EP3428934A1

EP3428934A1 - High voltage bushing with temperature sensor

Info

Publication number: EP3428934A1
Application number: EP17180606.0A
Authority: EP
Inventors: Jan Czyzewski; Victoria Maurer; Jakob Emmel
Original assignee: ABB Schweiz AG
Current assignee: ABB Schweiz AG
Priority date: 2017-07-10
Filing date: 2017-07-10
Publication date: 2019-01-16

Abstract

A high voltage bushing (1) is provided. It comprises a conductor (2) extending along an axis (A) defining an axial direction; a high voltage screen (5), provided around the conductor (2); a condenser core (8) which includes the high voltage screen (5); and a temperature sensor (14) comprising an optical fiber (15), wherein a first portion (15a) of the optical fiber (15) is located adjacent to the conductor (2) or in the conductor (2).

Description

TECHNICAL FIELD

This disclosure is in the field of high voltage technology and relates to a high voltage bushing with integrated temperature monitoring, in particular a high voltage bushing with an optical-fiber-based temperature sensor.

BACKGROUND OF THE INVENTION

A high voltage bushing is a component that is mainly used to carry current at high potential from an encapsulated active part of a first high voltage component, such as a transformer, a generator or a circuit breaker, through a barrier, like the grounded housing of the first component, to a second high voltage component, such as a high voltage line. Such a high voltage bushing is used in switchgear installations (such as gas-insulated switchgear, GIS) or in high voltage machines like generators or transformers, for voltages up to several hundred kV. In order to decrease and control the electric field, the high voltage bushing comprises a condenser core, which facilitates electrical stress control.
Nowadays, high voltage fine-graded bushings are either of the dry type (including resin-impregnated paper, resin-impregnated synthetics, or resin-impregnated fiber) or oil-impregnated paper (OIP), and are used in all kinds of applications with different insulation media. Non-limiting examples are oil-air, oil-oil, and oil-gas high voltage bushings for transformers, as well as air-gas and air-air high voltage bushings for an application through walls or in gas-insulated switchgear.
Most or all of these types of high voltage bushings comprise a conductor, which is on high voltage potential, a condenser core with a number of concentric field-grading layers embedded in insulating material, and a grounded flange. In dry-type high voltage bushings, the conductor is electrically connected to the innermost field-grading layer, being a high voltage screen, which shields from the electric field all the components and materials located between the screen and the conductor.
During operation, typically a significant increase of the temperature of internal components of the high voltage bushing occurs, mainly due to heat sources originating in the ohmic losses in the current path of the high voltage bushing and dielectric losses in the condenser core. The resulting hot spot(s) of a high voltage bushing are located, or distributed, at one or more locations along the conductor inside of the high voltage bushing. Standards like IEC and IEEE define maximum allowed temperatures within the high voltage bushing. At high temperature, the high voltage bushing insulation material ages more quickly, and if a certain temperature is exceeded for a longer time span, permanent damage may occur. This behavior - in line with the standards - leads to a maximum current rating under normal operating conditions, which is defined by the manufacturer of the high voltage bushing. It is common for transformer manufacturers to downrate the current rating by up to 20% with respect to the maximum current rating of the high voltage bushing, in order to account for potential overload situations. Additionally, most transformers are typically operated at less than their full nominal load, which provides a further safety margin.
In an overload situation, the temperature within the high voltage bushing typically increases slowly, with time constants depending on the location within the high voltage bushing, as well as depending on the high voltage bushing technology and type, but generally in the range of approximately 10 to 45 minutes. This shows that depending on the operating conditions, a high voltage bushing can withstand many different cases of overload situations without harm, particularly if the overload situation has a relatively short duration. However, it is also evident from the above findings that the exact load conditions and duration of overload under which a high voltage bushing might start to suffer damage are typically substantially unknown to operators, even more so in view of a potentially unknown health state of a high voltage bushing after some years of continuous operation.
In view of the above, the known technology leaves room for improvement, and there is a need for the present invention.

SUMMARY OF THE INVENTION

In a first aspect, a high voltage bushing is provided. It comprises a conductor extending along an axis defining an axial direction; a high voltage screen provided around the conductor; a condenser core which includes the high voltage screen; and a temperature sensor comprising an optical fiber, wherein a first portion of the optical fiber is located adjacent to the conductor, or in the conductor.
In a second aspect, an electrical installation is provided. It comprises an enclosure having a wall with an opening, and a high voltage bushing according to the first aspect, mounted to the wall and extending through the opening.
In a third aspect, a monitoring system for the temperature of a high voltage bushing is provided. The system comprises an electrical installation according to the second aspect, a control unit connected to the optical fiber and configured to detect light transmitted through the optical fiber and to employ information from the detected light to determine a temperature in the high voltage bushing.
With a high voltage bushing according to aspects, or an electrical installation employing it, and/or with a respective monitoring system, an operator of an electrical installation, such as a transformer, achieves knowledge about the current temperature within the high voltage bushing. Thus, the operation of, e.g., a transformer can be controlled to avoid harming the high voltage bushing due to an excessive load, and to operate the high voltage bushing close to a limit of what the high voltage bushing can withstand. Thus, an optimal load profile can be provided, ensuring both safe and stable operation of the high voltage bushing while providing an output as high as possible. The operator has information on how far the high voltage bushing is from the limit of its current carrying capability, and can safely increase the transmitted power even over a normally allowed limit, e.g. adapted to low ambient temperatures enabling higher loads. Typically, the temperature sensor(s) is or are located close to one or more hot-spot locations which are under high voltage. As the signal transmission of the sensor necessarily leads to ground potential, the voltage difference is insulated appropriately according to aspects described herein, and the sensor is provided so that it is neither influenced by the electromagnetic field inside the high voltage bushing nor in its surroundings, nor does the sensor compromise the properties of the high voltage bushing insulation.
Further aspects, advantages and features of the present invention are apparent from the dependent claims, claim combinations, the description, and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure, including the best mode thereof, to one of ordinary skill in the art is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, wherein:

Fig. 1 schematically shows a lateral cross-section of a high voltage bushing according to embodiments;
Fig. 2A schematically shows a cross-section of a conductor and the surrounding high voltage screen of a high voltage bushing according to embodiments, wherein the optical fiber is provided in a gap between the conductor and the high voltage screen;
Fig. 2B schematically shows a cross-section of a conductor and the surrounding high voltage screen of a high voltage bushing according to embodiments, wherein the optical fiber is provided in a groove in the surface of the conductor;
Fig. 2C schematically shows a cross-section of a conductor and the surrounding high voltage screen of a high voltage bushing according to embodiments, wherein the optical fiber is provided in a channel in the conductor;
Fig. 3 schematically shows a lateral cross-section of a further high voltage bushing according to embodiments, wherein a portion of the optical fiber is provided around the condenser core;
Fig. 4 schematically shows a front view on the partially dismantled high voltage bushing of Fig. 3;
Fig. 5 schematically shows a lateral cross-section of a further high voltage bushing according to embodiments, wherein a portion of the optical fiber is wound about the insulating housing;
Fig. 6 schematically shows a perspective front view of a high voltage bushing of a similar type as shown in Fig. 5;
Fig. 7 schematically shows a lateral cross-section of a high voltage bushing according to further embodiments;
Fig. 8 schematically shows a lateral cross-section of a high voltage bushing according to yet further embodiments;
Fig. 9 schematically shows a lateral cross-section of a directly molded high voltage bushing according to embodiments;
Fig. 10 schematically shows a lateral cross-section of a further, directly molded high voltage bushing according to embodiments;
Fig. 11 schematically shows a lateral cross-section of an oil insulated paper high voltage bushing according to embodiments;
Fig. 12 schematically shows a monitoring system for monitoring the temperature in a high voltage bushing and optionally in a transformer, according to embodiments.

ASPECTS OF THE INVENTION

In the following, some general aspects of the invention are described. Unless otherwise stated or not technically feasible, all aspects and embodiments described herein may be combined with each other to yield further embodiments.
Generally, aspects of the invention pertain to a high voltage bushing with built-in temperature sensor. The signal transmission from the sensor is carried out via one or more optical fibers, wherein the sensor(s) may be an integral part of the fiber(s). In the following, if one sensor and/or one fiber are mentioned or described, it is understood that the high voltage bushing may comprise also two or more sensors and/or fibers. Typically, sensors are employed which do not require an additional power supply at the sensing location. Optionally, power may be supplied via the optical fiber to the sensor, or a thermopile may be used to generate a voltage close to the sensor. Power may be supplied to the sensor via the transmission of light through an optical fiber. In this case, two separate fibers may be used, e.g. one fiber for the power supply and a second fiber for transmitting the sensor signal. At the sensor, a light converting device, e.g. a solar cell, may be employed to convert the supplied light power into a voltage for operating the sensor. Generally, in all embodiments described herein, multiple fibers may be used for the measurement or signal transmission and/or for the provision of power to the sensor.
According to aspects, the high voltage bushing is part of an electrical installation, such as, e.g., a transformer. The applied voltage, and thus the voltage rating of the high voltage bushing, may range from some kV to over 1000 kV, e.g. 5 kV to 1200 kV.
According to aspects, the sensor signals from the sensor(s) in the high voltage bushing may be monitored by a monitoring system. Optionally, this monitoring system also monitors other parameters of a transformer or another type of electrical installation which includes the high voltage bushing. To this end, further sensors of various types, e.g. also a hydrogen sensor, may be located at various positions on a transformer, e.g. at the winding, or at the top space above the oil volume. Their signals are routed to a control unit of the monitoring system.
According to aspects, the sensor(s) within the high voltage bushing is or are advantageously located adjacent to the central conductor, where the highest temperatures occur. In embodiments, the sensor or sensors are close to expected, simulated, or known hot-spot locations, such as, for example, at connection points of the current path. In embodiments, the sensor is provided in an area of the high voltage bushing which has no electric field, i.e. either inside the conductor or conductor tube, or between the conductor and the high voltage field grading layer (henceforth also called high voltage screen or HV screen). The optical fiber extends from the sensor along the conductor, either close or adjacent to its surface, or in a channel in the conductor or its surface, or between the conductor and the HV screen of the high voltage bushing, and extends further towards one of the end electrodes (terminals) of the high voltage bushing. By providing the sensor and the optical fiber in the manner described above, the dielectric properties of the condenser core and thus the high voltage bushing as a whole are not or only negligibly influenced by the optical fiber which is part of the temperature sensor.
According to aspects, the fiber can either exit the high voltage bushing at one end of the condenser core and run along the outer insulation (e.g. spirally within helical silicone sheds), or run along the outside of the condenser core to the flange of the high voltage bushing and exit through an opening in the flange to the outside area, and from there typically further to the control unit. The length of the portion of the optical fiber inside the high voltage bushing can be provided to be longer than the length of the insulator housing, e.g. by running the fiber spirally around the condenser core, allowing enhanced insulating properties. In particular for the air-side insulator, it may be provided to extend spirally around the condenser core in the filling material between the condenser core and an outer insulator, such as in a helical groove. For oil-sides or gas-sides without additional insulating housing around the condenser core, a groove can be provided in the condenser core that spirally runs from one end towards a flange area where the high voltage bushing is mounted, e.g. to an opening in a wall. This groove may additionally be filled up with a filling material in a second step.
Generally, for directly-molded type high voltage bushings, the fiber can extend along the longitudinal axis and inside the condenser core close to its surface, or can be wound around the condenser core and be over-molded with a sufficiently thick layer of the material forming the outer insulator.
Generally, for oil-insulated paper (OIP) type high voltage bushings, the fiber may leave the condenser core at one end and then, in a straight fashion or spirally wound, further extend to the flange area and exit the high voltage bushing there.
Generally, for dry type high voltage bushings, the sensing element is typically mechanically decoupled from the solid state insulation of the condenser core. Otherwise, mechanical stresses occurring in the conductor or the condenser core of the high voltage bushing may be transferred to the optical temperature transducer of the sensor. Those mechanical stresses can distort the optical signal generated or transmitted in the transducer, thus reducing the accuracy of the measurement or even rendering a proper measurement impossible. The mechanical decoupling can be achieved, for example, by embedding the sensor in a filling material, e.g. a gel. Conformable and compressible material can also be used, e.g. a gel filled with gas-filled microspheres, a foamed gel, a foamed elastomer, or a combination of the former. Also, the optical fibers running within the solid insulation need to be protected from mechanical stresses like vibration, thermal expansion or shrinkage of the core and could run in a tube or channel filled with a conformable and/or compressible material. This channel or tube can be within the condenser core or in the conductor. Similar materials to those applicable to mechanical decoupling of the transducer can be used. The exit port for the fibers is typically hermetically sealed, or other measures are taken to prevent liquids or gas from entering or leaking out of the high voltage bushing.
Generally, the optical sensors may be realized as a layer, coating, or crystal provided at an end or end portion of an optical fiber. For example, Gallium-Arsenide based sensors (GaAs) may be employed. In these sensors, white light from a light source is coupled into the optical fiber. This light passes through the GaAs crystal at the end of the fiber while being partially absorbed, and is then reflected back into the fiber by a mirror at the very tip of the sensor. The reflected light is detected and spectrally analyzed. The absorption spectrum of the GaAs crystal is temperature dependent, which makes it possible to infer a temperature from a given detected spectrum, which may typically be carried out by a control unit employing signal processing.
Another example of suitable sensors are fluorescence-based sensors. In these sensors, a light pulse is sent from an LED through the optical fiber to a fluorescent phosphor sensor located at the end of the fiber inside the high voltage bushing. After excitation by the incoming light, such a sensor emits light with an intensity that decays at a rate varying precisely with temperature. The emitted light is detected with a photodetector, and the decay rate is then converted into a temperature by a control unit. Further, measurement systems with optical fibers employing Raman spectroscopy or Brillouin scattering may be used to deliver a temperature profile along the portion of the optical fiber located inside the high voltage bushing. Such systems are known as such and are applied in some industrial applications.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to various embodiments, one or more examples of which are illustrated in each figure. Each example is provided by way of explanation and is not meant as a limitation. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet further embodiments. It is intended that the present disclosure includes such modifications and variations.
Within the following description of the drawings, the same reference numbers refer to the same components. Generally, only the differences with respect to the individual embodiments are described. When several identical items or parts appear in a figure, not all of the parts have reference numerals in order to simplify the appearance.
The systems and methods described herein are not limited to the specific embodiments described, but rather components of the systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. Thus, exemplary embodiments can be implemented and used in connection with many other applications.
Although specific features of various embodiments of the invention may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the invention, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing.
As used herein, the term "bent portion" is intended to mean a segment of an optical fiber having a curved shape. The bent portion is defined to be the portion of an optical fiber between the first part of the optical fiber, provided adjacent to or in the conductor, and the third part of the optical fiber (see further below), where the general direction of the optical fiber undergoes a significant change, i.e., more than about 20°. Typically, the direction of the optical fiber changes in a range from about 45° to 200°, example values being 90° and 180°. In a wider interpretation of the term, which is regarded to be included, a bent portion means any element connecting two parts of the optical fiber having different directions, wherein the bent portion may for example also be realized by a prism, a mirror, or the like, to which both parts of the optical fiber are optically coupled. Generally, in the attached drawings, some changes of direction of an optical fiber located within the bushing are depicted in a generalized form without having a significant radius. This is for illustrational purposes only, whereas in practice the optical fiber typically has a certain radius to avoid mechanical stress and light losses.
Fig. 1 shows a high voltage bushing 1 according to embodiments. The high voltage bushing 1 includes a conductor 2 which is typically a substantially cylindrical rod or tube or a flexible stranded conductor, and which extends along an axis A. A high voltage screen 5 is provided around the conductor 2 and is electrically connected (not shown) to the conductor 2, such that the high voltage screen 5 is on the same high voltage potential as the conductor 2. Thus, in a gap 3 (or space) provided between the conductor 2 and the high voltage screen 5 on the same potential, the electric field strength is zero. The gap 3 is typically filled with a solid dielectric material, such as a curable resin. Around the high voltage screen 5, a condenser core 8 comprising a dielectric material is provided, for example comprising a curable resin. An insulating housing 20, typically comprising ceramic material or a polymer, is provided around the condenser core 8. A filling material (not shown) may be provided between the condenser core 8 and the insulating housing 20.
The following description of a temperature sensor 14 provided with the high voltage bushing 1 is generally applicable to all embodiments described herein, with adaptions where mentioned with respect to some of the embodiments of high voltage bushing 1. A temperature sensor 14 is provided which includes an optical fiber 15. The temperature sensor 14 is configured to measure a temperature inside the high voltage bushing 1. The temperature sensor 14 may in embodiments be provided such that the measurement may be carried out at a single location, at several different locations, or over several locations along a defined path along at least a part of the optical fiber 15. As the highest temperature inside the high voltage bushing 1 often occurs in the conductor 2 or close to the conductor 2, a first portion 15a of the optical fiber 15 is located adjacent to the conductor 2, or in a groove or channel in the conductor 2. A first portion 15a of the optical fiber 15 extends along a longitudinal axis A of the conductor 2, which is also the longitudinal axis of the high voltage bushing 1. The first portion 15a of the optical fiber 15 is terminated by a sensor portion 16, which is either provided in an end zone or at the end of the first portion 15a, or is connected or attached to the end of the first portion 15a and thus of the optical fiber 15. The sensor portion 16 may be provided to be integrally formed with the optical fiber 15, for example as a coating which is applied via physical vapour deposition or the like to an end face of the first portion 15a of the optical fiber 15. The sensor portion 16 may also be provided as a separate item, which is principally separable from the optical fiber 15. As a non-limiting example, the sensor portion 16 may comprise a hollow cylindrical hull which carries the sensor material in a part of its interior space, and into which the end of the optical fiber 15 is inserted.
It goes without saying that a person skilled in the field of temperature sensors employing optical fibers knows that there exist as such a variety of technical realizations of a fiber-based temperature sensor with a sensor portion 16, employing various techniques and different underlying physical principles, of which some examples according to embodiments are described in the following. As most or all of the known optical-fiber-based temperature sensor types are applicable in the embodiments described herein, also sensor types and variants which are not explicitly described are regarded to be included in the definition and scope of the temperature sensor 14 as used herein.
According to some embodiments, the sensor portion 16 may comprise a Gallium-Arsenide (GaAs) crystal. The crystal may for example be mounted to an end face of the first portion 15a of the optical fiber 15. A light source 124 (not shown, see Fig. 12) with a known spectrum, which may also be frequently determined during operation, is coupled into the optical fiber 15 at the other end of the optical fiber 15, which extends on an outside of the high voltage bushing 1. This light passes through the GaAs crystal in the sensor portion 16 at the end of the first portion 15a of the optical fiber and is partially absorbed in the crystal. After passing the crystal, the light is reflected back into the fiber by a mirror at the very tip of the sensor portion 16. The reflected light is detected and spectrally analysed, for example by a spectrum analyser, being e.g. an array of photodetectors operatively coupled or being part of a control unit 120 (see Fig. 12). As the absorption spectrum of the GaAs crystal is temperature-dependent, the temperature of the GaAs crystal may be determined from the detected spectrum. The optical absorption, and its temperature dependency, of GaAs are very well known. Suitable wavelength ranges are in the visible range and the near infrared, so that e.g. a light bulb may be used as a light source 124.
Another example of suitable sensors 14 according to embodiments are fluorescence-based sensors. When using such a sensor, a light pulse is sent e.g. from an LED through the optical fiber 15 to a fluorescent phosphor sensor layer being the sensor portion 16 at the end of the first portion 15a. The phosphor sensor layer 16 emits light with an intensity with a decay rate. The decay rate varies precisely with temperature. The measured decay rate may thus be converted into a temperature by a software in the control unit, for example.
A further example of a sensor portion 16 according to embodiments comprises a thermopile, which comprises one or a plurality of thermocouples, and an electro-optical transducer converting the thermopile voltage into an optical signal. An example of an electro-optical transducer can be an LED, which emits light into the first portion 15a of the optical fiber, which may then be detected at the fourth portion 15d of the optical fiber extending from the high voltage bushing 1. The thermopile delivers a voltage to the LED which is related to the temperature. Thus, with rising temperature, also the current in the LED rises and with it the intensity of the light emission of the LED. A photodetector 125 (not shown, see Fig. 12) located outside of the high voltage bushing 1, typically at the end of the fourth portion 15d extending outwards from the high voltage bushing 1, receives the light transmitted through the optical fiber 15. The signal from the photodetector is then input to a control unit, which determines a temperature at the thermopile according to a calibration curve. Hence, the temperature at the sensor portion 16 located inside the high voltage bushing 1 is determined.
It is evident from the above that the length of the sensor portion 16 in a direction of the fiber varies greatly depending on the used sensor principle. For example, a thin-film metal sensor or a sensor having a number of coated dielectric layers may have a physical length as low as some 10 nanometers. On the other hand, a GaAs crystal may need a significant thickness, such as e.g. up to some millimeters. Hence, the sensor portion 16 may exhibit a length from about 10 nm to about 10 mm, more preferably from about 100 nm to about 5 mm.
In the other direction of the optical fiber 15, distant to where the sensor portion 16 is provided, the optical fiber 15 is guided away from the conductor 2 and has a bent portion 15b where the fiber changes direction, typically by an angle of effectively about 180°. The bent portion 15b is typically located close to an end of the condenser core 8. The optical fiber then further extends from the bent portion 15b in a direction back towards the other end of the condenser core 8, or respectively of the high voltage bushing 1. In other embodiments, the bent portion 15b may exhibit a change of direction of the fiber of about 90° or different, and thus further extends sideways away from the high voltage bushing 1. In order to protect the optical fiber 15 from breaking, the bent portion 15b may be guided to have a significant radius, such as exemplarily shown in Fig. 1. From there, a third portion 15c of the optical fiber 15 runs along the outside of the condenser core 8 towards the flange of the high voltage bushing and exits through an opening 13 in the flange 12 to the outside area and to the control unit (not shown, see Fig. 12). The opening 13 in the insulating housing 20 is serving as an exit port for the optical fiber 15 and is typically hermetically sealed to prevent liquids or gas from entering into or leaking out of the high voltage bushing 1.
For dry type high voltage bushings, the sensor portion 16 is typically mechanically decoupled from the solid insulation material of the condenser core 8. Otherwise, mechanical stresses occurring in the conductor 2, in the dielectric material filling the gap 3, or in the condenser core 8 of the high voltage bushing 1 might be transferred to, e.g., the sensor portion 16 or the first portion 15a of the optical fiber. Those mechanical stresses could distort the optical signal generated or transmitted in the sensor portion 16, thereby reducing the accuracy of the measurement or even rendering the measurement impossible. This mechanical decoupling can be achieved, for example, by embedding the sensor portion 16, and typically also the first portion 15a of the optical fiber, in a conformable material, e.g. a gel or foam. For this purpose, the first portion 15a may be provided in embodiments to run in a groove 6a or channel 6b (see description of Fig. 2B, 2C below), which is filled up with a conformable and/or compressible material as a filling material 7.
Fig. 2A shows the conductor 2 with surrounding high voltage screen 5, and the first portion 15a of the optical fiber provided there between and being embedded in the filling material 7. Compressible materials, which may be used as a filling material 7, are, e.g., a gel filled with gas-filled microspheres, a foamed gel, a foamed elastomer, or combinations of the former. Fig. 2B shows a substantially similar embodiment as in Fig. 2A, wherein the first portion 15a runs in a groove 6a in the surface of the conductor 2. In Fig. 2C, the first portion 15a, and the sensor portion 16 (not shown) are provided in a channel 6b filled up with the filling material 7.
In Fig. 3, a high voltage bushing 1 according to further embodiments is shown. The basic structure of the high voltage bushing 1 is substantially similar to that shown in Fig. 1. However, the length of the optical fiber 15, in particular of the third portion 15c, is provided to be significantly longer than the length of the insulating housing 20. This is achieved by running the optical fiber 15, more particularly the third portion 15c, spirally around the condenser core 8. This allows for improved insulating properties. In particular for the insulating housing 20 on the air side, it can go spirally around the condenser core 8 in the filling material between the condenser core 8 and the insulating housing.
Fig. 4 shows a similar high voltage bushing 1, according to embodiments, as is shown in Fig. 3, however in a front view with a virtually dismantled insulating housing 20 allowing a view on the outside of the condenser core 8. The third portion 15c of the optical fiber is guided, differently to Fig. 3, in a spiral groove 8a, which spirals around the outside of the condenser core 8.
Fig. 5 shows a high voltage bushing 1, where the third portion 15c of the optical fiber 15 is guided, substantially different to the previous embodiments, on an outside of the insulating housing 20. To this end, the insulating housing 20 is configured with a helical groove formed on its outside face. This is depicted in greater detail in Fig. 6, which is a front view of a high voltage bushing 1 with a similar concept, though different dimensions, than the one shown in Fig. 5. The third portion 15c of the optical fiber is extending spirally along the helical groove in the outer face of the insulating housing 20.
In Fig. 7, a high voltage bushing 1 for use with oil (provided at the lower side, second end terminal 1b) and air (upper side, first end terminal 1a) is shown. As, differently from the previously described embodiments, no insulating housing is provided on the oil-side but only on the air-side, the third portion 15c of the optical fiber 15 is provided to run spirally around the condenser core 8. In order to protect the fiber, it runs in a spiral groove 8a. The same concept can in embodiments be applied to oil-oil-bushings, an example of which is shown in Fig. 8. The inner structure of the high voltage bushing is substantially similar to the one shown e.g. in Fig. 5. The parts of the groove 8a not filled up by the optical fiber may optionally be filled with a filling material 7, similar to Fig. 2B and Fig. 2C.
Fig. 9 shows a high voltage bushing 1 according to embodiments, which is a directly molded high voltage bushing 1. The condenser core 8 comprises epoxy resin, in which a number of electrically floating concentric shields 5a are embedded. The insulating housing 20 comprises sheds, which typically comprise silicone rubber or another dielectric material. The conductor 2 is connected via connection 2a to the high voltage screen 5. Inside the insulating housing 20, the optical fiber may extend in a groove or in a channel in the epoxy resin, or other material, of the condenser core 8. The channel or groove may be filled up with a compressible and/or conformable filling material 7, similar as was exemplarily described with respect to Figs. 2A to 2C.
Fig. 10 shows a further directly molded high voltage bushing 1 based on the embodiment of Fig. 9. Differently, the bent portion 15b and the third portion 15c of the optical fiber 15 are embedded in the material of the insulating housing 20. The optical fiber 15 may thereby be wound about the condenser core 8 and then be overmolded with a layer of the material of the insulating housing 20, which in this example is silicone.
In Fig. 11, a high voltage bushing 1 according to embodiments is shown, which is an oil-impregnated paper (OIP) high voltage bushing. An oil reservoir 30 is provided on top of the high voltage bushing 1. The first portion 15a of the optical fiber 15 typically runs from the sensor portion 16 to one of the ends of the condenser core 8, where the bent portion 15b and the third portion 15c of the optical fiber follow. The optical fiber 15 inside the high voltage bushing 1 thereby typically extends through oil, or respectively is immersed in oil. The end of the third portion 15c is in an area of the flange of the high voltage bushing, where the optical fiber leaves the high voltage bushing 1 and extends outside from the high voltage bushing as the fourth portion 15d.
In Fig. 12, an electrical installation 110 according to embodiments is depicted, which in the non-limiting example of Fig. 12 includes a transformer 150 (only schematically shown). A control unit 120 is connected to an optical fiber 15 and configured to detect a signal transmitted through the optical fiber. The control unit 120 is adapted to use information on the detected light to calculate a temperature in the high voltage bushing 1. The electrical installation 110 comprises an enclosure 115, in which the transformer 150 is provided, with a wall 122 having an opening 125. The high voltage bushing 1 is mounted to the wall 122 and extends through the opening 125. A bent portion 15b of the optical fiber 15 is located at a first end terminal 1a of the high voltage bushing 1. The first end terminal 1a may be located on the outside of the enclosure 115, or on the inside of the enclosure 115. The optical fiber 15 comprises a fourth portion 15d which extends in a direction away from the high voltage bushing 1, wherein the boundary between the third portion 15c and the fourth portion 15d is located in the vicinity of the wall 122 of the electrical installation 110. Instead of the exemplary high voltage bushing 1 shown, all other high voltage bushings 1 according to embodiments described herein may be integrated in the electrical installation of Fig. 12, partially with minor adaptions like, e.g., an oil-filling of the enclosure 115.
A monitoring system 180 for monitoring a temperature of a high voltage bushing 1 comprises a control unit 120 which is operably connected to an optical fiber 15 being part of the monitoring system 180. The control unit 120 is configured to detect light from a sensor portion 16 transmitted through the optical fiber 15. The control unit is configured to determine a temperature in the high voltage bushing 1 from the detected light, which may be received and detected by at least one photodetector 125, or an array of photodetectors 125, being operably connected to or being part of the control unit 120, for example. The monitoring system 180 may further comprise a light source 124 adapted for coupling light into the optical fiber 15, for example an LED or a light bulb, which may be part of or be operatively coupled to the control unit 120. As is schematically shown in Fig. 12, the monitoring system 180 may be operably connected to further sensor strands 160, 161 to monitor other parameters of an electrical installation 110 including the high voltage bushing 1, such as, as non-limiting examples, a hydrogen content in the oil of transformer 150, or the temperature of the transformer 150.
According to an aspect, the monitoring system 180, typically the control unit 120, may further comprise a network interface for connecting the monitoring system to a data network, in particular a global data network. The data network may be a TCP/IP network such as internet, also called industrial internet of things (IoT). The monitoring system 180 is operatively connected to the network interface for sending data (monitoring data, etc.) or for carrying out commands received from the data network.
The data communication via network interface may include e.g. reporting data about: the current temperature, information about a rise of temperature, an alarm when a certain maximum temperature is exceeded, an alarm when the temperature rise per time exceeds a threshold value, and the like.
The commands may include e.g. control commands for controlling the monitoring system and to carry out tasks remotely, such as re-calibrating the control unit 120, or the like.
For such purposes, the monitoring system 180, in particular the control unit 120, further comprises a network interface for connecting the monitoring system 180 to a data network, wherein the monitoring system 180 is operatively connected to the network interface for at least one of: sending device status information to the data network, and carrying out a command received from the data network.
The data network may be an Ethernet network using TCP/IP such as local area network (LAN) and/or wireless local area network (WLAN), wide are network (WAN) or Internet, in particular industrial internet of things (IoT). The data network may comprise distributed storage units such as Cloud. Depending on the application, the Cloud can be in form of public, private, hybrid or community Cloud.
While the foregoing is directed to embodiments, other and further embodiments may be devised without departing from the basic scope, and the scope is determined by the claims that follow.

Claims

A high voltage bushing (1) comprising:
- a conductor (2) extending along an axis (A) defining an axial direction;

- a high voltage screen (5), provided around the conductor (2);

- a condenser core (8) which includes the high voltage screen (5);

- a temperature sensor (14) comprising an optical fiber (15), wherein a first portion (15a) of the optical fiber (15) is located adjacent to the conductor (2), or in the conductor (2).
The high voltage bushing of claim 1, wherein the first portion (15a) of the optical fiber (15) extends in parallel to an axial direction of the conductor (2) or in a spiral winding extending along an axial direction of the conductor.
The high voltage bushing of claims 1 or 2, wherein the first portion (15a) of the optical fiber (15) extends:
- between a surface of the conductor (2) and the high voltage screen (5), preferably in physical contact with the conductor (2), or

- in a groove (6a) in the surface of the conductor (2); or

- in a channel (6b) inside the conductor (2).
The high voltage bushing of any one of the claims 1 to 3, wherein the first portion (15a) of the optical fiber (15) is at least partially embedded in a filling material (7) to protect the optical fiber (15).
The high voltage bushing of claim 4, wherein the filling material (7) is provided to fill up gaps between the first portion (15a) of the optical fiber (15) and a groove (6a) or channel (6b) in the conductor (2).
The high voltage bushing of any one of the preceding claims, wherein the first portion (15a) of the optical fiber (15) has an end which is located at a position along the length of the conductor (2), preferably close to pre-defined temperature hot-spots.
The high voltage bushing of any one of the preceding claims, wherein a sensor portion (16) is provided at an end of the first portion (15a) of the optical fiber (15), and wherein the sensor portion (16) changes its optical properties depending on the temperature, wherein the sensor portion (16) comprises at least one of
- GaAs,

- phosphorus,

- a thermopile and an electro-optic transducer configured to convert a voltage created by the thermopile into an optical signal;
and in particular wherein the optical fiber (15) has a planar end face at the end of the first portion (15a) and the sensor portion (16) is coated to the planar end face or mounted at the planar end face.
The high voltage bushing of any one of the preceding claims, having a first end terminal (1a), at which the conductor (2) protrudes from the condenser core (8), and wherein a bent portion (15b) of the optical fiber (15) is located adjacent to the first end terminal (1a) of the high voltage bushing (1).
The high voltage bushing of claim 8, wherein the optical fiber (15) further comprises a third portion (15c), extending from the bent portion (15b) in a direction parallel to the axis (A) of the conductor (2), or in a spiral winding extending along an axis (A) of the conductor (2) in a direction towards the second end terminal (1b) of the high voltage bushing (1).
The high voltage bushing of claim 9, further comprising an insulating housing (20) provided around at least a part of the length of the condenser core (8), wherein the third portion (15c) of the optical fiber (15) is extending on the inside of the insulating housing (20) or on the outside of the insulating housing (20), and wherein the third portion (15c) is optionally located in a groove or channel formed in the insulating housing (20), or at the outer face of the condenser core (8) inside the insulating housing (20), and wherein the third portion (15c) of the optical fiber (15) is optionally spirally wound.
An electrical installation (110) comprising:
- an enclosure (115) having a wall (122) with an opening (125),

- a high voltage bushing (1) according to one of claims 1 to 10, mounted to the wall (122) and extending through the opening (125).
The electrical installation of claim 11, wherein the bent portion (15b) of the optical fiber (15) is located at the first end terminal (1a) of the high voltage bushing (1), wherein the first end terminal (1a) is located on the outside of the enclosure (115), or on the inside of the enclosure (115).
The electrical installation of any one of the claims 11 or 12, wherein the optical fiber (15) comprises a fourth portion (15d) extending in a direction away from the high voltage bushing (1), and wherein the boundary between the third portion (15c) and the fourth portion (15d) is located in the vicinity of the wall (122) of the electrical installation (110).
A monitoring system (180) for monitoring a temperature of a high voltage bushing (1), comprising:
- a control unit (120) operably connected to an optical fiber (15) and configured to detect light coming from a sensor portion (16) and being transmitted through the optical fiber (15), and further configured to determine a temperature in the high voltage bushing (1) from the detected light.
The monitoring system (180) of claim 14, further comprising a network interface for connecting the monitoring system (180) to a data network, such that the monitoring system (180) is operatively connected to the network interface for at least one of: sending temperature related data and/or device status information to the data network, carrying out a command received from the data network; in particular the data network being at least one of: LAN, WLAN, WAN or internet (IoT).