Field of the Invention
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The present invention relates to an electric arc interruption arrangement.
Background
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Electrical switching devices, such as circuit breakers and disconnect switches, are widely used in power distribution and electrical systems to control and interrupt electrical currents. These electrical switching devices are importantly able to interrupt fault currents and protect the electrical system from damage caused by overcurrent or short circuits. During the interruption of high fault currents, an electric arc forms between the contacts of the electrical switching device. This arc can generate significant heat and damage the components of the switching device if not properly controlled and extinguished.
Summary
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In view of the above-mentioned and other drawbacks of the prior art, it is an object of the present invention to provide an electric arc interruption arrangement that at least partly alleviates the deficiencies with prior art.
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According to a first aspect of the invention, there is provided a movable, electrically insulating barrier arranged to move from a first position to a second position, wherein in the second position, the movable, electrically insulating barrier is positioned within an arc zone between a first electrode and a second electrode, an electrically conducting coil comprising at least one turn about an axis, the coil having a first end and a second end, wherein the first end is positioned closer to the first and second electrodes compared to the second end, and second end is electrically connected to one of the first electrode and the second electrode without passing through the coil, wherein the movement of the electrically insulating barrier from the first position to the second position is parallel to an axis of the coil from the first end to the second end, wherein the electrically insulating barrier is arranged to push, by its movement, an arc formed in the arc zone between the first electrode and the second electrode into the coil at its first end, whereby the arc induces an electric current through the electrically conducting coil, thereby generating a magnetic field that acts on the arc.
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The present invention is at least partly based on the realization of a coil which is activated by the arc itself. That is, the arc energizes the coil when the arc is formed between the first electrode and the second electrode without the need for additional switches or power supplies.
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The magnetic field produced by the coil causes elongation and motion of the arc such that arc stagnation is prevented which may otherwise cause damage or wear on components of the electric switch comprising the electric arc interruption arrangement, or the electric arc interruption arrangement itself.
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The arc zone is the area or volume or location where the arc is formed and from which the electrically insulation barrier pushes the arc into the coil.
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The coil comprises at least one winding of electrically conducting material such as a metal wire or thread. As electric current is passed through the windings of the coil, a magnetic field is generated in the coil.
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When the electrically insulating barrier push the arc into the coil, the arc will at some time, once the electrically insulating has moved the arc sufficiently long, jump from the first- or second-second electrode to an auxiliary contact connected to first end of the electrically conducting coil. The electric current in the arc then travel through the coil before it reaches the second end of the coil and the second electrode. The magnetic field produced by the coil due to the electric current travelling though it acts on the arc to elongate and move the arc to prevent stagnation.
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In other words, in embodiments, the electric arc interruption arrangement may be configured such that, in the presence of an arc between the first electrode and the second electrode, when the movable, electrically insulating barrier reaches an axial position between the first end and the second end of the electrically conducting coil, the arc forms between the first electrode or the second electrode and the auxiliary contact at the first end of the electrically conducting coil. Hereby, a magnetic field is advantageously generated at the right time, when the arc is inside the coil, to act on the arc.
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In embodiments, the magnetic field generated by the electrically conducting coil may be configured to cause the arc to move in the azimuthal direction of the electrically conducting coil. The azimuthal direction being "around the curve" of the coil advantageously provides for maximizing the length of the elongation and motion of the arc in the space at hand.
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In embodiments, the electrically conducting coil may be configured to generate a radial magnetic field component that pushes the arc against the inner and/or outer surface(s) of the electrically insulating barrier. This advantageously further enhances the arc elongation.
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In embodiments, the electrically insulating barrier may be arranged to move to a location inside the coil. Thereby, the magnetic flux density acting on the arc is higher compared to outside the coil, thereby causing enhanced arc elongation.
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In embodiments, the movable electrically insulating barrier may be tubular. In this case, the electrically conducting coil may be a single layer solenoid that is coaxially arranged with the tubular and movable electrically insulating barrier. A tubular or cylindrical geometry of the barrier is advantageously geometrically compatible with the shape of the coil, especially for moving the arc into the coil. It further also facilitates when using tubular first and second electrodes.
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In embodiments, the electric arc interruption arrangement may comprise an insulating wall separating the movable electrically insulating barrier and the electrically conducting coil. This provides for forming a chamber into which the arc is forced by the barrier. Furthermore, the insulating wall provides a layer of electrical insulation between the coil and the barrier. This provides for shielding the coil from direct contact with the arc which could cause damage to the coil or safety hazards. The insulating wall can also serve as a thermal barrier, reducing the amount of heat produced by the arc to be transferred to the coil.
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In embodiments, the electric arc interruption arrangement may comprise more than one electrically conducting coils interleaved or layered with each other. One or more of the coils may advantageously be configured to provide for tailoring the magnetic field strength and direction to further control the arc's movement and quenching. The more than one electrically conducting coils are connected to the same second electrode.
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In embodiments, the electric arc interruption arrangement may comprise an auxiliary contact ring connected to the first end of the electrically conducting coil, the contact ring comprising slots that reach radially from an inner side towards an outer side of the contact ring. The slots prevent the currents from moving in the radial direction of the contact ring which facilitates stagnating the arc and spreading out the erosion on the barrier.
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In embodiments, an iron core is arranged inside the electrically conducting coil(s) to further increase the magnetic field strength.
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In embodiments, the electrically conducting coil comprises multiple turns of variable pitch with increasing density towards the second end. This may advantageously increase the field strength at the top of the coil to enhance the effect of rotating the arc.
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The electric arc interruption arrangement may preferably be configured for direct current applications.
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Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.
Brief Description of the Drawings
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These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing an example embodiment of the invention, wherein:
- Fig. 1A schematically illustrates an electric arc interruption arrangement according to embodiments;
- Fig. 1B schematically illustrates an electric arc interruption arrangement once an electric switch is opened according to embodiments.
- Fig. 2A is a cross-section of an electrical switch comprising an electric arc interruption arrangement according to embodiments.
- Fig. 2B is a cross-section of an electrical switch comprising an electric arc interruption arrangement having more than one coil according to embodiments.
- Fig. 3 is a cross-section of the electrical switch comprising the electric arc interruption arrangement with the insulating barrier moved compared to in fig. 2A according to embodiments.
- Fig. 4 is a cross-section of the electrical switch comprising the electric arc interruption arrangement with the insulating barrier further moved compared to in fig. 3 according to embodiments.
- Fig. 5 illustrates a coil connected with a slotted contact ring according to embodiments.
Detailed Description of Example Embodiments
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In the present detailed description, various embodiments of the present invention are herein described with reference to specific implementations. In describing embodiments, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected. While specific exemplary embodiments are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations can be used without parting from the scope of the invention.
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Fig. 1A schematically illustrates an electric arc interruption arrangement 100 according to embodiments. The electric arc interruption arrangement comprises a movable electrically insulating barrier 102 and an electrically conducting coil 104 having electrical resistance R and inductance L.
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The movable electrically insulating barrier 102 is arranged so that it can move to in-between a first electrode 106 and a second electrode 108 of an electric switch 110. In fig. 1A, the electric switch 110 is in a closed state which means that an electric current, I, can flow between the first electrode 106 and the second electrode 108, here illustrated as from the second electrode 108 to the first electrode 106.
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The electrically conducting coil 104 has a first end 112 and a second end 114. The first end 112 is positioned closer to the first 106 and second 108 electrodes compared to the second end 114. Moreover, the second end 114 is electrically connected to the first electrode 106. The connection between the second end 114 and the first electrode 106 is direct and not through the turns of the coil 104. The turns of the coil 104 are located between the first end 112 and the second end 114.
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In the closed state shown in fig. 1A, the electric current through the coil 104 is zero as all the current flows through the electric switch 110.
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Fig. 1B illustrates the electric switch 110 in three different states once it is opened. Generally, the switch 110 open so that there is no longer physical contact between the first 106 and second 108 electrodes.
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Immediately after opening the electromechanical switch 110, at time t1, an arc 116 is formed between the first 106 and second 108 electrodes. Furthermore, the movable, electrically insulating barrier 102 moves into an arc zone 118 between the first electrode 106 and the second electrode 108, where the arc 116 is formed. As the barrier 102 continues moving, it forces the arc 116, at time t2 to connect to the first end 112 of the coil 104, such that current i starts flowing also through the coil 104.
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At time t3, with the arc pushed into to coil 104, the arc is no longer between the first 106 and second 108 electrodes, instead, the arc current flows through the coil 104 and the arc is sustained between the first end 112 of the coil 104 and the second electrode 108. This induced electric current through the electrically conducting coil generates a magnetic field that acts on the arc 116.
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More specifically, when the voltage across the coil 104 is lower than the voltage across the first 106 and second 108 electrodes, the arc between the first 106 and second 108 electrodes cannot be sustained, and it is extinguished at t3 such that all the fault current flows through the coil 104. This introduces the impedance (R, L) of the coil circuit by adding the resistance R, and inductance L, of the coil 104, which could limit the electric current in DC applications. It also fully energizes the coil 104 at the fault current level. In case that the coil design does not allow a sufficiently low voltage drop that quenches the arc between the first 106 and second 108 electrodes, the electric current through the coil 104 will be at least half of the total fault current.
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Once the coil 104 is activated, it produces a magnetic field which can be used to either attract, repel or push the arc 116 through Lorentz forces I x B into a predefined, intentional direction or position.
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Fig. 2A is a cross-section of an electrical switch 200 comprising an electric arc interruption arrangement 100. The electrical switch 200 and electric arc interruption arrangement 100 are preferably configured for direct current applications. The applications may be for renewable energy plants and industrial applications. Typical electric current strengths are about 85kA at 1500V DC, 50 kA at 2000V DC, or 50 kA at 2000V AC.
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The electric arc interruption arrangement 100 comprises a movable, electrically insulating barrier 102 arranged to move from a first position to a second position. In fig. 2 the electrically insulating barrier 102 is in its first position still outside the coil 104. In the second position to be described in more detail with reference to subsequent drawings, the movable, electrically insulating barrier 102 is positioned within an arc zone between a first electrode 106 and a second electrode 108. The arc zone is where the arc 116 is formed during an electric current interruption event. The first electrode 106 and the second electrode 108 may be cylindrical or tubular.
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The electric arc interruption arrangement 100 further comprises the electrically conducting coil 104 comprising at least one turn about an axis 122. The coil 104 has a first end 112 and a second end 114. The first end 112 is positioned closer to the first 106 and second electrodes 108 compared to the second end, and the second end 114 is directly electrically connected to the second electrode 108 without connecting through the windings 124 or turns of the coil 104. The second end 114 of the coil 104 is connected to the second contact 108 by suitable electrical leads or electrical wiring 125.
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For passing a current through the windings 124 the current must pass between the first and second ends 112, 114.
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The coil 104 comprises multiple turns or electrically conducting wire would about the longitudinal axis 122. In this embodiment, the movable electrically insulating barrier 102 is tubular and the electrically conducting coil is a single layer solenoid that is coaxially arranged with the tubular and movable electrically insulating barrier 102. The diameter of the tubular barrier 102 is smaller than the diameter of the coil 104 such that the tubular barrier 102 can move inside the diameter of the coil along the axis 122. The insulating barrier may be a single wall barrier as shown herein but may also be a double wall or multiwall barrier such as disclosed in
EP4095876 .
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Optionally, an iron core 130 is arranged inside the electrically conducting coil 104 to enhance the magnetic field density and field strength inside the coil 104. The iron core 130 is arranged inside an insulating barrier 133, shaped as a cylinder such that electric current from the electrodes 106/108 is not conducted to the iron core 130.
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The windings 124 of the coil may be homogenous and uniform throughout the coil 104. However, it is also envisaged that the electrically conducting coil comprises multiple turns of variable pitch with increasing density towards the second end 114.
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The electric arc interruption further comprises an auxiliary contact 126 connected to the first end 112 of the electrically conducting coil. The auxiliary contact 126 may be contact ring that circumvents the tubular barrier 102 once it has moved to its second position.
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Furthermore, an insulating wall 132 separates the movable electrically insulating barrier 102 and the electrically conducting coil 104 when the tubular barrier has moved inside the coil. This prevents the arc 116 from forming directly between the first electrode and the second end 114 bypassing the windings 124 of the coil 104. The insulating wall 132 may be tubular with a diameter smaller than the diameter of the coil 104 but larger than the diameter of the tubular barrier 102 such that the tubular barrier 102 fits inside the tubular insulating wall 132.
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In addition, the insulating barrier 133, shaped as a cylinder, forms an inner wall for a chamber in which the tubular barrier 102 moves to push an arc inside the chamber formed between the barrier 133 and the wall 132.
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The arc chamber formed between the barrier 133 and the wall 132 is shaped to receive at least part of the length of the tubular barrier 102.
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Additionally, as schematically illustrated in fig. 2B, the electric arc interruption arrangement 100 may comprising more than one electrically conducting coil interleaved or layered with each other. In this example, two coils 104a and 104b are layered with each other with the second coil 104b placed radially outside the first coil 104a. The electrically conducting coils 104a-b are connected to the same second electrode 108 and the same auxiliary contact 126.
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Still further, the electric arc interruption arrangement may comprise a further electrically conducting coil arranged on an opposite side of the electrically insulating barrier 102 compared to the first electrically conducting coil 104/104a/104b, the further coil comprising windings in an opposite direction compared to the first electrically conducting coil(s).
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In fig. 3, the electrically insulating barrier 102 has moved towards a second position along the axis 122 of the coil 104 from the first end 112 to the second end 114. This corresponds to time t2 referred to in fig. 1B.
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The electrically insulating barrier 102 is arranged to push, by its movement, the arc 116 formed in the arc zone between the first electrode 106 and the second electrode 108, see fig. 2A, into the coil 104 at its first end 112. The coil 104 surrounds the chamber formed between the insulating wall 132 and the insulating wall 133 into which the arc is pushed by the electrically insulating barrier 102. The arc 116 now connects to the auxiliary contact 126 connected with the first end of the coil 104. The arc energizes the electrically conducting coil 104 by an induced electric current through the electrically conducting coil 104, thereby generating a magnetic field, Br, Bz that acts on the arc 116. Thus, in the presence of the arc 116 between the first electrode 106 and the second electrode 108, when the movable, electrically insulating barrier 102 reaches an axial position between the first end 112 and the second end 114 of the electrically conducting coil, the arc forms between the first electrode and the auxiliary contact 126 at the first end 112 of the electrically conducting coil 104.
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More specifically, as the barrier 102 starts to move the current is shared between auxiliary contact ring 126 and the second contact 108. Once the tubular barrier 102 reach close to the location of the auxiliary contact ring 126 at time t2, the current commutates into the coil 102 and the remaining arc 117 between the contact ring 126 and the second electrode 108 gets quenched. The fault current now flows now through the coil 104 and produces an additional magnetic field distribution. As a consequence, there is a strong Lorentz force Ir x Bz on the upper section of the arc 116 which is forced to move into the azimuthal θ direction of the coil 104. The weaker radial magnetic field forces the motion -Iz x Br of the arc root outside the tubular barrier 102 into the negative azimuthal θ direction and the arc column inside the tubular barrier 102 in the opposite direction. As a consequence, the arc root on the contact ring 126 will mainly start moving along the azimuthal θ direction while the upper arc sections move in the opposite direction thereby causing an elongation of the arc 116. That is, the magnetic field generated by the electrically conducting coil 104 is configured to cause the arc 116 to move in the azimuthal direction of the electrically conducting coil 104.
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Fig. 4 illustrates the electric arc interruption arrangement 100 when the electrically insulating barrier 102 has moved further into the coil 104, at time t3. The arc 116 is now fully between the first electrode 106 and the auxiliary contact ring 126.
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The arc 116 continues elongating along the azimuthal θ direction due to the different magnitude and direction of the magnetic forces Fθ along the plasma column, that is, along the axis 122 of the coil 104. This makes the arc 116 wound up about the tubular barrier 102 such that a component of the arc current starts flowing in the azimuthal direction θ . As a consequence, a strong magnetic force in the radial direction Fr is also produced, which pushes the arc against the inner and outer faces of the tubular barrier 102.
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Fig. 5 illustrates an example coil 104 having a first end 112 and a second end 114. The coil 104 is a single layer solenoid with the first end 112 connected to an auxiliary contact ring 126. An arc 116 is schematically shown being formed between the first contact 106 and the auxiliary contact ring 126. The azimuthal direction θ about the axis 122 of the coil 104 is indicated.
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The contact ring 126 comprises slots 140 that reach radially from the inner side towards the outer side of the contact ring 126. The arc, under the influence of the magnetic field produced by the coil, moves tangentially around the coil in the azimuthal direction θ. The slots 140 prevent the currents from moving in the radial direction of the contact ring 126. The slots in the contact ring provides for avoiding magnetic dead points at the inner tips 160 meaning that the arc 116 gets stagnated. Rotating the arc at the tip and on the barrier facilitates to maintain homogeneous erosion on the barrier 102 surface.
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An electrically insulating material may electrically insulating material, may be a ceramic or a polymer, where the polymer may be a thermoset or thermoplastic polymer, such as polyoxymethylene (POM), poly(methyl methacrylate) (PMMA), polyimide (PI), polyamide (PA) and/or a polyolefin, such as polypropylene (PP) or polymethylpentene (PMP) or another such polymer.
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Circular or cylindrical geometry of the herein described switches and electric arc interruption arrangements is preferred, however, it is also envisages that the shape of the coil, barrier and arc chamber may take other forms, such as a square or rectangular geometry.
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Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art.
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Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.