Arc detection system and transformer having an arc detection system

Abstract

The invention relates to an arc detection system, in particular for use as an arc detection system in a transformer having an optical waveguide comprising a core and, at least in some regions, a casing enclosing the core and having a lower refractive index than the core, and at least in some regions a light shielding element, for receiving electromagnetic radiation and for forwarding at least some of the electromagnetic radiation to a light detector which is arranged at one end of the optical waveguide, characterised in that the optical waveguide is formed, in at least one portion, without a light shielding element and has at least one first subregion and at least one second subregion there, wherein the optical waveguide has the core and the casing in the first subregion(s) and has only the core in the second subregion(s). The invention also relates to a transformer having a housing, wherein the housing is filled with a dielectric fluid, in particular an oil, and at least one arc detection system.

Description

[0001] Arc detection system and transformer with arc detection system

[0002] The present invention relates to an arc detection system according to the preamble of claim 1 and a transformer with an arc detection system.

[0003] Transformers, rectifier transformers, phase shifters, and inductors comprise a housing containing one or more coils, some of which are coupled to each other via their magnetic fields. Rectifier transformers also contain semiconductor elements. These are cooled by dielectric coolants, such as dielectric oils. During their service life of up to 50 years, the power delivered, combined with environmental factors such as extreme weather conditions, can cause wear on the insulation of the transformer windings. This wear can lead to short circuits, which in turn cause arcing. These arcs can result in a temperature increase and gas evolution, accompanied by a pressure increase inside the transformer housing.The pressure can build up to such an extent that the casing cracks, and the coolant and gases contained inside can cause a fire or even an explosion upon contact with air.

[0004] To protect the transformer and its surroundings from damage, various transformer safety systems have been developed. Electrical protection systems, such as a relay with differential current measurement, disconnect the transformer when anomalies occur. In liquid-cooled transformers, Buchholz relays are also used to simultaneously monitor the coolant level and the transformer's internal pressure. In the event of damage, the coolant can be drained by opening a valve, thus relieving the overpressure. Additionally, an inert gas, such as nitrogen, can be introduced into the tank. It is crucial that the anomaly is detected quickly.

[0005] Transformer protection devices are also known that allow the use of an optical fiber whose outer plastic sheath (or "jacket" in English) has been removed. Such a transformer protection device is described in WÖ02 / 21657.

[0006] Based on this, the invention aims to improve the sensitivity of such a solution.

[0007] According to the invention, this problem is solved by the features of claim 1. The arc detection system according to the invention is particularly intended for use as an arc detection system in a transformer. It comprises an optical waveguide comprising a core and at least partially a cladding enclosing the core with a lower refractive index than the core and at least partially a light-shielding element, wherein the optical waveguide is configured to receive electromagnetic radiation and to transmit at least a portion of the electromagnetic radiation to a light detector arranged at one end of the optical waveguide.This arc detection system is characterized in that the optical waveguide is designed without a light shielding element in at least one section and has at least a first sub-section and at least a second sub-section, wherein the optical waveguide has the core and the cladding in the first sub-section(s) and has only the core in the second sub-section(s).

[0008] A light shielding element is any device that prevents light from entering the optical fiber; this is particularly important when part of the optical fiber is located outside a transformer.

[0009] Surprisingly, it has been shown that by using two different sections, one with and one without the cladding, the sensitivity of the detection system can be increased compared to optical fibers without these two sections. This can be attributed to the fact that the probability of incoming light reaching the light detector via total internal reflection is improved.

[0010] According to one embodiment, the arc flash detection system can be configured with multiple first and second sub-sections, wherein the first and second sub-sections are arranged alternately. According to another embodiment, the first and second sub-sections can be arranged periodically, alternating with each other. According to yet another embodiment, the first and second sub-sections can have a longitudinal extent of 0.5 cm to 5 cm along the optical fiber, with the longitudinal extent of the first and second sub-sections being, in particular, the same. This further improves the performance of the optical fiber.

[0011] According to one embodiment, the at least one section can be at least 0.5 meters long. This allows large areas of a transformer to be monitored, especially if the lateral section is also free of the light-shielding element. According to another embodiment, the optical waveguide can have a lens, particularly a hemispherical lens, at a second end opposite the end where the light detector is located. This allows more light to enter the optical waveguide.

[0012] According to one embodiment, the optical waveguide can have at least one branch with multiple arms. This makes it possible to reach even difficult-to-access areas in a transformer without having to bend the optical waveguide excessively to return from these areas. The branching also allows for a large volume coverage for detecting electromagnetic radiation.

[0013] According to one embodiment, the at least one optical waveguide can have a second section in which the optical waveguide continuously incorporates a light-shielding element up to the light detector in order to shield the second section against electromagnetic radiation, in particular sunlight. The optical waveguide is thus protected from the penetration of external electromagnetic radiation, such as sunlight, as soon as the second section of the optical waveguide is located outside a transformer. Detection is therefore limited to the safety-relevant arcs within the transformer housing.

[0014] According to one embodiment, the second section of the at least one optical waveguide can be at least 0.5 meters long, preferably at least 5 meters. Lengths of over 50 meters are also possible. Due to the length of the second section of the light transmission medium, the light detector can be positioned for easy access without compromising its functionality.

[0015] According to one embodiment of the arc detection system, the light detector can be one of the following: semiconductor-based light-sensitive sensors, in particular a photodiode, an avalanche photodiode, a phototransistor, a photoresistor, a CCD sensor, an APS-CMOS sensor, a pyroelectric sensor, or a vacuum tube-based light-sensitive sensor, in particular a photomultiplier or a photocathode.

[0016] Since the detector can be positioned outside the transformer housing, detectors or sensors suitable for use at normal ambient temperatures and pressures can be employed. According to one embodiment, the optical fiber can be flexible. Preferably, the bending radius can be at least ten times larger than the fiber diameter, and at least fifteen times larger under mechanical stress. For fiber diameters of 1 mm, the bending radius should therefore be at least 15 mm. This allows the optical fiber to be routed around components inside the transformer housing.

[0017] The object of the invention is also achieved with a transformer according to claim 8.

[0018] The transformer according to the invention comprises a housing, wherein the housing is filled with a dielectric fluid, in particular an oil, and at least one arc flash detection system, in particular as described above. Thanks to the arc flash detection system, safety measures can be taken at an early stage in a transformer. In the variant in which the arc flash detection system described above is used, the sensitivity of the light detection can be increased in particular.

[0019] According to one embodiment, the inside of the housing can be polished at least partially, and in particular completely, and / or have a light-reflecting coating, especially a white paint layer. This allows light from an arc reflected on the inside to enter the optical waveguide and thus increase the sensitivity of the arc detection.

[0020] According to one embodiment, the refractive index of the dielectric fluid can be lower than the refractive index of the core and / or the cladding. This allows total internal reflection of at least some of the incident light, so that the light detector can ultimately detect an electric arc.

[0021] According to one embodiment, the light detector can be arranged outside the housing, and the optical fiber can be arranged at least partially inside the housing. At least a portion of the optical fiber within the transformer can be configured to receive electromagnetic radiation emitted inside the housing. This increases the reliability of the light detection and the safety of the transformer. When such an arc detection system is installed in a transformer, the optical fiber can receive the electromagnetic radiation when an arc occurs within the transformer. Simultaneously, the light detector can be arranged outside the housing. This further increases the reliability of the light detection and the safety of the transformer.If the optical fiber (or fibers) itself receives the electromagnetic radiation emitted by an arc occurring between the windings of a transformer and transmits it to the light detector, the position of the light detector can be chosen arbitrarily. This makes the position of the light detector independent of the position of the windings. Thus, a position outside the transformer can be selected. By using the detector in a less harsh environment, wear is reduced, and the detector itself becomes easily accessible. Furthermore, the use of the optical fiber(s) allows the device to be adapted to different transformer sizes. For this, it is sufficient to select a suitable length.

[0022] According to one embodiment, the optical fiber can be attached at at least one, and in particular several, points within the housing, wherein the optical fiber has a further sheath there, in particular a sheath impermeable to electromagnetic radiation. This ensures the positioning of the optical fibers in the housing and allows the detection system to reliably detect arcs over a long period of time.

[0023] According to one embodiment, the optical fiber can be mounted in such a way that one or more of the first sub-sections and / or the second sub-sections are located opposite a current-carrying component or components in the housing, separated only by a dielectric cooling fluid. Thus, the optical fiber can directly "see" the light of an electric arc and does not rely on reflections from other components to detect the arc.

[0024] According to one embodiment of the transformer, the at least one optical fiber can be routed through the transformer housing using a sealed bushing. The use of a sealed bushing does not impair the normal operation of the transformer while improving safety monitoring. Furthermore, the sealed bushing also allows for the coaxial connection of different optical fibers at the bushing. For example, one optical fiber without a light-shielding element is used inside the transformer, and a second optical fiber with a light-shielding element is used on the outside.

[0025] Thus, mounting the arc flash detection system with a sealed feedthrough not only increases the transformer's safety but also facilitates retrofitting the arc flash detection system to transformers already delivered that include corresponding connections, such as blanking flanges. According to one embodiment, the transformer can be configured with multiple optical fibers that are routed independently of one another, and in particular sealed, through the transformer housing, and which can be connected to one, or in particular only one, optical detector. This allows even large volumes to be effectively monitored.

[0026] According to one embodiment, at least one optical waveguide can be arranged within one or more windings and / or wound together with one or more windings, in particular such that the first sub-areas and the second sub-areas are arranged at least partially within the windings.

[0027] Due to the proximity of the light transmission medium to the transformer's live windings, even low-intensity arcs, especially those below 1 candela, can be detected. Partial discharges, arcs that do not span the entire insulation gap, can also be detected. This allows for timely intervention, leading to increased system safety.

[0028] Since optical fibers are typically non-conductive, they can be routed directly alongside live parts in transformers, even those carrying high voltage. A flexible optical fiber can be wrapped around the windings and easily adapted to the various sizes and types of transformers, making it particularly advantageous for retrofitting. This also allows for the detection of small arcs and further enhances system safety.

[0029] According to one embodiment, the transformer can include a control unit configured to switch off the transformer and / or isolate an expansion tank and / or open a drain valve on the transformer housing and / or initiate the introduction of an inert gas, in particular nitrogen, via an inlet valve when the light detector detects electromagnetic radiation via the at least one optical fiber. In particular, the control unit disconnects the transformer from the power supply when the signals from the light detector exceed a corresponding threshold value with respect to duration, and / or intensity, and / or wave spectrum.

[0030] Disconnecting the transformer from the power supply early prevents further energy input into the transformer. Opening the valve allows excess pressure to be released. Introducing an inert gas reduces the risk of fire. This light detection system increases the transformer's safety, and the maintenance required after the described fault is comparatively minimal. The invention also relates to an energy transmission device, in particular a rectifier transformer, a phase shifter, or a choke coil with an arc detection system, according to any one of claims 1 to 7.

[0031] The invention is described in further detail below with reference to the figures and exemplary embodiments. Individual features of the respective exemplary embodiments can be combined arbitrarily to achieve new embodiments according to the invention.

[0032] Figure 1 schematically shows a transformer according to the invention with an arc detection system according to a first embodiment.

[0033] Figure 2 schematically shows a transformer with an arc detection system according to a second embodiment.

[0034] Figure 3 shows an arc detection system according to a third embodiment of the invention.

[0035] Figure 1 shows a transformer 1 with a housing 3 that can be closed with a cover 5. Schematically shown inside the housing 3 are a high-voltage winding 7 and a low-voltage winding 9, which are wound around a common iron core 11. Depending on the transformer, there may also be several high- and low-voltage windings. The high-voltage winding 7 is connected via high-voltage connecting lines 13 to external first insulated contacts 15a and 15b. The low-voltage winding 9 is similarly connected via low-voltage connecting lines 17 to the external second insulated contacts 19a and 19b. The external high-voltage line 21 and the external low-voltage line 23 are connected to these contacts.

[0036] According to one variant of the invention, the housing 3 and the lid 5 are partially and / or completely polished on their inside and / or formed with a light-reflecting coating 6, for example a white paint layer.

[0037] The high- and low-voltage windings 7, 9 are cooled by a coolant 25 filled in tank 3. A dielectric fluid, such as an oil, is typically used for this purpose. This fluid can be flammable.

[0038] Also shown schematically are known protective devices for the transformer 1, such as a fire alarm 27, a Buchholz relay 29 arranged between the tank 3 and an expansion tank 30, a drain valve 31 for coolant 25, an inlet valve 33 for injecting an inert gas, for example nitrogen, a relay with differential current measurement 35, a first circuit breaker 37 on the high-voltage side and a second circuit breaker 39 on the low-voltage side. These devices are connected to a control unit 41.

[0039] The transformer 1 can also be equipped with additional protective devices, such as a rupture disc. Such a rupture disc breaks at a predetermined pressure, allowing coolant 25 to flow out to relieve the pressure before the housing 3 bursts. The transformer 1 can also be equipped with fewer protective devices.

[0040] The control unit 41 is designed so that, in the presence of predetermined parameters, such as a stop of the Buchholz relay 29 and / or an unusual voltage value at the relay 35, safety measures such as switching off and / or draining of coolant 25 and / or injecting an inert gas, such as nitrogen, are initiated.

[0041] According to the invention, the transformer further comprises an arc flash detection system 43. The arc flash detection system 43 comprises an optical fiber 45 and a light detector 47, which is connected to a first end 45a of the optical fiber 45. The arc flash detection system 43 can be arranged on the housing 3 of the transformer 1. The light detector 47 can be arranged outside the transformer 1 and the optical fiber 45 inside it. The arc flash detection system 43, or the light detector, is also connected to the control unit 41.

[0042] According to one variant, more than one arc detection system 43 or several optical fibers 45 connected to a common light detector 47 could be provided.

[0043] The optical fiber 45 is designed such that it can receive light from the outside at least partially, preferably along its entire length, and not only at its second end 45b. This allows a larger area inside the transformer 1 to be monitored.

[0044] Figure 1 schematically shows the enlarged cross-section 45c of the optical waveguide 45, here using the example of a typical fiber optic cable. The optical waveguide comprises a core 81 made of glass or plastic and is surrounded by a cladding 83 that encloses the core 81. This cladding has a lower refractive index than the core 81. A light-shielding element 85 in the form of another sheath is in turn surrounded by the cladding 83. Additional layers, such as a lacquer layer, can be arranged between these two layers. The refractive index of the dielectric coolant can be lower or higher than the refractive index of the cladding 83, depending on the coolant used. However, it is important that the refractive index of the cladding 83 is lower than the refractive index of the core 81.

[0045] In such an optical waveguide 45, when used in communication technology, light coupled in at the second end 45b of the core 81 is guided through the optical waveguide. At the other end 45a of the core 81, the light can then be coupled out again and detected and analyzed by the light detector 47.

[0046] Light coupled into the core 81 is totally internally reflected according to the laws of refraction from the critical angle at the transition to the cladding 83. At angles smaller than the critical angle, the light rays are absorbed in the cladding 83 and the light-shielding element 85. To increase the angle of incidence for light entering at end 45b of the optical waveguide 45, a lens 87, in particular a hemispherical lens, can be arranged at end 45b according to one variant.

[0047] According to the invention, the optical fiber 45 has a section 46 with first subsections 46a and second subsections 46b. Here, section 46 is located directly opposite the low-voltage winding 9. However, the optical fiber can also have further such sections, which, for example, are located opposite the high-voltage winding 7 or other current-carrying components.

[0048] In the first subsections 46a, the optical waveguide 45 has no light-shielding element 85, but only the core 81 and the cladding 83. In the second subsections 46b, the optical waveguide has only the core 81.

[0049] According to the variant shown in Figure 1, the first sub-regions 46a and second sub-regions 46b can be arranged alternately, in particular periodically alternating with each other. In this context, periodically alternating with each other means that the extension 11 of the first sub-regions 46a in section 46 is all of the same length, and the extension I2 of the second sub-region 46b is also of the same length. According to another variant, 11 and I2 can be of the same length. According to yet another variant, third sub-regions can be arranged between the first and second sub-regions 46a and 46b, in which the optical waveguide 45 also includes the light-shielding element 85.

[0050] According to one variant, the first sub-sections 46a and second sub-sections 46b can have a longitudinal extent 11 and 12, respectively, of 0.5 cm to 5 cm along the optical waveguide 45. Since there is no longer a light-shielding element on the optical waveguide 45 in section 46, light can enter the optical waveguide 45 along its length. Because the dielectric coolant can have a refractive index lower than that of the core 81, at least some of the light entering the optical waveguide can remain within it by total internal reflection and reach the light detector 47. Even in the reverse case, light can reach the detector by partial internal reflection.

[0051] Since the signals do not involve the transmission of information streams, it is irrelevant whether the light emitted can be fully or only partially fed into the optical fiber 45. What is crucial is that at least some of the light is transmitted within the fiber optic cable so that it can ultimately reach the light detector 47. For detecting an arc, it may be sufficient if less than 1% of the light enters and remains in the fiber.

[0052] The light detector 47 can be a semiconductor-based light detector, such as a CCD camera, a photodiode, an avalanche photodiode, a phototransistor, a photoresistor; an APS-CMOS camera, a pyroelectric sensor or a vacuum tube-based light-sensitive sensor, such as a photomultiplier or a photocathode.

[0053] To secure the position of the optical fiber 45 in the housing 3, the optical fiber can be fastened inside the housing 3 with at least one fastening element, in this case two fastening elements 89a and 89b. The fastening elements 89a and 89b can be clamps, screws, or flanges.

[0054] Here, the optical waveguide 45 is attached directly to the iron core 11. In the area of ​​attachment, the optical waveguide 45 preferably has a further sheath 91, in particular a sheath that is opaque to electromagnetic radiation. In the area of ​​the fastening element 89a, this is, for example, the light-shielding element 85.

[0055] The arc detection system 43 in the transformer 1 functions according to the invention as follows.

[0056] If an arc occurs between the high-voltage winding 7 and the low-voltage winding 9, or at any other point, the optical fiber 45 can absorb the electromagnetic radiation emitted by the arc. At least a portion of this radiation then travels through the optical fiber 45 to the light detector 47, where it can be detected. The corresponding signal is then forwarded from the light detector 47 to the control unit 41. If a predetermined limit value with respect to the intensity and / or duration and / or wavelength spectrum of the detected radiation is exceeded, one or more of the safety measures described above will be initiated.

[0057] Since the light detector 47 is mounted outside the housing 3 according to the invention, it is protected from the heat and the electric field inside the transformer 1. This simultaneously increases the accessibility, reliability and service life of the light detector 47 and thus improves the safety of the transformer 1.

[0058] It has also been shown that the alternating arrangement of areas with and without sheathing 83 improves the sensitivity of the detection device compared to fiber optics completely without sheathing 83 or completely with sheathing 83.

[0059] According to one variant, the first areas 46a are arranged where the optical waveguide 45 must have a greater curvature, while the second areas 46b are arranged where the optical waveguide 45 is straight.

[0060] Figure 2 shows a transformer 51 according to a second embodiment. Features with reference numerals that have already been used in connection with the transformer 1 of the first embodiment are not described again. Reference is made to the description of Figure 1.

[0061] In comparison to the first embodiment, the arc detection system 53 used differs from the arc detection system 43 in that the light detector 47 is not arranged on the housing 3, but is detached from it and located further away, for example near the control unit 41 or in the control unit 41.

[0062] The illustrated arc detection system 53 in the second embodiment comprises an optical waveguide 55, which can be divided into a first section 55a inside the housing 3 and a second section 55b outside the housing 3.

[0063] The first section 55a of the optical fiber 55 in the second embodiment further comprises two arms 57a and 57b. Arm 57a is inserted into or wound within the low-voltage winding 9. Within the winding 9 are the alternating first and second subsections 46a and 46b, as described in the first embodiment. In subsection 46a, the optical fiber has the core 81 and the cladding 83, while in subsection 46b only the core 81 is present. The second arm 57b extends to the high-voltage winding 7 and, like arm 57a, can also be inserted into the winding according to one variant. In the illustrated embodiment, arm 57b branches again into a third arm 57c and a fourth arm 57d.

[0064] The third arm 57c divides at its end into three further arms 57e, 57f and 57g. A lens 87 is arranged at each end. The arms 57e, 57f and 57g are designed without a light-shielding element 85 and have first and second sub-sections 46a and 46b according to the first embodiment.

[0065] The fourth arm 57d has the light-shielding element 85 extending to its end. Alternatively, a section with first and second sub-areas according to the first embodiment could also be formed here. A lens 87 is located at the end of the fourth arm 57d.

[0066] Since the wires of windings 7 and 9 are live, there is a high probability that an arc will occur in this area within transformer 1. Due to the proximity of the light transmission medium 55 to windings 7 and 9, even arcs with very low intensity, especially below 1 candela, can be detected. Arcs that do not span the entire insulation gap, so-called partial discharges, can also be detected. This allows any wear on the conductor insulation to be detected early, thereby increasing the safety of the overall system.

[0067] According to further variations, the optical fiber 55 can have additional arms leading to other areas of the housing 3. Thanks to the use of multiple arms, a single detector 47 is sufficient. Simultaneously, it becomes possible to monitor the entire volume of the transformer. The branches also allow access to areas that would be inaccessible when laying a single optical fiber due to the minimum bending radius dictated by the material properties of the optical fiber. For example, in transformers with many windings, the branches allow the optical fiber to be laid in a straight line between each pair of windings. With a single optical fiber, the fiber would have to be bent to reach the next pair of windings. Space for this is not always available.

[0068] In the second embodiment, the optical fiber 55 exits the interior of the housing 3 through a sealed feedthrough 59 and terminates at the light detector 47. The light detector 47 is connected to the control unit 41 via a cable 63. As in the first embodiment, the optical fiber 55 can have first and second sections 46a and 46b. In particular, as in the first embodiment, the optical fiber 55 can be a flexible optical fiber that can be adapted to the interior of the transformer 1.

[0069] This makes retrofitting transformers of various sizes and shapes particularly easy. Furthermore, the overall system safety can be increased again, as the ability to route the optical fiber almost arbitrarily allows for optimized arc detection by placing the fiber optic cable near hazardous areas.

[0070] In particular, optical fibers with a minimum length of 0.5 meters of the first section of the light transmission medium 55a are used.

[0071] In the second embodiment, the optical waveguide 55 is designed in such a way that light can penetrate the optical waveguide 55 laterally over a large part of its length and not only at the end. As mentioned, however, one or more sections, particularly those further away from the areas where arcs are expected, can also be covered within the housing 3 with the opaque light-shielding element 85.

[0072] The optical fiber 11 is provided externally with an opaque light-shielding element 85, in particular an opaque coating. The opaque light-shielding element 85 prevents external light rays from the environment, such as sunlight, from entering the optical fiber 55. This ensures that the light detector 47 does not receive false signals, thus preventing unnecessary shutdown of the system.

[0073] According to one variant, two different optical waveguides can be used inside and outside the housing 3, which are then coaxially connected to each other at the feedthrough 59.

[0074] The sealed bushing 59 increases the compatibility of the arc fault detection system with various transformer models, which has a particularly positive effect on its suitability for retrofitting. Furthermore, sealing enhances system safety.

[0075] Since the light absorbed into the optical waveguide does not leave it, and the absorption rate is low, in particular less than 20% per kilometer, the second section of the optical waveguide 55b can be relatively long, for example even over 50 meters. Thus, the location of the light detector 47 can be chosen to be any distance from the transformer 1, in particular within the control unit 41. The light detector is therefore easily accessible and protected.

[0076] To further improve the monitoring of the interior, one or more additional optical fibers 65 can be provided. The second optical fiber 65 is connected to the same light detector 47 at its first end 65a via a second sealed feedthrough 67, but could also have its own light detector. A lens 87 is arranged at the second end 65b. In the area in front of the lens 87, the sheathing 83 and the light-shielding element 85 have been removed, so that the core 81 lies freely in the dielectric fluid.

[0077] Figure 3 shows an arc flash detection system 71 according to a third embodiment, separate from the transformer. Such an arc flash detection system 71 can be used as a retrofit kit to subsequently install the safety functionality according to the invention into a transformer, for example on a blank flange in the housing.

[0078] Features with reference numerals that have already been used in connection with transformer 1 or 51 of the first or second design form are not described again. Reference is made to the descriptions in Figure 1 and 2, respectively.

[0079] The arc detection system 71 according to the third embodiment partially incorporates the arc detection system of the second embodiment. The optical fiber 75 comprises two sections 75a and 75b as well as two arms 77a and 77b. According to one variant, the arc detection system 43 of the first embodiment can be used, or further variants with multiple arms, as shown in Figure 2.

[0080] The arc detection system 71 comprises an optical fiber 75, a light detector 47, and a sealed feedthrough 59. The feedthrough 59 allows for sealing against a housing by means of suitable seals, such as O-rings on the flange surface. The optical fiber 75 can be arranged through the feedthrough 59, or two optical fibers can be coaxially connected to each other at the feedthrough 59.

[0081] The optical fiber 75 can be divided into a first section 75a and a second section 75b.

[0082] The optical waveguide 75 is covered with the light-shielding element 85 in the first section 75a towards the feedthrough 59. Subsequently, the optical waveguide 75 branches in the first section 75a into two arms 77a and 77b. At the end 79a of the first arm 77a, the light-shielding element 85 and the sheathing 83 are removed, so that the core 81 is exposed. A lens 87 can be arranged at the end.

[0083] On the second arm 77b, the light-shielding element 85 is removed in the end region 79b, and a lens 87 can be arranged at the end. According to the invention, the arm 77b therefore has a section 46 at the end region 79b with first sub-regions 46a and second sub-regions 46b. In the first sub-regions 46a, the optical waveguide 75 has only the core 81 and the cladding 83. In the second sub-regions 46b, the optical waveguide 77 has only the core 81.

[0084] According to the variant shown in Figure 3, the first sub-sections 46a and second sub-sections 46b can be arranged alternately, in particular periodically, as in the first embodiment. According to a further variant, 11 and I2 can be of equal length. According to a further variant, third sub-sections can be arranged between the first and second sub-sections 46a and 46b, in which the optical waveguide 45 also includes the light-shielding element 85.

[0085] According to one variant, the first sub-areas 46a and second sub-areas 46b can have an extent 11 or I2 in the longitudinal direction of the optical waveguide 45 of 0.5 cm to 5 cm.

[0086] The optical waveguide 75 in the second section 75b between feedthrough 59 and the light detector 47 is completely covered by the light shielding element 85 to prevent light ingress, e.g. sunlight.

[0087] The light detector 47 can be connected via a connection 73 to an external control unit, such as the unit 41 in Figure 1 or Figure 2.

[0088] The arc fault detection system 71 allows existing transformers to be retrofitted. For this purpose, the optical fiber is inserted through an opening in the transformer housing in the first section 75a. The bushing is then sealed to the transformer flange, and the light detector 47 is connected to the control unit. Simultaneously, the arms 77a and 77b are routed inside the detector housing and positioned near the critical areas of the transformer.

[0089] Thanks to the invention, it is possible to utilize the advantages of light detection to quickly identify problems in the transformer and initiate countermeasures, while simultaneously allowing the sensitive detectors to be positioned outside the transformer and thus protected from the harsh conditions inside. For this purpose, an optical waveguide is used according to the invention, which captures the light from electric arcs and transmits it to the detector. The design with first and second sub-sections increases the sensitivity.

[0090] The invention has been explained using a transformer as an example, but can be used for other energy transmission devices as well, for example in a rectifier transformer, a phase shifter or a choke coil.

[0091] Reference symbol:

[0092] IT transformer

[0093] 3 Housing (of the transformer)

[0094] 5 Case covers

[0095] 6 light-reflecting coating / paint layer

[0096] 7 High-voltage winding

[0097] 9 Low-voltage winding

[0098] II Iron core

[0099] 13 high-voltage transmission lines

[0100] 15a, 15b first isolated contacts

[0101] 17 low-voltage connecting lines

[0102] 19a, 19b second isolated contacts

[0103] 21 High-voltage line

[0104] 23 Low-voltage line

[0105] 25 Coolant

[0106] 27 fire alarms

[0107] 29 Buchholz relays

[0108] 30 expansion tanks

[0109] 31 Drain valve

[0110] 33 Inlet valve

[0111] 35 relays

[0112] 37 circuit breakers

[0113] 39 circuit breakers

[0114] 41 Control unit

[0115] 43 Lichtbogenerkennungssystem

[0116] 45 Lightwell Leader

[0117] 45a first end of the optical fiber b second end of the optical fiber Section a first subsection b second subsection Optical detector Transformer Arc detection system Optical fiber a first section of the optical fiber b second section of the optical fiber a first arm of the optical fiber b second arm of the optical fiber c third arm of the optical fiber d fourth arm of the optical fiber e fifth arm of the optical fiber f sixth arm of the optical fiber g seventh arm of the optical fiber Feedthrough Cable of further optical fiber Second feedthrough Arc detection system Connection Optical fiber a first section of the optical fiber b second section of the optical fiber a first arm of the optical fiber b second arm of the optical fiber a End section b End section Core Sheath Light shielding element Lens a, 89b Fastener Casing

Claims

Claims 1. Arc detection system, in particular for use as an arc detection system in a transformer (1), comprising an optical waveguide (45) comprising a core (81) and at least partially a sheath (83) enclosing the core (81) with a lower refractive index than the core (81) and at least partially a light shielding element (85), for receiving electromagnetic radiation and for transmitting at least a part of the electromagnetic radiation to a light detector (47) arranged at one end (45a) of the optical waveguide (45), characterized in that the optical waveguide (45) is formed in at least one section (46) without a light shielding element (85) and has at least a first subsection (46a) and at least a second subsection (46b) therein,wherein the optical waveguide (45) has the core (81) and the cladding (83) in the first sub-section(s) (46a) and has only the core (81) in the second sub-section(s) (46b).

2. Arc detection system according to claim 1, comprising several first sub-areas (46a) and second sub-areas (46b), wherein the first sub-areas (46a) and second sub-areas (46b) are arranged alternately.

3. Arc detection system according to claim 2, wherein the first sub-areas (46a) and second sub-areas (46b) are arranged periodically alternately with each other.

4. Arc detection system according to one of claims 1 to 3, wherein the first sub-areas (46a) and second sub-areas (46b) have a longitudinal extent of the optical waveguide (45) of 0.5 cm to 5 cm, wherein in particular the longitudinal extent of the first sub-areas (46a) and the second sub-areas (46b) is the same.

5. Arc detection system according to one of claims 1 to 4, wherein the optical waveguide (45) is connected at a second end (45b) to the end (45a) where the light detector is located. (47) is arranged opposite, and has a lens (87), in particular a hemispherical lens.

6. Arc detection system according to one of claims 1 to 5, wherein the optical waveguide has at least one branch with multiple arms (57a, 57b).

7. Arc detection system (43) according to one of claims 1 to 6, characterized in that the at least one optical waveguide (55) has a second section (55b) in which the optical waveguide (55) continuously extends to the light detector (47) and has the light shielding element (85) to shield the second section (55b) against electromagnetic radiation, in particular sunlight.

8. Transformer (1) with a housing (3), wherein the housing (3) is filled with a dielectric fluid, in particular an oil, and has at least one arc detection system (43), in particular according to one of claims 1 to 7.

9. Transformer according to claim 8, wherein the inside of the housing (3) is at least partially, in particular completely, polished and / or has a light-reflecting coating (6), in particular a white paint layer.

10. Transformer according to claim 8 or 9, wherein the refractive index of the dielectric fluid is lower than the refractive index of the core (81) and / or the casing (83).

11. Transformer according to one of claims 8 to 10, wherein the light detector (47) is arranged outside the housing (3) and the optical waveguide (45, 55) is arranged at least partially inside the housing (3) and at least a part of the optical waveguide (45, 55) inside the transformer (1) is configured such that the optical waveguide (45) receives electromagnetic radiation that occurs inside the housing (3).

12. Transformer according to one of claims 8 to 11, wherein the optical waveguide (45) is attached at least one, in particular several, locations within the housing (3), wherein the optical waveguide has a further covering there, in particular a covering impermeable to electromagnetic radiation.

13. Transformer according to claim 12, wherein the optical waveguide is attached such that one or more of the first sub-areas (46a) and / or the second sub-areas (46b) are opposite a current-carrying component or several current-carrying components in the housing, separated only by a dielectric cooling fluid.

14. Transformer (1) according to one of claims 8 to 13, comprising several optical waveguides which are independently of one another, in particular sealed, guided through the housing (3) of the transformer (1) and are connected to a, in particular only one, light detector (47).

15. Transformer (1) according to one of claims 8 to 14, characterized in that at least one optical waveguide (55) is arranged within one or more windings and / or is wound together with one or more windings (7, 9), in particular such that the first sub-areas (46a) and the second sub-areas (46b) are arranged at least partially within the windings (7, 9).

16. Transformer (1) according to one of claims 8 to 15, comprising a control unit (41) configured to switch off the transformer and / or insulate an expansion tank (30) and / or open a drain valve (31) on the transformer housing (3) and / or initiate the introduction of an inert gas, in particular nitrogen, via an inlet valve (33) when the light detector (47) detects electromagnetic radiation via the at least one optical fiber (45, 55).

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