Patent Publication Number: US-11043758-B2

Title: Bushing adapter and bushing with superior mechanical characteristics

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of PCT International Application No. PCT/EP2018/052398, filed on Jan. 31, 2018, which claims priority under 35 U.S.C. § 119 to European Patent Application No. 17305104.6, filed on Jan. 31, 2017. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a bushing and, more particularly, to a bushing for connecting an external cable and an internal conductor of a housing. 
     BACKGROUND 
     In many technical fields electrical power has to be supplied by or to certain components, such as sophisticated switches, transformers, motors, and the like, which may frequently be positioned, at least partially, in an appropriate housing. On the other hand, outside the housing the required electrical power may be supplied by or to one or more appropriately dimensioned cables connected to a respective power supply or electric component. The electrical power may be provided as AC or DC or both. Depending on the application, the respective electrical power may range from several tens of kilowatts to several hundred of kilowatts and even higher, thereby requiring respective cable configurations in terms of cross-section and insulation characteristics. For example, high electrical power may frequently be provided in the context of medium voltages to high voltages, ranging from several hundred volts to several thousand volts, thereby resulting in relatively low currents to be conveyed in the external cables. In other applications, relatively low voltages may be used, for instance in mobile DC applications, such as electric vehicles, thereby imposing superior requirements with respect on the drive current capability of the respective cables. 
     The corresponding external cables may require an appropriate configuration with respect to conductor material, conductor cross-section, insulating sheath, and the like, thereby typically resulting in a cable configuration including one or more copper-based or aluminum-based core wires with a cross-section of several centimeters surrounded by an appropriate sheath or cover material that provides for the required insulating behavior and integrity of the entire cable. These cables may frequently be exposed to relatively harsh environments, for instance such cables may be exposed to outside conditions including exposure to direct sunlight, extreme temperatures ranging from −50° C. to 70° C., and the like, thereby necessitating the usage of appropriate sheath materials, which may therefore also contribute, in addition to the core material, to additional weight of the respective cables. 
     Power receiving components or power supplying components, such as switches, transformers, motors, and the like are often encapsulated in an appropriate housing so as to provide for superior integrity of such components or at least of any contact structures thereof. Due to the protected interior of the housing, any requirements for housing-internal conductors may be significantly less stringent, thereby even allowing the usage of such housing-internal conductors without external insulating material, and the like. One critical interface of a housing-internal conductor and an external cable is a respective bushing, which is to be understood as a component that is appropriately mounted to the housing and provides a passage for the exchange of electrical power between the external cable and the housing. 
     A corresponding bushing typically comprises a highly conductive metal conductor, typically in the form of a copper bolt, which is surrounded by an insulating material that is formed from an appropriate material, such as epoxy resin. Epoxy resin is known to exhibit high mechanical strength and stiffness and superior insulating characteristics. In order to provide a mechanically and electrically stable bushing, the metal core and the epoxy resin are typically formed into an integral component by, for instance, injection molding, thereby obtaining a robust and stiff product. Consequently, by providing an appropriate mounting flange at any appropriate position the bushing may be inserted into a corresponding bore provided in the housing and may be fixed thereto by the mounting flange, providing for high mechanical and electrical integrity of the resulting connection between an external cable attached to the bushing at one end thereof and a housing-internal conductor connected to the bushing at the other end thereof. 
     These well-established high-power bushings, however, may suffer from increased failure events when used in applications associated with harsh external conditions. For example, the robust and stiff configuration of the conventional high-power bushing may exhibit an increasing number of device failures upon being exposed to relatively extreme temperatures, for instance ranging from approximately −50° C. to approximately 70° C., as are typically encountered under various environmental conditions in various geographic locations. For instance, power supply in many types of vehicles, such as trains, may result in exposure to harsh conditions, such as the above-referenced temperatures, for instance upon direct exposure to sunlight, while in cold winter days extremely low temperatures may occur. Such extreme temperatures may by itself represent a significant stress for the bushing, as typically epoxy resin and the usually highly conductive copper material may have very different coefficients of thermal expansion, which may result in cracks or any other damage in the insulating epoxy resin, in particular, when certain mechanical forces may additionally act on certain bushing components. 
     As an example, the external cable, which may have a relatively high weight, is typically connected to the bushing so that an end face of the copper bolt of the bushing is in firm contact with a respective end face of the external cable or in most cases with a contact assembly connected thereto, which may result in a more or less pronounced bending force exerted on the copper bolt of the bushing. Under extreme temperature conditions, as discussed above, however, these relatively high bending forces may promote the creation of damage in the insulating material, since the difference in the thermal expansion in combination with the additional mechanical forces acting the copper bolt and hence on the epoxy resin may finally result in a breakage of the external sheath, thereby also typically resulting in a failure of the entire high-power connection. Similarly, at moderately high temperatures the mechanical properties of the epoxy resin may also be subjected to degradation, thereby also increasing the probability of resulting in a severe device failure. 
     The situation described above may even become worse in circumstances, in which the respective forces acting on certain components of the bushing may vary timely and spatially, for instance, when externally or internally induced vibrations are present. The source of such vibrations may be, for instance, in mobile applications the movement along respective railroad rails, wherein the joints between adjacent rails may cause significant vibrations in a more or less regular manner, depending on the overall speed of the respective electric vehicle and the distance of the joints. Similar vibrations, however, with reduced regularity, may be encountered in street-bound vehicles, wherein speed and surface conditions of a respective road may significantly determine the resulting “spectrum” of vibrations acting on the corresponding bushing components. 
     Moreover, in train applications or similar use cases, sophisticated contactors or switching devices may have to be used, in which moderately high masses are accelerated and moved during a corresponding switching process, thereby typically involving a direct impact of the corresponding contact components and introducing respective mechanical vibrations into the bushing components. Although rare events of such induced vibrations may not necessarily significantly affect the bushing and the electrical and insulating state of the various components, over an extended lifetime, which is typically required in many applications, such as 10 to 15 years, the conventional robust and stiff configuration, for instance obtained on the basis of an integrally molded epoxy resin and copper bolt component may result in a significant reliability issue, thereby rendering the conventional configuration less than desirable for a high-power bushing to be used in harsh environmental conditions. 
     In view of the above described situation, a reliable mechanical connection between the housing-internal cable and the bushing is required. Furthermore, in addition to superior mechanical reliability, a corresponding connection may also have to provide for superior installation and maintenance performance, since typically the installation and regular and non-scheduled maintenance activities may significantly contribute to overall cost of ownership of such sophisticated electric installations. For example, in conventional bushings the connecting portion to be connected to the housing-internal conductor is typically obtained by providing a threaded recess in the conductor, which may be screwed onto the housing-internal conductor or any contact member connected thereto. 
     Consequently, upon installing or dissembling the connection between the housing-internal conductor and the bushing, a respective relative rotation between the conductor and the bushing has to be carried out, wherein typically the bushing is usually the component to be rotated. Therefore, a respective mechanical connection between the housing and the bushing has to be detached prior to actually dissembling the mechanical connection between the housing-internal conductor and the bushing. Similarly, after reinstalling the mechanical connection between the housing-internal conductor and the bushing, the bushing has to be fixed to the housing, which may typically require a new alignment procedure for appropriately connecting the housing and the bushing. Similarly, upon an initial installation of the bushing, a precise and permanent alignment and fixation of the bushing with respect to the housing may not be feasible as long as the mechanical connection between the housing-internal conductor and the bushing is not completed. 
     SUMMARY 
     A bushing adapter comprises an insert having a bore extending through the insert along a length direction of the insert and a fastening member extending through the bore. The insert is configured to be attached to a bushing conductor of a bushing. The fastening member has an operating portion positioned outside of the bore at a bushing internal end of the fastening member and a fastening portion positioned outside of the bore at a bushing external end of the fastening member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described by way of example with reference to the accompanying Figures, of which: 
         FIG. 1  is a sectional view of a bushing according to an embodiment connected to an external conductor; 
         FIG. 2A  is a sectional view of a bushing according to another embodiment; 
         FIG. 2B  is a sectional view of the bushing of  FIG. 2A  with a housing and an external cable; and 
         FIG. 2C  is a sectional view of an end portion of the bushing of  FIG. 2A . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT(S) 
     Exemplary embodiments of the present invention will be described hereinafter in detail with reference to the attached drawings, wherein like reference numerals refer to like elements. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure will convey the concept of the disclosure to those skilled in the art. 
     A bushing  100  according to an embodiment, as shown in  FIG. 1 , comprises a bushing conductor  120 , a bushing adapter  170  that is attached to the bushing conductor  120 , and an insulating body  110 . In various embodiment, the insulating body  110  may be formed of any appropriate material, such as epoxy resin, possibly in combination with other materials, as will also be discussed later on. The insulating body  110  encloses the bushing conductor  120  and is in mechanical contact therewith so as to form a mechanically robust component of the bushing  100 . 
     The bushing  100  and thus the bushing adapter  170  may be appropriately dimensioned and configured so as to be used for high power applications requiring the transfer of electrical power in the range of several tens of kilowatts to several hundred kilowatts and higher. For example, transferring such amounts of power may be required in mobile applications, such as electrically driven vehicles, such as trains, cars, vans, and the like, or in other stationary applications, such as transformers, electric motors or generally electric machines in the form of motors and/or generators, as for instance used in wind power stations, and the like. It should be appreciated that in other embodiments the respective dimensions of the bushing  100  may be reduced so as to comply with low-power applications requiring the transfer of electrical power in the range of few watts to several hundred watts. 
     The bushing  100  may be configured so as to connect to an external cable, such as via a contact or plug assembly, by connecting a corresponding end face  121 F at a first end of the bushing  100  to a corresponding contact face of the external cable or the corresponding contact assembly connected therewith. A second end of the bushing  100  may be configured to be connected, electrically and mechanically, to an external conductor  152  or a corresponding contact assembly associated therewith, wherein the external conductor  152  may typically be provided within a specific housing, as will be explained later on in more detail. The mechanical connection to the external conductor  152  and the electrical connection may be established on the basis of the bushing adapter  170 , as in the embodiment shown in  FIG. 1 , while in other embodiments, such as will be described below with reference to  FIG. 2 , the electrical connection may be established on the basis of the bushing conductor. 
     The bushing conductor  120 , as shown in  FIG. 1 , includes a recess  126 , which accommodates a part of the bushing adapter  170 . The bushing adapter  170  comprises an insert  171 , which is appropriately adapted in size and shape to the recess  126 . In the embodiment shown, the insert  171  is formed so as to enclose the recessed portion of the bushing conductor  120 , thereby completing the conductor  120  and providing one or more end faces  171 F for electrically contacting the external conductor  152 . The insert  171  may be attached to the conductor  120  in the recess  126  by any appropriate connecting technology, such as providing a threaded surface portion on the insert  171  and a complementary threaded surface portion on the recessed part of the conductor  120 , which defines the recess  126 . In other cases, the insert  171  may be attached to the conductor  120  by press fitting, pinning, gluing, soldering, welding, and the like. It should be appreciated, however, that the bushing adapter  170  is typically provided as a separate component and is attached to the remaining part of the bushing  100  on the basis of one or more of the above-specified connection techniques. 
     The bushing adapter  170 , as shown in  FIG. 1 , comprises an operable fastening member  173  that, in illustrative embodiments, is rotatable with respect to the insert  171 , for instance by being provided as a separate member that is partially inserted into a bore  172  formed in the insert  171 . In other embodiments, the fastening member  173  may be operated on by shifting or moving the fastening member  173  in any other way so as to establish and hold mechanical contact to a counterpart component, such as an external conductor, a housing, and the like. 
     The fastening member  173  has an operating portion  173 A, which may be accessed by any appropriate tool so as to be rotated relatively to the insert  171 . 
     That is, the fastening member  173  comprises the operating portion  173 A at a bushing internal end thereof so as to be positioned within the bushing  100  in the attached state. Moreover, the fastening member  173  comprises a fastening portion  173 B positioned outside the bore  172  at a bushing external end of the bushing adapter  170 , thereby enabling engagement with a corresponding counterpart opening of the external conductor  152 . For example, the fastening member  173  may be provided in the form of a screw or bolt having a threaded portion so as to engage with the counterpart opening of the conductor  152  and provide for a reliable mechanical connection therewith. In other embodiments, the fastening portion  173 B may comprise in addition or alternatively to a threaded area any appropriate locking member so as to be guided by the counterpart opening of the conductor  152  into a counterpart locking member for entering a locked state upon rotating the operating portion  173 A relatively to the insert  171  and the external conductor  152 . It should be appreciated that the corresponding locking member may be represented by the fastening portion  173 B having an appropriate configuration, for instance a key-type configuration, which cooperates with a respective lock-type opening as a counterpart locking member of the conductor  152 . 
     In an embodiment, the fastening member  173  may “snap” into a locked position upon rotating the fastening member  173  by a certain angle of rotation, for instance by 90° or greater, thereby reducing the time required for actually securing the fastening member  173  to the respective housing internal conductor or any associated contact assembly. To this end, the fastening member  173  and the counterpart member have respective complementary shapes and dimensions so as to enable mechanical contact and a guiding function, thereby finally providing for a locked state upon completing a specific rotation, which may substantially not unintentionally be released. 
     In an embodiment, the fastening member  173  may be provided in the form of a screw or bolt having a standard size, for instance M8-M16 in applications, in which the transfer of relatively high electrical power is required. In other embodiments, the fastening member  173  may be attached and locked to the counterpart locking member by any other mechanism, which may not require a relative rotation between the fastening member  173  and the counterpart member. To this end, the fastening member  173  may be operated on by a tool in a substantially linear manner, thereby, for instance, press-fitting the fastening portion to the counterpart locking member. 
     In the embodiment shown in  FIG. 1 , the electrical connection between the conductor  152  and the bushing  100  is established on the basis of the insert  171 , for instance by using the end faces  171 F as contact surfaces. In the shown embodiment, the insert  171  is formed of a highly conductive material, such as copper, aluminum, and the like. In an embodiment, the fastening member  173  may be formed of any appropriate material, such as a non-conductive material, steel, such as stainless steel, and the like in order to provide for superior mechanical robustness, wherein, for instance, the operating portion  173 A, for example provided in the form of a screw head, may have a significantly increased mechanical strength compared to, for instance, a copper bolt. Furthermore, the fastening portion  173 B may thus provide a highly durable and robust mechanical connection with the corresponding counterpart opening in the conductor  152 , irrespective of whether a threaded connection or a connection on the basis of one or more locking members is established. 
     A washer  175 , as shown in the embodiment of  FIG. 1 , may be positioned between the insert  171  and the operating portion  173 A, enabling the adjustment of any appropriate distance of these components and/or providing for superior force distribution from the operating portion  173 A into the insert  171 . To this end, the washer  175  may be provided in the form of any appropriate material, which may or may not have electric conductivity, since basically the fastening member  173  may not take part in the overall conduction of electricity in the bushing  100 . In other embodiments, in addition to or instead of these functions, the washer  175  may provide for a locking function in order to substantially eliminate unintended rotation of the fastening member  173  with respect to the insert  171  after having established the mechanical connection with the external conductor  152 . 
     After providing the individual components of the bushing adapter  170  and after the assembling these components, i.e. after the insertion of the optional washer  175  and the fastening member  173  into the bore  172 , the bushing adapter  170  may be attached to the remaining components of the bushing  100  on the basis of any appropriate connection techniques, as described above. Thereafter, an appropriate tool, for example an Allen Key, may be inserted into the inner bore  125  of the conductor  120  so as to finally reach the operating portion  173 A. After engagement of the respective tool with the operating portion  173 A and after positioning the conductor  152  relatively to the bushing  100 , the mechanical connection may be established by rotating the operating portion  173 A and thus the fastening member  173 , thereby finally obtaining a locked state, however, without requiring a rotation of the bushing  100  as a whole. 
     Consequently, the bushing  100  and in particular its insulating body  110  may be configured so as to allow the mounting of the bushing  100  to any appropriate component, such as a housing, without having to take into consideration a relative rotation of the bushing  100  with respect to the housing or component. In particular, the modular design of the bushing  100  in the form of the bushing adapter  170  including the rotatable fastening member  173  allows permanent installation of the bushing  100  while still providing for the possibility of installing and dissembling the mechanical connection between the conductor  152  and the bushing  100 . When dissembling the mechanical connection between the bushing conductor  120  and the external conductor is required, there is no need to dissemble the entire bushing  100  from a corresponding housing or other component and therefore the mounted and aligned state of the bushing  100  with respect to the housing or other component may be maintained throughout the entire process. Additionally, at the side of the external conductor  152 , a minimum of installation space is required. 
     In another embodiment of a bushing  200  shown in  FIGS. 2A-2C  described in greater detail below, the insert of the corresponding bushing may not represent an electrically active part of the bushing conductor. 
     The bushing  200  according to another embodiment, as shown in  FIG. 2A , comprises a bushing adapter  270 , a bushing conductor  220 , and an insulating body  210 . The bushing conductor  220  has a connecting portion  221  including an end face  221 F, which represents a contact surface for connecting to an external cable or a contact assembly associated therewith. Moreover, contrary to the embodiment shown in  FIG. 1 , the conductor  220  has at its opposite end an end surface  222 F for connecting to an external conductor, such as the conductor  152  as shown in  FIG. 1 . It should be appreciated that the cross sectional area of the end face  222 F is appropriately dimensioned so as to provide for the required current drive capability, thereby avoiding the necessity of using one or more components of the bushing adapter  270  as a conducting element. 
     In the embodiment shown in  FIG. 2A , the insulating body  210  may have a specific design, in which a highly insulating material, such as an epoxy resin  215  may provide for the insulating characteristics in a radial direction, while a shielding sheath  214  may additionally be provided as an inner surface of the insulating body  210 , thereby imparting superior electrical and interface characteristics to the insulating body  210 . For example, the shielding sheath  214  may be formed of a metal, such as aluminum, which may have a similar coefficient of thermal expansion compared to an epoxy resin, while on the other hand, a superior mechanical contact may be established to the bushing conductor  220 , which is typically formed of copper, copper alloys, and the like. In other embodiments, the shielding sheath  214  may be provided as a coating having a thickness of less than 0.1 mm and made of any conductive material. Furthermore, a mounting structure  230  as shown in  FIG. 2A  may be provided at any appropriate position along the insulating body  210 , wherein, as previously discussed, the mounting structure  230  may have any appropriate configuration for connecting to a further component or housing without having to take into consideration a rotation of the bushing  200  as a whole when mechanically connecting the external conductor to the bushing adapter  270 . Similarly, internal reinforcement components of the insulating body  210 , such as a ridge, and the like, may be provided without restriction that is conventionally caused by the requirement of a rotation of the entire bushing  200  upon installing the mechanical connections. 
     The bushing adapter  270 , as shown in  FIG. 2A , comprises an insert  271 , which may have a reduced size so as to fit into a corresponding recess  226  formed in the conductor  220 . It should be appreciated that generally the insert  271  may have reduced dimensions with respect to the insert  171  of the bushing  100  of  FIG. 1 . The insert  271  may be made of any appropriate material, such as stainless steel, a non-conductive material, or any combination thereof in order to obtain the desired mechanical characteristics. The insert  271  may be attached to the conductor  220  within the recess  226  by any appropriate connection technique, such as by a threaded connection, press fitting, pinning, gluing, welding, soldering, and the like. Non-conductive materials may be used for the insert  271  in terms of superior mechanical robustness and/or temperature behavior, for instance in view of coefficient of thermal expansion, and the like, in order to meet the specific requirements for the use case of interest. Since the overall conductivity of the bushing conductor  220  may suffice for transferring the required electrical power, a corresponding conductivity of the insert  271  may be significantly lower compared to the bushing conductor  220  or the material thereof may be basically non-conductive. Due to the possibility of specifically selecting the material characteristics of the insert  271  it may be formed with reduced size, thereby leaving sufficient highly conductive material of the bushing conductor  220  that is available for electrical connection to the external conductor. 
     The bushing adapter  270 , as shown in  FIG. 2A , further comprises a rotatable fastening member  273  that extends through a bore  272  and comprises an operating portion  273 A and a fastening portion  273 B. Similarly, as is also described above with reference to the bushing adapter  170 , the fastening member  273  may thus be movable and in particular rotatable with respect to the insert  271  and may be formed of any appropriate material, such as stainless steel, any non-conductive material, or any combination thereof. Furthermore, an optional washer  275  may be provided so as to adjust the distance and/or force distribution from the member  273  into the insert  271  and/or providing a locking function so as to hinder unintended rotation of the member  273  after having been connected to the external conductor. 
     In the embodiment shown in  FIG. 2A , the bushing adapter  270  may be formed as a separate component including the rotatable member  273  and may be attached to the remaining part of the bushing  200  at the installation location or may be provided as a pre-assembled component by appropriately attaching the adapter  272  to the remaining components of the bushing  200  at any appropriate time prior to actually installing the bushing  200 . The bushing  200  may then be aligned with respect to an external conductor, possibly after having been mounted to a respective component, such as a housing, and thereafter an appropriate tool may be inserted into the inner bore  225  so as to finally engage with the operating portion  273 A. Upon rotating the member  273  it may engage with a corresponding counterpart opening so as to establish a robust mechanical connection. It should be appreciated that with respect to the type of mechanical connection, for instance based on a threaded portion, one or more locking members, and the like, in cooperation with a corresponding counterpart configuration at the side of the external conductor, it is also be referred to the embodiments described with reference to  FIG. 1 . 
     As shown in  FIG. 2B , the bushing  200  may be mounted to a housing  250 , which may have any appropriate size and shape as determined by the specific application under consideration. For example, the housing  250  may typically represent a metal housing that accommodates specific electrical components, for instance a switch assembly, such as a magnetic contactor, a transformer or at least a portion thereof, an electric machine or a contact portion thereof, and the like. The bushing  200  protrudes into the interior of the housing  250  and may connect to any appropriate housing internal conductor  252 , which may also be referred to as an external conductor, and which may represent any appropriately dimensioned and shaped conductor for connecting to a further component within or outside the housing  250 . Similarly, the bushing  200  may connect to a respective terminal portion or any other contact assembly provided in combination with an external cable  240 . To this end, the bushing conductor  220  may be connected with its connecting portion  221  to the terminal portion or contact assembly of the cable  240  so as to be in mechanical and thus electrical contact therewith. In particular, the end face  221 F of the connecting portion  221  is in contact with a respective part of the cable  240  and may be mechanically fixed thereto by any appropriate fastening device, such as a screw or bolt  241 , which may be threaded into a corresponding bore  224  that is formed in the bushing conductor  220 . As previously discussed, the fastening device  241  and the threaded bore  224  may be configured so as to comply with specific standards in order to allow the connection of any terminal portion or contact assembly complying with the corresponding standards. Consequently, when the external cable  240  or a corresponding terminal portion or contact assembly thereof is mechanically connected to the connecting portion  221 , the electrical connection is basically established by the end face  221 F and a corresponding surface portion of the cable  240 , possibly in combination with the fastening device  241 , while any outer surface areas of the connection portion  221  may substantially not contribute to the electrical and mechanical connection with the cable  240 . 
     As shown in  FIG. 2B , the bushing conductor  220  may electrically connect with its end face  222 F to the housing internal conductor  252 , whereas a respective mechanical connection is established by the bushing adapter  270 . That is, the rotatable fastening member  273  may engage with a corresponding counterpart opening  252 A formed in the conductor  252 , wherein, as previously discussed, the mechanical connection may be established on the basis of a threaded connection, a key-lock-type connection, and the like. Furthermore, in some embodiments, a locking element  276  may be provided in combination with the insert  271  so as to engage with a counterpart locking element  252 B of the conductor  252 , thereby substantially eliminating the possibility of unintended rotation of the insert  271  with respect to the conductor  252 . In an embodiment, the locking element  276  is a lock pin and the counterpart locking element  252 B is an opening or cavity. 
     Upon installing the bushing  200  on the housing  250 , the mounting structure  230  may be used for mechanically connecting the bushing  200  to the housing  250 , thereby positioning the bushing  200  in an appropriate position for establishing the mechanical connection between the bushing adapter  270  and the housing internal conductor  252 . It should be appreciated that mounting the bushing  200  to the housing  250  may be established so as to obtain a desired relative orientation of these two components without requiring any readjustment after having connected the conductor  252  to the bushing adapter  270 . Thereafter, the conductor  252  may be positioned in an appropriate manner with respect to the bushing  200  and an appropriate tool, such as an Allen Key, and the like, may be inserted into the inner bore  225  so as to finally engage with the member  273 , as is already discussed above. Consequently, by operating the member  273 , the desired mechanical connection between the conductor  252  and the bushing  200  may be established. It should be appreciated that due to the presence of the locking element  276  and its counterpart locking element  252 B, unintended relative rotation of the insert  271  with respect to the conductor  252  may reliably be avoided. Next, the external cable  240  may be connected to the conductor  220  after removal of the corresponding tool. To this end, well-established standardized connection means, such as the screw or bolt  241  in combination with a threading formed within the recess  224  may be employed. As a consequence, a mechanically robust connection along a length direction L of the bushing  200  may be established with the conductor  252  on the basis of the rotatable fastening member  273 . 
     In other embodiments, in addition or alternatively to the central fastening member  273 , the insert  271  may comprise two or more respective bores, through which corresponding fastening members may extend into the housing  250 . Similarly, a respective plurality of bores  225  may be provided in the conductor  220  so as to allow accessing the respective fastening members by a corresponding tool, as also discussed above. In this case, the conductor  252  or its contact assembly may have to be appropriately designed so as to correspond to at least one of the plurality of fastening members  273 , thereby establishing a highly robust mechanical connection with one or more of the plural fastening members. 
     At an end portion of the bushing  200 , shown in  FIG. 2C , superior mechanical contact is not only obtained at the side of the external conductor on the basis of the bushing adapter  270  but also at the side of the contact assembly connected to the external cable  240 . To this end, the connecting portion  221  of the bushing conductor  220  may be configured so as to be elastically displaceable or deformable with respect to a respective body end portion  211  of the insulating body  210 , shown in  FIG. 2C . 
     As explained above, in many sophisticated applications, significant mechanical stress may not only be introduced into the bushing  200  at the side of the conductor  252  but also at the opposite side, wherein in addition to the overall mechanical stress in particular significant radial forces may be introduced, for instance induced by oscillations and vibrations in combination with the moderately heavy weight of the corresponding external cable connected to the connecting portion  221 . In the embodiment shown in  FIG. 2C , a significant mechanical decoupling between the connecting portion  221  of the conductor  220  and the corresponding body end portion  211  of the insulating body  210  may be achieved by the elastic displacement ability of the connecting portion  221 . 
     In the embodiment shown in  FIG. 2C , a clearance  260  is provided between the connecting portion  221  and the body end portion  211 . For example, a maximum width W, for instance taken at or in the vicinity of the end face  221 F may range from 0.1-1.0 mm, which may suffice for accommodating a corresponding vibration amplitude or radial force acting on the connecting portion  221 . On the other hand, the remaining insulating body  210  may be in tight mechanical contact, for instance based on the superior interface characteristics provided by the shielding sheath  214 , with the conductor  220 , thereby providing an overall mechanically stiff and robust configuration except for the clearance  260 , which may have a length of 15-30 mm. 
     In an embodiment, the clearance  260  between these two components is selected such that a maximum displacement of the connecting portion  221  that is expected to occur in the specific application may be accommodated by the clearance  260 . For example, in specific applications requiring the transfer of high power of several tens of kilowatts and higher the weight of the external cable  240  and/or the corresponding contact assembly thereof may result in the introduction of radial forces that cause a displacement of the connecting portion  221  of up to 0.3 to 0.4 mm. By providing the clearance  260  with a width in accordance with the above-identified range, a significant mechanical contact between the displaced connecting portion  221  and the moderately stiff insulating body  210  may be avoided. 
     In other embodiments, the elastic deformation capability of a connecting portion of the bushing conductor  220  may also be implemented at the opposite side of the bushing  200 . For instance, a respective clearance, as schematically shown in  FIG. 2A , may be provided, thereby obtaining a similar configuration as described above in the context of the clearance  260  and the connecting portion  221 . 
     The embodiments discussed above in the context of  FIGS. 1-2C  refer to a modular system of the bushing  100 ,  200  including the bushing adapter  170 ,  270 . In other embodiments, the operable fastening member  173 ,  273  may be provided as a permanent component within the bushing  100 ,  200 , as long as the fastening member  173 ,  273  is accessible through the bushing conductor, as is similarly described above for the modular versions of the bushing  100 ,  200 . For instance, the fastening member  173 ,  273  may be inserted into the bushing upon forming the bushing conductor and assembling these components.