Radio transmission through the transformer tank

Abstract

The present disclosure relates to a transformer system (10) comprising a power transformer (1) with a metal tank (2) filled with an electrically insulating liquid (3), and a wireless sensor device (11) submerged in the insulating liquid within the tank. The sensor device comprises a wireless transmitter (12) for wirelessly transmitting sensor readings to the exterior of the transformer through openings (4a and / or 4b) in the tank, the openings being provided with a liquid-tight seal comprising a solid insulator to prevent leakage of the insulating liquid from the tank, and the wireless transmitter (12) is configured to transmit the sensor readings using a carrier frequency in the range of 100 kHz to 1 MHz.

Description

[Technical field]

[0001] The present disclosure relates to communication of sensor readings in liquid-filled transformers. [Background technology]

[0002] background Continuous measurements of various parameters such as temperature, humidity, pressure, etc. from an active transformer are used to monitor its operating conditions and, as a consequence, its reliability. If the transformer is enclosed and embedded in oil, both powering the power sensors, transmitting the power inside the transformer and transmitting the acquired data, and transmitting the sensor data outside the transformer tank, are particularly difficult. Especially the latter problem has not yet been solved. The transfer of data / information outside the sealed transformer tank, which is impermeable to liquids and air, is a challenge. Any holes made in the tank to pass cables through it are problematic because they may eventually start to leak over time (e.g. due to aging of the insulation, including O-rings, for example). It can also be problematic because such a cable would pass from a high potential inside the transformer to a low potential outside the transformer.

[0003] US2002 / 107657 discloses a device for measuring the contact pressure exerted by a winding compression element on a winding in a power transformer in a tank. A sensor and a sensor antenna are arranged in the area of ​​the upper compression element. Checking electronics are provided on the outside of the tank. A checking antenna in the tank is connected to the checking electronics via a radio frequency bushing that penetrates the tank wall.

[0004] DE2427830 relates to an electric thermal sensor that is soldered to the conductors of the windings or inserted between the parallel conductors of the windings. The transmitted signal is scanned by a receiving antenna mounted on the inside wall of the transformer tank and passed through the bushing insulator to the outside of the tank.

[0005] US2019 / 286146 shows an underwater ROV for inspecting liquid-filled housings, such as electrical transformers. The ROV communicates wirelessly through a hole in the housing with a base station outside the housing. Summary of the Invention [Problem to be solved by the invention]

[0006] It is an object of the present invention to provide improved communication of sensor data from inside a liquid-filled transformer to the outside of the transformer tank. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a transformer system comprising a power transformer comprising a metal tank filled with an electrically insulating liquid and a wireless sensor device submerged in the insulating liquid in the tank, the sensor device comprising a wireless transmitter for wirelessly transmitting sensor readings to an exterior of the transformer through an opening in the tank, the opening being provided with a liquid-tight seal comprising a solid insulator to prevent leakage of the insulating liquid from the tank, the wireless transmitter being configured to transmit the sensor readings using a carrier frequency in the range of 100 kHz to 1 MHz.

[0008] According to another aspect of the present invention, there is provided a method of transmitting sensor readings in an embodiment of the transformer system of the present disclosure, the method including a sensor device obtaining sensor readings on the power transformer and a wireless transmitter transmitting the sensor readings using a carrier frequency in the range of 100 kHz to 1 MHz.

[0009] It is now recognized that radio waves may be able to pass through openings in a transformer tank that has a liquid-tight (i.e., liquid-impermeable) seal, for example, including a solid insulator of a dielectric material. Thus, data / information regarding sensor readings can be wirelessly transmitted from inside the power transformer, typically at HV potential, to the outside of the power transformer, typically at low potential. Radio waves will pass through the solid insulator from inside the transformer tank (which is typically metallic and thus generally shields electromagnetic waves, i.e., radio waves). Thus, no cable needs to pass through the tank or from high potential to low potential. Preferably, the seal is also air-tight to prevent air from entering the transformer tank and contaminating the insulating liquid, e.g., mineral oil or ester liquid.

[0010] The solid insulator may for example be in a conventional bushing used to pass electrical conductors, e.g. electrical phases, through a transformer tank. Additionally or alternatively, the solid insulator may be a sealing element between the outside of the (metal) transformer tank and a metal cap covering a hole in the transformer tank, e.g. a hole for accessing the inside of the tank during installation or maintenance. Depending on the physical properties of the opening, the insulating liquid and the solid insulator, the frequency of the carrier wave used for wirelessly transmitting the sensor readings by radio may be specifically adapted to pass through the solid insulator and reach the outside of the tank.

[0011] It should be noted that any feature of any aspect may be applied to any other aspect, where appropriate. Similarly, any advantage of any aspect may apply to any other aspect. Other objects, features, and advantages of the embodiments will become apparent from the following detailed disclosure, the dependent claims, and the drawings.

[0012] Generally, all words used in the claims should be interpreted according to their ordinary meaning in the art, unless expressly defined otherwise herein. All references to "elements, apparatus, components, means, steps, etc." should be openly interpreted as referring to at least one example of that element, apparatus, component, means, step, etc., unless specifically stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless expressly stated. The use of "first," "second," etc., for different features / components of the present disclosure is intended only to distinguish that feature / component from other similar features / components, and is not intended to impose any order or hierarchy on that feature / component.

[0013] BRIEF DESCRIPTION OF THE DRAWINGS Embodiments will now be described, by way of example only, with reference to the accompanying drawings in which: [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic cross-sectional side view of a transformer system according to some embodiments of the present invention. [Diagram 2] 1 is a schematic diagram of a longitudinal cross section of a bushing according to some embodiments of the present invention. [Figure 3a] FIG. 2 is a schematic cross-sectional detail view of a transformer tank having an opening covered by a metal cap according to some embodiments of the present invention. [Figure 3b] FIG. 3b is a schematic top view of an embodiment of the metal cap of FIG. 3a. [Figure 4] 1 is a schematic flow chart of a method according to some embodiments of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Detailed Description The embodiments will now be further described below with reference to the accompanying drawings, in which specific embodiments are shown. However, other embodiments in many different forms are possible within the scope of the present disclosure. Rather, the following embodiments are provided as examples so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like numbers refer to like elements throughout the description.

[0016] FIG. 1 shows a transformer system 10 comprising a power transformer 1 , for example an HV transformer, and a sensor device 11 .

[0017] The transformer 1 comprises an induction device 8 with a transformer winding immersed in an electrically insulating liquid 3 contained in a tank 2, typically completely filling the tank. The liquid may be any suitable transformer liquid, for example an oil such as mineral oil, or an ester liquid. The tank is typically made of a metal, for example steel, that is a high frequency shield. The tank 2 has at least one opening 4 through the wall 9 of the tank. For example, the transformer may comprise at least one, typically several bushings 5, for passing electrical conductors 6, for example for the electrical phases, through the openings 4a in the wall 9 of the tank 2. The transformer may also comprise an inspection opening 4b in the wall 9 of the tank 2, which is typically covered by a metal cap 7 of the same material as the tank 2. The openings 4a are thus provided with a liquid-tight seal including the bushings 5, and the openings 4b with a liquid-tight seal including the caps 7.

[0018] The sensor device 11 includes a sensor 13 immersed in the insulating liquid 3 and configured to measure a characteristic of the transformer, e.g., an inductive device 8. The sensor 13 is connected to a wireless transmitter 12 of the sensor device 11 to wirelessly transmit sensor readings to the exterior of the transformer 1 through the openings 4a and / or 4b in the tank 2. The wireless transmitter 12 may be configured to transmit the sensor readings using a predetermined carrier frequency within a frequency range empirically selected taking into account the physical characteristics of the opening 4, the solid insulator, and the insulating liquid 3 to allow the wireless transmission to pass through the opening 4. It has been determined that carrier frequencies within any of the ranges of 100 kHz to 1 MHz and 300 MHz to 10 GHz may be particularly useful for passing through sealed openings 4.

[0019] FIG. 1 also shows several different possible paths (a), (b) and (c) for wireless transmission of sensor readings from wireless transmitter 12. Path (a) is through opening 4a sealed by bushing 5 and goes through solid insulation within said bushing. Path (b) is also through opening 4a sealed by bushing 5, but through solid insulation between bushing 5 and tank 2, e.g. solid insulation (possibly including O-rings etc.) placed between flange 25 of bushing 5 (see FIG. 2) and the outside of wall 9 of tank 2. Path (c) is through opening 4b covered by cap 7 and goes through solid insulation between tank 2 and cap 7, e.g. solid insulation (possibly including O-rings 31 etc., see FIG. 3a) placed between cap 7 and the outside of wall 9 of tank 2.

[0020] FIG. 2 shows a bushing 5 that may be placed through an opening 4a of the tank 2. The bushing may be substantially rotationally symmetrical and arranged to allow the conductor 6 to pass through a central longitudinal through-hole that passes through the bushing. The bushing 5 comprises a capacitor core 26 arranged around the conductor 6 to insulate it from the surroundings, in particular from the tank 2. The capacitor core 26 comprises a solid insulator 21 and a conductive field gradient layer 22, for example in the form of an aluminum foil. The field gradient layer 22 may form a substantially concentric tube around and parallel to the conductor 6. The field gradient layer may for example be interleaved between layers of wrapped material of solid insulator, for example of cellulose-based paper, when manufacturing the capacitor core 26. Typically, the outer field gradient layer 22 has a reduced longitudinal extension L1 (corresponding to the height of the concentric tube) compared to the inner field gradient layer 22, such that the longitudinal extension gradually decreases from the innermost field gradient layer to the outermost field gradient layer.

[0021] Each of the electric field gradient layers may have a thickness of less than 100 μm, for example in the range of 10 to 40 μm, and the radial distance L2 between the electric field gradient layer and the adjacent inner or outer electric field gradient layer may be in the range of 0.1 mm to 10 mm, for example about 1 mm, corresponding to a number of turns of the web of solid insulator 21 material. The longitudinal extension (height) L1 of the electric field gradient layer may be in the range of 1 to 10 m. Typically, the bushing is filled with the same insulating liquid 3 as the tank 2. However, the bushing is liquid-tight, and preferably also gas-tight, providing a liquid-tight seal of the opening 4a of the tank when the bushing is placed through the opening 4a of the tank. The solid insulator 21 may be impregnated with an insulating liquid, for example an oil-impregnated paper.

[0022] It has been found that radio transmissions using carrier frequencies in the range of 100 kHz to 1 MHz (path (a) in FIG. 1) can pass through a solid insulator 21 in a gap 23 between two adjacent electric field gradient layers 22 (i.e., two electric field gradient layers with no electric field gradient layer between them, typically just a solid insulator 21 possibly impregnated with an insulating liquid 3).

[0023] The bushing 5 may also conventionally be provided with an outer weatherproof insulator 24 and / or a flange 25 for fixing the bushing to the outside of the wall 9 of the tank 2 .

[0024] FIG. 3a shows an opening 4b in the wall 9 of the tank 2, e.g. an inspection hole for accessing the inside of the tank during installation and / or inspection of the transformer 1. The opening 4b is typically covered by a (e.g. substantially flat) metal cap 7 fastened to the wall 9 by a metal fastening means 32, such as a screw or a bolt, exemplified here by a screw 32. The cap 7 may have any suitable shape, e.g. a rectangular or circular shape, when viewed from above. A solid insulator 31, e.g. comprising an O-ring of elastic material, is disposed continuously around the opening 4b between the metal cap 7 and the outside of the tank wall 9, providing a liquid-tight, preferably also gas-tight, seal of the opening 4b.

[0025] When the cap 7 is fastened to the tank wall 9 by the metallic fastening means 32, at least one slit 33 is formed between the outer surface of the wall 9 and the inner surface of the metallic cap 7 (i.e. the surface facing the opening 4b). Each of the at least one slit 33 has a length l1 defined by the distance (typically a linear distance) between two adjacent metallic fastening means 32 (i.e. between two metallic fastening means without further metallic fastening means between them, for example along the outer edge of the cap 7). It has been found that in such a slit 33 defined by the metallic cap, the wall and the fastening means, radio waves (of path (c) in FIG. 1) can pass through the solid insulator 31 without being blocked by said metallic cap, the wall and the fastening means. Similarly, the radio waves of path (b) in FIG. 1 may pass through solid insulator 31 with cap 7 exchanged against flange 25 of bushing 5, i.e., at a slit 33 defined by the outer surface of wall 9 and the inner surface of flange 25 (i.e., the surface facing opening 4a) and two adjacent fastening means 32, such as bolts or screws, that fasten flange 25 to wall 9 around opening 4a.

[0026] The length l1 of the slit 33 is preferably in the range of 0.03 m (corresponding to a frequency of 10 GHz) or 0.1 m (corresponding to a frequency of 3 GHz) to 1 m (corresponding to a frequency of 300 MHz). In that case, it was found that a carrier wave having a carrier frequency in the range of 300 MHz to 10 GHz, preferably up to 3 GHz, passes through the solid insulator 31 to the outside of the tank 2. The height l2 of the slit 33 should be large enough to prevent direct contact between the wall 9 and the cap 7, for example at least 10 μm, such as in the range of 10 μm to 1 cm or 1 mm. The radial length l3 of the slit 33, i.e. the overlap distance between the outer surface of the wall 9 around the opening 4b and the cap 7, is preferably less than 10 cm, for example in the range of 0.5 cm to 4 cm.

[0027] Figure 3b shows an embodiment of the cap 7 viewed from the top, with a number of fastening means 32, e.g. screws or bolts, disposed along the outer edge of the cap. In the embodiment of Figure 3b, the cap is substantially circular, which may be preferred in some embodiments. As explained in relation to Figure 3a, the length l1 of the slit 33 may be defined by the linear distance between any two adjacent fastening means 32.

[0028] 4 is a flow chart of one embodiment of a method of the present disclosure for transmitting sensor readings in an embodiment of a transformer system 10 discussed herein. A sensor device 11 obtains sensor readings on the power transformer 1, e.g., measurements of temperature, pressure, flow rate, etc., of insulating liquid in the tank 2, e.g., in or at the induction device 8 (S1). A wireless transmitter 12 then wirelessly transmits the sensor readings (S2), e.g., through the solid insulation 21 in the bushing 5, e.g., using a carrier frequency in the range of 100 kHz to 1 MHz, or through the solid insulation 31 between the cap 7 and the tank wall 9, e.g., using a carrier frequency in the range of 300 MHz to 10 GHz.

[0029] In some embodiments of the invention, the solid insulator 21 is included in the bushing 5 disposed in the tank opening 4a. In some embodiments, the solid insulator 21 comprises a cellulose-based paper impregnated with the insulating liquid 3. In some embodiments, the solid insulator 21 is disposed between longitudinal conductive electric field gradient layers 22 in the capacitor core 26 of the bushing 5. In some embodiments, the electric field gradient layers 22 are disposed within a radial distance L2 from each other in a range of 0.5-2 mm. In some embodiments, each of the electric field gradient layers 22 has a longitudinal extension L1 of at least 1 m, for example, in a range of 1-10 m. In some embodiments, the wireless transmitter 12 transmits or is configured to transmit the sensor readings using a carrier frequency in a range of 100 kHz-1 MHz.

[0030] In some embodiments of the invention, the solid insulator 31 is contained within a slit 33 formed between the wall 9 of the tank 2 and the metal cap 7 (or possibly the flange 25) covering the tank opening 4b (or 4a). In some embodiments, the solid insulator 31 comprises an O-ring of elastic material disposed between the metal cap 7 or flange 25 and the outside of the tank wall 9. In some embodiments, the slit 33 has a length l1 in the range of 0.03 to 1 m. In some embodiments, the wireless transmitter 12 is configured to transmit sensor readings using a carrier frequency in the range of 300 MHz to 10 GHz.

[0031] The present disclosure has been described above primarily with reference to certain embodiments, however, as will be readily appreciated by those skilled in the art, other embodiments than those disclosed above are equally possible within the scope of the present disclosure as defined by the claims.

Claims

1. A transformer system (10), comprising: A power transformer (1) comprising a metal tank (2) filled with an electrically insulating liquid (3); a wireless sensor device (11) that is submerged in the insulating liquid in the tank; The tank has a wall (9) provided with a first opening (4a) and a second opening (4b), the sensor device comprises a wireless transmitter (12) for wirelessly transmitting sensor readings to an exterior of the transformer through the first opening (4a) and the second opening (4b); each of the first (4a) and second (4b) openings is provided with a liquid-tight seal comprising a solid insulator (21; 31) to prevent leakage of the insulating liquid from the tank, and the wireless transmitter (12) is configured to transmit the sensor readings using a carrier frequency in the range of 100 kHz to 1 MHz, A transformer system (10), wherein the position of the wireless transmitter (12) in a linear direction passing through the first opening (4a) and the second opening (4b) is between the first opening (4a) and the second opening (4b).

2. 2. The transformer system of claim 1, wherein the solid insulator (21) is included in a bushing (5) that is placed in the first opening (4a) of the tank.

3. 3. The transformer system of claim 2, wherein the solid insulation (21) comprises a cellulose-based paper impregnated with the insulating liquid (3).

4. 4. The transformer system of claim 2 or 3, wherein the solid insulator (21) is disposed between longitudinal conductive field gradient layers (22) in a condenser core (26) of the bushing (5).

5. 5. The transformer system of claim 4, wherein the electric field gradient layers (22) are arranged at a radial distance (L2) from each other in the range of 0.5 to 2 mm.

6. 6. A transformer system according to claim 4 or 5, wherein each of said electric field gradient layers (22) has a longitudinal extension (L1) of at least 1 m.

7. A method for transmitting sensor readings in a transformer system (10) according to any one of claims 1 to 6, comprising the steps of: The sensor device (11) acquires (S1) a sensor reading at the power transformer (1); and the wireless transmitter (12) transmitting (S2) the sensor readings using a carrier frequency in the range of 100 kHz to 1 MHz.

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