Patent Application
20130021709
This application claims priority under 35 U.S.C. §119 to European Patent Application No. 11174464.5 filed in Europe on Jul. 19, 2011, the entire content of which is hereby incorporated by reference in its entirety.
The present disclosure relates to a conductor arrangement for reducing very fast transients or impact of very fast transients. More particularly, the present disclosure relates to a conductor arrangement representing a resonant circuit for reducing very fast transients or the impact of very fast transients.
Electromagnetic transients (EMTs) appear in power generation and distribution systems as an inevitable consequence of switching, faults, or any other sudden topological change of the network. These transients generally have non-harmonic time dependence which, in superposition with the harmonic nominal voltage, produces hazardous voltage peaks. The amplitude and frequency ranges of EMTs depend mainly on the rated voltage and the local network configuration. According to the existing standards for high voltage (HV) equipment, the ratio between the lightning impulse withstand voltage (LIWV) and rated voltage level decreases with higher rated voltage. As an illustration the gas insulated switchgear (GIS) standard IEC 62271-203, “High-Voltage Switchgear and Controlgear”, International Electrotechnical Commission, Geneva, Switzerland, 2003 gives the following ULIWV/URATED ratios: 1050 kV/245 kV˜4.3, and 2500 kV/1100 kV˜2.3. At the same time, the transient voltage peaks in GIS remain 2-3 times higher than the rated voltage. Therefore, at a certain rated voltage level the electromagnetic transients become relevant for the dielectric design. Due to larger clearance distances, high-voltage (HV) and ultra-high-voltage (UHV) devices and components have lower lumped and distributed electric capacitances and magnetic inductances. Hence, the corresponding electromagnetic transients cover higher frequencies and they are therefore called the Very Fast Transients (VFTs) or Very Fast Front Transients (VFFT). Other causes for VFTs can be faults in GIS (in the frequency range of 100 kHz-50 MHz), lightning surges and faults in substations (10 kHz-3 MHz), and multiple re-strikes of circuit breakers (10 kHz-1 MHz). It is desired to damp the VFTs, mostly associated with the disconnector switching (multiple re-strikes and multiple pre-strikes).
Very fast transient over-voltages (VFTO, also referred to as very fast front over-voltages VFFO) are of paramount importance for the dielectric design of high voltage and ultra-high voltage devices. The damping of VFTs in UHV gas insulated switchgears by using resistor-fitted disconnectors was reported in Y. Yamagata, K. Tanaka, S. Nishiwaki, “Suppression of VFT in 1100 kV GIS by Adopting Resistor-fitted Disconnector”, IEEE Transactions on Power Delivery, Vol. 11, No. 2, pp. 872-880, 1996. The achieved damping efficiency was rather high, but this solution is very costly and makes the dielectric and mechanical design of the disconnector much more demanding. As an alternative, the VFT damping solution utilizing ferrite rings has also been analyzed and tested, as described in W. D. Liu, L. J. Jin, J. L. Qian, “Simulation Test of Suppressing VFT in GIS by Ferrite Rings”, in Proceedings of 2001 International Symposium on Electrical Insulating Materials, pp. 245-247, 2001. The measurements show that the damping effect can be achieved, but with an important drawback, namely that the magnetic material goes easily into saturation, which complicates the design and reduces its generality and robustness. EP 2 234 232 A2 and its corresponding US 2010/0246085 describe a device for damping of very fast transients in GIS. One idea was to use the existing metallic shells of the GIS conductor joints in order to ignite a spark that will partially dissipate the VFT energy.
An exemplary embodiment of the present disclosure provides a conductor arrangement for reducing very fast transients in high voltage applications. The conductor arrangement includes a conductor element having a main conducting orientation, and a conductive annular shell element that circumferences the conductor element to form an annular cavity around the conductor element. The annular shell element in the main conducting orientation comprises a first end portion and a second end portion. The first end portion is conductively connected to the conductor element. The second end portion includes an annular collar. The collar is substantially coaxial to the conductor element, and together with the conductor element forms a coaxial capacitor. The coaxial capacitor is at least partially filled with a solid dielectric filling for increasing the capacitance of the coaxial capacitor. The coaxial capacitor comprises a surge arrester portion.
An exemplary embodiment of the present disclosure provides a conductor arrangement for reducing very fast transients in high voltage applications. The conductor arrangement includes a conductor element having an annular shape and a main conducting orientation, and a conductive shell element of annular shape. The conductor element circumferences the conductive shell element to forman annular cavity between the conductor element and the conductive shell element. The conductive shell element in the main conducting orientation comprises a first end portion and a second end portion. The first end portion is conductively connected to the conductor element. The second end portion comprises an annular collar. The collar is substantially coaxial to the conductor element, and together with the conductor element forms a coaxial capacitor. The coaxial capacitor is at least partially filled with a solid dielectric filling for increasing the capacitance of the coaxial capacitor. The coaxial capacitor comprises a surge arrester portion.
Exemplary embodiments of the present disclosure will be described in the following with reference to the following drawings.
Exemplary embodiments of the present disclosure provide a conductor arrangement for reducing very fast transients and the impact of very fast transients, respectively.
An exemplary embodiment of the present disclosure provides a conductor arrangement for reducing very fast transients in high voltage applications. The conductor arrangement includes a conductor element having a main conducting direction or orientation and a conductive annular shell element that circumferences the conductor element, thus forming an annular cavity around the conductor element. The annular shell element in the main conducting orientation includes a first end portion and a second end portion, wherein the first end portion is conductively connected to the conductor element, and the second end portion includes an annular collar, which is substantially coaxial to the conductor element, thus together with the conductor element forming a coaxial capacitor. The coaxial capacitor is at least partially filled with a solid dielectric filling for increasing the capacitance of the coaxial capacitor, and the capacitor includes a surge arrester portion.
An exemplary embodiment of the present disclosure provides a conductor arrangement for reducing very fast transients in high voltage applications. The conductor arrangement includes an annular conductor element having a main conducting direction or orientation and a conductive annular shell element. The annular conductor element circumferences the conductive annular shell element, thus forming an annular cavity between the annular conductor element and the annular shell element. The annular shell element in the main conducting orientation includes a first end portion and a second end portion, wherein the first end portion is conductively connected to the annular conductor element, and the second end portion comprises an annular collar, which is substantially coaxial to the conductor element, thus together with the conductor element forming a coaxial capacitor. The coaxial capacitor at least partially is filled with a solid dielectric filling for increasing the capacitance of the coaxial capacitor, and the capacitor includes a surge arrester portion.
Exemplary embodiments of the disclosure provide a device for damping VFTs and, as a special case of this general concept, and provide a general purpose low-quality (Q) high frequency (HF) resonator capable of receiving and dissipating the energy of VFTs in a wide frequency range. Thus, the device for receiving and dissipating the VFT energy may allow for more compact and cheaper designs, and may avoid the need for damping resistors. Depending on the material used for magnetic and dielectric components like rings, this solution may be very compact and therefore applicable to any situation. Consequently, this solution is very simple, cheap, and fabrication-friendly. The resonance frequency depends on the capacitance, so that a high capacitance can be obtained by increasing the permittivity of the dielectric filling. Thus, the entire geometry may be kept small.
It should be noted that a bended conductor element may also be used which has a longitudinal direction or orientation. The surge arrester may operate as an energy converter for converting electric energy into thermal energy. Reducing very fast transients means reducing the very fast transients as such as well as reducing the impact thereof. It should be noted that the impact may also be reduced by eliminating the very fast transients. The annular shell may be made of metal. However, the shell may also be made of plastic material having a conductive coating. The annular cavity may be of a torus form, for example, of a constant cross-section along a circular, oval, elliptic or annular rounded circumference. It should be noted that the inventive conductor arrangement may also have a first conductor, for example, an inner conductor, and a first annular shell element that circumferences the first conductor element as described above as well as a second annular shell element and a second annular conductor, for example, an outer conductor being coaxially arranged to the first conductor. The outer conductor circumferences the second annular shell element as described above. Thus, the effect of reducing impact of very fast transients may be divided among two elements. The first annular shell and the second annular shell may be shifted along the longitudinal conducting direction, so that insulation distances between the first annular shell and the second conductor, and between the second annular shell and the first conductor may be maintained. In other words, when combining a first and second shell element, those shell elements should not be positioned opposite to each other between the first and second conductor, particularly in case that the shell elements extend over the surface of the respective conductor element. Consequently, all embodiments referring to the first conductor or inner conductor may be combined with embodiments referring to the second conductor or outer conductor.
According to an exemplary embodiment, the dielectric filling may be designed as an annular ring, so that the cavity may be a more or less hermetically closed cavity. Thus, any dirt can be prevented from entering the cavity. Further, the cavity can be sealed in a pressure tight manner so that it is not necessary to fill insulating gas like sulfur hexafluoride (SF6) into the cavity. As the cavity is almost free of electric field, no SF6 is required inside the cavity. The cavity may also be filled with stabilizing foam so that the shape of the cavity can be maintained even if the annular shell is manufactured from a thin metal plate.
According to an exemplary embodiment of the disclosure, the solid dielectric filling is adapted for maintaining the capacitor geometry.
Thus, the sensitive geometry or useful or critical shape of the capacitor can be maintained, for example, when mounting the conductor arrangement. The dielectric filling may serve as a centering ring so that the predetermined distance between the capacitor electrodes, for example, the conductor surface and the collar, may be maintained. The dielectric filling may be selected or adapted such that the filled capacitor has a capacitance which is 10 to 100 times higher compared to that of a gas-filled capacitor with almost the same dimensions. The filling may be made of a filled epoxy resin. The coaxial capacitor may have a high conductivity. The high conductivity and low resistivity, respectively, may be established by the dielectric filling. The resistivity of the capacitor may be in the range of 1 to 100 Ohm, for example, 5 to 50 Ohm, such as 10 to 15 Ohm.
According to an exemplary embodiment of the disclosure, the collar includes a first surface. The conductor element includes a conductor surface. The first surface of the collar faces the conductor surface of the conductor element, and the conductor surface of the conductor element and the first surface of the collar are substantially parallel to each other, thus forming a cylinder capacitor.
Thus, the capacitor formed by the conductor surface of the conductor element and the corresponding facing surface of the collar of the annular shell may be considered as a cylinder capacitor which can be easily and reproducibly dimensioned. The edges of the first surface of the annular shell circumferencing the conductor may have a Rogowski-profile for reducing field strength at the edges. “Parallel” in this respect means that the longitudinal extension of the components in question are parallel.
According to an exemplary embodiment of the disclosure, the surge arrester portion includes a spark gap.
Thus, the overvoltage can easily be reduced. The spark gap may have electric field enhancing ridges on one or both sides of the spark gap. Thus, the locations for igniting a spark are well defined. This allows to prepare the locations with particular spark-proof material, like tungsten copper (WCu), for example. The well-defined spark gap geometry may be a circumferential or sectional edge on either one surface or on both surfaces, the conductor surface and the facing shell surface. The well-defined spark gap geometry may also be one or more punctual protrusions on either one or both surfaces.
According to an exemplary embodiment of the disclosure, the surge arrester portion includes an element having a conductivity characteristic with an increasing conductivity at an increasing electric field.
Thus, over-voltages automatically lead to a reduced resistivity so that the impact of VFTs may be reduced or eliminated. Further, the surge arrester may have an almost linear conductivity characteristic. The surge arrester may also have a varistor characteristic.
According to an exemplary embodiment of the disclosure, the dielectric filling has a surge arrester characteristic having a conductivity characteristic with an increasing conductivity at an increasing electric field.
Thus, a separate surge arrester besides the dielectric filling may be avoided, as the lossy dielectric filling serves for both the surge arrester function and the capacitance increasing dielectric filling of the capacitor. The solid dielectric filling may have a varistor-like characteristic or may be a varistor. The dielectric filling of the capacitor may have a significant dielectric loss, for example, a high tan delta. The shell side surface of the capacitor may have a Rogowski-profile for avoiding an inhomogeneous electric field. It should be noted that only a part or the entire capacitor may be filled with a dielectric filling having a conductivity characteristics with an increasing conductivity at an increasing electric field. It should be noted that the entire capacity may be filled with a dielectric filling, but only a part of it may have the above mentioned conductivity characteristics, so that the dielectric filling has different properties in different zones of the capacitor.
According to an exemplary embodiment of the disclosure, a cross-sectional profile of the annular shell element cut along the main conducting orientation has an un-branched single line profile, wherein the collar is inwardly directed so that a second surface of the collar being opposite to the first surface of the collar faces the cavity.
An un-branched single line profile may be a profile which can be continuously drawn with a pen, for example, with no branches. In other words, the shell can be manufactured by forming a single metal sheet without welding or soldering an additional metal sheet for the collar. The shell may be made of aluminum or metal evaporated plastic. The latter may have reinforced metal sections for spark stressed portions.
According to an exemplary embodiment of the disclosure, the first end portion is conductively connected substantially along the entire circumference of the conductor element.
Thus, the cavity may have a defined geometry and unintended sparking at the first end portion may be avoided.
According to an exemplary embodiment of the disclosure, a cross-section of the annular shell element cut along an orthogonal orientation of the main conducting orientation has a circular outer shape.
The cross-section of the annular shell element cut along an orthogonal orientation y of the main conducting orientation x may also be oval or elliptical or may have a rounded outer shape.
According to an exemplary embodiment of the disclosure, in a cross-section of the conductor element cut along an orthogonal orientation of the main conducting orientation the outer contour of the conductor element may have a circular shape.
According to an exemplary embodiment of the disclosure, in a cross-section of the annular conductor element cut along an orthogonal orientation of the main conducting orientation the inner contour of the annular conductor element may have a circular shape.
The respective cross-section of the conductor element, for example, annular conductor element, cut along an orthogonal orientation y of the main conducting orientation x may also be oval or elliptical or may have a rounded outer shape.
According to an exemplary embodiment of the disclosure the conductor arrangement further includes a magnetic element that circumferences the conductor element or inner conductor element, wherein the magnetic element is arranged within the annular cavity.
According to an exemplary embodiment of the disclosure the conductor arrangement further includes a magnetic element that circumferences the conductive annular shell element, wherein the magnetic element is within the annular cavity. This embodiment is applicable for the outer conductor element.
Thus, the inductance of the cavity may be increased so that the entire geometry of the arrangement can be kept smaller or be made smaller while maintaining the resonant frequency of the arrangement.
According to an exemplary embodiment of the disclosure the conductor element in a surface facing a conductor counter pole includes an annular groove, the groove being covered by the annular shell element thus forming the cavity.
The magnetic element may be located around the conductor element or inner conductor element, and the conductor element or outer conductor element may be located around the magnetic element, respectively, so that the magnetic element is located between the shell and the respective conductor element. The magnetic element may have a low saturation at nominal currents and nominal frequency, e.g. 1000 A at 50 Hz-60 Hz, wherein the saturation may be high or higher at frequencies of very fast transients to be expected.
The magnetic element may be located in the annular groove. Thus, the cavity can be kept large in volume or, vice versa, the outer diameter of the shell can be kept small resulting in a lower diameter of the outer tube of the grounded housing of e.g. GIS.
According to an exemplary embodiment of the disclosure for a groove on the outer surface of the inner conductor element, the outer diameter of the conductive annular shell or shell element is equal or smaller than the outer diameter of the conductor element before and/or behind the groove. Diameter is to be understood with respect to the main conducting orientation or main axis x of the conductor arrangement.
According to an exemplary embodiment of the disclosure for a groove on the inner surface of the outer conductor element, the inner diameter of the conductive annular shell or shell element is equal or larger than the inner diameter of the conductor element before and/or behind the groove. Diameter is to be understood with respect to the main conducting orientation or main axis x of the conductor arrangement.
Thus, the annular shell does not extend over the surface before and behind the groove so that the isolation distance between an inner and outer conductor in a coaxial conductor arrangement may be maintained while keeping the outer dimensions of the conductor arrangement tight or small.
According to an exemplary embodiment of the disclosure, the magnetic element along the main conducting orientation is located between the coaxial capacitor and the first end portion of the shell within the annular groove.
Thus, the magnetic element may be positioned in an almost field free space at rated voltage conditions. The magnetic element thus has a direct impact on the inductance of the cavity.
According to an exemplary embodiment of the disclosure, the magnetic element is a magnetic core having a tubular shape in the main conducting orientation, wherein the magnetic core includes at least one air gap with at least one directional component thereof extending into the main conducting orientation.
The magnetic material that circumferences the conductor may have a large hysteresis and high eddy current losses at VFT voltages. This may lead to a damping of the very fast transients. The material may be of a nano-crystalline material structure. The material of the magnetic ring may be ferrite. The form of the magnetic element may have an annular core shape, e.g. a tube, a tube with a slot or air gap in longitudinal orientation, a number of tube sectors together forming the magnetic element or an annular tube shape with one or more air gaps. The one or more air gaps may run in a main conducting orientation, but may also run helically.
According to an exemplary embodiment of the disclosure, the annular cavity is at least partially coated with a lossy dielectric resistive layer.
According to an exemplary embodiment of the disclosure, there is provided a gas insulated switchgear with the inventive conductor arrangement. According to an exemplary embodiment, the annular shell covers a joint of the conductor so that the annular shell not only serves as a cavity wall, but also as a field smoothing element for the joint. Thus, sharp edges of conductor joints may be covered by the annular shell.
It should be noted that the above features may also be combined. The combination of the above features may also lead to synergetic effects, even if not explicitly described in detail.
These and other aspects of the present disclosure will become apparent from and elucidated with reference to the embodiments described hereinafter.
With respect to
It should be noted that the cross-sectional views of
The resonator structure depicted in
The dielectric ring 34 and magnetic ring 60 may be made of materials with pronounced dielectric and magnetic (hysteresis and eddy-currents) losses, respectively. The electromagnetic resonator may comprise a solid state switching element placed in the gap 50. A solid state switching element may maintain its state, whereas a spark gap returns to the non-conducting state when the voltage decreases. The conductor surface may have a groove 14 in the conductor 10 for receiving the magnetic material 60. The shell 20 has a first end 22 being connected to the conductor 10 and a second opposing end 24. The shell 20 encircles a cavity 40 and may have a tubular collar 26 at the second end 24, wherein the tubular collar 26 forms one electrode of the capacitor 30. The conductor arrangement 100 may be embedded into a GIS or gas insulated transmission line (GIL/GITL) having an outer housing 70 for receiving an insulating gas 65. As can be seen from
In
It should be noted that the disclosure may be applied for example in GIS, GIL bushings, gas circuit breakers, transformer-bushings, tap changers, bus bars in power electronic systems (e.g. drives, converters . . . ), vacuum circuit breakers, etc. to efficiently block VFTs at their source. The disclosure may be implemented in bushings, so that this solution allows to offer to customers a completely new concept of VFT-free GIS substations that imposes no over-voltage risk to the adjacent power transformers and other equipment.
It should be noted that the term ‘comprising’ does not exclude other elements or steps and the ‘a’ or ‘an’ does not exclude a plurality. Also elements described in association with the different embodiments may be combined.
It should be noted that the reference signs in the claims shall not be construed as limiting the scope of the claims.
Thus, it will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 11174464.5 | Jul 2011 | EP | regional |
