The project investigates the deterioration of contact surface resistance of isolators due to atmospheric pollution. It examines the use of different materials for isolator contacts and how resistance is affected. It explores how corrosion occurs from pollution in damp or gaseous environments. Laboratory experiments are conducted on an isolator to monitor how material degradation impacts performance over time. The conclusion determines pollution is a factor and recommendations suggest ways to reduce contact resistance deterioration, such as modifying the environment or materials.

1. DEPARTMENT OF ELECTRICAL ENGINEERINGDEPARTMENT OF ELECTRICAL ENGINEERING
(Bellville Campus)
TITLE: DETERIORATION OF CONTACT SURFACE
RESISTANCE OF ISOLATORS AS A FUNCTION OF
ATMOSPHERIC POLLUTION AND ITS IMPACT
FINAL DOCUMENT
NAME : Kwandiwe B. Noah
STUDENT NUMBER : 190056649
SUPERVISOR : Mr. M. A. Kusekwa
DATE : 26 November 2007
TABLE OF CONTENTS
1

2. PAGE
1. SUMMARY 4
1. CHAPTER 1 5
1.1 Introduction 5
1.1.1 Background 5
1.1.2 Problem Identification 5
1.2. Objectives 6
The main objective description 6
1.2.1 Specific objectives 6
Detail breakdown of objectives 6
1.2.2 The aim of the project 7
2. CHAPTER 2 8
2.1 Structural design of isolators 8
3. CHAPTER 3 11
3.1 Investigate the use of different materials on High Voltage isolator surface
contact 11
3.1.1 Electrical resistance 11
4. CHAPTER 4 12
4.1 Investigate the deterioration of contact surface resistance due to atmospheric
pollution. 12
4.1.1 Metal joint wetting 12
4.1.2 Metal to metal contact 12
4.1.3 Potential Difference 12
4.1.4. The corrosion process 14
2

3. 4.1.4.1 Corrosion in a gaseous environment 14
4.1.4.2 Corrosion in a damp environment 14
4.1.5 Pollution 16
4.1.5.1 Industrial Pollution 16
4.1.5.2 Marine Pollution 16
5. CHAPTER 5 17
5.1 Laboratory tests that show the effect of material or contact surface degradation
have on isolator contact performance 17
6. CHAPTER 6 21
6.1 Conclusion 21
6.2 Recommendations 21
6.2.1 Ways to reduce or slow down the deterioration of surface contacts resistance
21
6.2.1.1 Modify environment 21
6.2.1.2 Modify the properties of a material 21
6.2.1.3 Install a protective coat over the metal 21
6.2.1.4 Impose an electric current to supply electron 21
7. CHAPTER 7 22
7.1 Cost estimates 22
8. CHAPTER 8 23
8.1 List of References 23
9. CHAPTER 9 24
9.1 Glossary of terms 24
3

4. SUMMARY
The project outlines the investigation done on the deterioration of contact surface
resistance of isolators as a function of atmospheric pollution and its impact. The main
objectives investigated are: use of different materials on High Voltage isolator surface
contacts. Investigate the deterioration of contact surface resistance due to atmospheric
pollution. The laboratory experiments were done on the isolators. The conclusion is then
drawn up and recommendations suggested.
Different materials were investigated in properties, electro-negativity and structural
design. Different types of isolators and its applications were also considered. Electrical
resistance of materials was considered and what impacts resistance has in relation to
ohms law.
Investigation of electrolytic or galvanic corrosion was considered. How corrosion
impacts on different materials. The corrosion process and environment was studied in
depth. Different types of pollution were investigated in the Eskom Acacia and Koeberg
substations. Experiments were done at the Koeberg (ERID) Eskom Research and
Innovation Department with a Hudaco make Isolator and results were recorded and
analysed. They were done under controlled environment inside a lab. The conclusion was
drawn to continue with the experiment in an outdoor environment where the test object
will be subjected to real environmental condition. Recommendations on the ways to
reduce or slow down the deterioration of surface contact resistance were also given so as
to avoid this phenomenon.
4

5. CHAPTER 1
1. Introduction
1.1 Background
Eskom is divided into three Divisions in its core business of supplying electricity.
Generation is the different types of Power Stations. Transmission is the bulk transporter
of electricity from Generation to Distribution by the use of long lines. Lastly, Distribution
is the supplier to end users which are our municipalities, industrial, commercial and
domestic loads. These are interconnected by different substations at different voltages
levels. Inside the substations there is High Voltage (HV) equipment which is configured
to ensure that electricity flows from Generation to end user with minimal interruptions.
1.2 Problem Identification
Transmission in the Western Cape Region has identified the deterioration in contacts
surface of the High Voltage isolators or disconnectors which is associated with different
types of pollution found in substation in the areas of concern. Hence a study was
proposed to look into this concern.
Isolators or disconnectors, as they are sometimes referred to, are pieces of equipment
which are the points of isolation of power supply in a substation. They are the only points
that are visible that indicates whether there is continuity of supply or not in a High
Voltage (HV) circuit. They also vary in size for different voltage applications. There are
different types of isolators depending on designs by different manufacturers (see figure1
in appendix A).
We need to establish ways to mitigate or curb this deterioration of isolator (disconnector)
contacts surface due to atmospheric pollution. By doing so, this will enhance the isolator
performance to even beyond its life expectancy. That would then meet and exceed the
economic benefit to Eskom as well as keeping the maintenance costs low.
We will look at pollutants that are affecting the area of interest. Analysis of the trends
and effects of different types of pollution experienced in the area of concern will be
conducted in the form of experiments. Isolator or disconnector contact resistance will be
measured and monitored during the experimentation.
Studies will be conducted from various institutions including Original Equipment
Manufactures (OEM) of such problems encountered and what ways were implemented to
minimise or curb the phenomenon.
5

6. 1.3 Objectives
The main objective is to ensure that the following are researched:-
 Investigate the use of different materials on High Voltage (HV) isolator surface
contacts.
 Investigate the deterioration of contact surface resistance due to atmospheric
pollution.
 Perform laboratory tests that will show the effects of material or contact surface
degradation have on isolator contact performance.
 Suggest ways to reduce or slow down the deterioration of surface contact
resistance.
1.3.1 SPECIFIC OBJECTIVES
 Use of different materials on High Voltage isolators or disconnectors contacts
surface.
This topic will be discussed in depth to quantify the use of different materials. An
overview of contact resistance will be studied in relation to different materials used.
How and why you choose a certain type of contact material will be answered.
Internet, Eskom, ABB, Alstom, Areva and EPRI together with Libraries (manuals,
journals, books etc.) will be our source of information gathering.
 Investigate the deterioration of contact surface resistance due to atmospheric
pollution.
Climatic and environmental conditions will be studied and effects of applicable types
of pollution in the area
 Perform laboratory tests that show the effects that material or contact degradation
have on the isolator contact performance.
A complete isolator with three phases and support insulators will be sourced within
Eskom to perform experimentation.
Laboratory tests will be done to simulate pollutants that affect the surface contacts of
the disconnectors. Sea or marine pollution will be applied on the contact surface of
the isolator which will then be monitored and measured over a period of time. Air
(dust) pollution will be applied on contact surfaces which will be monitored and
measured to see if there are any deviations.
 Suggest ways to reduce the deterioration of surface contact resistance.
Best possible practices will be explored and suggested for implementation from the
information gathered in the study.
6

7. 1.4 The aim of the project
This project will introduce a student to how switchgear problems are investigated by
using the root cause analysis to resolving a problem.
At the end of the project the following deliverables are expected to be demonstrated at
the final presentation.
• Isolator sample for experimentation using dust as a pollutant
• Using sea water for marine pollution
• Micro ohmmeter for resistance measurement and test leads
The results are measured and monitored over a period of time then analysed.
7

8. CHAPTER 2
2.1 Structural design of isolators
Isolators or disconnectors are mechanical switching devices which in the open position
provide an isolating distance. They are able to open or close a circuit, if either a
negligible current is switched or if no significant change occurs in the voltage between
the terminals of the poles. Under normal operation they carry current according to their
design specification and voltage levels of application. However under abnormal
conditions (e.g. short circuit) they can carry current for short periods of time. Negligible
currents have values ≤ 0.5A and they include the capacitive charging currents of
bushings, busbars, connections, very short lengths of cable and the currents of voltage
transformers.
Isolating distances are gaps of specified dielectric strength in gases or liquids in the open
current paths of switching devices. These are means of protection for people and
equipment. They must satisfy special conditions and their existence must be clearly
visible when the switching device is open.
2.1.1 Different types of isolators or disconnectors and applications
(a) The figure below shows the vertical break type isolator which is mostly used as
line or bypass isolator on lower substation voltages, 11, 22, 33, 66, and 88 kV.
Figure 1: Type VB vertical break
8

9. (b) The figure below shows the center rotating double sided break type which is normally
used on 66, 88, 132, 220 and 275kV substation voltages. It is used in back-to-back double
busbar configuration to either switch the plant to one or the other busbar.
Figure 2: Type TC rotating double sided break
(c) The figure below shows a single column Pantograph or vertical-reach disconnector
type which is commonly used in high substation voltages of 400 and 765kV. Its
application is for multiple busbars and requires less ground area than other kinds of
isolators.
Figure 3: Type PD Pantograph
9

10. (d) The figure below shows the side break isolator type which is used in substation
voltages of 22, 33, 66, 88 and 132kV. It is used on line and bypass isolator applications.
Figure 4: Type SB side break
(e) The figure below shows the centre breaks isolator type which is used in substation
voltages of 33, 66, 88 and 132kV. It is used on back-to-back double busbar selection
isolator applications.
Figure 5: Type CB centre break
10

11. CHAPTER 3
3.1 Investigate the use of different materials on High Voltage (HV)
isolator surface contacts.
Due to the nature of design of an isolator and flexibility that is required in design,
different types of materials are used in its construction. The three materials that are
mostly used are copper, stainless steel and Aluminium for isolator applications. The
amount and use of these metals depend on what voltage or environment is the isolator or
disconnector going to be used in.
3.1.1 Electrical Resistance of materials
The resistance (R) to allow flow of electric current in a material is determined by the
dimension of the material (length L and cross-sectional area A) and specific resistance (ρ-
rho) at 20 degrees C of the material. R=ρ (L/A)
L = total length of conductor
A = Cross-sectional area of conductor
ρ (rho) = specific resistance (at 20degrees ºC) in (mm^2Ω/m)
X=1/ρ conductance (m/mm^2Ω)
α (alpha) = temperature coefficient (in Kelvin)
Density of material in kg/dm^3
The values for ρ (rho), conductance (X) and alpha (α) are normally given. For other
temperatures, θ1, (theta1 in degrees C).
ρ (θ) =ρ@20ºC [1+α (θ-20ºC)]. This is valid for temperatures from -50 ºC to 200 ºC and
hence for the conductor resistance
R (θ) =L/A*ρ (20 deg) [1+α (θ-20ºC)]
Similarly for the conductivity
X(θ) =X@20ºC [1+α(θ-20ºC)]inverse
The temperature rise of a conductor or a resistance is calculated as:
Δ θ = [(Rw/Rk) -1]/ α.
The values of Rk and Rw are found by measuring the resistance of the conductor in the
cold or hot conditions respectively.
These materials are generally good conductors of electricity (electrical properties) that is
shown by their wide use in the construction of HV Primary plant and equipment.
The measurement of resistance by a micro ohmmeter obeys ohms law
11

12. CHAPTER 4
4.1 Investigate the deterioration of contact surface resistance due to
atmospheric pollution.
As more than 95% of Eskom Transmission substations are outdoor and located in areas
that are affected differently by Environment. Different types of metals (dissimilar) are
used without encountering major problems. However galvanic or dissimilar or
electrolytic metal corrosion can sometimes happen. The following conditions which
cause galvanic metal corrosion must be avoided or minimised:-
4.1.1 The metal joint must be wet with a conductive liquid
4.1.2 There must be metal to metal contact
4.1.3 The metals must have sufficiently different potential
4.1.1 Metal joint wetting
The electrolyte could sometimes be rain water, a combination of mist and sea water or
even water from condensation. When conductivity increases it results in increased levels
of dissimilar metal corrosion. Salt or industrial pollution severely affects the conductivity
of water resulting in accelerated electrolytic corrosion especially in coastal or industrial
areas. As rain occurs without impurities, it generally causes slight galvanic effects. The
complication starts when evaporation takes place forming a water film that increases in
conductivity and may cause active electrolytic corrosion. This is normally concentrated in
the crevice under a bolt, or clamp. Water may be prevented or its effect delayed by design
or the use of an adhesive sealant.
4.1.2 Metal to metal contact
Electrolytic or Galvanic metal corrosion can only occur if the dissimilar metals are in
electrical contact. The electrical contact may be direct or by an external object such as
wire or bolt. Insulating dissimilar metals from each other by suitable washers or sleeves
you eliminate the occurrence of galvanic corrosion.
4.1.3 Potential difference
All metals when wetted with a conductive liquid dissolve to some extent. The degree of
dissolution is more with active metals such as magnesium and zinc and they are more
electro-negative in potential. Noble metals such as gold or graphite are relatively inert or
stable and have a more positive potential. Stainless steel is in the middle of the table
below although it is noble or stable. Potential difference can be measured with a
reference electrode and used to construct a galvanic series as shown in the table below.
12

13. Table 4-1: Shows the electro-negativity of metals
ASTM Standard G82
If two metals are bonded together and get in contact with a conducting liquid, the more
active metal will corrode and protect the noble metal. Zinc is more negative than steel
and so the zinc coating of galvanised steel will corrode to protect the steel at scratches or
edges that are cut. Stainless steel including 304 and 316 are more positive than zinc and
steel. When stainless steel is in contact with galvanised steel and is wet the zinc will
corrode first followed by steel, while the stainless steel will be protected by this galvanic
activity and will not corrode. As a rule of thumb, if the potential difference is less than
0.1 volt, then it is unlikely that galvanic corrosion will be significant.
13

14. If all three conditions are met then galvanic corrosion is probable and the rate of
corrosion will be significantly influenced by the relative area and the current density
delivered by the noble metal.
4.1.4 The corrosion process
In general it is a chemical reaction process between metal surface and its environment. It
can occur in a gaseous environment or damp environmental conditions.
4.1.4.1 Corrosion in a gaseous environment
Corrosion in a gaseous environment produces a surface layer of converted metal. For
example atmospheric corrosion of zinc produces the dull, grey zinc oxide layer seen on
galvanised street lamp posts. Un-oxidised zinc coating fresh from the hot dip galvanisers
is bright and shiny. The metal and oxygen combine to produce an oxide on the surface
because the reaction leads to a compound (the oxide) at a lower level. The oxide then
shields the metal from oxygen and forms a barrier. The oxide will not react with the
oxygen in the air or the metal. The barrier makes it difficult for oxygen in the air to
contact the metal and it eventually grows thick that the movement of electrons and ions
across it stop. Provided that the oxide film is not cracked or removed the metal is
temporarily protected from corrosion.
4.1.4.2 Corrosion in a damp environment
Corrosion in a damp environment attacks the metal by removing the atoms on the metal
surface. The atoms on the surface start losing electrons and become actively charged ions
that leave the metal and enter the damp electrolyte. The ions join the oppositely charged
ions (positive and negative ions attract) from another chemical and form a new stable
compound. Corrosion requires energy to be accelerated. The components go from higher
to a lower energy state and release the energy needed for the reaction. The electrons from
the corroding anode metal move to the connected cathode where they recombine with the
atoms of oxygen and water in the electrolyte to make a new hydroxyl ion (OH-). The new
negatively charged ions then react to make a stable compound with the positively charged
metal ions (M++) that originally lost the electrons.
14

15. Figure 6: Shows corrosion of the stud fixation of the female contact of isolator.
Figure7: Shows corrosion of male contact surface of isolator
4.1.5 Pollution
Pollution is the introduction of substances or form of energy into the atmosphere which
results in depletion of nature as to endanger human health, living resources and
ecosystems. There are many substances in the air which may impair the health of living
things, plants and animals, or reduce visibility. These come about due to natural
processes and human activity. These substances that are not naturally found in air are
known as pollutants. They are classified as either primary or secondary pollutants.
Primary pollutants are directly produced by a process such as carbon monoxide gas from
motor vehicle exhaust. Secondary pollutants are not emitted they are rather formed in the
air when primary pollutants react or interact. Ground level ozone is an example of
secondary pollutants which is one of many that make up photochemical smog. There are
15

16. different types of pollution that affect nature. I will concentrate on two types of pollution
that are major in the Western Cape environment. These are air (Industrial) and water
(marine) pollution.
4.1.5.1 Industrial pollution
Industries use different types of chemicals for various reasons depending on what type of
business they are in. This has an adverse effect on the atmosphere as it packs up on a lot
of things. High voltage equipment in general is affected by this phenomenon at Acacia
substation and isolator contacts in particular. Isolator contacts are not exceptional to this
pollution as they are situated in outdoor substations. The pollution then forms a film on
the surfaces of isolators and as current flows heat is generated to the contacts. Over long
periods this effect gets worsened and corrosion starts.
4.1.5.2 Marine pollution
This effect is severe as it causes particles of different chemicals into the ocean. At
Koeberg (HV) substation this phenomenon is quite severe as sand is blown with pollution
particles through the Capes South Westerly winds. This then sit on equipment and
corrosion after some time takes effect.
16

17. CHAPTER 5
5.1 Laboratory tests that show the effects of material or contact surface
degradation have on isolator contact performance
At Koeberg’s Eskom Research and Innovation Departmental (ERID) test site, I have set
up three samples of isolators (three separate phases) of the same type and make. Under
energised conditions they normally operate at 66kV. However under no circumstances
will the isolators be energised at high voltage (i.e.66kV) in that environment. My
laboratory experimentation was done under controlled environmental conditions and
constantly monitored for about two months. The resistance of the isolator contacts was
measured and monitored at regular intervals. The benchmark results used were from the
Original Equipment Manufacturer (OEM) for this particular type of isolator.
The simulation of marine pollution by spraying sea water on the isolator contact of the
white phase was done. On the blue phase dust was applied to simulate industrial pollution
on the contacts. On the red phase it was cleaned and no substance or chemical was
applied on it.
The three phases were then constantly monitored for any variation in resistance over the
period of the experimentation. The micro-ohm meter was used to take measurements of
these resistance readings.
17

18. Figure 8: Shows the Micro-ohm meter
18

19. Figure 9 shows the connection of the micro-ohm meter
The two thick blue leads are your current injecting leads and the small blue and brown
leads are the voltage measuring leads. There is a digital display for results and an
analogue display for current injection which is varied by the black big circular dial. There
is a push button for micro-ohm (µΩ) which when pressed gives you the reading displayed
on the digital display.
19

20. The table below shows the results of the measurements taken at regular intervals.
Table 5-1: Experiment Results
Red
Phase
White
Phase
Blue Phase
Male
contact
Female
contact
Male
contact
Female
contact
Male contact Female
contact
14/0
9/07
@
18º
C
58µΩ 29µΩ 59µΩ 55µΩ 59µΩ 35µΩ
Nothing
applied
to
contact
Nothing
applied to
contact
After
spraying sea
water
After
spraying sea
water
After
applying
dust/ sand
After
applying
dust/ sand
10/1
0/07
@
24º
C
62µΩ 27µΩ 63µΩ 32µΩ 62µΩ 25µΩ
Nothing
applied
to
contact
Nothing
applied to
contact
After
spraying sea
water
After
spraying sea
water
After
applying
dust/ sand
After
applying
dust/ sand
16/1
0/07
@
22º
C
63µΩ 29µΩ 63µΩ 31µΩ 62µΩ 23µΩ
20

21. CHAPTER 6
6.1 CONCLUSION
The introduction of foreign substances resembling pollutants did not make significant
deviations on the resistance of the contacts. As the experiment was conducted under
controlled environment there were no significant changes in contact surface resistance.
6.2 RECOMMENDATIONS
The experimentation is going to be continued in an outside substation environment so as
to expose the isolators to real weather conditions. At regular intervals measurements will
be taken and monitoring of deviations will be observed.
6.2.1 Ways to reduce or slow down the deterioration of surface contact
resistance.
There are quite a number of ways that can be employed to reduce the effects of
deterioration on isolator contacts. These depend on the careful evaluation of the nature of
deterioration. The common methods used are the following:-
6.2.1.1 Modify the environment
Removal of oxygen from the environment has a reduction effect on corrosion thereby
slows chemical reaction. This is done by keeping away oxygen from the protected
cathode the electrons will not flow, so as to cause reduction in current that in turn slows
down corrosion.
6.2.1.2 Modify the properties of a metal
Removing the oxide layer that is generally present on a metal and exposing the bare
metal directly with an acid. The acid then reacts with the metal surface to make a new
compound with more noble properties.
6.2.1.3 Install a protective coat over the metal
Metallic or non-metallic coatings are used as a protective layer. In order for this to be
effective, use of a different material with better corrosion resistant properties is
employed.
6.2.1.4 Impose an electric current to supply electrons
By connecting a more anodic metal into the corrosion circuit than the metal to be
protected the more anodic metal will corrode first and provide an alternative source of
electrons.
21

22. CHAPTER 7
7. 1 COST ESTIMATES
TASK BRIEF DESCRIPTION COST IN ZAR (R)
1. Project Specification Windows & photos 100
2. Evaluation 1 :
Specification Document
Paper and printing 50
3. Specification document
presentation
Transport usage 200
4. Investigation and research
(ESKOM)
Time 6 000
5. Literature study Internet and telephone
usage
2 200
6. Literature and consulting
Eskom Koeberg weather
station and environmentalist
Area climate and
effects
3 000
7. 66kV Isolator sample and
base plates
Source from ESKOM 180 000
8. Experimentation @
Eskom Research &
Innovation Department
(ERID)
Laboratory 75 000
9. Experimentation Transport usage 2 000
10. Micro-ohm meter Conducting resistance
tests
120 000
11. Evaluation 2: Progress
Report
Paper and printing 200
12. Progress Report
Presentation
Transport usage 280
13. Further Investigation
and research
Information gathering
and massage
1 600
14. Evaluation 3: Final
Documentation
Paper and printing 220
15. Final Project
Presentation
Transport 350
TOTAL COSTS 389 600
22

23. CHAPTER 8
8.1 List of References
1.GERD BALZER, BERNHARD BOEHLE, KURT HANEKE et al: Switchgear manual
9th
Edition, ABB Calor Emag Schaltangen Ag, Manheim, July 1993
2. Dr Wallace Vosloo, Raphael Swinny and Thamsanqa Mvayo: Eskom Research and
Innovation Department
3. http://en.wikipedia.org/wiki/pollution: Wikipedia, the free encyclopedia
4. http://en.wikipedia.org/wiki/corrosion: Wikipedia, the free encyclopedia
5. Hennnie de Bod and Samir Buffkins: Eskom High Voltage Plant
6. http://www.reliability.com/articles: Corrosion chemical reactions
7. Marry Anne White, Oxford University Press 1999: Properties of Materials
8. Ulick R. Evans, The Corrosion and Oxidation of Metals: Scientific Principles and
periodical applications
9. www.corrosionsource.com: handbook and periodic table information
10. WWW.assda.asn.au: Galvanic/dissimilar Metal corrosion and its chemical
composition
11. WWW.Engineersedge.com/manufacturing_menu.shtml: dissimilar metals,
Galvanic and corrosion Capability Chart
23

24. CHAPTER 9
9.1 GLOSSARY OF TERMS
Generation The production of electricity in power stations.
Transmission The bulk transportation of electricity with long lines to different
parts of the electricity national grid or network.
Distribution The supplier of end users, which are our municipalities, industrial,
commercial and domestic loads.
National Grid The interconnected electric power system between Generation,
Transmission, Distribution and end users.
Isolators Isolators (disconnectors) are the visible points of isolation in an
outdoor electrical installation.
OEM It is the Original Equipment Manufacturers.
Pollution It is the introduction of substances or energy into the environment
resulting in damaging effects of such a nature as to
endanger humans, livings resources and ecosystems.
ABB Asea Brown Boveri initially, a company manufacturing Electrical
equipment from Low, Medium, High and Extra High Voltages
(i.e.from11kV up to 800kV) It is situated in Ludvika (North-West
of Stockholm), Sweden. They have many branches around the
world.
Areva Manufacturing Electrical apparatus from Low, Medium, High and
Extra High Voltages (i.e.from11kV up to 800kV) situated
in Lyonn, France and branches around the world. They own
Alstom South Africa.
EPRI Means Electric Power Research Institute, world wide research
body with branches and members across the different
electrical utilities, learning institutions and companies.
24

25. Inert Chemistry term referring to a stable element of the periodic table
in a chemical reaction.
25