GB2621856A

GB2621856A - Fluid monitoring

Info

Publication number: GB2621856A
Application number: GB2212303.8A
Authority: GB
Inventors: Larkin Stephen; Omar Muhammad; Jamal Khan Haris; Usman Muhammad; Raw Brendon; Saleem Khan Saad
Original assignee: African New Energies Ltd
Current assignee: African New Energies Ltd
Priority date: 2022-08-24
Filing date: 2022-08-24
Publication date: 2024-02-28
Also published as: GB202212303D0

Abstract

A dielectric permittivity sensor 500 for sensing permittivity of a fluid, the sensor comprising an electrically conductive structure 502 with an input 504 and output 506, including first and second elements 520, 522 the extend into the fluid 505, a microwave transmitter connected to the input of the structure and arranged to energise it to produce an output signal, and an electromagnetic sensor connected and responsive to the output of the structure, so as to enable the permittivity of the fluid to be determined. The sensor may be part of a system also comprising a calibration device for automatically calibrating the sensor, including a movable conductive element and a stationary conductive element spaced apart from one another to define a zone to be filled with fluid, wherein the movable conductor moves relative to the stationary element so as to vary the quantity of fluid.

Description

FLUID MONITORING

FIELD OF THE INVENTION

The present disclosure relates to fluid monitoring, including for example sensors, sensing systems and sensing methods for fluid monitoring. More particularly, but not exclusively, the present disclosure relates to a dielectric permittivity sensor for sensing a permittivity of a fluid, such as insulating oil of a transformer.

BACKGROUND TO THE INVENTION

In recent times, demand for electrical power has increased exponentially. A transformer typically consists of a primary coil and a secondary coil wrapped around an iron core, covered with an insulating paper, and then immersed in insulating oil. Transformers are commonly used to step-up AC voltages at a generation end, making it possible to transmit electrical power over long distances. Transformers also step-down AC voltages at the consumer end to operate low voltage devices safely. Transformers are an expensive element in a power delivery system. Unwanted power outages can cause significant damage to power distribution systems.

Transformer failure can be classified as an internal or external fault. Internal faults range from insulation deterioration, overheating, partial discharge, and increased moisture and oxygen content inside the transformer. External faults range from lighting strikes, switching transients and overloading to system faults such as short circuits, etc. Faults usually occur when a transformer experiences excessive electrical and thermal stress when operated under abnormal conditions like overloading. External weather conditions like temperature, humidity, etc., can also contribute to faults.

Mineral oil is commonly used in transformers as a coolant for heat dissipation and as an insulator that helps preserve the transformer's core and winding. Insulation oil has greater breakdown strength and thermal conductivity than gaseous insulation. It prevents oxygen contact with the cellulose-based insulating paper, which would otherwise cause oxidation. Insulation oil also provides good electrical properties like arc quenching and compatibility with the insulating paper used in transformer windings. There are two main types of mineral oils used in transformers, namely Naphtha oil and Paraffin oil. Naphtha oil is easily oxidized, and this oxidation product is soluble. It does not accumulate in the bottom of the transformer, thus not obstructing the circulation of the oil, unlike the paraffin oil, which has a lower oxidation rate but is more soluble and forms a sludge in the bottom of the transformer affecting the circulation of oil and the cooling process.

Over time different impurities develop in transformer oil like metals, insulation paper residue, moisture, and dissolved combustible gases, to name a few, which may significantly degrade oil quality leading to partial discharges and insulation failure.

Dissolved Gas Analysis (DGA) identifies dissolved gases in oil formed by the decomposition of aging and deteriorating insulating material immersed in oil due to excess heat produced. The moisture or water content concentration in transformer oil above a specific limit is undesirable. It affects the dielectric properties of oil and the insulating properties of the cellulose paper, which is hygroscopic and absorbs moisture present in the oil and reduces the actual operating life of the insulating material.

The concentration of each contaminant is conventionally calculated using a standardized process performed after a sample is extracted from a transformer and sent to a lab off-site, where it is processed. This process takes time, which affects the power delivery cycle because the transformer must be taken offline. There is also a possibility of contamination during the transition of the sample.

Several techniques may be used for transformer oil analysis which include Insulation Resistance (IR), Dielectric Loss Factor (DLF), Partial Discharges (PD), Interfacial Polarization (IP) using frequency dispersion capacitance, oil quality, moisture content, Dissolved Gas Analysis (DGA) and tensile strength of cellulosic paper and pressboard. Dissolved gas analysis may provide a good technique used in transformer oil analysis to detect abnormalities. Several failures can occur in a transformer, but a primary reason for most of these failures is associated with the evolved gasses dissolved in insulating oil, mainly during an overload condition. When a fault occurs, it may bring energy capable of breaking molecular bonds in oil; as a result, several gases may be generated and dissolved in oil as a by-product. The main gases generated may include Hydrogen (H2), Methane (CH4), Acetylene (C2H2), Ethylene (C2H4), Ethane (C2H6), Carbon monoxide (CO), and Carbon dioxide (002), depending on the type of fault. Each fault may be associated with the production of one or more of the gases mentioned above. This method of identifying fault using the production of these gasses may be referred to as the key gas method and it may serve as an indicator to diagnose the fault. This method may include measuring the percentage or amount of gas produced in terms of total combustible gases. Four major types of faults can be detected by measuring the concentration of these dissolved gasses. Carbon monoxide is mainly generated due to overheated cellulose and ethane from overheated oil, whereas hydrogen is produced with partial discharge and arcing in oil. Traces of other gases may also be produced along with the corresponding gas for each fault and may pose difficulty in interpretation.

The conventional methods used for DGA may include Gas Chromatography (GC), Photoacoustic Spectroscopy (PAS), solid-state (IC), Thermal Conductivity Detector (TCD), Non-Dispersive Infrared (NDIR), Infrared (IR), Near-Infrared (NIR), Fourier Transform Infrared (FTIR), Fuel Cell (EC), microelectronic sensor or electrochemical cell. All of the techniques mentioned above have their pros and cons. Some are expensive or have less accuracy based on the number and concentration of gases that can be accurately detected. Most of these procedures are performed in a lab off-site which is cumbersome and inefficient.

CN203800702U discloses a power transformation equipment monitoring system for monitoring gases dissolved in transformer oil, partial discharge of transformer, transformer temperature, and water content in oil. Similarly, CN2689230Y, and CN104090080A discloses an apparatus comprising of data processing unit, gas separator, and individual sensors for detecting hydrogen gas, carbon monoxide gas in oil, reducing the disadvantages caused by the manual sampling. It can take samples of transformer oil and analyze them daily for the safe operation of equipment. In contrast, a sensor is developed by Applied Nanotech Inc. (ANI) that utilizes Palladium (Pd) nanoparticles to lower the H2 partial pressure for phase transition and can detect even small concentrations of hydrogen Transformers typically experience thermal and electromechanical stresses during their operation, leading to degradation of both insulating oil and cellulose paper, resulting in insulation paper becoming less effective against mechanical stress. Meanwhile, glucose molecules in cellulose material can break down, producing water, and with increasing moisture content, the breakdown voltage of insulating oil and paper reduces, leading to insulation failure.

The standard method used for estimating degradation in cellulose material is the degree of cellulose polymerization value. This method may be used in measuring cellulose aging due to thermal stress but at the same time is not practical because a sample has to be taken from the transformer and must be removed from service. As a result of this degradation process, one more contaminants known as furanic compounds are generated, which dissolves in oil, making it detectable. The Degree of polymerization (PD) helps estimate the aging of cellulose material.

CN102103109A discloses a system for monitoring of moisture content inside a transformer. A humidity sensor, temperature sensor, a single processing unit, and a client monitoring terminal are disclosed. Similarly, an intelligent sensor-based device is proposed in CN2570789Y to monitor the moisture in transformer oil. US5343045A discloses a backscattered radiation technique to determine the absorption of light for measuring moisture content on paper insulation inside a transformer. A microprocessor-based transformer monitoring system to provide monitoring and analysis of transformer operation is disclosed in US4654806A.

These systems are complex, expensive and cumbersome. The applicant considers there to be room for improvement.

The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present disclosure there is provided a dielectric permittivity sensor for sensing permittivity of a fluid, the dielectric permittivity sensor comprising: an electrically conductive structure that has an input and an output, the structure including first and second elements that operatively extend at least partially into the fluid; a microwave transmitter which is connected to the input of the electrically conductive structure and arranged to energise it in use, so as to cause an output signal to be generated at microwave frequency; and an electromagnetic sensor which is connected and responsive to the output of the electrically conductive structure, so as to enable the permittivity of the fluid to be determined.

The dielectric permittivity sensor may be a microwave sensor.

The electrically conductive structure may be ring-shaped, or c-shaped, or u-shaped. The first and second elements of the electrically conductive structure may be first and second prongs that are curved or angled. The first and second elements may be curved or angled so as to extend towards one another to form a gap between the first and second elements.

The electrically conductive structure may be a microstrip structure. The electrically conductive structure may be a split ring or a split ring resonator.

The electrically conductive structure may, in use, be immersed in the fluid.

The dielectric permittivity sensor may further include a ground element or a ground structure. The ground structure may be electrically conductive and it may, in use, extend at least partially into the fluid, or it may at least partially be in contact with the fluid. A zone may be defined between the electrically conductive structure and the ground element. The zone may, in use, be filled by the fluid which, when occupying a volume defined by the zone, acts as a dielectric substrate. The zone may, alternatively or in addition, be defined between the first and second elements of the electrically conductive structure.

The fluid may be insulating oil of a transformer. The dielectric permittivity sensor may be arranged to sense the dielectric permittivity of insulating oil of a transformer.

The input and/or the output may be connected to a processing unit. The processing unit may be arranged to determine the dielectric permittivity of the fluid responsive to the output signal.

The dielectric permittivity sensor may be used for sensing one or more contaminants or impurities in the fluid. The dielectric permittivity sensor may be capable of generating a frequency response which is indicative of one or more contaminants or impurities in the fluid.

In accordance with another aspect of the present disclosure there is provided a calibration device for a dielectric permittivity sensor as defined above, the calibration device comprising: a moveable conductive element; and a stationary conductive element which is spaced apart from the moveable conductive element so as to define a zone which in use is filled with fluid, wherein the moveable conductive element is configured to move relative to the stationary conductive element so as to operatively vary a quantity of fluid in the zone.

The calibration device may facilitate calibration of an associated dielectric permittivity sensor.

The moveable conductive element may be rotatable, pivotable, or linearly moveable. The moveable conductive element may be rotatable or pivotable by a screw device so as to move the moveable conductive element relative to the stationary conductive element, thereby varying a volume or quantity of fluid located, in use, in the zone or volume between the moveable conductive element and the stationary conductive element.

The moveable conductive element may be moveable by way of a biasing arrangement such as a biasing spring or biasing device.

The moveable conductive element may rest upon a biasing spring or biasing device, so as to be moveable against the biasing arrangement in a first direction by virtue of a weight or pressure of fluid acting on the moveable conductive element. The biasing arrangement may be configured to urge the moveable conductive element in a second direction when the weight or pressure of fluid acting on the moveable conductive element is reduced.

The stationary conductive element may be ring shaped or disc shaped. The moveable conductive element may be ring shaped or disc shaped.

The calibration device may include a proximity sensor for sensing a location of the moveable conductive element.

In accordance with another aspect of the present disclosure there is provided a dielectric permittivity sensing system comprising: a dielectric permittivity sensor that includes: an electrically conductive structure that has an input and an output, the structure including first and second elements that operatively extend at least partially into a fluid for sensing a permittivity of the fluid; a microwave transmitter which is connected to the input of the electrically conductive structure and arranged to energise it in use, so as to cause an output signal to be generated at microwave frequency; and, an electromagnetic sensor which is connected and responsive to the output of the electrically conductive structure and capable of generating sensor data; and, a calibration device for automatically calibrating the dielectric permittivity sensor, the calibration device including a moveable conductive element and a stationary conductive element spaced apart from the moveable conductive element so as to define a zone which in use is filled with fluid, wherein the moveable conductive element is configured to move relative to the stationary conductive element so as to operatively vary a quantity of fluid in the zone, thereby facilitating calibration of the dielectric permittivity sensor; and a processing unit that is arranged to determine the permittivity of the fluid based on sensor data received from the electromagnetic sensor.

In accordance with yet another aspect of the present disclosure there is provided a dielectric permittivity sensing method comprising: providing a dielectric permittivity sensor that includes an electrically conductive structure that has an input and an output, the structure including first and second elements that operatively extend at least partially into a fluid; providing a microwave transmitter connected to the input of the electrically conductive structure; by the microwave transmitter, energising the electrically conductive structure in use and generating an output signal at microwave frequency; providing an electromagnetic sensor connected and responsive to the output of the electrically conductive structure so as to be capable of generating sensor data; providing a calibration device for automatically calibrating the dielectric permittivity sensor, the calibration device including a moveable conductive element and a stationary conductive element spaced apart from the moveable conductive element so as to define a zone which in use is filled with fluid, wherein the moveable conductive element is configured to move relative to the stationary conductive element so as to operatively vary a quantity of fluid in the zone, thereby facilitating calibration of the dielectric permittivity sensor; and by a processing unit, operatively determining the permittivity of the fluid based on the sensor data received from the electromagnetic sensor.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings: Figure 1 is a high-level block diagram of an exemplary dielectric permittivity sensing system; Figure 2 is a schematic diagram illustrating an exemplary position of the dielectric permittivity sensing system, and an exemplary connector assembly; Figure 3 is a schematic diagram that illustrates flow of fluid from exemplary standalone sensors that may be cascaded such that the output of one sensor is the input of another sensor; Figure 4 is a schematic diagram of an exemplary capacitive sensor that may be arranged to detect a change in dielectric constant of a fluid sample under test; Figure 5 is an exemplary circuit diagram of the capacitive sensor of Figure 4; Figure 6 is a schematic diagram illustrating a top view of an exemplary microwave sensor that may be arranged to detect a change in dielectric constant and dielectric losses of a fluid sample under test, Figure 7 is a schematic three-dimensional view of the exemplary microwave sensor of Figure 6, illustrating the sensor immersed in fluid; Figure 8 is a graph illustrating exemplary normalized frequency responses of the microwave sensor of Figure 6, for a pure oil or pure fluid sample and an oil sample or dielectric fluid sample that has moisture contents therein; Figure 9 is another graph illustrating exemplary normalized frequency responses of the microwave sensor of Figure 6 where dielectric losses are absent, and where a dielectric loss factor is present; Figure 10 is a schematic diagram illustrating exemplary parameters on which an operational frequency of an exemplary microstrip resonant sensor may depend, Figure 11 is a schematic diagram illustrating exemplary parameters that may be changed during calibration of the sensor; Figure 12 is a schematic diagram illustrating an exemplary sliding conductive layer, plate or strip that may be added to the sensor so as to change an operative width of the sensor; Figure 13 is a graph illustrating a normalised frequency for exemplary thicknesses of a substrate against an exemplary dimension of a conducting layer; Figure 14 is a schematic diagram illustrating an exemplary cylindrical housing for a sensor or calibration device having two conducting discs that may be used to change a thickness of a substrate between the discs; Figure 15 a schematic diagram of a calibration scale illustrating exemplary shifts in a frequency response of the sensor or calibration device of Figure 14; Figure 16 is a schematic diagram illustrating an exemplary calibration device that may be used for automatic calibration of a sensor, for example in an online monitoring system; Figure 17 is a three-dimensional view of a portion of an exemplary microwave sensor which may be coated with nanoparticles to facilitate gas sensing; Figure 18 is an exemplary flow diagram illustrating the use of first and second sensors where the first sensor may act as a reference sensor for calibration; Figure 19 is a three-dimensional view of an exemplary sensor or calibration arrangement having first and second microwave sensors that are located adjacent to one another; Figure 20 is a schematic diagram of an exemplary heating device that may be used together with a sensor, for example to facilitate calibration of moisture content sensing; and Figure 21 is a high-level flow diagram of an exemplary dielectric permittivity sensing method.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

A fluid quality sensing device, system and method are disclosed. The sensing device, system and method may be configured for detecting contaminants in a fluid being monitored. Aspects of the present disclosure may provide systems, methods and devices for fluid monitoring, for example for fluid quality monitoring. For example, aspects of the present disclosure may provide systems, methods and devices for monitoring the quality of a fluid in an apparatus over time. The monitoring may be real-time monitoring of the fluid while the apparatus is in service. In some embodiments, a dielectric permittivity sensor measures permittivity of a fluid under test, which measurements may be used to monitor the quality of the fluid. For example, changes in permittivity of the fluid may imply or indicate changes in quality of the fluid. For example, in some use cases, changes in permittivity can indicate an increase in contaminants present in the fluid.

The system may be an online system, e.g., arranged to transmit sensor data over a communication network such as the Internet. However, offline embodiments are also possible.

The system may be arranged to monitor quality or dielectric permittivity of a fluid. The fluid may be a dielectric fluid. In some embodiments, the fluid may be an insulating fluid, for example insulating oil (also termed "transformer oil"), in a transformer or other apparatus. Aspects of the present disclosure may therefore extend to sensing and monitoring various types of fluids, such as dielectric fluids, insulating fluids or the like.

The system may include a plurality of sensors and calibration devices. The sensors may be used to sense contaminants such as gas or particles in a fluid. The calibration device(s) may be used to calibrate the one or more sensors, either prior to installation to the monitored equipment (such as a transformer), or during the lifetime of the sensing system. Calibration may be performed automatically by the system, i.e., without requiring human input or intervention. In some embodiments, the calibration devices may be used for detecting changes in quality of the fluid under test.

The various sensors disclosed may be capable of generating response signals, for example a frequency response, when energised by a transmitter such as a microwave transmitter. The one or more sensors may be resonant sensors. Any one or more of the sensors may be capable of sensing dielectric permittivity of the fluid. Any one or more of the sensors may also be configured to sense moisture, or gas, or other impurities inside the fluid. The response signal from one or more of the sensors may be received by a processor and these response signals may be compared to one another by a comparing component. If one or more of the response signals or readings from the sensors exceeds a threshold, a message may be generated by the processor, which may communicate this message over a communications network such as the Internet.

The sensors may be in fluid flow communication with the monitored equipment, such as the transformer. In the case of the fluid being transformer oil, the transformer oil may for example be introduced (e.g. via pumping or other mechanism) through one or more housings of the sensing system and/or of the one or more sensors or calibration devices. One or more of the sensors may act as reference sensors, for example sensing a pure oil sample, which may then be compared to a response from another sensor which may sense oil from the transformer, e.g., for calibration. Any one or more of the sensors disclosed may be used as a standalone sensor, or in conjunction with the sensing system and method of the present disclosure.

Aspects of the present disclosure may relate to online health monitoring of a transformer and its oil quality analysis for early fault detection and estimating the operational life of the transformer. Embodiments of the system of the present disclosure may include one or more of a highly sensitive microwave sensor, a gas sensor, a temperature sensor, a pressure sensor, and a particle sensor. The system may be arranged to detect moisture content in transformer oil, a dielectric loss factor of the transformer oil, cellulose paper content, the presence or absence of metal particles, temperature inside the transformer, and pressure inside the transformer. Different low-cost and highly accurate calibration techniques are disclosed which may help to decrease noise floor, dynamic range, and wideband matching issues. The gas sensor disclosed herein may contain a sensitive layer of nanoparticle coating, which may help to detect different gasses both in dissolved and undissolved forms. Aspects of the present disclosure may enable detection and localization of faults by measuring concentration and the rate at which contaminations are produced, thereby eliminating or alleviating false alarms and enhancing the transformer's operational life. Remote monitoring may also be implemented. Aspects of the present disclosure may have applications that are not limited to transformer oil analysis and other equipment or apparatuses (such as a shunt reactor) which require fluid, such as dielectric fluid, for their operation may also be monitored.

Aspects of the present disclosure may facilitate an effort to provide a reliable and efficient electrical power distribution system. Estimation of the transformer's service life may be proportional to its insulation quality, consisting of both oil and cellulose paper. Increasing efficiency and safety may effectively save electrical service providers a lot of money and time in repairs. Aspects of the present disclosure may also protect a power distribution system from unwanted power outages. Difficulty in interpretation of traces of other gases produced by the key gas method mentioned in the background of this specification may be alleviated or improved by

the present disclosure.

In the drawings, relative dimensions may not be drawn to scale, and like reference numerals may indicate like features of the various embodiments depicted.

In Figure 1 is shown an example embodiment of a dielectric permittivity sensing system (100).

The system (100) may for example be implemented in an Internet of Things (loT) environment, so as to provide on-line monitoring or sensing. In an exemplary implementation, the system may be used to sense the quality of a fluid (such as transformer oil of an oil-filled transformer). It will be appreciated that the present embodiment may be used together with any of the other embodiments of the present disclosure, or it may implement one or more features of the other embodiments. The present disclosure may enable precautionary measures against faults associated with transformers or other equipment. This may improve safety and/or reliability of power delivery systems. Dissolved gas analysis, oil quality analysis, and analysis of the content of furfuraldehyde in oil may be performed by the system in order to estimate the health, quality or state of a transformer.

In the exemplary embodiment, the system (100) may include a sensing unit (102). The sensing unit (102) may include a first microwave sensor (104), in the present embodiment a moisture sensor, and a second microwave sensor (106), in the present embodiment a gas sensor. The sensing unit (102) may also include a temperature sensor (108), a pressure sensor (110), and an optical particle sensor (112). The system (100) may further include at least one electromagnetic transmitter (114) and at least one electromagnetic detector (116). The sensing unit (102) may be provided in a housing, and a processor (118) may be arranged to receive and process data from the sensors (104, 106, 108, 110, 112). The sensing unit may also include a memory component. The sensing unit (102) may also include electronic circuitry (120) and loT electronics (122). The dielectric permittivity system (100) may also include an interface component (136), which may contain a display (124), an antenna (126), and an alarm (128) which may optionally include a warning indicator such as a Light Emitting Diode (LED). The interface component (136) may for example be provided outside the housing so as to be usable by a user. The system (100) may further include an loT platform (130) which may have access to cloud memory or storage, or physical memory or storage. Software and mobile applications (134), as well as web services (138) may be provided. It will be appreciated that the various components of the system (100) illustrated in the block diagram of Figure 1 may connect through wired or wireless connections and may be capable of wired or wireless data communication. The permittivity sensing system according to some embodiments of the present disclosure may be capable of monitoring fluid such as oil online or over a communication network such as the Internet. Other embodiments may implement offline sensing.

Referring to Figure 2, in an exemplary embodiment (200), the housing of a sensing unit (102) may be attached to or otherwise integrated into or with a transformer (202). The housing may for example house the sensing unit (102) and/or one or more components of the system (100) illustrated in Figure 1. One or more valves, check valves, strainers, fillers, and pressure safety valves (not shown) may be provided in a connector assembly (206, 208). The connector assembly (206, 208) may enable fluid flow communication (209) of a fluid with the dielectric permittivity sensing system (100). The fluid flow communication (209) may, for example, enable a fluid sample to enter the dielectric permittivity sensing system (100) where it may be sensed by the one or more sensor(s) (e.g., 104, 106, 108, 110, 112). The antenna (126) is also shown diagrammatically in Figure 2, which may for example provide data communication between the system (100) and a remote server. In an exemplary embodiment, the display (124) may be located on or held by the housing. The transformer's coils (204) are illustrated diagrammatically in Figure 2, and the transformer may have fluid (217) therein. It will be appreciated that the present embodiment may be used together with any of the other embodiments of the present disclosure, or it may implement one or more features of the other embodiments.

Referring to Figures 1 to 3, the system (100) may include a plurality of sensing units (102), and each of these sensing units (102) may have an associated housing. Each housing may be arranged to store fluid samples for testing or sensing. In an exemplary embodiment (300), fluid may flow to and from the sensor unit (102) as shown in Figure 3. The fluid may enter through an inlet (302), and it may exit the sensing unit (102) through an outlet (304). As before, the sensing unit (102) may also include a processor (118) and a memory. In the present embodiment (300), a plurality of sensors (306, 308, 310, 312) may be used, and these may include one or more sensors such as the sensors (104, 1061, 108, 110, 112) described above with reference to Figure 1. Fluid may flow from the input (302) to the one or more sensors (306, 308, 310, 312) and through the output (304) back to the transformer or other equipment. A pump (not shown) may be provided to pump the fluid from the transformer to the one or more sensors. The sensors may be cascaded, or provided in series, e.g., so that the output of one sensor is the input of another sensor. An effect of cascading the sensors may be that the same sample is passed through all sensors in the cascade, which may in turn mean that the reference or sample under test is the same for each sensor. It will be appreciated that the order of the sensors (306, 308, 310, 312) may be changed, or the number of sensors may be changed, depending on practical considerations. In the present embodiment (300), first, second, third and fourth sensors (306, 308, 310, 312) are provided in series.

Using the combination of a temperature sensor (108), pressure sensor (110), and particle sensor (112) may enhance system performance and may enable a better estimation of any contaminants in the fluid. However, other embodiments may be provided in which one or more of the sensors are omitted, e.g., due to cost considerations. The moisture and gas sensors (104, 106) and their calibration techniques are described in more detail below.

For example in some use cases, the presence of water content above a specific limit in fluid (e.g., in oil or other dielectric fluid) may be undesirable, and the water or moisture content may be detected by measuring a change in relative permittivity or dielectric constant of the fluid. The relative permittivity of water is about 80, whereas the relative permittivity of a dielectric fluid such as oil may be significantly different from that of water. For example, the relative permittivity of transformer oil is about 2. This considerable difference in the dielectric constant or relative permittivity may efficiently be utilized to detect the presence or even a near exact amount of moisture present in the fluid. For example in some use cases, this information may be used to determine the quality of new fluid before installation into the transformer.

One example embodiment of a dielectric permittivity sensor is illustrated in Figure 4. In the example embodiment of Figure 4, the dielectric permittivity sensor is in the form of a capacitive sensor. The exemplary embodiment (400) of a capacitive sensor illustrated in Figure 4 may be used in any one or more of the embodiments of sensor systems of the present disclosure. A ground plate (412) and a potential plate (414) may be provided so as to form a capacitor, and a section (416) of the capacitor may be immersed in fluid (417) such as oil. Sensor electronics (418) may also be provided. The capacitive sensor (400) may be at least partially immersed in the fluid (417).

An associated circuit diagram is illustrated in Figure 5, showing a variable capacitor (406) which may function as the capacitive sensor, such as that described above with reference to Figure 4.

The capacitive sensor (400) may also be termed an RLC resonant tank, or a resonant capacitive sensor which may be implemented e.g., in conjunction with the system of Figure 1. The capacitive sensor (400, 406) may be arranged to detect any variation in the quality of the fluid being tested or sensed. The exemplary resonant circuit includes a resistor (R) (402), an inductor (L) (404), and a variable capacitor (C) (406). The capacitor is variable by virtue of the varying quantity and/or quality of fluid that may be present between plates thereof. An electrical potential (408) terminal may be provided, as well as a ground reference (410) terminal. In the present embodiment, the capacitive element (406) of the RLC resonator is a parallel plate capacitor which may be used as a variable capacitor. Varying a level (415) of fluid (417) between capacitor plates (412) and (414) may have an effect of shifting an associated frequency response. Varying the quality of fluid (417) may also result in a shift of the associated frequency response. An area and distance between the plates may be used to calculate the capacitance by measuring the frequency response and utilizing the relationship of capacitance with the dielectric constant (Cr) or relative permittivity. Dielectric constant or relative permittivity may be calculated with known parameters (such as the area of the plates and/or the distance between them), and when compared with standard values, it can indicate contaminants in the fluid (417). This method may provide a simple way to measure contaminants or relative permittivity of the fluid (417). It will be appreciated that the present embodiment may be used together with any of the other embodiments of the present disclosure, or it may implement one or more features of the other embodiments.

One example embodiment of a dielectric permittivity sensor is illustrated in Figure 6. The dielectric permittivity sensor may be in the form of a microwave sensor. In some embodiments, the dielectric permittivity sensor may be a Fano-based sensor, in other words, a sensor which is capable of Fano resonance. The term "Fano" may refer herein to a physical resonance phenomenon exhibited by resonant structures placed near to or proximate each other. The microwave structure disclosed may include two resonators tuned to resonate almost at the same frequency, which may in turn result in the development of Fano resonance.

The dielectric permittivity sensor may be used as a standalone sensing device, or in conjunction with the system and method or other embodiments of the present disclosure. The dielectric permittivity sensor may provide good spatial resolution and may be sensitive to a loss tangent, which may be used in identifying maximum contaminants in fluid such as insulation oil. This may alleviate problems of spatial resolution that may otherwise have been encountered. A fluid sample may cover a conducting surface of the dielectric permittivity sensor as a superstrate and substrate as will be described in more detail below.

The dielectric permittivity sensor (500) may provide high sensitivity. In this arrangement the dielectric permittivity sensor may include a split ring (502) or plate or disc. An input port (504) and an output port (506) of the sensor may be provided, as well as a gap (508). The gap (508) may for example be provided between first and second prongs (520, 522) or elements of the split ring (502). Each of the first and second prongs (520, 522) may be tuned or configured to resonate almost at the same frequency. The input port (504) may be connected to the microwave transmitter (114) (see Figure 1) through a microstrip waveguide (not shown). The output port (506) may be connected to the electromagnetic detector (116) through a microwave connector (not shown). It will be appreciated that the present embodiment may be used together with any of the other embodiments of the present disclosure, or it may implement one or more features of the other embodiments. The dielectric permittivity sensor (500) may be arranged to sense or detect moisture contents, paper particles, metal particles, and similar contaminations in the fluid, for example by enabling the processing unit (118) to receive data relating to the frequency response(s) of the fluid being sensed. Examples of these frequency responses are described in more detail below.

Data relating to the sensed contaminants may be received by the processing unit (118) and this data may optionally be transmitted to a remote server. The processing unit and/or the remote server may be arranged to determine the dielectric permittivity of the fluid responsive to the received data. The received data may include data relating to the frequency response of the sensor (500) or other sensed data, and the processing unit (118) may be arranged to process this data in order to determine the dielectric permittivity of the fluid so as to estimate or determine the level of contamination of the fluid.

The present disclosure thus extends to a dielectric permittivity sensor (500) for sensing permittivity of a fluid (e.g., 505, 217). The dielectric permittivity sensor may include an electrically conductive structure (502) that has an input (504) and an output (506). In the present embodiment, the structure includes first and second elements (520, 522) that operatively extend at least partially into the fluid (e.g., 505, 217). The microwave transmitter (114) (see Figure 1) may be connected to the input (504) of the electrically conductive structure and arranged to energise it in use, so as to cause an output signal to be generated. The output signal may preferably be generated at microwave frequency and wavelength. The electromagnetic detector or sensor (116) (see Figure 1) may be connected and responsive to the output of the electrically conductive structure (502), so as to enable the permittivity, or relative permittivity, of the fluid (e.g., 505, 217) to be determined, e.g. by the processing unit (118), or by a remote server, for example as described in greater detail below.

The dielectric permittivity sensor may be a microwave sensor. The electrically conductive structure may be ring-shaped, or c-shaped, or u-shaped. It will be appreciated that many other types of electrically conductive structures may be used, for example the electrically conductive structure of the capacitor sensor of Figure 4, or electrically conductive structures that have first and second plates or elements, as will be described with reference to e.g., Figures 11, 12, 14, 16, 17 and 19 below. The first and second elements of the electrically conductive structure could also be first and second plates that are spaced from one another, and a zone may be defined between the first and second plates. Referring again to Figure 6, the first and second elements (520, 522) of the electrically conductive structure (502) may be first and second prongs that are curved or angled. The first and second elements (520, 522) may be curved or angled so as to extend towards one another to form the gap (508) between the first and second elements. The electrically conductive structure may be a split ring. The electrically conductive structure may, in use, be immersed in the fluid (e.g., 505).

The dielectric permittivity sensor (500) may further include a ground element (507) or a ground structure. The ground structure may also be electrically conductive, and it may, in use, extend at least partially into the fluid, or adjacent thereto. The ground element (507) may, in use, be at least partially in contact with the fluid (505). A zone, having an associated volume, may be defined between the electrically conductive structure (502) and the ground element (507). The zone (or the volume defined by the zone) may, in use, be filled by the fluid (505) which, when occupying the zone or volume, may act as a dielectric substrate. The zone may, alternatively or in addition, be defined between the first and second elements (520, 522) of the electrically conductive structure (520). In use, the substrate (505) of the fluid may be located between the ground element (507) and the electrically conductive structure (502). The fluid may be insulating oil of a transformer, however, many other types of insulating fluids may be sensed by the sensor, system and method of the present disclosure.

In Figure 7 is shown a diagrammatic three-dimensional view of the exemplary dielectric permittivity sensor (500) immersed in fluid (503, 505) such as oil. The sensor may operatively be immersed in the fluid sample under test to achieve, preferably, maximum sensitivity. A superstrate (503) and substrate (505) of fluid may contribute to the sensing process, and hence maximum sensitivity may preferably be achieved. A ground terminal plate or disc (507) may also be provided. Many possible calibration strategies can be used with the sensor of the present embodiment (500).

The normalized frequency response of the dielectric permittivity sensor (500) disclosed above is illustrated in the exemplary graph (600) in Figure 8. Normalized frequency (602) is taken along the x-axis, and magnitude (604) is taken along the y-axis. A sharp Fano curve (606) with a high Q or high apex may represent the response for a pure fluid sample such as a pure oil sample.

This may also be termed a first frequency response (606). A second curve (608) may represent the response in the case of moisture contents present in the fluid sample (e.g., the response for moisture contents in an oil sample). This may be termed a second frequency response (608) which may indicate contaminants causing a change in sensed dielectric permittivity. The graph (600) shows that in the case of contamination, the resonance frequency may shift to the left in the frequency scale, representing an increase in the permittivity of the fluid sample under test. This may enable the system (100) to accurately measure or sense the permittivity of a fluid in use. The dielectric permittivity sensor (500) may be arranged to sense or detect a change in the dielectric constant or relative permittivity of the fluid or oil under test, and the system may for example generate data relating to the graph (600) in order to determine the permittivity or relative permittivity of the fluid. The dielectric permittivity sensor may be capable of generating the frequency response which may be indicative of one or more contaminants or impurities in the fluid.

Many types of contaminations may affect the dielectric loss factor of the fluid and hence can be detected through the dielectric loss factor. The dielectric permittivity sensor (500) of the present disclosure may be arranged to detect the dielectric losses. Figure 9 illustrates an exemplary graph (700) in which the normalized frequency (702) is taken along the x-axis, and magnitude (704) is taken along the y-axis for the dielectric permittivity sensor (500). In the exemplary embodiment, the Fano resonance may be represented by a first curve (706), for the case when there are no dielectric losses. This may also be termed a third frequency response (706). A second curve (708) may represent the response in the presence of the dielectric loss factor, thus enabling the system (100) to determine a change in dielectric permittivity of the fluid being tested or monitored. This fourth curve (708) may also be termed a fourth frequency response (708). It will be appreciated that further graphs may be generated for the other sensors of the system and method of the present disclosure. The system may be arranged to utilise data relating to the graphs (600, 700), or other sensed data in order to sense or estimate the permittivity or relative permittivity of the fluid.

The input (504) and/or the output (506) may be connected to the processing unit (118) which may also include a memory. The processing unit may be arranged to determine the dielectric permittivity of the fluid responsive to the output signal received from the output (506). The dielectric permittivity sensor may be used for sensing one or more contaminants or impurities in the fluid. In an example embodiment, the processing unit (118) may compare data relating to the first frequency response (606) (e.g., for a pure fluid sample) to data relating to the second frequency response (608) (e.g., for contaminated fluid having contaminants therein) to determine a difference. This determined difference may be indicative of the permittivity of the fluid (e.g. the fluid in the transformer), and the system (100) may be arranged to estimate how contaminated the fluid is based on the comparison. The processing unit (118) may alternatively, or in addition, be arranged to compare data relating to the third frequency response (706) to data relating to the fourth frequency response (708), and the system (100) may be arranged to estimate how contaminated the fluid is based on the comparison. Data relating to the various frequency response(s) may be included in the output signal generated by the relevant sensor and received by the processing unit.

Any number of dielectric permittivity sensors (500) may be implemented by the system (100), for example with one of the sensors sensing pure fluid and generating an associated response, and another one of the sensors sensing contaminated fluid (e.g., contaminated by particles, gas, moisture, etc) and generating an associated response. Alternatively, data relating to the frequency response of a pure fluid (or reference data) may be pre-stored (e.g., at a back end or remote server), and the system (100) may be arranged to compare sensed data with the pre-stored data to determine the dielectric permittivity of a fluid, e.g., in near real-time.

Referring to Figure 10, there is shown another exemplary embodiment (800) of a microstrip-based resonant sensor. The sensor (800) may include first and second conducting layers (802, 804) or plates. The first plate (802) may provide a ground plate, and the second plate (804) may provide a conduction layer. A substrate (806) of fluid (e.g., oil) may operatively be located between the plates (802, 804). In other words, the fluid (806) may, in use, be filled in a zone or volume defined between the plates (802, 804), or the zone may be occupied by fluid. The substrate may have an associated thickness (808) as indicated by the symbol (Ah). A resonance frequency of a microstrip may depend on the width of the microstrip, the thickness of the substrate, and the permittivity of the substrate. As explained with reference to the embodiment (400) of Figure 4, frequency response may be significant because it may be used by the system (100) to measure or sense the dielectric constant or permittivity of the fluid being monitored or sensed in use. The ground element or ground plate (802) may, in use, be at least partially in contact with the fluid, so as to enable a substrate of the fluid to occupy or fill the zone between the ground element (802) and the electrically conductive structure (804).

The sensor (800) of the present embodiment in Figure 10 may be used in conjunction with the system (100) of Figure 1, and it may alleviate problems that may be encountered when designing an RE front-end (transmitter and receiver) for larger bandwidths. The present disclosure may also enable reduced design complexity, and lower the associated costs of the overall system. It should be appreciated by those skilled in the art that dynamic range, noise figure, and wideband matching may be important considerations, which may normally increase system complexity. The present embodiment (800) may effectively decrease or alleviate these issues. It will be appreciated that the present embodiment may be used together with any of the other embodiments of the present disclosure, or it may implement one or more features of the other embodiments.

The sensor (800) may be tuned to any frequency, e.g., by changing at least one of the parameters described above. During a calibration process, frequency may be changed depending on the area of the plate (804) (or an area of a cavity formed between the first and second plates (802, 804)), thickness (808) of the substrate, and the dielectric constant or relative permittivity of the fluid. The dielectric constant may be fixed as it may be dependent on the type of fluid under consideration.

The thickness (808) or the area of a cavity between the plates (802, 804) may be changed or varied in order to shift the frequency in a sampling window. By keeping the frequency response in the sampling window; the sensor may not need to cover the entire frequency range.

Exemplary parameters which can be changed for tuning the sensor are illustrated in the schematic diagram of Figure 11. The area and the thickness of the substrate may be varied as illustrated in the exemplary embodiment (900). The present embodiment (900) may also include first and second plates (902, 904). The operational frequency may be varied by changing the thickness of the substrate (906) between the plates from a first level (904) to a second level (906). Alternatively, or in addition, the width of the microstrip sensor may be changed from a first width (908) to a second width (910). These exemplary changes in thickness and width parameters are illustrated by broken lines in Figure 11. The thickness of the substrate (906) may for example be changed by varying a height (Ah) between the plates. The area of the substrate (906) may for example be changed by varying a width (Aw) of the plate(s), or by varying a depth (Ad) of the plate(s). Accordingly, a volume or quantity of the substrate (906) being tested or sensed may be varied.

Referring to Figure 12, the width of the microstrip sensor may be increased or decreased by introducing an additional sliding conducting layer (1006) or third plate in the exemplary embodiment (1000) depicted. The sliding conducting layer (1006) may be configured to be moveable to reconfigure the width across the second and third (sliding) layer in use. The layer (1006) or third plate may be arranged to slide over the conducting layer or second plate (1004), which may increase the area of the substrate (1016) between the plates, and hence the frequency may be shifted to a desired range. A change in normalized resonant frequency may be implemented with a corresponding change in width (or other dimension) of the plate or microstrip.

Impedance mismatching may be alleviated by changing the height (1008, hi) of the second plate (1004) to be as close as possible to the height (1010, h2) of the third plate relative to the first plate (1002). This may inhibit height differences between the second and third plates to affect the sensor's (1000) response. The first plate (1002) may also be referred to as a ground element or ground plate.

Referring to Figure 13, there is shown a graph (1100) depicting an exemplary change in the thickness of the substrate and plotting the associated normalized frequency (1104). The frequency may shift from left to right in the graph with a decrease in the thickness of the substrate (1102). The same result may happen in the case of an increase in a dimension (e.g., width) of the conducting layer(s) or plates.

Referring to Figure 14, there is shown an exemplary embodiment (1200) of a cylindrical housing (1202) for a sensor or calibration device having two conducting discs (1204, 1206) or plates that may be used to change a thickness of a substrate between the discs. The present embodiment (1200) may provide a mechanism through which the thickness of the substrate can be changed.

A bottom disc (1204) may be rotatable or pivotable about an axis (such as an axis extending from a centre of the disc). When the disc is rotated or pivoted clockwise, a distance (1208) between the conducting discs may be decreased in the exemplary embodiment (1200). The distance (1208) between the discs may increase when the lower disc is rotated anti-clockwise. Through this mechanism, the thickness of the substrate of fluid may be increased or decreased, resulting in a frequency shift on the frequency scale. The first disc (1204) may also be referred to as a moveable conductive element, and the second disc (1206) may be referred to as a stationary conductive element. It will be appreciated that the clockwise and anti-clockwise movements and corresponding axial movements may be reversed in some embodiments.

The moveable conductive element (1204) may be rotatable, pivotable, or linearly moveable. The moveable conductive element (1204) may be rotatable by a screw device (not shown) so as to move the moveable conductive element relative to the stationary conductive element (1206), thereby changing a volume or quantity of fluid capable of filling or occupying a zone between the moveable and stationary conductive elements (1204, 1206). The screw device may be configured to move the ground plate (1204) up and down along an axis. For example, rotating a screw of the screw device in a clockwise direction may cause the ground plate (1204) to move along the vertical axis towards the stationary conductive element (1206). Similarly, rotating the screw of the screw device in an anti-clock wise direction may cause the ground plate (1204) to move along the vertical axis away the stationary conductive element (1206).

As an alternative to the screw device, a piston device or actuating rod may be used to move the moveable conductive element relative to the stationary conductive element. Either of the stationary conductive element (1204) and the moveable conductive element (1204) may also act as a ground element. The moveable and stationary conductive elements may also be termed first and second elements of the electrically conductive structure.

The present disclosure extends to a calibration device (1200) for a dielectric permittivity sensor (e.g., 500). The calibration device may include a moveable conductive element (1204), and a stationary conductive element (1206) which is spaced apart from the moveable conductive element (1204) so as to permit a fluid (1205) to be operatively located between the moveable and stationary conductive elements, or to fill or occupy the zone between them. In the present embodiment, the stationary conductive element may have a central aperture therein, enabling the fluid to flow therethrough. An inlet and an outlet for the fluid may be provided (not shown), to enable fluid flow of the fluid into and out of the housing (1202). The moveable conductive element (1204) may be configured to move relative to the stationary conductive element (1206), so as to vary one or more dimensions of the zone and consequently a quantity of fluid occupying the zone between the elements (1204, 1206). The calibration device (1200) may facilitate calibration of an associated dielectric permittivity sensor (e.g., 500).

The operation of the calibration device is described in detail below with reference to Figure 15. When fluid under test enters the sensor, the frequency detected by the sensor may shift. The shift in the frequency depends on the amount of the contamination present in the fluid (or the extent to which the fluid is contaminated). The calibration device may be configured shift the frequency back to an initial point by changing a dimension or thickness of the sensor plates (e.g., by operating the screw or sliding a third plate, etc.). For example, the extent to which the height (or thickness) needs to be changed may depend on the amount of contamination, hence the amount of the contamination can be determined.

The scale and calibration of the sensor or calibration device of the embodiment (1200) may be changed depending on practical considerations. A schematic diagram (1300) of an exemplary scale and calibration is shown in Figure 15. One complete rotation of 360° (1302) may equal a 1 GHz shift in the frequency response of the sensor (1200). A half rotation of 180° (1306) may equal a 500 MHz shift in the frequency response of the sensor (1200). A 300° (1312) rotation or pivot may equal a 83.33 MHz shift in the frequency response of the sensor (1200).

The system (100) of Figure 1 may be arranged for online monitoring or sensing, or offline monitoring or sensing. An automatic calibration device is shown in the exemplary embodiment (1400) of Figure 16. The present embodiment may include a chamber or vessel (1422) with a base (1423) on which a biasing spring (1404) may be attached. Whenever fluid flows into the chamber through an opening (1408), e.g., using a pump (1402), a first conductive plate (1410) may move along a major axis of the chamber, e.g. a substantially vertical axis of the chamber, or the first plate may move lengthwise inside the chamber (1422). A rate of fluid entering into the chamber (1422) may be proportional to a corresponding deflection of the spring (1404) (e.g., depending on an associated spring constant) and the rate of fluid flow may be controlled through the pump (1402) such that the ingress of fluid urges the plate (1410) along the axis against the bias of the spring. The cylinder or chamber (1422) may include at least one inlet (1408) and at least one outlet (1412). The biasing spring (1404) may facilitate the first plate (1410), which may also be termed a ground plate to move back to its initial position after testing. The present embodiment (1400) may also include a stationary conductive element (1418), which may for example be ring shaped, so as to enable fluid to flow through a central aperture thereof. As discussed above, the movement of the disc or plate (1410) may be utilized to find a corresponding frequency shift. For example, data relating to a frequency response of each the conductive elements or plates (1410, 1418) may be received by the processing unit (118), and this data may be utilised to determine the permittivity of the fluid (1405). Each of the conductive elements (1410, 1418) may be electrically connected to the processing unit (118). One or more microwave transmitter(s) may be used to energize each of the elements (1410, 1418). One or more electromagnetic detector(s) may be used to read a frequency response of each of the elements (1410, 1418). The frequency response(s) may be received by the processing unit (118). A proximity sensor (1414) may be arranged to measure or sense a change in a height (1420) of the ground plate (1410) above the base (1423). The sensed height may be used by the system (100) to determine a deflection, compression, or corresponding movement of the spring (1404), which may be indicative of the pressure or quantity of fluid (1405) e.g., between the plates (1410, 1418). It will be appreciated that various types of sensors may be used instead of the proximity sensor (1414), for example a pressure sensor for measuring a pressure in the fluid (1405). This change in height (1420) may also be measured by the system (100) through a flow sensor (1427) which may be arranged to measure a flow rate of the fluid.

The embodiment of Figure 16 may thus include a moveable conductive element (1410), which may be moveable by way of the biasing arrangement such as the biasing spring (1404). It will be appreciated that another type of biasing arrangement may be used instead of the spring. The present embodiment (1400) may also include the stationary conductive element (1418), which may for example be ring shaped. The moveable conductive element (1410) may rest upon the biasing spring (1404), so as to be moveable against the biasing arrangement in a first direction by virtue of a weight or pressure of fluid (1405) acting on the moveable conductive element. The biasing arrangement (1404) may be configured to urge the moveable conductive element (1410) in a second direction when the weight or pressure of fluid (1405) acting on the moveable conductive element (1410) is reduced, e.g., if the flow rate is reduced, or if the pressure in the fluid is reduced. The second direction may for example be opposite to the first direction. The stationary conductive element (1418) may be ring shaped or disc shaped. The moveable conductive element (1410) may be ring shaped or disc shaped. Either or both of the moveable and stationary conductive elements may be conductive plates or elements that are exposed to the fluid, or at least partially immersed therein. The calibration device (1400) may include a proximity sensor (1414) for sensing a location of the moveable conductive element (1410).

A housing (1406) of the sensor or calibration device (1400) may be cylindrical. The housing (1406) may house the moveable conducting disc (1410), which may, in the present embodiment, move up and down substantially vertically and it may change the thickness of a substrate of fluid (1405) between the discs (1418, 1410). The housing (1202) may include at least one fluid inlet and at least one fluid outlet (1408, 1412). The spring (1404) may be attached at the bottom of the moveable disc (1410), and it may help to restore an initial position of the moveable disc (1410).

The proximity sensor (1414) or the flow sensor (1427) may be arranged to detect a change in the position of the moveable disc (1410). The sensor or calibration device (1400) may include a static ring resonator (1418) which may be arranged to sense the quality of the fluid (1405) (e.g., oil) being tested or sensed. The device may function as a calibration device or as a sensing device. Calibration may for example be achieved by changing a position of the moveable disc (1410), thereby varying a quantity of fluid (1405) which is operatively occupying a zone between the moveable plate or disc (1410) and the stationary plate or disc (1418).

It will be appreciated that many types of contaminants may affect the permittivity of the fluid, e.g. inside a transformer. Another type of contamination that may affect the transformer's "health" or the quality of the fluid inside the transformer is the presence of gas or gases produced as a by-product. The gases may be in a dissolved or undissolved form. Different techniques for measuring the presence or absence of gas may be possible. Each technique may provide advantages.

Nanoparticles that change their characteristics due to interaction with the gases may be used to detect the gases. A nanoparticle coating may for example be used to achieve high sensitivity and accuracy. It will be appreciated that a specific type of nano-material may be suitable for detection of a specific gas. The coated material may react with a gas being tested or sensed, and this may change the resonance frequency, indicating the presence of contaminants or gas(es) in the fluid (e.g., oil). The microwave sensor (500) described above with reference to Figures 6 and 7, or any of the other dielectric permittivity sensor(s) or calibration device(s) of the present disclosure may be implemented with a suitable nanoparticle coating, so as to additionally enable gas sensing, e.g., in conjunction with the system (100) of Figure 1. An exemplary embodiment (1500) of a microwave sensor (1504) such as a Fano sensor with a coat of suitable nanoparticle (1502) on its surface is shown in Figure 17. The nanoparticle (1502) coating may be arranged to react with a gas in the fluid being tested (whether the gas is in dissolved form or not). It will be appreciated that the sensor (1504) illustrated in Figure 17 may be representative of a portion of the (502) split ring or plate or disc, as the case may be. The same microwave sensor may be used for detecting moisture content, gasses, metallic particles or filings, and degraded insulating material like cellulose paper, to name a few. The nanoparticle coating (1502) may provide gas sensing. It will be appreciated that any one or more of the sensors of the present disclosure may implement nanoparficles on one or more plate(s) or disc(s) or split ring(s), e.g., to facilitate gas sensing. There are multiple advantages of using a gas sensor of the same kind as the moisture sensor. A few are discussed below.

Using similar sensors may facilitate detection and calibration, as shown in the exemplary embodiment (1600) in Figure 18. First and second sensors (1602, 1604) may be implemented, and the first sensor (1602) may act as a reference sensor for calibration. The first sensor (1602) may be a sensor without the nanoparticle coating, e.g., functioning as a reference sensor. The second sensor (1604) may also be used as a second check and it may improve the system's (100) overall accuracy. A flow conduit (1608) may be provided to enable fluid flow between the first and second sensors (1602, 1604). A fluid sample (1606) (e.g., a sample of oil) may enter into both sensors (1602) and (1604). Under normal conditions, the frequency response of the first and second sensors (1602, 1604) may be the same as the fluid may, for example, not contain any gases that react to the first sensor (1602). However, in the presence of a gas, the frequency response of the second sensor (1604) with its nanoparticle coating may change. This change may be detected through the frequency response by processing unit (1610) (which may for example be implemented as a Digital Signal Processing unit). In other words, the system (100) may implement a comparing component for comparing the frequency responses of the first and second sensors, so as to sense the presence of gas or other contaminants in the fluid. This may enable the system to be self-calibrated or automatically calibrated, e.g., for the case of gas sensing. Hence, the gas sensor (1604) may be arranged to detect the presence of a gas inside the fluid without requiring manual calibration. The first sensor (1602) may for example be a moisture detection sensor, and the second sensor (1604) may be a gas detection sensor. In other words, the microwave sensor for moisture detection (1602) can be used to calibrate the gas sensor (1604).

Referring to Figure 19, there is shown an exemplary sensor or calibration arrangement having first and second microwave sensors (1702, 1704) that are located adjacent to one another. This embodiment (1700) may provide a joint calibration technique. Two Fano-based sensors, similar to the split ring sensor (500) described above may be provided, and the two split ring sensors (1702, 1704) may be placed side by side or adjacent to one another facing away from one another. A plurality of openings (1706) may be provided in a body of the sensor arrangement to facilitate the flow of fluid (e.g., oil) inside a chamber or interior of the sensor.

The combination of first and second sensors (1702, 1704) may be arranged to detect the presence of gas(es), but their response against moisture content, cellulose paper residue, etc., may be the same or similar. In the present embodiment, a pure fluid sample (e.g., a pure oil sample) may be used for the first sensor which may act as a reference sensor (1702). In such an embodiment the flow of fluid may for example not extend from the first sensor to the second sensor, and an associated fluid conduit may only extend from the transformer or other equipment to the second sensor (1704) and back into the transformer. Each of the first and second sensors (1702, 1704) may have their associated housing (1712, 1714). In a first housing (1712) of the first sensor (1702) the pure fluid sample may be located, and the sample under test (e.g., oil from the transformer or other equipment) may be located in a second housing (1714) of the second sensor (1704), or it may flow therethrough. This configuration of sensors may be arranged to perform a benchmark between pure fluid and contaminated fluid and can also be implemented with liquids used in any equipment. The pure fluid may be filled into the reference sensor's housing, e.g. prior to testing or calibration.

In some embodiments, the calibration device or reference sensor may form part of a system installed onto the transformer. The reference sensor (1702) or calibration device may be used together with the other sensor (1704) in practice. In other words, a pure fluid sample may be filled inside the reference sensor for automatic calibration and contaminated fluid may be received from the apparatus in question for the other sensor continuously during the lifetime of the system for ongoing monitoring of the fluid.

Water content sensor calibration may be facilitated by introducing a heating device (1804), as shown in the exemplary embodiment (1800) in Figure 20. The heating device (1804) may be attached to the Fano sensor (1802) or microwave sensor, or to another sensor of the present disclosure. The reason for introducing a heating device is that the dielectric constant or relative permittivity of pure fluid (e.g., the relative permittivity of pure oil) may be less dependent on temperature variation. On the other hand, the dielectric constant or relative permittivity of water or moisture content may be highly temperature dependent. In other words, sensing at different temperatures may enable the system (100) to determine the presence or absence of water content in the fluid sample being tested. This may provide a sensing system which is space efficient (i.e., which is not bulky) and it may alleviate the need for multiple sensors for sensing gas as well as moisture or water content in the fluid. A single sensor may be implemented with the heating device, in order to sense both gas contents and moisture contents in the fluid.

Referring to Figure 21, there is shown a high-level flow diagram of an exemplary dielectric permittivity sensing method (1900) according to aspects of the present disclosure. The method (1900) may include providing (1910) a dielectric permittivity sensor that includes an electrically conductive structure that has an input and an output, the structure including first and second elements that operatively extend at least partially into a fluid. The method may further include providing (1912) a microwave transmitter connected to the input of the electrically conductive structure. The method may include, by the microwave transmitter, energising (1914) the electrically conductive structure in use and generating an output signal. The output signal may preferably be generated at microwave frequency and wavelength. The method may include providing (1916) an electromagnetic sensor connected and responsive to the output of the electrically conductive structure so as to be capable of generating sensor data. The method may include providing (1918) a calibration device for automatically calibrating the dielectric permittivity sensor, the calibration device including a moveable conductive element and a stationary conductive element spaced apart from the moveable conductive element so as to define a zone which in use may be filled with fluid, wherein the moveable conductive element is configured to move relative to the stationary conductive element so as to operatively vary a quantity of fluid in the zone, thereby facilitating calibration of the dielectric permittivity sensor. The method may further include, by a processing unit, operatively determining (1920) the permittivity of the fluid based on the sensor data received from the electromagnetic sensor.

The present disclosure extends to a dielectric permittivity sensing system (100). The system may include any one or more of the sensors or devices disclosed herein. The system (100) may include a dielectric permittivity sensor (500) that includes an electrically conductive structure (502) that has an input (504) and an output (506). The structure (502) may include first and second elements (520, 522) that operatively extend at least partially into the fluid (e.g. 505, 217, 1205, 1405) for sensing a permittivity of the fluid in use. The system (100) may further include a microwave transmitter (114) which may be connected to the input (504) of the electrically conductive structure (502) and arranged to energise it in use, so as to cause an output signal to be generated. The output signal may preferably be generated at microwave frequency and wavelength. The system (100) may further include an electromagnetic sensor (116) which may be connected and responsive to the output (506) of the electrically conductive structure (502) and capable of generating sensor data. The system may further include a calibration device (e.g., 900, 1000, 1200, 1400, 1600, 1700) for automatically calibrating the dielectric permittivity sensor (500). The calibration device may include a moveable conductive element (e.g., 904, 1006, 1204, 1410) and a stationary conductive element (e.g., 902, 1002, 1206, 1418) spaced apart from the moveable conductive element so as to define a zone which in use may be filled with fluid (e.g., 217, 505, 1205, 1405). The moveable conductive element may be configured to move relative to the stationary conductive element so as to operatively vary a quantity of fluid (e.g., 217, 505, 1205, 1405) in the zone, thereby facilitating calibration of the dielectric permittivity sensor (e.g., 500).

The system (100) may further include a processing unit (118) that may be arranged to determine the permittivity of the fluid (e.g., 217, 505, 1205, 1405) based on sensor data received from the electromagnetic sensor (116).

It will be appreciated that any of the other sensors of the present disclosure (e.g., 800, 900, 1000, 1200, 1400, 1500, 1600, 1700, 1800 discussed herein) may also include one or more features of the microwave sensor (500), such as an input and an output (e.g. connected to the processing unit), as well as the first and second electrically conductive elements that extend at least partially into the fluid in use.

Referring again to Figure 1, the present disclosure extends to an online fluid quality monitoring device or system (100) that includes a microwave sensor (100, 500) configured to monitor moisture and similar contaminants in the fluid (e.g., inside insulating oil of the transformer). The microwave sensor may be highly sensitive. The fluid quality monitoring system (100) may further include a gas sensor (106) configured to monitor gas contaminants in the fluid. The gas sensor may be highly sensitive. The fluid quality monitoring system (100) may include an optical particle sensor (112) configured to monitor contaminant particles inside the fluid. The fluid quality monitoring system (100) may further include a temperature sensor (108) which may be configured to monitor the temperature of the fluid inside the transformer. The fluid quality monitoring system (100) may further include a pressure sensor (110) which may be configured to monitor pressure inside the transformer. The fluid quality monitoring system (100) may further include a control module (118) configured to control sensors (e.g., 104, 106, 108, 110, 112).

The fluid quality monitoring system (100) may further include an electromagnetic source generator (114) and an electromagnetic detector (116). The system (100) may further include loT electronics (122) to send data to an loT platform, and an antenna (126) to send data to a gateway or remote server. The system (100) may further include a display (124), e.g., attached outside a housing of the system. The display may be configured to show data of the sensors. The system may further include an alarm (128) and at least one LED configured to switch on if the reading of at least one sensor deviates outside a predefined level, or exceeds a predefined threshold. The processing unit (118) may also be configured to generate an alarm signal which may be transmitted over an loT network or over another communications network, e.g., to the remote server. The system may be used for online sensing, or it may be used for offline sensing. The system may also be used to monitor any equipment which requires fluid, such as dielectric or other compatible fluid for operation. The microwave sensor may include a microstrip structure. The microstrip structure may for example be a split ring resonator. The microwave sensor may exhibit Fano resonance. The asymmetric high Q curve response (e.g., Figure 8) may be suitable for achieving high selectivity and spatial resolution.

The microwave sensor (e.g., 500) may have two ports (e.g. 504, 506), one (504) to receive the electromagnetic signal from the transmitter (114) and the second (506) to send a generated signal to the electromagnetic detector (116). Embodiments are possible in which the detector (116) and transmitter (114) may be tuned to the same frequency. The split-ring resonator (500) may provide a Fano resonance with a high-Q factor suitable for sensing. The microwave sensor (500) may enable the superstrate (503) and substrate (505) of a fluid sample to be tested or sensed. In use, the microstrip ring resonator may be entirely submerged within the fluid such as oil. The microwave sensor (500) may have a housing (e.g., made from plastic, metal or another rigid material), which allows the fluid to fill the cavity and to be sensed by the microwave sensor. The microwave sensor (500) may be used as a gas sensor. The microwave sensor (500) may include a nanoparticle coating, e.g., so as to provide gas sensing capabilities. The gas sensor (500) may be arranged, depending on the nanoparticle coating, to detect multiple gases in both dissolved and undissolved forms in the fluid. The gas sensor (106, 500) may also be connected to the detector (116) and transmitter (114). The same detector (116) and transmitter (114) may be used for a microwave moisture sensor (104) and the gas sensor (106). The gas sensor (106, 500) may also have an input port connected to the transmitter (114) and an output port which is connected to the detector (116). The system (100) may be arranged such that the microwave sensor (104) may also be a reference sensor for the gas sensor (106) (e.g., as described with reference to Figure 18). The optical particle sensor (112) may be arranged to detect contamination particles like tiny particles of metals and cellulose paper particles in the fluid. Data relating to the detected particles may also be received by the processing unit and/or relayed to a remote server over a communications network such as loT.

The system (100) may further provide a calibration mechanism for a microwave moisture sensor, e.g., by implementing a heating device (e.g., 1804) to increase the temperature of the fluid sample under test, and the temperature sensor (108) may be arranged to detect the temperature of the fluid under test. The heating device (1804) and temperature sensor (108) may be arranged so as to provide a feedback loop in order to control the speed or operation of the heating device. The system (100) may provide a calibration mechanism in which the dielectric constant or dielectric relative permittivity of the fluid at different temperatures may be used to detect moisture content in the fluid. The fluid quality monitoring device or system (100) may include a communication arrangement (e.g., 122) configured to communicate one or more readings from the device or sensors to a remote recipient via a telecommunications network. The remote recipient may for example be a cloud-based computer system configured to store one or more readings and, in response to the one or more readings triggering a reporting threshold, a reporting message may be sent to a designated recipient with details or data relating to the one or more readings.

The foregoing description has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the

above disclosure.

The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.

Finally, throughout the specification and accompanying claims, unless the context requires otherwise, the word 'comprise' or variations such as 'comprises' or 'comprising' will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

CLAIMS: 1. A dielectric permittivity sensor for sensing permittivity of a fluid, the dielectric permittivity sensor comprising: an electrically conductive structure that has an input and an output, the structure including first and second elements that operatively extend at least partially into the fluid; a microwave transmitter which is connected to the input of the electrically conductive structure and arranged to energise it in use, so as to cause an output signal to be generated at microwave frequency; and an electromagnetic sensor which is connected and responsive to the output of the electrically conductive structure, so as to enable the permittivity of the fluid to be determined.
2. The dielectric permittivity sensor as claimed in claim 1, wherein the dielectric permittivity sensor is a microwave sensor.
The dielectric permittivity sensor as claimed in claim 1 or claim 2, wherein the electrically conductive structure is ring-shaped, c-shaped, or u-shaped.
4. The dielectric permittivity sensor as claimed in any one of the preceding claims, wherein the first and second elements of the electrically conductive structure are first and second prongs that are curved or angled so as to extend towards one another to form a gap between the first and second elements.
5. The dielectric permittivity sensor as claimed in any one of the preceding claims, wherein the dielectric permittivity sensor further includes a ground element which, in use, is at least partially in contact with the fluid, so as to define a zone between the electrically conductive structure and the ground element, and wherein the zone is arranged, in use, to be filled with the fluid to act as a dielectric substrate.
The dielectric permittivity sensor as claimed in any one of the preceding claims, wherein the input and the output are connected to a processing unit which is arranged to determine the dielectric permittivity of the fluid responsive to the output signal.
7. The dielectric permittivity sensor as claimed in any one of the preceding claims, wherein the dielectric permittivity sensor is capable of generating a frequency response which is indicative of one or more contaminants or impurities in the fluid.
8. A calibration device for a dielectric permittivity sensor as claimed in any one of the preceding claims, the calibration device comprising: a moveable conductive element; and a stationary conductive element which is spaced apart from the moveable conductive element so as to define a zone which in use is filled with a fluid, wherein the moveable conductive element is configured to move relative to the stationary conductive element so as to operatively vary a quantity of fluid in the zone.
The calibration device as claimed in claim 8, wherein the moveable conductive element is rotatable.
The calibration device as claimed in claim 9, wherein the moveable conductive element is rotatable by a screw device so as to move the moveable conductive element relative to the stationary conductive element, thereby varying the quantity of fluid located, in use, in the zone between the moveable conductive element and the stationary conductive element.
The calibration device as claimed in any one of claims 8 to 10, wherein the moveable conductive element is moveable by way of a biasing arrangement.
The calibration device as claimed in claim 11, wherein the biasing arrangement is provided by a biasing spring, and wherein the moveable conductive element rests upon the biasing spring, so as to be moveable against the biasing spring in a first direction by virtue of a weight or pressure of fluid acting on the moveable conductive element.
The calibration device as claimed in any one of claims 8 to 12, wherein the calibration device includes a proximity sensor for sensing a location of the moveable conductive element.
A dielectric permittivity sensing system comprising: a dielectric permittivity sensor that includes: an electrically conductive structure that has an input and an output, the structure including first and second elements that operatively extend at least partially into a fluid for sensing a permittivity of the fluid; a microwave transmitter which is connected to the input of the electrically conductive structure and arranged to energise it in use, so as to cause an output 9. 10. 11. 12. 13. 14.signal to be generated at microwave frequency; and, an electromagnetic sensor which is connected and responsive to the output of the electrically conductive structure and capable of generating sensor data; and, a calibration device for automatically calibrating the dielectric permittivity sensor, the calibration device including a moveable conductive element and a stationary conductive element spaced apart from the moveable conductive element so as to define a zone which in use is filled with fluid, wherein the moveable conductive element is configured to move relative to the stationary conductive element so as to operatively vary a quantity of fluid in the zone, thereby facilitating calibration of the dielectric permittivity sensor; and a processing unit that is arranged to determine the permittivity of the fluid based on sensor data received from the electromagnetic sensor.
15. A dielectric permittivity sensing method comprising: providing a dielectric permittivity sensor that includes an electrically conductive structure that has an input and an output, the structure including first and second elements that operatively extend at least partially into a fluid; providing a microwave transmitter connected to the input of the electrically conductive structure; by the microwave transmitter, energising the electrically conductive structure in use and generating an output signal at microwave frequency; providing an electromagnetic sensor connected and responsive to the output of the electrically conductive structure so as to be capable of generating sensor data; providing a calibration device for automatically calibrating the dielectric permittivity sensor, the calibration device including a moveable conductive element and a stationary conductive element spaced apart from the moveable conductive element so as to define a zone which in use is filled with fluid, wherein the moveable conductive element is configured to move relative to the stationary conductive element so as to operatively vary a quantity of fluid in the zone, thereby facilitating calibration of the dielectric permittivity sensor; and by a processing unit, operatively determining the permittivity of the fluid based on the sensor data received from the electromagnetic sensor.