-2-
FIELD OF INVENTION
The present invention relates to epoxy based insulators used as terminal bushings in high voltage electrical appliances like motors, switchgear etc. The insulators shall be capable of withstanding high fault currents with optimized insulation creepage.
BACKGROUND OF THE INVENTION
Existing terminal bushings for low and medium voltage electrical appliances like motors, generator etc uses inorganic based ceramic material or epoxy resins as main insulation.
The ceramic material based terminal bushings are fragile in nature and need careful handling. Their mechanical strength is weak and while assembling on to the electrical appliances, chances of breakage are more. Process cycle for making these bushings with ceramic insulation takes long duration because it involves various steps like moulding, firing at high temperatures, pre-stage machining, sintering and final machining to the required dimensions. Dimensional tolerance is poor and there is high shrinkage while manufacturing.
-3-
The epoxy resin moulded terminal bushings use a central metal conductor integrated with a radiai built-up insulation of epoxy resin. The length of the bushing on either side of the system commensurates with the medium (air or oil). The bushing assembly is housed in a terminal box with suitable fixing arrangement.
The reliability of the above two systems are governed by following parameters:
• Quality of the metal conductor and connectors during service.
• Void free preparation of the ceramic and/or epoxy insulation.
• Heat conduction and thermal expansion based incompatibilities.
• Life of ceramic and/or epoxy insulation.
The performance of porcelain insulators is limited by weak mechanical link between grounded terminal and insulation. Even though the performance of the insulator at higher fault currents is improved by isolating HT conductor from the porcelain insulation, the arrangement may not be able to withstand for medium and higher voltage systems because of partial discharges in service. This is due to air gap or trapped gases or moisture between conductor and insulation.
-4-
OBJECTS OF THE INVENTION
It is therefore the object of the present invention to propose a high-fault current proof insulator, which does not have the disadvantages of the prior art.
A further object of the present invention is to propose a high-fault current proof insulator, which can withstand higher fault currents at higher system voltages.
Still another object of the present invention is to propose a high-fault current proof insulator, which is simple in design and takes less time for manufacture and assembly.
Yet another object of the present invention is to propose a high-fault current proof insulator, which can be used to extend HT connection from one media to another.
Yet another object of the present invention is to propose a high-fault current proof insulator, which is optimizing insulation creepage as well as the arcing distance.
Still further object of the present invention is to propose a high-fault current proof insulator, which is effective for use in controlled environment of terminal box.
-5-
SUMMARY OF THE INVENTION
Accordingly, there is provided a high fault current proof insulator for high voltage electrical appliances comprising an epoxy body, a high tension (HT) conductor and locking system. The epoxy body comprises brass/steel sleeve and a grounded aluminum/steel terminal. The grounded terminal being configured on an outer surface of the epoxy body, the HT-conductor being inserted through the epoxy body to serve as an electrical connection between an electric appliance and a power supply source. The HT-conductor is configured as a separate replaceable component being assembled in the brass sleeve by means of suitable locking arrangement. The copper conductor (HT conductor) has provision for sealing arrangement to extend this connection from one medium to another. The grounded terminal is also provided with appropriate sealing arrangement to meet this requirement. In highly polluted areas, the performance of the insulators and the connections can be achieved by controlling the environmental conditions of the terminal box. The controlled environment of terminal box would be possible using pressurized gas like Nitrogen, air etc.
-6-
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.l. Shows schematically an assembly of the conventional insulator according to prior art.
Fig.2 to 7. Schematically show various components and assembly of an insulator as per present invention.
Fig.2. Brass sleeve of the high fault current proof insulator.
Fig.3. Grounded terminal of the high fault current proof insulator.
Fig.4. HT conductor of the high fault current proof insulator.
Fig.5. Hardwares for high fault current proof insulator.
Fig.6. Epoxy body of the high fault current proof insulator.
Fig.7. Assembly of the proposed high fault current proof insulator.
-7-
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The high tension (HT) sleeve [04] 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 [05] to enhance the mechanical strength of the insulator at the interface of epoxy and sleeve. The thickness of HT sleeve may not be same throughout its length. The grooves on HT sleeve shall be located with respect to the position of the grounded terminal. The HT brass sleeve is provided with a flat/polygonal lock arrangement [06] on one side matching with a locking means provided to the HT conductor [07] and to a locking ring [08] as per fig. (5) respectively. The HT conductor is designed in such away that one of its ends enters inside the epoxy body. A D-lock arrangement [10] as per fig. (4) has been made on the front portion of the HT conductor. A lock ring is designed in such a way that its inner surface shall have D-lock provision for locking against HT conductor and its outer surface shall have flat/polygonal lock provision for locking against HT sleeve [04].
The grounded terminal [11] as per fig. (3) is proposed on the outer surface of the epoxy body [12] as per fig (6). The inner surface of the grounded terminal is provided with profiled holes [13] to enhance
-8-
themechanical strength of the insulator at the interface of epoxy and grounded terminal. The outer surface of the grounded terminal is provided with a locking means to ensure fastening to connecting
modules like terminal box or mounting flanges. Suitable sealing arrangement [14] has been provided to this grounded terminal to control the operating environment of the terminal box.
The HT conductor [07] as per fig. (4) which is riot an integral part of the epoxy body of the proposed insulator [15] is inserted through the epoxy body [12] to serve as an electrical connection between the electrical equipment and the incoming/outgoing of the power supply. The HT conductor has a provision for sealing arrangement [16] to provide electrical connection extending from one medium to another. After inserting the HT conductor through the epoxy body, the lock washer [17] as per fig. (5) is placed and securely tightened with a lock nut [09]. The unique arrangement arrests any movement of the copper conductor during service. Since the HT conductor is not an integral part of the insulator, this arrangement facilitates easy assembly, maintenance and replacement.
-9-
The moulding of the insulator is carried out through a process as described in the Patent Application No. 1218/DEL/2002 dt 09.12.2002. Brominated epoxy resin is thoroughly mixed with fillers, like Aluminium trihydrate and silica powder for about 8 hours in a chamber which is maintained under vacuum of 5 torr 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 brominated epoxy resin, 135 parts each of fillers aluminium thrighydrate and silica powder are added and 65 parts by weight of carboxylic acid anhydride is used. For moulding of this material into an insulator of the present invention, mould is fabricated to the required dimensions of the high fault current proof insulator [15]. The grounded terminal [11] and HT sleeve [04] are placed inside the mould. The homogenous resin mix, which will be
-10-
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 [12] 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.
-11-
WE CLAIM:
1. A high fault current proof insulator assembly for high voltage
electrical appliances comprising of an epoxy body [12] and a high
tension (HT) conductor [07], the epoxy body [12J accommodates
a brass sleeve [04] and a grounded aluminium/steel terminal
[11], the grounded terminal being configured on an outer surface
of the epoxy body [12], the HT-conductor [07] being inserted
through the epoxy body [12], to serve as an electrical connection
between an electric appliance and a power supply source,
characterized in that the HT-conductor [07] is configured as a
separate replaceable component being assembled with the brass
sleeve [04] by means of locking arrangement [08, 09, 17].
2. The insulator assembly as claimed in claim 1, wherein the HT
sleeve [04] made of brass or stainless steel, a plurality of profiled
grooves [05] are configured on the periphery of HT-sfeeve [04],
The location of these grooves shall be in line with the position of
grounded terminal. The thickness of the sleeve is not necessarily
the same throughout its length,
-12-
3. The insulator assembly as claimed in claim 1, wherein the HT
conductor [07] is made of copper with suitable sealing
arrangement.
4. The insulator assembly as claimed in claim l, wherein the
grounded terminal [11] made of aluminium or steel, a profiled
hole [13] on the inner surface, and wherein a sealing
arrangement [14] is provided on its collar.
5. The insulator assembly as claimed in claim 1, wherein the HT-
sleeve [04] is provided with flat/polygonal locking [06] on one
side matching with correspondingly matching means provided to a
lock ring [08].
6. The insulator assembly as claimed in claim 1, wherein the
creepage and arcing distance of the insulator, which is placed in
environmental controlled terminal box is optimized/controlled.
-13-
7. The insulator assembly as claimed in claim 3, 4 & 5", wherein the HT-conductor [07] is tightened against HT sleeve [04] and lock ring [08] with a lock nut [09] and said locking means.

Accordingly, there is provided a high fault current proof insulator for high voltage electrical appliances comprising an epoxy body, a high tension (HT) conductor and locking system. The epoxy body comprises brass/steel sleeve and a grounded aluminum/steel terminal. The grounded terminal being configured on an outer surface of the epoxy body, the HT-conductor being inserted through the epoxy body to serve as an electrical connection between an electric appliance and a power supply source. The HT-conductor is configured as a separate replaceable component being assembled in the brass sleeve by means of suitable locking arrangement. The copper conductor (HT conductor) has provision for sealing arrangement to extend this connection from one medium to another. The grounded terminal is also provided with appropriate sealing arrangement to meet this requirement. In highly polluted areas, the performance of the insulators and the connections can be achieved by controlling the environmental conditions of the terminal box. The controlled environment of terminal box would be possible using pressurized gas like Nitrogen, air etc.