Power Utility Perspective on Site Pollution Severity Assessment
Wallace Vosloo*, Richardo Davey and Frans Jooste
Eskom Research Testing and Development, *Retired, South Africa
Keywords: Insulator, Site Pollution Severity, Type A, Type B, ESDD, NSDD, DDGI and Surface Conductivity.
Introduction
The focus is to show how the old technical recommendation, i.e., IEC/TR 60815 [1] and the new technical specification,
i.e., IEC/TS 60815 [2], is being used by a Power Utility to determine the Site Pollution Severity (SPS) for the selection
and dimensioning of outdoor insulators to be used in polluted environments. Emphasis is placed on using pollution
severity measurements (ESDD, NSDD, DDGI and Surface conductivity), instead of the previous qualitative assessment,
to characterise more accurately the type and level of the pollution present at the site.
Using the recommendation IEC/TR 60815 “Guide for the selection of insulators in respect of
polluted conditions” [1]
The philosophy used for pollution monitoring by Eskom, is as per the methods proposed in Section 7 of IEC/TR 60815
[1] and documented in Chapter 4 of “The Practical Guide to Outdoor High Voltage Insulators” [3] part of the Eskom
Power Series.
Pollution levels (I to IV) were mostly determined from IEC/TR 60815 [1] tables as shown in Figure 1, service experience,
or when possible, by doing site pollution severity (SPS) measurements using Equivalent Salt Deposit Density (ESDD)
and/or Directional Dust Gauges (DDG).
Figure 1: Extract from IEC/TR 60815 showing examples of typical environments for pollution levels (I to IV) [1].
Table 1 shows typical ESDD and DDGI values used to classify the site pollution level [3].
Table 1: Typical ESDD and DDGI values used by Eskom to classify the site pollution level [3].
Pollution Level
ESDD (mg/cm2)
DDGI (µS/cm)
I
Light
< 0.06
0 to 75
II
Medium
0.06 – 0.12
76 to 200
III
Heavy
> 0.12 – 0.24
201 to 350
IV
Very Heavy
> 0.24
> 350
As shown in Figure 2 below, a pollution level map for South Africa was created using data captured over a period of
more than 40 years. The coastal areas are characterised by very heavy marine pollution with occurring fog and
temperature inversions, in some cases combined with industrial and/or agricultural pollution. Heavy industrial pollution
is localised in the north and northeast of the country.
Figure 2: Pollution level map for South Africa.
Using the latest specification IEC/TS 60815-1 “Selection and dimensioning of high-voltage
insulators intended for use in polluted conditions” [2]
“The following major changes have been made with respect to IEC/TR 60815 [1]:
•
Encouragement of the use of site pollution severity measurements, preferably over at least a year, in order to classify
a site instead of the previous qualitative assessment.
•
Recognition that "solid" pollution on insulators has two components, one soluble quantified by ESDD, the other
insoluble quantified by NSDD.
•
Recognition that in some cases measurement of layer conductivity should be used for SPS determination.
•
Recognition of the varying importance of parameters according to the type of pollution.”
Summary of pollution monitoring methods as recommended in IEC/TS 60815-1 [2] used by Eskom (see Figure 3):
1.
Pre-deposited pollution, Type A :
•
Equivalent salt deposit density (ESDD) and non-soluble deposit density (NSDD) using standard U120B
glass disk insulator strings (monthly) [1].
•
Directional dust deposit gauge (DDDG) with climatic factor (CF) and non-soluble deposit (DDDG NSD)
correction (monthly) [1].
2.
Instantaneous pollution, Type B :
•
Insulator Pollution Monitoring Device (IPMD) for Surface Conductivity (10 min interval) and calculated daily
maximum ESDD and estimated NSDD values.
Figure 3: Monthly collection of ESDD, NSDD, DDDG and IPMD data along the west coast of South Africa.
An example of how Eskom determines Site Pollution Severity
The following process is used as an example by Eskom to fully characterise the to-be-expected pre-deposit Type A and
instantaneous Type B pollution severity levels at a site.
A newly proposed 132 kV high voltage overhead line and substation extension (≈ 600 m from the coastline) requires a
site pollution severity assessment to obtain the pollution severity class.
Personnel from the nearby weather station classifies this specific west coast area as follows:
•
•
•
•
•
Average ambient temperatures varying between 14 and 20°C (minimum 4°C and maximum 36°C)
Exposed to strong coastal winds (gusts up to 35 m/s)
Low rainfall area (≈ 320 mm per year) with only 3 to 5 rainy days in summer (≈ 80 mm)
Dry months for the area (≈ 6 months)
High humidity levels at night/early morning and regular salt fog events (≈ 40 per year)
ESDD, NSDD, and DDDG measurements have been recorded, approximately 1 km from the newly proposed 132 kV
high voltage overhead line and substation extension, over a period of 5 years and supplemented with IPMD data.
ESDD and NSDD measurements on nearby site
Monthly ESDD and NSDD measurements (see Figure 4 below) were taken and gives a snapshot of the pollution present
at that specific time.
Maximum : 0,278 mg/cm2
Average : 0,067 mg/cm2
Maximum : 0,162 mg/cm2
Average : 0,052 mg/cm2
Figure 4: Monthly ESDD and NSDD values measured over 5-year period on nearby site.
To determine the Type A SPS, the ESDD and NSDD measurements as presented in Figure 4, are plotted onto Figure 1
of IEC/TS 60815-1 (see Figure 5 below). The Type A SPS was determined using the maximum values of ESDD and
NSDD as class d, which is Heavy.
Figure 5: Monthly relation between ESDD/NSDD and SPS plotted according to IEC/TS 60815- 1 Figure 1. The
Type A SPS is shown as class d, which is characterised as Heavy.
DDDG measurements on nearby site
The monthly DDDG measurements of the four directional gauges, are averaged and give DDGI-S and DDGI-N values
as shown in Figure 6 below.
Maximum : 1046 µS/cm
Average : 437 µS/cm
Maximum : 0,198 g
Average : 0,053 g
Figure 6: Monthly DDGI-S and DDGI-N values measured over 5-year period on nearby site.
Unfortunately, this method averages out any instantaneous Type B pollution events into the monthly measured value.
Eskom corrects the DDGI-S value with the measured DDGI-N and Climatic Factor (as shown in Figure 7).
(a)
(b)
Figure 7: (a) Extracts from IEC/TS 60815-1 [2] showing the site pollution severity class vs. the directional dust
deposit gauge pollution index values with climatic factor (CF) and non-soluble deposit correction. (b)
Climatic factor (CF), fog days and dry months map for South Africa.
The DDGI is determined using the corrected DDGI-S value, which characterises the site as class e, Very Heavy (see
Figure 8).
Maximum : 1479 µS/cm
Average : 618 µS/cm
Maximum DDGI-N : 0,198 g
Climatic Factor : 1,41
DDGI (µS/cm)
Site pollution severity class
Average Maximum
< 25
< 50
a
25 to 75
50 to 175
b
76 to 200
176 to 500 c
Very light
Light
Medium
201 to 350 501 to 850 d
Heavy
351 to 950 851 to 2350 e
Very heavy
> 950
> 2350
f
Extremely heavy
Eskom added class f - Extremely heavy
Figure 8: Monthly DDGI based on DDGI-S corrected for DDGI-N and Climatic Factor on site.
characterised as class e, which is Very heavy.
The site is
IPMD measurements on nearby site
An IPMD measures peak leakage current at 10-minute intervals on a hydrophilic porcelain insulator shed energised at
0,6 kVp for 100 ms, which is then converted into Surface Conductivity values using the parameters and equations shown
in Figure 9.
Maximum : 36,5 µS
Average : 1,8 µS
σs (µS) = 0,251 · 10 min peak leakage current (mA) / 0,6 (kVp)
Form Factor = 0,251
Creepage Distance (mm) = 117
Figure 9: IPMD Surface Conductivity 10-minute interval measurements on nearby site.
Daily maximum IPMD ESDD, as shown in Figure 10 below, is calculated from the Surface Conductivity values. The
estimated daily maximum IPMD NSDD (see Figure 10) is also calculated by multiplying the IPMD ESDD value with the
NSDD/ESDD ratio obtained from average monthly ESDD and NSDD measurements (see Figure 4).
Maximum : 0,365 mg/cm2
Average : 0,074 mg/cm2
IPMD ESDD (mg/cm2 ) = σs (µS) / 100
Maximum : 0,282 mg/cm2
Average : 0,057 mg/cm2
NSDD/ESDD : 0,773
IPMD NSDD (mg/cm2 ) = IPMD ESDD · 0,773
Figure 10: IPMD calculated daily maximum ESDD and estimated NSDD.
The daily maximum IPMD calculated ESDD and estimated NSDD relation is plotted onto Figure 2 of IEC/TS 60815-1
due to the similar profile of the test insulators. The Type B SPS, as shown in Figure 11, was determined using the
maximum values of the IPMD daily maximum calculated ESDD and estimated NSDD as class e, which is Very heavy.
Figure 11: Relation between ESDD/NSDD and SPS based on IPMD daily maximum values plotted according to
IEC/TS 60815-1 Figure 2. The Type B SPS is shown as class e, which is characterised as Very heavy.
Discussion
As per Figure 1 in the old IEC/TR 60815 [1] and Eskom pollution classification map (see Figure 2), the site pollution
level, as per Table 1, can be classified as very heavy for both ESDD and DDGI.
Applying the methods covered in the new IEC/TS 60815-1 [2], the site pollution severity, as per ESDD and NSDD values,
can be characterised as heavy for pre-deposit Type A pollution. In contrast, the site pollution severity can be
characterised as very heavy according to the DDGI values obtained.
Eskom's experience has shown that the DDDG values give a result that represent pre-deposit Type A pollution.
The above shows how accurately the IPMD captures possible instantaneous Type B pollution events. From the
IPMD measurements, the site pollution severity for instantaneous Type B pollution can be characterised as class e,
very heavy.
A comparison of the site pollution severity class percentage of occurrence for the various pollution monitoring methods
is shown in Figure 12.
Figure 12: Site pollution severity percentage occurrence for Type A (DDGI, ESDD, NSDD) and Type B (IPMD).
It is shown that the monthly ESDD/NSDD classification (heavy) could underestimate the site pollution severity, when
compared to the monthly DDGI (very heavy) and daily maximum IPMD (very heavy) classification.
Conclusions and Recommendations
In summary it has been shown, demonstrated with a practical example, how the old technical recommendation, i.e.,
IEC/TR 60815 [1] and the new technical specification, i.e., IEC/TS 60815-1 [2], is successfully being applied by a Power
Utility (i.e., Eskom) to perform and assess site pollution severity to determine the SPS class.
The area for the newly proposed 132 kV high voltage overhead line and substation extension, as shown above, can be
characterised as class e, very heavy.
It is found by Eskom, over the past few decades, that the use of DDDG measurements combined with the IPMD is the
most accurate method of determining both Type A and Type B pollution classes.
Eskom’s experience has shown that there are areas in South Africa that can be characterised as class f, extremely
heavy.
It is highly recommended that the site pollution severity assessment as per Section 8 IEC/TS 60815-1 [2] is specified as
part of the environmental impact study to be performed before any new build of high voltage power lines or substations.
Acknowledgements
The authors acknowledge the key role of Eskom in supporting the funding of the research.
References
[1]
IEC/TR 60815, Guide for the selection of insulators in respect of polluted conditions. 1986.
[2]
IEC/TS 60815-1, Selection and dimensioning of high-voltage insulators intended for use in polluted conditions –
Part 1: Definitions, information and general principles. 2008.
[3]
W. L. Vosloo, R. E. Macey, and C de Tourreil, The practical guide to outdoor high voltage insulators. Eskom
Power Series, 2004.
[4]
W. Vosloo, R. Davey and J. Bekker, “Power Utility Perspective on Outdoor Insulator Selection for Polluted
Environments,” INMR World Congress, Berlin, Germany, October 2022.
Wallace Vosloo has more than 35 years of HV Engineering experience at Eskom. He has
authored over 100 papers and presents courses in the field of HV insulators. He co-authored the
books “The Practical Guide to Outdoor High Voltage Insulators”, and “High Voltage Engineering
Practice and Theory”. Received the SAIEE President’s Award for his contributions towards Insulator
Research and the Claude de Tourreil Lifetime Achievement award for his work in the Field of
Electrical Insulation.
Richardo Davey has more than 10 years of experience as an engineer in the field of HV insulator
research at Eskom. He is currently busy with an MSc, “Statistical Selection of High Voltage
Insulators Using Environmental and Leakage Current Data Obtained Under Natural Severe Marine
Pollution”. He is project managing the construction of the new Koeberg Insulator Pollution Test
Station with 11, 22, 33, 66, 132 and 400kV test bays along the West coast in South Africa.
Frans Jooste has over 20 years of experience in management, research, testing and
development of power system technologies and standards. He has more than 10 years of
experience in the field of HV insulator research and application, investigating field failures and
authoring several insulator-related engineering instructions for business implementation. He is
currently doing research to establish a correlation between the site pollution severity and the
influence of the location on the natural ageing and pollution performance of insulator materials
between the original decommissioned and the newly built Koeberg Insulator Pollution Test Station.