TRANSFORMER TECHNICAL FIELD

[0001] The present disclosure generally relates to a bushing connection shielding system and particularly to the connection of a bushing to a high voltage power transformer. In particular, the bushing connection shielding system is preferably provided in a turret assembly of a high voltage transformer to prevent occurrence creepage path at a transformer side connection end of a bushing. The shielding system preferably comprises a plurality of barriers which are seamlessly connected with a paper covering of a central insulation tube.

BACKGROUND [0002] High-voltage (HV) bushings are attached to a power transformer tank either directly or indirectly via turrets, wherein turrets are typically used to achieve certain requirements, including tank size. In particular, for connecting bushings to a power transformer, an exit insulation system (EIS) is provided comprising insulation component connecting elements between high voltage winding end of the transformer and the bottom end of a bushing.

[0003] A high voltage winding end can be positioned at the top or in the middle of the axial height of the coil. Common practice for exit insulation systems is connection through a turret to the bushing bottom end. The bushing is designed to withstand the electrical field strength produced in the insulation, especially when any earthed material is present nearby. As the strength of the electrical field increases, leakage paths may develop within the insulation of the bushing or at any connection ends of the bushing. The risk of occurrence of leakage paths may be increased, e.g. upon thermal expansion or vibrations.

[0004] At high-voltage transformers, not only the bushing but also the connection of the bushing to the transformer must be designed to avoid leakage paths. Fig. 7 shows a prior art design for connecting a bushing (not shown) from the top to an oil power transformer. A metal shielding tube 90 is used for shielding a current carrying conductor from the winding to the bushing. The metal shielding tube 90 is fixed within a turret via support 91. The oil side end or bottom end of the bushing is connected to the metal shielding tube via equalizing ball or shielding 92. However, since the metal shielding tube 90 and the shielding 92 are made of different parts, there exists the risk of a the gap occurring (illustrated as squiggly line 93) between these parts being too large and/or to create a creepage path for electric flashover. This may lead to a risk of flashover possibility between the shielding tube and the equalizing ball and a low electrical safety. [0005] Accordingly, in view of the above, there is a demand for improved connection shielding systems which overcome at least some of the problems of the state of the art.

SUMMARY

[0006] In light of the above, a bushing shielding system, a slip-free mounting device for the bushing shielding system and a turret assembly with a bushing shielding system mounted within said turret assembly as well as a power transformer with an exit insulation system according to the independent claims are provided. Further aspects, advantages and features are apparent from the dependent claims, the description, and the accompanying drawings.

[0007] In particular, according to the present invention, a paper covered concentric metal shielding tube is supported by a slip-free mounting device. According to a further or additional aspect, said paper covered concentric metal shielding tube is integrated with an equalizing ball that electrically shields a high voltage bushing end connection. According to a further or additional aspect, dielectric barriers, separated by spacers, are integrated with the tube paper creating a seamless interface between paper and the barriers.

[0008] In the prior art, when shielding tube and equalizing ball are separated, the gap between the shielding tube and the equalizing ball causes danger for electrical flashovers or partial discharge. With the seamless integration, particularly when combined with the improved slip-free support of the shielding tube, this gap is eliminated, and the electrical strength of the insulation system is increased.

[0009] Such electrical shielding of high voltage bushing end connections may be used inside electrical devices, for example in high voltage transformers. According to an aspect of the present disclosure, a bushing connection shielding system is provided, said system comprising a shielding tube with an equalizing ball at an upper end of the shielding tube, said equalizing ball being configured to electrically shield a lower end of a connected high voltage bushing.

[0010] The shielding tube is covered by paper, preferably multiple paper layers, and an electrical shield formed by a dielectric barrier which comprises at least one barrier layer, preferably three or more barrier layers, is provided to the equalizing ball, preferably at its upper end. [0011] A seamless interface between the paper and the at least one dielectric barrier layer is provided in that at least a lower end of the dielectric barrier layer is integrated in the paper. Preferably, the barrier layer is at least partly sandwiched between different paper layers. Also preferably, the barrier layer comprises, at its lower end, multiple legs or protrusions which may be integrated in the paper layers and/or closely follow the contour of the shielding tube and/or equalizing ball.

[0012] The shielding tube preferably is a metal tube concentrically covered by a plurality of paper layers, preferably oil impregnated paper layers.

[0013] The dielectric barrier may comprise a plurality of dielectric barrier layers which are separated by spacers and paper layers at the lower part. Preferably, the spacers are arranged at positions more upwardly than the paper layers. [0014] The dielectric barrier layers preferably are formed from oil impregnated pressboard. The spacers are preferably formed from oil impregnated pressboard.

[0015] Moreover, the spacers may be elongate and extend substantially in the axial direction of the tube, particularly between the top of the equalizing ball and the top end of the paper, and preferably, a plurality of spacers is circumferentially spaced.

[0016] The equalizing ball is preferably fixed to or integrated with the metal shielding tube, wherein the equalizing ball preferably comprises a lower conical section, a middle cylindrical section and/or a substantially dome shaped upper section. [0017] The barrier layers may be dome shaped rings with leg members at the lower end of the barrier layers. Said leg members may be sandwiched in the paper and extend along part of the middle cylindrical section and/or along part of the conical section. Preferably, said leg members are bent along said conical section of the equalizing ball.

[0018] The shielding tube, the conical section, the cylindrical section and/or the dome shaped upper section are preferably made from the same material, preferably metal. A pressboard layer, preferably an oil impregnated pressboard layer may be additionally applied at the at the outer surface of the dome shaped upper section of the equalizing ball.

[0019] According to an additional and/or alternative aspect of the present invention, there is provided a slip-free mounting device for supporting the above described system [0020] This mounting device preferably comprises: a mounting device clamp, which may be configured to be fixed inside a transformer or a turret assembly, and a mounting device insulation.

[0021] Said mounting device clamp supports the mounting device insulation and the mounting device insulation supports the bushing connection shielding system.

[0022] An outermost layer of the mounting device insulation of the slip-free mounting device may comprise at least a protrusion, which may extend partially or fully around the circumference of the mounting device insulation. Said protrusion is preferably supported by at least one clamp fixation means which is fixed to the mounting device clamp. [0023] The slip-free mounting device may further comprise a stop ring for axially supporting the bushing connection shielding system.

[0024] Said stop ring may further comprise a stop ring band for fixing the stop ring to the bushing connection shielding system. This stop ring may be made of one part or two parts or more. It may extend fully or partially around the mounting device.

[0025] In particular, the stop ring may be adapted to circumferentially extend around the outermost layer of the paper cover of the bushing connection shielding system at a transition region between the cylindrical region of the shielding tube and the lower conical section of the equalizing ball.

[0026] Moreover, said stop ring may comprise a circumferential groove for receiving the stop ring band. Said stop ring may also comprise an inner supporting surface for supporting a conical section of the bushing connection shielding system and a lower supporting surface for being supported by the mounting device insulation.

[0027] The mounting device insulation preferably comprises a plurality of circumferentially arranged barrier layers, spaced apart by spacers. The spacers may comprise hook spacers, the hook spacers preferably comprising a lower hook for supporting an inwardly arranged barrier layer and an upper hook for being supported by an outwardly arranged barrier layer.

[0028] A radial inner barrier layer may be supported by the closest or neighbouring radially outer barrier layer, and the radially innermost barrier layer may be adapted to sheath or surround (partially or fully) the shielding tube. [0029] Furthermore, the radially outermost barrier layer may be supported by the clamp fixation means.

[0030] In the context of the present invention, a turret assembly of a high voltage transformer may be provided with a bushing connection shielding system described herein, preferably by a mounting device discussed herein being provided within the turret assembly.

[0031] The present invention also provides for a power transformer with an exit insulation system, EIS, said exit insulation system having a connecting element for connection between a high voltage winding end of the transformer and the bottom/lower bushing end, and a bushing connection shielding system as described herein, preferably mounted in the transformer by the slip-free mounting device discussed herein.

[0032] In short summary, the present invention provides a shielding system which can be used, e.g., for shielding an oil side bushing end connection. The design of the present invention provides a seamless combination of paper covering and barriers. In particular, according to the present invention at least one, preferably a plurality of outer barriers is integrated in paper layers which cover the metal tube. This construction creates a seamless passage from the paper covering to the barriers such that creation of a creepage path is avoided in said transition. Since the barriers of the present invention are preferably seamlessly integrated into the paper layers, flashover possibility between the shielding tube and the equalizing ball is diminished or even removed such that increased electrical safety is achieved. [0033] Additionally, individually and in combination, the present invention provides for a slip-free mounting device for the bushing shielding system. This particularly allows appropriate and reliable positioning of the shielding tube and the equalizing ball with respect to the bushing and thus further improves shielding with a reduced risk of flashover and a further increased electrical safety.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] To allow the above recited features of the present disclosure to be further understood in detail, a more particular description of the disclosure, as briefly summarized above, is made by reference to preferred embodiments. The accompanying drawings relate to preferred embodiments of the disclosure and are described in the following: Fig. 1 shows a schematic partial cross-sectional view of a preferred embodiment of the present shielding system;

Fig. 2a shows a side view of a turret,

Fig. 2b shows a cross-sectional view of the turret with a busing connection shielding system inside the turret; Fig. 3a shows a cross-sectional view the bushing connection shielding system,

Fig. 3b shows a side view of the system of Fig. 3a;

Fig. 3c shows an enlarged view of the top part from Fig. 3a; Fig. 4a shows a perspective side view of the bushing connection shielding system and a slip-free mounting device;

Fig. 4b shows a cross-sectional view of the bushing connection shielding system with the mounting device;

Fig. 4c shows a top view of the bushing connection shielding system; Fig. 5a shows a side view of a barrier layer; Fig. 5b shows a top view of a barrier layer;

Figs. 6 shows a perspective views of the bushing connection shielding system mounted to the slip-free mounting device of the present invention;

Fig. 7 shows a prior art busing connection shielding arrangement.

DETAILED DESCRIPTION OF EMBODIMENTS

[0035] Reference will now be made in detail to the various embodiments, one or more examples of which are illustrated in each figure. Each example is provided by way of explanation and is not meant as a limitation. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with any other embodiment to yield yet a further embodiment. It is intended that the present disclosure includes such modifications and variations.

[0036] Within the following description of the drawings, the same reference numbers refer to the same or to similar components. Generally, only the differences with respect to the individual embodiments are described. Unless specified otherwise, the description of a part or aspect in one embodiment can apply to a corresponding part or aspect in another embodiment as well.

[0037] With exemplary reference to Fig. 1 , a schematic partial cross- sectional view of a preferred embodiment of the present bushing connection shielding system (in the following also called shielding system or just system) is described. A shielding metal tube 1 , which preferably is cylindrical, is provided around an electrical conductor (not shown). Said shielding tube 1 is connected to an equalizing ball 6 or is integrally formed with the equalizing ball 6. Fig. 1 shows only a part of the metal tube 1 with an integral equalizing ball 6. The equalizing ball 6 is preferably hollow inside such that the equalizing ball is preferably formed from an outer wall. The equalizing ball 6 preferably comprises a lower conical or tapered section 61 , extending radially outwardly with respect to the tubel , connected to the cylindrical tube 1 or integrally formed with said tube. It is further preferred that on top of the conical section 61 a substantially cylindrical section 62 is formed. Moreover, it is further preferred that the (lower) conical section 61, the cylindrical section 62 and/or the tube 1 are formed from the same material, e.g. metal.

[0038] As illustrated in the cross-sectional view of Fig. 1 and visible, e.g., in the perspective view of Fig. 6, a substantially dome shaped upper section 63 is provided on top of the cylindrical section 62. According to a preferred embodiment, said dome shaped section 63 comprises a central hole 64 on top, configured to receive and accommodate the end 5 of a high voltage bushing. According to a preferred embodiment, said dome shaped upper section 63 is preferably also formed from the same material as the metal tube 1 , and is preferably additionally covered at the outer surface by a pressboard element 35, preferably oil impregnated pressboard element, exhibiting a dome shape corresponding to the one of the dome shape section 63. Said dome shaped section 63 may be integrally formed or connected to the cylindrical part 62. Pressboard element 5 may be mounted directly on the metal dome part.

[0039] The diameter of the lower conical section 61 of equalizing ball 6 preferably increases along the axially upward direction.

[0040] The metal tube 1 is concentrically covered by paper 2, preferably by a plurality of oil impregnated paper layers. Said oil impregnation generally may take place after manufacturing and assembly, e.g. when the transformer is filled with oil. Paper and pressboard preferably is not impregnated when applied. A mounting device 7 is provided for supporting the shielding system 80 and preferably supports the tube 1 at the paper 2 which covers the metal shielding tube For instance, the mounting device 7 is used for mounting the shielding system 80 within a turret or turret assembly, as shown, e.g., in Fig. 2b. Preferably, the mounting device is a slip-free mounting device according to a preferred aspect of the invention, which will be discussed in further detail below.

[0041] The bottom or oil sided end 5 of the bushing is connected to the current carrying cable. Preferably, the bushing is not connected to the equalizing ball 6, wherein this conjunction is preferably shielded by the novel design of the connection shielding system 80. [0042] It is noted that the present application refers to upper and lower parts which are understood as relating to the relative position regarding gravity, i.e. , an upper part is above a lower part with regard to gravity as shown in the Figs. The present invention, however, is not restricted to an exact aligned orientation with the gravitational field such that the terms “upper”, “top” can be replaced by “distal” and “lower”, “bottom” can be replaced by “proximal” in case the system is oriented tilted or even downwardly oriented. In the latter case, an additional cone in the (in the Figs downward) end of the shielding tube will be provided to cooperate with the stop ring as discussed herein. Proximal, in this context, may mean closer to the high voltage power transformer. Flowever, for the sake of simplicity, the typical preferred substantial vertical orientation of the system will be discussed in the examples.

[0043] The shielding system 80 comprises at the upper section 63 dielectric barriers 3 or barrier layers 3 which are separated by spacers 4. These spacers 4 are preferably vertically oriented, from top to bottom or vice versa and preferably circumferentially spaced apart, preferably in a regular pattern or distribution, as shown, for example, in Fig. 6. For instance, Fig. 6 shows spacer assemblies 4 which are circumferentially spaced apart. The remaining parts are preferably ring like and extend around the hole circumference of the system.

[0044] The barriers 3 are seamlessly integrated in the layers of the paper cover 2 which avoids the creation of any gaps. Such a seamless interface is preferably achieved by winding a plurality of paper layers at different radial levels around the lower ends 32 of the barriers 3 (compare Fig. 5). The barriers 3 are preferably formed from pressboard, preferably oil impregnated press board and preferably dome shaped as shown in the figures.

[0045] The illustrated embodiments show four barriers 3. According to the present invention, however, it is also feasible to use less or more barrier layers, e.g., only 2 or 3 barriers, or 5, 6, or even more barriers. A person skilled in the art would preferably adapt the number of barrier layers depending on the voltage or potential difference provided at the bushing end connection.

[0046] Figs. 5a and 5b show a side view and a top view of a single barrier layer 3. Preferably, the barrier layer 3 is a dome shaped barrier layer with a central hole 31 in the ring-shaped top view to receive the bottom end of the bushing. The diameter of the hole 31 in the barriers is substantially the same as of the central hole 64 in the dome shaped part 63 of the equalizing ball 6. At the lower end of the barrier 3, a plurality of, preferably individual, extensions 32 in the form of arms, legs, leg members or tines are provided. These may further facilitate either of winding paper layers around them for seamless connection to the paper cover 2 and bending of these parts of the barrier layer 3, e.g., along the conical section 61 of the equalizing ball 6 (see e.g., Fig. 1). [0047] As mentioned above, the lower leg members 32 of the barrier layers 3 are preferably seamlessly integrated in the paper cover 2, preferably at the lower conical section 61 of the equalizing ball and preferably also at the cylindrical middle section 62 of the equalizing ball 6. The upper parts of the barrier layers 3, which are preferably dome shaped, are preferably separated by a plurality of spacers 4 from one another and preferably separated from the paper cover 2 by being axially distanced thereof. The space between the vertically oriented elongate spacers 4 and the barrier layers 3 at the upper part are left empty or may be filled with additional filling material.

[0048] The design of the present invention is preferably used for electrical shielding of high voltage bushing end connections, e.g. inside electrical devices for example high voltage transformers, preferably AC high voltage oil transformers or reactors. For instance, the construction of the present invention can be used for in oil transformers which typically comprise exit insulation systems (EIS) on top or middle exit systems with turret assemblies for connecting the winding of the transformer to bushings. Thus, it is preferred that the bushing end connection shielding can be used at more than 200kV, more than 400kV, more than 800kv or even up to 1200kV or even more.

[0049] In general, the bushing connection shielding system may be used for any kind of exit insulation system. In particular, an exit insulation system (EIS) comprises an insulation component and a connecting element between high voltage winding end and the bottom of the bushing end. High voltage winding end may be positioned at the top or in the middle of the axial height of the coil. Common practice for each exit insulation system is the phase current through a turret or inside a main tank to the bushing bottom end. The turret diameter depends on system voltage and design of the EIS. For instance, determining of the turret diameter will certainly affects the quantity of steel, mineral oil, etc. and this is important for both material cost and the weight and dimensions of the transformers by making big oil gap into the smaller oil gap. Moreover, common positions of EIS are in a turret or in a tank of the transformer and/or connection to winding can be at the top or in the middle of winding for each position.

[0050] For instance, Fig. 2a shows a perspective view of a turret or turret assembly 400 of a high voltage transformer, wherein Fig. 2b shows the shielding system 80 mounted inside the turret assembly by means of a mounting device 7 which comprises a mounting device clamp 200 and a mounting device insulation 100 (see e.g. Fig. 6). According to the present invention it is preferred that the bushing bottom end is not connected to the equalizing ball 6. Instead, the present invention provides a design in which the equalizing ball 6 is fixed or integrally formed to/with the shielding tube 1. Thus, in order to fix the position of the shielding system 80 within the turret assembly 400, it is preferred that the shielding system 80 of the present invention itself is fixed by a slip-free mounting device 7 and not indirectly via a bushing connection. Slip-free in the sense of the present invention means that a vertical movement of the system 80 is extremely reduced or even avoided. This allow an exact positioning of the shielding system 80 with regard to the bushing 5 and avoids occurrence of critical misplacement.

[0051] Figs. 3a - 3c show the bushing connection shielding system 80 in further detail. In particular, Fig. 3b shows a side view of the system 80 with the lower shielding tube 1 covered concentrically by paper 2 and the upper part comprising the equalizing ball 6 with a conical or tapered section 61. Preferably, the equalizing ball 6 comprises a tapered/conical lower section 61, a substantially cylindrical mid section 62 and/or a substantially dome shaped upper section 63 (see e.g. Figs. 1 and 7). The dome shaped upper section 63 comprises a central upper hole 31 to receive and accommodate the busing bottom end 5. The barriers 3 comprise corresponding holes 31, the holes being substantially concentrically. The entire system 80 is substantially rotationally symmetrical around the central axis A of the shielding tube 1 as evident from the perspective view of Fig. 6 and Figs. 4a to 4c.

[0052] Fig. 3a shows a cross-sectional view of the system 80, wherein the hashed layer 2 around the shielding tube 1 is formed by a plurality of oil impregnated paper layers wound concentrically around the tube 1. Also the lower conical section 61 of the equalizing ball 6 is preferably only covered by paper layers 2. The middle section 62 is preferably covered by the seamless transition of paper 2 and barrier 3 and the upper part or top-section 63 is preferably only shielded by the barrier layers 3. The covering/ shielding with the respective layers 2 and 3 and the equalizing ball 6 is shown in further detail in Fig. 3c. [0053] Figs. 4a to 4c show the system 80 mounted to the mounting device 7 which comprises the mounting device clamp 200 and the mounting device insulation 100 in a side view (Fig. 4a), a cross- sectional view (Fig. 4b) and a top view (Fig. 4c). Preferably, the mounting device 7 comprises an upper clamp 200 and a lower clamp 200 which are preferably identical or similar. The details of the mounting device 7 is further discussed with regard to Fig. 6.

[0054] Fig. 6 shows a perspective schematic view of the bushing connection shielding system 80 mounted to the mounting device clamp 200 via mounting device insulation 100. The mounting device insulation 100 comprises a substantially cylindrical outer shape which is supported by the correspondingly (concave) formed (upper) clamp bracket 222 and the (lower) clamp bracket 220. Upper and lower fixation means 212, 210 are connected to the corresponding clamp brackets 222, 220, respectively. Preferably, the upper and lower fixation means 212 and 210 are formed as bands. [0055] As shown in Fig. 6, and also illustrated in Fig. 4a, the outer surface of the outermost mounting device insulation barrier 110 comprises barrier protrusions 112 and 114. Said barrier protrusion 112, 114 may be fixed to the outer surface of the mounting insulation, e.g., by gluing, etc. or may be integrally formed therewith. The barrier protrusions 112 and 114 may be (further) fixed to the outer mounting device insulation by bands 120. Such bands are preferably foreseen anyway to connect the mounting device insulation barrier 110c, which may be formed of two halves. An advantage of providing such protrusions is derivable from Fig. 6, which shows that this protrusion may form a shoulder which is supported by fixation means 212 and 214. In particular, the upper barrier protrusion 114 is supported by the upper clamp fixation means 212 below located said upper barrier protrusion 114 and the lower barrier protrusion 112 is supported by the lower clamp fixation means 210. In other words, the gravitational downwardly directed force results in a hanging or suspension mounting of the bushing connection shielding system. This suspension or hanging mounting type may assist in achieving in the slip-free mounting arrangement. [0056] The mounting device insulation 100 comprises a plurality of mounting device insulation barriers 110a,b,c,d, concentrically arranged around one another while the mounting device insulation barrier 110a constitutes the innermost barrier and the mounting device insulation barrier 110d constitutes the outermost barrier (see Fig. 1). Advantageously, three, four, or more or less barriers may be provided.

[0057] Between the different mounting device insulation barriers 110a,b,c,d, there is provided a plurality of spacers 130, 140, which will be discussed further below. The spacers 130, 140 are preferably elongate and are arranged, circumferentially spaced, extending in the axial direction of the system 80. [0058] In order to ease assembly, the mounting device insulation barriers 110a,b,c,d may be made of one piece or may be formed of two halves each’, which may be connected to one another and around the system 80 [0059] As discussed above, the outermost mounting device insulation barrier 110c/d comprises one or two barrier protrusions 112 and 114 which are supported by fixation means 212 and 214 of the clamp bracket 220, 222. Each radially inwardly provided mounting device insulation barrier 110b, a is supported by the respective next outer mounting device insulation barrier 110c, b.

[0060] In particular, as indicated above, spacers 130, 140 are arranged between neighboring mounting device insulation barriers 110d,c,b,a. One type of spacers 140 is of a substantially S-shape. In other words, such spacer 140 comprises a radially outwardly extending hook 142 at its upper end and a radially inwardly extending hook 144 at its lower end.

[0061 ] The radially outwardly protruding upper protruding hooks 142b of spacer 140b, which is arranged radially outside of mounting device insulation barrier 110b/c and radially inwards of outermost mounting device insulation barrier 110c/d, are adapted to engage with the outer mounting device insulation 110c/d, preferably with its upper end, further preferred in a hanging or suspension fashion. The corresponding inwardly protruding lower hook 144b supports the next radially inwardly mounting device insulation barrier, namely the middle mounting device insulation barrier 110b/c, preferably with its lower end, further preferred in a supporting fashion. The same functionality preferably applies to all hook spacers 140.

[0062] As shown in Figs. 1 , the mounting device insulation 100 further comprises a stop ring 126. The stop ring 126 may be of one piece or may be comprised of two halves. Preferable, one half of the stop ring extends about and angle b = 180° or less and preferably about 170°. . The stop ring 126 comprises an inner ring surface which is angled, preferably by an angle a of preferably between 10 and 30° and preferably of about 20°. Said surface preferably corresponds in orientation to the conical section 61 and serves as an abutment surface. Preferably, the outer ring surface is at least partially equally angled. On it outer and/or lower surface, the stop ring is provided with abutment surfaces for abutting against, e.g., an innermost barrier 110a and/or spacers 130, 140.

[0063] In its mounted position, stop ring 126 is circumferentially formed (at least partially) around the outer surface of the paper cover 2 at the transition region between the substantially cylindrical region of the tube 1 and the lower conical section 61 of the equalizing ball 6. [0064] The force, mainly gravitational force, of the system 80 can thereby be supported via the stop ring 126 on which part of the system’s conical section 61 rests. The stop ring 126, on the other hand, is supported by the mounting device insulation 100. Preferably, it is supported by the innermost mounting device insulation 110a and/or innermost hook spacers 140. In other words, the entire bushing connection shielding system 80 may hang on the suspension arrangement of the mounting device insulation 100 with its hook members, wherein said mounting insulation 100 is supported by the mounting device clamp 200. By this arrangement, a substantially slip- free mounting is achieved, allowing exact positioning of the bushing connection shielding system 80, particularly with regard to bushing 5.

[0065] This structure particularly allows the gravitationally downward directed force of the bushing connection shielding system 80 to be transferred via a stop ring band 124, via the mounting device insulation barriers 110 and the hook spacers 140 and finally via the barrier protrusions 112 and 114 to the suspension design.

[0066] The structure of the mounting device insulation 100 is shown in Fig. 1 , which show, for example, the different radial layers of the mounting device insulation 100 in line with the above discussion. Fig. 6 shows the entire mounting device insulation with all “layers”. The mounting device insulation barriers 100 are preferably formed from pressboard, preferably oil-impregnated pressboard.

[0067] In a three barrier design, the outer mounting device insulation barrier 100c is preferably similarly designed as the middle insulating barrier 100b. Preferably, the outer mounting device insulation barrier 100c and/or the middle insulating barrier 100b are formed from two half cylinders. Moreover, the outer mounting device insulation barrier 100c may comprise a barrier mounting protrusion which is preferably supported by the clamp bracket or the clamp fixation means. As shown for example in Fig. 6, the outer mounting device insulation barrier 100c comprises two axially spaced apart protrusions which circumferentially extend along the outer surface of the barrier 100c. In particular, a lower barrier mounting protrusion 112 and an upper barrier mounting protrusion 114.

[0068] In Figs. 1 and 6 (outer) hook spacers 140b are visible, as an example. These outer hook spacers 140b are elongated and vertically oriented (extend in axial direction) and spaced apart arranged circumferentially around the shielding tube 1. At least one, preferably more than one and further preferred each hook spacer 140b preferably comprises a radially outwardly protruding hook end 142b at the upper end and a radially inwardly protruding hook end 144b. The upper hook end(s) 142b preferably engage with the (radially) outer barrier 110c. The lower hook ends 144b preferably engage with the middle barrier 110b. Additional (outer) spacers 130b may be formed substantially parallel to the (outer) hook spacers 140b. The illustrated embodiment shows spacers 130b between two (outer) hook spacers 140b along the circumference. These spacers 130 may be also formed from pressboard, particularly oil impregnated pressboard. For the (more inwardly) arranged spacers 140a, 130a, the same applies as for the (outer) spacers 140b, 130c.

[0069] The inner hook spacers 140a comprise, similar like the outer hook spacers 140b a radially outwardly protruding hook end 142a at the upper end and preferably also a radially inwardly protruding hook end 144a at the lower end.

[0070] In Fig. 1 the stop ring 126 is visible at the transition between the cylindrical part of the tube and the lower conical/tapered part 61 of the equalizing ball 6. It should be noted that the stop ring 126 is mounted to the outer most layer of the paper cover 2. Said stop ring 126 is preferably formed from pressboard, preferably oil impregnated pressboard.

[0071] The bushing connection shielding system of the present invention is not restricted to end connections between bushings and power transformers but can also be used for reactors.

[0072]

[0073] While the foregoing is directed to embodiments, other and further embodiments may be devised without departing from the basic scope, and the scope is determined by the claims that follow. REFERENCE NUMBERS

1 shielding tube

2 paper / paper cover

3 dielectric barrier 31 hole

32 extensions

4 spacer

5 end of high voltage bushing

6 equalizing ball 61 conical lower section

62 cylindrical mid section

63 dome shaped upper section

64 central hole 7 mounting device 71 supporting ring

80 bushing connection shielding system 100 mounting device insulation 200 mounting device clamp

110a, b, c (mounting device insulation) barrier (a=inner, b=middle, c=outer)

[pressboard, oil-impregnated]

112 lower barrier mounting protrusion

[supported by lower clamp bracket / lower clamp fixation means] 114 upper barrier mounting protrusion

[supported by upper clamp bracket / upper clamp fixation means]

130a,b spacer 140a, b hook spacer 142a, b [outwardly protruding hook end at upper end] [engaging with (radially) outwardly arranged barrier] 144a,b [inwardly protruding hook end at lower end]

[engaging with/supporting (radially) inwardly arranged barrier]

210 (lower) clamp fixation means (band) 212 (upper) clamp fixation means (band)

220 (lower) clamp bracket 222 (upper) clamp bracket 400 turret assembly