Oil level alarm sensor and method of using same

Abstract

Apparatus and methods for determining if fluid contained within a housing is leaking. A level sensor is provided for determining a measured level of fluid within the housing. A reference sensor is provided for determining a reference parameter that can be used to provide a predicted level of fluid within the housing. The measured level of fluid is compared with the predicted level of fluid to determine if it is likely fluid is leaking from the housing.

Description

OIL LEVEL ALARM SENSOR AND METHOD OF USING SAMECROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to, and the benefit of, United States provisional patent application No. 63 / 688268 filed 28 August 2024 entitled OIL LEVEL ALARM SENSOR AND METHOD OF USING SAME, the entirety of which is incorporated by reference herein for all purposes.TECHNICAL FIELD

[0002] Some embodiments relate to sensors for determining a level of a fluid contained within a housing. Some embodiments relate to sensors for signaling that a level of fluid contained within a housing is outside a target range. Some embodiments relate to methods of determining when a level of a fluid contained within a housing has moved outside a target range. Some embodiments relate to methods of providing a signal that a level of fluid contained within a housing has moved outside a target range. Some embodiments provide a method of determining when fluid contained within a housing is leaking or otherwise being lost.BACKGROUND

[0003] Electrical equipment such as transformers are generally filled with an insulating dielectric fluid such as transformer oil. The transformer oil both electrically insulates and helps to cool the windings of the transformer. Examples of fluids that are frequently used in transformers include mineral oil, ester or vegetable oil, fluorocarbon-based oil, silicone-based compounds, or other insulating gases.

[0004] Natural fluctuations in operating conditions, for example changes in ambient temperature, variations in electric load, or the like will cause changes in a level of the insulating dielectric fluid within the transformer. However, abnormal operating conditions such as degradation or failure of components within the transformer, or leakage or loss of the insulating dielectric fluid out of the transformer, for example due to corrosion of the transformer, can lead to changes inthe level of the insulating dielectric fluid. Loss of the insulating dielectric fluid from the transformer can be difficult to observe visually, and also increases the risk of arcing occurring within the transformer which may result in severe damage or destruction of the transformer and an outage to utility customers. This also presents a safety risk to members of the general public and employees of the utility who may come in proximity with the transformer. Release of the insulating dielectric fluid from the transformer also presents an environmental issue.

[0005] It is important that utilities be promptly notified of such undesirable changes in the level of the insulating dielectric fluid within any particular transformer, while avoiding the inconvenience associated with false positive notifications, for example as may occur due to expected fluctuations in the level of the insulating dielectric fluid within normal operating parameters, particularly fluctuations in temperature. Prompt notification can help to ensure for example that damage to the transformer is repaired at an early stage before more serious damage occurs, equipment is not operated for long periods under conditions that are likely to stress or thermally overload and therefore damage the equipment, or that any leaks in the transformer are repaired before they become catastrophic and / or before any significant amount of fluid has leaked from the transformer.

[0006] There is a need for apparatus and methods capable of determining when an undesirable change in the level of the insulating dielectric fluid within a transformer or other oil-filled electrical equipment has occurred, and there is further a need for such apparatus and methods capable of notifying a utility promptly when such a change has occurred.SUMMARY

[0007] In one aspect, apparatus for determining if fluid contained within a housing is leaking is provided. The apparatus has a level sensor that can be used to determine a measured level of the fluid within the housing, and a reference sensor that can be used to determine a reference parameter that can be used to provide a predicted level of fluid within the housing. The level sensor can be a vertically extending array of individual sensors. The apparatus can have a communication module to transmit data from the level sensor and data from thereference sensor to a central processor for processing, and / or the apparatus can have an on-board processor for processing data from the level sensor and data from the reference sensor. The central processor and / or the on-board processor can be configured to determine the measured level of the fluid within the housing using data from the level sensor and configured to determine the predicted level of the fluid within the housing using data from the reference sensor, and the central processor and / or the on-board processor can be configured to provide a leak indication if the measured level of the fluid within the housing is determined to be below the predicted level of the fluid within the housing. In some aspects, the apparatus has an on-board signal generation unit for generating a perceptible signal responsive to the leak indication, to provide a perceptible signal that a leak is occurring. In some aspects, the communication module transmits the leak indication by wired or wireless means to a central monitoring location. In some embodiments, the central processor generates an electronic or perceptible signal that a leak indication has been received or has been determined to have occurred by the central processor.

[0008] In some aspects, the level sensor is provided by a vertically extending array of individual sensors. In some aspects, at least two or at least three individual sensors are provided in the vertically extending array. In some aspects, one of the individual sensors also acts as the reference sensor. In some aspects, the level sensor is a plurality of temperature sensors, one or more capacitance sensors, one or more ultrasonic transducers, one or more thermographic sensors, a float, an oil sight gauge, or one or more static pressure sensors.

[0009] In some aspects, the reference sensor is a temperature sensor positioned to measure a temperature of the fluid within the housing, a non-invasive temperature sensor positioned to estimate a temperature of the fluid within the housing, or a sensor for measuring a parameter reflecting an electrical load passing through a transformer contained within the housing. In some aspects, more than one reference sensor is used, and a reference sensor may also be provided to measure ambient temperature, wind speed, solar irradiation, and / or incident precipitation to help provide the predicted level of fluid within the housing.

[0010] In some aspects, a system is provided that includes an apparatus as described herein as well as a central processor for remotely comparing the measured level of the fluid within the housing with the predicted level of fluid within the housing, the central processor further being configured to provide a leak indication if the measured level of the fluid within the housing is determined to be below the predicted level of the fluid within the housing. In some aspects, the central processor processes data received from the level sensor and the reference sensor to determine the measured level and the predicted level of the fluid within the housing.

[0011] In some aspects, a method of determining if fluid contained within a housing is leaking is provided. A level sensor is used to determine a level of fluid within the housing to provide a measured fluid level. A reference sensor is used to determine a reference parameter, and the reference parameter is used to provide a predicted level of fluid within the housing. The measured fluid level is compared with the predicted fluid level, and if it is determined that the measured fluid level is below the predicted fluid level, it is concluded that fluid is likely leaking from the housing. In some aspects, the level sensor is provided by a vertically extending array of individual sensors and the measured fluid level is determined by determining which ones of the vertically extending array of individual sensors are positioned below a surface of the fluid and which ones of the vertically extending array of individual sensors are positioned above a surface of the fluid and concluding that the surface of the fluid is above the individual sensors positioned below the surface of the fluid and below the individual sensors positioned above the surface of the fluid. In some aspects, the level sensor is provided by a vertically extending array of individual temperature sensors, and determining the measured fluid level includes determining a temperature gradient of the fluid within the housing and using the temperature gradient to estimate the location of the surface of the fluid within the housing. In some aspects, one of the individual sensors is also used as the reference sensor. In some aspects, the reference parameter is a temperature of the fluid within the housing, and the temperature of the fluid is directly measured, is estimated using a non-invasive method of measuring internal fluid temperature, or is estimated based on a measure of an electrical load passingthrough the housing. In some aspects, multiple parameters are used as the reference parameter, and in some aspects, the temperature of the fluid within the housing is further estimated taking into account ambient temperature, wind speed, solar irradiation and / or incident precipitation.

[0012] Further aspects and embodiments will become apparent with reference to the following description, which is illustrative and not limiting in nature.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 shows schematically an example embodiment of an apparatus for determining if fluid is leaking from a housing.

[0014] FIG. 2 shows schematically a second example embodiment of an apparatus for determining if fluid is leaking from a housing.

[0015] FIG. 3 shows schematically a third example embodiment of an apparatus for estimating a level of a fluid contained within a housing.

[0016] FIG. 4 shows the apparatus of FIG. 3 but with a lower fluid level in the housing.

[0017] FIG. 5 shows a fourth example embodiment of a device for determining if fluid is leaking from a housing and the mounting of the device on the outside surface of the housing containing the fluid using temperature sensors to determine the level of the fluid within the housing.

[0018] FIG. 6 shows a front view of the device of FIG. 5 showing the array of temperature sensors positioned thereon.

[0019] FIGs. 7A and 7B show a fifth example embodiment of a device for determining if fluid is leaking from a housing using a capacitance sensor to determine a level of fluid within the housing.

[0020] FIG. 8 shows a sixth example embodiment of a device for determining if fluid is leaking from a housing using an infrared camera to determine a level of fluid within the housing.

[0021] FIG. 9A shows a seventh example embodiment of a device for determining if fluid is leaking from a housing using a pressure sensor to determine a level of fluid within the housing, and FIG. 9B shows an example implementation of such an embodiment.

[0022] FIG. 10 shows an eight example embodiment of a device for determining if fluid is leaking from a housing using an oil sight gauge to measure a level of fluid within the housing.

[0023] FIG. 11 is an example embodiment of a method for determining whether fluid has leaked from a housing containing the fluid.

[0024] FIG. 12A is a second embodiment of a method for determining whether fluid has leaked from a housing containing the fluid.

[0025] FIG. 12B is a third example embodiment of a method for determining whether fluid has leaked from a housing containing the fluid.

[0026] FIG. 13 shows results for an array of temperature sensors measuring fluid at a temperature of 60°C within a housing as a level of oil within the housing is decreased. FIG. 14 shows the corresponding positions of the temperature sensors relative to each one of the levels to which the surface of the oil was decreased.

[0027] FIG. 15 shows results for an array of temperature sensors measuring fluid at a temperature of 90°C within a housing as a level of oil within the housing is decreased. FIG. 16 shows the corresponding positions of the temperature sensors relative to each one of the levels to which the surface of the oil was decreased.

[0028] FIG. 17 shows the position of temperature sensors relative to an oil level in an example embodiment in which the temperature sensors were mounted on the outside of the housing for testing.

[0029] FIG. 18 shows temperatures measured by a plurality of temperature sensors mounted on the outside of a housing containing transformer oil at a temperature of 42°C, and FIG. 19 shows temperatures measured by a plurality of temperature sensors mounted on the outside of a housing containing transformer oil at a temperature of 32°C.

[0030] FIG. 20 shows capacitance measured at varying oil levels using cold oil, and FIGs. 21 and 22 show capacitance measured at varying oil levels using oil at 60°C and 90°C, respectively.

[0031] FIG. 23 shows the results of experiments using an FLIR. camera to determine a level of fluid within the housing at a plurality of different fluid temperatures.

[0032] FIG. 24 shows the result of a representative experiment using a static pressure sensor to determine a level of fluid within the housing.

[0033] FIG. 25 shows the changes in pressure with changes in temperature when using a static pressure sensor to determine a level of fluid within a housing.DESCRIPTION

[0034] The following description contains details which are illustrative and not limiting in nature.

[0035] As used herein, the term "determining" a parameter such as fluid level or temperature includes using an appropriate sensor to measure such parameter, or using suitable measurements to estimate that parameter.

[0036] In various embodiments, the apparatus and methods described herein can be applied to any desired system. In some embodiments, the apparatus and methods described herein are applied to a piece of electrical equipment, including a transformer including power transformer, a distribution transformer, a pole-mounted transformer, a pad-mounted transformer, or the like.

[0037] With reference to FIG. 1, an example embodiment of an apparatus 10 for determining if fluid is leaking from a housing is illustrated. A housing 12, for example a housing of a piece of electrical equipment such as a transformer, contains a fluid 14, such as a dielectric insulating fluid used in a transformer. Fluid 14 is filled to a fluid level 16 (illustrated as 16A, 16B and 16C as described below and collectively referred to as fluid level 16) within the housing 12, and air or other compressible material is provided in the headspace 18 of housing 12. The presence of air in headspace 18 allows fluid 14 to expand and contract depending on the temperature of the fluid 14. Expansion and contraction of fluid 14 will cause the fluid level 16 to move up and down within housing 14 in the vertical direction 20. This is represented in FIG. 1 as a plurality of different fluid levels 16A, 16B, 16C at a plurality of different vertical elevations within housing 12.

[0038] Apparatus 10 is provided with a vertically extending array of 50 of sensors 52, which can be used as a level sensor to determine or estimate the fluid level 16 of fluid 14 within housing 12. Vertically extending array 50 of sensors 52 spans across the depth of fluid 14 and into headspace 18, so that some sensors 52are positioned below the surface of the fluid 14 and some sensors 52 are positioned above the surface of the fluid 14. Any suitable array of sensors that can be used to determine or estimate the fluid level 16 can be used for array 50 of sensors 52, for example ultrasonic transducers, thermographic sensors such as infrared cameras including forward looking infrared (FLIR.) cameras, temperature sensors, static pressure sensors mounted inside a tube disposed within fluid 14, capacitance sensors, or the like. Any suitable algorithm or interpretation method that can be used to estimate the fluid level 16 of fluid 14 based on the data obtained by such sensors can be used to provide the fluid level 16.

[0039] In the illustrated embodiment, array of sensors 50 is provided by a plurality of individual sensors 52, (14 in the illustrated embodiment) illustrated as 52A, 52B, 52C, 52D, 52E, 52F, 52G, 52H, 521, 52J, 52K, 52L, 52M and 52N and collectively referred to as sensors 52. Each one of sensors 52 is mounted at a different vertical elevation within housing 12, e.g. sensor 52A is mounted at the highest vertical elevation, sensor 52B is mounted at a slightly lower vertical elevation, sensor 52C is mounted at a still further slightly lower vertical elevation, and so on to sensor 52N which is mounted at the lowest vertical elevation within housing 12. In the illustrated embodiment, the plurality of individual sensors 52 are equally spaced apart, that is the distance between each adjacent pair of individual sensors (e.g. 52A and 52B) is the same as the distance between each other adjacent pair of individual sensors (e.g. 52K and 52L). In other embodiments, the plurality of individual sensors 52 may be spaced apart by different distances.

[0040] While in the illustrated embodiment the provided array 50 of sensors 52 are mounted vertically aligned, i.e. without being displaced from one another in the horizontal direction, in alternative embodiments sensors 52 could be mounted at other horizontal locations within housing 12, so long as sensors 52 are provided with a plurality of different elevations within housing 12. Further, sensors 52 can be placed anywhere within housing 12, e.g. mounted to the inside surface or outside surface within housing 12, or provided on a separate component such as a rod that can be inserted inside housing 12 or otherwise mounted in thermal contactwith fluid 14 and / or headspace 18 to provide the vertically extending array 50 of sensors 52.

[0041] Any number of sensors 52 may be used in array 50 of sensors 52, as long as at least two sensors are present to be able to evaluate the fluid level within housing 12 at at least two different elevations. In some embodiments, at least three sensors 52 are provided in array 50 to enable determination of which ones of the plurality of sensors 52 in vertically extending array 50 are positioned above or below the surface or fluid level 16 of fluid 14 and / or to enable determination of a temperature gradient along the vertical elevation of housing 102. Increasing the number of sensors 52 will allow for a more precise determination of the fluid level 16, i.e. will increase the accuracy with which the fluid level 16 can be detected. In some embodiments, anywhere between 2 and 30 sensors 52 may be used in array 50 of sensors 52, including any value or subrange therebetween, e.g. 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28 or 29 sensors 52, with each one of the sensors 52 being disposed at a different vertical elevation of housing 12. In other embodiments, the device used to provide the array of data points detected by sensors 52 can provide a significant number of points of data equivalent to that captured by array 50 of sensors 52 (e.g. if an infrared camera is used to provide array 50 of sensors, each vertically ascending pixel or group of pixels imaged will correspond to one of sensors 52), so that in some embodiments a virtually infinite number of sensors 52 may be provided.

[0042] Array 50 of sensors 52 can be used as described in more detail below to determine or estimate the fluid level 16 within housing 12. However, because the fluid level 16 is expected to fluctuate with variations in normal operating conditions, particularly those conditions that impact the fluid temperature, e.g. load on the transformer or other device in which apparatus 10 is installed, and / or the external temperature, knowing the fluid level 16 alone is not sufficient to determine whether fluid 14 is leaking out of housing 12. Accordingly, in addition to the array of sensors that can be used to determine or estimate fluid level 16, apparatus 10 is further provided with at least one reference sensor 60, which can be used to provide an expected reference level of fluid 14 within housing 12 based on the reference parameter(s) measured by reference sensor 60.

[0043] The reference level of fluid 14 is the expected fluid level 16 that would be expected under normal operating conditions based on the parameter measured by reference sensor 60. In some embodiments, a plurality of different reference sensors 60 can be used to measure different parameters that can be used to provide the reference level of fluid 14. For example, in some embodiments, reference sensor 60 can be one or more of one or more temperature sensors deployed at predetermined locations to measure oil temperature and / or ambient temperature, a sensor for measuring a parameter indicative of the electrical load on the transformer, a wind speed sensor, a sensor for measuring solar irradiation, a sensor for measuring incident precipitation, or the like. In some embodiments, the measure of electrical load on the transformer can be a measure of the current flowing through the transformer, e.g. as determined using Rogowski coils or current transformers (CTs).

[0044] By comparing the fluid level 16 determined by array 50 of sensors 52 and the reference level of fluid 14 predicted based on the reference parameter(s) determined by reference sensor(s) 60, a determination can be made as to whether fluid is or may be leaking from housing 12. Specifically, if the fluid level 16 determined by array 50 of sensors 52 matches within a reasonable margin of error the reference level of fluid 14 predicted based on the reference parameter(s) determined by reference sensor(s) 60, it can be concluded that it is unlikely that fluid 14 is leaking from housing 12. However, if the fluid level 16 determined by array 50 of sensors 52 is lower than the reference level of fluid 14 predicted based on the reference parameter(s) determined by reference sensor 60, it can be concluded that it is likely that fluid 14 may be leaking from housing 12 so that closer inspection of housing 12 is warranted. For example, in an embodiment in which the predicted level 62A of fluid 14 within housing 12 based on the parameter(s) measured by reference sensor 60 is close to the determined level 16A of fluid 14 as illustrated in FIG. 1, it can be concluded that it is unlikely that fluid 14 is leaking from housing 12. If on the other hand the predicted level 62B of fluid 14 within housing 12 based on the parameter(s) measured by reference sensor 60 is significantly below the determined level 16B of fluid 14 as alsoillustrated in FIG. 1, it can be concluded that it is likely that fluid 14 is leaking from housing 12.

[0045] In some embodiments, the values measured by array 50 of sensors 52 or at least one of the sensors 52 can be used to determine the reference level of fluid 14, so that in some embodiments reference sensor 60 may be one or more of sensors 52 rather than being provided as a separate sensor. For example, in embodiments in which array 50 of sensors 52 is an array of temperature sensors, then a temperature measured by at least one of the temperature sensors 52 that is believed to be in thermal contact with fluid 14 can be used to provide a reference temperature of the fluid 14 that can be used as a reference parameter to estimate the fluid level 16 that would be expected within housing 12 at that particular fluid temperature, and thus that particular sensor 52 can act both as one of sensors 52 and as reference sensor 60.

[0046] In some embodiments, the reference parameter that is used to estimate the predicted level of fluid 14 is the internal temperature of the fluid 14 itself. In some embodiments in which one or more temperature sensors are provided within the fluid 14 inside housing 12, such temperature sensor(s) can be used as the reference sensor 60 to directly measure the temperature of fluid 14. The temperature of fluid 14 may vary throughout housing 12, for example fluid 14 may be characterized by a top oil temperature in the fluid at the top of fluid level 16, and / or may be characterized by a hot spot temperature, for example proximate the windings of a transformer within the fluid 14, and the selected temperature sensor 52 can be selected for its proximity to such a location within the transformer to enable an accurate determination of such temperature to be made.

[0047] In some embodiments, the housing 12 is provided with an aperture or suitable indentation to allow the insertion of a temperature sensor or other reference sensor therein to measure the temperature of fluid 14 or other reference parameter directly to act as reference sensor 60. For example, a temperature sensor can be inserted into a thermowell provided within housing 12 to measure the temperature of fluid 14, for example as described in some aspects of Patent Cooperation Treaty patent publication WO 2022 / 266748, the entirety of which is incorporated by reference herein.

[0048] In some embodiments, temperature sensors may not necessarily be provided within housing 12 to act as reference sensor 60. In such embodiments, an apparatus and method for non-invasively determining the temperature of the fluid inside the housing 12 based on a surface temperature of housing 12 can be used as reference sensor 60 to determine the internal temperature of fluid 14, for example as described in Patent Cooperation Treaty patent publication WO 2022 / 266748.

[0049] In other embodiments, any other suitable method or methods of determining or estimating the temperature of the fluid 14 within housing 12 can be used to provide the reference parameter that can be used to determine the predicted level of fluid within housing 12 and a corresponding sensor for measuring such reference parameter can be used as reference sensor 60. For example, methods of estimating the temperature of transformer oil based on the electrical load passing through the transformer and / or the ambient temperature or the like can be used as are known in the art, so that in some embodiments the reference parameter is the ambient temperature outside the transformer or a measure indicative of the electrical load passing through the transformer, e.g. as determined using Rogowski coils or current transformers (CTs).

[0050] In some embodiments, apparatus 10 is provided with an on-board processor 80 suitable for comparing the measured level of fluid 14 with the reference level of fluid predicted based on the parameter(s) measured by reference sensor 60. In other embodiments, rather than being provided with an on-board processor 80, suitable processing of the data measured by array 50 and reference sensor(s) 60 can be carried out by a remote processing unit, for example a centrally located computer system containing a central processor operated by the utility responsible for the electrical equipment on which apparatus 10 is installed. For example, in some embodiments, apparatus 10 is provided with an on-board communications module 85 that can be used to transmit data obtained by apparatus 10 by wired or wireless means (e.g. by cellular communications network, radiocommunications network, or any other desired communications protocol) for further processing. In some embodiments, apparatus 10 is provided with a signal generation unit 90, which can generate a perceptible signal (e.g. a visual indicationsuch as an indicator light or actuation of an indicator arm, or an audible indication such as a warning tone or sound) or an electronic signal that can be transmitted by on-board communications module 85 to indicate when a determination that fluid is likely leaking from the housing 12 is made. In alternative embodiments, e.g. where processing of data generated by apparatus 10 is carried out remotely, the generation of an appropriate perceptible or electronic signal to indicate that a leak of fluid is likely occurring from housing 12 can be generated at the remote location where the data is processed and a central signal generation unit can be used to provide an electronic signal and / or a perceptible signal such as a visual signal such as a mechanical indication, or an audible signal such as a tone, alarm or voice message.

[0051] With reference to FIG. 2 in which like components are illustrated with the same reference numerals as in FIG. 1, in some embodiments rather than an array 50 of sensors 52 being provided by a plurality of sensors 52, a single sensor 51 is used that can determine or estimate fluid level 16 within housing 12. For example, in some embodiments a single pressure sensor can be used as sensor 51 to estimate the fluid level 16 within housing 12, a single capacitance sensor can be used as sensor 51 to estimate the fluid level 16 within housing 12, a single ultrasonic sensor can be used as sensor 51 to estimate the fluid level 16 within housing 12, a single thermographic imaging apparatus can be used to estimate the fluid level 16 within housing 12, or the like, as described in greater detail below.

[0052] With reference to FIG. 3, an example embodiment 100 of an apparatus for estimating a level of a fluid contained within a housing is shown. A plurality of temperature sensors 104 are mounted in thermal contact with the housing 102. Housing 102 contains an electrically insulating fluid 106, which has a surface 108 which defines the level of fluid 106 within housing 102.

[0053] In the illustrated embodiment, temperature sensors 104 (illustrated as 104A, 104B, 104C and 104D and referred to herein collectively as temperature sensors 104) are mounted on the internal surface of housing 102. In alternative embodiments, temperature sensors 104 are mounted on the external surface of housing 102. Mounting sensors on the external surface of housing 102 may be particularly desirable if an existing transformer is being retrofit with monitoringequipment such as apparatus 100. In still other embodiments, temperature sensors 104 are suspended in any suitable manner in a vertically extending array directly within fluid 106; for example temperature sensors 104 can be mounted to a support, e.g. a vertically extending rod, and suspended within fluid 106 so that some temperature sensors 104 are disposed beneath the surface 108 of fluid 106 and some temperature sensors 104 are disposed above the surface 108 of fluid 106.

[0054] In the illustrated embodiment of FIG. 3, temperature sensors 104 are mounted in thermal contact with the surface of housing 102. In some embodiments, temperature sensors are mounted directly on the surface of housing 102. In other embodiments, some other material may interpose temperature sensors 104 and housing 102, so long as temperature sensors 104 are in thermal contact with housing 102, i.e. able to sense a relative temperature of housing 102. Because housing 102 is in thermal contact with fluid 106, temperature sensors 104 are also in thermal contact with fluid 106. In alternative embodiments, temperature sensors 104 can be placed in thermal contact with fluid 106 in any suitable manner.

[0055] Temperature sensors 104 are mounted in an array at a plurality of different elevations in the vertical direction 110 on housing 102. For example, temperature sensor 104A is mounted at the highest elevation on housing 102, while temperature sensor 104B is mounted at a slightly lower elevation on housing 102, with temperature sensor 104C mounted at yet a lower elevation on housing 102 and temperature sensor 104D mounted at the lowest elevation on housing 102. In the illustrated embodiment, the distance between each adjacent pair of temperature sensors 104 is the same, although in other embodiments the distance between each adjacent pair of temperature sensors 104 could vary.

[0056] While in the illustrated embodiment the provided array of temperature sensors 104 are mounted vertically aligned, i.e. without being displaced from one another in the horizontal direction, in alternative embodiments temperature sensors 104 could be mounted at other horizontal locations within housing 102, so long as temperature sensors 104 are provided with a plurality of different vertical elevations within housing 102.

[0057] Any number of temperature sensors 104 may be used, as long as at least two temperature sensors are present to be able to evaluate the temperature within housing 102 at at least two different vertical elevations. In some embodiments, at least three temperature sensors 104 are provided to enable determination of which ones of the plurality of temperature sensors 104 in the vertically extending array of temperature sensors 104 are positioned above or below the surface 108 of fluid 106, and / or to enable determination of a temperature gradient along the vertical elevation of housing 102. Increasing the number of temperature sensors 104 will allow for a more precise determination of the elevation of the surface 108 of fluid 106, i.e. will increase the accuracy with which the elevation of the surface 108 of fluid 106 can be detected. In some embodiments, anywhere between 2 and 30 temperature sensors may be used, including any value or subrange therebetween, e.g. 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28 or 29 temperature sensors 104, with each one of the temperature sensors being disposed at a different vertical elevation of housing 102.

[0058] Any suitable type of temperature sensor may be used for temperature sensors 104, for example resistance temperature detectors, thermistors, thermocouples or the like. In one example embodiment, temperature sensors 104 are type K thermocouples, which are designed to operate within a temperature range of 0°C to 400°C.

[0059] Without being bound by theory, the temperature of the fluid 106 is higher than the temperature of the air in the headspace 112 above fluid 106. The array of temperature sensors 104 is provided at suitable elevations on housing 102 so that some of the temperature sensors 104 are above the surface 108 of fluid 106 while other of the temperature sensors 104 are below the surface 108 of fluid 106. For example, in the embodiment illustrated schematically in FIG. 3, temperature sensors 104C and 104D are positioned below the surface 108 of fluid 106, while temperature sensors 104A and 104B are positioned above the surface 108 of fluid 106. Because the temperature of the fluid 106 is higher than the temperature of the air in the headspace 112 above surface 108, temperature sensors 104C and 104D will read a higher temperature than temperature sensors104A and 104B. Thus, it can be concluded that the surface 108 is somewhere between temperature sensors 104B and 104C.

[0060] Furthermore, the temperature measured by any specific temperature sensor that is close to the surface 108 of fluid 106 can also give information about how far that particular temperature sensor is to the surface 108 of fluid 106, since the temperature within the headspace 112 increases closer to the surface 108 of fluid 106. Thus, temperature sensors 104 can provide not just a binary indication of whether each temperature sensor 104 is above or below the surface 108, but also can help to provide a temperature gradient along the vertical elevation of housing 102 at intermediate temperatures between the high temperature experienced by temperature sensors that are fully below the surface 108 and the low temperature experienced by temperature sensors 104 that are well above surface 108, so that the temperature measured by temperature sensors 104 can be used to estimate the level of surface 108 relative to that temperature sensor 104.

[0061] FIG. 4 shows the apparatus 100 of FIG. 3, but wherein the surface 108 of fluid 106 has moved to a lower elevation (for example after a portion of fluid 106 has leaked out of housing 102). In FIG. 4, temperature sensor 104D will read a higher temperature than temperature sensors 104A, 104B and 104C, so that it can be concluded that the surface 108 of fluid 106 is now positioned between temperature sensor 104C and temperature sensor 104D. Additionally, because temperature sensor 104C is closer to the surface 108 than temperature sensors 104A and 104B, the temperature of temperature sensor 104C will be higher than that of temperature sensors 104A and 104B (although lower than the temperature of temperature sensor 104D), so that information as to the temperature gradient along the vertical elevation of housing 102 can be evaluated, so the temperature read by temperature sensor 104C can provide additional information as to how close surface 108 is to temperature sensor 104C.

[0062] With reference to FIGs. 5 and 6, an example embodiment of a device 200 for determining whether fluid is leaking from a housing and the mechanism for mounting such device on an external surface of a housing 202 are illustrated. Device 200 includes a sensor unit 220 and a mounting frame 222. Sensor unit220 is provided with an array of ten temperature sensors 204 (illustrated as 204A, 204B, 204C, 204D, 204E, 204F, 204G, 204H, 2041, 204J and collectively referred to as temperature sensors 204). Each one of the temperature sensors 204 is mounted on sensor unit 220 so that when sensor unit 220 is deployed, each one of the temperature sensors 204 will be at a different vertical elevation relative to a surface of the fluid contained within housing 202. As can be seen in FIG. 6, in this embodiment, some of the temperature sensors 204 are horizontally displaced form one another, i.e. the temperature sensors 204 are not provided in a horizontally aligned vertically extending array. Any suitable type of temperature sensor may be used for temperature sensors 204, for example resistance temperature detectors, thermistors, thermocouples or the like. In one example embodiment, temperature sensors 204 are type K thermocouples, which are designed to operate within a temperature range of 0°C to 400°C.

[0063] In one example embodiment, one or both of sensor unit 220 and mounting frame 222 are provided with an adhesive surface that can be used to temporarily secure sensor unit 220 and / or mounting frame 222 in position on housing 202. The adhesive surface can be covered with a protective liner to protect the adhesive surface, and the protective liner can be removed at the time of installing device 200. The mounting frame 222 can be secured in position on the exterior of housing 202 with the adhesive, and then sensor unit 220 can be positioned within mounting frame 222, optionally also being held in place temporarily by removing a protective liner from the adhesive surface provided on sensor unit 220 to allow sensor unit 220 to be adhered to housing 202 via the adhesive. Any suitable fasteners such as screws 224 can then be used to secure both sensor unit 220 and mounting frame 222 in position on housing 202. In some embodiments, mounting frame 222 can be omitted and sensor unit 220 can be directly secured to housing 202.

[0064] In some embodiments, sensor unit 220 contains appropriate insulation to ensure that temperature sensors 204 are protected from exposure to external elements (e.g. sun / solar irradiation, wind / variations in wind speed, precipitation, fluctuating temperatures) that might alter the temperature measured by temperature sensors 204. In some embodiments, sensor unit 220 is not insulatedor is only minimally insulated, because if all of the temperature sensors 204 are equally affected by exposure to external elements, then the relative differences in temperature measured by temperature sensors should consistently enable the accurate evaluation of the level of fluid within housing 202. In some embodiments, the presence of the body of sensor unit 220 which physically shields housing 202 from cooling due to moving air passing by housing 202 provides a sufficient degree of insulation to protect temperature sensors 204 from undesired effects due to external elements.

[0065] In some embodiments, an external temperature sensor 230 is provided external to or on the outside of device 200 to act as a reference sensor to determine a reference temperature of the fluid contained with in the housing to be able to determine a reference level for the expected fluid level within housing 202 given the temperature of the fluid as described above. In some embodiments, the external temperature sensor 230 is a temperature sensor that allows for the noninvasive determination of the temperature of the fluid inside the housing 202, for example as described in Patent Cooperation Treaty patent publication WO 2022 / 266748. The electrically insulating fluid will change in volume with changes in temperature, so that the surface of the fluid will be higher at higher temperatures and lower at lower temperatures. Such fluctuations are expected during the normal operation of electrical equipment such as a transformer, but mean that simply comparing the determined level of the surface of the fluid inside of the housing with a static level position cannot be used to determine if fluid is leaking out of housing 202. By determining the expected level of fluid within housing 202 at any particular fluid temperature, the measured level of fluid within housing 202 can be compared with that expected level, and appropriate further action such as triggering a signal, alarm, warning or the like can be taken if the measured level of fluid is less than the expected level.

[0066] In various embodiments, device 200 and any of the devices described herein can be provided with an on-board processor, communications module and / or signal generation unit as described for apparatus 10, including an on-board processor 80, an on-board communications module 85 and / or a signal generation unit 90 and / or be used as part of a system having a remote processor and aremote signal generation unit that process and act on the data generated by device 200 and transmitted via communications module 85.

[0067] With reference to FIGs. 7A and 7B, a further example embodiment of an apparatus 300 for determining if fluid is leaking from a housing is provided. In apparatus 300, the sensor for determining a level of the fluid within the housing is provided by a capacitance sensor. As shown in FIG. 7A, a housing 302 contains a fluid 306 having a surface 308 and a headspace 312 above surface 308. A vertically extending metal rod 314 is mounted inside housing 302, with a gap 316 between metal rod 314 and housing 302 to form a capacitor in which the fluid 306 acts as the dielectric and the capacitance varies with the level of fluid 306.

[0068] In one example embodiment, gap 316 has a length of approximately1 / 2 inch (about 1.25 cm), although those skilled in the art can modify the spacing of gap 316 to provide a suitable capacitor as desired.

[0069] In the illustrated embodiment of FIGs. 7A and 7B, the sensor for determining the level of fluid 306 is provided by a capacitance sensor 304 mounted to measure capacitance provided by the metal rod 314. In alternative embodiments, rather than using a single capacitor, an array of vertically spaced capacitors could be deployed as sensors 52 in an array 50 of sensors 52, as described above. Each such individual capacitor would have a capacitance that varied depending on whether the capacitor was above or below the surface of the fluid 306, and thus could be used to determine a level of the fluid 306 within housing 302 by determining which capacitors are above and which capacitors are below the level of fluid 306 as described above for temperature sensors 52. Such an array of capacitors would provide only binary data as to the level of the fluid 306 relative to that capacitor (e.g. reading one capacitance when the sensor is below the surface of the fluid, and a different capacitance when the sensor is above the surface of the fluid), so the accuracy with which the level of the fluid could be determined could be slightly less than when using an array of temperature sensors. However, such an array of sensors could still be used to determine which of the plurality of the vertically extending array of sensors are above or below a surface 308 of fluid 306 to enable a determination of the position of surface 308 to be made.

[0070] The example embodiment illustrated in FIG. 7B is substantially similar to that illustrated in FIG. 7A, except that vertically extending metal rod 314 is inserted inside a metal tube 318 to form a larger capacitance system by increasing the surface area.

[0071] With reference to FIG. 8, an example embodiment of a device 340 for determining if fluid is leaking from a housing using a thermographic imaging device such as an infrared camera to determine a level of fluid within the housing is illustrated. An infrared camera 346 is positioned to image a surface of a housing 342 containing the fluid. The infrared camera 346, which is an FLIR. camera in some embodiments, is positioned to image the external surface of the housing in a region spanning the surface of the fluid, and each pixel imaged by the camera in a vertical direction is equivalent to a pixel in a vertically extending array of sensors 52 as described for array 50 of sensors 52. Differences in temperature of the housing 342 in the vertical direction can be used to extrapolate the level of the fluid within the housing 342, for example by determining which vertically extending pixel or group of pixels imaged by the infrared camera 346 are positioned above or below the surface of the fluid and / or to enable determination of a temperature gradient along the vertical elevation of housing 342.

[0072] With reference to FIG. 9A, an example embodiment of a device 360 for determining if fluid is leaking from a housing using a pressure sensor to determine a level of fluid within the housing is illustrated. A pressure sensor 366, which in the illustrated embodiment is a heat-resistant tube, is positioned to measure hydrostatic pressure by being placed in fluid communication with the liquid contained within the housing. In some embodiments, pressure sensor 366 is a flexible heat-resistant tube. The tube is secured in place in any suitable manner, for example by securing the free end of the tube to the bottom of the tank using a weight so that the static pressure inside the tube increases proportionally with the level of fluid within the housing 362.

[0073] In some embodiments, two pressure sensors are used to increase accuracy and allow calculation of differential pressure accurately. FIG. 9B shows an example implementation of such a system that can be used to determine if fluid is leaking from a housing in an apparatus such as a transformer. In the illustratedembodiment, pressure sensor 366 has a first pressure sensor 366A positioned within the headspace 368 above the surface 370 of the fluid 364 within the housing 362 and in fluid communication with the air in headspace 368, and a second pressure sensor 366B positioned below the surface 370 of the fluid 364 and in fluid communication with fluid 364. In some embodiments, pressure sensor 366A is positioned near the top of housing 362 and pressure sensor 366B is positioned near the bottom of housing 362.

[0074] In an alternative embodiment as illustrated in FIG. 10, rather than measuring the level of fluid directly within a housing 382, a device 380 can be provided that can measure the level of the fluid outside of the housing, for example through an externally mounted oil sight gauge 384. Oil sight gauge 384 has a first arm 384A that is in fluid communication with the headspace 392 above the level of fluid 390 within housing 382, and a second arm 384B that is in fluid communication with the fluid 390 within housing 382. Fluid will flow in and out of second arm 384B as the level 388 of fluid 390 within housing 382 fluctuates, and gravity will ensure that the level of fluid within oil sight gauge 384 is the same as level 388 within housing 382. Thus, changes in the level of fluid within housing 382 can be monitored by monitoring the level 388 of fluid within oil sight gauge 384. The level 388 of fluid within oil sight gauge 384 can be measured in any suitable manner, for example by using a magnetic float 394 positioned within oil sight gauge 384 to float on the surface of the fluid coupled with appropriate sensors to detect changes in the height of the float, appropriate pressure sensors disposed within oil sight gauge 384 to measure the pressure above and below the level 388 of the liquid as described for pressure sensors 366A, 366B, appropriate visual detection means to detect changes in the level 388 of the liquid within oil sight gauge 384, or the like.

[0075] In various embodiments, each of apparatus 100, 200, 300, 340, 360 and 380 includes reference sensor 60, on-board processor 80, on-board communications module 85 and / or signal generation unit 90, as described for apparatus 10 to facilitate processing and downstream use of data obtained by the level and reference sensors of the apparatus to provide a signal that a leak has occurred.

[0076] With reference to FIG. 11, an example embodiment of a method 400 for determining if fluid is leaking from a housing being monitored is illustrated. At 404, a level of a surface of the fluid within the housing is determined or estimated in any suitable manner, for example using a float or any of the apparatus or methods described herein, including by using any of apparatus 10, 100, 200, 300, 340, 360 or 380. At 406, a reference parameter that can be used to provide an expected reference level of the fluid within the housing is evaluated in any suitable manner, for example by determining a temperature of the fluid within the housing, a measure indicating an electrical load passing through the housing, evaluating ambient temperature, evaluating wind speed, evaluating solar irradiation and / or evaluating incident precipitation, including by using any of the apparatus or methods described herein. In some embodiments, the reference parameter is one or more of ambient temperature, internal fluid temperature, or electrical load passing through the housing. In some embodiments, additional reference parameters such as wind speed, solar irradiation, ambient temperature or the like are used to further refine the expected reference level of the fluid within the housing.

[0077] At 408, the expected fluid level based on the measured reference parameter(s) is determined, for example based on a previously determined calibration curve or a calculated correction factor for the particular piece of electrical equipment being monitored.

[0078] At 410, the measured level of the surface of the fluid within the housing determined at 404 is compared with the expected level of the surface of the fluid within the housing determined at 408. If the two values are the same or fall within a reasonable margin of difference of one another, then at 412 no action is needed and nothing further needs to be done. Method 400 can optionally be repeated at periodic intervals, to monitor for leakage of fluid from the housing on an ongoing basis. If at 410 it is determined that the two values determined at 404 and 408 are different or at least outside a reasonable margin of difference, then a signal, alert or warning can be triggered to indicate that there is a problem with the piece of electrical equipment being monitored that requires further attention, for example because fluid may be leaking out of the housing.

[0079] With reference to FIG. 12A, an example embodiment of a method 500 for determining if fluid is leaking from a housing being monitored is illustrated. At 502, a temperature gradient of the fluid within the housing in a vertical direction is measured, for example using an apparatus such as apparatus 100 or 200 described above. At 504, based on the measured temperature gradient, a level of a surface of the fluid within the housing is determined or estimated. At 506, a suitable reference parameter or parameters are determined, e.g. in some embodiments a temperature of the fluid contained within the housing is determined or estimated in any suitable manner. At 508, the expected fluid level based on the measured or estimated fluid temperature from 506 is determined, for example based on a previously determined calibration curve or a calculated correction factor for the particular piece of electrical equipment being monitored.

[0080] At 510, the measured level of the surface of the fluid within the housing determined at 504 is compared with the expected level of the surface of the fluid within the housing determined at 508. If the two values are the same or fall within a reasonable margin of difference of one another, then at 512 no action is needed and nothing further needs to be done. Method 500 can optionally be repeated at periodic intervals, to monitor for leakage of fluid from the housing on an ongoing basis. If at 510 it is determined that the two values determined at 504 and 508 are different or at least outside a reasonable margin of difference, then a signal, alert or warning can be triggered at 514 to indicate that there is a problem with the piece of electrical equipment being monitored that requires further attention, for example because fluid may be leaking out of the housing.

[0081] In alternative embodiments, other methods of determining a temperature gradient along a vertically extending portion of a fluid within the housing can be substituted for the use of temperature sensors 104 or 204 as described herein to determine the level of fluid within the housing, or other methods of determining a level of the fluid within the housing can be used. For example, using a static pressure sensor or mounting an ultrasonic transducer to the housing to detect variations in fluid level along a vertically extending portion of the housing or the like could be used to determine the level of fluid within the housing in alternative embodiments.

[0082] FIG. 12B illustrates an example embodiment of a method 600 for determining if fluid is leaking from a housing being monitored. Method 600 is generally similar to method 500 and like steps have been illustrated with like reference numerals incremented by 100. Method 600 differs from method 500 in that rather than measuring a temperature gradient, at step 602 a determination is made as to which ones of a plurality of a vertically extending array of sensors are above or below a surface of the fluid. Based on this determination, the level of the fluid within the housing can be determined to be above the location of those plurality of sensors that are positioned below the surface of the fluid, but below the location of those plurality of sensors that are positioned above the surface of the fluid to provide the measured level of the fluid within the housing at 604. Based on this determination, method 600 carries on in a similar manner to method 500 to measure a reference parameter at 606, predict the expected fluid level based on the measured reference parameter at 608, compare the measured and expected fluid levels at 610, take no action at 612 if the two levels are determined to be the same or the same within a reasonable level of tolerance, or generate a signal, alert or warning at 614 if the measured and expected fluid levels are determined to be outside a reasonable margin of difference.

[0083] In various embodiments, appropriate wired or wireless communications apparatus are provided to enable the apparatus as described herein to communicate with external systems to allow for a signal that fluid may be leaking from a housing to be generated and relayed to a utility or other end user to enable appropriate investigative and remedial measures to be undertaken. In some embodiments, data generated by the various sensors described herein is transmitted, for example through a cellular network or a radiocommunication network, to an external processor where further data analysis is carried out, including the generation of a signal if it is determined that fluid is leaking from the housing. In other embodiments, a processor is provided as part of the system to enable data processing and analysis to be carried out on site.

[0084] In various embodiments, any appropriate method for determining a fluid level within a housing based on data acquired from one or more sensors can be used, including use of a float as known in the art or use of any of the methodsdescribed herein, and any appropriate method for estimating a reference fluid level within a housing based on any suitable reference parameter or parameters can be used. In some embodiments, machine learning algorithms are used to process the data obtained by the level sensor and / or the reference sensor, to determine the level of fluid that is present within the housing based on the data determined by the level sensor and / or to estimate the reference level of fluid that should be present within the housing based on the data determined by the reference sensor and to determine when a signal should be generated indicating that fluid is or may be leaking from the housing.Examples

[0085] Further embodiments are illustrated with reference to the following examples, which are intended to be illustrative and not limiting in nature.Example 1.0 - Determination of Fluid Level Using an Internal Array of Temperature Sensors

[0086] An example embodiment in accordance with the schematic shown in FIG. 3 was tested, wherein the temperature sensors were mounted on the interior of the housing, in direct contact with the fluid itself. Eight different temperature sensors were positioned at different elevations spaced 3" (~7.6 cm) vertically apart within a housing. Oil contained within the housing was maintained at a fluid temperature of 60°C, and the temperature of the airspace above the fluid was somewhat cooler, around 40-45°C. The level of the oil was decreased by up to 9 inches (~22.9 cm) from its topmost level and the temperature measured by each one of the temperature sensors was plotted relative to the oil level from the top.

[0087] As can be seen in FIG. 13, as the oil level drops, more and more of the temperature sensors show a cooler reading that corresponds to that particular temperature sensor being positioned above the surface of the oil. Specifically, when the oil is at the top, thermocouples 1-7 all read a temperature of approximately 60°C, indicating that these thermocouples are all below the surface of the oil. Only thermocouple 8 reads a relatively cooler temperature ofapproximately 45°C, indicating that thermocouple 8 is positioned above the surface of the oil.

[0088] As the oil level within the housing begins to decrease, more of the temperature sensors read cooler temperatures, indicating that those temperature sensors are positioned above the surface of the oil. For example, when the oil level is decreased by 1" (~2.5 cm) from the top, thermocouple 7 reads a cooler temperature of 55°C, indicating this thermocouple is above the surface of the oil. When the oil level is decreased by 3" (~7.6 cm) from the top, still only thermocouple 7 reads a cooler temperature of approximately 50°C, indicating only thermocouple 7 is above the surface of the oil. When the oil level is decreased by 5" (~12.7 cm) from the top, both thermocouples 7 and 6 read relatively cooler temperatures of approximately 45°C and 50°C, indicating both thermocouples 6 and 7 in addition to thermocouple 8 are above the surface of the oil.

[0089] As the oil level is further reduced by 7" (~17.8 cm) from the top, thermocouple 5 begins to read a slightly cooler temperature less than 60°C, indicating thermocouple 5 is approximately at the surface of the oil, and as the oil level is further reduced by 9" (~22.9 cm) from the top, thermocouple 5 reads a cooler temperature of approximately 45°C, indicating that thermocouple 5 is above the surface of the oil.

[0090] The relative positions of the temperature sensors relative to the oil as it decreases from its top level to -9" (~22.9 cm) from the top is illustrated in FIG. 14 to visually show how the changes in temperature measured by the temperature sensors correlate to the position of each temperature sensor relative to the surface of the oil in the housing.

[0091] The same experiment was repeated with the oil at a temperature of 90°C, and similar results were observed as shown in FIGs. 15 and 16. Additional experiments were conducted with used transformer oil at fluid temperatures of 70°C and 95°C and again similar results were observed, with the temperature measured by each temperature sensor decreasing as the oil level moved lower relative to that temperature sensor.

[0092] An algorithm was developed to extrapolate the oil level based on the temperature measured by each one of the temperature sensors. The algorithmevaluates the slope between the temperature measured by each adjacent pair of sensors and determines which two adjacent sensors have the largest temperature difference between them. The algorithm then uses linear interpolation to determine the fluid level between those two adjacent sensors based on the temperatures measured by each. The algorithm was able to calculate the oil level within the testing tank to a resolution equal to the spacing of the temperature sensors used (3", ~7.6 cm).Example 1.1 - Determination of Fluid Level Using an External Array of Temperature Sensors

[0093] To determine whether temperature sensors could be positioned on the outside of the housing of the testing tank and still provide sufficiently accurate readings to allow a determination of a level of the surface of the liquid within the tank, a testing apparatus similar to that shown in FIG. 3 but with ten temperature sensors mounted on the outside of the housing of the tank was made. FIG. 17 shows the position of the temperature sensors relative to the top initial level of the oil. Experiments were conducted to show that the externally mounted thermocouples can be used to determine oil levels in the same manner as the internally mounted thermocouples.

[0094] The use of externally mounted thermocouples may be preferred for ease of installation of the sensors, particularly in retrofit applications. Externally mounted thermocouples may be used to interpolate values along with linear or spline interpolation.Example 1.2 - Determination of Minimum Fluid Temperature Differential Required When Using an Array of Temperature Sensors

[0095] As the temperature of the transformer oil within the tank decreases, the difference in temperature between the temperature sensors positioned below and above the surface of the oil will correspondingly begin to decrease. Experiments were conducted to evaluate the lowest oil temperature at which a sufficient temperature differential between temperature sensors below and above the surface of the oil exists to reliably estimate the position of the surface of the oil. It wasdetermined under the conditions tested that an oil temperature of approximately 3°C above ambient produced some signal although with a significant noise component, while at as little as 5°C a strong signal is observable that will allow for a determination of the surface of the oil level within the tank.

[0096] FIG. 18 shows temperatures measured by the plurality of externally mounted temperature sensors illustrated in FIG. 17 at an oil temperature of 42°C. As can be seen, thermocouples 1 and 2 which are positioned above the surface of the transformer oil are at a cooler temperature than the remaining thermocouples, which are positioned below the surface of the transformer oil. Similar results were observed at an oil temperature of 32°C, as shown in FIG. 19.Example 2.0 - Determination of Fluid Level Using Liquid Capacitance Level Sensor

[0097] An experimental apparatus using a liquid capacitance sensor with a stainless steel metal rod mounted inside the housing of the tank with a1 / 2 inch (~1.3 cm) gap between the rod and the housing to form a capacitor according to the example embodiment illustrated in FIG. 7A was tested. The capacitance of the system varied with changes in the oil level, and was measured using a multimeter using both polarities.

[0098] Results are shown in FIGs. 20-22. As can be seen, capacitance decreased with corresponding decreases in the level of oil from the top of the test tank using both cold oil (FIG. 20) and hot oil at both 60°C (FIG. 21) and 90°C (FIG. 22). This example confirms that a capacitance sensor can be used to determine a level of fluid within a housing.Example 3.0 - Determination of Fluid Level Using FLIR Camera

[0099] An experimental apparatus using an FLIR camera to determine the level of fluid within a housing in accordance with the embodiment illustrated in FIG. 8 was tested. Results are shown in FIG. 23, which shows captured images for 3 experiment runs. Row 1 shows new oil at 60°C. Row 2 shows new oil at 90°C. Row 3 shows used oil at 95°C. In each experiment, the oil was heated to the desired temperature, then a small amount of oil was pumped out, thermal image captured, and repeated. The oil level can be observed from the sharp temperature gradientseen on the outside of the tank. These images also show the output of a computer vision algorithm used to estimate the level of oil. The estimated oil level is shown as a horizontal thin line in the images.Example 4.0 - Determination of Fluid Level Using Static Pressure Sensor

[0100] An experimental apparatus using a static pressure sensor in accordance with the embodiment illustrated in FIG. 9 to measure fluid level was set up and tested to compare the measured pressure versus fluid height for various fluid temperatures. Representative results for new oil at a temperature of 60 °C are shown in FIG. 24. The results of these experiments show a linear relationship between pressure at the bottom of the housing and fluid level height, as predicted by the hydrostatic equation P = p * g *h.

[0101] A difference in absolute pressure reading was noticed for different temperatures, with higher temperatures having a higher pressure. This is expected due to the heating and expansion of both the oil itself and the air inside the tube. To verify the relationship is linear (as predicted by the ideal gas law p*v=n*R*T and thermal expansion AV = Vo * / 3 * AT) the pressure readings were recorded as oil temperature was increased. As shown in FIG. 25, the relationship is linear and can be accounted for to report accurate oil levels from pressure.

Claims

WHAT IS CLAIMED IS:

1. Apparatus for determining if a fluid contained within a housing is leaking, the apparatus comprising: a level sensor for determining a measured level of the fluid within the housing; and a reference sensor for determining a reference parameter that can be used to provide a predicted level of the fluid within the housing.

2. The apparatus as defined in claim 1, wherein the level sensor comprises a vertically extending array of individual sensors.

3. The apparatus as defined in claim 2, wherein the individual sensors in the vertically extending array of individual sensors are equally spaced apart.

4. The apparatus as defined in either one of claims 2 or 3, wherein the vertically extending array of individual sensors is provided on an inside surface of the housing, on an outside surface of the housing, or directly within the fluid, optionally wherein the individual sensors are mounted in thermal contact with the housing.

5. The apparatus as defined in any one of claims 1 to 4, further comprising a communication module to transmit data from the level sensor and data from the reference sensor to a central processor.

6. The apparatus as defined in any one of claims 1 to 5, further comprising an on-board processor configured to determine the measured level of the fluid within the housing using data from the level sensor and configured to determine the predicted level of the fluid within the housing using data from the reference sensor, the on-board processor further being configured to provide a leak indication if the measured level of the fluid within the housing is determined to be below the predicted level of the fluid within the housing.

7. The apparatus as defined in claim 6, further comprising an on-board signal generation unit for generating a perceptible signal upon occurrence of the leakindication, the signal generation unit being configured to receive the leak indication from the onboard processor.

8. The apparatus as defined in any one of claims 6 or 7, further comprising a communication module to transmit the leak indication to a central processor.

9. The apparatus as defined in any one of claims 1 to 8, wherein the reference sensor comprises a temperature sensor positioned to measure a temperature of the fluid within the housing, a non-invasive temperature sensor positioned to estimate the temperature of the fluid within the housing, or a sensor for measuring a parameter reflecting electrical load passing through a transformer comprising the housing.

10. The apparatus as defined in claim 9, wherein the reference sensor comprises a plurality of reference sensors, and wherein the plurality of reference sensors further comprises a temperature sensor for measuring ambient temperature, a wind speed sensor for measuring wind speed, and / or a sensor for measuring solar irradiation.

11. The apparatus as defined in any one of claims 1 to 10, wherein the level sensor comprises a plurality of temperature sensors, one or more capacitance sensors, one or more ultrasonic transducers, one or more thermographic sensors, a float, an oil sight gauge, or one or more static pressure sensors.

12. The apparatus as defined in claim 11, wherein the oil sight gauge comprises a floating magnetic ball and one or more magnetic sensors for determining an elevation of the floating magnetic ball within the oil sight gauge, wherein the oil sight gauge comprises pressure sensors to measure pressure above and below a level of the fluid within the oil sight gauge to determine the level of fluid within the oil sight gauge, or wherein the oil sight gauge comprises a visual sensor for determining a level of fluid within the oil sight gauge.

13. The apparatus as defined in claim 11, wherein the one or more static pressure sensors comprises a first pressure sensor positioned to measure pressurebelow the level of the fluid within the housing, and a second pressure sensor positioned to measure pressure above the level of the fluid within the housing.

14. The apparatus as defined in any one of claims 2 to 13, wherein the reference sensor comprises one or more of the individual sensors.

15. The apparatus as defined in any one of claims 2 to 14, wherein the vertically extending array of individual sensors comprises at least two individual sensors or at least three individual sensors, optionally between five and thirty individual sensors.

16. The apparatus as defined in any one of claims 2 to 15, wherein the vertically extending array of individual sensors comprises a vertically extending array of temperature sensors.

17. The apparatus as defined in any one of claims 1 to 16, wherein the reference parameter comprises a temperature of the fluid.

18. The apparatus as defined in any one of claims 1 to 17, wherein the housing is part of an electrical transformer and wherein the reference parameter comprises a measure of load on the electrical transformer.

19. A system for determining if fluid contained within a housing is leaking, the system comprising: the apparatus as defined in any one of claims 1 to 18; and a central processor for comparing the measured level of the fluid within the housing with the predicted level of the fluid within the housing; the central processor being configured to provide a leak indication if the measured level of the fluid within the housing is determined to be below the predicted level of the fluid within the housing.

20. The system as defined in claim 19, wherein the central processor is configured to determine the predicted level of the fluid within the housing using the data from the reference sensor and wherein the central processor is configured todetermine the measured level of fluid within the housing using the data from the level sensor.

21. The system as defined in any one of claims 19 to 20, further comprising a central signal generation unit for generating a perceptible signal upon occurrence of the leak indication, the central signal generation unit being configured to receive the leak indication from the central processor.

22. The apparatus as defined in any one of claims 1 to 18 or system as defined in any one of claims 19 to 21, wherein the perceptible signal is a visual signal, optionally a light or a mechanical indicator arm, or wherein the perceptible signal is an audible signal.

23. A method of determining if a fluid contained within a housing is leaking, the method comprising the steps of: using a level sensor to determine a level of the fluid within the housing to provide a measured fluid level; using a reference sensor to determine a reference parameter; using the reference parameter to provide a predicted level of fluid within the housing; comparing the measured fluid level with the predicted fluid level; and if it is determined that the measured fluid level is below the predicted fluid level, concluding that fluid is leaking from the housing.

24. The method as defined in claim 23, wherein the level sensor comprises a vertically extending array of individual sensors and wherein using the level sensor to determine the level of the fluid within the housing to provide the measured fluid level comprises determining which ones of the vertically extending array of individual sensors are positioned below a surface of the fluid and which ones of the vertically extending array of individual sensors are positioned above a surface of the fluid, optionally wherein the individual sensors comprise temperature sensors.

25. The method as defined in claim 23, wherein the level sensor comprises a vertically extending array of individual temperature sensors, and wherein using the level sensor to determine the level of the fluid within the housing to provide the measured fluid level comprises determining a temperature gradient of the fluid within the housing and using the temperature gradient to estimate the level of the fluid within the housing.

26. The method as defined in any one of claims 23 to 25, wherein the level sensor comprises a vertically extending array of at least three individual sensors.

7. The method as defined in any one of claims 23 to 26, wherein the reference parameter comprises a temperature of the fluid.

28. The method as defined in claim 27, wherein the temperature of the fluid is directly measured, is estimated using a non-invasive method of measuring internal fluid temperature, or is estimated based on a measure of an electrical load passing through the housing.

29. The method as defined in claim 28, wherein the temperature of the fluid is estimated further taking into account ambient temperature, wind speed, and / or solar irradiation.

30. The method as defined in any one of claims 23 to 29, wherein the level sensor comprises the same sensor as the reference sensor, or wherein where the level sensor comprises a vertical array of individual sensors, the reference sensor comprises one or more of the individual sensors.

31. The method as defined in any one of claims 23 to 30, further comprising generating a signal to indicate that the fluid is leaking from the housing upon a determination that the measured fluid level is below the predicted fluid level, wherein the signal optionally comprises a mechanical indication, a visual indication, an audible indication, or an electronic signal that is transmitted by wired or wireless means.

32. The method as defined in any one of claims 23 to 31, conducted using the apparatus as defined in any one of claims 1 to 18 or 22 or the system as defined in any one of claims 19 to 22.

33. Apparatus comprising: at least two temperature sensors, each one of the at least two temperature sensors being mounted in thermal contact with a liquid contained in an enclosure, each one of the at least two temperature sensors being positioned at a different elevation of the enclosure; and a processor for estimating a position of a surface of the liquid within the enclosure based on a temperature measured by each one of the at least two temperature sensors.

34. An apparatus for estimating a position of a surface of a liquid contained within an enclosure, the apparatus comprising: at least two temperature sensors mountable on a surface of the enclosure or within the liquid contained within the enclosure; and a processor for estimating the position of the surface of the liquid based on a temperature measured by each one of the at least two temperature sensors.

35. The apparatus as defined in any one of claims 11, 16, 33 or 34, comprising at least three temperature sensors.

36. A method of estimating a position of a surface of a liquid contained within an enclosure, the method comprising: measuring a temperature gradient of the liquid contained within the enclosure; and correlating the measured temperature gradient with the position of the surface of the liquid.

37. The method as defined in claim 36, wherein measuring the temperature gradient of the liquid comprises measuring a temperature of the surface of the enclosure at at least two different elevations, optionally wherein measuringthe temperature gradient of the liquid comprises measuring a temperature of the surface of the enclosure at at least three different elevations.

38. The method as defined in any one of claims 36 or 37, wherein the step of measuring the temperature gradient of the liquid comprises measuring a temperature gradient on an external surface of the enclosure, or comprises measuring a temperature gradient on an internal surface of the enclosure.

39. A method of estimating a position of a surface of a liquid contained within an enclosure, the method comprising: providing a vertically extending array of individual sensors; determining which ones of the vertically extending array of individual sensors are positioned above the surface of the liquid; determining which ones of the vertically extending array of individual sensors are positioned below the surface of the liquid; and concluding that the position of the surface of the liquid is above the individual sensors that are positioned below the surface of the liquid and below the individual sensors that are positioned above the surface of the liquid.

40. The method as defined in any one of claims 24 to 25 or the apparatus as defined in any one of claims 11, 16 or 33 to 35, wherein the temperature sensors are mounted in thermal contact with the housing or the enclosure.

41. The apparatus as defined in any one of claims 11, 16 or 33 to 35 or the method as defined in any one of claims 24 to 25, wherein the temperature sensors comprise resistance temperature detectors or thermocouples.

42. The apparatus, system or method as defined in any one of claims 1 to 41, wherein the enclosure or housing comprises a pad-mounted transformer.

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