Patent Publication Number: US-7901234-B2

Title: Connecting plug for a high-voltage cable

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119(a)-(d) to prior-filed, co-pending French patent application serial number 0759067, filed on Nov. 15, 2007, which is hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The field of the invention concerns a connecting plug for a high-voltage cable. 
     2. Description of Related Art 
     In the field of medical diagnostic X-ray equipments, special connecting devices are provided for electrically connecting an appliance, such as an X-ray source for example, to a generator of high-voltage power. 
     Standards exist to specify the electrical and structural constraints that must be fulfilled by these connecting devices. 
     In particular, the XR-7 standard, established by the NEMA (National Electrical Manufacturers Association) for power-supply voltages of between 10 kV (kilovolts) and 200 kV, specifies constraints of shape and geometrical dimensions that must be fulfilled by the different components of connecting devices. 
     Compliance with these standards allows interoperability to be provided between the generators of high-voltage power and the different medical appliances requiring a high-voltage power supply. 
     A connecting device typically has two separable parts, namely a male part (known also as a plug), which constitutes one end of the high-voltage cable, and a female part (also called a receptacle or a socket), which is fixed in a permanent manner to the casing of the generator or of the equipment to be supplied, and designed to receive the male part. In order to withstand high voltages, the receptacle and the plug are made from rigid and electrically insulating materials. The receptacle and the plug have shapes and dimensions that are imposed by the standards. 
     The plug and the receptacle must be insulated from each other in order to avoid the formation of electrical arcs between the receptacle, the plug and the metallic envelopes of the cable forming an earth. 
     At the present time, the electrical insulation between the plug and the receptacle is generally achieved by means of an insulating liquid. The space that exists between the plug and the receptacle is filled with a liquid insulator, such as oil or grease for example. 
     In practice, the use of an insulating liquid raises certain problems. 
     In particular, the introduction of oil or of grease is a difficult operation since it requires a total absence of air bubbles or of polluting conducting particles between the plug and the receptacle. 
     In addition, there is always a risk that the operator who makes the connection will forget to inject the liquid insulator or will do so imperfectly. 
     Moreover, the presence of an insulating liquid imposes a substantially vertical orientation of the connecting device during fitting and removal. 
     In operation, the connecting device can be at a relatively high temperature. The differences in thermal expansion between the different components of the device, including the liquid insulator, give rise to a potential risk of breaking the seal of the device, which can lead to leakage of the liquid insulator and, as a consequence, deterioration of the electrical insulation. 
     Finally, the sealing problems arise even more in the case of radiological appliances whose X-ray source, powered at high voltage, is in motion. This is the case, for example, of computed tomography (CAT scan) appliances in which the X-ray source is rotated around the patient. The movement of the source favours the leakage of liquid insulator, in the event of a poorly sealed connection. 
     Document FR 2 879 031 A1 proposes replacement of the liquid insulator by an insulating interface in the form of a sleeve made of a flexible insulating material, such as a silicone elastomer for example. The interface includes segments that have elongated rings separated by air chambers. 
     This type of interface is particularly suitable for connecting devices of small size, but is not suitable for connecting devices of large dimension, of the type that are specified by the XR-7 standard. 
     In fact, with connecting devices that have a large longitudinal dimension, the sleeve of flexible material has a tendency to slide along the plug and to deform during insertion of the plug into the receptacle. The consequence is to render difficult the insertion of the plug into the receptacle and to result in incorrect positioning of the sleeve in the connecting device. 
     BRIEF DESCRIPTION OF THE INVENTION 
     One aim of the invention is to propose a means of electrical insulation that is more suitable for connecting devices of large dimension. 
     This problem is solved in the context of the present invention by virtue of a connecting plug for high-voltage cable, which includes:
         a jacket that is intended to be inserted into a connection receptacle of a high-voltage electrical appliance to connect the cable to the appliance, the jacket including a recess created in the jacket, and   a sleeve positioned around the jacket to form an insulating interface between the jacket and the receptacle, the sleeve being located in the recess of the jacket in order to maintain the sleeve on the jacket.       

     The recess provided in the jacket holds the sleeve in place on the jacket, and ensures correct initial positioning of the sleeve on the jacket. 
     In addition, the recess serves to limit the sliding of the sleeve in relation to the jacket during insertion of the plug into the receptacle. 
     Preferably, the plug includes a multiplicity of sleeves, and the jacket includes a multiplicity of recesses, with each recess accommodating a sleeve. 
     Because the plug is fitted with a multiplicity of separate sleeves, held individually in recesses, each sleeve can be of a length that is less than the total length of the plug. This limits the risk of deformation of the sleeves during insertion of the plug into the receptacle. 
     Depending on the embodiment, the plug can also have any one of the following characteristics:
         the sleeves are placed one after the other along a longitudinal direction of the jacket,   each sleeve includes a multiplicity of beadings that are intended to make contact with the connection receptacle,   the beadings are of a generally annular shape,   the beadings are of a generally helical shape,   at least one of the beadings include slots allowing passage of air through the beadings,   the beadings are positioned to form spaces between them that are filled with air, each space being located between two successive portions of beading,   each sleeve is made in one piece from a silicone-based elastic material,   the plug includes two sleeves, with each sleeve extending over approximately a third of a longitudinal dimension of the jacket,   the plug has three sleeves, with each sleeve extending over approximately a quarter of a longitudinal dimension of the jacket,   the jacket includes a multiplicity of recesses, shaped by smaller-diameter portions of the jacket, with these portions having diameters that decrease along a longitudinal direction of the plug.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages of the invention will emerge from the description that follows, the latter being purely illustrative and non-limiting, and should be read with reference to the attached figures, in which: 
         FIG. 1  represents, schematically and in longitudinal section, a receptacle of a high-voltage connecting device according to a first embodiment of the invention; 
         FIG. 2  represents, schematically and in longitudinal section, a plug of the connecting device according to the first embodiment of the invention; 
         FIG. 3  represents, schematically and in longitudinal section, a plug of a connecting device according to a second embodiment of the invention; 
         FIG. 4  represents, schematically and in perspective, an insulating sleeve of a first type; and 
         FIGS. 5A and 5B  represent, schematically and respectively in side and perspective views, an insulating sleeve of a second type. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 and 2  depict an embodiment of a high-voltage connecting device that is configured in accordance with the XR-7 standard. This device is typically intended to be subjected to high voltages, of the order of 100 to 150 kilovolts, and generally of the order of 120 kilovolts. 
     The connecting device includes two separable parts, namely a first female part or receptacle  100 , and a second male part or plug  200  designed to be accommodated in the female part  100  in order to create an electrical connection. 
     The receptacle  100  is typically intended to be fixed to an appliance that is working at high voltage, such as an X-ray source of a radiological imaging device, or to a high-voltage generator designed to power such an appliance. 
     The receptacle  100  comprises a hollow body  101  made from a rigid and insulating material (such as a plastic for example) and a multiplicity of connectors  110  made from a conducting material (such as a metal). The body  101 , of generally cylindrical shape, includes a cylindrical wall  102  and a bottom  103  to create a cavity  104  to receive the plug  200 . The connectors  110  pass through the bottom  103  of the body, between the cavity  104  and the exterior of the receptacle  100 . 
     The plug  200  is configured to be fixed to one end of a high-voltage power cable used for electrical connection of a high-voltage generator to an appliance. 
     The plug  200  includes a jacket  201  made from a rigid and insulating material (such as a plastic for example), a multiplicity of connectors  210  made from a conducting material (such as a metal), and two removable sleeves  220  made from a flexible and insulating material (such as a silicone-based material for example). 
     The jacket  201  includes a body  202  that accommodates an end portion of a high-voltage cable  230 . The body  202  has a generally cylindrical shape, and is configured to be located in the cavity  104  of the receptacle  100 . 
     The connectors  110  of the receptacle  100  and the connectors  210  of the plug  200  are arranged so that, when the plug  200  is inserted into the receptacle  100 , each connector  210  is brought into contact with a corresponding connector  110 , so as to electrically connect the cable to the high-voltage generator or to the equipment. 
     The sleeves  220  are placed one after the other along a longitudinal direction of the jacket  201 . 
     The body  202  includes two sections  203  which have a diameter that is less than the outside diameter of the body. The sections  203  of smaller diameter form recesses  204 , with each recess  204  being designed to receive a sleeve  220 . Each recess  204  is used to keep the sleeve  220  in place during insertion of the plug  200  into the receptacle  100 . 
     The recesses  204  prevent the sleeves from sliding along the jacket  201  during insertion. 
     Preferably, each sleeve  220  (and each corresponding recess  204 ) extends over about a third of a longitudinal dimension of the jacket  201 . 
       FIG. 3  represents a plug  300  of a high-voltage connecting device according to a second embodiment of the invention. In this second embodiment, the plug has a larger longitudinal dimension than the plug of the connecting device of  FIGS. 1 and 2 . According to this second embodiment, the device is typically intended to be subjected to high voltages, of the order of 200 kilovolts. 
     The plug  300  is configured to be fixed to one end of a high-voltage power cable used for the electrical connection of a high-voltage generator to an appliance. 
     The plug  300  includes a jacket  301  made from a rigid insulating material (such as a plastic for example), a multiplicity of connectors  310  made from a conducting material (such as a metal), and three removable sleeves  220  made from a flexible and insulating material (such as a silicone-based material for example). 
     The jacket  301  includes a body  302  that accommodates an end portion of a high-voltage cable  330 . The body  302  has a generally cylindrical shape and is configured to be located in a cavity of a receptacle (not shown). 
     The sleeves  220  are placed one after the other along a longitudinal direction of the jacket  301 . 
     The body  302  includes three sections  303  that have a diameter less than the outside diameter of the body. The sections  303  of smaller diameter form recesses  304 , each recess  304  being designed to receive a sleeve  220 . Each recess  304  is used to keep the sleeve  220  in place during insertion of the plug  300  in the receptacle. 
     The recesses  304  prevent the sleeves from sliding along the jacket  301  during insertion. 
     Preferably, each sleeve  220  (and each corresponding recess  304 ) extends for about a quarter of a longitudinal dimension of the jacket  301 . 
     As can be seen from  FIGS. 2 and 3 , the sections  203 ,  303  of smaller diameter have a diameter that decreases slightly along the plug in the longitudinal direction of the plug, from one end of the cable to the end carrying the connectors. This reduction is due to the slightly tapered shape of the cavity of the receptacle. 
     The sleeves all have the same inside diameter. The elasticity of the sleeves allow the latter to adapt to recesses of dimensions that vary slightly. 
       FIGS. 4 ,  5 A and  5 B represent two types of sleeve that can be used in the context of this present invention. 
     In  FIG. 4 , the sleeve  220  represented is made in one piece. The sleeve  220  includes a cylindrical tube  221  and a multiplicity of annular beadings  222  positioned around the tube  221 . 
     The beadings  222  are intended to make contact with the inner surface of the wall  102  of the receptacle when the plug  200  is inserted into the receptacle  100 . In this configuration, the body  201  of the plug  200  is held at a distance from the body  101  of the receptacle  100  by means of the sleeves  220 . In addition, the beadings  222  form spaces  224  between them that are filled with air, thus contributing to the electrical insulation of the plug  200  and the receptacle  100 . 
     The receptacle  100  and the plug  200  are therefore insulated from each other firstly by the beadings  222  and secondly by the air-filled spaces  224 . 
     Each annular beading  222  is interrupted by a slot  223  that allows the passage of air through the beading  222 . Each slot allows communication between two successive air spaces  224 . 
     The insertion of the plug  200  into the receptacle  100  is facilitated by the presence of the slots  223 , which allow the air initially contained in the cavity  104  of the receptacle  100  to escape when the plug  200  is inserted into the receptacle  100 . 
     In  FIGS. 5A and 5B , the sleeve  240  represented is made in one piece. The sleeve  240  includes a cylindrical tube  241  and one or more helical beadings  242  positioned around the tube  241 . 
     The beading or beadings  242  are intended to make contact with the inner surface of the wall of the receptacle when the plug is inserted into the latter. In this configuration, the body of the plug is held at a distance from the body of the receptacle by means of the sleeves  240 . In addition, the turns of the beadings  242  form spaces between them  244  that are filled with air, thus contributing to the electrical insulation of the plug and the receptacle. 
     The receptacle and the plug are therefore insulated from each other firstly by the beadings  242  and secondly by the air-filled spaces  244 . 
     The helical shape of the beading or beadings  242  allow the air initially contained in the cavity of the receptacle to escape when the plug is inserted into the receptacle. 
     However, the turns of the beading  242  can be equipped with slots (as in the sleeve of  FIG. 4  so as to further facilitate the removal of the air. 
     The helical shape of the beading or beadings  242  result in greater dielectric strength of the sleeve. As a consequence, the sleeve  240  of  FIGS. 5A and 5B  provides better electrical insulation than the sleeve  220  of  FIG. 4 . 
     The sleeve  240  can be used in place of the sleeve  220  used in the connecting devices of  FIGS. 1 ,  2  and  3 . 
     Since each sleeve  220 ,  240  is elastic, it can be replaced easily in the event of damage. This allows easy maintenance of the connecting device. 
     In addition, this can be useful in the case where the plug  200 ,  300  is used with a receptacle of a connecting device of prior art. 
     On making contact with oil, whether mineral or synthetic, the silicone sleeve expands, since one of the advantages of the sleeves that have just been described arises from the fact that the air-filled spaces constitute so many spaces that contribute to this expansion. As a consequence, despite the accidental presence of oil in the receptacle, the male part (the plug) will continue to be easily fitted to and removed from the female part (the receptacle). This would not be the case if the sleeve were solid, since then the sleeve would have no space for expansion, leading to jamming of the expanded sleeve in the receptacle. 
     Moreover, since it is not necessary to fill the receptacle with a liquid insulator, the receptacle can be oriented in a variety of directions, providing greater freedom in the positioning of the receptacle on the high-voltage generator or the equipment. 
     Finally, the replacement of the conventional insulating liquids by an insulator in the form of a removes the risk of leakage, which is particularly advantageous in the case of radiological imaging appliances in which the source, powered at high voltage, is rotated around the patient. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 
     Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. Other embodiments will occur to those skilled in the art and are within the scope of the following claims.