Patent Application
20220005657
The present invention concerns a disconnector comprising a filter.
Consequently, the present invention suggests a disconnector for interrupting a high voltage current. The disconnector is configured to reduce considerably high voltage and high frequency current generated during the service no-load opening and closing.
The disconnector comprises a first main contact, a second main contact, a sliding contact and an arcing horn having a length,
The disconnector may further comprise
The filter may comprise a conducting wire wound upon a support, preferably such that two layers or more of wound wire are provided.
Preferably, the filter is configured such that, in use,
The filter of the arcing horn may comprise a stabilization layer, preferably a stabilization layer comprising an aluminiumoxide, the stabilization layer being provided between the wire and the support.
Preferably, a cement is filled between windings of the conducting wire.
The filter and the sliding contact may further be configured such that the sliding contact is in contact with at least three windings of the wire while sliding on the filter.
The filter can comprise an electrically conducting band,
Preferably, the filter is connected to the arcing horn via a connection cylinder,
An opening and/or closing operation may be configured such that the sliding contact moves with a constant sliding speed while the sliding contact is in contact with the filter.
The disconnector can also be configured as a vertical type disconnector with an arcing horn comprising a left branch with a first electrical filter and a right branch with a second electrical filter, wherein
An opening and/or closing operation is advantageously configured such that the sliding contact moves with a sliding speed, whereby
An advantageous form of the sliding contact comprises a first sliding part, a second sliding part and a spring, wherein
Further, the disconnector may comprise a length adjustable tie-rod, wherein
Further, the sliding contact may be pressed with a force between about 50 N and about 100 N on the arcing horn.
The present invention will be more clearly understood based on the following drawings:
The present invention concerns a disconnector for isolating parts of a high-voltage grid. These high voltage grids are an interconnected network for delivering electricity from producers to consumers and generally present an alternating frequency of 50 or 60 Hertz (alternating current, AC current).
A high voltage disconnector is a mechanical switching device which provides an isolating distance for isolating a circuit or equipment from the source of power (for example a generator) when the disconnector is in an open position. In other words, in an open position, a gap isolates a load side from a source side. In disconnectors working in air (called high-voltage air break disconnectors), this isolating distance is air-filled (air gap).
Two typical high-voltage air break disconnector are the vertical-break disconnector and the pantograph type disconnector.
The disconnectors may further be equipped with an arcing horn, which is also called a horn gap device. The arcing horn provides the last point of conductor to conductor contact during the opening procedure. For example, the arcing horn provides the last contact point or contact position by a metal to metal contact during the opening procedure of the disconnector. After this point or past this position, at the end of the opening procedure, when the disconnector is fully opened, only the air-filled isolating distance (air gap) separates a first electrical side (which can be a source side of the network) from a second electrical side (which can be a load side of the network) of the disconnector. The air gap providing the separation between the source side and the load side is therefore established between a part of the arcing horn and a further contact of the disconnector.
The fixed portion (110), the arcing horn (60) and the first main contact (10) form a first electrical side (30). The first electrical side can be a source side i.e. a side of the disconnector where a power source, such as a generator, is situated. The pivoting portion (100) with the second main contact (20) and the sliding contact (50) form a second electrical side (40). The second electrical side can be a load side i.e. a side of the disconnector where a power consumer is situated, such as a network of houses. The disconnector is used to establish a disconnection by an air gap between the first electrical side and the second electrical side. The sliding contact preferably comprises a steel inox material for providing an electrical contact. The sliding contact may be a Carbon 40 steel i.e. Fe C40.
In the following, the opening operation of the disconnector will be described. At the beginning of the operation, the disconnector is in the closed state (
The sliding contact (50) remains in physical contact with the arcing horn until the sliding contact (50) has reached the upper end (170) of the arcing horn length (70). After this point and continuing the opening movement (150), an air gap is established between the sliding contact and the arcing horn. At this point, the first electrical side (30) is isolated from the second electrical (40) side by an air gap. The first main contact and the second main contact are separated by an air gap. The arcing horn and the sliding contact are separated by an air gap.
Under certain circumstances, an arc (90) may occur between the pivoting portion (100) and the arcing horn (60) directly after the air gap between the sliding contact and the upper end (170) of the arcing horn length becomes established. An arc will occur in most working conditions under which the present disconnector is used. The arc intensity and duration vary in dependence of the conditions in which the disconnector is operated (air humidity, atmospheric pressure, grid's topology, voltage difference across the open-gap and current passing through the contacts in the moment of opening operation).
More precisely, the arc will occur between the pivoting portion end (220) and near the upper end (170) of the arcing horn. Continuing the opening movement (150) increases the air gap between the pivoting portion and the arcing horn. The arc (90) remains existent until the air gap has reached a given limit size and then becomes extinguished. The limit size depends on electrical conditions and air conditions. The arc will become extinguished when the power dissipated by the medium surrounding the arc (for example air as medium) is more than the power generated by the arc. In this case, the electrons and ions that compose the arc channel recombine, thereby resuming the insulating property of the medium (for example air as medium). The power generated by the arc is reduced by increasing the arc's length when opening the disconnector. By increasing the arc's length, the arc's resistance is increased and thereby lowering the arc current and thereby the arc power (P=R*I2, P: power, R: arc resistance, I: current). The power dissipated by the arc is also increased by the arc lengthening because the heat exchanged between the arc and the surrounding medium (i.e. the heat exchanged between the arc and the surrounding air) is increased with an increased arc length. The arc's length is increased by separating the disconnector contacts. Once the arc has been extinguished, the arc will not resume if the ionized path left by the extinguished arc has been swept away and the open-gap distance of the insulating medium is enough to withstand the voltage difference between source and load side i.e. when the energy injected into the elongated arc is no more sufficient to maintain the arc.
During the existence of the arc (90) a current continues to flow via the arc. The current flows from the pivoting portion end (220) via the arc (90) to the upper end (170) of the arcing horn, then through the arcing horn length (70) to the fixed portion (110) and then further to the equipment connected to this side.
During the existence of the arc, the arc repeatedly breaks down and re-strikes. This breaking down and re-strike is caused by the alternating voltage. Repeated breaks and re-strikes of the arc occur as a consequence of the interaction between the arc, the disconnector and a network attached to the disconnector. When the arc is conducting, the voltage of both source and load side are assumed the same. The moment the arc is extinguished, the voltages are no longer the same. An electrical source side voltage assumes the grid's voltage whilst an electrical load side voltage assumes a DC voltage level related to the trapped charges that remained in the electrical load side part which is isolated from the grid. These voltage levels are different and, therefore, a voltage difference across the contacts appears. When this voltage difference is enough to break the medium's dielectric withstand, the arc resumes (re-strikes) after having been extinguished.
The arc itself and the breaking and re-striking of the arc cause transient oscillations of voltage and of current. These transient oscillations are produced in the disconnector and propagate into the network to which the disconnector is connected.
The frequency of these transient oscillations is by far higher than the frequency of the voltage and current at normal operation (grid nominal frequency), when the disconnector is closed. This grid nominal frequency is 50 Hz or 60 Hz.
The reliability of the network equipment will be affected by the transient oscillations. The transient oscillations cause an increased wear. The transient oscillations may encounter a resonance in the equipment, in particular in the component closest to the disconnector, for example in the current transformer. The reliability of the current transformer can therefore be compromised due to this high frequency oscillation. The transient voltage and current may therefore endanger components of the network. It is therefore highly recommendable to reduce the occurrence of these voltage and current transients. The frequency of the oscillation caused by the arc varies widely and is related to the grid's topology and the electrical parameters of the grid's components (capacitance inductance). The frequency of the oscillations can reach several mega Hertz (MHz).
To reduce the transients an inductive-resistive filter is integrated into the arcing horn. The inductive-resistive filter has an inductive part and a resistive part. The inductive part filters the transient oscillations. The resistive part smoothes abrupt voltage transitions which occur during restrikes of the arc.
The arcing horn as shown in the present figures has a left branch (65) and a right branch (65). However, the arcing horn could also have only one branch, the left branch or the right branch. In an arcing horn comprising a left branch and a right branch, the filter can be integrated into the left branch or into the right branch. It is also possible to integrate a first filter into the left branch and to integrate a second filter into the right branch i.e. to integrate two filters into the arcing horn. Using a first filter and a second filter (i.e. two filters) allows dissipating a greater amount of power during the opening of the disconnector as the current propagates at the same time through the first filter and through the second filter. Furthermore, a mechanical stability of the pivoting is improved. A force exerted from the first filter on the sliding contact is counterbalanced by a force exerted from the second filter on the sliding contact. In summary, a mechanical balance during movement exists. The shape of the two resistors is similar to a fork with the sliding contact inside. This shape closes the forces on itself and the stresses don't affect the main arm.
Furthermore, the two resistors are advantageous when the arc is very extendable as it is the case for the vertical break that drags the arc behind it during the opening phase.
The filter (180) is connected to the arcing horn (60) by a connection cylinder (300). The connection cylinder contacts the wire (310) of the filter on a first end and the arcing horn (60) on a second end and thereby establishes an electrical and a mechanical connection.
The connection cylinder preferably comprises copper and/or aluminum as material. The connection cylinder is dimensioned such that an impedance provided by the connection cylinder is adapted to the filter. The connection cylinder provides an impedance i.e. a resistance and an inductance. The impedance of the connection plate adds to the impedance of the filter. The connection plate provides an impedance for a current flowing along the arcing horn and the filter. The cylinder thickness is chosen thin enough such that the impedance produced by the cylinder remains acceptable with respect to the impedance of the filter and is thereby adapted to the filter. The cylinder thickness is chosen thick enough such that the cylinder assures the mechanical connection between the filter and the arcing horn. The connection cylinder may have a diameter of about 50 mm, a wall thickness of about 1 mm and a cylinder length of about 100 mm. Connecting the filter to the arcing horn using the connection cylinder is particularly advantageous as an electrical contact between the arcing horn and the filter is improved.
The filter comprises a wire wound on a cylindrical support. For example, a Ni—Cr alloy or a twisted constantan wire can be used. The wire can be wound upon a ceramic support. Preferably, the ceramic support is a ceramic insulator or a porcelain insulator. Porcelain insulators may comprise clay, quartz or alumina and feldspar. The support may be covered with a smooth glaze to shed water. A porcelain rich in alumina has the advantage of providing a high mechanical strength. Therefore, the support may comprise a porcelain insulator comprising alumina. Advantageously, the porcelain is configured to have a dielectric strength of about 4-10 kV/mm. As the current needs to flow through this wire, a resistance and inductance is provided by the length of the wire and the geometry of the coil. Consequently, the size of the resistance and inductance opposed to the current depends on the length of the wire the current needs to pass. A longer distance therefore leads to a greater resistance opposed to the current. The wire needs to be isolated to avoid a shortcut between the turns of the coil. The isolation is provided such that a contact with the sliding contact can be established. The contact between the wire of the filter and the sliding contact can be provided by an electrically conducting band on the resistor. The band provides the galvanic contact between the wire of the filter and the sliding contact. The band also provides a sliding surface on the filter for the sliding contact.
When opening the disconnector, the sliding contact (50) now first slides on the length of the arcing horn (70) until reaching the lower filter end (185). The sliding contact then continues to slide on the filter surface (190) from the lower filter end (185) to the upper filter end (200). The sliding contact then continues to slide on the arcing horn length until reaching the upper end (170). Continuing the opening movement (150), an air gap is established. An arc (90) may occur between the pivoting portion (100) and the arcing horn (60).
During the sliding of the sliding contact along the arcing horn length (70), an electrical contact remains established between the sliding contact (50) and the arcing horn length (70) at the contact position (160).
During the opening movement (150), the position where an electrical contact is established moves from the lower end (210) to the upper end (170). While the sliding contact slides on the filter during the opening movement (150), the length of the part of the filter through which the current needs to flow becomes gradually increased. Therefore, the resistance and inductance, provided by the filter, opposed to the current becomes gradually increased. In other words, the resistance and inductance become gradually inserted into the current flow by the opening movement (150). This means that the impedance inserted into the circuit becomes gradually increased. Gradually increasing the circuit impedance is particularly advantageous over abruptly changing the circuit impedance. Abruptly increasing or decreasing the circuit impedance causes switching overvoltage oscillations which may also be harmful to the grid's components. The filter can be configured and dimensioned such that an opening angle alpha between a horizontal line and the pivoting portion is about 30 degrees when the pivoting portion end (220) is situated near the upper filter end (200). Opening angle alpha is indicated in
As stated beforehand, continuing the opening movement (150), an air gap is established. An arc (90) may occur between the pivoting portion (100) and the arcing horn (60). When the arc occurs, a current continues to flow from the pivoting portion end (220) via the arc (90) to the upper end (170) of the arcing horn, then through the complete filter (180) from the upper filter end (200) to the lower filter end (185) and then to the fixed portion (110) and to network to which the disconnector is connected.
A current flow through the filter, as described beforehand, provokes a heating of the filter. The heating depends on a time duration during which the current flows through the filter. This time duration depends on a sliding speed of the sliding contact on the arcing horn. The sliding speed determines a duration of an opening process of the disconnector. Therefore, it determines a time duration during which the current flow through the filter exists. A lower sliding speed therefore leads to a longer time duration during which the current flows through the filter and thereby leads to more heating of the filter than a higher sliding speed. A lower sliding speed leads to more filter heating compared to a higher sliding speed.
The filter has an inductive property or inductance and a resistive property or resistance. Both properties together provide an impedance. The impedance is gradually inserted into the circuit during the opening of the disconnector as described beforehand.
The inductance of the filter opposes to a change in the electric current flowing through the filter. A faster change, i.e. a higher frequency, leads to a greater opposition. At the frequency range of the transient oscillations of the current and the voltage, the inductance of the filter has an influence on the current and the voltage. The filter provides an impedance at the frequency range of the transient oscillations. The high-frequency currents generated by the arc restrikes are therefore blocked and/or smoothed by the inductive part of the filter. The filter therefore acts like a coil, opposing the oscillating transient current which is passing through the filter. The inductive part of the filter blocks the higher frequency part of the voltage transient's frequency spectrum. This blockage results in part of the voltage transients which would have been applied on the grid's components are now being applied in the filter itself.
The inductance of the filter depends on the number of turns of the coil and on the physical dimension of the coil. The value of the inductance is determined by simulations. The value of the inductance is achieved during manufacturing of the filter by choosing a number of turns of wire as well as a length and a diameter of the filter.
The resistive part or resistance of the filter increases the time constant of the charge transferring between a source side and a load side of the filter. The increase of the time constant lowers the frequencies associated with the transient oscillations. The resistance decreases the magnitude of the transient current.
The inductive part and the resistive part alone or in combination reduce the amount of energy which is transferred to the grid's components. The inductive part and the resistive part of the filter thereby reduce the damage which an energy surge may cause in components of the grid.
The opening operation of the disconnector is preferably adapted when a filter is added to the disconnector. The sliding speed of the sliding contact (50) between the lower filter end (185) and the upper filter end (200) is adapted as well as the speed with which the pivoting portion (100) moves between the lower end (210) and the lower filter end (185) and between the upper filter end (200) and the upper end (170) and the speed after the upper end (170). It is preferable to use a constant sliding speed in order to prevent damages to a surface of the filter. The opening and/or closing operation are configured such that the sliding contact moves with a constant sliding speed while the sliding contact is in contact with the filter. The sliding speed of the opening movement (150) is configured high enough such that an overheating of the filter does not occur. In other words, the sliding speed is configured high enough such that an opening operation is short enough in time such that the heating of the filter remains low enough.
The sliding speed is configured low enough that a surface damage to the filter does not occur by a too important friction between the sliding contact and the surface of the filter. An increase in sliding speed leads to an increase in friction between the sliding contact and the filter surface. Preferably the sliding speed is adapted to have a short arc duration. The sliding speed may be adapted such that an arc is present during a few seconds, more preferably during 2 seconds or less. Preferably, an actuation control mechanism is used to control the opening movement. The actuation control mechanism may be the device and method described by document US2013307439A1. Typically, sliding speed during a contact between the sliding contact and the filter is about 1 m/s. A total duration of the opening movement may be between about 10 seconds and about 12 seconds. At a maximal open position, the sliding speed may slow down to about 0.1 m/s. If a constant sliding speed is used for the whole opening process a sliding speed of about 0.3 m/s may be used.
At the beginning of an opening movement (
A pressure between the sliding contact (50) and the filter (180) can be adapted to prevent damages to the filter and to assure a sufficient electrical contact between the sliding contact and the filter. An increase in pressure leads to an improved electrical contact. An increase in pressure also leads to an increase in friction between the sliding contact and the filter surface, and this increase in friction leads to an increase of wear of the filter and of the sliding contact. The pressure therefore needs to be high enough to assure the electrical contact and low enough to keep the friction below an acceptable level. A wear of the sliding surfaces is caused by a combination of the sliding speed and the pressure. A higher pressure therefore requires a lower sliding speed in order to maintain an acceptable wear. In summary, a sliding speed and a pressure need to be adapted to provide a sufficient electrical contact, a low enough wear of the surfaces sliding on each other and an opening duration short enough to result in a low enough heating of the filter.
A commercially available resistor (wire wound upon a cylindrical support) is modified in order to adapt it to the integration to the disconnector. The filter which is used together with the arcing horn typically has two layers of windings i.e. two stacks. A total length of a wire may be about 1200 mm and the wire may have a thickness of about 2 mm. The diameter of the filter on the cylindrical support may be about 60 mm or about 80 mm. A resistance of about 1000 Ohm per layer or per stack may thereby be provided.
A stabilization layer (330) is inserted between the wire and the cylindrical support. This layer provides structural support. The stabilization layer preferably comprises aluminiuoxide (Al2O3).
The filter is preferably configured such that a dielectric gradient is below 20 kV per cm in order to avoid a discharge between consecutive turns of the filter coil. The dielectric gradient on the live part is less than 20 kV per cm to avoid discharge between turns. A voltage between consecutive turns of the coil is typically 1.2 kiloVolt (kV). The filter preferably has a length of 1 m to 2 m.
The filter and the sliding contact are configured such that the sliding contact has a contact with about three turns of the wire of the filter at the same time when the sliding contact is in contact with the filter.
The electrical properties of the filter may be selected based on a simulation of equivalent circuits and existing electrical grids. The values are chosen in order to provide a compromise between feasibility, filtering frequency range and presenting a good attenuation factor. A power test was carried out to demonstrate the effectiveness of the selected properties of the filter. This test used a standardized equivalent circuit representing the most stringent scenario stated by the standard IEC 62271-305:2009.
The material for the filter may be the same as for a normal commercially available filter. The material needs to work with the sliding contact at the pressure chosen and the speed chosen. A tolerance of 10% in material properties is compatible with the present application. The length of the filter is chosen from an electrical point of view. The filter diameter and tie rod are dimensioned in order to withstand mechanically the environmental conditions, i.e. a temperature range of 0° C. to +50° C. and wind and sun.
The sliding contact with the integrated filter works particularly well in a network with a Cload/Csource up to 10/1.
The pantograph comprises a first turning portion (101) and a second turning portion (102).
The first turning portion and the second turning portion are connected at a folding point (81). The sliding contact (50) is situated at an end of the second turning portion opposite the folding point (81).
During an opening movement (151, 152, 153), the first turning portion turns around the pivot point (80) in a first folding movement (151). The second turning portion (102) moves around the folding point in a second folding movement (152). During this movement, the first and the second main contact become separated and the sliding contact slides on the arcing horn (60). The arcing horn moves in a drag movement (153) while dragged by the sliding contact (see
As described for the vertical break disconnector, a filter (180) is integrated into the arcing horn. The sliding contact therefore slides on the filter during the opening movement and the filter becomes gradually inserted.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20183533.7 | Jul 2020 | EP | regional |
