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

1

TABLE OF CONTENTS

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

2

4.1.4. The corrosion process 14

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

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

CHAPTER 11. 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

1.3 ObjectivesThe 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

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

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

(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

(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

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 conductorA = Cross-sectional area of conductorρ (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^3The 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 resistanceR (θ) =L/A*ρ (20 deg) [1+α (θ-20ºC)]Similarly for the conductivityX(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

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 liquid4.1.2 There must be metal to metal contact4.1.3 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

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

13

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.

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

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

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

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

Figure 8: Shows the Micro-ohm meter

18

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

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

14/09/07 @ 18ºC

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

10/10/07 @ 24ºC

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

16/10/07 @ 22ºC

63µΩ 29µΩ 63µΩ 31µΩ 62µΩ 23µΩ

20

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 environmentRemoval 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 metalRemoving 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 metalMetallic 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 electronsBy 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

CHAPTER 7

7. 1 COST ESTIMATES

TASK BRIEF DESCRIPTION COST IN ZAR (R)1. Project Specification Windows & photos 1002. 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 00010. Micro-ohm meter Conducting resistance

tests120 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

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 Department3. 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

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 differentparts 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 anoutdoor electrical installation.

OEM It is the Original Equipment Manufacturers.

Pollution It is the introduction of substances or energy into the environmentresulting 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 andExtra High Voltages (i.e.from11kV up to 800kV) situated

in Lyonn, France and branches around the world. They ownAlstom South Africa.

EPRI Means Electric Power Research Institute, world wide researchbody with branches and members across the different

electrical utilities, learning institutions and companies.

24

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

25