AU2005200514B2

AU2005200514B2 - Electrical component with fault-arc protection

Info

Publication number: AU2005200514B2
Application number: AU2005200514A
Authority: AU
Inventors: Bernhard Doser; Robert Hauser; Markus Staubli
Original assignee: Hitachi Energy Ltd
Current assignee: Hitachi Energy Ltd
Priority date: 2004-02-19
Filing date: 2005-02-07
Publication date: 2009-06-04
Anticipated expiration: 2025-02-07
Also published as: ATE367670T1; ZA200501412B; DE502004004354D1; ES2290656T3; AU2005200514A1; PT1566869E; EP1566869B1; EP1566869A1

Abstract

On one electrode of the arcing protection system has arcing projections (21-24) each with successive circumferential sections (b, c) around the cup wall (12). One section (b) set back from the cup edge, is angled with respect to the projecting section. Sections are held in the cup wall (12).

Description

AUSTRALIA Patents Act 1990 ABB TECHNOLOGY AG COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Electrical component with fault-arc protection The following statement is a full description of this invention including the best method of performing it known to us:- ]A DESCRIPTION Electrical component with fault-arc protection 5 Technical Field The invention is based on an electrical component with fault-arc protection. The invention also relates to an arcing electrode specifically for this component. The component has an insulator in the form of a pillar, a first electrical conductor 10 system, which can be connected to a high-voltage potential, being fixed to the head of said insulator. A second electrical conductor system, which can be connected to ground potential, is fixed to the insulator foot. The first and the second electrical conductor systems each have an arcing electrode for the purpose of accepting an fault arc occurring in the event of a discharge between the first and the second electrical 15 conductor system. At least one of the two arcing electrodes is in the form of a cup. At least two arcing fingers forming the cup rim are formed in the cup wall. An fault-arc, which is formed in the event of an undesirable discharge between the two electrical conductor systems, is commutated onto the cup rim. The influence of the magnetic field of the current which supplies the fault-arc and is guided in the cup rim to the arc, 20 causes the predominantly axially aligned fault-arc to rotate and be quenched at the current zero crossing. Prior Art 25 The invention is in the field of electrical components with fault arc 819249_1.doc - 2 protection, such as that described in EP 1 283 575 Al. A component which is disclosed in this prior art and is in the form of a surge arrestor contains two electrical conductor systems which are held such that they are 5 electrically insulated from one another by an outdoor insulator in the form of a pillar and are at different electrical potentials. Each of these electrical conductor systems has an arcing electrode for the purpose of accepting an fault-arc occurring in the 10 event of a discharge between the two electrical conductor systems. The two arcing electrodes are in the form of cups. Two or more arcing fingers, which form sections of the cup rim, are formed in the wall of each cup. The feed current from the arc flowing in these 15 sections to the base point of the fault-arc ensures that a radially directed magnetic field acts at the base point of the arc. The arc is therefore subjected to a tangentially directed, electrodynamic force and is rotated around the insulator along the cup rim until 20 the arc is quenched. Even in the case of an electrical component with fault arc protection as was previously known from US 5,903,427 A, an outdoor insulator in the form of a 25 pillar holds two electrical conductor systems which are electrically insulated from one another and are at different electrical potentials. Each of these systems contains in each case one conductor section which is in the form of an open, annular loop and is routed with a 30 gap around the insulator in the region of the insulator head or the insulator foot. If, during operation of the component in a high-voltage system, an undesirable fault-arc occurs on the component, for example owing to a lightning strike or owing to a switching process, the 35 fault-arc is guided into a current path containing the conductor sections as arcing electrodes. The fault-arc is now aligned predominantly axially, with its base on the two annular arcing electrodes which lie in the 3 circumferential direction. Electromagnetic forces cause the fault-arc, which rests on the arcing electrodes to rotate about the insulator of the component until it is quenched at the zero crossing of the fault-arc current. The component is thus protected against the eroding and corroding effect of the fault-arc. 5 A further electrical component with fault-arc protection and in the form of a surge arrestor is specified in US 6,018,453A. With this component too, undesirable fault-arcs are commutated onto two arcing electrodes which are spaced apart from one another in the direction of one axis of the component, are forced to rotate about this axis and are 10 thus quenched at the current zero crossing. In contrast to the above mentioned prior art, however, with this component the two arcing electrodes are each in the form of a plate, and a large number of predominantly radially guided slots are formed in each of the plates. 15 Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim 20 of this application. Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, 25 integer or step, or group of elements, integers or steps. Description of the Invention According to the present invention, there is provided an electrical component protected 30 against accidental arcing with -an insulator designed in the form of a column -a first power conductor system, provided at the insulator head and directable to a first electrical potential, and with 819249_1.doc 3A -a second power conductor system, provided at the insulator foot and directable to a second electrical potential, in which the first and the second power conductor system in each case has an arc electrode for the accommodation of an arc accidentally occurring in the event of a 5 discharge between the first and second power conductor systems, and in which at least one of the two arc electrodes is designed in the form of a cup, and has at least two arc fingers, moulded into the cup wall and forming the cup edge characterised in that the arc fingers in each case have two finger sections following each other in the circumferential direction of the cup wall, of which a further from the cup edge section 10 of a first of the fingers and the axis are arranged in a skewed manner relative to each other, and a cup edge-forming section of a second of the fingers is held at a distance in the axial direction from the further cup edge section in the cup wall. 819249_1.doc 4 Owing to this arrangement and formation of the arcing fingers, a strong, predominantly radially directed magnetic field is built up over the entire cup rim at the base point of the fault-arc. A large, tangentially directed, electrodynamic force, which causes the arcing base point to rotate until the arc is quenched at the current zero crossing, thus 5 always acts on the base point, which is held on the cup rim, of the arc. This constant force is achieved by a radially directed, strong magnetic field being maintained constantly in the arc base point independently of its present position on the cup rim. Even at the unction point between one finger and the subsequent finger in the circumferential direction, this magnetic field is maintained, since at least one of the two 10 finger sections which are one above the other accepts current flowing predominantly in the tangential direction at the arc base point as a predominantly axially guided arc current. A comparatively small number of arcing fingers is required if the section, forming the 15 cup rim, of the arcing fingers is guided predominantly tangentially. The predominantly tangential guidance also comprises curvatures of the sections forming the cup rim in the axial direction. In one embodiment of the component according to the invention which is particularly 20 simple in manufacturing terms, the arcing fingers over their entire length and the axis are arranged such that they are arranged skew with respect to one another. In a related aspect, the present invention provides an electrical component protected against accidental arcing with 25 -an insulator designed in the form of a column -a first power conductor system, provided at the insulator head and directable to a first electrical potential, and with -a second power conductor system provided at the insulator foot and directable to a second electrical potential, in which the first and the second power conductor 30 system in each case has a arc electrode, for the accommodation of an arc accidentally occurring in the event of a discharge between the first and second power conductor system, and in which at least one of the two arc electrodes is designed in the form of a cup, and has at least two arc fingers moulded into the cup wall and forming the cup edge characterised in that the arc fingers in each case have two predominantly 35 tangentially directed sections of which one is set on the cup floor, and the other forms the cup edge, in that each arc finger has an at least in the axial direction directed centre 819249_1.doc 5 section which connects the cup floor-side section with the cup edge-forming section, and in that the cup edge-forming section of a first of the fingers is held at a distance in the axial direction from the cup floor-side section of a second of the fingers in the cup wall. 5 Owing to this arrangement and design of the arcing fingers, a particularly strong, predominantly radially directed magnetic field is built up over the entire cup rim at the base point of the fault-arc. A particularly well formed loop, which results in a high radial magnetic field and thus considerably simplifies the current commutation at the unction point, is forced on the current, which feeds the fault-arc and propagates in the 10 fault-arc, at the junction from one finger to the other. The central section is advantageously guided not only in the axial direction but at the same time also in the tangential direction. The central section and the axis are then arranged such that they are skew with respect to one another. the section on the cup 15 base side and the inclined central section then ensure at the unction form the central section tot the cup rim an effective formation of a current loop and thus the desirably strong radial magnetic field at the arc base point. A sufficiently strong magnetic field at the junction point form one finer to the other can 20 also be achieved when the central section is guided predominantly axially and possibly radially. However, in this case, the section on the cup base side should be separated from the section forming the cup rim only by an air gap which is relatively narrow compared to the diameter of 25 819249_1.doc -6 the section, since, otherwise, the radial component of the magnetic field may be too small at the location of the arc base point. 5 In one embodiment of the component according to the invention which is economically particularly advantageous, the arcing electrode provided on the insulator head is formed by an electrical connection supplying the first electrical potential. This 10 embodiment also has the advantage that, owing to the thermal effect of the fault-arc, it prevents the fault arc from migrating from the electrode, which is otherwise provided on the insulator head and has the same rotation sense, to the electrical connection. 15 Rotations of the arc base points in the opposite direction are achieved if the arcing electrode arranged on the insulator head has a different rotation sense than the arcing electrode arranged on the insulator 20 foot. These opposing movements result in particularly effective magnetic blowing of the fault-arc. With the component according to the invention, the insulator is generally hollow, and an active part is 25 provided which is guided axially through the insulator. Particularly preferred components are therefore outdoor bushings, surge arrestors, in particular having an active part based on metal oxide, current transformers, voltage converters, or switches or circuit breakers. If 30 the component, however, has only a supporting function, the insulator may also be solid. Further advantageous developments of the component according to the invention are described below. 35 - 7 BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained below with reference to 5 exemplary embodiments. In the drawing: Figure 1 shows a side view of a component according to the invention in the form of a surge arrestor having two arcing 10 electrodes 4, 7, which each contain six arcing fingers, Figure 2 shows a side view of the arcing electrode 4 of the surge arrestor shown 15 in figure 1, and Figure 3 shows a plan view of the arcing electrode 4, 20 Figure 4 shows a side view of one embodiment of the arcing electrode 4, which contains only two arcing fingers instead of six, Figure 5 shows a perspective view of a further 25 embodiment of the arcing electrode 4 having six arcing fingers, but with the arcing fingers being modified compared to the embodiment shown in figures 2 and 3, and 30 Figures 6 to 9 show further embodiments of the arcing electrode 4. WAYS OF IMPLEMENTING THE INVENTION 35 In the figures, identical parts are identified by the same reference symbols. The surge arrestor illustrated in figure 1 has an outdoor insulator 1 which is in the - 8 form of a pillar and is formed, for example, from a polymer, for example based on epoxy or silicone, or a ceramic, for example a porcelain. The insulator is hollow and has an active part (not shown in the 5 figure), which is arranged along an axis 2 (pillar axis), having at least one nonlinear resistance element, preferably based on metal oxide, such as, in particular, zinc oxide. 10 A first electrical conductor system is provided on the insulator head and can be connected to a first electrical potential, for example a high-voltage potential. The first electrical conductor system is electrically conductively connected to the head end of 15 the active part and has an electrical connection 3, which can be connected to a high-voltage line, and an arcing electrode 4, which is in the form of a cup and is aligned concentrically with respect to the axis 2 and is open at the bottom towards the insulator foot. 20 This electrode may be produced, for example, by casting or by machining, for example by turning on a lathe and milling. The arcing electrode 4 is surrounded concentrically by a cover hood 5 which is closed at the top. A second electrical conductor system is provided 25 on the insulator foot and can be connected to a second electrical potential, for example ground potential. The second electrical conductor system is electrically conductively connected to the foot end of the active part and has an electrical connection 6, which can be 30 connected to a ground conductor, and an arcing electrode 7, which is in the form of a cup and is aligned concentrically with respect to the axis 2 and is open at the top towards the insulator head. The arcing electrode 7 is surrounded concentrically by a 35 cover hood 8 which is closed at the top. The two arcing electrodes 4 and 7 are made of an electrically highly conductive material, in particular of copper or a copper alloy, for example brass. In a particularly - 9 advantageous manner, this material may be composed of graphite or some other particularly fire-resistant or melting-loss-resistant material. At least the downward ly pointing rim 9 of the arcing electrode 4 or the 5 upwardly pointing rim 10 of the arcing electrode 7 are made from a fire-resistant or melting-loss-resistant material, for example a refractory (=high-melting-point) brass, or a copper/tungsten or copper/chromium alloy. The two arcing electrodes 4 and 7 are arranged mirror 10 image - symmetrically with respect to one another. The design of the arcing electrode 4 can be seen in figures 2 and 3. These figures show that the arcing electrode 7 has a cup base 11 and a cup wall 12, which 15 is adjacent to the cup base, extends in the direction of the axis 2 of the pillar, and in which are formed six arcing fingers, which are of identical design, form the cup rim 9 and are spaced apart from one another by air gaps 13. Figure 2 shows only the four fingers 21, 20 22, 23 and 24. These fingers each extend predominantly in the circumferential direction and each have three sections which are spaced apart from one another in the axial direction and are successive in the circumferential direction. The three sections can be 25 seen in figure 2 only for the two fingers 22 and 23 and are given in this order the reference symbols a, b, c and a', b', c', respectively. A section of the fingers 22, 23 which is marked with the reference symbol a or a', respectively, rests on the base 11 and is 30 tangentially guided in the same manner as a section c or c', respectively, forming the cup rim. The two sections a and c and a' and c', respectively, are connected to one another by means of a section b or b', respectively, which is remote from the cup rim and is 35 guided predominantly tangentially, but at an angle to the axis 2. Sections b and b', respectively, and axis 2 are arranged such that they are directed skew to one another. The section b', which is remote from the cup - 10 rim, of the finger 23 and the section c, forming the cup rim, of the finger 22 are held in the cup wall 12 one above the other with an axial gap in the same manner as the section b, which is remote from the cup 5 rim, of the finger 22 and a section c'', forming the cup rim, of the finger 21 and, respectively, as a section b'', which is remote from the cup rim, of the finger 24 and the section c', forming the cup rim, of the finger 23. Provided concentrically with respect to 10 the axis 2 in the cup base 12 is an opening 14, through which a section of the electrical connection 6 (illustrated only in figure 1) is passed. This surge arrestor operates as follows: 15 If, during operation of the surge arrestor in a high voltage system, an undesirable fault-arc occurs between the electrical connections 3 and 6 on the active part and/or on the insulator 1, the base points of said fault-arc are each guided to the cup rims 9, 10 under 20 the influence of its own magnetic field. The arcing current then flows from the electrical connection 3 via the cup base 11, the arcing fingers, for example 21, 22, 23 or 24, the cup rim 9, the arc, the cup rim 10 and the arcing electrode 7 to the electrical connection 25 6. Since the cup rims 9, 10 are relatively close to one another compared to the cup bases 11, the cup rims define a small gap, and in this manner the arc has a secure base, and good thermal protection is thus ensured. In addition, a tangentially directed, high 30 electrodynamic force, which causes the arc to rotate until it is quenched at the current zero crossing, always acts on the base point 15, held on the cup rim 9, of the arc (figure 2) . The constant force is ensured by a radially inwardly directed, strong magnetic field 35 being constantly maintained in the arc base point 15 independently of its position on the cup rim 9. This constant force results from the design and arrangement of the arcing fingers described above. If the arc is - 11 based on the section c of the finger 22, a current I, which is indicated in figure 2 by an arrow and which continues in the axially directed arc (illustrated as a jagged arrow in figure 2), flows in the section c. The 5 current thus forms a well formed current loop at the arc base point 15 and produces at the location of the base point 15 a strong magnetic field, which is directed away from the viewer, i.e. radially inwards. A tangentially directed force, which guides the base 10 point 15 on the air gap 13 separating the two fingers 22 and 23, acts on the arc in the counterclockwise direction. Irrespective of whether the base point 15 has not yet bridged the air gap or has partially or even completely bridged it, the radially inwardly 15 directed magnetic field is maintained, since at least one of the two sections b' and c accepts the current I. At the end of the section c' which faces the section c, no such current loop which is as pronounced as it is at the end of the section c which faces the section c' is 20 formed once the current I has been commutated, since the current I in fact runs obliquely with respect to the axis 2 in the section b'. This current loop, however, is sufficient to produce a sufficiently large radial magnetic field to allow the arc base point 15 to 25 move further. In contrast to the embodiment of the arcing electrode shown in figures 2 and 3, the arcing electrode 4 in the form shown in figure 4 has only two arcing fingers 22 30 and 23. With this electrode, the sections b, c' and b', c of the two fingers 22 and 23, which are remote from the cup rim and, respectively, form the cup rim, are arranged with an axial gap between them as in the embodiment described above, with the result that this 35 embodiment has the same advantageous effects. In terms of manufacture, these electrodes can be produced in a particularly simple manner, although this is at the - 12 cost of the mechanical robustness of the arcing fingers. The tangentially guided section a', which rests on the 5 cup rim 11, improves the formation of the loop in the exemplary embodiments shown in figures 2 to 4, and thus also increases the radial magnetic field. If the air gap 13 has only a comparatively small width between two arcing fingers, for example 22, 23, the radial magnetic 10 field is sufficient even if the section b', which is remote from the cup rim, and the axis 2 are no longer arranged obliquely inclined or skew with respect to one another, but the section b' without tangential component is guided predominantly axially (depending on 15 the inclination of the wall, also with a radial component) . Such an embodiment of the electrode 4 is shown in figure 5. The current loop, defined by the junction from the section a' to the section b' perpendicular to it, produces a magnetic field, whose 20 component in the radial direction is sufficient to allow the arc base point on the cup rim 9 to move further at the junction from one arcing finger 23 to the adjacent arcing finger 22. 25 The arcing fingers, for example 22 to 23, need not necessarily have an exclusively tangentially guided finger section c or c' forming the cup rim. Loop formation and a sufficiently strong radial field are also achieved when the arcing fingers and the axis 2 30 are arranged such that they are obliquely inclined or skew with respect to one another (embodiment of the electrode 4 shown in figure 6) or when only the section b, b' which is remote from the cup rim and the axis 2 are arranged obliquely inclined or skew with respect to 35 one another, but the section c, c' forming the cup rim is guided tangentially (embodiment of the electrode 4 shown in figure 7) or such that it is curved (embodiment of the electrode 4 shown in figure 7 with - 13 the section c' of the arcing finger 23', forming the cup rim, shown with dashed lines). However, it is important that the section c forming the cup rim and the section b' remote from the cup rim of successive 5 arcing fingers 22, 23 are held in the cup wall 11 one above the other with an axial gap. In the embodiments for the electrode 4 shown in figures 6 and 7, the arcing fingers rest on the cup base 11 10 with the section b, b' being guided at an angle to the axis 2. The tangentially guided section a, a', which is provided in the embodiments shown in figures 2 to 5, can therefore in principle be dispensed with, since in general the sections b, c and b', c' of successive 15 arcing fingers 22, 23 can produce a sufficiently strong radial magnetic field during current flow. Since they are both made of an insulating material, preferably such as a polymer based on silicone, epoxy, 20 polycarbonate or polyamide, to which fillers, in particular such as flame-retarding low-combustibility materials, are advantageously added, the arcing electrode 4, 7 is protected against contact, for example by animals or by items falling on it. At the 25 same time, the surrounding area is also protected against the influence of heated material, which may be ejected from the component by the influence of the fault-arc, and represents a considerable fire risk. Components protected in this manner can thus be used 30 without any problems in dry regions with vegetation posing a fire hazard, such as dried-out grass or shrubbery. With the embodiments of the electrode 4 shown in 35 figures 8 and 9, six material recesses 16 are formed in the cup base 11 and each open into one of the air gaps 13. These embodiments of the electrode can be formed in a simple manner by stamping and cold forming a metal - 14 sheet, for example by stamping a flat blank 25, containing the material recesses, for the electrode from the metal sheet and then bending a sheet-metal tab located between in each case two material recesses 16 5 so as to form six contact fingers and the air gaps 13 arranged therebetween (for reasons of clarity only four fingers 21 to 24 are illustrated in figures 8 and 9) In this case, it is possible to achieve, in a manner which is particularly simple to manufacture, a 10 polygonal cup base 11, with one of the material recesses 16 being arranged at each corner of said cup base 11 (embodiment shown in figure 8 having a cup rim in the form of a polygon). However, it is also possible to produce an embodiment of the electrode 4 having a 15 circular cup rim 9 corresponding to the embodiment shown in figures 2 to 5. The cup wall 12 in all the exemplary embodiments is illustrated predominantly inclined at an angle of 90* 20 with respect to the cup base 11, but may also include a different angle of at most 1500 and at least 300, without losing the above-described advantageous effects.

- 15 LIST OF REFERENCE NUMERALS 1 Insulator 2 Axis 3, 6 Electrical connections 4, 7 Arcing electrodes 5, 8 Cover hoods 9, 10 Cup rims 11 Cup base 12 Cup wall 13 Air gap 14 Opening 15 Arc base point 16 Material recesses 21, 22, 23, 24 Arcing fingers 25 Blank a, a', a'', b, b', c, Sections of the arcing fingers c', c'' Feed current for the arc

Claims

2. The component according to Claim 1, characterised in that the cup edge forming section of the arc fingers is predominantly directed in a tangential direction. 20 3. The component according to Claim 1, characterised in that the arc fingers and the axis are arranged in a skewed manner relative to each other.
4. An electrical component protected against accidental arcing with -an insulator designed in the form of a column -a first power conductor system, provided at the insulator head and directable to 25 a first electrical potential, and with -a second power conductor system provided at the insulator foot and directable to a second electrical potential, in which the first and the second power conductor system in each case has a arc electrode, for the accommodation of an arc accidentally occurring in the event of a discharge between the first and second power conductor 30 system, and in which at least one of the two arc electrodes is designed in the form of a cup, and has at least two arc fingers moulded into the cup wall and forming the cup edge characterised in that the arc fingers in each case have two predominantly tangentially directed sections of which one is set on the cup floor, and the other forms the cup edge, in that each arc finger has an at least in the axial direction directed centre 35 section which connects the cup floor-side section with the cup edge-forming section, and in that the cup edge-forming section of a first of the fingers is held at a distance in 561493_1.doc 17 the axial direction from the cup floor-side section of a second of the fingers in the cup wall.
5. The component according to Claim 4, characterised in that the centre section in addition is also directed tangentially. 5 6. The component according to Claim 5, characterised in that the centre section is predominantly directed axially, and radially as required.
7. The component according to any one of the Claims I to 6, characterised in that at least two material recesses are moulded into the cup floor, which in each case open out into an air gap provided between the first and the second or the third contact finger. 10 8. The component according to Claim 7, characterised in that the cup edge has a circular or polygonal shape.
9. The component according to any one of the Claims I to 8, characterised in that the cup floor is embodied in the form of a polygon, at each of whose corners one of the material recesses is arranged. 15 10. The component according to any one of the Claims I to 9, characterised in that the cup wall is arranged inclined at an angle between 300 to 150' relative to the cup floor. I1. The component according to any one of the Claims I to 10, characterised in that the arc electrode provided at the insulator head is formed from a power connection 20 supplying the first electric potential.
12. The component according to any one of the Claims I to 11, characterised in that the arc electrode provided at the insulator head ha a direction of rotation other than that of the arc electrode arranged at the insulator foot.
13. An electrical component protected against accidental arcing substantially as 25 hereinbefore described with reference to the accompanying drawings.