Abstract:
A boot/ring comprising an annular core made of a closed-cell elastomer foam entirely coated with elastomer foam entirely coated with an elastomer covering that can withstand the electric insulating and cooling liquid contained in connector, at the connector operating temperature. Application: to high-voltage connectors for X-ray apparatuses.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates in general to a high-voltage (HT) connector, particularly for providing power to X-ray tubes. 
     The HT current source for powering an X-ray tube is conventionally encased in a box filled with an insulating and cooling medium, generally a mineral oil, while the X-ray tube is itself also encased in another box filled with an insulating and cooling medium, for example a mineral oil. 
     Depending on the type of HT current source and the type of X-ray tube, whether it is monopole or symmetric, one or more HT cables convey HT current from the source to the X-ray tube. These power leads are connected to the HT source and to the X-ray tube by means of hermetically sealed HT connectors. 
     These HT connectors generally consist of two parts, a female part or receptacle which is attached permanently to the box and a male part or plug intended to plug into the receptacle to produce electrical continuity and which constitutes the end of the HT cable. 
     To withstand the high voltages of the source and of the X-ray tube, which may be as much as 150 kV or more, the receptacle and the plug of the HT connector are made of an insulating material and have shapes and sizes which are generally dictated by international standards. 
     To protect the users, the boxes of the HT source and of the X-ray tube are earthed and an external jacket of the HT cable is also earthed by metal parts of the receptacle and of the plug. 
     The HT source and the X-ray tube are electrically connected to the HT cable by interacting metal contacts arranged in receptacle of the connectors. 
     To avoid electrical discharge between the contacts and the metal parts of the connector of the HT source or of the X-ray tube, the gap between the receptacle and the plug is filled with an electrically insulating fluid, for example a mineral oil or grease such as a silicon oil or grease. 
     To keep this insulating fluid in the gap between the receptacle and the plug, an annular seal is arranged between the open end of the receptacle and a flange of the plug. As the volume of insulating fluid varies with temperature, and in fact increases as the temperature rises, it is necessary, in order to avoid excessively high pressures which could lead to leaks of insulating fluid and even to the destruction of the receptacle with a risk of HT electrical discharge, that this increase in volume of the insulating fluid be compensated. 
     To compensate for such variations in volume of the insulating fluid, use is made of a boot/ring, the volume of which varies as a function of the pressure of the insulating fluid in order to accommodate the increase in volume of the insulating fluid. 
     Furthermore, this annular seal needs to operate over a wide temperature range and be chemically able to resist the hot insulating fluid. 
     A first boot/ring conventionally used is depicted in FIG.  2 . This ring  41  is a ring made of metal which has a accordion side wall  42 . This ring is easy to handle and reliable in the long term but is very expensive to manufacture. 
     Another boot/ring also used is depicted in FIG.  3 . This composite ring  43  is composed of a flat metal annulus  44  to which an elastomer annulus  45  is attached, forming a half torus inside the metal annulus  44 . This boot/ring is difficult to handle, and requires extremely accurate fitting means to avoid leaks and is expensive. 
     BRIEF SUMMARY OF THE INVENTION 
     The purpose of the present invention is therefore to provide a boot/ring for a high-voltage connector which overcomes the drawbacks of the boot/rings of the prior art, and in particular which is reliable, easy to manufacture and inexpensive. 
     Also, the subject of the present invention is an HT connector comprising a boot/ring of this kind. 
     An embodiment of the invention is a boot/ring for an HT connector which is composed of an annular core made of a closed-cell elastomer foam entirely coated with a covering made of an elastomer that can withstand the insulating and cooling liquid at the HT connector operating temperature. 
     For the core of the boot/ring according to the invention, use may be made of any closed-cell elastomer foam, for example, a polyurethane or neoprene foam. 
     Given that the usual elastomer foams do not have the desired resistance to the insulating and cooling liquid (for example an oil) present in the HT connector, particularly when hot, the elastomer foam is entirely coated with a covering made of elastomer that can resist the insulating and cooling liquid at the HT connector operating temperature. 
     For the covering, use may be made of any elastomer which satisfies the above requirement. Among the elastomers that can be used, mention may be made of olefin elastomers such as neoprene, elastomeric polyesters, silicone elastomers, halogenated-olefin elastomers, particularly chlorinated olefin elastomers, and polyurethane elastomers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of an HT connector including a boot/ring; 
     FIG. 2 is a sectional view of a boot/ring of the prior art; 
     FIG. 3 is a sectional view of another boot/ring of the prior art; and 
     FIG. 4 is a sectional view of an embodiment of a boot/ring of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 depicts an HT connector into which a boot/ring can be incorporated. 
     The HT connector in FIG. 1 comprises a female part or receptacle  10  and a male part or plug  20 . 
     The receptacle  10  is fixed to the box  30  of an HT device such as an HT power supply source or of an X-ray tube. This receptacle  10  comprises a casing which is generally insulating, of frustoconical shape, with a side wall  11 , an end wall  12 , and an open end with a coupling flange  13 . 
     An electrical contact  14 , for example a female contact, is arranged inside the receptacle  10  on the end wall  12 . 
     The plug  20  of the connector, electrically connected to an HT cable  24 , comprises a body  21  made of an electrically insulating material with a frustoconical shape that complements that of the receptacle  10  and an annular flange  22 , generally made of metal, where the insulating body  21  meets the HT cable  24 . 
     The front face of the insulating body  21  has an electrical contact  23 , for example a male contact, connected to the conductor of the HT cable  24  and interacting with the contact  14  of the receptacle  10  to produce electrical continuity between the HT power supply or the X-ray tube and the HT cable  24  when the plug  20  is plugged in to the receptacle  10 . 
     As depicted in FIG. 1, the receptacle  10  is held on the metal box  30  via the flange  13  by means of an intermediate threaded annular nut  31  interacting with a complementary threaded vertical wall of the box  30 . 
     Between the flange  13  of the receptacle  10  and an annular rim of the intermediate ring  31  there is a boot/ring  40  according to an embodiment of the invention. 
     The plug  20  of the connector is held in the receptacle  10  by the compressive force exerted by a threaded annular nut  32  interacting with the threaded vertical wall of the box  30 , on the annular flange  22  so as to press the latter against the intermediate nut  31 . 
     The box  30 , the intermediate nut  31  and the nut  32  which are made of electrically conductive material, ensure earth continuity of the screening of the HT cable  24  to the box. 
     Conventional O-ring seals  34 ,  35 ,  36  are generally arranged between the box  30  and the flange  13  of the receptacle  10  and between the intermediate nut and the flanges  13  and  22  of the receptacle  10  and of the plug  20 . 
     The space between the insulating body  21  of the plug  20  and the internal surface of the receptacle  10  is filled with an electrically insulating and cooling liquid  25 , for example an oil. 
     When the HT connector is in operation, the increase in temperature of the insulating and cooling liquid increases the pressure exerted by the liquid. The boot/ring  40  according to the invention makes it possible to maintain sealing between the receptacle  10  and the plug  20  of the connector by accommodating the increase in pressure of the insulating liquid. 
     As shown in FIG. 4, the boot/ring  46  according to an embodiment of the invention comprises an annular core  47  made of a closed-cell elastomer foam which is completely coated with a covering  48  made of an elastomer that can resist the insulating and cooling liquid at the connector operating temperature. 
     Because of the presence of the closed-cell elastomer foam core  46 , the boot/ring has enough elasticity to compensate for the increases in volume of the insulating liquid. The elastomer covering  48  gives the boot/ring the ability to resist the corrosive action of the hot insulating liquid, as conventional elastomer foams do not have sufficient resistance. 
     Various modifications in structure and/or function and/or steps may be made by one skilled in the art to the disclosed embodiments without departing from the scope and extent of the invention.