Gas-insulated surge arresters and gas-insulated surge arrester monitoring systems

Abstract

Disclosed is a gas-insulated surge arrester (1a, 1b, 1c) comprising a metal-clad housing (3) in which a block stack (4) is disposed. The block stack (4) includes at least one metal-oxide resistor post (2), and the gas-insulated surge arrester (1a, 1b, 1c) is characterized by a capacitive element (9a, 9b, 9c) configured to obtain an electric field measurement of the gas-insulated surge arrester (1a, 1b, 1c), and a bushing (10a, 10b, 10c) disposed through the metal-clad housing (3) and configured to provide a capacitive third harmonic current measurement to an input of a surge arrester monitoring device (7). Also provided is a monitoring system (100) comprising the gas-insulated surge arrester (1a, 1b, 1c) connected to the surge arrester monitoring device (7).

Description

[Technical Field]

[0001] The technology disclosed herein relates generally to the field of gas-insulated surge arresters, and more particularly to gas-insulated surge arresters enabled for condition monitoring, and gas-insulated surge arrester monitoring systems. [Background technology]

[0002] background A gas-insulated substation (GIS) is a metal-enclosed substation with a fairly small footprint. It is therefore often used where space is limited, such as on offshore platforms or within urban buildings. GIS contain high-voltage components such as surge arresters, circuit breakers, and disconnectors, and use dielectric gas at moderate pressures for phase-to-phase and phase-to-earth insulation.

[0003] GIS are impervious to and separate from the external atmosphere, which is beneficial, for example, from an environmental point of view, but also presents challenges. Surge arresters in GIS are subject to the same or even stricter operational duties as surge arresters in air-insulated substations (AIS). If any degradation occurs as a result, it is advantageous to detect it before it leads to surge arrester failure and subsequent power outage. It is fairly easy to perform meaningful in-service diagnostics on AIS arresters, and in fact, products exist for such diagnostic purposes. In contrast, no such products exist for GIS surge arresters.

[0004] One challenge, therefore, is monitoring the condition of GIS surge arresters. A known surge arrester diagnostic method used for AIS is third-harmonic analysis of leakage current with compensation for harmonics in voltage (International Standard IEC 60099-5, Method B2). This requires an input for capacitive third-harmonic current in the surge arrester to perform the necessary compensation. This can be done using a field probe attached to the base of the AIS surge arrester. However, this is not applicable to GIS surge arresters, which are placed inside a metal enclosure filled with insulating gas. Therefore, GIS surge arresters are monitored only by conventional surge counters with surge recording and total leakage current measurements, which only provide information about surge arrester activity and are not a meaningful diagnostic for the surge arrester's condition.

[0005] Therefore, condition monitoring of GIS surge arresters is required. Summary of the Invention [Problem to be solved by the invention]

[0006] overview An object of the present invention is to enable condition monitoring of GIS surge arresters. [Means for solving the problem]

[0007] This object, as well as other objects, is achieved, according to one aspect, by a gas-insulated surge arrester. The gas-insulated surge arrester includes a metal-clad housing having a block stack disposed therein. The block stack includes at least one metal oxide resistor post. The gas-insulated surge arrester is characterized by a capacitive element configured to obtain an electric field measurement of the gas-insulated surge arrester and a bushing disposed through the metal-clad housing. The bushing is configured to provide a capacitive third harmonic current measurement to an input of a surge arrester monitoring device.

[0008] Gas-insulated surge arresters offer several advantages. For example, the gas-insulated surge arrester according to the invention is adapted so that existing surge arrester monitoring equipment may be used for its condition monitoring. Gas-insulated surge arresters are cost-effective in that existing components may be used with additional means to extract the required measurement signals outside the gas-insulated surge arrester, allowing the use of existing surge arrester monitoring equipment.

[0009] Historically, the ability to obtain meaningful diagnostic measurements from the metal-oxide resistor columns inside GIS surge arresters has been difficult, and devices capable of evaluating them are lacking. However, there has been resistance to even considering making changes to existing GIS designs, primarily due to concerns about the impact on reliability. The additional cost was also unacceptable. Therefore, there is a long-felt need for improved meaningful condition monitoring of gas-insulated surge arresters.

[0010] To improve GIS surge arrester monitoring, the present invention proposes some redesign of existing assemblies and enclosures to incorporate new components, possibly with some individual customization of existing monitoring equipment. The combination of existing and well-established components minimizes the cost of the solution while providing the required functionality without adversely affecting overall reliability. The direct cost increase to the entire GIS surge arrester design, including the monitoring system, is easily offset by the significant cost reduction that would otherwise result from an unplanned incident due to the failure of an unmonitored GIS surge arrester.

[0011] In one embodiment, the capacitive element is configured to extract a capacitive third harmonic component in the leakage current of the surge arrester.

[0012] In a different embodiment, the capacitive element is a capacitive tap configured to extract a capacitive third harmonic component in the leakage current of the surge arrester.

[0013] In a variation of the above embodiment, the bushing includes a first side and a second side, one for placement on the capacitive element and the other electrically connectable to a field probe input of the surge arrester monitoring device.

[0014] In some embodiments, the capacitive element includes an internal capacitive element disposed within the metal-clad housing, while in other embodiments, the capacitive element includes an external capacitive tap disposed outside the bushing.

[0015] In various embodiments, the capacitive element comprises a metal plate. Such embodiments are very cost-effective and easily adaptable to the particular requirements at hand. In still other embodiments, various other sensor devices for measuring the electric field may be used, such as microelectromechanical systems (MEMS) sensors.

[0016] In various embodiments, the outside of the bushing is electrically connected by an electrical conductor to the input of the surge arrester monitoring device.

[0017] This object, among other objects, is achieved according to another aspect by a monitoring system including a gas-insulated surge arrester according to any of the above embodiments connected to a surge arrester monitoring device.

[0018] Further features and advantages of the present teachings will become apparent from the following description and accompanying drawings. [Brief explanation of the drawings]

[0019] [Figure 1] GIS surge arrester 1 is shown. [Figure 2] 1 shows a first embodiment of the present invention. [Figure 3] 2 shows a second embodiment of the present invention. [Figure 4] 3 shows a third embodiment of the present invention. [Figure 5] 1 illustrates an exemplary capacitive element for use in embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] Detailed Description In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular architectures, interfaces, techniques, etc., to ensure a thorough understanding. In other instances, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description with unnecessary detail. The same reference numbers refer to the same or similar elements throughout the description.

[0021] The present applicant has developed two commercially available surge arrester monitoring systems, the EXCOUNT-II and EXCOUNT-III types. These surge arrester monitoring systems allow for the recording of, for example, the number of discharges seen by the surge arrester and their amplitude (with timestamps), as well as measurements of the total leakage current and resistive current through the surge arrester. One version of the EXCOUNT-III can also measure surge impulse steepness, which provides additional information to the user. This allows for valuable diagnostic analysis of the AIS surge arrester's performance and state of health over time to be performed based on the output data.

[0022] However, these existing surge arrester monitoring systems are only for use in AIS applications. They incorporate electric field probes to provide the necessary input for compensation so that an estimate of the resistive component of the leakage current can be made for meaningful condition monitoring purposes. The electric field probe needs to be attached to the base of the surge arrester with the ability to detect the ambient electric field, which does not present a challenge since its enclosure is not metallic.

[0023] The present invention also provides a means for enabling input for compensation of GIS surge arresters, as described in various embodiments herein, and therefore the use of existing surge arrester monitoring systems can also be used for GIS surge arresters and therefore their condition monitoring.

[0024] For a complete understanding of the present invention, some further details regarding surge arresters and related measurements are provided below. As previously mentioned, the measurement of total leakage current is commonly used for all types of surge arresters, including GIS. The total leakage current of a metal oxide (MO) surge arrester can be separated into capacitive and resistive portions, with the capacitive component predominating and the resistive portion significantly smaller. It is recognized that the total leakage current is not suitable for surge arrester diagnostic purposes, and that only the resistive component of the leakage current is a sensitive indicator of any changes in the voltage-current characteristics of an MO surge arrester.

[0025] MO surge arresters have a nonlinear voltage-current characteristic that causes harmonics in the total leakage current when energized with a sinusoidal voltage. The harmonic content of the total leakage current can be used as an indicator of resistive leakage current. Using harmonics to measure resistive leakage current is advantageous compared to other methods because it does not require a voltage reference to determine the resistive portion of the total leakage current. The third harmonic is of particular interest in this regard, as it has the largest magnitude of the current harmonics.

[0026] Another source of harmonics in the total leakage current is the harmonic content in the voltage of the system to which the arrester is connected and configured to protect. System voltage harmonics generate capacitive harmonic currents in MO surge arresters. The capacitive harmonic currents generated by system voltage harmonics can be of the same order of magnitude as the harmonic currents generated by nonlinear resistive leakage currents. This means that the third harmonic content arising from the system voltage interferes with the third harmonic content associated with the resistive leakage current of the MO surge arrester. Therefore, to perform an accurate measurement of resistive leakage current through third harmonic analysis, it is necessary to compensate for the third harmonic content in the system voltage.

[0027] This compensation is performed by simultaneous measurement of both the total leakage current of the MO surge arrester and the current induced in the capacitive element, the latter being configured to provide a proportional value for the harmonic content of the system voltage.

[0028] FIG. 1 shows a GIS surge arrester 1. The GIS surge arrester 1 comprises one or more columns of metal-oxide-semiconductor (MO) resistors, connected in series and shown in cross section on the right side of FIG. 1. The MO resistor columns 2 form the active part of the GIS surge arrester 1 and handle any surges that may occur. The one or more MO resistor columns 2 are disposed within a metal-clad housing 3. The metal-clad housing 3 of the GIS surge arrester 1 is filled with a pressurized dielectric gas, typically sulfur hexafluoride gas (SF6 gas), as an insulating medium.

[0029] In contrast to AIS applications, where the electric field generated by the MO resistor posts can be measured from outside the surge arrester, the metal-clad housing 3 of the surge arrester 1 allows any electric field to be captured externally. The present invention addresses this difficulty. In order to perform diagnostic measurements of the condition of the GIS surge arrester 1, and in particular the condition of the MO resistor posts 2, it is necessary to directly access the MO resistor posts 2 inside the metal-clad housing 3 and then transmit the required measurement signal to the outside. This can be done in different ways according to various embodiments of the present invention, as will now be explained.

[0030] As illustrated in FIGS. 2-5, the monitoring system 100 includes a GIS surge arrester 1a and a monitoring arrangement 7 connected thereto. The monitoring arrangement 7 may be, for example, the EXCOUNT-II and EXCOUNT-III monitoring devices developed by and available from the present applicant. FIG. 2 illustrates a first embodiment of the present invention. The GIS surge arrester 1a includes a metal-clad housing 3 and a surge arrester block stack 4, hereinafter simply referred to as the block stack 4, including one or more MO resistor posts 2 (not shown in detail). Furthermore, a grading hood 5 may be disposed on the block stack 4, for example, to ensure linear voltage distribution along the block stack 4. Depending on the specific design and the voltage at hand, it may be omitted and / or have any other design than that shown. A grounding bushing 6 is connected from the block stack 4 to a surge arrester monitoring device 7, which may be, for example, one or both of the aforementioned EXCOUNT-II and EXCOUNT-III monitoring devices. The surge arrester monitoring device 7 connected to the GIS surge arrester 1 a constitutes a GIS surge arrester monitoring system 100.

[0031] In this embodiment, the internal capacitive element 9a is fitted to the end cap or end flange of the MO resistor post of the surge arrester block stack 4 within the metal-clad housing 3. The capacitive element 9a may be embodied, for example, in the form of a capacitive tap, a tapped capacitive graded bushing, or a metal field probe. It should be noted that the capacitive element 9a may be located other than at the base of the MO resistor post 2. The capacitive element 9a may be located at the high-voltage end, particularly in embodiments without a grading hood 5. The capacitive element 9a enables extraction of the capacitive component of the leakage current. The capacitive element 9a may include, for example, a metal plate or other sensor device for measuring the electric field, such as a microelectromechanical system (MEMS), or may be a capacitive test tap. The capacitance of the capacitive element 9a is selected depending on the particular surge arrester 2, taking into account, for example, its rated voltage, self-capacitance, leakage current, or field strength.

[0032] An internal electrical connection 11 is made from the capacitive element 9a to a bushing 10a for GIS applications. The bushing 10a then allows the signal to be guided outside the metal-clad housing 3. The bushing 10a should be designed taking into account the characteristics of the particular surge arrester 1a at hand. For example, the size of the bushing 10a should be selected to accommodate the hermeticity, and the electrical insulation and separation should also be selected taking into account the particular surge arrester 1a and its characteristics. An external connection 8a, including, for example, an electrical conductor, is connected from the GIS bushing 10a to the surge arrester monitoring device 7. The connection 8a may thereby provide an input signal for the field probe input of the surge arrester monitoring device 7. The external connection 8a may be connected to the surge arrester monitoring device 7 via a plug, bushing, or other intermediate connection device (not shown).

[0033] FIG. 3 illustrates a second embodiment of the present invention. The metal-clad housing 3, block stack 4, grounding bushing 6, and grading hood 5 have been described in connection with the previous figure and will not be repeated here. In this embodiment, instead of the MO resistor posts 2 as in the previous embodiment, a capacitive element 9b is attached to a bushing 10b. An internal electrical connection 12 is then made from the MO resistor posts of the block stack 4 to the capacitive tap 9b attached to the bushing 10b. The capacitive element 9b may be attached to the bushing 10b in different ways, for example, with a thread or as a plug. As with the previous embodiment, this embodiment also includes an external connection 8b from the bushing 10b to the field probe input of the surge arrester monitoring device 7. The external connection 8b described in connection with the previous embodiment may also be used in this embodiment to provide an input signal for the field probe input of the surge arrester monitoring device 7.

[0034] In the above embodiments, the capacitive elements 9a, 9b are fitted to the end caps or end flanges of the MO resistor posts 2, or to the bushings 10b. That is, the capacitive elements 9a, 9b are located inside the metal-clad housing 3. In the following, an embodiment will be described in which the bushings are internal and located within the metal-clad housing 3, while the capacitive elements are instead embodied as external capacitive taps.

[0035] FIG. 4 illustrates a third embodiment of the present invention. Again, the metal-clad housing 3, block stack 4, grounding bushing 6, and grading hood 5 have been described in connection with the previous embodiment and will not be repeated here. To enable extraction of the capacitive component of the leakage current, a capacitively graded bushing 10c is electrically connected to the stack block 4, e.g., at its lower portion, e.g., its base. This internal electrical connection may be made, for example, by a direct connection or a jumper connection. A bushing 10c suitable for GIS applications extends all the way to the exterior of the metal-clad housing 3. The bushing 10c includes a connection 8c on its exterior, e.g., a capacitive test tap connection 8c, which has a suitably sized capacitance ratio. That is, its electrical and mechanical characteristics should be adapted to the conditions of use. The connection 8c, particularly the capacitive test tap connection 8c, provides the desired input signal to the field probe input of the surge arrester monitoring device 7, e.g., via a plug or bushing (not shown). A connection 14 should be formed from the bushing 10c to ground. The connection 14 may be made directly to ground as shown in Figure 4. However, depending on, for example, the particular situation at hand, such a connection 14 may instead be indirect, for example connected via a monitoring device 7.

[0036] FIG. 5 illustrates an exemplary capacitive element suitable for use in the above-described embodiments. In the above-described embodiment of the present invention, a bushing 10c is disposed through a metal-clad housing 3 (not shown) of the surge arrester. The bushing 10c may be, for example, a bushing for a GIS application. To acquire the measurement signal, a capacitive element, for example, in the form of a metal field probe plate 17, may be used. The metal field probe plate 17 is disposed inside the metal-clad housing 3 and configured to perform measurements on the stack block 4, particularly its MO resistor posts. The metal field probe plate 17 may be connected to the bushing 10c via a jumper connector 15 or the like. An insulator 16 should be disposed between the metal field probe plate 17 and a mounting plate 18. It is understood that these devices 15, 16, 17, and 18 may be designed differently or may be replaced with devices having the same functionality. For example, while the insulator 16 is shown as having a shed, in some embodiments, the insulator 16 may be designed without a shed. It should be noted that while the metallic field probe plate 17 is used herein as an example of how the electric field may be measured, it is understood that various other methods and devices for measuring the electric field are possible as well, e.g., MEMS sensors.

[0037] In order to gain the desired direct access to the MO resistor posts 2 inside the metal clad housing 3 and then bring the required measurement signal externally, a field probe, for example a capacitive element as described, is provided, allowing the required measurement signal to be provided to the field probe input of the surge arrester monitoring device 7. The field probe can be embodied in different ways, as described.

[0038] A capacitive element (e.g., a capacitive test tap or a capacitive graded bushing with a test tap) may be used as a field probe to provide the required type of input, as well as configured insulation and isolation. Commercially available capacitive test taps may be used for this purpose. The test taps connected to the GIS surge arresters 1a, 1b, and 1c provide the required input to the surge arrester monitoring device 7, which allows the surge arrester monitoring device 7 to perform meaningful condition monitoring functions for GIS arresters as well as AIS arresters.

[0039] Various embodiments have described capacitive elements 9a, 9b, and 9c configured to obtain electric field measurements of the gas-insulated surge arresters 1a, 1b, and 1c. As previously described, such capacitive elements may be embodied in the form of, for example, capacitive taps, capacitive graded bushings with test taps, or metallic field probes. The electric field measurements are preferably of the capacitive component of the leakage current of the surge arresters. Furthermore, in various embodiments, bushings 10a, 10b, and 10c have been described as being disposed through the metal-clad housing 3 and configured to provide the electric field measurements to the field probe input of the surge arrester monitoring device 7. The electric field measurements may be obtained by extracting the capacitive third harmonic component of the leakage current of the surge arresters 1a, 1b, and 1c.

[0040] It should be noted that while the various bushings 10a, 10b, 10c are shown and described as being located at the bottom of the metal tank next to the MO resistor posts, various other arrangements are possible. For example, the bushings may instead be located directly below the MO resistor posts, on the side of the tank, or even on top of the inverted mounting unit in different embodiments. The space within which the gas-insulated surge arrester must be located for operation may be a consideration when designing and determining bushing placement.

[0041] As a further design consideration, some additional insulation may be required between the various metal contact surfaces of different embodiments. The physical connections, placement, and mechanical design needs may need to be adjusted to account for the specific design of the GIS at hand. Given the teachings of the disclosed guidance provided herein, one of ordinary skill in the art will be able to make such considerations and specific design implementations.

[0042] The present invention provides for condition monitoring of GIS surge arresters by enabling the use of a surge arrester diagnostic method of third-harmonic analysis of leakage current with compensation for harmonics in voltage. The necessary input for capacitive third-harmonic current in GIS surge arresters is provided, allowing the necessary compensation to be performed in the diagnostic method. The resistive portion of the total leakage current can be determined.

[0043] There is also provided a monitoring system 100 comprising the gas-insulated surge arrester 1a, 1b, 1c as described in the various embodiments. The monitoring system 100 further comprises a surge arrester monitoring device 7 connected to the gas-insulated surge arrester 1a, 1b, 1c.

[0044] In some embodiments, the surge arrester monitoring device 7 comprises a surge arrester monitor that allows recording of the number of discharges seen by the surge arrester and their amplitude, and / or measuring the total leakage and resistive currents through the surge arrester, and / or measuring the surge impulse steepness.

[0045] The present invention has been described herein primarily with reference to certain embodiments, however, as will be understood by those skilled in the art, other embodiments than the specific ones disclosed herein are equally possible within the scope of the present invention as defined by the claims.

Claims

1. A gas-insulated surge arrester (1a, 1b, 1c) comprising a metal clad housing (3) in which a block stack (4) is arranged, the block stack (4) including at least one metal oxide resistor post (2), the gas-insulated surge arrester (1a, 1b, 1c) comprising: - capacitive elements (9a, 9b, 9c) arranged to obtain electric field measurements of said gas-insulated surge arresters (1a, 1b, 1c); a bushing (10a, 10b, 10c) arranged through said metal clad housing (3) and configured to provide capacitive third harmonic current measurements to an input of a surge arrester monitoring device (7); the capacitive elements (9a, 9b, 9c) are configured to extract a capacitive third harmonic component in a leakage current of the gas-insulated surge arrester (1a, 1b, 1c); The gas-insulated surge arrester (1a, 1b, 1c), wherein the capacitive element (9a, 9b, 9c) is a capacitive tap (9a, 9b, 9c) configured to extract the capacitive third harmonic component in a leakage current of the gas-insulated surge arrester (1a, 1b, 1c).

2. 2. The gas-insulated surge arrester (1a, 1b, 1c) according to claim 1, wherein the bushing (10a, 10b, 10c) comprises a first side and a second side, one of which is arranged on the capacitive element (9a, 9b, 9c) and the other of which is electrically connectable to an electric field probe input of the surge arrester monitoring device (7).

3. 3. The gas-insulated surge arrester (1a, 1b, 1c) according to claim 1 or 2, wherein the capacitive elements (9a, 9b, 9c) include internal capacitive elements (9a, 9b) arranged within the metal-clad housing (3).

4. 3. The gas-insulated surge arrester (1a, 1b, 1c) according to claim 1 or 2, wherein the capacitive element (9c) comprises an external capacitive tap (9c) arranged outside the bushing (10c).

5. The gas-insulated surge arrester (1a, 1b, 1c) according to any one of claims 1 to 4, wherein the capacitive element (9a, 9b) comprises a metal plate or a micro-electromechanical system sensor for measuring an electric field.

6. The gas-insulated surge arrester (1a, 1b, 1c) according to any one of claims 1 to 5, wherein the outer side of the bushing (10a, 10b, 10c) is electrically connected to the input of the surge arrester monitoring device (7) by a conductor (8a, 8b, 8c).

7. A monitoring system (100) comprising a gas-insulated surge arrester (1a, 1b, 1c) according to any one of claims 1 to 6 connected to a surge arrester monitoring device (7).

8. 8. The monitoring system (100) according to claim 7, wherein the surge arrester monitoring device (7) comprises a surge arrester monitor that enables recording of the number of discharges seen by the gas-insulated surge arrester and their amplitude, and / or measurement of the total leakage current and resistive current through the gas-insulated surge arrester, and / or measurement of surge impulse steepness.

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