Claims:We claim:
1. A process (100) for manufacturing of composite insulators having AC voltage rating of 25KV with a creepage distance of 1600mm that has three types of configurations which are a stay arm type, a bracket type and a 9-Tonne type respectively for using as an electrical insulation material or an insulation structure in electrical equipment and applications including overhead traction lines in electrically-powered railways, specifically under polluted environments (101), comprising the steps of:-
a. moulding the plurality of a insulation sheds (102);
b. holding the insulation sheds by a core structure of a fibre reinforced polymer (FRP) rod (103);
c. fixing of one or more types of a metallic hardware at a terminal ends of the core FRP rod (104); and
d. application of an interface bonding/reinforcing agent between the insulation sheds and the FRP rod for the interface bonding (105).
2. The process (100) as claimed in claim 1, wherein the plurality of insulation sheds in the composite insulators with the creepage distance of 1600mm is an additive-modified high temperature vulcanized (HTV) silicone rubber material (methyl vinyl silicone rubber), that is having shore hardness (Shore A) of 67+8.
3. The process (100) as claimed in claim 1 or 2, wherein the plurality of insulation sheds is moulded by using the said additive-modified HTV silicone rubber material in a die in an injection moulding machine at a temperature range of 165-175o C with curing time in a range of 650-750 seconds and a counter injection pressure level in the range of 200-220 Bar.
4. The process (100) as claimed in the claims 1-3, wherein the core structure is the elongated fibre reinforced polymer (FRP) rod upto a length of 422 mm with a diameter of 33 mm that holds the insulation sheds.
5. The process (100) as claimed in the claims 1-4, wherein the surface treatment of the FRP rod is carried out by a chemical treatment process followed by using a silane-based catalyst-modified adhesive material in xylene solvent, followed by a heat-treatment process at any temperature in the range of 100-130 o C for a period of 20-25 minutes, prior to the injection moulding process, which is performed for strengthening the bonding between the interface region of silicone rubber insulation sheds and the FRP rod in the composite insulator structure.
6. The process (100) as claimed in the claims 1-5, wherein the fabrication process allows the plurality of insulation sheds to get aligned continuously throughout the FRP rod structure with nearly uniform thickness of about 4mm with a insulation sheath diameter (big) is about 185mm and a insulation sheath diameter (small) about 141mm by maintaining “big sheath to big sheath” pitch of about 70.5mm across the axial direction of the rod, sheath of which has a tapered angle of about 7 o at the top and about 3.5 o at the bottom of each sheath.
7. The process (100) as claimed in the claims 1-6, wherein the metallic end-fittings are galvanized SGI casting materials, wherein one terminal of the end-fitting is known as a tube-side and other terminal as mast-side for both in stay arm and bracket type insulator while in case of 9-Tonne insulator type, both the end-fittings are known as 9-tonne.
8. The process (100) as claimed in the claims 1-7, wherein prior to the injection moulding for generating the insulation sheds on the core FRP rod structure, metallic hardware conductors are fitted over the terminal-ends of the FRP rod by using an appropriate metallic jaw and also by applying a crimping pressure level in the range of 150-170 Bar with holding time in the range of 5-10 seconds that the metallic hardware fixes at the terminal ends of the FRP rod.
9. The process (100) as claimed in the claims 1-8, wherein the metallic hardware conductor-fitted FRP rod structure is placed in the mould for generating the plurality of insulation sheds by injection moulding process with prior cleaning, and the said hardware ultrasonically by using a non-aqueous solvent, including trichloro-ethelene in order to remove dirt/greasy matter from the surface.
10. The process (100) as claimed in the claims 1-9, wherein the interface bonding/reinforcing agent is a silane-based catalyst-modified adhesive in xylene-solvent and is used for strengthening the interface bonding between the silicone rubber and the FRP rod.
11. The process (100) as claimed in the claims 1-10, wherein the total length including the hardware fittings of the composite insulators with the creepage distance of 1600mm is 491 + 10 mm in case of stay arm type having tensile strength of 7000kgf and bending strength of 200kgf.m, with AC voltage rating of 25kV.
12. The process (100) as claimed in the claims 1-10, wherein the total length including the hardware fittings of the composite insulators with creepage distance of 1600mm is 555 + 10 mm in case of stay arm type having tensile strength of 7000kgf and bending strength of 200kgf.m, with AC voltage rating of 25kV.
13. The process (100) as claimed in the claims 1-10, wherein the total length including the hardware fittings of the composite insulators with creepage distance of 1600mm is 540 + 10 mm in case of 9-Tonne type having tensile strength of 11000kgf and bending strength of 210kgf.m, with AC voltage rating of 25kV.
14. The process (100) as claimed in the claims 1-13, wherein the composite insulators with Ac voltage rating of 25kV having a creepage distance of 1600mm comprising the types of stay arm type, bracket type and 9-Tonne type respectively.
, Description:TECHNICAL FIELD

[0001] The present disclosure, in general, relates to manufacturing of composite insulators particularly with a preferred creepage distance of 1600mm creepage distance, which could be used as an electrical insulation material or insulation structure, specifically in polluted environments.

BACKGROUND

[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0003] Composite insulators were introduced about three decades ago as a good alternative to then conventional porcelain and glass insulators. Over the last three decades and more so in the last one decade, composite insulators have become very popular and becomes highly reliable products in HV primarily because of the innovation in new insulation materials with superior properties with associated design improvements in the insulators besides innovations in fabrication equipments as well as commercial availability of superior quality low-cost raw materials.

[0004] The key features those attributed to the popularity of composite insulators are compact design, light weight (10-15% weight over porcelain insulators), low maintenance, high strength to weight ratio, higher Short Circuit loading reliability, superior seismic performance, superior contamination performance due to hydrophobic nature, vandal and shatter proof material unlike porcelain insulators that lead applications in line insulation system, substation applications of post, hollow core in CTS, PTS and so on.

[0005] Electrically-powered railway networks (as evident in Indian Railways) typically use three major types of insulators, either composite-based insulator or porcelain-based insulators. The configuration/type of said insulators comprise, Stay Arm type, Bracket tube type and 9-Tonne type respectively. Such insulators are particularly used in railway overhead traction lines in various modes of vertical, horizontal and also at angled positions respectively. However, with the rapid industrialization, and with the significant increase in the pollution levels in the environment over the years, existing sets of insulators do not work efficiently, causing uncertainty on performance and issues on safety as well. So, there are new challenges that need to be addressed which work under polluting or even in over-polluting environmental conditions. These challenges pose to address on new design of the existing sets of insulators in a manner that the performance of the insulators with new design is guaranteed thereby ensuring higher safety and reliability as well.

[0006] One aspect that could efficiently deal with satisfactory performance in polluting or even heavily polluting environment (where Salt Deposit Density (SDD) goes upto a level of 0.3 mg/sq.cm.) is to enhance creepage distance of the composite insulators. The creepage distance is defined as the shortest path between two conductive parts, or between a conductive part and the bounding surface of the equipment, measured along the surface of the insulation. The creepage distance of an electrical insulator is therefore the shortest distance along the insulator surface between the metal parts at each end of the insulator. Creepage distance is often referred as leakage distance for insulators. The creepage distance is decided depending upon the climatic and weather condition of the application. However, if the surface of the insulator is clean and smooth, there will be minimum deposition of the dust particles on the insulator surfaces.

[0007] In case of high voltage transmission lines, the leakage current is caused by atmospheric conditions, such as, dirt, pollution, salt depositions and particularly rain water that finally lead to flashover of the insulator. So in order to decrease the leakage current, the surface is molded into a series of corrugations or concentric disc shapes. These usually include one or more sheds, which are downward facing cup-shaped surfaces that act as umbrellas to ensure that the part of the surface leakage path under the ‘cup’ stays dry in wet weather. So the creepage distance is one tool to manipulate the leakage current in the insulators that is caused by various factors as described.

[0008] Now, reference may be made to the following publications:

[0009] Patent publication of CN103377781A dated 30th October 2013 discloses an outdoor epoxy resin insulator with high weather fastness. The outdoor epoxy resin insulator comprises an epoxy resin insulator body, and a teflon coating is arranged on the surface of the epoxy resin insulator body. Therefore, the weather fastness of epoxy resin can be improved and the requirement for the weather fastness of the epoxy resin insulator of outdoor high-voltage electrical equipment is met. The pollution flashover that happens because of the hydrophobic nature of silicon rubber insulator in pollution regions, is reduced and solved. The weather fastness and the hydrophobic nature of the epoxy resin are further improved and the anti-pollution flashover capacity of the epoxy resin is also improved besides external insulation material cost and manual maintenance cost of the electrical equipment are reduced, and reliability of a whole high-voltage electrical system is improved.

[0010] Patent publication number CN 103308656A dated 18th September 2013 discloses a method for measuring the equivalent salt density and the ash density of a cluster parachute surface of a composite insulator. The method is characterized by comprising the following steps of: cleaning a foul layer on the cluster parachute surface by distilled water serving as a cleaning solution, and respectively measuring the equivalent salt density ESDD1 and the ash density NSDD1 of sewage obtained by cleaning by the distilled water; then cleaning a stubborn foul layer on the cluster parachute surface by an organic solvent serving as a cleaning solution, and respectively measuring the equivalent salt density ESDD2 and the ash density NSDD2 of sewage obtained by cleaning by the organic solvent; and taking sums of the twice measured results as the equivalent salt density and the ash density of the cluster parachute surface of the composite insulator. According to the method, the measured result can accurately represent the actual sewage accumulation condition of the surface of the composite insulator; accurate reference data are supplied to analysis of a pollution condition of a running environment and judgment of external insulation fouls of a power grid.

[0011] Patent Publication number CN103545068A dated 4th May 2016 discloses a method for performing repairing renovation on surfaces of aged composite insulators. The method comprises the steps of cleaning the surfaces of the aged or degraded composite insulators, and removing surface foul and pulverized layers; uniformly spraying RTV (room temperature vulcanization) coating on the surfaces of the composite insulators; and checking the surface of coats after the RTV coating is solidified. The performance of the composite insulators is improved by smearing the RTV coating on the surfaces of the composite insulators, new surfaces of the composite insulators with excellent performance are formed, and cracks and holes in the surfaces of the aged composite insulators are filled; and the RTV coating has excellent hydrophobicity and excellent hydrophobic migration, so that the renovated composite insulators also have the excellent hydrophobicity and the excellent hydrophobic migration, the service lives of the composite insulators are prolonged, the problem that the existing composite insulators are aged and degraded is well solved, the cost is reduced to a certain degree, and the work efficiency is improved.

[0012] Patent publication of WO2010143995A1 describes the diagnosis of the insulation state of the substation substation, linear, cantilever, clamp, linear and suspension insulators for high-voltage substations, power lines and railway contact network. It further describes a high-voltage insulation condition indicator made of toughened electrical grade glass in which the indicator makes it possible to quickly and visually monitor the condition of high-voltage insulation, to identify a faulty insulator and to replace the same in due time, and to prevent emergency situations due to insulator failures. The indication of a potential failure of an insulator is given by the breakage of the indicator.

[0013] Patent publication number CN202996431U dated 12.06.2013 describes a rod-shaped integral-type location polymer composite insulator for an overhead contact system of an electric railway. The composite insulator comprises a core rod, armor clamps which is disposed at two ends of the core rod, and a sheath covered on the outside of the core rod and provided with a plurality of umbrella skirts. Sealing structures are formed at joints between the armor clamps and the sheath through curing. The umbrella skirts on the sheath comprise a plurality of big umbrella-shaped projections coaxial with the core rod. The umbrella extensions of the big umbrella-shaped projections are 30mm-60mm long. One end of the insulator is provided with a location tube. The location tube and the insulator body are integrated in structure. The rod-shaped integral-type location polymer composite insulator for the overhead contact system of the electric railway is high in flashover voltage, has the properties of bird trouble prevention, prevention of damage caused by rats, sand wind resistance and external damage resistance, and can be climbed and treaded, and brittle failure of the composite insulator during use is prevented.

[0014] Publication of WO1996004667A1 dated 15th February 1996 by Ceramtec Ag Innovative Ceramic Engineering, describes a plastic electric high-voltage insulator that has at least one glass fibre rod and at least one shielding sleeve, which is made of silicon rubber that surrounds the glass fibre rod. The shielding sleeve has concentric, umbrella-shaped bulges with a convex top surface and a concave or flat bottom surface, as well as metal fittings at both ends of the insulator. The bottom surface of the umbrella-shaped bulges has at least one groove with at least 1 mm depth. The invention was explained above using a high-voltage insulator for overhead lines as an example besides usage in high-voltage composite insulators with a shield cover made of silicone rubber, which are used as support insulators or as hollow insulators, which serve as housings for transducers, bushings and the like. The invention can be used advantageously in cases where conventional insulators of a fixed height in electrical pollution areas cause electrical problems with regard to flashovers. With the help of the invention, isolators can be built, the creepage distance of which can be adapted to the atmospheric conditions while maintaining the overall height.

[0015] US patent number 20050120975A1 dated June 09, 2005 by Takanori Kondo, NGK Insulators Ltd., Japan described how to prevent breakage of a cover member of a polymer insulator caused by pecking by a bird, through use of an avian repellent which is carried by the polymer insulator and an avian repellence maintained at least during construction of power transmission equipment, thereby inhibiting pecking of the polymer insulator by birds. The bird-pecking-preventive polymer insulator according to the invention includes an insulator body, and a holding metal piece is fitted on each end of the insulator body, the insulator body being composed of a core member is formed of a reinforced plastic material and a cover member is formed of a rubber material and covering the periphery of the core member, wherein the cover member carries an avian repellent such as capsaicin.

[0016] The manufacturing of composite insulators by utilizing specified materials, process parameters along with designs for specified applications is a continued interest. The applications of composite insulators are constantly being monitored by the End Users depending on what kind of circumstances and difficulties they come across while these composite insulators on the job and hence invention in this field have been taking place to address new challenges and technical necessities. Further, as the environmental pollution have witnessed to increase substantially in many parts across the globe, the composite insulators are selected depending on the pollution level/type in the geographical regions of the transmission line/s and hence composite insulators must be complied with specific pollution norms depending on the geographical location of the transmission lines.

[0017] Precisely, in the above background and context, the present describes the manufacturing of composite insulators having AC voltage rating of 25kV with a preferred creepage distance of 1600mm creepage, comprising three varities, i.e., stay arm type, bracket type and 9-Tonne type respectively that could be used an electrical insulation material or as an insulation structure in various equipments or various applications including overhead traction lines in electrically-powered railways, particularly in polluting environments, where the Salt Deposit Density (SDD) goes upto a level of 0.3 mg/sq.cm. The said composite insulators are manufactured by an injection moulding process by using additive-modified high temperature vulcanized (HTV) silicone rubber-based material (chemically known as methyl vinyl silicone rubber). The fabricated insulation body has a core structure of an elongated ‘fibre reinforced polymer (FRP)’ rod, while the hardware of the said insulators are forged steel materials, and the interface bonding/reinforcing material is silane-based catalyst-modified adhesive material respectively. As described, such insulators of which could safely be used in highly polluting environments wherein the ‘Salt Deposit Density (SDD)’ of the environment is upto a level of 0.3 mg/sq.cm.

[0018] Therefore, there is a requirement of manufacturing of Composite Insulators for use as an Electrical Insulation Structure in Polluted Environments.

OBJECTS OF THE DISCLOSURE

[0019] Some of the objects of the present disclosure, which at least one embodiment herein satisfy, are listed herein below.

[0020] It is a general or primary object of the present disclosure to provide a process for manufacturing of composite insulators with Ac voltage rating of 25kV having a preferred creepage distance of 1600mm, for using as an electrical insulation material or an insulation structure in various equipments and applications including overhead traction lines for electrically-powered railways etc., specifically in polluted environments wherein the ‘Salt Deposit Density (SDD)’ of the environment is upto a level of 0.3 mg/sq.cm.
[0021] It is another object of the present disclosure to describe the types or configurations of such composite insulators, i.e., stay arm type, bracket type and 9-Tonne type respectively, types or configurations of which are different only with the terminal fittings of metallic hardware of the insulators, although the preferred creepage distance, i.e., 1600mm along with the AC voltage rating of 25kV remain the same.

[0022] These and other objects and advantages of the present disclosure will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present disclosure is illustrated.

SUMMARY
[0023] This summary is provided to introduce concepts related to manufacturing of composite insulators for use as an electrical insulation structure in polluted environments. The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0024] One or more drawbacks of conventional systems and process are overcome, and additional advantages are provided through the apparatus and a method as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be part of the claimed disclosure.
[0025] The present invention is devised to provide a fabrication method for manufacturing of composite insulators having AC voltage rating of 25kV with a preferred creepage distance of 1600mm for using an insulation material or as an insulation structure in equipments or various applications including overhead traction lines in electrically-powered railways, specifically in highly polluted environments, wherein the ‘Salt Deposit Density (SDD)’ is upto a level of 0.3 mg/sq.cm.

[0026] The invention utilizes an injection moulding process, wherein the plurality of insulation sheds of the said composite insulator is molded in desired patterns by using an additive-modified high temperature vulcanized (HTV) silicone rubber material (chemically known as methyl vinyl silicone rubber having shore hardness of (67+8), a core structure of an elongated ‘fibre reinforced polymer (FRP)’ rod, galvanized SGI casting metallic hardware structure at the terminal ends, another commercial-grade adhesive material for interface bonding/reinforcing material respectively.

[0027] The invention further provides the description of the types or configurations of the composite insulators, with the same preferred creepage distance of 1600mm, i.e., stay arm type, bracket type and 9-Tonne type respectively, types of which are different with the metallic hardware of the insulator terminals only.

[0028] According to the present invention, there is provided a process (100) for manufacturing of composite insulators, with AC voltage rating of 25kV with a preferred creepage distance of 1600mm with various configurations of metallic hardware at the terminal ends of the insulator, i.e., stay arm type, bracket type and 9-Tonne type respectively, comprising the steps of:-
a. moulding of a plurality of insulation sheds,
b. holding the insulation sheds by a core structure of fibre reinforced polymer (FRP) rod,
c. fixing of different types of metallic hardware/s at the terminal ends of the core FRP rod, resulting various configurations of stay arm type, bracket type and 9-Tonne type respectively
d. application of interface bonding/reinforcing agent between the insulation sheds and the FRP rod for interface bonding.

[0029] The plurality of insulation shed structure in the composite insulators with the preferred creepage distance of 1600mm is generated by moulding an additive-modified high temperature vulcanized (HTV) silicone rubber material (methyl vinyl silicone rubber) with Shore hardness (Shore A) of 67+8 by using an appropriate die in an injection moulding machine at temperature range of 165-175oC with curing time in the range of 650-750 seconds and counter injection pressure level in the range of 200-220 Bar.

[0030] The plurality of insulation sheds are also generated by maintaining a thickness of 4mm in all three varieties of the composite insulator, i.e., stay arm type, bracket type and 9-Tonne type respectively.

[0031] The plurality of the said insulation sheds in the said composite insulators are further generated by maintaining the big-diameter of 185mm and small-diameter of 141mm in all the three types, i.e., stay arm type, bracket type and 9-Tonne type respectively
[0032] The core structure of the said composite insulator is an elongated ‘fibre reinforced polymer (FRP)’ rod that holds the insulation sheds is having a length of about 422mm and a diameter of 33mm for all the three types of composite insulators.

[0033] The length of the composite insulator along with the metal end-fitting is different, i.e., i) 491mm for stay arm type, ii) 555mm in case of Bracket type and 540mm in case of 9-Tonne type respectively.

[0034] The surface treatment of the FRP rod is carried out by a chemical treatment process followed by using a silane-based catalyst-modified adhesive material in xylene solvent, followed by a heat-treatment process at any temperature in the range of 100-130oC for a period of 20-30 minutes, prior to the injection moulding process, which is done for strengthening the bonding between the interface region of silicone rubber insulation sheds and FRP rod in the composite insulator structure.

[0035] The fabrication process allows the plurality of insulation sheds to get aligned continuously throughout the FRP rod structure with nearly uniform thickness of about 4mm by maintaining a pitch (from one big sheath to another big sheath) of about 70.5mm across the axial direction of the entire FRP rod repeatedly, sheath of which has a tapered angle (top sheath to bottom sheath in degree) of about 7/3.5o in all the three varieties, i.e., stay arm type, bracket type and 9-Tonne type respectively.

[0036] The metallic hardware for connecting the terminal ends of the composite insulators are galvanized SGI casting materials, wherein one terminal of the end-fitting is known as tube-side and other terminal is mast-side for both in stay arm and bracket type insulator types respectively, while in case of 9-Tonne insulator type, both the end-fittings are known as 9-tonne, which makes unique to each type of insulators thereby describing stay arm type, bracket type and 9-Tonne type respectively.

[0037] Prior to the injection moulding for generating the insulation sheds on the core FRP rod structure, metallic hardware conductors are fitted over the terminal-ends of the FRP rod by using an appropriate metallic jaw and also by applying a crimping pressure level in the range of 150-170 Bar with holding time in the range of 5-10 seconds that the metallic hardware fixes at the terminal ends of the FRP rod.

[0038] The metallic hardware conductor-fitted FRP rod structure in each case of the composite insulators, i.e., stay arm type, bracket type and 9-Tonne type respectively, is placed in the mould for generating the plurality of insulation sheds by injection moulding process with prior cleaning the said hardware ultrasonically by using a non-aqueous solvent, including trichloro-ethelene in order to remove dirt/greasy matter from the surface.

[0039] The interface bonding/reinforcing agent is a silane-based catalyst-modified adhesive in xylene-solvent and is used for strengthening interface bonding between silicone rubber and FRP rod.

[0040] The AC voltage rating of the said composite insulators combining all the three types is 25kV with counter mechanical strength (tensile) of 7000 kgf in stay arm type and bracket type and 11000kgf in 9-Tonne type with associated bending mechanical strength of 200+10 kgf.m in case of both stay arm type and bracket type, while it is 210+10 kgf.m in case of 9-Tonne type insulators respectively.
[0041] The technical properties of various types of Composite insulators with 1600mm Creepage are tabulated in the below Table 1.
Table 1:
S No.
Description Unit
Type of Composite Insulators
Stay Arm Type Bracket Type 9-Tonne Type
1 Mechanical strength (Tensile) kgf 7000 7000 11000
2 Insulator length mm 491 555 540
3 Creepage distance mm 1600 1600 1600
4 Core diameter mm 33 33 33
5 Bending moment kgf.m 200 200 210
6 Insulation Sheath - Big (Diameter) mm 185 185 185
7 Insulation Sheath – Small (Diameter) mm 141 141 141
8 Pitch (Big Sheath to Big Sheath) mm 70.5 70.5 70.5
9 Insulation Sheath Thickness mm 4 4 4
10 Shed (tapered) angle-Top/Bottom in degree
Degree 7/3.5 7/3.5 7/3.5
11 Shore Hardness of the Silicone Rubber Shore A 67 ± 8 67 ± 8 67 ± 8
12 AC Voltage rating kV 25 25 25

[0042] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

[0043] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.

[0044] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and methods that are consistent with the subject matter as claimed herein, wherein:

[0046] FIG. 1 shows a block diagram of a process for manufacturing of composite insulators, in accordance with an embodiment of the present disclosure.

[0047] The figures depict embodiments of the present subject matter for illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION

[0048] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to con all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0049] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.

[0050] FIG. 1 shows a block diagram of a process (100) for manufacturing of composite insulators, in accordance with an embodiment of the present disclosure. The present invention provides a fabrication process (100) for the manufacturing of composite insulators with AC voltage rating of 25kV with a preferred creepage distance of 1600mm than usual of 1050mm, suitable for using such insulators as an electrical insulation material or as an insulation structure in electrical equipments and applications including overhead traction lines in electrically-powered railways, more so in polluting environments wherein the ‘Salt Deposit Density (SDD)’ of the environment is upto a level of 0.3 mg/sq.cm.

[0051] The structure of said composite insulator comprises a core FRP rod, plurality of insulation sheds of which are continuously aligned towards the axial direction of the entire core FRP rod and the metallic hardware, which are fitted at the terminal ends of the insulator structure for ohmic contacts respectively.

[0052] There are three configurations of the metallic hardware, those fitted at the terminal ends of the insulator, which make three different types of configuration of the composite insulator under the same creepage of 1600mm and AC voltage rating of 25kV, i.e., i) stay arm type, ii) bracket type and iii) 9-Tonne type respectively.

[0053] As per the basic construction of materials for the said 25kV AC composite insulator with preferred creepage distance of 1600mm, the core rod is an elongated fiber-reinforced polymer (FRP) material, the plurality of insulation sheds is an additive-modified high-temperature vulcanized (HTV) silicone rubber material having Shore hardness of 67+8 and the metallic hardware parts are made of galvanized SGI casting material of the said insulator structure.

[0054] As per the invention, the insulation sheds which cover the entire length of core elongated FRP rod surface, in which a plurality of sheds are formed by integrally molding an insulating material, i.e., additive-modified silicone high-temperature vulcanized (HTV) rubber by an injection molding machine at definite temperature/s with a definite period of curing time of the HTV rubber material, prior surface treatment of the FRP rod. During the molding process, the insulation sheds get aligned to one another in the axial direction of the core FRP rod. The surface treatment of the FRP rod is carried out in order to strengthen the bonding between the interface region of silicone rubber insulation material & FRP rod in the composite insulator structure. Hardware fittings, which are cleaned ultrasonically by using non-aqueous solvent, are manually inserted over the terminal-ends of the FRP rod and fixing of the hardware at the terminal ends of the FRP rod is carried out by a so-called ‘crimping technique’ using appropriate metallic jaws and also by applying sufficient pressure in a manner that the metallic hardware fixes at the terminal ends of the FRP rod. Hence, hardware-fitted FRP rod structure is placed in the mould for generating the plurality of insulation sheds by injection moulding process at an elevated temperature and pressure.

[0055] Further, each shed in the composite insulator structure is aligned axially to the adjacent shed on the surface of the FRP rod by maintaining a pre-determined parameters, i.e., insulation sheath thickness, insulation sheath 0diameter (both big & small diameter), insulation sheath pitch (big sheath to big sheath), tapered angle of the top to bottom sheath etc. and then continuously molded with the same insulating material, i.e., additive-modified silicone HTV rubber in a monolithic manner.

[0056] It is often thin fibrous structure of HTV silicone rubber insulation material also formed on the surfaces of the insulation sheds during the injection moulding process. These extra fibrous materials on the surface of moulded insulation sheds is termed as ‘flashes’, which were removed, after which the fabricated composite insulators are preliminary tested by NDT method for correctness of interfaces.

[0057] The fabricated insulators belonging to all the three types of configurations, i.e., stay arm type, bracket type, 9-Tonne type respectively are then subjected to routine visual checks and the next level of testing comprising various type tests, electrical tests, mechanical tests, vibration tests and pollution tests respectively by following validated testing procedures in accredited laboratories.

[0058] The fabricated insulators need to essentially pass all the type of tests after which it is confirmed for the desired quality with reliable performance of the 25kV AC composite insulators with preferred creepage distance of 1600mm for various applications as an electrical insulating material, or as an insulating structure more so, in polluted environment wherein the ‘Salt Deposit Density (SDD’) of the environment is upto a level of 0.3 mg/sq.cm.

[0059] The following examples will bring more detailed explanation about the fabrication process for manufacturing of the composite insulators with desired quality with reliable performance for applications in polluting environments as described.
[0060] Example 1:

[0061] This example describes the “stay arm type” of composite insulator, which has a AC voltage rating of 25kV, having a total length (including hardware fittings) about 491+10mm with counter i) creepage distance is about 1600 mm, ii) length of FRP rod is about 422mm with a diameter of about 33mm, iii) thickness of the insulation sheath is about 4mm, iv) diameter of the insulation sheath (big) is about 185mm and to that of small is 141mm, v) pitch (big sheath to big sheath) is about 70.5mm vi) tapered angle ‘top/bottom’ of the sheath is 7/3.5 Degree, vii) mechanical strength (tensile) is about 7000kgf, viii) bending moment is about 200kgf.m is fabricated by following an injection moulding technique by using HTV silicone rubber with Shore Hardness about 67+8.

[0062] The said 25kV AC composite insulator with 1600mm creepage distance that represent the stay arm variety, structurally comprise primarily, i) plurality of insulation sheds, which is moulded in an appropriate die in an injection moulding machine by using an additive-modified high temperature vulcanized (HTV) silicone rubber material (chemically known as methyl vinyl silicone rubber) with Shore Hardness about 67+8, ii) a core structure, which is an elongated ‘fibre reinforced polymer (FRP)’ rod upto a maximum length of 422mm with a diameter of about 33 mm that holds the insulation sheds, iii) metallic hardware, which are forged steel materials, fixed at the terminal ends of the core rod and another iv) interface bonding/reinforcing agent which is used for strengthening interface bonding between silicone rubber and FRP rod respectively.

[0063] The surface treatment of the FRP rod was carried out in order to strengthen the bonding between the interface region of silicone rubber insulation sheds and FRP rod in the composite insulator structure. Hence, the surface of the FRP rod was modified by a chemical treatment process, followed by using a silane-based catalyst-modified adhesive material in xylene solvent followed by a heat-treatment process at a temperature of 120oC for a period of 20 minutes prior to the injection moulding process. Prior conducting the surface treatment of the FRP rods, the rods were also cleaned with a non-aqueous solvent, i.e., iso-propyl alcohol.

[0064] Further, prior to the injection moulding for generating the insulation sheds on the core FRP rod structure, metallic hardware fittings were manually inserted over the terminal-ends of the FRP rod, which was carried out by a so-called ‘crimping technique’ using an appropriate metallic jaw and also by applying a crimping pressure of 150 Bar with holding time of 5 seconds during crimping, so that the metallic hardware fixes at the terminal ends of the FRP rod. The metallic hardware were cleaned ultrasonically by using a non-aqueous solvent, trichloro-ethelene in order to remove any dirt/greasy matter from the surface. However, similar other non-aqueous solvents can also be used for this purpose. Therefore, hardware-fitted FRP rod structure was placed in the mould for generating the plurality of insulation sheds by injection moulding process. The hardware material for metallic end-fittings are galvanized SGI casting materials, wherein one terminal of the end-fitting is known as tube-side and other terminal as mast-side respectively. The total length including the hardware fittings of the aforesaid stay arm type with rating of 25kV AC of the composite insulator having 1600mm creepage distance is 491+10mm.

[0065] In this example, the aforesaid stay arm type 25kV AC composite insulator with 1600mm creepage was fabricated by placing the surface-modified core FRP rod by a chemical treatment process in a stainless steel die in the injection moulding machine, wherein the said additive-modified HTV silicone rubber material is moulded in the form of round sheds at a temperature of 170oC with counter injection pressure of 210 Bar on the surface of core FRP rod having curing time of 650 seconds.

[0066] The insulation sheds which cover the entire length of core elongated FRP rod surface, in which a plurality of sheds are formed by integrally molding the said additive-modified silicone high-temperature vulcanized (HTV) rubber material by the injection molding machine, prior surface treatment of the FRP rod. During the molding process, the insulation sheds got aligned to one another in the axial direction of the core FRP rod.

[0067] The injection moulding process that allowed the plurality of insulation sheds to get aligned continuously throughout the FRP rod structure with nearly uniform thickness of 4mm by maintaining pitch (big sheath to big sheath) of 70.5mm in the axial direction of the FRP rod with a core diameter of 33mm, sheath of which has a tapered angle of about 7o at the top and about 3.5o at the bottom.

[0068] After the injection moulding process, HTV silicone rubber insulation material in the form of thin fibers got deposited on the surface of the insulation sheds, which are termed as ‘flashes’, were removed from the surface. Therefore, the flash-free surfaces of the said insulators are then subjected to routine visual checks & other routine tests, primarily, mechanical test (tensile load) by NDT method (ultrasonically) for correctness of interfaces.

[0069] The fabricated insulators after the preliminary routine tests were then subjected to other testing, comprising type tests, electrical tests, mechanical tests respectively by following validated testing procedures in accredited laboratories.
[0070] The fabricated insulator i.e., stay arm type 25kV AC composite insulator with 1600mm creepage distance has passed through all the desired testing, i.e., mechanical, electrical testing, therefore confirms its suitability as an insulator in polluting environments wherein the Salt Deposit Density (SDD) of the environment is upto a level of 0.3 mg/sq.cm.

[0071] The following stay arm type 25kV AC composite insulator with 1600mm creepage fabricated in this example, showed the following properties, as per Table A:

[0072] Table A: Technical properties of the stay arm type 25kV AC composite insulator with 1600mm creepage under Example 1:
Sl. No.
Description Unit
Type of Composite Insulators – “Stay Arm”
1 Mechanical strength (Tensile) Kgf 7000
2 Insulator length Mm 491
3 Creepage distance Mm 1600
4 Core diameter Mm 33
5 Bending moment Kgf.m 200
6 Insulation Sheath - Big (Diameter) Mm 185
7 Insulation Sheath – Small (Diameter) Mm 141
8 Pitch (Big Sheath to Big Sheath) Mm 70.5
9 Insulation Sheath Thickness Mm 4
10 Shed (tapered) angle-Top/Bottom in degree Degree 7/3.5
11 Shore Hardness of the Silicone Rubber Shore A 67 ± 8
12 Ac Voltage Rating kV 25

[0073] Example 2:

[0074] This example describes the “Bracket type” composite insulator, which is having a total length (including hardware fittings) about 555+10mm with counter i) creepage distance about 1600 mm, ii) length of the FRP is about 422mm with a diameter of about 33mm, iii) thickness of the insulation sheath is about 4mm, iv) diameter of the insulation sheath (big) is about 141mm, v) pitch (big sheath to big sheath) is about 70.5mm vi) tapered angle ‘top/bottom’ of the sheath is 7/3.5 Degree, vii) mechanical strength (tensile) is about 7000kgf, viii) bending moment is about 200kgf.m is fabricated by following an injection moulding technique by using HTV silicone rubber with Shore Hardness about 67+8.
[0075] The process parameters for the fabrication of the said composite insulator remained the same to that of the Example 1.

[0076] The following Bracket type 25kV AC composite insulator with 1600mm creepage fabricated in this example, showed the following properties, as per Table B:
[0077] Table B: Technical properties of the Bracket type 25kV AC composite insulator with 1600mm creepage under Example 2:
Sl. No.
Description Unit
Type of Composite Insulators – “Bracket”
1 Mechanical strength (Tensile) Kgf 7000
2 Insulator length Mm 555
3 Creepage distance Mm 1600
4 Core diameter Mm 33
5 Bending moment Kgf.m 200
6 Insulation Sheath - Big (Diameter) Mm 185
7 Insulation Sheath – Small (Diameter) Mm 141
8 Pitch (Big Sheath to Big Sheath) Mm 70.5
9 Insulation Sheath Thickness Mm 4
10 Shed (tapered) angle-Top/Bottom in degree Degree 7/3.5
11 Shore Hardness of the Silicone Rubber Shore A 67 ± 8
12 Ac Voltage Rating kV 25

[0078] Example 3:

[0079] This example describes the “9-Tonne type” composite insulator, which is having a total length (including hardware fittings) about 540+10mm with counter i) creepage distance about 1600 mm, ii) length of the FRP rod is about 422mm with a diameter of about 33mm, iii) thickness of the insulation sheath is about 4mm, iv) diameter of the insulation sheath (big) is about 141mm, v) pitch (big sheath to big sheath) is about 70.5mm vi) tapered angle ‘top/bottom’ of the sheath is 7/3.5 Degree, vii) mechanical strength (tensile) is about 11000kgf, viii) bending moment is about 210kgf.m is fabricated by following an injection moulding technique by using HTV silicone rubber with Shore Hardness about 67+8.

[0080] The process parameters for the fabrication of the said composite insulator remained the same to that of the Example 1.

[0081] The following 9-Tonne 25kV AC composite insulator with 1600mm creepage fabricated in this example, showed the following properties, as per Table C:
[0082] Table C: Technical properties of the 9-Tonne Type 25kV AC composite insulator with 1600mm creepage under Example 3:

Sl. No.
Description Unit
Type of Composite Insulators – “Bracket”
1 Mechanical strength (Tensile) Kgf 11000
2 Insulator length Mm 540
3 Creepage distance Mm 1600
4 Core diameter Mm 33
5 Bending moment Kgf.m 210
6 Insulation Sheath - Big (Diameter) Mm 185
7 Insulation Sheath – Small (Diameter) Mm 141
8 Pitch (Big Sheath to Big Sheath) Mm 70.5
9 Insulation Sheath Thickness Mm 4
10 Shed (tapered) angle-Top/Bottom in degree Degree 7/3.5
11 Shore Hardness of the Silicone Rubber Shore A 67 ± 8
12 Ac Voltage Rating kV 25

[0083] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.

[0084] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.

[0085] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particulars claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances, where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B”.

[0086] The above description does not provide specific details of manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.

[0087] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.

[0088] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
[0089] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.