FIELD OF THE INVENTION
[01] The present invention relates to a method for localization of partial discharge sensors in gas insulated substation (GIS). Also, this present invention relates to a method of identifying number of sensors required, location and evaluation at site conditions. Also the present invention relates to the GIS modules for enabling on-site evaluation
BACKGROUND OF THE INVENTION
[02] Gas insulated substations (GIS) require very less space in comparison to the air insulated substations. Thus GIS substations have become ideal solution due to space/land constraint. In GIS, two major insulation used are SF6 gas (under pressurized condition) and the epoxy material (for insulators which support the HV conductor). Any degradation in the GIS insulation may lead to generation of partial discharges (PD). Partial discharges are the localized discharge point under energized condition, of the insulation. In GIS, PD could originate due to voids in the solid insulation (epoxy insulator) or due to presence of foreign particles/components (metallic or non-metallic and floating or fixed) inside the GIS enclosure.
[03] Measurement of partial discharge provides an indication of the condition of the GIS insulation. Partial discharge phenomena create measurable effects like current pulse, UHF emissions, sound, light and chemical by products. The conventional method (or electrical method) involves measurement of the PD generated current pulse using appropriate test setups. Alternatively, unconventional methods are being employed for continuous online PD monitoring of GIS insulation at site installations. Out of these methods, the UHF method has been the most acceptable and accurate method for partial discharge measurements in GIS installations.

[04] The generation of UHF signals inside GIS insulation is due to PD generated current pulse which has a very short rise time of few picoseconds. The generated UHF signal is captured by installing UHF sensors/couplers at strategic locations across the GIS bay. The captured UHF signals represent direct indication of the partial discharges (PD) occurring inside the GIS modules. But to have effective and reliable PD monitoring/measurement using the UHF sensors, localization of these sensors for optimal coverage of GIS is utmost important. Further, the sensitivity of these sensors need to be checked, verified and quantified during installation of the Online UHF PD monitoring system.
[05] In general, to monitor healthiness of GIS insulation, partial discharge (PD) is measured. The conventional or electrical method which is used for routine PD measurement in GIS cannot be used for PD measurement at site installations. This is because of significant noise signals present at site installation which affect the measurement of PD generated electrical pulses. To overcome this problem UHF based PD measurement and monitoring is being employed for GIS site installations. Over the years this method has gained prominence and is being widely accepted by power utilities as an effective tool to know the insulation health of the operating GIS.
[06] In case of conventional PD measurement it is clearly indicated in relevant IEC standards that any PD levels of more than 5pC in GIS is not acceptable. The same cut-off acceptable PD levels, cannot be specified for the UHF method as in this method, apparent charge (i.e. Pico columb-pC) based output from the monitoring system is not available. In UHF method, the intensity of generated UHF waves (as a consequence of PD source) is measured in terms of dBm. There cannot be any direct correlation between the pC levels (of conventional method) and the dBm levels (of the UHF method). Thus in absence of any correlation between the two, when the

UHF method is used for PD monitoring at site the sensitivity of this method (which depends on the sensors design, the PD processing hardware as well as the UHF signal loss inside GIS due to its configuration/design) is ascertained time to time by both manufacturers and utilities. For undertaking this sensitivity verification, a known PD pulse is injected inside the GIS and the same is measured using the installed UHF sensors.This verification also confirms that the installed sensors cover the full GIS bay and PD from any defect inside the GIS would be picked up by one or multiple sensors.
[07] To address this issue, the Chinese patent publication CN103278787A titled “On-line GIS (gas-insulated switchgear) partial discharge monitoring and check method” Disclose about injecting the PD inside the GIS, disc insulator ring opening or open insulator. These ring openings are provided in the GIS for external PD sensor mounting or sometimes they are the port for epoxy filling during manufacturing of the GIS insulator.
[08] In the solution proposed in US 5396180A titled “System for monitoring gas insulated substations” describes about measurement and monitoring of the UHF PD, suitable UHF couplers are fitted to the GIS pressure vessels. Generated UHF signals are taken from the UHF couplers mounted on inside of the hatch cover formed on the bus chamber. For sensitivity verification purpose, these internally fixed sensors could also be used. They form an ideal point to inject artificial known magnitude PD pulse inside the GIS.
[09] Existing major inventions for on-site sensitivity verification of the UHF PD monitoring method uses the following as a point for injecting the external PD pulse: a) An internal PD sensor, b) An external sensor mounted on open or bare insulator and c) An external sensor mounted on small opening or

aperture of GIS insulator. In first two cases, sufficient amount of PD can be injected for sensitivity verification. The use of open or bare spacers in ultra-high voltage class may not be reliable due to electromagnetic interference related problems in control equipment of GIS. Thus, when we use external type of PD sensors, they mostly are mounted on an opening/slot/aperture of the GIS insulator (point no. c). In case using this arrangement i.e. external sensor mounted on small aperture of the GIS spacer, it is practically impossible to inject sufficient amount of external PD pulse for sensitivity verification purposes.
[010] Accordingly, there exists a need in the art to improve the existing
technologies to facilitate development and implementation of a technique for onsite estimation and verification of attenuation factors of GIS modules for external type of UHF PD sensors in GIS. The present invention is related to a process which overcomes the problem of sensitivity verification in case of external type of UHF PD sensors mounted on an aperture of GIS spacer. The invention presented is related to the development and implementation of a technique for onsite estimation and verification of attenuation factors of GIS modules for external type of UHF PD sensors in GIS. The technique further helps for localization of PD sensors in GIS and ensures availability of system for optimum coverage of GIS.
OBJECTS OF THE INVENTION
[011] The main objective of the invention is to develop a novel on-site
sensitivity verification technique for UHF external PD sensors in GIS .
[012] Another objective of the invention is to developing a technique to
establish the location of sensors across GIS bay for optimum coverage.

[013] Another objective of the invention is to develop a technique for
estimation and verification of attenuation offered by each module of GIS.
[014] Another objective of the invention is to develop a method to minimize
the UHF cable length by optimum placement of local units.
[015] Further the objective of the invention is to develop a novel technique to
estimate the number of UHF sensors for a typical GIS bay.
[016] Another objective of the invention is to design of a novel provision in
GIS bay to inject external PD pulses for sensitivity verification.
[017] Another objective of the invention is to design a concept of application
of novel insulating ports for injection of external PD sources
[018] Another objective of the invention is to develop on-site method to
verify and quantify the accuracy of PD location using UHF technique.
SUMMARY OF THE INVENTION
[019] The present invention discloses a system and method of estimating and verifying of attenuation factors of gas insulated substation (GIS). The system comprises a plurality of UHF sensors which are configured at strategic locations across the GIS bay. A partial discharge pulses are generated by an electronic module. The partial discharge pulse is injected through insulated earth switch or composite insulator to estimate attenuation offered by various modules of GIS. The partial discharge pulses are injected to the configured plurality of UHF sensors one by one and the corresponding generated UHF signal inside GIS is measured on an adjacent sensors and a location of sensor is determined based

on an attenuation offered by each module of GIS for partial discharge UHF signals and the attenuation offered by each GIS module is considered as input for estimation of distance between two UHF sensors.
[020] In one embodiment the method of estimating and verifying of attenuation factors of Gas insulated substation (GIS), the method comprising: configuring a plurality of UHF sensors at strategic locations across the GIS bay; generating a partial discharge pulse by an electronic module; injecting a partial discharge pulse through insulated earthing switch to estimate attenuation offered by various modules of GIS, wherein the partial discharge pulses is injected to the configured the plurality of UHF sensors one by one and the corresponding generated UHF signal inside GIS is measured on an adjacent sensors and determining a location of sensor based on an attenuation offered by each module of GIS for partial discharge UHF signals , wherein estimating a distance between two UHF sensors (02) based on the attenuation offered by each GIS module.
[021] In one embodiment to develop and implement a technique for onsite estimation and verification of attenuation factors of GIS modules for external type of UHF PD sensors in GIS. This is achieved by means of following: 1. By introducing an optimized provision in GIS for non-invasive PD pulse injection for sensitivity verification, attenuation factors of each module of GIS are estimated and verified. Optimal location of sensors and optimal coverage of sensors in gas insulated switchgear bay is done by estimating attenuation of each GIS module. An insulated opening is provided in the earthing switch (ES) and adopting

composite insulator of bushing for PD injection. The system and method is used to verify the sensitivity of UHF external sensors installed across GIS bay.
[022] Other objects, features and advantages of the present disclosure will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating specific embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[023] FIG.1. shows a conventional measurement of PD signal through
support insulator without Metallic Cover according to a prior art.
[024] FIG.2 shows an insulated aperture on LT of support insulator for
external UHF sensors according to an embodiment of the present invention.
[025] FIG. 3 shows a layout of 420 kV GIS bay of the preferred embodiment
of the present invention.
[026] FIG. 4 shows a front view of a view of Support insulator mounted with
a sensor of the preferred embodiment of the present invention.
[027] FIG. 5 shows the front view of a PD injection through insulator of
earthing switch according to an embodiment of the present invention.
[028] FIG. 6 shows a perspective view of a PD injection through Composite
insulator of gas-to-air bushing according to an embodiment of the present
invention.

[029] FIG. 7 shows a perspective view of PD injection points in GIS bay of
the preferred embodiment of the present invention.
[030] FIG. 8 shows a PD injection for Gas insulated bus duct of the preferred
embodiment of the present invention.
[031] FIG. 9 shows a sensor layout for Bus I and Bus II according to an
embodiment of the present invention.
[032] FIG.10 shows a sensor layout for Circuit Breaker and MES-DS-FES in
an embodiment of the present invention.
[033] FIG.11 shows a sensor Layout for Gas insulated bus duct in an
embodiment of the present invention
DETAILED DESCRIPTION OF THE INVENTION
[034] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[035] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles,

aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[036] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, “consisting” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof. [037] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[038] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[039] FIG.1. shows a conventional measurement of PD signal through a support insulator without metallic cover according to a prior art. Detection of partial discharge is useful for condition monitoring of gas insulated switchgear. For the insulation diagnosis of GIS, the ultra-high frequency (UHF) method which detects PD induced electromagnetic wave (EM-wave) in the UHF band with negligible noise influence. This system offers the utilities, continuous PD monitoring of their GIS while it is in operation. Any degradation in the healthiness of the GIS insulation is detected by these systems. The discharge signal emanates from insulated flange of support insulator. A support insulator (01) without metallic flange/cover is disclosed. High frequency discharge signal emanate from insulated spacer/support insulator (01) is sensed by a UHF sensor (02) fixed to it. All the installations support insulators are not purely insulated type. Further, high voltage class GIS, support insulators are integrated with metallic cover or LT (low tension / grounded) flange (03). These insulators have circular holes for processing of insulators but these holes are not be good enough to measure PD signals. Hence opening should be provided with higher surface area and preferably rectangular / elliptical shape. This is mainly due to limited width (thickness) of support insulator. [040] FIG.2 shows an insulated aperture on LT of support insulator for external UHF sensors according to an embodiment of the present invention. In a preferred embodiment a rectangular slot with necessary fastening arrangement (05) is configured on the support insulator (01). The partial discharge sensor integrate mechanically to the LT flange (03) of the support insulator (01). Implementing a non-invasive PD monitoring in the (GIS) Gas

insulated substation is as shown in Figure 2. An insulated aperture (04) is positioned above the fastening arrangement (05).
[041] FIG. 3 shows a layout of 420 kV GIS bay of the preferred embodiment of the present invention. In one embodiment UHF based PD monitoring is performed by configuring a plurality of partial discharge sensors across GIS bay in a substation. The layout of sample bay of the GIS on which the scheme was implemented is as shown in FIG 3. The sensitivity verification of the installed UHF sensors (02) is a must before the sensors are employed for actual monitoring of PD. The verification helps to check the proper functionality and PD signal sensing accuracy of the installed UHF sensors (02). The verification process ascertain the fact that any partial discharge phenomenon occurring in the GIS bay could be detected successfully. A gas insulated Bus (11), GIS HALL (12), gas insulated bus duct (09), HV bushing (13) are configured in the layout of 420 kV GIS bay for efficient monitoring.
[042] In one embodiment a single line diagram is considered as input and based on configuration, it is found that 4 to 5 sensors are sufficient in each phase of GIS bay (Referring to FIG. 3). In a preferred embodiment if the GIS bay is like bus coupler or bus sectionalizer, then three sensors are sufficient enough to identify partial discharges and their location. In a preferred embodiment for configuration like incomer bay, five sensors are required as there are some additional modules like surge arresters and potential transformers are there in GIS. For configuration like transformer/outgoing feeder bay, four sensors are sufficient enough for accurate PD measurement. In ideal conditions, an attenuation of UHF signal in the order of 5 to 10 dBm

could be allowed between two sensors. In case, if attenuation is more, then there is a possibility of under estimation of discharges and could lead to catastrophic failures. In case, if it is less, then investment cost of sensors is more. In one particular scheme of GIS bay (In FIG. 3) with 35 meters of gas insulated bus duct (09), it is proposed to use six sensors in each phase for accurate estimation of PD location and to get an optimum coverage for PD monitoring.
[043] FIG. 4 shows a front view of a view of Support insulator (01) mounted with a sensor of the preferred embodiment of the present invention. The UHF sensors (02) which are used for onsite PD monitoring could be of two types: 1) Internal Type of sensors and 2) External Type of sensors. The usage of a particular type of sensor depends on the provision available in the GIS for installation of these sensors. The internal sensors are mounted on ports specially designed for the purpose on the GIS enclosure. The external sensors are mounted either on a small aperture made on the LT of the support insulators (01) or on the viewing window opening in the GIS. Internally mounted couplers sensitivity is compared to the PD measurement sensitivity in the conventional electrical method. In this present invention, the PD monitoring sensitivity is achieved through a non-invasive approach. To verify the sensitivity of the externally mounted sensors, a PD pulse (short duration voltage signal) is generated by a special electronic module, which is injected at all the installed UHF sensors (02) one-by-one and the corresponding generated UHF signal inside GIS is measured on the adjacent sensors. This procedure helps to verify the sensitivity of UHF PD measurement across the GIS bay. The UHF couplers

used for this process are non-invasive passive type which could be mounted externally without the need to open the GIS chamber or to take a shut-down of the GIS installations. Special fastening arrangement (05) is made on the GIS for fixing the couplers to them from outside. The installed couplers from outside capture the leaking UHF signal which is generated inside the GIS due to a PD (Partial discharge) source. The typical output of the coupler is a voltage signal. The coupler output depends on the UHF field strength inside the GIS enclosure, coupler design and the external port provision on the GIS spacer. [044] FIG. 5 shows the front view of a PD injection through insulator of earthing switch according to an embodiment of the present invention. Designed insulated opening of earthing switch in GIS is disclosed. The designed insulated portion in the ES has sufficient large insulated surface to inject the external PD signals. This insulated portion is totally uncovered, with no metallic portion and an ideal port is provided for injecting the external PD signals for sensitivity verification. In one embodiment launching sufficient amount of PD signals inside GIS for sensitivity verification purpose particularly in case of external sensors being used for on-line PD monitoring.
A special provision of Delrin/ PTFE insulation (14) with limited diameter has been used in the earthing switch (15,16) of GIS modules, so that injection of good quality PD signals could be achieved. The design of these insulators `should meet two requirements. First one is to meet the requirement of insulated flange type of gas insulated earthing switch (15,16). Second one is to feed PD calibrating signal through UHF sensors (02). A double insulator (14,14A) has been adopted to isolate the grounded high voltage circuit from

grounded enclosure. These two insulators are of same profile and dimensions. One of these insulators could be used for feeding the calibrating PD signal. One more insulator (14A) could be used to verify the feeding signal intensity as there is negligible attenuation of signal between the two insulators (14, 14A). A PD injection points (17, 18) are disclosed in FIG.5.
[045] FIG. 6 shows a perspective view of a PD injection through Composite insulator of gas-to-air bushing according to an embodiment of the present invention. To verify the sensitivity of the sensors mounted near the HV bushings (13), PD injection was done using the composite insulation portion of the bushing. A PD injection point (19) is disclosed in FIG. 6.
[046] FIG. 7 shows a perspective view of PD injection points in GIS bay of the preferred embodiment of the present invention. FIG. 7 shows the injection of PD signals inside GIS using this insulated port on earthing switch. This type of provision is available for both maintenance earthing switch (15) and fast acting earthing switch (16). Similarly, FIG. 8 shows the injection of PD signals for the bus duct located outside GIS bay through composite insulator. More clearly, the composite insulator is used as injection point for the sensitivity verification of sensors installed near the bushings as well as sensors located outside GIS bay or in long bus duct sections (13). The injection of PD signals inside GIS using this insulated port on earthing switch (15). This type of provision is available for both maintenance earthing switch (15) and fast acting earthing switch (16).

[046] In one embodiment the UHF PD signal travel through the GIS and the signal reduces as it travels. The amount that the signal reduces is affected by many factors, for example: physical design of that GIS. Using the plurality of sensors better results are achieved. An optimum plurality of sensors provide sufficient sensitivity. To determine the location of sensor, considering the attenuation offered by each module of GIS for partial discharge UHF signals. The attenuation offered by each GIS module is considered as input for estimation of distance between two UHF sensors. The attenuation offered by angled enclosure (06) modules, disconnector switch (07), and circuit breaker (08) etc. is more than gas insulated bus duct modules (09) or current transformer (10) or bus bar modules (11).
[047] FIG. 8 shows a PD injection for Gas insulated bus duct of the preferred embodiment of the present invention. The injection of PD signals for the bus duct located outside GIS bay is performed through a composite insulator. The composite insulator is used as injection point for the sensitivity verification of sensors installed near the bushings as well as sensors located outside GIS bay or in long bus duct sections (13).
[049] In one embodiment verify the PD monitoring sensitivity of all the installed UHF sensors (02) by performing the following steps. For injecting PD, a portable PD injector/calibrator (with output range from 5V to 100V) is used. Step: An injector/calibrator output is connected to the UHF sensor (02) and the UHF sensor (02) is firmly placed on the injection points. Step 2: Since the injection point (on ES or bushing) having exposed insulation, the known PD signal could be successfully injected inside the GIS. Step 3: Using 20V at the

injector which is equivalent to approx. 5pC of injected PD. Step 4: Using internal sensors are optional. Step 5: External sensors are used, and more amount of injection voltage is required to inject 5 pC equivalent of PD. Step 6: An injection of 50 V is around 5pC value is provided. Step 7: 50V PD pulse injection is used to verify the sensitivity of the installed UHF sensors. [050] In one embodiment by using the measurements of PD levels at sensor location, estimating the attenuation factors of each module for example: current transformer (10), disconnector switch (07), fast acting earthing switch (16), maintenance earthing switch (15), circuit breaker (08), gas insulated bus duct (09) of one unit, angled enclosures (06) etc. Further, these attenuation factors is are verified by comparing with measurements obtained from third injection point. Similar procedure is applied to other phases of GIS bay. [051] FIG. 9 shows a sensor layout for Bus I and Bus II according to an embodiment of the present invention. In one embodiment two commonly used locations (per phase) for injecting known PD signal inside the GIS are through insulator of earthing switch (15, 16) and other one is through composite insulator. The insulator of earthing switch (15, 16) is to insulate earthing switch module from grounded enclosure. Through this insulator, providing an insulated earthing switch (15,16) as required by GIS.
[052] FIG.10 shows a sensor layout for Circuit Breaker and MES-DS-FES in an embodiment of the present invention. In actual configuration of GIS, the plurality of the sensors inside GIS building are verified or calibrated or evaluated through insulator of earthing switch (15, 16). The UHF sensors (02)

covered for the sensitivity verification using these two injection points (per
phase) i.e., through insulators of earthing switch (15, 16).
[053] In one embodiment Sensors covered from PD injection point 1 (17):
3 Sensors R1, Y1, B1 – BUS I (FIG. 9)
3 Sensors R2, Y2, B2– BUS II (FIG. 9)
3 Sensors R3, Y3, B3 - Circuit Breakers of all three phases (FIG. 10) [054] FIG.11 shows a sensor Layout for Gas insulated bus duct in an embodiment of the present invention. Sensitivity verification for Bus duct sensors covered through composite insulator is shown in FIG. 11.
Sensor covered from PD injection point 2 (18):
3 Sensors R4, Y4, B4 – DS-FES-ES (FIG. 10)
3 Sensors R5, Y5, B5 - Bus Duct- I of all three phases (FIG. 11)
Sensor covered from PD injection point 3 (19):
3 Sensors R6, Y6, B6 – Near Bushing (FIG.11) [055] In one embodiment a method for attenuation of each module is estimated, wherein the method comprising the following steps: the attenuation offered by each module is predicted by injecting known PD level into the system. When, External PD pulses are injected inside the GIS using maintenance earth switch (MES) through one of the insulator, PD level is established through sensor located on second insulator. As both the insulators are positioned nearby, the attenuation in PD signal is negligible. PD pulse is injected through injection point 1 of R phase insulated earthing switch (15,16) and confirmation of PD level through second insulator (14A). For this input PD pulse, measure PD levels at sensor locations of R1, R2, R3, R4, R5 and R6.

Reduction in PD levels at these locations from the input gives attenuation factor of single module or multiple modules depending on the physical distance. Similarly, PD pulse is injected through injection point 2 of R phase insulated earthing switch (15,16) and confirmation of PD level through second insulator (14A). For this input PD pulse, measure PD levels at sensor locations of R1, R2, R3, R4, R5 and R6. Reduction in PD levels at these locations from the input gives attenuation factor of single module or multiple modules depending on the physical distance.
[056] In one embodiment the system of estimating and verifying of attenuation factors in Gas insulated substation (GIS), the system comprising the plurality of UHF sensors (02) are configured at strategic locations across the GIS bay. The partial discharge pulse is generated by the electronic module. The partial discharge pulse is injected through insulated earthing switch (15, 16) to estimate attenuation offered by various modules of GIS. The partial discharge pulses are injected to the configured plurality of UHF sensors (02) one by one and the corresponding generated UHF signal inside GIS is measured on an adjacent sensors and a location of sensor is determined based on an attenuation offered by each module of GIS for partial discharge UHF signals, wherein the attenuation offered by each GIS module is considered as input for estimation of distance between two UHF sensors (02).
[057] In one embodiment establishing the location of sensors across GIS bay for optimum coverage of sensors. The earthing switch is of two types i) fast acting earthing switch (15) and maintenance earthing switch (16). In a preferred embodiment the earthing switch (15,16) is of insulated type and

used for grounding of main circuit. Also, the insulated type earthing switch is used for estimation of accuracy of current transformer metering cores. Insulated earthing switch has been used to verify sensitivity of external UHF partial discharge sensors installed on slots/apertures of GIS insulators, across GIS bay at site.
[058] In one embodiment the method of estimating and verifying of attenuation factors in Gas insulated substation (GIS), the method comprising the following steps of: configuring a plurality of UHF sensors (02) at strategic locations across the GIS bay. Generating a partial discharge pulse by an electronic module. Injecting a partial discharge pulse through insulated earthing switch (15, 16) to estimate attenuation offered by various modules of GIS, wherein the partial discharge pulses is injected to the configured the plurality of UHF sensors (02) one by one and the corresponding generated UHF signal inside GIS is measured on an adjacent sensors and determining a location of sensor based on an attenuation offered by each module of GIS for partial discharge UHF signals , wherein estimating a distance between two UHF sensors (02) based on the attenuation offered by each GIS module. In a preferred embodiment further estimating and determining attenuation rate of each module of GIS by using different PD injection points. In one embodiment determining localization of partial discharge sensors in GIS. Configuring the UHF sensor (02) to a grounded LT flange (03) through insulated aperture (04) of elliptical or rectangular slot. To minimize the UHF sensors (02) cable length by optimum placement of local units. A composite insulator of bushing for calibration of all partial discharge sensors in the GIS bay is used. The composite

insulator of bushing is for feeding calibrating pulses of UHF sensors. The earthing switch (15, 16) is of insulated type and used for feeding calibrating partial discharge pulses of UHF sensors. The insulator is a double insulator (14, 14A) for insulated type earthing switch, one is for feeding PD signal and other is for estimation of calibration signal. The PD levels at the UHF sensor (02) locations provides attenuation factor of single module or multiple modules depending on a physical distance.
[059] In one embodiment the electronic module comprises a dedicated hardware, according to substantially known technology. To perform this localization function, it is known attenuation systems that perform an addition and subtraction of the signals detected. In a preferred embodiment the PD detection, processed by both hardware and software, and presented at software side in the form of PD pulses. With the widening of the application abovementioned PD attenuation, nowadays there is wider optional scope with respect to attenuation devices corresponding to the same principle. Attenuation rate of each module of GIS by using different PD injection points is measured and the attenuation signal is processed by the processing hardware, and the attenuation factor is measured.
[060] While certain embodiments of the present invention have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. The novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes may be made without departing from the spirit of the inventions.

WE CLAIM:
1. A system of estimating and verifying of attenuation factors in Gas insulated
substation (GIS), the system comprising:
- a plurality of UHF sensors (02) configured at strategic locations across the GIS bay;
- an electronic module for generating a partial discharge pulse;
- a plurality of insulated earthing switch (15, 16) to estimate attenuation offered by various modules of the GIS based on the partial discharge pulse injected via the switches;
- a plurality of UHF sensors (02) generating UHF signal inside the GIS based on the partial discharge pulses injected via the switches, which are measured by the adjacent sensors;
- wherein a location of each sensor is determined based on the attenuation offered by each module of GIS for partial discharge and the UHF signals, and wherein the attenuation offered by each GIS module is considered as input for estimation of the distance between two UHF sensors (02).

2. The system as claimed in claim 1, wherein the strategic locations of the sensors across GIS bay is determined for optimum coverage of the GIS bay by the sensors.
3. The system as claimed in claim 1, wherein the earthing switches comprises fast acting earthing switch (15) and maintenance earthing switch (16).
4. The system as claimed in claim 1, wherein the earthing switch (15,16) is of insulated type and used for grounding of main circuit of the GIS.

5. The system as claimed in claim 1, wherein the insulated type earthing switch is used for estimation of accuracy of metering cores of current transformer.
6. The system as claimed in claim 1, wherein partial discharge sensors are installed on slots/apertures of GIS insulators, across GIS bay at site.
7. A method of estimating and verifying of attenuation factors in Gas insulated substation (GIS), the method comprising:
configuring a plurality of UHF sensors (02) at strategic locations across
the GIS bay;
generating a partial discharge pulse by an electronic module;
injecting a partial discharge pulse through insulated earthing switch (15,
16) to estimate attenuation offered by various modules of GIS, wherein
the partial discharge pulses is injected to a plurality of UHF sensors (02)
one by one and the correspondingly generated UHF signals inside GIS is
measured by adjacent sensors, and
determining location of the sensors based on the attenuation offered by
each module of GIS for partial discharge and the generated UHF signals ,
wherein estimating a distance between two UHF sensors (02) is
determined based on the attenuation offered by each GIS module.
8. The method as claimed in claim 7, comprising estimating and determining attenuation rate of each module of GIS by using different PD injection points.
9. The method as claimed in claim 7, wherein determining localization of partial discharge sensors in GIS.

10. The method as claimed in claim 7, wherein the UHF sensor (02) is disposed on a grounded LT flange (03) through insulated aperture (04) of an elliptical or rectangular slot.
11. The method as claimed in claim 7, wherein a composite insulator of bushing for calibration of all partial discharge sensors in the GIS bay is used.
12. The method as claimed in claim 7, wherein the earthing switch (15, 16) is of insulated type and used for feeding calibrated partial discharge pulses of UHF sensors.
13. The method as claimed in claim 7, wherein the insulator is a double insulator (14, 14A) one each for feeding PD signal and for estimation of calibration signal.
14. The method as claimed in claim 7, wherein PD levels at the UHF sensor (02) locations provides attenuation factor of single module or multiple modules depending on a physical distance.