Claims:WE CLAIM:

1) An insulator (1) for air-insulated electrical equipment, said insulator (1) comprising:

three high voltage conductors (2) coupled with the insulator (1);

bushes (4); and

said bushes (4) being affixed integrally to the thin section of the insulator (1) using a plurality of fasteners;

characterized in that the bushes (4) are interposed between the flanges of the metal containers enabling the flanges being coupled by a plurality of fasteners.

2) A method for making of an insulator (1) for air-insulated electrical equipment comprising:

Providing an injection mold using automatic pressure gelation technique first half of the mold;

second half of the mold interacting with the first half of the mold along a parting plane;

cavity corresponding to the insulator encompassed by the first and the second half of the mold;

injection nozzle arranged at the first half of the mold suitable to discharge liquefied material into the cavity directly or indirectly;

Closing the mold by relative movement of the first half of the mold with respect to the second half of the mold until the cavity is closed;

Injecting polymer composite dough/ liquefied material through the injection nozzle;

Opening the mold by relative movement of the first with respect to the second half of the mold; and

Removing the insulator from the mold cavity.

3) The method as claimed in claim 2, wherein the injection mold comprises three adapters which may form part of one of the mold halves.

4) The method as claimed in claim 2, wherein the three adapters have a cylindrical shape.
5) The method as claimed in claim 2, wherein mold comprises at least six to twelve adapters to receive and temporarily hold a bush/conductor during injection molding of the insulator, one injection nozzle arranged at the first half and second half of the mold discharging directly or indirectly into the cavity.

6) The method as claimed in claim 2, wherein the three adapters comprise of clamping means to temporarily receive and hold the conductor.

7) The method as claimed in claim 2, wherein the injection nozzle may discharge into the cavity through a gap designed to act as a film gate wherein the gap may be interconnected to a chamber into which the material is to be discharged
, Description:FIELD OF THE INVENTION
[001] The present invention in general relates to an insulator for air insulated substation. The present invention more particularly relates to an insulator comprising three high voltage conductors accommodated in a single insulator.
BACKGROUND OF THE INVENTION
[002] Air insulated switchgear (AIS) accommodates high voltage conductors to which high voltage is applied. In order to shield and insulate the high voltage conductor from other components and from outside, the apparatus is firmly attached to a grounded metal enclosure via fastening with suitable metal fittings.
[003] In order to hold the high voltage conductor firmly to the electrically grounded metal enclosure, in a position sufficiently far away from the grounded enclosure to avoid dielectric breakdown, an insulator is provided with metal fittings to the enclosure.
[004] The insulator should satisfy required insulation requirement and should have proper mechanical strength enough and for this purpose the insulators are processed with aluminum filled or silica filled epoxy resin system. A material, such as epoxy, is usually selected which has a coefficient of expansion similar to the metal/copper conductor so as to minimize the possibility of voids being formed at the critical interface where the insulator meets the conductor. This is because such voids are subjected to high electrical fields at the critical insulator conductor

[005] interface region, which can lead to ionization within the voids, flashover and a reduced life expectancy for the insulator. This high electrical field at this critical region approaches a value equal to the product of the field at the inner conductor in the gas and the dielectric constant of the insulator.
[006] Conventional high voltage insulating products such as spacer insulator and/support insulator uses epoxy-anhydride resin system to mold or cast the products.
[007] Conventional cast epoxy insulating products for air insulated switchgear applications are molded with epoxy-anhydride resin system having silica filler or alumina filler / additives in the system, with single central electrode and electrically grounded metal enclosure.
[008] According to US Patent US4458100, a common insulator used for supporting the inner high voltage conductor within the outer conductor. A material, such as epoxy, is selected which a coefficient of expansion similar to the metal has selected for the inner conductor so as to minimize the possibility of voids being formed at the critical interface where the insulator meets the conductor.
[009] According to US7795541B, relates to an insulating device for medium or high voltage electrical equipment in the shape of a disc inside an enclosure acting as a support for an electrical conductor. The disc is made of thermoplastic polyester. The disc can be worked starting from a thick board using conventional machining tools and it can be provided with particular arrangements, for example to facilitate its assembly or connection of conductors supported on it.
[0010] The need exists for an insulator which accommodates the high voltage conductors in a common electrically insulated enclosure and the need also exists for the less expensive insulator with three high voltage conductors and which replaces the common metallic conductor with bushes to reduce the final weight and cost of the insulator.
[0011] The need exists for less expensive insulator resin systems and manufacturing process for the manufacture of high voltage insulating products such as cast epoxy insulator and other high voltage insulating products, which are void free and which meet the depicted high voltage insulation requirements.
OBJECTS OF THE INVENTION
[0012] It is an object of the invention to provide an insulator for insulating three high voltage conductors from electrically grounded metal enclosure/fitting.
[0013] Yet another object of the invention is to propose an alumina filled epoxy resin formulation with improved partial discharge extinction voltage level and breakdown voltage level.

[0014] Yet another object of the invention is to propose an alumina filled epoxy resin formulation with reduced weight and size of the insulator.

SUMMARY OF THE INVENTION
[0015] The present invention provides an insulator for air insulated electrical equipment having such a construction that a molded insulator; three conductor being embedded in the molded insulator; and a metal material being arranged at the peripheral dimension of the molded insulator, the metal material with the molded insulator being placed between flanges of metal containers, the flanges being coupled by a plurality of fasteners.
[0016] In accordance to this invention, there is also provided a method for manufacturing the insulator by epoxy resin composition comprising of formulating the additive mix polymer dough, molding it to require geometry in a mold and gelling the polymer filled mold.
[0017] According to the invention there is provided an improved epoxy resin composition for high voltage insulation comprising of inorganic additive system in a polymer of Bisphenol–A epoxy resin of 90-100 parts by weight wherein the said additive comprises of a micro structured alumina powder of 40-70 parts by weight.
[0018] Micro structured alumina filler / additive content of 40%-70% parts by weight can easily fill up the intra-molecular voids thereby improving the electrical, mechanical, thermal properties. Due to the availability of more surface area for these fillers, suitable filler composition can improve the properties of the molded epoxy insulator.
BRIEF DESCRIPTION OF DRAWNGS
The proposed invention will be better understood by the following description with reference to the accompanying drawings:
Fig. 1: insulator comprising three high voltage conductors accommodated in a single insulator according to the present invention
DETAIL DESCRIPTION OF THE INVENTION
[0019] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative systems embodying the principles of the present subject matter. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and executed by a computer or processor, whether or not such computer or processor is explicitly shown.
[0020] In the present disclosure, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.
[0021] While the present disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the present disclosure to the particular forms disclosed, but on the contrary, the present disclosure is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the present disclosure.
[0022] The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or apparatus.
[0023] In the following detailed description of the embodiments of the disclosure, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense.
[0024] The present invention will be described in detail below with reference to an embodiment as shown in the drawing.
[0025] With the configuration of an insulator for air-insulated electrical equipment as defined by the present invention, the insulator (1) with three high voltage conductors (2), which is provided through steps of manufacturing separately the molded insulator having a thin section and the rectangular shaped metal fitting replaced with bushes (4) and affixing the rectangular shaped metal fitting replaced with bushes integrally to the thin section of the molded insulator using a plurality of fasteners, can be interposed between the flanges of the metal containers enabling the flanges being coupled by a plurality of fasteners.
[0026] The Bisphenol ‘A’ epoxy resin is a reaction product of Bisphenol ‘A’ with epichlorohydrin or the like, as is well known in the art. The Bisphenol ‘A’ epoxy resin used in the present invention usually has an epoxy equivalent of 170 or more. Such a Bisphenol ‘A’ epoxy resin is commercially available as EPIKOTE series from Yuka Shell, Japan, ARALDITE series from Huntsman, Germany, Lapox series from Atul Limited, India and such similar sources. Suitable heat curing hardeners of carboxylic acid anhydride type matching with the epoxy resins so selected are also available with the respective manufacturers.
[0027] THE POLYMERIC SYSTEM
[0028] The identified polymers are of Bisphenol ‘A’ epoxy resin, which is a reaction product of Bisphenol ‘A’ with epichlorohydrin or the like that normally has an epoxy equivalent of 170 or more. However, the additive system along with the process mentioned in the invention is also applicable to similar group of polymers.
[0029] Besides, the polymer Bisphenol ‘A’, a hardener, carboxylic acid anhydride is also to be used along with the polymer for accelerating the setting and hardening process of the polymer. The hardener need to be selected on the basis of compatibility of mixing and hardening process to that of its base polymer. However, different other hardener could find compatibility with base polymer described here and could be available from a number of commercial sources.
[0030] FABRICATION / MANUFACTURING OF THE INSULATOR
[0031] A mold for making of an insulator in general comprises: two part mold in which, a second half of the mold interacting with the first half of the mold along a parting plane, at least one cavity corresponding to an insulator disc encompassed by the first and the second half of the mold. The mold may further comprise at least six to twelve adapters suitable to receive and temporarily hold a bushes/conductor during injection molding of the insulator, one injection nozzle arranged at the first half and second half of the mold discharging directly or indirectly into the cavity. The injection mold comprises three adapters which may form part of one of the mold halves. These three adapters may have an in general cylindrical shape. These three adapters may comprise clamping means to temporarily receive and hold the conductor. These three adapters may be arranged displaceable independent of a movement of the mold halves.
[0032] The Injection nozzle may discharge into the cavity through a gap designed to act as a film gate, this gap may be interconnected to a chamber into which the material is to be discharged. This gap may have a variable geometry in circumferential direction and/or have several segments. In a preferred embodiment, the material is injected by one distribution channel arranged at a circumferential position with respect to the insulator disc. The distribution channel partially encompasses the insulator disc. If appropriate, the distribution channel may be separated in segments.
[0033] A method for making of an insulator as described above in general comprises the following method / steps:
1. Providing an injection mold using automatic pressure gelation technique
first half of the mold;
second half of the mold interacting with the first half of the mold along a parting plane;
cavity corresponding to the insulator encompassed by the first and the second half of the mold;
injection nozzle arranged at the first half of the mold suitable to discharge liquefied material into the cavity directly or indirectly;
2. Closing the mold by relative movement of the first half of the mold with respect to the second half of the mold until the cavity is closed;
3. Injecting liquefied material through the injection nozzle
4. Opening the mold by relative movement of the first with respect to the second half of the mold
5. Removing the insulator from the mold cavity.
[0034] The injection compression molding process can further increase the advantages of the injection molding process, especially help to reduce residual stress in the part through the evenly distributed pressure throughout the mold cavity during the compression step. This favorable pressure distribution will also lead to a superior surface quality - when used in combination with a mirror polished mold cavity surface. A further advantage of an insulator surface having a surface roughness that is as low as possible resides in that the electric field is locally less intensified at the insulator surface compared to an insulator surface having a higher roughness.
[0035] For the fabrication of the epoxy insulator, the inorganic additive system comprising i) micro structured alumina (40-70 part by weight), ii) white pigment (0.5 – 2.0 part by weight), iii) accelerator (0.5 – 2.0 part by weight) and in the desired proportion are to be mixed homogeneously with the epoxy resin Bisphenol ‘A’ (90 – 100 parts) along with the carboxylic acid anhydride hardener (90 – 100 parts) in a mixing chamber for a period of 6 – 10 hours using a homogenizer by maintaining a temperature of the mixing chamber in the range of 60-650C with counter vacuum level in the range of 4-5 Torr in order to get an additive-mixed polymer dough. The range of formulations comprising inorganic additive and the polymer along with its counter hardener is furnished in the Table 1.
[0036] Table 1: Composition of the Composite Body

Micro structured Alumina Powder (part by weight) Pigment white color (part by weight) Accelerator (part by weight) Bisphenol ‘A’ (parts be weight) Carboxylic acid anhydride as hardener (parts by weight)
40-70 0.5 – 2.0 0.5 – 2.0 90 – 100 90 - 100

[0037] The so-derived additive-mixed polymer mix is now poured into an alloy steel mold with required geometry and dimension depending on the dimension and geometry/profile of the composite body to be fabricated.
[0038] Alternatively, there is also a provision to fabricate the said composite body by molding with the homogenous resin mix prepared according to the former one by providing alloy steel die fabricated to the required dimension of the insulator
[0039] and letting into the mold the homogenous resin mix which is in low viscosity liquid state under a pressure of 2-4 atmospheres. Furthermore, another way to fabricate the composite body by maintaining the temperature of the mold at about 130-150 deg. C, thereby keeping the epoxy mix under these conditions in the mold for a period of 30-50 minutes for gelling and then post curing the insulator in an air-circulating oven for a period of 8-12 hours at 130-140 deg. C to help in cohesive bonding of the resin and the hardener system.
[0040] The derived composite body / insulator are subjected to the requisite dielectric tests like proof voltage, dissipation factor, and breakdown voltage as per the specified test procedures to obtain the properties enlisted in Table 2.
[0041] Table 2. Properties of a Composite Body
AC high voltage withstand test (one minute) Dissipation factor Partial discharge test
More than 100 kV 0.00010 – 0.00012 PD less than 1pC

[0042] The derived composite body / insulator having reduced weight as enlisted in Table 3.
[0043] Table.3 Weight of the Composite Body
Weight of the Composite Body with rectangular metal fitting In Kgs Weight of the Composite Body without rectangular metal fitting In Kgs
80-90 60-75

[0044] The invention would be more understood in terms of taking various examples, which are explained in the following:
[0045] Example1:
[0046] An insulator for insulating three high voltage conductors (2) supported by square/rectangular shaped aluminium metal insert (4) which is connected to electrically grounded enclosure are manufactured as per the chemical composition mentioned in Table.1 above, by injection compression molding in which the inorganic additive system comprising i) micro structured alumina (40-70 part by weight), ii) white pigment (0.5 – 2.0 part by weight), iii) accelerator (0.5 – 2.0 part by weight) and in the desired proportion are to be mixed homogeneously with the epoxy resin Biphenyl ‘A’ (90 – 100 parts) along with the carboxylic acid anhydride hardener (90 – 100 parts) in a mixing chamber for a period of 6 – 10 hours using a homogenizer by maintaining a temperature of the mixing chamber in the range of 60-650C with counter vacuum level in the range of 4-5 Torr in order to get an additive-mixed polymer dough. The range of formulations comprising inorganic additive and the polymer along with its counter hardener is furnished in the Table 1. The so-derived additive-mixed polymer mix is now poured into an alloy steel mold with required geometry and dimension depending on the dimension and geometry/profile of the composite body to be fabricated. The same insulator is tested electrical properties as mentioned in Table.2. Test results confirm that the invented insulator as in Fig.1 complies with the international standards.
[0047] Example 2:
[0048] An insulator for insulating three high voltage conductors (2) supported by aluminium metal Bushes (4) instead of square/rectangular shaped aluminium metal insert as mentioned in Example 1 (fig 2.) which are interposed at specified locations in square/rectangular shape manner connected to electrically grounded enclosure are manufactured as per the chemical composition mentioned in Table.1 above, according to steps mentioned in Fabrication/Manufacturing of the insulator mentioned in example 1.
[0049] The same insulator is tested for electrical properties as mentioned in Table.2. Test results confirm that the invented insulator as in Fig.1 complies with the international standards.
[0050] Example 3:
[0051] An insulator for insulating three high voltage conductors (2) supported by Stainless Steel (S.S) metal Bushes (4) instead of square/rectangular shaped aluminium metal insert as mentioned in Example 1 (fig 2.) which are interposed at specified locations in square/rectangular shape manner connected to electrically grounded enclosure are manufactured as per the chemical composition mentioned in Table.1 above, according to steps mentioned in Fabrication/Manufacturing of the insulator mentioned in example 1. The same insulator is tested electrical properties as mentioned in Table.2. Test results confirm that the invented insulator as in Fig.1 complies with the international standards.
[0052] It should be noted that the description and figures merely illustrate the principles of the present subject matter. It should be appreciated by those skilled in the art that conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present subject matter. It should also be appreciated by those skilled in the art that by devising various assembly that, although not explicitly described or shown herein, embody the principles of the present subject matter and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art and are to be construed as being without limitation to such specifically recited examples and conditions. The novel features which are believed to be characteristic of the present subject matter, both as to its organization and method of operation, together with further objects and advantages will be better understood from the description when considered in connection with the accompanying figures.
[0053] These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
[0054] It will be further appreciated that functions or structures of a plurality of components or steps may be combined into a single component or step, or the functions or structures of one-step or component may be split among plural steps or components. The present invention contemplates all of these combinations. Unless stated otherwise, dimensions and geometries of the various structures depicted herein are not intended to be restrictive of the invention, and other dimensions or geometries are possible. In addition, while a feature of the present invention may have been described in the context of only one of the illustrated embodiments, such feature may be combined with one or more other features of other embodiments, for any given application. It will also be appreciated from the above that the fabrication of the unique structures herein and the operation thereof also constitute methods in accordance with the present invention. The present invention also encompasses intermediate and end products resulting from the practice of the methods herein. The use of “comprising” or “including” also contemplates embodiments that “consist essentially of” or “consist of” the recited feature.
[0055] Although embodiments for the present subject matter have been described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system/component of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the scope of the present subject matter.