FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
PROVISIONAL SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Outdoor Hollow insulator
APPLICANTS
Name: CROMPTON GREAVES LIMITED
Nationality: Indian Company
Address: CG House, Dr Annie Besant Road, Prabhadevi,
Mumbai 400030, Maharashtra, India
INVENTOR
Names : Raghavan Venkatesh and Kirjat Ramdas Shridhar
Nationality: both Indian Nationals
Address: Crompton Greaves Ltd, Switchgear-6 & Power Quality Business Unit, D2,
MIDC, Waluj, Aurangabad 431136, Maharashtra, India
PREAMBLE TO THE DESCRIPTION
The following specification describes the invention:

FIELD OF INVENTION
This invention relates to an outdoor hollow insulator with integral insulating flanges.
BACKGROUND OF THE INVENTION
Hollow insulators or hollow bushings are extensively used in electrical power equipment such as instrument transformers, vacuum circuit beakers, gas circuit breakers etc. The function of the hollow insulator is to contain a insulating fluid such as oil, gas which is an integral part of the electrical equipment. The second function of the housing is to provide an insulating external outdoor weather cover to the main insulation, which in most cases will be suitable only for indoor applications. In some cases the insulating hollow insulator also provides the required structural strength to the equipment.
As per prior art, substantially the outdoor hollow insulators are made of a ceramic hollow housing of appropriate dimensions and with shed profile to give adequate electrical creepage distance as required for the specific application fixed to a metallic flange using cement or other types of organic binders and resins. This is as depicted in figure 1. The end metallic flanges are required to facilitate mechanical assembly of the hollow insulating housing to the electrical equipment, which it forms part of.
In anther variant of the prior art, the insulating hollow housing is made of a fiber-reinforced tube with a polymeric sheath such as Silicone rubber or EPDM rubber instead of ceramic and again jointed to a metallic flange using binders / adhesives etc.. The
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metallic flange in all cases is made of materials such as Aluminum, cast Iron, steel etc. This is as depicted in figure 2.
The disadvantage of the prior art designs is that the end flanges are not an integral part of the insulating housing and are jointed using a binding agent, which represents a weak link structurally.
The second disadvantage of the prior art is that the total electrical creepage is lower as the effective distance is from the end of the metal flange along the surface of the insulator.
All the described prior art does not have a provision for embedding capacitive elements in the wall thickness of the housing.
All the prior art have the internal profile of the hollow insulator as a cylinder and does not have additional internal creepage by the way of special shed profiles.
An object of the invention is to provide outdoor hollow insulator with integral flanges, which is mechanically stronger and provides a longer electrical creepage distance.
Another object of the invention is to provide a hollow insulator with embedded capacitors, which help to reduce the surface voltage stress by uniform distribution of electric field lines.
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Another object of invention is to provide a hollow insulator with embedded capacitors, which can be configured as live line indicators.
Another object of invention is to provide a hollow insulator with embedded capacitors, which can be configured as capacitive voltage dividers to measure the voltage across the hollow insulator.
Another object of the invention is to provide a hollow insulator with internal shed profile as to increase the internal creepage distance.
DESCRIPTION OF INVENTION
According to the invention there is provided a outdoor hollow insulator with integral end flange, wherein the complete insulator along with the flanges are made of a single outdoor insulating material integrally cast under vacuum and vibration.
The polymer concrete material is made of a special formulation comprising of a base polymer made of polyester, Acrylic or epoxy resin systems or a combination of such resin systems. Suitable catalysts such as methyl ethyl ketone peroxide or benzoyl peroxide or combinations of such catalysts are used in suitable proportions to create an exothermic reaction to polymerize the unsaturated system, which acts as a binder.
The resin is filled with appropriate filler materials such as graded silica, aluminum tri hydrate, Titanium Dioxide, clay, fly ash, chopped glass strands, glass fiber, Kevlar fibers,
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carbon fibers etc. in selected proportions to achieve the desired electrical, mechanical, thermal, physical and chemical properties.
The composition and the proportion of various materials is so chosen to achieve the desired electrical, mechanical, thermal, chemical and physical properties.
Special additives such as wetting & coupling agents such as Silane, UV stabilizers, plasticizers, accelerators such as cobalt solutions, are added to improve the mechanical and outdoor weathering properties.
Typical composition by weight comprises of resin system in the proportion of 10% to 30%, coupling/wetting agents in the proportion of 0.1% to 2%, Graded silica in the portion of 50% to 80%, alumina trihydrate in the portion of 1% to 30%, Titanium dioxide in he portion of 0.1% to 10%, and reinforcing elements such as glass fibers etc in the proportion of 0.01% to 20%. Additional filler materials such as fly ash, clay etc. are added in proportion of 0.005% to 30% to get the required properties depending upon the application and specific property requirements.
The polymer concrete slurry is cast into desired shapes, which include the required electrical clearances and profiles (sheds) to enhance the outdoor electrical performance.
The casting is done under a vacuum with a pressure level in the range of 5 mm to 740 mm of Hg , in controlled temperature of 10°C to 75°C and the slurry is poured into a
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mound kept in vacuum, with pressure in the range of 5 mm to 740 mm of Hg, and controlled temperature in the range of 10°C to 75°C and is vibrated with an amplitude of 0.01 mm to 5 mm of vertical displacement with a frequency of 0.01 Hz to 400 Hz. The choice of process parameters such as Vacuum (pressure) level, temperature and vibration are controlled to get the desired properties and depends upon the shape and size of castings. The pouring rate of the slurry into the moulds is at a controlled rate of 0.1 kG to 10 kG per minute.
The polymeric reaction is exothermic and the temperature increase due to the exothermic reaction itself is used to complete the polymerization and cure the resin system. The temperature of the exothermic reaction is dependant upon the ambient temperature, resin system, proportion of various elements of the polymer concrete slurry, total mass of casting, material of mould etc. and is controlled to get the desired properties by controlling the proportion of various elements and the ambient temperature as to maintain the temperature in the range of 45°C to 120°C. This temperature range is adequate to completely cure the resin system without any additional heat input and is also low enough to be compatible with all materials used in the system for embedding or casting.
The mould is made of steel, aluminum, FRP or silicone rubber. The mould is preassembled with the metal parts to be cast into the polymer concrete. Suitable mould release agents are applied to the mould to facilitate easy mould release.
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In the basic embodiment of the invention the hollow insulator is integrally cast with end flanges as to increase the electrical creepage distance between the ends of the hollow insulator. This integral casting of the end flange also eliminates the need for any secondary cementing operation for fixing the end flanges to the main body of the hollow insulator.
In anther embodiment of the invention, capacitor elements connected in series are connected between two metallic discs and are embedded into the wall of the hollow insulating housing during casting. The two metallic discs are located as to provide external electrical connection from the two ends of the capacitor elements.
In another embodiment of the invention, the hollow housing is provided with internal shed profile using a special collapsible inner mould as to increase the internal creepage distance between the ends of the hollow housing.
In prior art with hollow insulating housing made of a ceramic material such as porcelain and end flanges made of material such as cast iron, steel, aluminum wherein the end metallic flange is cemented /jointed to the main body of hollow insulator using cement, organic resins etc. This suffers from drawbacks such as the need for secondary cementing operation and reduced electrical creepage distance between the end metallic parts.
In another prior art with hollow insulating housing made of a polymer composite material such as Silicone / EPDM rubber with FRP tubes and end flanges made of material such as
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cast iron, steel, aluminum wherein the end metallic flange is cemented / jointed to the main body of hollow insulator using suitable adhesives. This suffers from drawbacks such as the need for secondary cementing operation and reduced electrical creepage distance between the end metallic parts.
The invention is superior to the prior art designs as the secondary cementing operations for end flanges are eliminated by integral casting of end flanges in one single operation. This also increases the electrical creepage distance between the two ends of the hollow insulator there by improving the electrical performance.
In another embodiment of the invention, capacitor elements are embedded inside the wall of the hollow housing during casting and the ends of the capacitor elements are connected to suitable metallic objects embedded in the end flange as to facilitate external connection of the capacitor elements. The embedded capacitors facilitate uniform distribution of electric field lines and improve the electrical performance of the hollow insulator. The embedded capacitors can also be configured as live line indicators and/or as capacitive voltage dividers to measure the voltage across the hollow housing.
In another embodiment of the invention the hollow insulator is cast with an inner profile, which increases the internal creepage distance. The casting is done with a special collapsible or a withdrawable inner mould section with required profile.
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In accordance with the present invention, an outdoor hollow insulator cast with integral end flanges made of the same insulating material as that of the main body of the hollow insulator.
In accordance with the present invention, an hollow insulator is provided with embedded capacitor elements and with internal profile is provided to increase the internal electrical creepage distance.

Dated this 30th day of March 2007
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