Title of Invention

AN EPOXY RESIN MOULDED TERMINAL BUSHING ASSEMBLY FOR HYDROGEN COOLED HIGH VOLTAGE ELECTRICAL GENERATOR

Abstract

The invention relates to epoxy resin moulded terminal bushing assembly for hydrogen cooled high voltage electrical generator comprising an epoxy resin body (14) which accommodates a high tension sleeve (01) and a grounded insert (10), the grounded insert is inserted in the volume of epoxy body (14), an H.T conductor (05) plugged through the epoxy body by means of a locking arrangement (08) to serve as electrical connection between the generator and an electrical bus transmission system, the HT conductor (05) is configured as a separate replaceable component being assembled in the high tension sleeve by means of suitable locking arrangement.

Full Text

FIELD OF INVENTION The present invention relates to an epoxy resin moulded terminal bushing assembly for hydrogen cooled high voltage electrical generator. The bushing assembly shall be compatible for hydrogen environment, capable of withstanding high fault currents with optimized insulation creepage and heat dissipation rate. BACKGROUND OF THE INVENTION A high voltage bushing is conventionally used to transmit electrical current and voltage from an electrical generator to an electrical bus transmission system. Existing high voltage bushings for electrical generators use inorganic based ceramic material or glass epoxy/epoxy resins as main insulation. The epoxy resin moulded terminal bushings device is provided with a central metal conductor integrated with a radial built-up insulation of epoxy resin. The length of the bushing on either side of the system is commensurate with the medium (air or gas). In conventional bushings, the conductor is directly inserted in pre-fabricated insulation tube assembly, which is difficult to withstand for higher system voltages. Similarly, the grounded terminal is fixed on outer surface of insulating tube instead of being in the volume of insulation. This arrangement gives high electrical surface stress on the insulating tube, which is not acceptable for higher system voltages. The bushing will have suitable flange assembly for mounting the same to the generator body (refer Fig. 1). The reliability of the high voltage bushing devices are 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. • Gas-leakage rate. • Leakage current levels. • Heat dissipation rate. Due to the transmission of high current through the conductor, for hydrogen cooled generators, conventionally, the heat generated from the conductor is cooled with pressurized hydrogen gas by appropriate methods, necessitating appropriate sealing arrangements to prevent leakage of hydrogen gas from the generator. As the bushing device need to be mounted on to the generator wall with the aid of appropriate flange assembly, likelihood of high electric field need to be carefully addressed so that there is no leakage of current and voltage to the generator ground. Optimum arrangements for electrostatic field control with adequate design features can improve the manufacturability of the bushing device and can reduce the cost of the bushing. An Indian Patent Application No. 1218/DEL/2002 dated 9.12.2002 discloses a process of moulding of bushing by epoxy resin. OBJECTS OF THE INVENTION It is therefore an object of the present invention to propose an epoxy resin moulded terminal bushing assembly for hydrogen cooled high voltage electrical generator which eliminates the disadvantage of the conventional one. A further object of the present invention is to propose a terminal brushing assembly which can withstand higher fault currents at higher system voltages. A still further object of the present invention is to propose an epoxy resin moulded terminal bushing assembly for hydrogen cooled high voltage electrical generator which can be used to extend HT connection from one media to another. An yet further object of the invention is to propose an epoxy resin moulded terminal bushing assembly for hydrogen cooled high voltage electrical generator which is effective for dynamic forces/mechanical loading encountered during or in service conditions, Another object of the present invention is to propose an epoxy resin moulded terminal bushing assembly for hydrogen cooled high voltage electrical generator which has effective heat dissipation rate. A still another object of the present invention is to propose an epoxy resin moulded terminal bushing assembly for hydrogen cooled high voltage electrical generator which provides effective sealing arrangement to prevent the gas leakage. An yet another object of the present invention is to propose an epoxy resin moulded terminal bushing assembly for hydrogen cooled high voltage electrical generator which optimizes surface stresses and hence insulation creepage. Still another object of the present invention is to propose a high voltage generator bushing device which is simple in design and takes less time for manufacturing and assembly. SUMMARY OF THE INVENTION : According, there is provided a high voltage generator bushing device for high voltage, hydrogen cooled electrical generators comprising an epoxy body, a high tension (HT)-conductor and locking system. The epoxy body comprises brass/steel sleeve and a grounded aluminum/steel insert. The grounded terminal is inserted in the volume of the epoxy body. The HT-conductor is configured as a separate replaceable component being assembled in the brass sleeve by means of suitable locking arrangement. The HT-conductor has provision for arresting gas leakage and extends this connection from one medium to another. The grounded insert is also provided with appropriated sealing arrangement to meet the requirement. The surface electrical stress of the bushing is controlled by optimizing grounded insert profile. The heat generated from the conductor is effectively dissipated by optimizing gas circulation passage in the annular gap between HT sleeve and HT conductor. A suitable mechanism for gas circulation between generator and bushing has been arranged. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS : Fig. 1. Shows schematically an assembly of the conventional high voltage generator bushing. Fig. 2. HT sleeve of the high voltage generator bushing device as per present invention Fig. 3. HT conductor of the high voltage generator bushing device as per present invention Fig. 4. Locking nut of the high voltage generator bushing device as per present invention Fig. 5. Grounded terminal/insert of the high voltage generator bushing device as per present invention Fig. 6. Epoxy body of the high voltage generator bushing device as per present invention Fig. 7. Assembly of the proposed high voltage generator bushing device as per present invention DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT : The high tension (HT) sleeve [01] made of brass/stainless steel is arranged at the center of the mould as per Fig. 2. The periphery of the sleeve is provided with number of profiled grooves [02] to enhance the mechanical strength of the bushing device at the interface of epoxy and sleeve. The thickness of HT sleeve may not be uniform throughout its length. The grooves on HT sleeve shall be located with respect to the position of the grounded terminal/insert. The HT sleeve [01] has flanges on its either end. The flange towards air side (FLANGE - A) is provided with multiple grooves [03] required for arresting hydrogen gas leakage. The flange towards gas side (FLANGE-G) has provision for the hydrogen gas inlet [04]. For the gas circulation, appropriate holes [06] have been provided over the radial surface of the HT conductor [05]. The heat dissipation rate is controlled by keeping these passages at a strategic distance with respect to the gas inlet location. The HT conductor [05] is further designed in such a way that it enters in the epoxy body [14] from one end. HT conductor [05] is integrated with stopper [07] as per Fig. 3 to arrest gas leakage when it is tightened against HT sleeve [01] flange (FLANGE -A). Suitable provision has been made to the HT conductor [05] towards gas end for providing high voltage connection to the hydrogen cooled generator. A lock nut [08] as per Fig. 4 is provided to secure the HT conductor [05] inside the HT sleeve [01] of epoxy body [14]. To avoid rotation of lock nut [08] during service, provision is made for locking the lock nut [08] against FLANGE-G of HT sleeve [01]. Suitable gas passage opening [09] has been facilitated on the face of lock nut [08] for allowing gas to flow from generator to the annular space between HT conductor [05] and HT sleeve [01] through FLANGE-G of HT sleeve [01]. The ground terminal/insert [10] as per Fig. 5 is inserted in the volume of the epoxy body [14] as per Fig.6. The inner surface of the grounded terminal/insert is provided with profiled holes [11] as well as communicating holes [12] from inner to outer surface to enhance the mechanical strength of the bushing at the interface of epoxy body [14] and ground terminal/insert [10]. The grounded terminal / insert [10] has provision for fastening to the generator mounting flanges. Suitable sealing arrangement [13] has been provided to this grounded terminal / insert [10] to arrest the gas leakage. The HT conductor [05] as per Fig. 3 which is not an integral part of the epoxy body (refer Fig. 5) is inserted through the epoxy body [14] to serve as an electrical connection between the electrical generator and the electrical bus transmission system. After inserting the HT conductor [05] through the epoxy body [14], the lock nut [08] as per Fig. 4 is placed and securely tightened. The unique arrangement arrests any movement of the HT conductor during service. This entire assembly can be used as terminal bushing [15] for hydrogen cooled generators. Since the HT conductor is not an integral part of the bushing, this arrangement facilitates easy assembly, maintenance and replacement. The moulding of 'the bushing is carried out with the selected epoxy resin system through a process as described in the Patent Application No. 1218/DEIV2002 dated 09.12.2002. Solventless Bisphenol 'A' epoxy resin is thoroughly mixed fillers, like silica powder for about 8 hours in a chamber which is maintained under vacuum of 5 toor and at a temperature of about 65°C. The hardener used in the present invention is carboxylic acid anhydride. Hardener is also kept in another chamber maintained under the same conditions. This operation of maintaining the vacuum and temperature in both the chambers for about 8 hours is necessary to remove any dissolved gases present in the materials. After this operation, the filler mixed resin and the hardener are blended to get a homogenous material. For 100 parts by weight of solventless Bisphenol 'A' epoxy resin, 375 parts of silica powder filler is added and 100 parts by weight of carboxylic acid anhydride is used. For moulding of this material into a bushing of the present invention, mould is fabricated to the required dimensions of the high fault current proof bushing [14]. The grounded terminal / insert [10] and HT sleeve [01] are placed inside the mould. The homogenous resin mix, which will be in semi-solid ' state, is pumped into the mould under pressure of 2 to 3 atmospheres. The temperature of the mould is constantly maintained at about 130°C to 150°C and pressure of 2 to 3 atmospheres. Under these conditions of pressure and temperature, the resin mix is kept in the mould for 3 to 5 hours for curing. The cured epoxy body [14] is then removed form the mould and kept in an air-circulating oven at a temperature of 130°C to 150°C for 07 to 09 hours. WE CLAIM: 1. An epoxy resin moulded terminal bushing assembly for hydrogen cooled high voltage electrical generator comprising: an epoxy resin body (14) which accommodates an HT sleeve (01) and a grounded insert (10); a locking means (08); wherein the terminal/ insert (10) being located in the volume of epoxy body (14) and HT Conductor (05) being plugged through the epoxy body (14) configured as a separate replaceable component and retained in the position by lock nut (08) to serve as a high voltage bushing for power transmission from generator to bus transmission system. 2. An epoxy resin moulded terminal bushing assembly as claimed in claim 1, wherein HT conductor (05) is configured as a separate replaceable component being assembled inside the HT sleeve (01) of epoxy body (14) by means of a locking nut (08). 3. An epoxy resin moulded terminal bushing assembly as claimed in claim 1, wherein HT sleeve (01) is made of brass or stainless steel material, a plurality of profiled grooves (02) are configured on the periphery in the line with the position of grounded terminal/ insert and thickness of the sleeve is not necessarily uniform throughout its length. 4. An epoxy resin moulded terminal bushing assembly as claimed in claim 3, wherein HT sleeve (01) is provided with one flanges on air side FLANGE - A with a provision for sealing arrangement (03) and one flange FLANGE - G on gas side with a provision for locking the nut against movement. 5. An epoxy resin moulded terminal bushing assembly as claimed in claim 4, wherein Flange G of the HT sleeve (01) has a provision for the hydrogen gas inlet (04) into the annular space between the HT sleeve (01) and the HT conductor (05) for effective heat dissipation from the HT conductor (05). 6. An epoxy resin moulded terminal bushing assembly as claimed in claim 1, wherein the HT conductor (05) is made of high conductive material with suitable stopper (07) to arrest gas leakage from bushing device where it is tightened against FLANGE - A of HT sleeve (01). 7. An epoxy resin moulded terminal bushing assembly as claimed in claim 1 wherein the grounded terminal (10) is made of aluminium or steel and provided with profiled holes (11) on the inner surface and communicating holes (12) from inner surface to outer surface and a sealing arrangement (13) on its collar. 8. The terminal assembly with epoxy resin moulded bushing as claimed in claim 1, wherein creepage /arcing distance of the bushing is optimized / controlled by providing a profile of grounded terminal designed specifically not to initiate disruptive discharges during high voltage application in such a way that the electric field levels are within allowable levels at the electric field controlled grounded terminal (10). 9. An epoxy resin moulded terminal bushing assembly as claimed in claim 1 to 8, wherein the HT conductor (05) is tightened against HT sleeve (01) with a locking nut (08). 10. An epoxy resin moulded terminal bushing assembly as claimed in claim 1 to 9, wherein the lock nut (08) has suitable gas passage opening (09) for allowing gas to flow from generator to annular space between HT conductor (05) and HT sleeve (01). ABSTRACT AN EPOXY RESIN MOULDED TERMINAL BUSHING ASSEMBLY FOR HYDROGEN COOLED HIGH VOLTAGE ELECTRICAL GENERATOR The invention relates to epoxy resin moulded terminal bushing assembly for hydrogen cooled high voltage electrical generator comprising an epoxy resin body (14) which accommodates a high tension sleeve (01) and a grounded insert (10), the grounded insert is inserted in the volume of epoxy body (14), an H.T conductor (05) plugged through the epoxy body by means of a locking arrangement (08) to serve as electrical connection between the generator and an electrical bus transmission system, the HT conductor (05) is configured as a separate replaceable component being assembled in the high tension sleeve by means of suitable locking arrangement.

Documents:

00417-kol-2008-abstract.pdf

00417-kol-2008-claims.pdf

00417-kol-2008-correspondence others.pdf

00417-kol-2008-description complete.pdf

00417-kol-2008-drawings.pdf

00417-kol-2008-form 1.pdf

00417-kol-2008-form 2.pdf

00417-kol-2008-form 3.pdf

00417-kol-2008-gpa.pdf

417-KOL-2008-(26-08-2013)-ABSTRACT.pdf

417-KOL-2008-(26-08-2013)-AMANDED PAGES OF SPECIFICATION.pdf

417-KOL-2008-(26-08-2013)-CLAIMS.pdf

417-KOL-2008-(26-08-2013)-CORRESPONDENCE.pdf

417-KOL-2008-(26-08-2013)-FORM-1.pdf

417-KOL-2008-(26-08-2013)-FORM-2.pdf

417-KOL-2008-CORRESPONDENCE.pdf

417-KOL-2008-EXAMINATION REPORT.pdf

417-KOL-2008-FORM 18-1.1.pdf

417-kol-2008-form 18.pdf

417-KOL-2008-GPA.pdf

417-KOL-2008-GRANTED-ABSTRACT.pdf

417-KOL-2008-GRANTED-CLAIMS.pdf

417-KOL-2008-GRANTED-DESCRIPTION (COMPLETE).pdf

417-KOL-2008-GRANTED-DRAWINGS.pdf

417-KOL-2008-GRANTED-FORM 1.pdf

417-KOL-2008-GRANTED-FORM 2.pdf

417-KOL-2008-GRANTED-FORM 3.pdf

417-KOL-2008-GRANTED-SPECIFICATION-COMPLETE.pdf

417-KOL-2008-REPLY TO EXAMINATION REPORT.pdf