Wireless transmission through a transformer tank

Abstract

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

Description

Technical Field

[0001] This disclosure relates to the communication of sensor readings for a liquid-filled transformer. Background Technology

[0002] Continuous measurements of various parameters from active transformers, such as temperature, humidity, and pressure, are used to monitor their operating conditions and thus their reliability. When the transformer is enclosed and embedded in oil, powering the sensors, transmitting power and acquiring data inside the transformer, and transmitting sensor data to the outside of the transformer tank become particularly difficult. The latter problem, in particular, remains unresolved. Transmitting data / information to the outside of a tightly sealed transformer tank—which is impermeable to liquids and air—is a challenge. Any holes made in the tank to allow cables to pass through would be problematic, as they could eventually begin to leak over time (e.g., due to aging of the insulation—including O-rings). Additionally, this could be problematic because such cables would transfer a high potential inside the transformer to a low potential outside.

[0003] US2002 / 107657 discloses an instrument for measuring the contact pressure applied to the windings of a power transformer within a housing by a winding compression element. A sensor and sensor antenna are arranged in the region of the upper compression element. An electronic inspection device is located outside the housing. An inspection antenna inside the housing is connected to the inspection device via a radio frequency (RF) bushing that passes through the housing wall.

[0004] DE2427830 relates to an electrothermal sensor that is welded to a conductor of a winding or inserted between parallel conductors of the winding. The transmitted signal is scanned by a receiving antenna attached to the inner wall of the transformer tank and transmitted through the bushing insulator to the outside of the tank.

[0005] US2019 / 286146 discloses a submersible ROV for inspecting liquid-filled enclosures—such as those used in transformers. The ROV wirelessly communicates with a base station outside the enclosure via holes in the enclosure. Summary of the Invention

[0006] One object of the present invention is to provide improved sensor data communication from the inside of a liquid-filled transformer to the outside of the transformer tank.

[0007] According to one aspect of the invention, a transformer system is provided, comprising: a power transformer including a metal tank filled with an electrically insulating liquid; and a wireless sensor device immersed in the insulating liquid within the tank. The sensor device includes a radio transmitter for wirelessly transmitting sensor readings through an opening in the tank to the outside of the transformer, the opening being provided with a liquid-tight seal comprising a solid insulator for preventing leakage of the insulating liquid from the tank, and wherein the radio transmitter is 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 invention, in one embodiment of the transformer system disclosed herein, a method for transmitting sensor readings is provided, the method comprising: a sensor device acquiring sensor readings on a power transformer; and a radio 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 can penetrate openings in a transformer tank having a liquid-tight (i.e., liquid-impermeable) seal comprising a solid insulator, such as a dielectric material. Therefore, data / information regarding sensor readings can be wirelessly transmitted from the inside of the power transformer—typically at an HV potential—to the outside of the power transformer—typically at a low potential. Radio waves will pass through the solid insulator from the inside of the transformer tank (which is typically made of metal and therefore typically shields against electromagnetic waves, i.e., radio waves). Therefore, no cables are needed to pass through the tank, nor is there a need for transmission from a high potential to a low potential. Preferably, the seal is also airtight to prevent air leakage into the transformer tank and contamination of the insulating liquid, such as mineral oil or ester.

[0010] The solid insulator may, for example, be located within a conventional bushing used to allow an electrical conductor—e.g., a phase—to pass through the transformer tank. Additionally or alternatively, the solid insulator may be a sealing element between the exterior of the (metallic) transformer tank and a metal cover covering an opening in the transformer tank—e.g., an opening for access to the interior of the tank during installation or maintenance. Depending on the physical properties of the opening, the insulating fluid, and the solid insulator, a carrier frequency for wirelessly transmitting sensor readings via radio may be particularly suitable for penetrating the solid insulator to the exterior 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 be applied to any other aspect. Further objects, features, and advantages of the appended embodiments will become apparent from the following detailed disclosure, from the appended dependent claims, and from the accompanying drawings.

[0012] Generally, all terms used in the claims should be interpreted according to their ordinary meaning in the art, unless otherwise expressly defined herein. Unless otherwise expressly stated, all references to “a / an / element, instrument, component, device, step, etc.” should be publicly interpreted as referring to at least one instance of said element, instrument, component, device, step, etc. Unless expressly stated otherwise, the steps of any method disclosed herein need not be performed in the exact order disclosed. The use of “first,” “second,” etc., for different features / components of this disclosure is only for distinguishing said feature / component from other similar features / components, and not for assigning any order or hierarchy to said features / components. Attached Figure Description

[0013] The implementation scheme will be described by way of example with reference to the accompanying drawings, in which:

[0014] Figure 1 This is a schematic cross-sectional side view of a transformer system according to some embodiments of the present invention.

[0015] Figure 2 This is a schematic view of a longitudinal section of a sleeve according to some embodiments of the present invention.

[0016] Figure 3a This is a schematic cross-sectional detail of a transformer box having an opening covered by a metal cover, according to some embodiments of the present invention.

[0017] Figure 3b yes Figure 3a A schematic top view of one embodiment of the metal cover.

[0018] Figure 4 This is a schematic flowchart of a method according to some embodiments of the present invention. Detailed Implementation

[0019] Embodiments will now be described more fully below with reference to the accompanying drawings, in which certain embodiments are illustrated. However, many other embodiments in various forms are possible within the scope of this disclosure. Rather, the following embodiments are provided by way of example so that this disclosure will be comprehensive and complete, and will fully convey the scope of this disclosure to those skilled in the art. The same numerals refer to the same elements throughout the description.

[0020] Figure 1 A transformer system 10 is illustrated, which includes a power transformer 1—for example, an HV transformer—and a sensor device 11.

[0021] Transformer 1 includes an inductor 8, the inductor arrangement including transformer windings immersed in an electrically insulating liquid 3 contained within a tank 2, the insulating liquid typically completely filling the tank. This liquid can be any suitable transformer fluid, such as oils like mineral oil or ester solutions. The tank is typically made of radio frequency shielded metal—e.g., steel. Tank 2 has at least one opening 4 through a wall 9 of the tank. For example, the transformer may include at least one, and typically multiple, bushings 5 ​​for allowing an electrical conductor 6—e.g., for an electrical phase—to pass through the opening 4a in the wall 9 of tank 2. Additionally, the transformer may include a maintenance opening 4b in the wall 9 of tank 2, covered by a metal cap 7, typically made of the same material as tank 2. Thus, opening 4a is provided with a liquid-tight seal including the bushing 5, while opening 4b is provided with a liquid-tight seal including the cap 7.

[0022] Sensor device 11 is immersed in insulating liquid 3 and includes sensor 13, which is configured to measure properties of the transformer, such as those of inductor 8. Sensor 13 is connected to radio transmitter 12 of sensor device 11 for wirelessly transmitting sensor readings to the outside of transformer 1 through openings 4a and / or 4b in housing 2. Radio transmitter 12 can be configured to transmit sensor readings using a predetermined carrier frequency within a frequency range, empirically selected based on the physical properties of opening 4, solid insulator, and insulating liquid 3, to allow radio transmission through opening 4. It has been determined that carrier frequencies within either the range of 100 kHz to 1 MHz and 300 MHz to 10 GHz can be particularly useful for transmission through sealed opening 4.

[0023] Figure 1 Several different possible paths (a), (b), and (c) for wirelessly transmitting sensor readings from radio transmitter 12 are also illustrated. Path (a) passes through opening 4—which is sealed by means of sleeve 5—and through the solid insulation within the sleeve. Path (b) also passes through opening 4a—which is sealed by means of sleeve 5—but through the solid insulation between sleeve 5 and housing 2, such as that arranged in flange 25 of sleeve 5 (see...). Figure 2 The solid insulator (possibly including O-rings, etc.) between the cover 7 and the exterior of the wall 9 of the housing 2. Path (c) passes through the opening 4b, which is covered by the cover 7, and through the solid insulator between the housing 2 and the cover 7, such as the solid insulator (possibly including O-rings 31, etc., see [link]). Figure 3a ).

[0024] Figure 2An example is illustrated of a sleeve 5 arranged through an opening 4a in a housing 2. This sleeve may be substantially rotationally symmetrical and arranged to allow a conductor 6 to extend through a central longitudinal through-hole. The sleeve 5 includes a condenser core 26 arranged around the conductor 6 to insulate the conductor from its surroundings—particularly the housing 2. The condenser core 26 includes a solid insulator 21 and a conductive field-grading layer 22, for example, in the form of aluminum foil. The field-grading layer 22 may be formed in a substantially concentric tube around and parallel to the conductor 6. When manufacturing the condenser core 26, the field-grading layers may be interleaved, for example, between layers of a winding material for the solid insulator—e.g., cellulose-based paper. Typically, the outer field-grading layer 22 has a reduced longitudinal extension L1 (corresponding to the height of the concentric tube) compared to the inner field-grading layer 22, such that this longitudinal extension gradually decreases from the innermost field-grading layer to the outermost field-grading layer.

[0025] Each of the field-grading 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 field-grading layer and the adjacent inner or outer field-grading layer may be in the range of 0.1 mm to 10 mm, for example, about 1 mm, corresponding to multiple turns of the web of solid insulator material 21. The longitudinal extension (height) L1 of the field-grading layer may be in the range of 1-10 m. Typically, the bushing and the housing 2 are filled with the same insulating liquid 3. However, the bushing is liquid-tight and preferably also airtight, so as to provide a liquid-tight seal for the opening 4a in the housing when the bushing is placed through it. The solid insulator 21 may be impregnated with an insulating liquid, such as oil-impregnated paper.

[0026] It has been found that radio transmissions using carrier frequencies in the range of 100 kHz to 1 MHz ( Figure 1 The path (a) can pass through the solid insulator 21 in the gap 23 between two adjacent field classification layers 22 (i.e., the two field classification layers that do not have any field classification layers between them, but generally only have solid insulator 21, which may be impregnated with insulating liquid 3).

[0027] The sleeve 5 may also conventionally include an external rain shed insulator 24 and / or a flange 25 for securing the sleeve to the outside of the wall 9 of the housing 2.

[0028] Figure 3aAn opening 4b in the wall 9 of the enclosure 2 is illustrated, for example, as a maintenance port for accessing the interior of the enclosure during the installation and / or maintenance of the transformer 1. The opening 4b is covered by a (e.g., substantially flat) metal cover 7, which is typically fastened to the wall 9 by means of a metal fastening device 32—such as a screw or bolt, exemplified herein as a screw 32. The cover 7 can have any suitable shape as viewed from above, such as a rectangular or circular shape. A solid insulator 31—e.g., an O-ring comprising an elastic material—is continuously arranged around the opening 4b between the metal cover 7 and the exterior of the enclosure wall 9 to provide a liquid-tight seal for the opening 4b, and preferably also to provide a gas-tight seal.

[0029] When the cover 7 is fastened to the box wall 9 by means of metal fastening devices 32, at least one slit 33 is formed between the outer surface of the wall 9 and the inner surface of the metal cover 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 straight-line distance) between two adjacent metal fastening devices 32 (i.e., between two metal fastening devices that do not have another metal fastening device between them, for example, along the outer edge of the cover 7). In such slits 33 defined by the metal cover, the wall, and the fastening devices, it has been found that, Figure 1 The radio waves of path (c) can pass through the solid insulator 31 without being shielded by the metal cover, wall, and fastening device. Similarly, Figure 1 The radio waves of path (b) can pass through the solid insulator 31, where the cover 7 is replaced by the flange 25 of the sleeve 5, i.e., in the slit 33 defined by the outer surface of the wall 9 and the inner surface of the flange 25 (i.e. the surface facing the opening 4) and by fastening the flange 25 to two adjacent fastening devices—e.g., bolts or screws—32 on the wall 9 around the opening 4a.

[0030] Preferably, the length l1 of the slit 33 is 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). It has been found that a carrier with a carrier frequency in the range of 300 MHz to 10 GHz or to 3 GHz passes through the solid insulator 31 to the outside of the housing 2. The height l2 of the slit 33 should be large enough to prevent direct contact between the wall 9 and the cover 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 and the cover 7 around the opening 4b, is preferably less than 10 cm, for example in the range of 0.5 cm to 4 cm.

[0031] Figure 3bAn embodiment of the cover 7, viewed from above, is illustrated, and the cover has a plurality of fastening devices 32, such as screws or bolts, arranged along the outer edge of the cover. Figure 3b In some embodiments, the cover is substantially circular, which may be preferred. (See also: Regarding...) Figure 3a The length l1 of the slit 33 discussed can be defined by the straight-line distance between any two adjacent fastening devices 32.

[0032] Figure 4 This is a flowchart of one embodiment of the method disclosed herein. The method is used to transmit sensor readings in one embodiment of the transformer system 10 discussed herein. Sensor device 11 obtains sensor readings on power transformer 1, such as measurements of temperature, pressure, flow rate, etc., of the insulating fluid inside tank 2—e.g., in or at sensing device 8. Then, radio transmitter 12 wirelessly transmits the sensor readings—using a carrier frequency in the range of 100 kHz to 1 MHz, for example, through the solid insulator 21 in bushing 5, or using a carrier frequency in the range of 300 MHz to 10 GHz, for example, through the solid insulator 31 between cover 7 and tank wall 9.

[0033] In some embodiments of the invention, a solid insulator 21 is included in a sleeve 5 disposed in an opening 4a of the housing. In some embodiments, the solid insulator 21 comprises cellulose-based paper impregnated with an insulating liquid 3. In some embodiments, the solid insulator 21 is disposed between longitudinal conductive field grading layers 22 in the condenser core 26 of the sleeve 5. In some embodiments, the field grading layers 22 are arranged at a radial distance L2 between each other in the range of 0.5 to 2 mm. In some embodiments, each of the field grading layers 22 has a longitudinal extension L1 of at least 1 m—for example, in the range of 1 to 10 m. In some embodiments, the radio transmitter 12 uses a carrier frequency in the range of 100 kHz to 1 MHz to transmit sensor readings or is configured to use said carrier frequency to transmit sensor readings.

[0034] In some embodiments of the invention, a solid insulator 31 is included in a slit 33 formed between the wall 9 of the housing 2 and a metal cover 7 (or possibly a flange 25) covering the housing opening 4b (or 4a). In some embodiments, the solid insulator 31 comprises an O-ring of elastic material disposed between the metal cover 7 or flange 25 and the exterior of the housing 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 radio transmitter 12 is configured to transmit sensor readings using a carrier frequency in the range of 300 MHz to 10 GHz.

[0035] The foregoing description of this disclosure primarily refers to several embodiments. However, as will be readily understood by those skilled in the art, other embodiments besides those disclosed above are also possible within the scope of this disclosure, as defined by the appended claims.

Claims

1. A transformer system (10), comprising: A power transformer (1) includes a metal box (2) filled with an electrically insulating liquid (3); as well as The wireless sensor device (11) is immersed in the insulating liquid inside the box; The wireless sensor device includes a radio transmitter (12) for wirelessly transmitting sensor readings to the outside of the transformer through an opening (4a) in the enclosure, the opening being provided with a liquid-tight seal comprising a solid insulator (21; 31) for preventing the insulating liquid from leaking from the enclosure, and wherein the radio transmitter (12) is configured to transmit the sensor readings using a carrier frequency in the range of 100 kHz to 1 MHz. The radio transmitter transmits the sensor readings through the solid insulator. The solid insulator (21) is included in a sleeve (5) arranged in the opening (4a) of the box, and The solid insulator (21) is arranged between the longitudinal conductive field hierarchical layers (22) in the condenser core (26) of the sleeve (5).

2. The transformer system according to claim 1, wherein the solid insulator (21) comprises cellulose-based paper impregnated with the insulating liquid (3).

3. The transformer system according to claim 1 or 2, wherein the field-level layers (22) are arranged at a radial distance (L2) between each other in the range of 0.5 to 2 mm.

4. The transformer system according to claim 3, wherein each of the field-level layers (22) has a longitudinal extension (L1) of at least 1 m.

5. The transformer system according to claim 4, wherein the longitudinal extension (L1) is in the range of 1 to 10 m.

6. A method for transmitting sensor readings in a transformer system (10) according to any one of the preceding claims, the method comprising: The wireless sensor device (11) obtains sensor readings on the power transformer (1) (S1); as well as The radio transmitter (12) transmits (S2) sensor readings using a carrier frequency ranging from 100 kHz to 1 MHz.

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