Partial discharge sensor assembly and method

Abstract

A partial discharge sensor assembly 10 for monitoring partial discharge activity in a substation asset, comprises a bolt 14 having a head 16 at a first end 18 and an opposite second end 24. A through

Description

Technical Field Of The Invention This invention relates to a partial discharge sensor assembly and method for monitoring partial discharge (PD) activity in substation assets. In particular, the present invention relates to a partial discharge sensor assembly that can be received inside a threaded hole that extends from the exterior to the interior of the substation asset, such a hole being usually intended for securing panels or other components on, or within, the substation asset. When installed in this manner, the partial discharge sensor assembly can monitor partial discharge activity on, or within, the substation asset through an unobstructed air path. Background For many years, it has been known to inspect or monitor substation assets for partial discharge (PD) activity to provide an early warning of the deterioration of assets. Such non-intrusive condition monitoring of PD activity has now been adopted as standard practice for substation assets around the world. Partial discharge is a well-understood mechanism which begins within voids, cracks or inclusions within solid insulation, or in bubbles within liquid insulation. Partial discharge is a localised dielectric breakdown of a small portion of a solid or liquid electrical insulation system under high voltage stress but which does not completely bridge the space between the conductors. Once begun, partial discharge causes progressive deterioration or degradation of insulation material, and ultimately leads to dielectric breakdown and hence asset failure. Partial discharges emit energy that can be detected in several ways. Electromagnetically, they produce radio waves, visible light, and heat. Acoustically, they generate both audible sound and ultrasonic waves. Additionally, they may result in the emission of gases, such as ozone and nitrogen oxides. Practical techniques for non-intrusive PD testing are based on the detection of the radio frequency part of the electromagnetic spectrum and ultrasonic emissions. One of the well-established and convenient methods of PD detection is to measure transient earth voltages (TEV) induced in the surrounding metalwork of the substation asset. It is possible to detect TEV via periodic inspections using handheld instruments which do not make any electrical connection to the substation asset. A popular handheld instrument for inspection and early detection of PD activity is the UltraTEV™ Plus2 device available from EA Technology Limited. This handheld device includes sensors which can detect transient earth voltages (TEV) and also acoustic ultrasonic signals which enable an operator to distinguish between true PD activity, noise and other interference in a straightforward and quick measurement. The UltraTEV™ Plus2 device is successful at detecting partial discharge acoustic activity provided there is an air passage between the source and the sensor. Whilst handheld instruments are useful for regular inspection of PD activity, there are also semi-portable and fixed solutions available in the marketplace that can be retrofitted to switchgear and cables and which can be continuously monitored to provide an early indication of degradation of assets. Such semi-portable and fixed monitoring equipment generally comprises partial discharge sensors, data collection and communication modules which are retrofitted either inside and / or outside the switchgear asset under test. Online monitoring of PD events using such monitoring equipment allows asset owners to more accurately anticipate potential issues, as well as forecasting when an asset may need replacing. Such semi-portable and fixed monitoring systems are also available from EA Technology Limited, including the Astute HV Monitoring® service. The skilled person will be aware that should semi-portable or fixed monitoring equipment need to be installed within the interior of the asset, this will necessitate a planned outage. These handheld, semi-portable and fixed monitoring solutions all allow for additional sensor technologies to be provided over-and-above the detection of transient earth voltages, and these can include airborne ultrasonic sensors for detecting ultrasonic emissions which can provide further information about the condition of the substation asset. The skilled person will no doubt be aware that an increasing proportion of modern switchgear comprises an enclosure which is sealed or has a double-skin construction, and which poses difficulties for the detection of both transient earth voltages and ultrasonic emissions. The construction of such sealed or double-skin substation assets hinders the external detection of ultrasonic emissions originating from within the asset. At a general level, the skilled person will understand that ultrasonic sensors positioned on the exterior of the substation asset will experience attenuation of ultrasonic emissions caused by dielectric breakdown within the electrical insulation system. Largely informal ad hoc measurement techniques have been tried over the years in an attempt to improve detection of ultrasonic emissions originating from within the asset. Invariably, this involves a user trying to achieve an unobstructed or clear air path by inserting the ultrasonic sensor into an air vent or by removing a threaded bolt, such as one securing a removable panel on the substation asset, and placing the sensor into the empty hole. Although this ad hoc measurement approach provides certain advantages, it has several drawbacks. Firstly, introducing a sensor into a high voltage environment poses significant safety risks. Secondly, the ad hoc placement of the sensor leads to inconsistent measurements, as the sensor’s position and orientation relative to the substation asset can vary. For at least these reasons, and the difficulties involved in producing ultrasonic sensors with sufficient small size, it remains difficult to accurately detect such internal ultrasonic emissions. Whilst the need for both handheld inspection instruments, and semi-portable and fixed monitoring systems which can locate, measure and record PD activity in all types of modern substation assets continues to grow, there is a corresponding need for a partial discharge sensor assembly that can essentially function as a component part of the substation asset. It is an object of the present invention to provide a partial discharge sensor assembly that is configured as a bolt which can be received inside a threaded hole that extends from the exterior to the interior of the substation asset, such a hole being usually intended for securing panels or other components on, or within, the substation asset. A partial discharge sensor assembly configured in this manner is able to monitor partial discharge activity on or within the substation asset via a clear air path, thereby reducing signal attenuation and variability. This provides greater sensitivity than using external sensors, and a convenient installation due to the threaded hole already being present in the substation asset. It is a further object of the present invention to provide a partial discharge sensor assembly which is configured as a component part of the substation asset. Using such a bolt to monitor for partial discharge activity is a completely new and non-invasive means for monitoring PD activity in switchgear. The partial discharge sensor assembly and method of use is safe as there is no need to open the switchgear, and obviates or reduces the need for an outage when installing or setting-up the sensor assembly. It is a further object of the present invention to provide a partial discharge sensor assembly and method which allows for repeatable measurements since the spatial position and orientation of the ultrasonic sensor relative to the substation asset is fixed. It is a further object of the present invention to provide a partial discharge sensor assembly and method having a partial discharge sensor that is compact and can be configured as a bolt. Summary Of The Invention The present invention is described herein and in the claims. According to a first aspect of the present invention there is provided a partial discharge sensor assembly for monitoring partial discharge activity in a substation asset, comprising: a bolt having a head at a first end and an opposite second end, and a through bore extending longitudinally from the head to the second end of the bolt, the bolt being insertable into a threaded hole that extends from the exterior to the interior of the substation asset; and a partial discharge sensor disposed within the through bore, the sensor monitoring partial discharge activity within the substation asset. An advantage of the present invention is that it can be used to reliably detect partial discharge activity on all types of substation assets by providing a clear air path and thereby reducing signal attenuation and variability. Preferably, the head comprising a plurality of tool-engaging faces and wherein the head is rotatable about the longitudinal axis to engage and disengage the bolt from the threaded hole. Further preferably, the tool-engaging faces of the bolt head being hexagonal, square, or other polygonal shape for engagement with a wrench or socket. In use, the bolt may be fully threaded along its longitudinal length for engagement with the threaded hole in the substation asset. Preferably, the partial discharge sensor is disposed within the through bore at or near the second end of the bolt. Further preferably, the output of the partial discharge sensor is connectable to the head of the bolt via electrical leads or a printed circuit board (PCB) that extends through the through bore of the bolt. In use, the partial discharge sensor assembly may further comprise a plurality of concentric conductive rings on the outer surface of the head of the bolt, the rings being connected to the electrical leads or printed circuit board (PCB) and configured to interface with external interface electronics via a push-fit connection. Preferably, the partial discharge sensor is a micro-electromechanical systems (MEMS) ultrasonic sensor. Further preferably, the bolt comprises a stub section at or near the second end having a reduced diameter, with an opening positioned along a chord of the stub into which the partial discharge sensor is mounted In use, the concentric conductive rings on the outer surface of the head of the bolt may meet with corresponding aligned contact points disposed on the interface electronics. According to a second aspect of the present invention there is provided a partial discharge sensor assembly for monitoring partial discharge activity in a substation asset, comprising: a bolt having a head at a first end and an opposite second end, the bolt being insertable into a threaded hole that extends from the exterior to the interior of the substation asset, the head including a plurality of tool-engaging faces and a through bore extending longitudinally from the first end to the second end of the bolt; and a partial discharge sensor disposed within an interface electronics assembly being connectable to the head of the bolt, the sensor being positioned adjacent to the first end of the through bore such that there is a continuous air passage through the bore for monitoring partial discharge activity within the substation asset. Preferably, the bolt is fully threaded along its longitudinal length for engagement with the threaded hole in the substation asset. Further preferably, the partial discharge sensor is a micro-electromechanical systems (MEMS) ultrasonic sensor. In use, the interface electronics assembly may be connected to the head of the bolt via a push-fit connection that aligns with concentric conductive rings disposed on the head of the bolt. Preferably, the tool-engaging faces of the bolt head are hexagonal, square, or other polygonal shape for engagement with a wrench or socket. According to a third aspect of the present invention there is provided a system for processing data from one or more partial discharge sensor assemblies as herein described being disposed about a substation asset, the system comprising a data acquisition system connected to the interface electronics, the system being configured to analyse partial discharge data from the sensors for monitoring and assessing the integrity and / or conditions within the substation asset. Preferably, the data acquisition system includes software algorithms for detecting anomalies in the partial discharge data indicative of potential issues within the substation asset. Further preferably, the data acquisition system is connected to a network for remote monitoring and reporting of the substation asset conditions. In use, the interface electronics may include signal conditioning circuits to filter and amplify signals from the partial discharge sensors before processing. According to a fourth aspect of the present invention there is provided a method of detecting partial discharge activity in a substation asset provided with a partial discharge sensor assembly as hereinbefore described, the method comprising the steps of: removing a conventional bolt from a threaded hole that extends from the exterior to the interior of the substation asset; inserting a partial discharge sensor assembly into the threaded hole; connecting interface electronics to the partial discharge sensor assembly; and monitoring partial discharge activity within the substation asset using the partial discharge sensor. In use, the step of inserting a partial discharge sensor assembly into the threaded hole may further comprise the step rotating the head of the bolt about the longitudinal axis to engage the bolt in the threaded hole and tightening the bolt into place to ensure secure engagement with the substation asset. Preferably, the partial discharge sensor is a micro-electromechanical systems (MEMS) ultrasonic sensor. Further preferably, the method further comprising the step of analysing the partial discharge data to detect anomalies indicative of substation asset integrity. It is believed that a partial discharge sensor assembly, and system for processing data from one or more partial discharge sensor assemblies and method for monitoring partial discharge activity in substation assets in accordance with the present invention at least addresses the problems outlined above. It will be obvious to those skilled in the art that variations of the present invention are possible and it is intended that the present invention may be used other than as specifically described herein. Brief Description Of The Drawings The present invention will now be described by way of example only, and with reference to the accompanying drawings, in which: Figure 1 illustrates a perspective view from the side and above of a partial discharge sensor assembly in accordance with the present invention which is configured as a threaded bolt and which is received in a threaded hole that extends from the exterior to the interior of the substation asset, such a hole being usually intended for securing panels or other components on, or within, the substation asset; and Figure 2 shows a perspective view from the side and above of the partial discharge sensor assembly in accordance with the present invention; and Figure 3 is a side sectional view of a second embodiment of the present invention, and which shows a partial discharge sensor being located in an accessory module which abuts, or is proximate to, a threaded bolt having a through bore. Detailed Description Of The Preferred Embodiments The present invention has adopted the approach of utilising a partial discharge sensor assembly that is configured as a bolt which can be received inside a threaded hole that extends from the exterior to the interior of the substation asset, such a hole being usually intended for securing panels or other components on, or within, the substation asset. A partial discharge sensor assembly configured in this manner is able to monitor partial discharge activity on or within the substation asset via a clear air path, thereby reducing signal attenuation and variability. This provides greater sensitivity than using external sensors, and a convenient installation due to the threaded hole already being present in the substation asset. Advantageously, the present invention provides a partial discharge sensor assembly which is configured as a component part of the substation asset. Using such a bolt to monitor for partial discharge activity is a completely new and non-invasive means for monitoring PD activity in switchgear. The partial discharge sensor assembly and method of use is safe as there is no need to open the switchgear, and no need for an outage when installing or setting-up the sensor assembly. Further advantageously, the present invention also provides a partial discharge sensor assembly and method which allows for repeatable measurements since the spatial position and orientation of the ultrasonic sensor relative to the substation asset is fixed. Further advantageously, the present invention also provides a partial discharge sensor assembly and method having a partial discharge sensor that is compact and can be configured as a bolt. Referring now to the drawings, a partial discharge sensor assembly 10 in accordance with the present invention is depicted in Figure 1. Figure 1 shows that, when deployed, the partial discharge sensor assembly 10 abuts, or is proximate to a substation asset 12 (only a small section of the enclosure of a substation asset 12 is shown in Figure 1). Although particular embodiments of the invention refer to utilising the partial discharge sensor assembly 10 with sealed or double-skin substation assets 12, this is in no way intended to be limiting as the present invention can be utilised with any number of different types of substation assets 12. As shown in Figure 1, the partial discharge sensor assembly 10 is configured as a threaded bolt 14 with a head 16 disposed at a first end 18 of the bolt 14. The head 16 having a plurality of tool-engaging faces 20, and a through bore 22 (as best illustrated in Figure 3) which extends longitudinally throughout the bolt 14 from the head 16 to an opposite second end 24. The bolt head 16 being designed with tool-engaging faces 20 being orientated so as to have a hexagonal, square, or other polygonal shape, to accommodate a wrench, socket, or other tool (not shown) which is used for tightening or loosening the bolt 14. In a preferred embodiment, the bolt 14 is fully threaded along its length, providing maximum engagement with a corresponding threaded hole (not shown) disposed in the substation asset 12. The bolt 14 features threads 26 extending largely along its longitudinal length from the head 16 to the opposite second end 24. This full-thread design maximises the contact surface area with a corresponding threaded hole, distributing the tensile load evenly across the bolt 14. This is in no way intended to be limiting as the bolt 14 may also be configured as a partial thread bolt having a shank between the head 16 and thread 26. As best shown in Figure 2, towards the second end 24 of the bolt 14 is located an unthreaded section or stub 28 having a reduced diameter. Positioned on a chord of the cylindrical stub 28 is an opening or window 30 into which the PD sensor 32 is mounted. The through bore 22 is drilled to house the PD sensor 32 near the opening at the second end 24 of the bolt 14 opposite to the head 16. The PD sensor 32 is mounted securely within the bore 22 through opening 30, and enabling it to monitor the PD activity within the switchgear 12. The placement of the PD sensor 32 within the bore 22 provides a clear air path for PD measurement, reducing inaccuracies caused by external factors and attenuation which would occur due to several factors, including absorption of the acoustic emissions, and internal reflections which would otherwise scatter the emissions. The internal retention of the sensor 32 inside the bore 22 also shields it from environmental hazards, such as moisture, debris and mechanical damage. In a preferred embodiment, the PD sensor 32 is a micro-electromechanical systems (MEMS) ultrasonic sensor, which is mountable proximate to, or in abutment with, the surrounding metalwork of the substation asset 12 being inspected. MEMS microfabrication technology integrates mechanical and electrical components on a single silicon chip. Such a MEMS sensor 32 converts ultrasonic sound waves into electrical signals and is notable for its small size, high sensitivity and low power consumption. In the embodiment shown in Figures 1 and 2, the PD sensor 32 is a microelectromechanical systems (MEMS) ultrasonic sensor that detects ultrasonic emissions. This is in no way intended to be limiting as any number of different forms of sensor to allow comprehensive testing and detection of PD in substation assets, such as, transient earth voltage (TEV) sensors, high-frequency current transformers (HFCTs) and / or environmental sensors (ambient temperature and relative humidity) can be utilised. The PD sensor 32 is connected to external monitoring equipment via flexible or rigid electrical leads (not shown) that extend through the internal bore 22. Alternatively, the PD sensor 32 is connectable to the head 16 of the bolt 14 via a flexible or rigid printed circuit board (PCB) or the like. In the embodiment shown in Figures 1 and 2 the leads can be routed to a separate data acquisition system or interface electronics (not shown) for monitoring of PD activity. Instead of a traditional plug-and-socket connection, the sensor’s 32 output is routed through leads or PCB that connect to a series of concentric conductive rings 34. The rings 34 are embedded in an insulating material on the outer surface 36 of the head 16, and arranged in a bullseye pattern. The interface electronics have corresponding contact points that align with the conductive rings 34 when pressed against them. This design allows for a user-friendly push-fit connection and disconnection without the wear and alignment issues associated with conventional connectors. Each concentric ring 34 would carry a different signal or power line, allowing multiple connections to be made simultaneously with a simple push-fit. This approach would be beneficial for those applications requiring quick and reliable connections that may be frequently engaged and disengaged, such as in modular systems, sensor arrays, or environments where traditional connectors are prone to failure. It is envisaged that other connections means are possible, and this is in no way intended to be limiting. The installation of the partial discharge sensor assembly 10 in accordance with the present invention will now be described, and it is recommended that the following procedure is followed by a user. Firstly, an operative removes a conventional bolt that is normally intended for securing panels or other components on, or within, the substation asset 12 using a wrench to expose a threaded hole that extends from the exterior to the interior of the substation asset 12. The user then replaces the conventional bolt with a measurement bolt 14, tightening it securely into place. Once the partial discharge sensor assembly 10 is installed, the interface electronics 38 are connected by pressing it against the exposed concentric rings 34 in the head 16. The partial discharge sensor assembly 10 is now fully integrated with the asset 12, monitoring for internal PD activity and transmitting data to the connected interface electronics 38. Figure 3 shows a second embodiment of the partial discharge sensor assembly 10. The construction of the second embodiment is very similar to that of the first embodiment and corresponding features have been given the same reference numerals. The second embodiment differs from the first embodiment in that instead of a PD sensor 32 being disposed in the through bore 22 at the second end of the bolt 14 and connected to the interface electronics 38 at the head 16 of the bolt 14, the second embodiment of the partial discharge sensor assembly 10 is configured as a bolt 14 which includes a through bore 22 providing a clear air path for evaluation of the asset 12, and the PD sensor 32 is disposed within interface electronics 38. Therefore, a partial discharge sensor assembly 10 and method for monitoring partial discharge activity in substation assets 12 is provided. When used in this specification and claims, the terms “comprises” and “comprising” and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components. 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 “includes” and / or “including” when used herein, specify the presence of stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof. The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, separately, or in any combination of such features, can be utilised for realising the invention in diverse forms thereof. The invention is not intended to be limited to the details of the embodiments described herein, which are described by way of example only. It will be understood that features described in relation to any particular embodiment can be featured in combination with other embodiments. It is contemplated by the inventor that various substitutions, alterations and modifications may be made to the invention without departing from the spirit and scope of the invention as defined by the claims.

Claims

1. A partial discharge sensor assembly for monitoring partial discharge activity in a substation asset, comprising:a bolt having a head at a first end and an opposite second end, and a through bore extending longitudinally from the head to the second end of the bolt, the bolt being insertable into a threaded hole that extends from the exterior to the interior of the substation asset; anda partial discharge sensor disposed within the through bore, the sensor monitoring partial discharge activity within the substation asset.

2. The partial discharge sensor assembly as claimed in claim 1, wherein the head comprising a plurality of tool-engaging faces and wherein the head is rotatable about the longitudinal axis to engage and disengage the bolt from the threaded hole.

3. The partial discharge sensor assembly according to claim 2, wherein the toolengaging faces of the bolt head being hexagonal, square, or other polygonal shape for engagement with a wrench or socket.

4. The partial discharge sensor assembly according to claim 1, wherein the bolt is fully threaded along its longitudinal length for engagement with the threaded hole in the substation asset.

5. The partial discharge sensor assembly according to claim 1, wherein the partial discharge sensor is disposed within the through bore at or near the second end of the bolt.

6. The partial discharge sensor assembly according to claim 1, wherein the output of the partial discharge sensor is connectable to the head of the bolt via electrical leads or a printed circuit board (PCB) that extends through the through bore of the bolt.

7. The partial discharge sensor assembly according to claim 6, further comprising a plurality of concentric conductive rings on the outer surface of the head of the bolt, therings being connected to the electrical leads or printed circuit board (PCB) and configured to interface with external interface electronics via a push-fit connection.

8. The partial discharge sensor assembly according to claim 1, wherein the partial discharge sensor is a micro-electromechanical systems (MEMS) ultrasonic sensor.

9. The partial discharge sensor assembly according to claim 1, wherein the bolt comprises a stub section at or near the second end having a reduced diameter, with an opening positioned along a chord of the stub into which the partial discharge sensor is mounted10. The partial discharge sensor assembly according to claim 7, wherein the concentric conductive rings on the outer surface of the head of the bolt meet with corresponding aligned contact points disposed on the interface electronics.

11. A partial discharge sensor assembly for monitoring partial discharge activity in a substation asset, comprising:a bolt having a head at a first end and an opposite second end, the bolt being insertable into a threaded hole that extends from the exterior to the interior of the substation asset, the bolt having a through bore extending longitudinally from the first end to the second end; anda partial discharge sensor disposed within an interface electronics assembly being connectable to the head of the bolt, the sensor being positioned adjacent to the first end of the through bore such that there is a continuous air passage through the bore for monitoring partial discharge activity within the substation asset.

12. The partial discharge sensor assembly according to claim 11, wherein the bolt is fully threaded along its longitudinal length for engagement with the threaded hole in the substation asset.

13. The partial discharge sensor assembly according to claim 11, wherein the partial discharge sensor is a micro-electromechanical systems (MEMS) ultrasonic sensor.

14. The partial discharge sensor assembly according to claim 11, wherein the interface electronics assembly are connected to the head of the bolt via a push-fit connection that aligns with concentric conductive rings disposed on the head of the bolt.

15. The partial discharge sensor assembly according to claim 11, wherein the toolengaging faces of the bolt head are hexagonal, square, or other polygonal shape for engagement with a wrench or socket.

16. A system for processing data from one or more partial discharge sensor assemblies according to any of claims 1 to 15 being disposed about a substation asset, the system comprising a data acquisition system connected to the interface electronics, the system being configured to analyse partial discharge data from the sensors for monitoring and assessing the integrity and / or conditions within the substation asset.

17. The system according to claim 16, wherein the data acquisition system includes software algorithms for detecting anomalies in the partial discharge data indicative of potential issues within the substation asset.

18. The system according to claim 16, wherein the data acquisition system is connected to a network for remote monitoring and reporting of the substation asset conditions.

19. The system according to claim 16, wherein the interface electronics include signal conditioning circuits to filter and amplify signals from the partial discharge sensors before processing.

20. A method of detecting partial discharge activity in a substation asset provided with a partial discharge sensor assembly according to any of claims 1 to 15, comprising the steps of:removing a conventional bolt from a threaded hole that extends from the exterior to the interior of the substation asset;inserting a partial discharge sensor assembly into the threaded hole;connecting interface electronics to the partial discharge sensor assembly; and monitoring partial discharge activity within the substation asset using the partial discharge sensor.

21. The method according to claim 20, wherein the step of inserting a partial discharge sensor assembly into the threaded hole further comprises the step rotating the head of the bolt about the longitudinal axis to engage the bolt in the threaded hole and tightening the 5 bolt into place to ensure secure engagement with the substation asset.

22. The method according to claim 20, wherein the partial discharge sensor is a microelectromechanical systems (MEMS) ultrasonic sensor.10 23. The method according to claim 20, further comprising the step of analysing thepartial discharge data to detect anomalies indicative of substation asset integrity.

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