Title of Invention

AN IMPROVED PLUG-IN SURGE ARRESTER FOR ELECTRICAL SUB-STATION APPLICATION.

Abstract

The invention relates to an improved plug-in surge arrester for electrical sub-station application, in particular indoor switchyard applications, comprising -an insulating tube assembly (01,02,03) having at an upper end a HT terminal (04) for electrically connecting the device with power systems; -a stress-grading assembly (06,07,08) slipped over said insulated tube assembly (01,02,03), said stress-grading assembly being disposed in a metallic housing (9) having a fixing means; -an insulated bushing assembly (05,10) disposed at said HT-terminal end (04) for lowering electric stress from the insulating medium; and -a low tension terminal (11) provided at an opposite end of said insulating tube assembly (01,02,03) being insulated from said metallic housing (9), characterized in that said insulating bushing assembly (05,10) comprises an insulated bushing (05) and an integrated HT-insert (10) having a plug-in means for fixing the surge arrester and In that said insulating tube assembly (01,02,03) comprises a plurality of non-linear elements (01) being connected through a metallic inter-stage heat sinks (02).

Full Text

FIELD OF INVENTION The invention relates to a novel plug-in surge arrester device for use in power system in general and in electrical substations, transmission and distribution lines, transformers of all voltage ranges to protect the power equipment from variety of temporary, switching and lightning over voltages. The invention in particular relates to a novel plug-in surge control device for indoor switchyard applications. PRIOR ART Conventional surge arresters use porcelain / composite housing to operate at higher electrical stresses. HT shield is used to balance voltage distribution across surge arrester blocks. Since, Porcelain clad equipment has electrical field in the vicinity, those can not be used for compact indoor applications. Alternatively, gas filled metal clad surge arresters of next generation is not a cost-effective solution for medium voltage application. Plug-in surge arresters introduced recently, use metallic housing with silicon rubber insulation for the stack assembly. Electrical stress is controlled using grading techniques at the interface between rubber insulation, bushing and grounded flange. The main flaw of these plug-in systems is that, it requires electric stress grading material to relieve electrical stresses at rated voltage. The deterioration in specific properties of this stress grading material effects the performance of these surge arresters. Further, these surge arresters have higher length to diameter ratio (L/D). It is therefore the object of the invention to provide a plug-in surge arrester device which obviates the disadvantages of the prior art devices. Another object of the invention is to provide a novel plug-in surge arrester device which achieves an improved voltage distribution across the metal oxide blocks. A further object of the invention is to provide a piug-in surge arrester device which is specifically suitable for compact indoor applications. Yet a farther object of the invention is to provide a plug-in surge arrester device which operates at a tow electrical stress with improved mechanical rigidity and configured with a reduced height. Still a further object of the Invention Is to provide a plug-in surge arrester device which warrants lesser assembly and maintenance time and simultaneously emerges as a cost-effect device. At tha outsat of tha description which follows, it is to be understood that the ensuing description only illustrates a particular form of the invention. However, such a particular form is only an exemplary embodiment and the teachings of tha invention is not intended to be taken restrictively. SUMMARY OF THE INVENTION Accordingly there is provided an improved plug-in surge arrester for electrical sub-station application, in particular indoor switchyard applications, comprising -an insulating tube assembly having at an upper end a HT terminal for electrically connecting the device with power systems; -a stress-grading assembly slipped over said insulated tube assembly, said stress-grading assembly being disposed in a metallic housing having a fixing means; -an insulated bushing assembly disposed at said HT-terminal end for lowering electric stress from the insulating medium; and -a low tension terminal provided at an opposite end of said insulating tube assembly being insulated from said metallic housing, characterized in that said insulating bushing assembly comprises an insulated bushing and an integrated insert having a plug-in means for fixing tha surge arrester and in that said insulating tube assembly comprises a plurality of nonlinear elements being connected through a metallic inter-stage heat sinks. Figure 1- Shows a conventional plug-in surge arrester device. Figure 2- Shows a novel plug-in surge arrester device according to a preferred embodiment of the invention. Figure 3- Shows a sub-assembly of linear elements of the device according to the preferred embodiment of the invention. Figure 4 - Shows an insulating tube assembly of the device of the invention. Figure 5 - Shows a stress grading assembly of the device according to the invention. Figure 6 - Shows an insulating bushing assembly of the device of the invention. Figure 7 - Shows an insulated bushing assembly integrated with HT- insert according to the preferred embodiment of the invention. DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENT Figure 1 shows the prior art device in which the metallic housing (02) is used with silicon rubber (05) insulation between the non-linear elements (03) for the stress-grading assembly. Figure 2 shows the new plug-in surge arrester assembly proposed in the present invention. Here, the non-linear elements (01) are stacked in series and connected by means of a metallic inter-stage heat sink (02) as detailed in Figure 3. The assembly of non-linear elements with inter-stage heat sinks is placed in a low permitivity, high dielectric strength insulating tube (03) shown in Figure 4. The Insulating tube assembly has a HT terminal (04) at the end to establish electrical connection to electrical systems via an insulated bushing (05). A silicon / flexible rubber boot (06) is integrated with HT shield (07) by slipping over the above insulating tube assembly (refer Figure 5 for details). The rubber boot is tipped with high permitivity material (08), to minimize the electrical stress near the grounded flange. The profile of HT shield (07) is designed in such a way that inter-block capacitive coupling is achieved resulting in uniform voltage distribution across the blocks. The rubber boot (06) slipped over the insulating tube assembly is placed in a metallic housing (09), which has a provision of fixing the surge arrester to the main equipment. Insulated bushing (05) is specially designed for lowering electric stress from insulating medium to solid insulated surge arrester and isolates the medium from ambient temperature (refer Figure 6). The electrostatic field, at high-tension end, is controlled using appropriate geometry of the insulated bushing and integrated HT Terminal called as HT insert (10). The HT insert of the bushing has the provision of plug-in arrangement for fixing proposed surge arrester. The low tension (LT) terminal (11) at the end of the stack is insulated from the metallic housing and hence the healthiness of the surge arrester can be evaluated by measuring the leakage current. Two variants are proposed based on placement of HT shield. In one form, the HT Shield (07,08) is placed over the plug-in-part (06) (Reference Fig-5), and in a variant form, the HT shield (07,10) is placed in a static part (05). WE CLAIM I 1. An improved plug-in surge arrester for electrical sub-station application, in particular indoor switchyard applications, comprising - an insulating tube assembly (01,02,03) having at an upper end a HT terminal (04) for electrically connecting the device with power systems; - a stress-grading assembly (06,07,08) slipped over said insulated tube assembly (01,02,03), said stress-trading assembly being disposed in a metallic housing (9) having a fixing means; - an insulated bushing assembly (05,10) disposed at said HT-terminal end (04) for lowering electric stress from the insulating medium; and - a low tension terminal (11) provided at an opposite end of said insulating tube assembly (01,02,03) being insulated from said metallic housing (9), characterized in that said insulating bushing assembly (05,10) comprises an insulated bushing (05) and an integrated HT-insert (10) having a plug-in means for fixing the surge arrester and in that said insulating tube assembly (01,02,03) comprises a plurality of non-linear elements (01) being connected through a metallic inter-stage heat sinks (02). 2. A surge arrester as claimed in claim 1, wherein the sub-assembly of the non-linear elements (01) and the Biter-stage heat sinks (02) is interposed in a bw permitvity, high dielectric strength insulating tube (03). 3. A surge arrester as claimed in claim 1, wherein said stress-grading assembly (06,07,08) comprises a silicon rubber boot (06) integrated with a HT-shield (07), said rubber boot being tipped with a high permitvity material (08). 4. A surge arrester as claimed in claim 3, wherein said HT shield (07) has a profile designed to achieve uniform voltage distribution across the non linear elements (blocks). 5. A surge arrester as claimed in claim 1, wherein said HT-shield (07) is disposed on said silicon rubber boot (06). 6. A surge arrester as claimed in claim 1, wherein said HT-shield (07) is disposed on said insulated bushing (05). 7. A plug-in surge arrester device for use in power systems, in particular indoor switchyard applications substantially as herein described and illustrated with reference to the accompanying drawings.

Documents:

176-del-2004-abstract.pdf

176-del-2004-claims.pdf

176-del-2004-correspondence-others.pdf

176-del-2004-correspondence-po.pdf

176-del-2004-description (complete).pdf

176-del-2004-drawings.pdf

176-del-2004-form-1.pdf

176-del-2004-form-19.pdf

176-del-2004-form-2.pdf

176-del-2004-form-3.pdf

176-del-2004-gpa.pdf

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