CA2028987A1 - Transformer bushing for field control of hvdc - Google Patents
Transformer bushing for field control of hvdcInfo
- Publication number
- CA2028987A1 CA2028987A1 CA 2028987 CA2028987A CA2028987A1 CA 2028987 A1 CA2028987 A1 CA 2028987A1 CA 2028987 CA2028987 CA 2028987 CA 2028987 A CA2028987 A CA 2028987A CA 2028987 A1 CA2028987 A1 CA 2028987A1
- Authority
- CA
- Canada
- Prior art keywords
- condenser
- condenser body
- transformer
- bushing
- circular
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F27/00—Details of transformers or inductances, in general
- H01F27/02—Casings
- H01F27/04—Leading of conductors or axles through casings, e.g. for tap-changing arrangements
Abstract
ABSTRACT
The invention relates to a condenser body for field control in transformer bushings and the connection of said body to the conductor of a transformer winding for transformers used in HVDC convertor plants. The condenser body is arranged as a solid of revolution with concentrically laid condenser layers. It is formed from one end with an outwardly-directed straight frustum of a cone and from the other end with an inwardly-directed straight frustum of a cone.
The invention relates to a condenser body for field control in transformer bushings and the connection of said body to the conductor of a transformer winding for transformers used in HVDC convertor plants. The condenser body is arranged as a solid of revolution with concentrically laid condenser layers. It is formed from one end with an outwardly-directed straight frustum of a cone and from the other end with an inwardly-directed straight frustum of a cone.
Description
'~ ~ 2 ~
ormer bushin~ fo~ ld_~Qn~E~l of HV~
Technical field The present invention relates to a special embodiment of a condenser body for field co~trol of transformer bushings.
The condenser body is designed for applicatlon substantially in connection with transformers which are conn~cted to I convertors.
Background art, Discussion of the problem If in a vessel with transformer oil two energized electrodes are postioned at a certain distance from each other, at a cer~ain voltage a flashover will occur between the electrodes. The flashover tendency may be minimized by inserting between the electrodes an insulator body which functions as a barrier.
Transformer bushings may comprise an upper insulator and a lower insulator of electric porcelain. At the joint between these there is a fixing flange which is connected to the transformer casing. In the centre of the bushing there is a tube on which is wound a condenser body to obtain a favourable electrical field distribution. The current can be conducted through the tube or a flexible conductor drawn through the tube.
Condenser bodies are describe~ in a number of patent specifications and publications of various kinds. In this connection, the following may, inter alia, be mentioned, namely, EP 0032690 "Foil~insulated high voltage bushing with poten-tial control", EP 0032687 "High-voltage bushing with layers oE embossed insulating foils"~ EP 0051715 "Safety device for high-voltage bushi.ng", ASEA Journal 1981, Volume 54, No. 4, pages 79-84. Common and typical for the design of the condenser bodies is thak they have a centxal circular-cylindrical p`ortion. From both ends this portion I
changes into outwardly-directed straight frustums of cones whose cross section areas have a decreasing radius A variant of the design of a condenser body is disclosed in GB 1,025,686, "Pothead for connecting oil-filled cables to transformers and other electrical apparatus". As above, the condenser body has a conical part terminating towards the transformer. However, towards the cable connection the condenser body terminates in a cross section area which is equal to the cross section area of the circular-cylindrical portion.
Another variant of the design of a condenser body is disclosed in a MICAFIL publication MNJ 11/12 from June 1969, in which a so-called "Re-entrant type bushing" is described.
This bushing is also intended to be used only within the a.c. field. Electrically, it is built up in the same way as a conventional a.c. bushing with a condenser body made of oil-impregnated paper, bakelite paper or is impregnated with molded resin and has concentric layers of a conducting material. The principle of the manufacture is that the transformer side of the body is first wound into an inward conical shape into a diameter where about 70% of the stress lies, whereupon the body is continuously wound into an I outward conical shape into the final outer diameter with 0%
of the stress. The advantage of such an embodiment is that a shorter bushing is obtained on the oil side. In addition, the shield may be omitted.
Power transformers which are used in convertor plants entail special problems from the point of view of insulation, which somehow have to be overcome in order to ensure a satisfactory function.
In high voltage direct current, HVDC, plants, there ls often used at least one convertor per pole and statlon. Normally, also, several bridges are connected in series. One of the poles oE a bridge is normally connected to ground and the other pole is connected to the next bridge, thus obtaining a series connection. The direct voltage potential of the respective bridge relative to ground is then increased according to the number of briclges which are connected in series.
Each bridge in the series connection is supplied ~Jith alternating voltage from a separate transformer. With increasing direct voltage potential on the brldges relative to ground, the insulation on bushings and windln~s on the transformers which are connected to the bridges will also be subjected to an increasingly higher direct voltage potential with a superimposed alternating voltage. The insulation of these must therefore be dimensioned so that they are capable of withstanding the increasingly higher insulating stresses to which they are then subjected.
The increasing direct voltage potential leads to special problems which do not exist in transformers used for pure I alternating voltage transformation.
For convertor transformers, the lower insulator o~ the bushing and the transition between the conductor of the transformer winding and the bushing present areas of problems from the point of view of insulation technique.
This is described, inter alia, in ~ow~x ~ra~mi~ion by Direct Current, by E Uhlmann, Springer Verlag 1975, pages 327-328.
The electric direct voltage fleld has a distribution different from that of the alternating voltage field. The distribution of the direct voltage is mainly determined by the resistivity of the various lnsulating mediums. It is true that both transformer oil, cellulose material and electric porcelain are good insulators, but a certain amount of electrlc current is conducted ln these ma-terials. The relation between the resistivity of cellulose material and transformer oil is a~oùt 100. This means that the cellulose . . .
~2~'7 in series with oil is subjected to considerably higher fi~lds than the oil, which in turn, therefore, imposes demands for a sufficient amount of solid insulatlng material in orcler not to exceed the electric withstand strength. The fielcl distribution as well as the field directions will thus be different from the case with alternating voltage. The current transport also entails a redistribution of charges i in the insulating mediums used.
Because of the heavy dependence of the resistivity on moisture content, field strength, temperature, etc., the distribution of direct current is di-fficult to predictO In addition, the physical nature of the direct voltage, i.e.
charge transport, charge, time-dependent behaviour, and so on, gives a picture of the insulation problems arising in connection with HVDC plants~ which is very complex and difficult to interpret. In "Space Charge and Field Distribution in Transformers under DC-stress" by U Gafvert and E Spicar, CIGRE Int. Conference on Large High Voltage Electric Systems, 1986 Session, 12-04, the complexity of the direct voltage distribution is illustrated. As prevlously mentioned, problems have arisen at the connection between the transformer bushing and the conductor o~ the transformer winding. This has led to the lower insulator of electric porcelain on the bushing having to be removed in order to manage the stresses at the HVDC terminal at the higher voltage levels.
I No simple explanation of the above phenomenon has been presented. However, there are reasons to suspect that the long surfaces which arise in connection wi~h bushings for high voltages in combination with the direction of the field along the long surface3 are of importance in this connectlon. Admittedly, also the alternating voltage fielcl ls directed along the surface of the lower poxcelain, but i.ts physical nature is different. One hypothesis is that the distribution of the direct voltage field runs the risk of becoming unstable a~d unevenly clistrlbu~ecl along - -`` 2 ~ 2 .~
sufficiently long surfacesO Another interesting hypothesis is described in an article entitled "Effect of Duct Configuration on Oil Activity at Liquid/Solid Dielectric Interfaces~ by R E James, F E Trick, R Willoughby in Journal of ~lectro~tatics, 12, 1982, pages 441-4~7. In this article it is stated that increased charge transport at surfaces caused by turbulence and access to charge is the reason for low electYic withstand strength.
One way of overcoming the above problems is disclosed in US
; patent application 539,209, "Barrier of condenser type for field control in transformer bushing terminals'l. In this case, the transformer bushing comprises a lower insulator.
To attain the desired field control, a condenser typé
barrier i5 used which has internal cones which make contact, with a certain oil gap, with the outer conical part of the lower insulator of the bushing as well as with the conically formed insulation surrounding the conductor of the transformer.
Summary of the invention, Advantages As has been described above, the invention relates to a condenser body for field control in transformer bushings for transformers used in convertor plants. The task of the condenser body is to overcome the flashovers which - as it has proved - may arise in transformer bushing terminals. It is designed so as to function as a barrier with both capacitive and resistive control of the electric field and I is dimensioned so that the condenser body withs-tands the voltages and fields occurring in this bushing and in particular in the sensitive region at the connection between the conductor of the transformer and the bushing.
It is assumed that the conductor coming from the transformer winding, and which i5 to be connected to the conductor of the bushlng, is surrounded by a conducting tube which is covered by wound electrical insulation. This insulation is formed, from the end of the conducting tube, as a straight frustum of a cone with cross sec~ion areas with an increasing radius which then changes into a circular-cylindrical portion towards the transformer. The conductor of the bushing also often consists of a conducting -tube.
That part of the condenser body which is situated on the air side of the transformer bushing is formed as a conven-tional condenser body. This means that, counting from the fixing flange of the transformer bushing, it has a circular-cylindrical portion which changes into an outwardly-directed straight frustum of a cone. Also other en~bodiments of this portion may be used.
I
That part of the condenser body which is covered by the invention, i.e. on the oil side of the transformer bushing, normally counting from the fixing flange of the bushing, starts with a circular-cylindrical portion and ends in an inwardly-directed straight frustum of a cone. The axial I length of the circular-cylindrical portion which is located on the oil side of the bushing is largely adapted such that its end coincides with the transition from conical to circular-cylindrical portion of the insulation of the conductor coming from the transformer winding. The conicity of the cone, which from that point is directed inwards, largely coincides (see, however, below) with the conicity of the insulation of the conductor of the transformer winding with space for an intermediate oil gap.
Such a design of a condenser body means that a conventional condenser body is integrated with a condenser type barrier.
This causes the electric field to be controlled in the desired way while at the same time obtaining a shielding of the conductor oE the transformer. In this way the condenser body according -to the invention serves as an insulation barrier both for dlrect voltage and alternating voltage fields.
r`l Otherwise, the condenser body according to the invention is built up as a conventional condenser body, i.e. it consists of wound insulating material with condenser layers of foil type concentrically inserted therein. The inner rad~us of the condenser body corresponds to the outer radius of the continuous current--carrying tube of the transformer bushing.
As mentioned above, the condenser body is manuEactured from an insulating agent alternating with conducting layers to obtain the desired capacitive control of the electrlc alternating field. The innermost condenser layer which is concentric with the conductor has an axial length which approximately corresponds tQ the inner axial length of the condenser body. Outside of this there are concentric layers alternating in a radial direction and tapering in an axi.al direction. The taper is made so that, concurrently with increasing radius of the condenser body counting rom the first layer, the layers are laid in an axial direction such that their outer edges connect with the outwardly-directed straight frustum of a cone of the condenser body on one side - the air side - and an evenly decreasing taper counting from the first layer towards the fixing flange on the other side. In addition there are short layers which are laid such that, concurrently with increasing radius of the condenser body counting from the first innermost layer, they are laid in an axial direction such that their outer edges connect with the inwardly-directed straight frustum of a cone of the condenser body. The axial length of these short layers is adapted such that their area is constant, i.e. the axial length decreases with increasing radius of the condenser body.
To ob-taln the desired field control, the innermost layer is connected to the central conducting tube, to which high voltage is applied, and the outermost layer at the fixing flange is connected to ground.
ormer bushin~ fo~ ld_~Qn~E~l of HV~
Technical field The present invention relates to a special embodiment of a condenser body for field co~trol of transformer bushings.
The condenser body is designed for applicatlon substantially in connection with transformers which are conn~cted to I convertors.
Background art, Discussion of the problem If in a vessel with transformer oil two energized electrodes are postioned at a certain distance from each other, at a cer~ain voltage a flashover will occur between the electrodes. The flashover tendency may be minimized by inserting between the electrodes an insulator body which functions as a barrier.
Transformer bushings may comprise an upper insulator and a lower insulator of electric porcelain. At the joint between these there is a fixing flange which is connected to the transformer casing. In the centre of the bushing there is a tube on which is wound a condenser body to obtain a favourable electrical field distribution. The current can be conducted through the tube or a flexible conductor drawn through the tube.
Condenser bodies are describe~ in a number of patent specifications and publications of various kinds. In this connection, the following may, inter alia, be mentioned, namely, EP 0032690 "Foil~insulated high voltage bushing with poten-tial control", EP 0032687 "High-voltage bushing with layers oE embossed insulating foils"~ EP 0051715 "Safety device for high-voltage bushi.ng", ASEA Journal 1981, Volume 54, No. 4, pages 79-84. Common and typical for the design of the condenser bodies is thak they have a centxal circular-cylindrical p`ortion. From both ends this portion I
changes into outwardly-directed straight frustums of cones whose cross section areas have a decreasing radius A variant of the design of a condenser body is disclosed in GB 1,025,686, "Pothead for connecting oil-filled cables to transformers and other electrical apparatus". As above, the condenser body has a conical part terminating towards the transformer. However, towards the cable connection the condenser body terminates in a cross section area which is equal to the cross section area of the circular-cylindrical portion.
Another variant of the design of a condenser body is disclosed in a MICAFIL publication MNJ 11/12 from June 1969, in which a so-called "Re-entrant type bushing" is described.
This bushing is also intended to be used only within the a.c. field. Electrically, it is built up in the same way as a conventional a.c. bushing with a condenser body made of oil-impregnated paper, bakelite paper or is impregnated with molded resin and has concentric layers of a conducting material. The principle of the manufacture is that the transformer side of the body is first wound into an inward conical shape into a diameter where about 70% of the stress lies, whereupon the body is continuously wound into an I outward conical shape into the final outer diameter with 0%
of the stress. The advantage of such an embodiment is that a shorter bushing is obtained on the oil side. In addition, the shield may be omitted.
Power transformers which are used in convertor plants entail special problems from the point of view of insulation, which somehow have to be overcome in order to ensure a satisfactory function.
In high voltage direct current, HVDC, plants, there ls often used at least one convertor per pole and statlon. Normally, also, several bridges are connected in series. One of the poles oE a bridge is normally connected to ground and the other pole is connected to the next bridge, thus obtaining a series connection. The direct voltage potential of the respective bridge relative to ground is then increased according to the number of briclges which are connected in series.
Each bridge in the series connection is supplied ~Jith alternating voltage from a separate transformer. With increasing direct voltage potential on the brldges relative to ground, the insulation on bushings and windln~s on the transformers which are connected to the bridges will also be subjected to an increasingly higher direct voltage potential with a superimposed alternating voltage. The insulation of these must therefore be dimensioned so that they are capable of withstanding the increasingly higher insulating stresses to which they are then subjected.
The increasing direct voltage potential leads to special problems which do not exist in transformers used for pure I alternating voltage transformation.
For convertor transformers, the lower insulator o~ the bushing and the transition between the conductor of the transformer winding and the bushing present areas of problems from the point of view of insulation technique.
This is described, inter alia, in ~ow~x ~ra~mi~ion by Direct Current, by E Uhlmann, Springer Verlag 1975, pages 327-328.
The electric direct voltage fleld has a distribution different from that of the alternating voltage field. The distribution of the direct voltage is mainly determined by the resistivity of the various lnsulating mediums. It is true that both transformer oil, cellulose material and electric porcelain are good insulators, but a certain amount of electrlc current is conducted ln these ma-terials. The relation between the resistivity of cellulose material and transformer oil is a~oùt 100. This means that the cellulose . . .
~2~'7 in series with oil is subjected to considerably higher fi~lds than the oil, which in turn, therefore, imposes demands for a sufficient amount of solid insulatlng material in orcler not to exceed the electric withstand strength. The fielcl distribution as well as the field directions will thus be different from the case with alternating voltage. The current transport also entails a redistribution of charges i in the insulating mediums used.
Because of the heavy dependence of the resistivity on moisture content, field strength, temperature, etc., the distribution of direct current is di-fficult to predictO In addition, the physical nature of the direct voltage, i.e.
charge transport, charge, time-dependent behaviour, and so on, gives a picture of the insulation problems arising in connection with HVDC plants~ which is very complex and difficult to interpret. In "Space Charge and Field Distribution in Transformers under DC-stress" by U Gafvert and E Spicar, CIGRE Int. Conference on Large High Voltage Electric Systems, 1986 Session, 12-04, the complexity of the direct voltage distribution is illustrated. As prevlously mentioned, problems have arisen at the connection between the transformer bushing and the conductor o~ the transformer winding. This has led to the lower insulator of electric porcelain on the bushing having to be removed in order to manage the stresses at the HVDC terminal at the higher voltage levels.
I No simple explanation of the above phenomenon has been presented. However, there are reasons to suspect that the long surfaces which arise in connection wi~h bushings for high voltages in combination with the direction of the field along the long surface3 are of importance in this connectlon. Admittedly, also the alternating voltage fielcl ls directed along the surface of the lower poxcelain, but i.ts physical nature is different. One hypothesis is that the distribution of the direct voltage field runs the risk of becoming unstable a~d unevenly clistrlbu~ecl along - -`` 2 ~ 2 .~
sufficiently long surfacesO Another interesting hypothesis is described in an article entitled "Effect of Duct Configuration on Oil Activity at Liquid/Solid Dielectric Interfaces~ by R E James, F E Trick, R Willoughby in Journal of ~lectro~tatics, 12, 1982, pages 441-4~7. In this article it is stated that increased charge transport at surfaces caused by turbulence and access to charge is the reason for low electYic withstand strength.
One way of overcoming the above problems is disclosed in US
; patent application 539,209, "Barrier of condenser type for field control in transformer bushing terminals'l. In this case, the transformer bushing comprises a lower insulator.
To attain the desired field control, a condenser typé
barrier i5 used which has internal cones which make contact, with a certain oil gap, with the outer conical part of the lower insulator of the bushing as well as with the conically formed insulation surrounding the conductor of the transformer.
Summary of the invention, Advantages As has been described above, the invention relates to a condenser body for field control in transformer bushings for transformers used in convertor plants. The task of the condenser body is to overcome the flashovers which - as it has proved - may arise in transformer bushing terminals. It is designed so as to function as a barrier with both capacitive and resistive control of the electric field and I is dimensioned so that the condenser body withs-tands the voltages and fields occurring in this bushing and in particular in the sensitive region at the connection between the conductor of the transformer and the bushing.
It is assumed that the conductor coming from the transformer winding, and which i5 to be connected to the conductor of the bushlng, is surrounded by a conducting tube which is covered by wound electrical insulation. This insulation is formed, from the end of the conducting tube, as a straight frustum of a cone with cross sec~ion areas with an increasing radius which then changes into a circular-cylindrical portion towards the transformer. The conductor of the bushing also often consists of a conducting -tube.
That part of the condenser body which is situated on the air side of the transformer bushing is formed as a conven-tional condenser body. This means that, counting from the fixing flange of the transformer bushing, it has a circular-cylindrical portion which changes into an outwardly-directed straight frustum of a cone. Also other en~bodiments of this portion may be used.
I
That part of the condenser body which is covered by the invention, i.e. on the oil side of the transformer bushing, normally counting from the fixing flange of the bushing, starts with a circular-cylindrical portion and ends in an inwardly-directed straight frustum of a cone. The axial I length of the circular-cylindrical portion which is located on the oil side of the bushing is largely adapted such that its end coincides with the transition from conical to circular-cylindrical portion of the insulation of the conductor coming from the transformer winding. The conicity of the cone, which from that point is directed inwards, largely coincides (see, however, below) with the conicity of the insulation of the conductor of the transformer winding with space for an intermediate oil gap.
Such a design of a condenser body means that a conventional condenser body is integrated with a condenser type barrier.
This causes the electric field to be controlled in the desired way while at the same time obtaining a shielding of the conductor oE the transformer. In this way the condenser body according -to the invention serves as an insulation barrier both for dlrect voltage and alternating voltage fields.
r`l Otherwise, the condenser body according to the invention is built up as a conventional condenser body, i.e. it consists of wound insulating material with condenser layers of foil type concentrically inserted therein. The inner rad~us of the condenser body corresponds to the outer radius of the continuous current--carrying tube of the transformer bushing.
As mentioned above, the condenser body is manuEactured from an insulating agent alternating with conducting layers to obtain the desired capacitive control of the electrlc alternating field. The innermost condenser layer which is concentric with the conductor has an axial length which approximately corresponds tQ the inner axial length of the condenser body. Outside of this there are concentric layers alternating in a radial direction and tapering in an axi.al direction. The taper is made so that, concurrently with increasing radius of the condenser body counting rom the first layer, the layers are laid in an axial direction such that their outer edges connect with the outwardly-directed straight frustum of a cone of the condenser body on one side - the air side - and an evenly decreasing taper counting from the first layer towards the fixing flange on the other side. In addition there are short layers which are laid such that, concurrently with increasing radius of the condenser body counting from the first innermost layer, they are laid in an axial direction such that their outer edges connect with the inwardly-directed straight frustum of a cone of the condenser body. The axial length of these short layers is adapted such that their area is constant, i.e. the axial length decreases with increasing radius of the condenser body.
To ob-taln the desired field control, the innermost layer is connected to the central conducting tube, to which high voltage is applied, and the outermost layer at the fixing flange is connected to ground.
2 ~ 7 AS mentioned above, the direct vol~age field is controlled by several factors. Thus, for example, the medium that has the lowest resistivity is field-controlling. Between the insulator body and the surrounding inwardly-directed straight frustum of a cone of the condenser body, an oil gap is formed, as already mentioned. Since the otl has lowest I resistivity, most of the current is conduc:ted in the oil gap, which therefore controls the field in parallel with surrounding surfaces. To obtain an even clistribution of the field along these sur~aces, it is therefore important that the width of the oil gap increases with decreasing radius.
Otherwise, the field would be concentrated towards that part where the radius is smallest, i.e. where there i5 the smallest axial cross section area. Thereore, the conicity of the inwardly-directed straight frustum of a cone of the condenser body and the conicity of the conical portion of the insulator body are suitably chosen such that the radial cross section area of the oil gap becomes approximately the same along the conical portion of the bodies.
Another field-controlling part is the radial distribution of the field in that part of the condenser body which does not contain any layers, i.e. around the innermost layer to which high voltage is applied. Between the oil gap towards the insulation on the conductor of the transformer winding and this region, the conducting layers function - in the direct voltage case - as equipotential lines which prevent the field from being concentrated to any part of the mentioned oil channel. With an accurately formed oil channel, the above-mentioned factors cooperate to obtain an even distribution of the field in the oil channel, the field being guided over, in the desired manner, to the insulation ! on the conductor of the transformer winding.
It is exceedingly desirable that the oil systems in the transformer and in the bushing consist of separate systems.
To achieve this, two different principal embodiments of the condenser body exist. `These will be described in gr~ater I
I
,?, ~ 2 ~ r~
detail under the "Description of the preferred embodiments", and therefore only a brief descriptlon of the principle will be given here. One alternative is that the condenser body is designed as a tight uni~ for example impregnated and cured with some suitable cast compound. The second alternative comprises enclosing the condenser body in a tight casing. This leads to the creation of two oil gaps at the transition bet~Jeen the insulation of the conductor oE
th~ transformer winding and the condenser body.
One advantage of the condenser body with the integrated condenser type barrier according to the inventlon in relation to the concept with a s~parate condenser type barrier disclosed in US application 539,209 is that the outer dimensions of the system can be made smaller. Ano~her advantage is that the extent of the interfaces which are subjected to tangential field stress i9 reduced.
Brief description of the drawings Figures 1 and 2 show two alternative embodiments of a condenser body according to the invention. To show the invention in the best way, the proportions between the diameter and axial length of the condenser body are not according to scale. The same is true also of the conicity oE the cones.
Description of the preferred embodlments The principal embodiment where the condenser body is formed as a tight cast unit is shown in Figure 1. As has been described, the condenser body 1 is built up as a solid of revolution which consists of wound insulating material with concentrically inserted foil type condenser layers. In order -to show the condenser body 1 to a certaln extent in its proper context, Figure 1 also shows the central current~
carrying part 2, i.n the form of a tube, of a transformer bushing around which the condenser body 1 is centered, as ~ i: 2 ~
well as the conductor of the transformer consisting of an inner energized tube 3 and insulating material 4 wound thereon, which material 4 has a conical taper 5 towards the tube end and then changes into a circul~r-cylindrical part 6.
A transformer bushing in which a condenser body according to the invention is to be included normally has an upper insulatox of electric porcelain acting towards the air side.
On the oil side transformer bushings normally also ha~e a lower insulator of, for example, electric porcelain. In an embodiment according to the invention, on the other hand, there is no such lower insulator of conventiQnal type.
The condenser body in ~he first alternative is impregnated with a suitable cast compound, for example epoxy. The condenser body is then wound Erom, for example~ an insulation paper which is impregnable by the cast compound used.
On the air side the condenser body is formed as a condenser body according to the state of the art, i.e. with a circular-cylindrical part 7 which changes into an outwardly-directed straight frustum of a cone 8. On the oil side the condenser body continues in a circular--cylindrical part 9 with the same outside diameter as the circular-cyllndrical part on the air side. The axial length of the outer contour of the circular-cylindrical part is adapted such that its end coincides with the transition of the insulation from the conical to the cixcular-cylindrical part of the conductor of the transformer winding. From the end of the condenser body there extends an inwardly-directed straight frustum of a cone 10 with a conici.ty which, according to the method previously described, somewhat deviates from the conicity of the conductor of the transformer winding. This leads to the creation of an oil gap between the condenser body and the conical part 5 oE the conductor of the transformer winding.
It is important for the distribution of the direct voltage field that the oil gap between the inwardly-di.rected straight frustum of a cone of the condenser body and the conical part of the conductor of the transformer winding should have largely the same radial cross section along the whole outer contour of the cones. The difference in radius is therefore greatest at the smallest base surfaces of the cones.
The first and innermost condenser layer 11 is electrically connected to the current-carrying tube 2 of the bushing, as indicated at the point of connection 120 This first layer has an axial length which corresponds to the inner axial length of the condenser body. It is surrounded by concentric layers 13 which are laid one above the other in a radial direction and tapering relative to the first layer in an axial direction. The taper is done by laying the layers, concurrently with increasing radius, in an axial dlrection so that the outer edges on one side connect with the conical contour of the air side and with an evenly decreasing taper towards the fixing ~lange of the transformer bushing on the 1 other side. The outermost o~ these layers is connected to ground potential.
Furthermore, the condenser body is provided with concentric short layers 14 whlch connect with the contour of the inwardly-directed straight ~rustum of a cone. The axial length of these short layers is adapted so as to have a practically constant area independently of the radius on which they are situated.
An embodiment of a condenser body according to the ~bove-mentioned second alternative is shown in Figure ~. The field-controlling parts oE the condenser body, i.e. the wound insulating material and the layers, are arranged, from the design point of view, in the same way as in Figure 1.
However, in this embodiment the insulation part consists, for example, of oil-inlpregnated insulation paper. In this alternative the entire`condenser body is surrounded by oil 12 2~ 7 enclosed in a tight casing 15. This leads to the creation of two oil gaps between the inwardly-directed cone of the condenser body and the conical part of the conductor of the transformer winding, i.e. inside and outside the tight casing, respectively. Both of these gaps must now be dimensioned in the same way as the oil gap in Figure 1. The demands that need to be placed on the materlal in this casing are that it must have sufficient mouldability and that its resistivity is to be greater than or at least as great as the resistivity of the oil.
Otherwise, the field would be concentrated towards that part where the radius is smallest, i.e. where there i5 the smallest axial cross section area. Thereore, the conicity of the inwardly-directed straight frustum of a cone of the condenser body and the conicity of the conical portion of the insulator body are suitably chosen such that the radial cross section area of the oil gap becomes approximately the same along the conical portion of the bodies.
Another field-controlling part is the radial distribution of the field in that part of the condenser body which does not contain any layers, i.e. around the innermost layer to which high voltage is applied. Between the oil gap towards the insulation on the conductor of the transformer winding and this region, the conducting layers function - in the direct voltage case - as equipotential lines which prevent the field from being concentrated to any part of the mentioned oil channel. With an accurately formed oil channel, the above-mentioned factors cooperate to obtain an even distribution of the field in the oil channel, the field being guided over, in the desired manner, to the insulation ! on the conductor of the transformer winding.
It is exceedingly desirable that the oil systems in the transformer and in the bushing consist of separate systems.
To achieve this, two different principal embodiments of the condenser body exist. `These will be described in gr~ater I
I
,?, ~ 2 ~ r~
detail under the "Description of the preferred embodiments", and therefore only a brief descriptlon of the principle will be given here. One alternative is that the condenser body is designed as a tight uni~ for example impregnated and cured with some suitable cast compound. The second alternative comprises enclosing the condenser body in a tight casing. This leads to the creation of two oil gaps at the transition bet~Jeen the insulation of the conductor oE
th~ transformer winding and the condenser body.
One advantage of the condenser body with the integrated condenser type barrier according to the inventlon in relation to the concept with a s~parate condenser type barrier disclosed in US application 539,209 is that the outer dimensions of the system can be made smaller. Ano~her advantage is that the extent of the interfaces which are subjected to tangential field stress i9 reduced.
Brief description of the drawings Figures 1 and 2 show two alternative embodiments of a condenser body according to the invention. To show the invention in the best way, the proportions between the diameter and axial length of the condenser body are not according to scale. The same is true also of the conicity oE the cones.
Description of the preferred embodlments The principal embodiment where the condenser body is formed as a tight cast unit is shown in Figure 1. As has been described, the condenser body 1 is built up as a solid of revolution which consists of wound insulating material with concentrically inserted foil type condenser layers. In order -to show the condenser body 1 to a certaln extent in its proper context, Figure 1 also shows the central current~
carrying part 2, i.n the form of a tube, of a transformer bushing around which the condenser body 1 is centered, as ~ i: 2 ~
well as the conductor of the transformer consisting of an inner energized tube 3 and insulating material 4 wound thereon, which material 4 has a conical taper 5 towards the tube end and then changes into a circul~r-cylindrical part 6.
A transformer bushing in which a condenser body according to the invention is to be included normally has an upper insulatox of electric porcelain acting towards the air side.
On the oil side transformer bushings normally also ha~e a lower insulator of, for example, electric porcelain. In an embodiment according to the invention, on the other hand, there is no such lower insulator of conventiQnal type.
The condenser body in ~he first alternative is impregnated with a suitable cast compound, for example epoxy. The condenser body is then wound Erom, for example~ an insulation paper which is impregnable by the cast compound used.
On the air side the condenser body is formed as a condenser body according to the state of the art, i.e. with a circular-cylindrical part 7 which changes into an outwardly-directed straight frustum of a cone 8. On the oil side the condenser body continues in a circular--cylindrical part 9 with the same outside diameter as the circular-cyllndrical part on the air side. The axial length of the outer contour of the circular-cylindrical part is adapted such that its end coincides with the transition of the insulation from the conical to the cixcular-cylindrical part of the conductor of the transformer winding. From the end of the condenser body there extends an inwardly-directed straight frustum of a cone 10 with a conici.ty which, according to the method previously described, somewhat deviates from the conicity of the conductor of the transformer winding. This leads to the creation of an oil gap between the condenser body and the conical part 5 oE the conductor of the transformer winding.
It is important for the distribution of the direct voltage field that the oil gap between the inwardly-di.rected straight frustum of a cone of the condenser body and the conical part of the conductor of the transformer winding should have largely the same radial cross section along the whole outer contour of the cones. The difference in radius is therefore greatest at the smallest base surfaces of the cones.
The first and innermost condenser layer 11 is electrically connected to the current-carrying tube 2 of the bushing, as indicated at the point of connection 120 This first layer has an axial length which corresponds to the inner axial length of the condenser body. It is surrounded by concentric layers 13 which are laid one above the other in a radial direction and tapering relative to the first layer in an axial direction. The taper is done by laying the layers, concurrently with increasing radius, in an axial dlrection so that the outer edges on one side connect with the conical contour of the air side and with an evenly decreasing taper towards the fixing ~lange of the transformer bushing on the 1 other side. The outermost o~ these layers is connected to ground potential.
Furthermore, the condenser body is provided with concentric short layers 14 whlch connect with the contour of the inwardly-directed straight ~rustum of a cone. The axial length of these short layers is adapted so as to have a practically constant area independently of the radius on which they are situated.
An embodiment of a condenser body according to the ~bove-mentioned second alternative is shown in Figure ~. The field-controlling parts oE the condenser body, i.e. the wound insulating material and the layers, are arranged, from the design point of view, in the same way as in Figure 1.
However, in this embodiment the insulation part consists, for example, of oil-inlpregnated insulation paper. In this alternative the entire`condenser body is surrounded by oil 12 2~ 7 enclosed in a tight casing 15. This leads to the creation of two oil gaps between the inwardly-directed cone of the condenser body and the conical part of the conductor of the transformer winding, i.e. inside and outside the tight casing, respectively. Both of these gaps must now be dimensioned in the same way as the oil gap in Figure 1. The demands that need to be placed on the materlal in this casing are that it must have sufficient mouldability and that its resistivity is to be greater than or at least as great as the resistivity of the oil.
Claims (6)
1. A condenser body for field control of the connection of a transformer bushing to the conductor of a transformer winding in convertor transformers, which condenser body is arranged as a solid of revolution with an inner circular-cylindrical opening the radius of which corresponds to the outer radius of the first current-carrying tube of the transformer bushing and which on the air side of the bushing has a circular-cylindrical outer part which terminates in a straight outwardly-directed truncated conical parts the condenser body consisting of insulating material with foil-type condenser layers concentrically laid therein and where the condenser body on the oil side of the bushing has a circular-cylindrical inner opening corresponding to the inner opening of the air side and an outer circular-cylindrical part which from the end is arranged with an inwardly-directed straight frustum of a cone towards the inner opening.
2. A condenser body for field control according to claim 1 and in which around the conductor of the transformer winding there is arranged an energized tube with a surrounding insulation with a circular-cylindrical part and with a straight conical taper towards the end of the tube and where the outer axial length of the condenser body on the oil side is arranged such that its end coincides with the transition between the circular-cylindrical part and the conical part of the insulation around the energized tube of the conductor of the transformer winding.
3. A condenser body for field control according to claim 1 and in which around the conductor of the transformer winding there is arranged an energized tube with a surrounding insulation with a circular-cylindrical part and with a straight conical taper towards the end of the tube and where the keenest of the inwardly-directed straight frustum of a cone of the condenser body is so arranged that the radial cross section area of the gap which is formed between this and the conical part of the insulation around the energized tube of the conductor of the transformer winding is constant along the entire length of the inwardly-directed cone.
4. A condenser body for field control according to claim 1, the transformer bushing of which is provided with a fixing flange, wherein a first inner condenser layer has an axial length which corresponds to the axial length of the inner circular-cylindrical opening, that outside of this there are arranged concentric condenser layers laid one above the other in a radial direction and tapering in an axial direction in such a way that the condenser layers, concurrently with increasing radius of the condenser body counting from the first layer, are laid in an axial direction such that their outer edges connect with the straight outwardly-directed frustum of a cone of the condenser body on one side and an evenly decreasing taper counting from the first layer towards the fixing flange of the transformer bushing on the other side, and that, in addition, the condenser body is provided with short condenser layers arranged such that, concurrently with increasing radius of the condenser body counting from the first layer, the layers are laid in an axial direction so that their outer edges connect with the inwardly-directed straight frustum of a cone of the condenser body and that their axial length is adapted such that their area is constant.
5. A condenser body for field control according to claims 1 and 2, wherein the first inner condenser layer is electrically connected to the current-carrying tube of the transformer bushing, to which tube high voltage is applied, and that the outer condenser layer at the fixing flange of the transformer bushing is connected to ground potential.
6. A condenser body for field control according to claim 1, wherein the condenser body is arranged to be enclosed in a tight casing or constitutes a tight body per se.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE8903633-9 | 1989-10-13 | ||
| SE8903633A SE464898B (en) | 1989-10-31 | 1989-10-31 | CONDENSOR BODY CONTAINS FAULT CONTROL OF A TRANSFORMER TRANSMISSION CONNECTOR TO A TRANSFORMER WIRING CONNECTOR WITH CIRCUIT TRANSFORMERS |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2028987A1 true CA2028987A1 (en) | 1991-05-01 |
Family
ID=20377340
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2028987 Abandoned CA2028987A1 (en) | 1989-10-31 | 1990-10-30 | Transformer bushing for field control of hvdc |
Country Status (7)
| Country | Link |
|---|---|
| EP (1) | EP0429843B1 (en) |
| JP (1) | JPH03180011A (en) |
| BR (1) | BR9005510A (en) |
| CA (1) | CA2028987A1 (en) |
| DE (1) | DE69024335T2 (en) |
| DK (1) | DK0429843T3 (en) |
| SE (1) | SE464898B (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102006008922B4 (en) * | 2006-02-21 | 2009-01-02 | Siemens Ag | Electric shielding arrangement |
| DE102006013927B4 (en) * | 2006-03-21 | 2008-11-20 | Siemens Ag | Connecting element for an electrical shielding arrangement |
| CN101136269B (en) | 2006-08-31 | 2013-03-27 | Abb研究有限公司 | High voltage bushing |
| CN101136268B (en) * | 2006-08-31 | 2012-02-08 | Abb技术有限公司 | High voltage DC bushing and device comprising such high voltage bushing |
| DE102010063979A1 (en) | 2010-12-22 | 2012-06-28 | Siemens Aktiengesellschaft | Electrical shielding arrangement of a separation point of a wiring for a HVDC component |
| DE102012203709B4 (en) * | 2012-03-08 | 2024-04-04 | Siemens Energy Global GmbH & Co. KG | High-voltage feedthrough for direct voltage |
| EP2922070A1 (en) * | 2014-03-19 | 2015-09-23 | ABB Technology Ltd | Electrical insulation system and high voltage electromagnetic induction device comprising the same |
| DE102017102370A1 (en) | 2017-02-07 | 2018-08-09 | nkt cables GmbH & Co.KG | coupling sleeve |
| DE102018116416A1 (en) | 2018-07-06 | 2020-01-09 | Nkt Gmbh & Co. Kg | coupling sleeve |
| DE102018215274A1 (en) * | 2018-09-07 | 2020-03-12 | Siemens Aktiengesellschaft | Arrangement and method for potential reduction in high voltage technology |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS499837B1 (en) * | 1968-12-11 | 1974-03-06 |
-
1989
- 1989-10-31 SE SE8903633A patent/SE464898B/en not_active IP Right Cessation
-
1990
- 1990-10-20 EP EP19900120182 patent/EP0429843B1/en not_active Revoked
- 1990-10-20 DK DK90120182T patent/DK0429843T3/en active
- 1990-10-20 DE DE1990624335 patent/DE69024335T2/en not_active Revoked
- 1990-10-30 BR BR9005510A patent/BR9005510A/en not_active Application Discontinuation
- 1990-10-30 JP JP29347790A patent/JPH03180011A/en active Pending
- 1990-10-30 CA CA 2028987 patent/CA2028987A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| EP0429843A1 (en) | 1991-06-05 |
| DK0429843T3 (en) | 1996-05-06 |
| BR9005510A (en) | 1991-09-17 |
| DE69024335T2 (en) | 1996-08-14 |
| EP0429843B1 (en) | 1995-12-20 |
| SE464898B (en) | 1991-06-24 |
| SE8903633L (en) | 1991-05-01 |
| JPH03180011A (en) | 1991-08-06 |
| DE69024335D1 (en) | 1996-02-01 |
| SE8903633D0 (en) | 1989-10-31 |
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| EEER | Examination request | ||
| FZDE | Dead |