1. About SRG Insulators SRG Insulators is one of the prominent Manufacturers, Suppliers and Exporters of wide array of Insulators, Industrial Cables, Transformer Brushings and Lighting Arresters. We develop the range of porcelain insulator in compliance with IEC/AS/BS/IS and as per customer’s unique requirements. These products are manufactured from various raw materials, semi finished and finished products. Our entire product is available as per CPRI Test Reports. SRG Insulators was incepted with the sole aim of catering to the requirements of clients for Insulators, Industrial Cables, Transformer Brushings and Lighting Arresters. Our company is engaged in manufacturing, supplying and exporting of electrical porcelain insulators from Bikaner. 1.1 Mission Our Mission is to provide our clients with Products and Services that fully satisfied their unique requirements and to provide superior Products and Services that are competitively priced with the highest quality and delivery in a timely manner. 1.2 Quality Assurance Our products are tested electrically and mechanically as per Indian standard procedures through different types of testing equipments to ensure quality. We also have a unique kiln design that is designed by highly qualified engineers, which vitrifies uniformly all the material fired in it. 1.3 Infrastructure & Geographical Advantage The state-of the-art infrastructure is supported by a well-maintained manufacturing unit having latest machinery and modern techniques. We frequently upgrade our infrastructural facilities that enable us to produce quality products with utmost precision. The unit is ideally located in respect to the availability of good quality raw materials in abundance within the state. 1.4 Human Resource The team comprises of both young and experienced members. Their dedication and commitment towards work not only help providing excellent quality in bulk orders but also assure supply within the stipulated time frame. 1
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1. About SRG Insulators
!SRG Insulators is one of the prominent Manufacturers, Suppliers and Exporters of wide array of
Insulators, Industrial Cables, Transformer Brushings and Lighting Arresters. We develop the range
of porcelain insulator in compliance with IEC/AS/BS/IS and as per customer’s unique
requirements. These products are manufactured from various raw materials, semi finished and
finished products. Our entire product is available as per CPRI Test Reports.
!SRG Insulators was incepted with the sole aim of catering to the requirements of clients for
Insulators, Industrial Cables, Transformer Brushings and Lighting Arresters. Our company is
engaged in manufacturing, supplying and exporting of electrical porcelain insulators from Bikaner.
!1.1 Mission
Our Mission is to provide our clients with Products and Services that fully satisfied their unique
requirements and to provide superior Products and Services that are competitively priced with the
highest quality and delivery in a timely manner.
!1.2 Quality Assurance
Our products are tested electrically and mechanically as per Indian standard procedures through
different types of testing equipments to ensure quality. We also have a unique kiln design that is
designed by highly qualified engineers, which vitrifies uniformly all the material fired in it.
!1.3 Infrastructure & Geographical Advantage
The state-of the-art infrastructure is supported by a well-maintained manufacturing unit having
latest machinery and modern techniques. We frequently upgrade our infrastructural facilities that
enable us to produce quality products with utmost precision. The unit is ideally located in respect to
the availability of good quality raw materials in abundance within the state.
!1.4 Human Resource
The team comprises of both young and experienced members. Their dedication and commitment
towards work not only help providing excellent quality in bulk orders but also assure supply within
the stipulated time frame.
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1.5 Products & Marketing
They are manufacturing various types of insulators for transmission and distribution lines.They are
supplying products to almost all the state electrical utilities including National Thermal Power
Corporation Ltd., National Hydro Power Corporation Ltd. and other government-undertaking units
to their utmost satisfaction.They are also one of the leading manufacturers of Transformer Bushings
and regularly supplying our products to more than 200 transformer manufacturing units spread all
over India.
!Some of the Valued Customers for Porcelain Insulators
• Central Power Distribution Co. Ltd. of A.P.
• Southern Power Distribution Co. Ltd. of A.P.
• Northern Power Distribution Co. Ltd. of A.P.
• Eastern Power Distribution Co. Ltd. of A.P.
• Jaipur Vidyut Vitran Nigam Ltd.
• Jodhpur Vidyut Vitran Nigam Ltd.
• Ajmer Vidyut Vitran Nigam Ltd.
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1.6 Machinery
Table:-1 Various Machinery Installed in the Plant
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2. Insulators
!A true insulator is a material that does not respond to an electric field and completely resists the
flow of electric charge. In practice, however, perfect insulators do not exist. Therefore,
dielectric materials with high dielectric constants are considered insulators. In insulating
materials valence electrons are tightly bonded to their atoms. These materials are used in
electrical equipment as insulators or insulation. Their function is to support or separate
electrical conductors without allowing current through themselves. The term also refers to
insulating supports that attach electric power transmission wires to utility poles or pylons.
Some materials such as glass, paper or Teflon are very good electrical insulators. Even though
they may have lower bulk resistivity, a much larger class of materials are still "good enough" to
insulate electrical wiring and cables. Examples include rubber-like polymers and most plastics.
Such materials can serve as practical and safe insulators for low to moderate voltages (hundreds,
or even thousands, of volts).
The advantages of porcelain insulators include superior electrical properties, good mechanical
properties (especially tensile strength), good creep resistance at room temperature and high
corrosion resistance.1
!An insulator might reach the end of its working life for many reasons. Cracks in the body might
be caused by a mechanical failure or a thermal mismatch between the ceramic part and the metal
part. In addition, flashover might result from contamination on the glaze or weathering that
leads to a small crack on the surface.2 Thermal cycling causes material failure since it promotes
the growth of micro-cracks on the surface. Thermal stress is generated by temperature
differences between day and night, which may result in 80ºC differences on the glaze surface.
The heat generated may also come from the passage of fault-current arcs in the insulator.3
!Generally, the mechanical strength of the porcelain body can be improved by reducing the
internal thermal mismatch between crystalline particles and glassy phases.4 An increase in
mullite crystals can result in a change of the thermal expansion property of the body. The
coefficient of thermal expansion is a thermal property related to chemical composition, firing
temperature, particle size distribution of raw materials, particle packing of green and fired
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bodies, crystal structure, and the glassy phase of the body. Crazing of the glaze can be caused by
a thermal mismatch between the body and glaze. Usually, the thermal expansion of the body
should be higher than that of the glaze in order to generate compressive stress (instead of
tension) in the glaze layer.
!Many methods are available to determine the coefficient of thermal expansion, including
calculation from the proportion and types of oxides in the body composition. However, this
method is not accurate because many factors affect the calculated values. The most precise
method is through measurement by a dilatometer.
!Insulators are produced in many shapes, which are formed by different forming processes. For
complicated shapes that cannot be formed by jiggering, slip casting is used. Other products, like
a fused support with a simple shape, can be formed by pressing.
!It is important to understand the physical, mechanical and thermal properties of porcelain bodies
that are formed by slip casting, extruding and pressing. The effects of forming processes on
fired properties can be explained by the phases and microstructures of the fired products.
Understanding all of these relationships will result in increased accuracy when predicting and
determining the thermal mismatch and life cycles of porcelain insulators.
! The insulators for overhead lines provide insulation to the power conductors from ground. The
insulators are connected to cross arms of the supporting structures of the power conductors and
the power conductors pass through a clamp of the insulators. The insulators are mainly made of
either glazed porcelain or toughened glass. The materials used for porcelain are silica 20%,
feldspar 30% and clay 50%. The porcelain should be ivory white, sound and free from defects.
It should be vitrified because the presence of air lowers the dielectric strength of porcelain. It is
therefore desirable that the porcelain to be used for insulators should be air free and impervious
to entrance of liquids and gases .The dielectric strength of porcelain should be 15 to 17 KV for
every 1/10th inch of thickness. Normally it is difficult to manufacture homogeneous porcelain,
and therefore for a particular operating voltage, two, three or more piece-construction is adopted
in which each piece is glazed separately and then they are cemented together. Porcelain is
mechanically strong, less affected by temperature and has minimum leakage problem.
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Toughened glass is also sometimes used for insulators because it has higher dielectric strength
(35 KV for1/10th inch thicknesses) which makes it possible for single piece construction,
whatever be the operating voltage. As glass is transparent, the flaws like trapping of air can be
detected. It has lowered co-efficient of thermal expansion. It has a disadvantage that moisture
condenses very easily on its surface, limiting its use to about 33KV.
! It is not desirable to allow porcelain and metal pieces to come together. So cement is used
between them. It is seen that cement does not cause fracture by expansion or contraction.
!The principal dielectric used on overhead power lines is air at atmospheric pressure. The air,
surrounding the bare high voltage aluminium or steel- cored aluminium (ACSR) conductors, is
a good insulating material, provided that the electric stress is kept below the ionisation
threshold. It is, however, necessary to attach the conductors at certain points onto the cross arms
of the pylons. The problem of reliably suspending the conductors of high voltage transmission
lines has therefore been with us since the turn of the century. The task is particularly complex,
bearing in mind the multiple extreme stresses present: mechanical, electrical and environmental.
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!
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2.1 Types of Insulators
There are three types of insulators used for overhead lines.
Pin type
Pin type insulators are normally used up to 33kv. In any case it is not desirable to use them
beyond 50 V as the cost of insulation becomes too high.
Fig 2.1 Pin Type Insulator ! Suspension type
! Suspension type insulators, in addition to being economical as compared to pin type for
voltage more than 33KV have the following further advantages:
!1) Each insulator is designed for 11KV and hence for any operating voltage a string of
insulators can be used.
!2) In case of failure of one of the units of string, only that particular unit needs replacement
rather the whole string.
!3) The operating voltage of existing transmission can be increased by adding suitable number of
disks.
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Fig 2.2 Suspension Type Insulator
Strain Type
Strain insulators are placed in horizontal plane rather the vertical plane
as is done in case of suspension. These are used to take the tension of conductors at line terminals,
angle towers, road crossings and junction of overhead lines with cables. For low voltages of order
11KV, the shackle insulators are used.
Fig 2.3 Strain Type Insulator
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2.2 The Advantages of Porcelain Insulators
!1. Environmental friendly. At its disposal, the porcelain insulator is not dangerous waste.It is
manufactured form natural materials by simple blending and curing; it may be stored in dumps with
other waste. It may serve as a recycled material for the production of ceramic and similar products.
!2. In comparison to the polymer, electrical strength of porcelain is higher: 25+ kV/mm v. 20 kV/mm
at the polymer. The porcelain insulator in the dry state as electric insulation material has better
electrical properties than the polymer, type electrical tests show better results, giving longer useful
life in terms of loads generated by electric charges and other temporary electrical phenomena.
!3. The porcelain insulator has demonstrably higher resistance to degradation of the surface, does not
degrade or carbonate during charges; the conductive path is created very slowly in comparison of
the surface of a composite-material insulator.High thermal resistance and strength, ceramics is
resistant to temperatures as high as 1000°C: the surface is resistant to any type of degradation
within the temperature range. The surface is stable against the effects of UV radiation.
!4. The ceramic material is resistant to rodents, termites, birds and other animals capable of
compromising the integrity of polymers.The surface of the insulator is highly glazed and hard,
making the product unfavourable to the tastes of the fauna.
!5. The ceramic insulator has a wide scope of application: Contractors, disconnectors, equipment
transformers, condensers, grommets also with extreme surface, atypical insulators (filters). The
features of high plasticity during production, the possibilities of precision grinding and quite easy
cementation and bonding with excellent mechanical properties permit that a multitude of shapes be
created and used in any type of application.
!6. The ceramic insulator is suitable for extreme hot/cold changes in the environment. It is suitable
for environments with dust, salt and high moisture, or for combination of all of the above. The
highly glazed surface gives the product better self-cleaning properties in high-pollution areas. The
product shows stable results in charges and short-circuit in this type of environment; it is highly
resistant to corrosion in acidic as well as caustic environments.
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7. The ceramic insulator does not suffer from defects in the ceramics-to-metal interface. The
combination of the ceramic insulator with cast-iron or aluminium structures using traditional
cementing agents is resistant to transition phenomena during the discharge or brush discharge.
!8. The ceramic material offers very high mechanical strength under pressure and hardness. The
ceramic insulator does not deform unless external force is deployed. Long useful life can be
guaranteed of lengths up to 40 years. Therefore, many users have provided long-term operational
references in a number of applications.
!9. The design is modified to suit the environment.The product offers many shapes during
production; glazing uses a wide scale of colours based on the needs of the customer, for example
grey or sky blue.
!10. The ceramic insulator is nicer to the eye
It has a timeless design.
!2.3 Terminology
When applying insulators, it is necessary to describe the insulator dimensions, using the
following terms:
• Creepage distance: the shortest distance between the metalware at the two ends of the
insulator, when following the contours of the insulator, excluding intermediate metal
fittings. This distance is easily measured by sticking masking tape to the insulator
surface.
• Specific creepage distance: The quotient of the creepage distance in mm and the line-
to-line rms. voltage of the three phase system in kV
• Connecting length: the axial length of the insulator between the end terminals
• Arcing distance: the distance between the metalware, measured as the length of a
tightly pulled piece of string
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• Intershed spacing: the distance between corresponding points on adjacent sheds.
2.4 Failure Modes of Insulators
Flashovers, caused by air breakdown or pollution, generally do not cause physical damage to the
insulators and the system can often be restored by means of auto closing. Some other events,
however, cause irreparable damage to the insulators.
Puncture
As previously mentioned, porcelain pin-type and cap and pin insulators may suffer punctures
between the pin and the either the pin or the high voltage conductor. These occurrences are usually
caused by very steep impulse voltages, where the time delay for air flashover exceeds that of
puncture of porcelain.
Punctures caused by severe stress over dry bands also occur on composite insulators on sheds and
through the sheath. A puncture of the sheath is particularly serious as this exposes the glass fibre rod
to the environment (see brittle fracture below).
Shattering
Glass insulators shatter when exposed to severe arcing or puncturing due to vandalism. One
advantage is that they retain their mechanical integrity.
Erosion
Prolonged arcing of glass insulators leads to erosion of the surface layer of the glass. This may lead
to shattering of the glass discs - a result of the tempering process used during manufacture. Arcing
and corona over long periods may cause removal of shed or sheath material in the case of polymeric
insulators. Severe erosion may lead to the exposure of the glass fibre core (see brittle fracture)
Tracking
Tracking occurs when carbonised tracks form because of arcing. These tracks are conductive. This
phenomenon only occurs in carbon-based polymers.
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Brittle fracture
Water entry into the glass fibre core of composite insulators, coupled with the influence of weak
acids, has been shown to lead to brittle fracture of the rod. The by-products of partial discharges in
the presence of water can lead to the formation of weak acids. The integrity of the metal/polymer
and glass/polymer interfaces is therefore extremely important - especially if acid-resistant glass is
not used.
Corrosion
The corrosion of metal fittings clearly affects the mechanical performance and lifetime of
insulators. The corrosion products, running onto the insulator sheds can also initiate deterioration.
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3. Production Processes 3.1 Overview
!
Fig 3.1 Flow Chart of the Production Process in Porcelain Insulators
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3.2 Raw material select
!Clay a universal component used in preparing ceramics owing to its extraordinary ease of
transformation through moulding and hardening processes. Although there are numerous
classifications, the most common classification in the manufacture of ceramic coverings is based on
the colour of the body-red or white-. Red-body clays are characterised by their high iron content,
low melting temperature, and moderate plasticity, whereas white-body clays are more plastic and
have no colouring oxides.
The Principle raw materials are ball clay, china clay, feldspar and quartz, roughly as 50% clays,
25% feldspar and 25% quartz
Both ball clays and china clay are decomposition products of granitic rocks and both comprise
mainly kaolinite.Kaolinite is a layered silicate: even at molecular level its structure comprises plans
of atoms, in a multi-deck sandwich assembly of oxygen, silicon, oxygen with hydroxyl, aluminium
and finally hydroxyl.The remarkable rheology of clays arises both from this layered form and from
the manner in which water is embodied into the material.
Fig 3.2 Structure of a clay
!!Feldspars are alkali-aluminium silicates.The alkali feldspars are as follows: