FIELD OF THE INVENTION

The present invention, in general, relates to a bushing device for high voltage electrical generators, and more particularly relates to a bushing device (15) for high voltage water cooled generator to withstand high fault currents with optimized insulation creepage and heat dissipation rate.
BACKGROUND OF THE INVENTION
A high voltage bushing is conventionally used for transmitting electrical current and voltage from an electrical generator to an electrical bus transmission system. Generally, inorganic based ceramic material or glass epoxy/epoxy resins are used as main insulation in existing high voltage bushings for electrical generators. The epoxy resin molded 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 air or gas medium. In conventional bushings, the conductor is directly inserted in a pre-fabricated insulation tube assembly, which reduces the system's capability to withstand higher system voltages. Similarly, the grounded terminal is fixed on outer surface of insulating tube instead of being inside the volume of insulation. This arrangement poses high electrical surface stress on the insulating tube, which is not acceptable for higher system voltages. The bushings have suitable flange assembly for mounting the same to the generator body as illustrated in figure 7.
The fundamental parameters that govern the reliability of the high voltage bushing devices are:
• 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
In conventional water cooled generators, due to high current transmission through the conductor, the generated heat in said conductor is cooled with pressurized water gas by appropriate methods. This necessitates an appropriate sealing arrangements for preventing leakage of water gas from the generator.
As the bushing device needs to be mounted on to the generator wall with the aid of appropriate flange assembly, likelihood of high electric field needs to be addressed carefully so as to ensure 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. Indian Patent No. 212079 discloses a process of moulding of bushing by epoxy resin.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide a high voltage generator bushing device which eliminates the disadvantages of the conventional one.
Another primary object of the present invention is to provide a high voltage generator bushing device to withstand higher fault currents at higher system voltages.
A further object of the present invention is to provide a high voltage generator bushing device to be used for extending HT connection from one media to another.

Another object of the present invention is to provide a high voltage generator bushing device to be effective for dynamic forces/mechanical loading encountered during a fault or in service conditions.
Still another object of the present invention is to provide a high voltage generator bushing device for providing effective heat dissipation rate.
Yet another object of the present invention is to provide a high voltage generator bushing device for improving sealing arrangement in order to prevent the gas leakage.
Yet another object of the present invention is to provide a high voltage generator bushing device to optimize surface stresses and hence insulation creepage.
Still another object of the present invention is to provide a high voltage generator bushing device to simplify the process of manufacturing and assembly, thereby reducing production cycle as well as cost of the finished product.
These and other objects and advantages of the present invention 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 invention is illustrated.
SUMMARY OF THE INVENTION
The present invention discloses a high voltage generator bushing device for high voltage, water 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.
Various objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description when taken in conjunction with the accompanying drawings in which like parts are designated by like numerals.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
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 apparatus that are consistent with the subject matter as claimed herein, wherein:
Figure 1 illustrates a high tension (HT) sleeve of the high voltage generator bushing device according to an embodiment of the present invention.
Figure 2 illustrates a HT conductor of the high voltage generator bushing device according to an embodiment of the present invention.

Figure 3 illustrates a locking nut of the high voltage generator bushing device according to an embodiment of the present invention.
Figure 4 illustrates a grounded terminal/insert of the high voltage generator bushing device according to an embodiment of the present invention.
Figure 5 illustrates an epoxy body of the high voltage generator bushing device according to an embodiment of the present invention.
Figure 6 illustrates an assembly of the proposed high voltage generator bushing device according to an embodiment of the present invention.
Figure 7 illustrates a schematic view of an assembly of the conventional high voltage generator bushing.
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 THE INVENTION
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.

The drawings illustrate only those specific details that are pertinent to understand the embodiments of the present disclosure, so as not to obscure the disclosure with details that will be clear to those of ordinary skill in the art having benefit of the description herein.
Figure 1 represents a high tension (HT) sleeve (1) made of brass/stainless steel which is arranged at the center of the mould. The periphery of the sleeve is provided with number of profiled grooves (2) 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 (1) has flanges on its either end. The flange towards air side (FLANGE –A) is provided with multiple sealing grooves (3) required for arresting water gas leakage. The flange towards gas side (FLANGE-G) has provision for the water gas inlet (4). For the gas circulation, appropriate holes (6) have been provided over the radial surface of the HT conductor (5). The heat dissipation rate is controlled by keeping these passages at a strategic distance with respect to the gas inlet location. The HT conductor (5) is further designed in such a way that it enters in the epoxy body (14) from one end.
Figure 2 illustrates the integration of HT conductor (5) with stopper (7) to arrest gas leakage when tightened against HT sleeve (1) flange (FLANGE –A). Suitable provision has been made to the HT conductor (5) towards gas end for providing high voltage connection to the water cooled generator.
Figure 3 illustrates a lock nut (8), provided for securing the HT conductor (5) inside the HT sleeve (1) of epoxy body (14). To avoid rotation of lock nut (8) during service, provision is made for locking the lock nut (8) against FLANGE-G of HT sleeve (1). Suitable gas passage opening (9) has been facilitated on the face of lock nut

(8) for allowing gas to flow from generator to the annular space between HT conductor (5) and HT sleeve (1) through FLANGE-G of HT sleeve (1).
The ground terminal/insert (10) as per figure 4, is inserted in the volume of the epoxy body (14) as illustrated in figure 5. 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 (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 (5) of figure 2, which is not an integral part of the epoxy body (refer figure 4), 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 (5) through the epoxy body (14), the lock nut (8) of figure 3 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 water 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 Indian Patent No. 212079. Solvent less Bisphenol ‘A’ epoxy resin is thoroughly mixed with fillers, like silica powder for about 8 hours in a chamber which is maintained under a vacuum pressure of 5 torr and at a temperature of about 65oC. In contrast, the present invention utilizes carboxylic acid anhydride as hardener. The hardener is also kept in another chamber and 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 solvent less 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 (1) 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 130oC to 150oC 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 130oC to 150oC for 7 to 9 hours.
LIST OF REFERENCE NUMBERS
1. High tension (HT) sleeve 9. Gas passage opening
2. Profiled grooves 10. Grounded terminal
3. Sealing Grooves 11. Profiled holes
4. Water gas inlet 30 12. Communicating holes
5. HT conductor 13. Sealing arrangement
6. Holes over radial surface of HT 14. Epoxy resin body
conductor 15. Terminal bushing for water cooled
7. HT conductor stopper generators
8. Locking nut

WE CLAIM:
1. A high voltage generator bushing device (15) for water cooled generator
comprising: -
- an epoxy resin body (14) accommodating an alloyed high tension (HT) sleeve (1) and a grounded terminal (10), wherein the grounded terminal (10) is positioned in the volume of the epoxy resin body (14);
- a separate replaceable high tension (HT) conductor (5); and
- a locking nut (8),
characterized in that said generator and the electrical bus transmission system is conductively connected by the HT conductor (5) plugged through said epoxy body (14), and is assembled inside the HT sleeve (1) of said epoxy body (14) by means of said locking nut (8).
2. The bushing device as claimed in claim 1, wherein a plurality of profiled grooves (2) are provided along the periphery of the HT sleeve (1) in line with the grounded terminal.
3. The bushing device as claimed in claim 1, wherein said HT sleeve (1) is having varying thickness along its length.
4. The bushing device as claimed in claim 3, wherein said HT sleeve (1) is provided with at least a flange on air side FLANGE-A with a provision for sealing arrangement (3) and at least a flange FLANGE–G on gas side with a provision for locking the nut against movement.

5. The bushing device as claimed in claim 4, wherein said FLANGE – G
of the HT sleeve (1) has a provision for a water gas inlet (4) into the annular space between the HT sleeve (1) and the HT conductor (5) for effective heat dissipation from the HT conductor (5).
6. The bushing device as claimed in claim 1, wherein the HT conductor (5) is made of high conductive material with suitable stopper (7) which is tightened against FLANGE - A of HT sleeve (1).
7. The bushing device as claimed in claim 1, wherein the grounded terminal (10) made of aluminum or steel 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 bushing device as claimed in claim 1, wherein creepage / arcing distance of the bushing is controllable under electric field of grounded terminal (10).
9. The bushing device as claimed in claim 1, wherein the HT conductor (5) is tightened against said HT sleeve (1) with the locking nut (8).

10. The bushing device as claimed in claim 1, wherein a gas passage opening (9) is provided on the lock nut (8) to facilitate gas flow from generator to annular space between the HT conductor (5) and the HT sleeve (1).