TECHNICAL FIELD
[001] The present disclosure, in general, relates to surge arresters installed in an electric substation that protect the electrical power system from surges caused by lightning. In particular, the present disclosure relates to improved surge arresters and the assembly incorporating various improved surge arresters for improving the performance of high voltage surge arresters being used in air-insulated switchgear or gas-insulated switchgear both in terms of capacity and compactness by introducing primary, secondary, and tertiary voltage grading-cum-electrostatic field controlled shields.
BACKGROUND
[002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[003] The present disclosure pertains to high voltage electrical power generation and transmission systems, and more specifically to high voltage surge arresters and the assembly incorporating various high voltage surge arresters.
[004] Under normal operating conditions, electrical transmission and distribution equipment are subject to voltages within a relatively narrow range. Due to lightning strikes, switching surges, or other system disturbances, portions of the electrical network may experience momentary or transient voltage levels that greatly exceed the levels experienced by the equipment during normal operating conditions. Left unprotected, critical, and costly equipment such as transformers, switching apparatus, computer equipment, and electrical

machinery may be damaged or destroyed by such over-voltages and the resultant current surges. Accordingly, it is routine practice to protect such apparatus from dangerous over-voltages through the use of surge arresters.
[005] A surge arrester is a protective device that is commonly connected in parallel with a comparatively expensive piece of electrical equipment to shunt or divert over-voltage-induced current surges safely around the equipment, thereby protecting the equipment and its internal circuitry from damage. When exposed to an over-voltage condition, the surge arrester operates in a low impedance mode that provides a current path to the electrical ground having a relatively low impedance.
[006] The surge arrester otherwise operates in a high impedance mode that provides a current path to the ground having a relatively high impedance. The impedance of the current path is substantially lower than the impedance of the equipment being protected by the surge arrester when the surge arrester is operating in the low-impedance mode and is otherwise substantially higher than the impedance of the protected equipment.
[007] Upon completion of the over-voltage condition, the surge arrester
returns to operation in the high impedance mode. This prevents
normal current at the system frequency from following
the surge current to ground along the current path through the surge arrester.
[008] Conventionally 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 GIS i.e., near the transformer, protection against overvoltages is limited by the electrical distance between the GIS and the arrester.

[009] The commonly utilized porcelain housing has placed severe and serious constraints upon the manufacture of surge arresters. It has been conventional to vacuum dry the assembly of the non-linear resistor arrangement with the porcelain housing. It is also conventional, particularly in the case of larger-sized, station class arresters but also in the case of smaller distribution type arresters, to provide a pressure relief diaphragm at one or both ends of the porcelain insulator housing.
[010] The cost of the porcelain housing itself contributes very significantly to the cost of a conventional surge arrester provided with such housing, and the cost of the treatments and arrangements which have been considered necessary to minimize or isolate the danger it presents by virtue of its risk of explosive shattering have caused the overall cost of a surge arrester to be relatively high.
[011] Given these disadvantages, there have been various previous attempts made to construct a surge arrester, suitable at least for electrical power transmission and distribution applications, which does not use a porcelain insulator housing, Further, a single grading shield is only used for uniform voltage distribution across surge arrester blocks. However, such a shield cannot be sufficient to achieve uniform voltage distribution across surge arrester blocks and uniform electric field around high voltage parts of extra and ultra-high voltage surge arresters. The present disclosure relates to single-phase very high voltage air-insulated switchgear.
[012] One of the prior art proposes a surge arrester with an elongated polymer housing that includes a stack of arrester elements, for example of zinc oxide. To limit the radial voltage stress which may arise in the polymer material upon pollution, the polymer housing is provided on the outside with field-equalizing control electrodes in the form of bands or rings of metal at regular distances along with the arrester. The control electrodes are electrically connected to the ZnO

stack inside the housing. This type of arrangement is not a cost-effective solution in the case of extra and ultra-high voltage air-insulated surge arresters. Manufacturing of this type of polymeric housing is not economical and complex. Fig. 1 (A) shows the conventional non-linear elements stack assembly with field-equalizing control electrodes.
[013] The other prior art proposes the surge arrester that comprises metal oxide arrester blocks, aluminum alloy spacer blocks, and terminal blocks structurally combined within a glass-reinforced plastic shell which is bonded to the outer cylindrical surfaces of the arrester blocks, spacer blocks, and terminal blocks. The arrester blocks, heat sink/spacer blocks, terminal blocks, and the glass-reinforced plastic shell constitute a unitary structural arrester core of great physical strength wherein the facing surfaces of the respective blocks are held in face-to-face physical and electrical contact without air entrapment or bleed of plastic material. However, such a system cannot be reusable in case if there is damage to insulation during service or rejection of arrester during the manufacturing stage. The usability of metal oxide blocks is lost. Further such systems are not proven for extra and ultra-high voltage applications. Fig. 1 (B) shows the molded surge arrester assembly.
[014] Another prior art discloses the metal-oxide blocks that are placed in an insulating tube for mechanical stability in conventional switchgear. In conventional stack assembly of surge arresters, the metal-oxide blocks are physically stacked and connected electrically in series through the metallic surface. The proposed design may not be useful in the case of solid metal-oxide blocks (different from metal-oxide blocks with central holes). Fig. 1 (C) shows the conventional non-linear elements stack assembly. Following are some of the drawbacks with this arrangement:

• Lack of effective heat transfer medium between blocks, results in confined heat dissipation from the blocks, mostly through the glazed surface of SA (stack assembly) elements only.
• Enhancement of the electrostatic field at the edges of the blocks that results in ionization of insulation medium.
• Highly difficult to achieve low electric field levels and low non-uniformity voltage factors simultaneously in the case of high voltage surge arresters. This is particularly difficult for single-column surge arresters.
[015] The other prior art proposes the grounded tank-type arrester i.e. GIS surge arresters, in which the cylindrical shields are used and the voltage non-uniformity cannot be limited beyond a certain level. Fig. 2 shows the GIS surge arrester with high voltage conventional shields. In surge arrester, one or more loop-shaped clamps of insulating material are/are used for mechanical stability of the arrester columns for outdoor applications. In some of the grounding tank-type arresters, the columns are made as to current folding columns and current pass columns. The current folding column includes stack sets of an element unit of zinc oxide elements and an insulating spacer.
[016] It is, therefore, desirable to provide the surge arresters with improved performance both in terms of capacity and compactness and being used in air-insulated switchgear or gas-insulated switchgear by introducing primary, secondary, and tertiary voltage grading-cum-electrostatic field controlled shields.

[017] Some of the objects of the present disclosure, which at least one embodiment herein satisfy, are listed hereinbelow.
[018] It is a general or primary object of the present disclosure is to provide an improved surge arrester for high voltage application.
[019] It is another object of the present disclosure is to provide multiple Voltage grading cum electric field controlled shields integrated to multiple stack assemblies of high voltage surge arresters used for uniform voltage distribution.
[020] It is another object of the present disclosure is to provide an electric field controlled shield at high voltage terminal called primary voltage grading cum electric field controlled shield to achieve uniform electric field around high voltage terminals of both air-insulated and gas-insulated surge arresters.
[021] It is yet another object of the present disclosure is to provide a primary voltage grading cum electric filed controlled shield having a tapered structure instead of a cylindrical structure with multiple grading rings.
[022] It is yet another object of the present disclosure is to provide a primary voltage grading cum electric field controlled shield with multiple rings of varying diameters at different heights.
[023] It is yet another object of the present disclosure is to provide an electric field-controlled shield for the second stack, the third stack of surge arresters placed in series to form a pillar-shaped structure.
[024] It is ye t another object of the present disclosure is to provide voltage grading-cum-electric field controlled shield for third stack or fourth stack or so on of high voltage gas insulated surge arresters if a number of stacks are more than four or five or so on.
[025] It is further another object of the present disclosure is to provide a voltage grading-cum-electric field controlled shield at the ground

terminal of high voltage gas insulated surge arresters to limit electric field at the interface of composite insulator and metallic flange.
[026] It is further another object of the present disclosure is to provide an electric field-controlled shield at the ground terminal of high voltage gas insulated surge arresters to achieve an optimized non-uniformity voltage factor.
[027] It is yet another object of the present disclosure is to propose an effective dynamic current transfer from surge arrester blocks to metallic support plate of composite insulator housing.
[028] It is further another object of the present disclosure is to propose an effective dynamic current transfer arrangement through a proposed surge arrester that is hermetically sealed from the environment.
[029] These and other objects and advantages will become more apparent when reference is made to the following description and accompanying drawings.
SUMMARY
[030] This summary is provided to introduce concepts related to the assembly that increases the efficiency of the surge arrester. The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[031] In an embodiment, the present disclosure provides a surge
arrester for high voltage application comprising a plurality of metal oxide elements stacked in series to form a MO stack assembly, in which the MO stack assembly in combination form a single surge arrester stack column, a plurality of inter-stage element, in which the plurality of inter-stage elements connect the metal oxide elements that are stacked in series; a composite insulator housing for incorporating

the plurality of MO stack assembly, in which the composite insulator housing attached to a current transfer cum spring holder plate at the upper end and profiled metallic flange at the lower end; and a plurality of solid insulated spacers placed in between the annular space between insulator housing and MO blocks to ensure proper holding of MO stack assembly in composite insulator housing.
[032] In an aspect, the present disclosure provides a surge arrester
wherein the composite insulator housing is made of fiber-reinforced polymer (FRP) tube cast with silicone rubber sheds.
[033] In an embodiment, the present disclosure provides an
assembly for high voltage application comprising a plurality of surge arrester stack column stacked one over the other to form a pillar-shaped structure; a plurality of voltage grading-cum-electric field controlled shields that are placed at above, in between, and below the surge arrester stack column; and a support structure placed at the bottom of the said pillar-shaped structure.
[034] In an aspect, the present disclosure provides the assembly, in
which the primary voltage grading-cum-electric field controlled shield is attached at the upper end of the first surge arrester.
[035] In an aspect, the present disclosure provides the assembly, in
which the primary voltage grading-cum-electric field controlled shield consisting of full HT shield and HT rings which are integrated by partial window created HT rods.
[036] In an aspect, the present disclosure provides the assembly, in
which the first ring is attached at the upper e nd of the first surge arrester near a high voltage terminal and epoxy support insulator.
[037] In an aspect, the present disclosure provides the assembly, in
which the diameter of the third ring is more than or equal to the diameter of the second ring which is more than the diameter of the first ring.

[038] In an aspect, the present disclosure provides the assembly, in
which the secondary voltage grading–cum-electric field controlled shield is placed at the second stack or the third stack depends upon the number of high voltage surge arrester stacks attached in the pillar.
[039] In an aspect, the present disclosure provides the assembly, in
which the tertiary voltage grading –cum- electric field controlled shield is placed at the ground potential of the last surge arrester placed in the pillar.
[040] In an aspect, the present disclosure provides the assembly, in
which the primary, secondary and tertiary voltage grading-cum-electric field controlled shields) are conical in shape with multiple rings of various diameters and heights depending on the type of shield, location of shield, and voltage level.
[041] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.
BRIEF DESCRIPTION OF THE DRAWINGS
[042] 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 devices, systems, and methods that are consistent with the subject matter as claimed herein, wherein:
[043] FIG.1 (a-c) illustrates the conventional air-insulated surge arrester stack assembly in accordance with the prior art.

[044] FIG.2 illustrates the conventional high voltage grading shield for GIS applications in accordance with the prior art.
[045] FIG.3 illustrates the configuration of the proposed surge arrester (100) having a stack of metal oxide blocks with i nter-stage cooling elements in accordance with an embodiment of the present disclosure.
[046] FIG.4 illustrates the configuration of the proposed surge arrester (100) and insulator housing in accordance with an embodiment of the present disclosure.
[047] FIG.5 illustrates an assembly (200) for high voltage application having two proposed surge arresters connected in series with primary voltage grading-cum-electric field controlled shield in accordance with an embodiment of the present disclosure.
[048] FIG.6 illustrates an assembly for high voltage application having proposed surge arrester connected in series to form a pillar-shaped structure with primary voltage grading-cum-electric field controlled shield in accordance with an embodiment of the present disclosure.
[049] FIG.7 illustrates an assembly for high voltage application having proposed surge arrester connected in series to form a pillar-shaped structure with primary and secondary voltage grading-cum-electric field controlled shield in accordance with an embodiment of the present disclosure.
[050] FIG.8 illustrates an assembly for high voltage application having proposed surge arrester connected in series to form a pillar-shaped structure with primary and tertiary voltage grading-cum-electric field controlled shield in accordance with an embodiment of the present disclosure.
[051] FIG.9 illustrates an assembly for high voltage application having proposed surge arrester connected in series to form a pillar-shaped structure with primary, secondary and tertiary voltage grading-cum-

electric field controlled shield in accordance with an embodiment of the present disclosure.
DETAILED DESCRIPTION
[052] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, a nd alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[053] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” a nd “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “o n” unless the context clearly dictates otherwise.
[054] As per the data, the conventional surge arresters fail to work effectively under high voltage applications.
[055] To overcome the issues related to the existing surge arresters, the present disclosure herein provides an assembly that improves the performance of surge arresters used in air-insulated switchgear or gas-insulated switchgear during high voltage condition both in terms of capacity and compactness by introducing primary, secondary, and tertiary voltage grading-cum-electrostatic field controlled shields.
[056] The present disclosure mainly uses multiple voltage grading-cum-electric field controlled shields instead of single grading shields, to achieve uniform electric field and optimized non-uniformity voltage factors less than 8 % irrespective of the rated voltage of surge arrester. In addition, the proposed grading shield design can be

extended to all voltage class surge arresters including extra and ultra-high voltage surge arresters of both air-insulated and gas-insulated types.
[057] The present disclosure clearly explains the configuration of the proposed surge arresters in the below-mentioned explanation of figures.
[058] FIG.3 illustrates the proposed improved surge arrester having a stack of metal oxide blocks with the inter-stage cooling element in accordance with an embodiment of the present disclosure.
[059] In the proposed improved surge arresters (100), the metal oxide elements [01] are stacked in series and connected by means of a thermally / electrically conducting inter-stage element [02]. The inter-stage element [02] is made from a highly conductive electrical grade aluminum or copper metal. It helps in maintaining uniform temperature and uniform electrostatic field across Metal Oxide (MO) elements [01] and overcomes thermal runaway problems in the surge arrester. During conduction of blocks, thermal energy generated within the MO elements [01] is dissipated through this inter-stage element [02] efficiently to the inert gas medium. The surface of the inter-stage element [02] has provision for gas circulation through suitable flow channels [03]. These flow channels [03] help in circulating gas from one MO block [01] to another. In addition, the metalized surface of the metal-oxide block is allowed to be exposed to the medium through these flow channels [03]. This is further possible through the peripheral surface of the inter-stage element [02] / glazed surface of the MO block [01].
[060] The element maintains a lower temperature at the metalized surface of the block as it is in contact with the air/other inert gaseous media during normal operation. The inter-stage element [02] also ensures low contact resistance between two metallic surfaces of the

metal-oxide block [01] during their service. Moreover, the profile [04] of inter-stage element [02] is structured in such a way that the resultant electrostatic field across the blocks is uniform and overall electrical stress levels are reduced to overcome the problem of ionization of the insulating medium at edges of metal-oxide blocks [01]. The inter¬stage elements [02] are of different sizes shall be provided to make up the stack height as required by composite insulator height.
[061] FIG.4 illustrates the configuration of the proposed surge arrester (100) and insulator housing in accordance with an embodiment of the present disclosure.
[062] The electro-mechanical-thermal performance of the surge arrester is further improved by keeping the MO stack [05] in Composite insulator housing [06] made of fiber-reinforced polymer (FRP) tube [06A] cast with silicone rubber sheds of high mechanical and dielectric strength. The Composite insulator housing [06] is terminated in field smoothen profiled metallic flanges [07].
[063] For proper support of the stack, the insulating housing [06] is fixed
to the current transfer plate [08] and current transfer cum spring holder
plate [09]. The current transfer plate [08] helps to provide a
connection with the HT terminal. The current transfer plate [08] provides a plug and socket type arrangement to give flexibility of 0.5-1% to adapt the dimensional changes if occurs in the stack assembly due to the thermo-mechanical effect. The current transfer cum spring holder plate [09] also has the arrangement to integrate to one more MO stack.
[064] The annular gap between insulator housing [06] and MO stack [05] is filled with insulated spacers [10] to ensure proper holding of MO Stack [05] in composite insulator housing [06]. The voltage distribution across the MO stack [05] is achieved highly uniform with the help of the Primary voltage grading-cum- Electric Field controlled shield [11].

The primary voltage grading-cum-Electric Field controlled shield [11] is conical in shape and consisting of a full HT shield [13] and HT rings [14A,14B,14C] as shown in FIG.5.
[065] Moreover, the current transfer cum spring holder plate [09] has provision to hold spring [12] that gets compressed against the current transfer plate [08] as per requirement. The combination of current transfer cum spring holder plate [09], spring [12], and current transfer plate [08] helps in surge current discharge through MO stack assemblies.
[066] Further, the current transfer arrangement is also made through a proposed surge arrester which is hermetically sealed from the environment.
[067] FIG.5 illustrates an assembly (200) for high voltage application having two proposed surge arrester stacks connected in series with primary voltage grading-cum-electric field controlled shield in accordance with an embodiment of the present disclosure.
[068] The assembly (200) for high voltage application having two proposed surge arrester stacks connected in series is illustrated. The primary voltage grading-cum-electric field controlled shield is attached at the upper end of the first surge arrester stack.
[069] Generally, in surge arresters, a non-linear voltage distribution arises across the blocks is mainly due to significant capacitive coupling between the MO stack [05] and the ground plane. The leakage current through stray capacitances will be compensated partly by Primary voltage grading-cum- Electric Field controlled shield [11] and improve voltage distribution across surge arrester blocks. The structure of primary voltage grading-cum- Electric Field controlled shield [11] is based on consideration of the electrical characteristics of blocks like stray capacitance from the MO blocks [01] to ground plane, the height of the stack, capacitance of the MO blocks [01], the

capacitance between HT grading-cum-Electric Field controlled shield [11] and the insulator housing [06], etc. Based on the above inputs, dimensions of the primary voltage grading-cum- Electric Field controlled shield [11] have been finalized to achieve optimum voltage distribution across the MO blocks [01].
[070] The primary voltage grading-cum-Electric Field controlled shield [11] is conical in shape and consisting of a full HT shield [13] and HT rings [14A,14B,14C] as shown in FIG.5. These parts are integrated by partial window-created HT rods [15].
[071] The first ring [14A] acts as a corona ring or it controls electric field around primary voltage grading-cum-Electric Field controlled shield [11] near the high voltage terminal [17] and epoxy support insulator [18]. The grounded metallic enclosure [19] is also placed in the vicinity of the high voltage terminal [17] results in the critical profile of primary voltage grading-cum-Electric Field controlled shield [11]. The first part of this shield is either a cylindrical ring or circular ring [14A]. It is either cylindrical or circular in structure. The second ring [14B] is generally of higher diameter than the first ring [14A]. The diameter of the third ring [14C] is more than or equal to the second ring [14B]. In other words, the diameter of rings increases continuously. The third ring [14C] is only optional and may be required in higher and higher voltages.
[072] In addition, the distance between the first ring [14A] and the second ring [14B] is not the same as between the second ring [14B] and the third ring [14C]. The half of the difference between outer and inne r diameter is called the thickness of the ring. Generally, the thickness of the third ring [14C] and first ring [14A] are higher than the second ring [14B]. In between the second ring [14B] and the third ring [14C], a window-type design is proposed.
[073] The primary function of the first ring [14A] is to limit the electrostatic field around the surge arrester. The second ring [14B]

and the third ring [14C] also help to limit electrostatic field levels along the insulator surface and at the interface of insulator and metal. These two rings are also helpful to limit non-uniformity voltage factors across the surge arrester. There are a multiple MO stacks [05] connected in series depending upon its voltage rating.
[074] FIG.5 illustrates the proposed surge arrester with primary voltage grading-cum-Electric Field controlled shield in accordance with an embodiment of the present disclosure.
[075] In the case of a high voltage air-insulated surge arrester, the number of series stacks can be possible three or more depending upon voltage class.
[076] For multiple numbers of SA stacks, the primary grading ring cum E-field controlled shield [11] is not sufficient to limit the non-uniformity voltage factor of surge arrester assembly.
[077] It is important to provide floating metallic rings at the second and third stack of surge arrester stack [16] to limit electric field around the second, third stack, and so o n. If a metallic ring or only an E-field controlled shield is used at the second and third stack [16], there is a possibility of an increase in non-uniformity voltage factor further.
[078] To overcome the above-mentioned problems, the present disclosure proposed a Voltage grading–cum-E-field controlled shield at second, third stack assembly, and so on as shown in FIG.6, and Fig.7. This shield primarily consists of a single-stage circular ring with less thickness than the primary grading–cum-E-field controlled shield [11]. Height of secondary grading–cum-E-field controlled shield [22] is limited as compared to primary grading–cum-E-field controlled shield [11]. The height of the shield is dependent on the voltage at which it is being operated, the total number of stacks, and the height of each stack.

[079] By providing secondary grading–cum-E-field controlled shield [22], E-field around the second stack also becomes highly uniform, and an electric field is further limited at the interface of a metal a nd composite insulation. Because of capacitive coupling with each surge arrester stack assembly [16] from this proposed shield, the non-uniformity voltage factor could also be improved.
[080] It is also important to note that the number of secondary grading– cum-E-field controlled shields [22] are required to be more dependent on the total number of SA stacks.
[081] In other words, the number of these shields increases with the increase of rated voltage of the surge arrester to achieve optimized non-uniformity factor along with uniform electric field around high voltage terminals of the SA stack assemblies [16]. These high voltage terminals may be at a full voltage or floated voltage depending on their location in the assembly.
[082] With both primary and secondary voltage grading–cum-E-field
controlled shields [11,22], the electric field is not highly uniform at the ground terminal. At the same time, the non-uniformity factor is high on the negative side (voltage appears across SA blocks is less than rated voltage) around the ground terminal due to primary and secondary grading–cum-E-field controlled shields [11,22].
[083] To limit electric field at ground terminal [20] and the interface of
the ground terminal and composite insulator, it is required to keep E-field controlled shield or metallic ring. This shield alone further increases the non-uniformity voltage factor and the design of surge arrester may not be feasible.
[084] To overcome this problem, the present disclosure has proposed
tertiary voltage grading–cum-E-field controlled shield [23] at the ground terminal [20]. This shield improves the electric field around the ground terminal [20] of the last SA stack assembly [16] and at the

interface of the ground terminal and composite insulation. This tertiary voltage grading–cum-E-field controlled shield [23] further improves the non-uniformity voltage factor by means of additional coupling between the last SA stack elements from the tertiary voltage grading–cum-E-field controlled shield [23]. [085] To limit electric field at ground terminal [20] and at the interface of the ground terminal and the composite insulator is required to keep E-field controlled shield or metallic ring. This shield further increases the non-uniformity voltage factor and the design of a surge arrester may not be feasible. Multiple numbers of SA stacks [16] are assembled on support structure [21]. The support structure [21] is designed by considering seismic load, wind load, and jumper loads that encounter in substation equipment or transmission network. The FRP insulator [06A] dimensions particularly thickness and diameter are optimized by considering the above loads.
[086] Moreover, grading ring cum E-field controlled shields are also provided at the second stack, third stack, and so on.
[087] All three shields that are primary, secondary, and tertiary
Voltage Grading-Cum-Electric field controlled Shields [11,22,23] are conical in shape with multiple rings of various diameters and heights depending on the type of shield, location of shield i.e. voltage level at which it is being used, number of columns of surge arrester, etc. The number of rings, their diameter, and height depend on the allowable E-field level and non-uniform voltage factor.
[088] The number of primary and tertiary voltage Grading-Cum-
Electric field controlled Shields [11,23] is only one for all voltage rating surge arresters. However, a number of secondary Voltage Grading-Cum-Electric field-controlled Shields [22] can be possible one or two or three depending on the total number of SA stack assemblies [16] that are connected in series and rated voltage of surge arrester. Further, instead of using a single grading shield, multiple Voltage

Grading-Cum-Electric field-controlled Shields [11,22,23] are adopted to achieve uniform electric field and optimized non-uniformity voltage factors less than 8 % irrespective of the rated voltage of surge arrester.
TECHNICAL ADVANTAGES
[089] The present disclosure proposes that a single grading shield is
not sufficient to achieve uniform voltage distribution across surge arrester blocks and uniform electric field around high voltage parts of extra and ultra-high voltage surge arresters. The surge arrester performance could be improved by optimizing the electric field around metallic flanges of the Surge arrester stack using multiple voltage grading cum E-field controlled shields. Further, the non-uniformity factor is improved to less than 8% even for very high voltage surge arresters.
TEST RESULTS
[090] The electric field will be improved by 30 to 40%
[091] Non-uniformity voltage factor improved by 50 to 60 %
depending on voltage class as compared to single shield design.
WORKING OF INVENTION
[092] Gas-insulated Surge arrester is developed and evaluated
successfully against all test duties as per IEC. Some design features are already demonstrated at the site and performance is found to be satisfactory. Features are implemented in the surge arrester stack of conventional AIS SA.
[093] Thus, with the proposed surge arrester and the assembly incorporating various surge arrester stacks described herein the present disclosure, various technical problems of the state of the art

are resolved. Also, although a number of exemplary method options are described herein, those skilled in the art can appreciate that the surge arrester and the assembly incorporating various surge arresters can be utilized for high voltage application, without deviating from the scope of the subject matter of the present disclosure. The major function of the present disclosure is to proposed a surge arrester and the assembly incorporating various surge arresters for high voltage application.
[094] Further, it will be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its scope.
[095] Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor(s) to furthering the art and are to be construed as being without limitation to such specifically recited examples and conditions. Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.
[096] While the foregoing describes various embodiments of the
invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

WE CLAIM
1. A surge arrester (100) for high voltage application comprising
a plurality of metal oxide elements (01) stacked in series to form a MO stack assembly (05), wherein the MO stack assembly (05) in combination form a single surge arrester stack column (16) ;
a plurality of inter-stage element (02), wherein the plurality of inter-stage elements connecting the metal oxide elements [01] that are stacked in series;
a composite insulator housing (06) for incorporating the MO stack (05), wherein the composite insulator housing attached to a current transfer cum spring holder plate (09) at an upper end and profiled metallic flange (07) at a lower end; and
a plurality of solid insulated spacers (10) placed in annular space between insulator housing (06) and MO blocks (01) to ensure proper holding of MO stack (05) in composite insulator housing [06].
2. The surge arrester (100) as claimed in claim 1, wherein the composite insulator housing (06) is made of fiber-reinforced polymer (FRP) tube (06A) cast with silicone rubber sheds.
3. An assembly (200) for high voltage application comprising
a plurality of surge arrester stack column (16) placed one over the other to form a pillar-shaped structure;

a plurality of voltage grading-cum-electric field controlled shields (11,22,23) are placed above, in between, and below of the surge arrester stack column (16); and
a support structure (21) is placed at the bottom of the said pillar-shaped structure.
4. The assembly (200) as claimed in claim 3, wherein the primary voltage grading-cum-electric field controlled shield (11) attached at the upper end / high voltage end of the first surge arrester stack.
5. The assembly (200) as claimed in claim 3, wherein the primary voltage grading-cum-electric field controlled shield comprises of full HT shield (13) and HT rings (14a,14b,14c) which are integrated by partial window created HT rods (15).
6. The assembly (200) as claimed in claim 5, wherein the first ring (14a) is attached at the upper end of the first surge arrester stack near a high voltage terminal (17) and epoxy support insulator (18).
7. The assembly (200) as claimed in claim 5, wherein the diameter of a third ring is more than or equal to the diameter of the second ring (14b) which is a higher diameter than the first ring (14a).
8. The assembly (200) as claimed in claim 3, wherein the secondary voltage grading–cum-electric field controlled shield (22) is placed at the second stack or the third stack depends upon the number of surge arrester stacks attached in the pillar.
9. The assembly (200) as claimed in claim 3, wherein the tertiary voltage grading –cum- electric field controlled shield (23) is placed at the ground potential of the last surge arrester stack attached in the pillar.

10. The assembly (200) as claimed in claim 3, wherein the primary, secondary and tertiary voltage grading-cum-electric field controlled shields (11,22,23) are conical in shape with multiple rings of various diameters and heights depending on the type of shield, location of shield, and voltage level at which it is being placed.