profile of the insulator
creepage path length
insulator radius at distance ‘s’
Calculated Number of Flashovers per Insulator per year
Determine What Insulation to Use
Predict In Service Insulation Performance
Transmission Line
Calculated
faults per year
Actual
faults per year
A
0,6
1,0
B
1,0
0,5
C
0,2
0,5
Future Work
• 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
Thank
You
Thank You