Title of Invention	AN INTER STAGE METALLIC DEVICE FOR IMPROVEMENT OF SURGE ARRESTERS
Abstract	An inter stage metallic device (2) for improvement of surge arresters (S) consists of thermally conducted inter stage metallic device/element made with a high conductive electrical grade material and is provided with suitable flow channels (4) for circulation of gas/liquid from one block to another and having an inner passage (6) for taking away heat from metal oxide block (1) to the insulating medium is connected to the surge arrester elements (1) stacked in series, the said device has a profile (7) for providing uniform electrostatic field across the blocks (1) and for reducing over all electrical stress levels and ionization of the insulating medium at edges of metal oxide blocks (1). The device maintains uniform temperature distribution across metal oxide blocks elements (1), uniform current over the surge arrester elements and uniform thermal distribution through insulating medium for enhancing performance and efficiency of surge arrester.

Title of Invention

AN INTER STAGE METALLIC DEVICE FOR IMPROVEMENT OF SURGE ARRESTERS

Abstract

An inter stage metallic device (2) for improvement of surge arresters (S) consists of thermally conducted inter stage metallic device/element made with a high conductive electrical grade material and is provided with suitable flow channels (4) for circulation of gas/liquid from one block to another and having an inner passage (6) for taking away heat from metal oxide block (1) to the insulating medium is connected to the surge arrester elements (1) stacked in series, the said device has a profile (7) for providing uniform electrostatic field across the blocks (1) and for reducing over all electrical stress levels and ionization of the insulating medium at edges of metal oxide blocks (1). The device maintains uniform temperature distribution across metal oxide blocks elements (1), uniform current over the surge arrester elements and uniform thermal distribution through insulating medium for enhancing performance and efficiency of surge arrester.

Full Text	FIELD OF INVENTION The present invention relates to an inter-stage metallic device for improvement of surge arresters. More particularly, the invention relates to the introduction of a metallic inter stage device to high voltage surge arresters to improve their efficiency and performance. BACKGROUND AND PRIOR ART OF THE INVENTION Gas or liquid insulated surge arresters are used to protect high voltage substation equipment against lightning, switching and temporary over voltages. The surge arrester (SA) assembly prematurely fails due to thermal run-away of metal oxide blocks in conventionally designed equipment. Generation, transmission and distribution substations are exposed to lightning, switching and temporary over voltages and required to be protected from their destructive effects. Surge arresters, which are being used for this purpose, are primarily installed at the line entrances and as a complementary protection at strategic points of the substation, often at the transformers. Conventional porcelain/composite insulator clad surge arresters are used for yard substation application. For compact substations or highly integrated substations (HIS), if surge arresters are installed outside the gas insulated substations (GIS) i.e., near the transformer, protection against over voltages is limited by the electrical distance between the GIS and the arrester. In order to maximize the benefits of the compact substations like gas insulated substations (GIS), it is desirable to use metal-clad gas insulated surge arresters as an integral part of these substations. The main advantages of the metal-clad surge arresters over conventional porcelain/composite insulator clad surge arresters are given below: 1. Improved insulation co-ordination. 2. Quick response for steep discharge current. 3. Immunity from external environment like pollution, snow, rain etc. 4. Reduced voltage stress to the connected equipment. 5. The flexibility of placement of the arrester at an optimum place in the GIS. 6. Significant reduction in size and weight. 7. Switching over voltages seen by the connected transformer/equipment is reduced significantly. To overcome the above problems, inventers have earlier proposed a fast acting surge arrester for high voltage substations (patent application No. 171/Del/2000 and patent No. 215560). In conventional stack assembly of surge arresters (A) as shown in Fig.l, the metal oxide blocks are physically stacked and connected electrically in series through the metallic surface. Fig.l shows the conventional non-linear elements (02) stack assemblies. Following are some of the drawbacks with this arrangement: 1. In the absence of inter-stage element contact resistance between blocks is poor. 2. Due to lack of effective heat transfer medium between blocks, heat dissipation from the blocks is confined mostly through the glazed surface of SA elements only. 3. Electrostatic field enhancement at the edges of the blocks due to their sharpness resulting in ionization of insulation medium. 4. Discharge capabilities of blocks are limited and utilized inefficiently due to poor voltage and temperature distribution. In some of the conventional surge arresters, metal elements/spacers are used in series to the metal-oxide blocks to achieve required arcing distance (refer US 006466425). Here, the metallic element thickness is much higher than metal-oxide element. In compact substations, such type of design hampers the uniform voltage distribution across metal-oxide blocks and hence performance of the surge arrester. In addition to the above, existing designs are also deficient in taking measures for effective heat dissipation. To address the above problems, stacks of surge arrester elements are formed with an invented inter-stage device. OBJECTS OF THE INVENTION Therefore it is an object of the invention to propose an inter stage metallic device for improvement of surge arresters which is capable of improving heat dissipation from metal-oxide blocks/surge arrestor elements. Another object of the invention is to propose an inter stage metallic device for improvement of surge arresters which is capable of improving circulation of cooling medium such as liquid or gas across metal oxide blocks. A still another object of the invention is to propose an inter stage metallic device for improvement of surge arresters which provides effective electrical contact between metal oxide blocks. Yet another object of the invention is to propose an inter stage metallic device for improvement of surge arresters which improves energy distribution across blocks. A further object of the invention is to propose an inter stage metallic device for improvement of surge arresters which utilizes discharge capabilities of metal oxide blocks stack/surge arrester assembly on par with a single metal oxide block. A still further object of the invention is to propose an inter stage metallic device for improvement of surge arresters which improves voltage distribution across blocks both for single column and multicolumn stack arrangements. A still another object of the invention is to propose an inter stage metallic device for improvement of surge arresters which improves electrostatic field at edges of metal oxide blocks to overcome the problem of ionization and hot spots. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Fig.1 - shows the conventional stack assemblies according to prior art. Fig.2 - shows concept of inter-stage device according to the invention. Fig.3 - shows details of inter-stage device according to the invention. Fig.4 - shows stack assembly with inter-stage device according to the invention. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION The main objective of the present invention is to improve the efficiency and performance of high voltage surge arresters by introducing metallic inter-stage device (2). In the proposed invention, the surge arrester (SA) elements (1) are stacked in series and connected by means of a thermally conducting inter-stage metallic device/element (2) as shown in Fig.2. The interstage element (2) helps in maintaining uniform temperature and current over the SA elements (1) and overcomes thermal runaway problems in the surge arrester (S). The device also improves the surge current carrying capabilities of the surge arrester (S) as it helps in creation of parallel paths across the elements. The device (2) is made with a high conductive electrical grade Aluminium or copper. During conduction of blocks, thermal energy generated within the SA elements (1) is dissipated through this interstage device (2) efficiently to the liquid/gas medium in addition through the peripheral surface/glazed surface of the block (3). The device (2) maintains a lower temperature at the metalized surface (5) of the block as it is in contact with the insulating medium during normal operation. Part of the heat, over a period of time, distributes to the adjacent blocks and temperature distribution becomes highly uniform. The surface of inter stage device (2) has provision for gas/liquid circulation through suitable flow channels (4), which have been provided in the device (2) as shown in Fig.3. These flow channels (4) help to circulate gas/liquid from one block to another. The metalised surface of metal-oxide block (1) is allowed to be exposed to the medium through these flow channels (4). This also facilitates circulation and mixing of hot gas/liquid to the medium in which blocks are assembled. The inter-stage element (2) also provides gas flow from peripheral surface of the block to its metalized surface (5) by means of these flow channels (4). An inner passage (6) helps in take away heat from metal-oxide block (l)/inter-stage device (2) to the insulating medium. The arrangement helps in achieving uniform thermal distribution through gas/liquid insulation medium. Precisely metal-oxide blocks (1) are at uniform temperature and result to a uniform voltage distribution across the blocks. The design of the interstage device (2) is decided by the requirements of heat dissipation capabilities, discharge current and the voltage rating/distribution across elements. Improvement in thermal conduction or more uniform temperature distribution is achievable further as the stack assembly is placed in an insulating housing of high mechanical and dielectric strength. The insulating tube is terminated in metallic flanges with openings for gas/liquid circulation. The inter-stage device (2) also ensures low contact resistance between two metallic surfaces (5) of the metal-oxide block (1) during their service as shown in fig.4. The profile (7) of inter-stage device (2) is designed in such a way that resultant electrostatic field across the blocks is uniform and over all electrical stress levels are reduced to overcome the problem of ionization of the insulating medium at edges of metal-oxide blocks (1). In multi-column arrangement invented inter-stage device (2) helps in achieving better capacitive coupling between blocks. The improved design maintains uniform temperature distribution across metal-oxide blocks (1), uniform thermal distribution through insulating medium and enhances surge arrester (S) performance and efficiency. WE CLAIM 1. An inter stage metallic device for improvement of surge arrester (S) comprising: a thermally conducted inter-stage metallic device/element (2) made with a high conductive electrical grade material provided with suitable flow channels (4) for circulation of gas/liquid from one block to another and having an inner passage (6) for taking away heat from metal-oxide block (1) to the insulating medium and connected to the surge arrester elements (1) stacked in series, the said device having a profile (7) for providing uniform electrostatic field across the blocks (1) and for reducing over all electrical stress levels and ionization of the insulating medium at edges of metal-oxide blocks; characterised in that the device (2) maintains uniform temperature distribution across metal-oxide blocks/elements (1), uniform current over the surge arrester elements (1) and uniform thermal distribution through insulating medium for enhancing performance and efficiency of surge arrester (S). 2. An inter stage device (2) as claimed in claim 1, wherein the device is made of high conductive electrical grade aluminium or copper. 3. An inter stage device (2) as claimed in claim 1, wherein the said device dissipates heat generated in the surge arrester elements (1) to the liquid/gas medium and through the peripheral surface/glazed surface of the block (3). 4. An inter stage device (2) as claimed in claim 1, wherein the said device provides uniform voltage distribution across the blocks. 5. An inter stage device (2) as claimed in claim 1, wherein the device (2) provides gas flow from peripheral surface (3) of the block to its metalized surface (5) through flow channels (4). 6. An inter stage device (2) as claimed in claim 1, wherein the device (2) ensures low contact resistance between two metallic surfaces (5) of the metal-oxide block (1) during the service. 7. An inter stage device (2) as claimed in claim 1, wherein the device (2) maintains a lower temperature at the metalised surface (5) of the block being in contact with the insulating medium during normal operation. An inter stage metallic device (2) for improvement of surge arresters (S) consists of thermally conducted inter stage metallic device/element made with a high conductive electrical grade material and is provided with suitable flow channels (4) for circulation of gas/liquid from one block to another and having an inner passage (6) for taking away heat from metal oxide block (1) to the insulating medium is connected to the surge arrester elements (1) stacked in series, the said device has a profile (7) for providing uniform electrostatic field across the blocks (1) and for reducing over all electrical stress levels and ionization of the insulating medium at edges of metal oxide blocks (1). The device maintains uniform temperature distribution across metal oxide blocks elements (1), uniform current over the surge arrester elements and uniform thermal distribution through insulating medium for enhancing performance and efficiency of surge arrester.

Full Text

FIELD OF INVENTION
The present invention relates to an inter-stage metallic device for improvement of surge arresters. More particularly, the invention relates to the introduction of a metallic inter stage device to high voltage surge arresters to improve their efficiency and performance.
BACKGROUND AND PRIOR ART OF THE INVENTION
Gas or liquid insulated surge arresters are used to protect high voltage substation equipment against lightning, switching and temporary over voltages. The surge arrester (SA) assembly prematurely fails due to thermal run-away of metal oxide blocks in conventionally designed equipment.
Generation, transmission and distribution substations are exposed to lightning, switching and temporary over voltages and required to be protected from their destructive effects. Surge arresters, which are being used for this purpose, are primarily installed at the line entrances and as a complementary protection at strategic points of the

substation, often at the transformers. Conventional porcelain/composite insulator clad surge arresters are used for yard substation application. For compact substations or highly integrated substations (HIS), if surge arresters are installed outside the gas insulated substations (GIS) i.e., near the transformer, protection against over voltages is limited by the electrical distance between the GIS and the arrester. In order to maximize the benefits of the compact substations like gas insulated substations (GIS), it is desirable to use metal-clad gas insulated surge arresters as an integral part of these substations. The main advantages of the metal-clad surge arresters over conventional porcelain/composite insulator clad surge arresters are given below:
1. Improved insulation co-ordination.
2. Quick response for steep discharge current.
3. Immunity from external environment like pollution, snow, rain etc.
4. Reduced voltage stress to the connected equipment.
5. The flexibility of placement of the arrester at an optimum place in the GIS.
6. Significant reduction in size and weight.
7. Switching over voltages seen by the connected transformer/equipment is reduced significantly.

To overcome the above problems, inventers have earlier proposed a fast acting surge arrester for high voltage substations (patent application No. 171/Del/2000 and patent No. 215560).
In conventional stack assembly of surge arresters (A) as shown in Fig.l, the metal oxide blocks are physically stacked and connected electrically in series through the metallic surface. Fig.l shows the conventional non-linear elements (02) stack assemblies. Following are some of the drawbacks with this arrangement:
1. In the absence of inter-stage element contact resistance between blocks is poor.
2. Due to lack of effective heat transfer medium between blocks, heat dissipation from the blocks is confined mostly through the glazed surface of SA elements only.
3. Electrostatic field enhancement at the edges of the blocks due to their sharpness resulting in ionization of insulation medium.
4. Discharge capabilities of blocks are limited and utilized inefficiently due to poor voltage and temperature distribution.
In some of the conventional surge arresters, metal elements/spacers are used in series to the metal-oxide blocks to achieve required arcing

distance (refer US 006466425). Here, the metallic element thickness is much higher than metal-oxide element. In compact substations, such type of design hampers the uniform voltage distribution across metal-oxide blocks and hence performance of the surge arrester. In addition to the above, existing designs are also deficient in taking measures for effective heat dissipation. To address the above problems, stacks of surge arrester elements are formed with an invented inter-stage device.
OBJECTS OF THE INVENTION
Therefore it is an object of the invention to propose an inter stage metallic device for improvement of surge arresters which is capable of improving heat dissipation from metal-oxide blocks/surge arrestor elements.
Another object of the invention is to propose an inter stage metallic device for improvement of surge arresters which is capable of improving circulation of cooling medium such as liquid or gas across metal oxide blocks.

A still another object of the invention is to propose an inter stage metallic device for improvement of surge arresters which provides effective electrical contact between metal oxide blocks.
Yet another object of the invention is to propose an inter stage metallic device for improvement of surge arresters which improves energy distribution across blocks.
A further object of the invention is to propose an inter stage metallic device for improvement of surge arresters which utilizes discharge capabilities of metal oxide blocks stack/surge arrester assembly on par with a single metal oxide block.
A still further object of the invention is to propose an inter stage metallic device for improvement of surge arresters which improves voltage distribution across blocks both for single column and multicolumn stack arrangements.
A still another object of the invention is to propose an inter stage metallic device for improvement of surge arresters which improves electrostatic field at edges of metal oxide blocks to overcome the problem of ionization and hot spots.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1 - shows the conventional stack assemblies according to prior art. Fig.2 - shows concept of inter-stage device according to the invention. Fig.3 - shows details of inter-stage device according to the invention. Fig.4 - shows stack assembly with inter-stage device according to the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
The main objective of the present invention is to improve the efficiency and performance of high voltage surge arresters by introducing metallic inter-stage device (2).
In the proposed invention, the surge arrester (SA) elements (1) are stacked in series and connected by means of a thermally conducting inter-stage metallic device/element (2) as shown in Fig.2. The interstage element (2) helps in maintaining uniform temperature and current over the SA elements (1) and overcomes thermal runaway problems in the surge arrester (S). The device also improves the surge

current carrying capabilities of the surge arrester (S) as it helps in creation of parallel paths across the elements.
The device (2) is made with a high conductive electrical grade Aluminium or copper. During conduction of blocks, thermal energy generated within the SA elements (1) is dissipated through this interstage device (2) efficiently to the liquid/gas medium in addition through the peripheral surface/glazed surface of the block (3). The device (2) maintains a lower temperature at the metalized surface (5) of the block as it is in contact with the insulating medium during normal operation. Part of the heat, over a period of time, distributes to the adjacent blocks and temperature distribution becomes highly uniform. The surface of inter stage device (2) has provision for gas/liquid circulation through suitable flow channels (4), which have been provided in the device (2) as shown in Fig.3. These flow channels (4) help to circulate gas/liquid from one block to another. The metalised surface of metal-oxide block (1) is allowed to be exposed to the medium through these flow channels (4). This also facilitates circulation and mixing of hot gas/liquid to the medium in which blocks are assembled. The inter-stage element (2) also provides gas flow from peripheral surface of the block to its metalized surface (5) by means of these flow channels (4). An inner passage (6) helps in take

away heat from metal-oxide block (l)/inter-stage device (2) to the insulating medium. The arrangement helps in achieving uniform thermal distribution through gas/liquid insulation medium. Precisely metal-oxide blocks (1) are at uniform temperature and result to a uniform voltage distribution across the blocks. The design of the interstage device (2) is decided by the requirements of heat dissipation capabilities, discharge current and the voltage rating/distribution across elements. Improvement in thermal conduction or more uniform temperature distribution is achievable further as the stack assembly is placed in an insulating housing of high mechanical and dielectric strength. The insulating tube is terminated in metallic flanges with openings for gas/liquid circulation.
The inter-stage device (2) also ensures low contact resistance between two metallic surfaces (5) of the metal-oxide block (1) during their service as shown in fig.4. The profile (7) of inter-stage device (2) is designed in such a way that resultant electrostatic field across the blocks is uniform and over all electrical stress levels are reduced to overcome the problem of ionization of the insulating medium at edges of metal-oxide blocks (1). In multi-column arrangement invented inter-stage device (2) helps in achieving better capacitive coupling between blocks. The improved design maintains uniform temperature

distribution across metal-oxide blocks (1), uniform thermal distribution through insulating medium and enhances surge arrester (S) performance and efficiency.

WE CLAIM
1. An inter stage metallic device for improvement of surge arrester (S) comprising:
a thermally conducted inter-stage metallic device/element (2) made with a high conductive electrical grade material provided with suitable flow channels (4) for circulation of gas/liquid from one block to another and having an inner passage (6) for taking away heat from metal-oxide block (1) to the insulating medium and connected to the surge arrester elements (1) stacked in series, the said device having a profile (7) for providing uniform electrostatic field across the blocks (1) and for reducing over all electrical stress levels and ionization of the insulating medium at edges of metal-oxide blocks;
characterised in that the device (2) maintains uniform temperature distribution across metal-oxide blocks/elements (1), uniform current over the surge arrester elements (1) and uniform thermal distribution through insulating medium for enhancing performance and efficiency of surge arrester (S).

2. An inter stage device (2) as claimed in claim 1, wherein the device is made of high conductive electrical grade aluminium or copper.
3. An inter stage device (2) as claimed in claim 1, wherein the said device dissipates heat generated in the surge arrester elements (1) to the liquid/gas medium and through the peripheral surface/glazed surface of the block (3).
4. An inter stage device (2) as claimed in claim 1, wherein the said
device provides uniform voltage distribution across the blocks.
5. An inter stage device (2) as claimed in claim 1, wherein the device (2) provides gas flow from peripheral surface (3) of the block to its metalized surface (5) through flow channels (4).
6. An inter stage device (2) as claimed in claim 1, wherein the device (2) ensures low contact resistance between two metallic surfaces (5) of the metal-oxide block (1) during the service.
7. An inter stage device (2) as claimed in claim 1, wherein the device (2) maintains a lower temperature at the metalised

surface (5) of the block being in contact with the insulating medium during normal operation.

An inter stage metallic device (2) for improvement of surge arresters (S) consists of thermally conducted inter stage metallic device/element made with a high conductive electrical grade material and is provided with suitable flow channels (4) for circulation of gas/liquid from one block to another and having an inner passage (6) for taking away heat from metal oxide block (1) to the insulating medium is connected to the surge arrester elements (1) stacked in series, the said device has a profile (7) for providing uniform electrostatic field across the blocks (1) and for reducing over all electrical stress levels and ionization of the insulating medium at edges of metal oxide blocks (1). The device maintains uniform temperature distribution across metal oxide blocks elements (1), uniform current over the surge arrester elements and uniform thermal distribution through insulating medium for enhancing performance and efficiency of surge arrester.

Documents:

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Patent Number

272258

Indian Patent Application Number

906/KOL/2009

PG Journal Number

14/2016

Publication Date

01-Apr-2016

Grant Date

25-Mar-2016

Date of Filing

25-Jun-2009

Name of Patentee

BHARAT HEAVY ELECTRICALS LIMITED

Applicant Address

REGIONAL OPERATIONS DIVISION (ROD), PLOT NO: 9/1, DJBLOCK 3RD FLOOR, KARUNAMOYEE, SALT LAKE CITY, KOLKATA-700091, HAVING ITS REGISTERED OFFICE AT BHEL HOUSE, SIRI FORT, NEW DELHI-110049

Inventors:

#	Inventor's Name	Inventor's Address
1	DR. HARI SHANKAR JAIN	REGIONAL OPERATIONS DIVISION (ROD), PLOT NO: 9/1, DJBLOCK 3RD FLOOR, KARUNAMOYEE, SALT LAKE CITY, KOLKATA-700091, HAVING ITS REGISTERED OFFICE AT BHEL HOUSE, SIRI FORT, NEW DELHI-110049
2	DR. MANDAVA MOHANA RAO	REGIONAL OPERATIONS DIVISION (ROD), PLOT NO: 9/1, DJBLOCK 3RD FLOOR, KARUNAMOYEE, SALT LAKE CITY, KOLKATA-700091, HAVING ITS REGISTERED OFFICE AT BHEL HOUSE, SIRI FORT, NEW DELHI-110049

PCT International Classification Number

H02H9/04

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA