WIRELESS TRANSMISSIONS THROUGH A TRANSFORMER TANK

Abstract

The present disclosure relates to a transformer system comprising a power transformer including a metal tank filled with an electrically insulating liquid, and a wireless sensor arrangement submerged in the insulating liquid within the tank. The sensor arrangement includes a radio transmitter for wirelessly transmitting sensor readings to the outside of the transformer through an opening in the tank, said opening being provided with a liquid-tight seal comprising a solid insulator for preventing leakage from the tank of the insulating liquid and wherein the radio transmitter is configured for transmitting the sensor readings using a carrier frequency within the range of from 100 kHz to 1 MHz.

Claims

1. A transformer system comprising: a power transformer comprising a metal tank filled with an electrically insulating liquid; and a wireless sensor arrangement submerged in the insulating liquid within the tank; wherein the sensor arrangement comprises a radio transmitter for wirelessly transmitting sensor readings to the outside of the transformer through an opening in the tank, said opening being provided with a liquid-tight seal comprising a solid insulator for preventing leakage from the tank of the insulating liquid, and wherein the radio transmitter is configured for transmitting the sensor readings using a carrier frequency within the range of from 100 kHz to 1 MHz.

2. The transformer system of claim 1, wherein the solid insulator is comprised in a bushing arranged in the tank opening.

3. The transformer system of claim 2, wherein the solid insulator comprises cellulose-based paper which is impregnated with the insulating liquid.

4. The transformer system of claim 2, wherein the solid insulator is arranged between longitudinal electrically conductive field-grading layers in a condenser core of the bushing.

5. The transformer system of claim 4, wherein the field-grading layers are arranged at a radial distance from each other within the range of from 0.5 to 2 mm.

6. The transformer system of claim 4, wherein each of the field-grading layers has a longitudinal extension of at least 1 m.

7. A method of transmitting sensor readings in a transformer system of claim 1, the method comprising: obtaining, using the sensor arrangement, sensor readings on the power transformer; and transmitting, the radio transmitter, the sensor readings using a carrier frequency within the range of from 100 kHz to 1 MHz.

8. The transformer system of claim 1, wherein the solid insulator comprises cellulose-based paper which is impregnated with the insulating liquid.

9. The transformer system of claim 3, wherein the solid insulator is arranged between longitudinal electrically conductive field-grading layers in a condenser core of the bushing.

10. The transformer system of claim 5, wherein each of the field-grading layers has a longitudinal extension of at least 1 m.

11. The transformer system of claim 10, wherein each of the field-grading layers has a longitudinal extension of less than about 10 m.

12. The transformer system of claim 6, wherein each of the field-grading layers has a longitudinal extension of less than about 10 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Embodiments will be described, by way of example, with reference to the accompanying drawings, in which:

[0015] FIG. 1 is a schematic sectional side view of a transformer system in accordance with some embodiments of the present invention.

[0016] FIG. 2 is a schematic view in longitudinal section of a bushing, in in accordance with some embodiments of the present invention.

[0017] FIG. 3a is a schematic sectional detail of a transformer tank having an opening covered by a metal cap, in accordance with some embodiments of the present invention.

[0018] FIG. 3b is a schematic top view of an embodiment of the metal cap of FIG. 3a.

[0019] FIG. 4 is a schematic flow chart of a method in accordance with some embodiments of the present invention.

DETAILED DESCRIPTION

[0020] Embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which certain 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 by way of example 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.

[0021] FIG. 1 illustrates a transformer system 10 comprising a power transformer 1, e.g., a HV transformer, and a sensor arrangement 11.

[0022] The transformer 1 comprises an inductive arrangement 8, comprising transformer windings, submerged in an electrically insulating liquid 3 contained in a tank 2, typically completely filling the tank. The liquid may be any suitable transformer liquid, e.g., an oil such as a mineral oil, and/or an ester liquid. The tank is typically of metal, e.g., steel, which is radio frequency shielding. The tank 2 has at least one opening 4 through a wall 9 of the tank. For instance, the transformer may comprise at least one, but typically a plurality of, bushing(s) 5 for passing an electrical conductor 6, e.g., for an electrical phase, through an opening 4a in a wall 9 of the tank 2. Also, the transformer may comprise a service opening 4b in a wall 9 of the tank 2, which is covered by a metal cap 7, typically of the same material as the tank 2. Thus, the opening 4a is provided with a liquid-tight seal comprising the bushing 5, while the opening 4b is provided with a liquid-tight seal comprising the cap 7.

[0023] The sensor arrangement 11 is submerged in the insulating liquid 3 and comprises a sensor 13 configured for measuring a property of the transformer, e.g., of the inductive arrangement 8. The sensor 13 is connected with a radio transmitter 12 of the sensor arrangement ii, for wirelessly transmitting sensor readings to the outside of the transformer 1 through an opening 4a and/or 4b in the tank 2. The radio transmitter 12 may be configured for transmitting the sensor readings using a predetermined carrier frequency within a frequency range which is empirically selected in view of the physical characteristics of the opening 4, solid insulator and insulating liquid 3 for enabling the radio transmission to pass through the opening 4. It has been determined that a carrier frequency within either of the ranges 100 kHz to 1 MHz and 300 MHz to 10 GHz may be especially useful for passing through a sealed opening 4.

[0024] FIG. 1 also illustrates a few possible different paths (a), (b) and (c) for the wireless transmission of the sensor readings from the radio transmitter 12. Path (a) is through the opening 4a, which is sealed by means of the bushing 5, through solid insulation within the bushing. Path (b) is also through the opening 4a, which is sealed by means of the bushing 5, but through solid insulation between the bushing 5 and the tank 2, e.g., solid insulation (possibly comprising an O-ring or the like) arranged between a flange 25 (see FIG. 2) of the bushing 5 and an outside of the wall 9 of the tank 2. Path (c) is through the opening 4b, which is covered by the cap 7, through solid insulation between the tank 2 and the cap 7, e.g., solid insulation (possibly comprising an O-ring 31 or the like, cf. FIG. 3a) arranged between the cap 7 and the outside of the wall 9 of the tank 2.

[0025] FIG. 2 illustrates a bushing 5 which may be arranged through an opening 4a in the tank 2. The bushing may be substantially rotational symmetric and arranged for allowing the conductor 6 to run through a central longitudinal through hole through the bushing. The bushing 5 comprises a condenser core 26 which is arranged around the conductor 6, insulating the conductor from the surroundings, especially from the tank 2. The condenser core 26 comprises a solid insulator 21 and electrically conductive field-grading layers 22, e.g., in the form of aluminium foils. The field-grading layers 22 may form substantially concentric tubes around and in parallel with the conductor 6. The field-grading layers may e.g., be interleaved between layers of wound material of the solid insulator, e.g., of cellulose based paper, when producing the condenser core 26. Typically, outer field-grading layers 22 have a reduced longitudinal extension L1 (corresponding to height of the concentric tubes) compared with inner field-grading layers 22 such that the longitudinal extension is gradually reduced from the innermost field-grading layer to the outermost field-grading layer.

[0026] Each of the field-grading layers may have a thickness of less than 100 μm, e.g., within the range of 10 to 40 μm, and the radial distance L2 between the field-grading layer and a neighbouring inner our outer field-grading layer may be within the range of 0.1 mm and 10 mm, e.g., about 1 mm, corresponding to a plurality of turns of a web of the solid insulator 21 material. The longitudinal extension (height) L1 of the field-grading layer may be within the range of 1-10 m. Typically, the bushing is filled with the same insulating liquid 3 as the tank 2. However, the bushing is liquid-tight may be gas-tight according to some embodiments, providing a liquid-tight seal of the opening 4a in the tank when the bushing is placed there through. The solid insulator 21 may be impregnated with the insulating liquid, e.g., oil-impregnated paper.

[0027] It has been found that, a radio transmissions (path (a) of FIG. 1) using a carrier frequency within the range of from 100 kHz to 1 MHz, may pass through the solid insulator 21 in the gap 23 between two neighbouring field-grading layers 22 (i.e., two field-grading layers which do not have any field-grading layer between them, but typically only solid insulator 21, possibly impregnated with insulating liquid 3).

[0028] The bushing 5 may conventionally also comprise an outer, weather shed insulator 24 and/or a flange 25 for fastening the bushing to the outside of the wall 9 of the tank 2.

[0029] FIG. 3a illustrates an opening 4b in a wall 9 of the tank 2, e.g., a service hole for accessing the interior of the tank during installation and/or service of the transformer 1. The opening 4b is covered by a metal cap 7 (e.g., substantially flat) which is typically fastened to the wall 9 by means of metal fastening means 32 such as screws and/or bolts, herein exemplified with screws 32. The cap 7 may have any suitable shape, as viewed from atop, e.g., a rectangular or circular shape. A solid insulator 31, e.g., comprising an O-ring of an elastic material, is arranged between the metal cap 7 and an outside of the tank wall 9 continuously around the opening 4b for providing a liquid-tight, and preferably also gas-tight, seal of the opening 4b.

[0030] When the cap 7 is fastened to the tank wall 9 by means of the metal fastening means 32, at least one slit 33 is formed between the outer surface of the wall 9 and the inner surface (i.e., the surface facing the opening 4b) of the metal cap 7. Each of the at least one slit 33 has a length l1 defined by the distance (typically the straight distance) between two neighbouring metal fastening means 32 (i.e., between two metal fastening means which do not have a further metal fastening means between them, e.g., along an outer edge of the cap 7). In such a slit 33, delimited by the metal cap, wall and fastening means, it has been found that radio waves (of path (c) of figure i) may pass through the solid insulator 31 without being shielded by said metal cap, wall and fastening means. Similarly, radio waves of path (b) of FIG. 1 may pass through a solid insulator 31, with the cap 7 exchanged for the flange 25 of a bushing 5, i.e., in a slit 33 delimited by the outer surface of the wall 9 and the inner surface (i.e., the surface facing the opening 4a) of the flange 25, and by two neighbouring fastening means, e.g., bolts or screws, 32 fastening the flange 25 to the wall 9 around the opening 4a.

[0031] In some embodiments, the length l1 of the slit 33 is within the range of from 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). Then, a carrier wave having a carrier frequency within the range of from 300 MHz to 10 GHz, or to 3 GHz, has been found to pass through the solid insulator 31 to the outside of the tank 2. The height 12 of the slit 33 should be large enough to prevent direct contact between the wall 9 and the cap 7, e.g., at least 10 μm such as within the range of 10 μm to 1 cm or 1 mm. The radial length l3 of the slit 33, i.e., the distance of overlap between the outer surface of the wall 9 and the cap 7 around the opening 4b, is preferably less than 10 cm, e.g., within the range of from 0.5 cm to 4 cm.

[0032] FIG. 3b illustrates an embodiment of the cap 7 viewed from the top and having numerous fastening means 32, e.g., screws and/or bolts, arranged along an outer edge of the cap. In the embodiment of FIG. 3b, the cap is substantially circular, which may be provided in some embodiments. As discussed in relation to FIG. 3a, the length l1 of the slit 33 may be defined by the straight distance between any two neighbouring fastening means 32.

[0033] FIG. 4 is a flow chart of an embodiment of a method of the present disclosure. The method is for transmitting sensor readings in an embodiment of the transformer system 10 discussed herein. The sensor arrangement 11 obtain S1 sensor readings on the power transformer 1, e.g., measurements of temperature, pressure, flow rate of the insulating liquid, or the like within the tank 2, e.g., in or at the inductive arrangement 8. Then, the radio transmitter 12 transmits S2 the sensor readings wirelessly using a carrier frequency within the range of from 100 kHz to 1 MHz, e.g., through solid insulation 21 in a bushing 5, or within the range of from 300 MHz to 10 GHz, e.g. through solid insulation 31 between a cap 7 and a wall 9 of the tank.

[0034] In some embodiments of the present invention, the solid insulator 21 is comprised in a bushing 5 arranged in the tank opening 4a. In some embodiments, the solid insulator 21 comprises cellulose-based paper which is impregnated with the insulating liquid 3. In some embodiments, the solid insulator 21 is arranged between longitudinal electrically conductive field-grading layers 22 in a condenser core 26 of the bushing 5. In some embodiments, the field-grading layers 22 are arranged at a radial distance L2 from each other within the range of from 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, e.g., within the range of from 1 to 10 m. In some embodiments, the radio transmitter 12 transmits, or is configured for transmitting, the sensor readings using a carrier frequency within the range of from 100 kHz to 1 MHz.

[0035] In some embodiments of the present disclosure, the solid insulator 31 is comprised in a slit 33 formed between a wall 9 of the tank 2 and a metal cap 7 (or possibly flange 25) covering the tank opening 4b (or 4a). In some embodiments, the solid insulator 31 comprises an O-ring of an elastic material arranged between the metal cap 7 or flange 25 and an outside of the tank wall 9. In some embodiments, the slit 33 has a length li within the range of from 0.03 to 1 m. In some embodiments, the radio transmitter 12 is configured for transmitting the sensor readings using a carrier frequency within the range of from 300 MHz to 10 GHz.

[0036] The present disclosure has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the present disclosure, as defined by the appended claims.