Claims:WE CLAIM:

1. A Medium voltage electrical bushing for electric traction application comprising of a bushing body [03] mounted on a High Tension Insert [01], wherein the bushing body [03] comprises of a hollow cylindrical body [3A], upper part of which is integrated to a plurality of disc like members [3B] maintaining a gap from each other and the lower part of the hollow cylindrical body [3A] ends with a tapered part [3C], in which a sleeve [02] is placed at one end of the bushing body [03] and Low Tension insert [04] is provided at intermediate part of the bushing body [03].

2. The Medium voltage electrical bushing for electric traction application as claimed in claim 1, wherein Said disc like member [3B] is having concave surface on one side and convex surface on other side.

3. The Medium voltage electrical bushing for electric traction application as claimed in claim 1 or 2, wherein Low Tension [LT] insert [04] is placed below the disc like members [3B] and on the hollow cylindrical body [3A].

4. The Medium voltage electrical bushing for electric traction application as claimed in claims 1-3, wherein the high tension insert (01) is configured as a conductive component for medium voltage being assembled inside the epoxy body (03) by a locking nut (05).

5. The Medium voltage electrical bushing for electric traction application as claimed in claims 1-4, wherein the Low Tension insert [04] is hollow cylindrical member [4A] with a flange [4B] there around, the sleeve [2] forms a cylindrical member and the High Tension Insert [01] constitutes a rod.

6. The Medium voltage electrical bushing for electric traction application as claimed in claims 1-5, wherein the depth up to which the insert [01] goes inside the epoxy body [03] is determined by optimization of electric field levels on the surface of the insulator body [03].

7. The Medium voltage electrical bushing for electric traction application as claimed in claims 1-6, wherein the part of the High Tension Sleeve [02] remains inside the epoxy body [03] and the shape of that part is configured to provide a maximum adherence between the High Tension Sleeve [02] and the epoxy body [03], in which the depth up to which the insert [02] goes inside the epoxy body [03] is determined by optimization of electric field levels on the surface of the insulator body [03].

8. The Medium voltage electrical bushing for electric traction application as claimed in claims 1-7, wherein the HT sleeve (02) is made of material including brass, stainless steel, in which a plurality of profiled grooves are configured on the periphery in the line with the position of grounded terminal / insert.

9. The Medium voltage electrical bushing for electric traction application as claimed in claims 1-8, wherein the outer body of the Low Tension insert [04] has regular grooves [4A] to increase its adhesion to the epoxy body [03], in which a hole is provided along the central axis of the Low Tension insert [04] corresponding to a fixing arrangement of the bus-bar enclosure.

10. The Medium voltage electrical bushing for electric traction application as claimed in claims 1-9, wherein the Low tension insert/grounded terminal (04) is made of material including Aluminium, Steel provided with profiled holes on the inner surface and communicating holes from inner surface to outer surface and a sealing arrangement on its collar.
, Description:A MEDIUM VOLTAGE ELECTRICAL BUSHING FOR ELECTRIC TRACTION APPLICATION

FIELD OF THE INVENTION :

[001] The present invention in general relates to medium voltage electrical bushing for electric traction application. More particularly, the present invention relates to medium voltage electrical bushing providing enhanced performance during short circuit conditions with optimized insulation creepage distance withstanding higher fault currents. The invention is specifically related to the design of medium voltage electrical bushing for electric traction application.

BACKGROUND OF THE INVENTION :

[002] 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.

[003] A medium voltage bushing is conventionally used for passing an electrical conductor through a locomotive or electric traction system to transmit electrical current and voltage from an overhead line to an electrical bus transmission system in the locomotive. Existing medium voltage bushings for locomotive or electric traction system uses inorganic based ceramic material as main insulation. These bushings are fragile in nature and need careful handling. Their mechanical strength is weak and while assembling on the loco of traction systems, chances of breakage are more. Process cycle for making these insulators takes long duration because it involves various steps like moulding, firing at temperatures of about 850 degree centigrade, pre-stage machining, sintering and final machining to the required dimensions. Dimensional tolerance is poor and there is high shrinkage while manufacturing. The length of the bushing on either side of the system is commensurate with the medium (air or gas). The bushing will have suitable flange assembly for mounting the same to the locomotive or electric traction system body.

[004] The reliability of the medium voltage bushings is governed by following parameters:
• Quality of the metal conductor and connectors during service.
• Void free preparation of the epoxy insulation.
• Heat conduction and thermal expansion based incompatibilities.
• Prevention of rainy water leakage.
• Prevention of leakage current during humid or rainy conditions.

[005] In order to hold the high voltage conductor firmly to the electrically grounded metal enclosure of locomotive or electric traction system, in a position sufficiently far away from the grounded enclosure to avoid dielectric breakdown, bushing is provided with metal fittings or metal flange to the enclosure.

[006] The bushing 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 metal/copper conductor. This is because such voids are subjected to high electrical fields at the critical bushing conductor interface region, which can lead to ionization within the voids, flashover and a reduced life expectancy for the bushing. 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 bushing.

[007] According to US patent US7795541B1 which 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.

[008] Another prior art US Pat 3,318,995 discloses cast electrical bushing construction having controlled and shielded shrinkage voids. In this patent cast resin bushings are disclosed, which remain electrically reliable even with differential thermal expansion or shrinkage due to cavitation between metal and cast resin. For this purpose, regions with increased cracking tendency are electrically shielded by partially conductive or semi conductive field shielding layers. The layers are either arranged on the high-voltage inner conductor or electrically connected to this end; or they are arranged on shielding electrodes and electrically connected to these end, wherein the shielding electrodes in turn are electrically connected to the grounded housing of the connected apparatus. The field shielding layers create a field-free space between themselves and the inner conductor or themselves and the shielding electrode and effectively shield cavities in the casting resin.

[009] Still there exists requirement 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 medium voltage conductors and which replaces the common metallic conductor or metal fitting or metallic flange with bushes to reduce the final weight and cost of the insulator.

[0010] The need exists for less expensive insulator systems and manufacturing process for the manufacture of medium voltage insulating products such as cast epoxy insulator and other medium voltage insulating products, which are void free and which meet the depicted medium voltage insulation requirements.

[0011] The present invention is directed to address the above problems and focus on medium voltage electrical bushing for insulating medium voltage conductor from electrically grounded metal enclosure/fitting of locomotive or electric traction system.

OBJECTS OF THE INVENTION :

[0012] It is an object of the invention to provide a medium voltage electrical bushing for insulating medium voltage conductor through metal enclosure of locomotive or electric traction system.

[0013] Yet another object of the invention is to provide the medium voltage electrical bushing used for electrical systems operated at 1 KV and up to 36 KV.

[0014] Another objective of the present invention is to provide improved elastomeric composition having good weathering and tracking resistance for withstanding most extreme environmental condition like dusty, deserted as well as coastal areas and suitable for the manufacture of protective weather sheds for the medium voltage electrical bushing.

[0015] Another objective of the present invention is to provide the medium voltage electrical bushing for electric traction application at lesser weight and lesser cost.

[0016] These and other objects and advantages of the present subject matter will be apparent to a person skilled in the art after consideration of the following detailed description taken into consideration with accompanying drawings in which preferred embodiments of the present subject matter are illustrated.

SUMMARY OF THE INVENTION :

[0017] One or more drawbacks of conventional systems and process are overcome, and additional advantages are provided through the apparatus/composition 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.

[0018] Accordingly, there is provided a medium voltage electrical bushing having enhanced performance during short circuit conditions with optimized insulation creepage distance withstanding higher fault currents. The medium voltage electrical bushing for electric traction application is used for transferring the power from overhead transmission line to electrics of locomotive.

[0019] According to the invention, one bushing is used for each locomotive. A High Tension (HT) insert, which is exposed to high voltage stresses, with optimized dimensions is arranged to provide better distribution of the electric field levels and improve the withstandability of the insulator under high short circuit forces. At least one Low Tension (LT) Insert is exposed to voltage stresses lower than that experienced by the High Tension (HT) inserts. On the peripheral side of the insulators, the LT inserts allow fastening of the medium voltage electrical bushing to the housing of the electric locomotive and provide rigidity to the bushing. Also, the epoxy body of the bushing is constructed to provide desired electric field stress distribution on the surface of the bushing's body.

[0020] 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.

[0021] 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.

[0022] 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 ACCOMPANYING DRAWINGS :

[0023] 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 processes that are consistent with the subject matter as claimed herein, wherein:-

Figure 1: Shows a medium voltage electrical bushing adapted for electric traction application according to the invention.

Figure 1A: Shows isometric view of medium voltage electrical bushing adapted for electric traction application in accordance with the invention.

Figure 2: Shows High Tension (HT) insert of the bushing of Figure 1.

Figure 3: Shows High Tension (HTS) Sleeve of the bushing of Figure 1.

Figure 4: Shows Low Tension (LT) Insert of the bushing of Figure 1.

[0024] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily 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 OF PREFERRED EMBODIMENT (S) OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS :

[0025] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.

[0026] The present invention makes a disclosure regarding a technology pertaining to a medium voltage electrical bushing for electric traction application.

[0027] Now, reference may be made to Figure 1 indicating the present invention, wherein the electrical bushing comprising of medium voltage electrical bushing body [03], a High Tension (HT) insert [01], High Tension (HT) Sleeve [02] and Locking Nut (LN) [05] provided along the central axis of the bushing, and a Low Tension (LT) Insert [04] disposed at the periphery. At least one Low Tension (LT) insert [04] is provided for each electrical bushing.
[0028] A side view of the High Tension [HT] Insert [01] is presented in Figure 2. Said medium voltage electrical bushing body [03] is mounted on the High Tension (HT) insert [01]. A part of the High Tension [HT][ Insert [01] remains inside the epoxy body [03] and the shape of that part is configured to provide a maximum adherence between the High Tension [HT] insert [01] and the epoxy body [03]. The depth up to which this insert [01] goes inside the epoxy body [03] is also determined by optimization of electric field levels on the surface of the insulator body [03]. The depth is determined by electrical stress or electrical field appearing on the HT inserts. The HT Insert/conductor [01] is made of high electrical conductive material.
[0029] As shown in Figure 1A, the bushing body [03] is mounted on the High Tension [HT] Insert [01]. The High Tension [HT] Insert [01] is substantially like a rod. The bushing body [03] comprises a hollow cylindrical body [3A], upper part of which is integrated to a plurality of disc like members [3B] maintaining a gap from each other as best seen in Figure 1A. Said disc like member [3B] is having concave surface on one side and convex surface on other side. The lower part of the hollow cylindrical body [3A] of bushing body [03] ends with a tapered part [3C]. The upper part of the electrical bushing [03] has profile substantially like a fir tree as shown in Figure 1. The bushing body [03] constitutes a single piece. The Low Tension [LT] insert [04] is placed below the set of the disc like members (3B) and on the hollow cylindrical body [3A]. The Low Tension [LT] insert [04] is hollow cylindrical member [4A] with a flange [4B] there around as shown in Figure 1A. The sleeve [2] forming a cylindrical member is positioned at one end of the bushing body [3]. The HT insert [01] is configured as a conductive component for medium voltage being assembled inside the epoxy body [03] by means of a locking nut [05].

[0030] A side view of the High Tension [HT] Sleeve Insert [02] is presented in Figure 3. A part of the High Tension [HT] Sleeve [02] remains inside the epoxy body [03] and the shape of that part is configured to provide a maximum adherence between the High Tension [HT] Sleeve [02] and the epoxy body [03]. The depth up to which this insert [02] goes inside the epoxy body [03] is also determined by optimization of electric field levels on the surface of the insulator body [03].

[0031] The HT sleeve [02] is made of material including brass/stainless steel. A plurality of profiled grooves are configured on the periphery in the line with the position of grounded terminal / insert and thickness of the sleeve [02] is not necessarily uniform throughout its length. Grooves are inside the HT sleeve, which will act as bonding between metallic LT insert to solidified epoxy resin system after curing.

[0032] A side view of the Low Tension (LT) insert [04] is presented in Figure 4. The outer body of the LT insert [04] has regular grooves to increase its adhesion to the epoxy body [03]. Regular grooves are inside of LT inserts, which will act as bonding between metallic LT insert to solidified epoxy resin system after curing. The electrical bushing body [03] is surrounded by the LT insert [4]. An optimum sized hole is provided along the central axis of the Low Tension (LT) insert [04] corresponding to a fixing arrangement of the bus-bar enclosure.

[0033] The Low tension insert/grounded terminal [04] is made of material including Aluminium, Steel provided with profiled holes on the inner surface and communicating holes from inner surface to outer surface and a sealing arrangement on its collar.
[0034] The grounded terminal / insert [04] is located in the volume of the epoxy body [03] and HT Insert/conductor [01] is plugged through the epoxy body [03] to serve as an electrical connection between the electric locomotive/traction system and the electrical bus transmission system.

[0035] The above materials are given as example without restricting scope of the invention to the same. Thus, other materials readily apparent to a person skilled in the art are understood to be within purview of the invention.

[0036] Reference may be made to Figure 1, wherein the electrical bushing [03], profile parameters of which are optimized for the specific electro-static field levels on its surface for the locomotive bushing.
[0037] The creepage / arcing distance of the bushing is optimized / controlled by providing electric field controlled grounded terminal. Here, incorporation of HT sleeve with optimum dimensions acts as an electrostatic shield and provides higher withstandability for short circuit stresses. Incorporation of LT Insert allows fixing of the electrical bushing to the enclosure of the electric locomotive.

ADVANTAGEOUS FEATURES :

- Improvement in the reliability of the electrical bushings by virtue of drastic reduction in size;
- Enhancing the heat transfer capability of the electrical bushing assembly due to the compact size of the bushing;
- Improved elastomeric composition having good weathering and tracking resistance for withstanding most extreme environmental condition like dusty, deserted as well as coastal areas;
- Suitable for the manufacture of protective weather sheds for the medium voltage electrical bushing;
- Provision of the medium voltage electrical bushing for electric traction application at lesser weight and lesser cost.

WORKING OF THE INVENTION:

[0038] The medium voltage electrical bushing for electric traction application is used as a link between the moving traction or locomotive system to stationary 25kV electrical transmission system. The pantograph collector is used to collect the electrical power from transmission system and the same is transferred to moving traction or locomotive system by placing these medium voltage electrical bushing.

TEST RESULT:
[0039] The medium voltage electrical bushing is tested for high voltage, capacitance and tan delta, partial discharge, switching and impulse voltage as well as cantilever test.
[0040] The medium voltage electrical bushing is also tested for mechanical vibration and withstood all the tests as recommended by IEC 60137 standard.

[0041] 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.

[0042] 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.

[0043] 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 analogues 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”.
[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.