High voltage connector for x-ray equipment

A high voltage cable connector has a flanged insulating sleeve terminating the cable. The sleeve inserts in an insulating receptacle with some clearance space around it for being occupied by a fluid dielectric medium. The receptacle has a flange which is axially spaced from the flange on the sleeve when the sleeve is fully inserted and secured in the receptacle. A ring element is sealed between the flanges. It defines an annular chamber which communicates with the dielectric medium filled clearance space. A compressible element such as a bellows or diaphragm is disposed in the chamber for accommodating thermal expansion and contraction of the medium or the connector assembly to allow sealing of the system to prevent loss of dielectric and thereby prevent formation of cavities in the medium which could cause electrical breakdown.

This invention relates to connecting high voltage cables to electrical 
apparatus such as X-ray tubes, X-ray transformers, high voltage rectifiers 
and the like. 
Medical X-ray systems commonly use voltages of up to 75 kilovolts peak 
(KVP) between respective power source terminals and ground. The type of 
cable connector generally used in such systems employs a female insulating 
receptacle on the X-ray tube or high voltage transformer and an insulating 
male sleeve which terminates the end of the high voltage cable and inserts 
in the receptacle to make an electrical connection. A fluid or viscous 
dielectric medium is used in the small clearance space between the 
receptacle and sleeve to displace air which would otherwise provide a path 
for high voltage arcing and breakdown. 
Because X-ray tubes operate at high temperatures and are subject to almost 
universal orientation when in use, a non-melting and viscous silicone 
grease has been used customarily to fill the space between the receptacle 
and sleeve, instead of using a medium that would be fluid at any 
temperature, to minimize the likelihood of the medium leaking through the 
seals of the connector. Further, when a liquid or viscous dielectric 
medium is elevated from ambient temperature to the maximum expected 
operating temperature of the X-ray tube and its casing assembly, thermal 
expansion and contraction of the dielectric medium occurs to the extent of 
about 5% of its volume. Further, the material of which the male connector 
and female receptacle portions of the high voltage connector assembly are 
constructed also expand and contract in varying amounts upon heating and 
cooling thereby changing the volume to be filled by the dielectric grease. 
The high viscosity of the various types of nonmelting electric media 
generally used in high temperature cable connectors make it difficult to 
assemble the cable terminal sleeve to the receptacle with a proper and 
adequate amount of dielectric medium between them and, as a practical 
matter, it is almost impossible to exclude air cavities from being 
entrapped in the dielectric medium. Even if air cavities could be 
excluded, experience has shown that when the connector and the dielectric 
medium heat expand some of the dielectric medium, being incompressible, is 
forced past the connector seals out of the interspace between plug and 
receptacle. Upon cooling, air is drawn into the interspace to replace the 
dielectric medium lost during heating. The minute air cavities thereby 
created provide high electrical intensity or stress regions which, in due 
course, lead to arcing, flashing and electrical breakdown along the 
clearance space between the outside of the cable terminal sleeve and the 
inside of the receptacle. In other words, current flows undesirably from 
the electrical connector pins on the male sleeve through air voids in the 
dielectric medium in the clearance, interspace and to ground by way of the 
metallic cable sheath. 
SUMMARY OF THE INVENTION 
The primary object of this invention is to provide a high voltage connector 
assembly which incorporates an effective seal against dielectric medium 
leakage and compensates for thermal expansion of the dielectric medium and 
the connector assembly so that conventional dielectric materials having a 
higher coefficient of thermal expansion such as oil or other low viscosity 
medium with a relatively low melting temperature such as petroleum jelly 
may be used to minimize the probability of air entrapment within the 
connector assembly. Moreover, the fundamental mechanism by which air 
voids, not present at assembly, but which are introduced by heating and 
cooling, is eliminated. 
Briefly stated, the new sealing and dielectric medium expansion and 
contraction accommodating means is used with a connector comprised of a 
female insulating receptacle having one closed end in which there are 
connector pin receivers and an open end which is surrounded by a radially 
extending flange. One face of the flange interfaces with a shoulder in a 
counterbore in the apparatus which is to be connected with a cable. The 
cable is terminated with a male insulating sleeve that has connector pins 
in its end and fits with a small clearance space around it into the 
receptacle. The male sleeve is also provided with a radially outwardly 
extending integral flange which is in axial spaced relationship to the 
flange on the receptacle when the sleeve with the cable attached to it is 
inserted in the receptacle. 
The insulating flanged female receptacle and the insulating male sleeve are 
basically conventional components of high voltage connectors. Employing 
seals between the flanges is also conventional. In accordance with the 
invention, however, an annular space or chamber is defined between the 
interfacing surfaces of the flange on the male sleeve and the flange on 
the receptacle. An annular resilient (compressible) element is disposed. 
The chamber is in fluid exchange communication with the clearance space 
between the sleeve and internal surface of the receptacle which is 
occupied by the dielectric medium. Thus, as the dielectric within the 
sealed region increases in volume when it heats, it compresses the 
resilient compressible element which is then loaded with a restorative 
force. When the dielectric medium cools and shrinks, the element expands 
under the influence of the force which is has stored and compensates for 
the dielectric volume decrease without creating air-filled cavities that 
would otherwise occur in the dielectric medium when it cools. The result 
is that no air-filled cavities nor vacuum pockets can occur in the 
dielectric medium. 
How the foregoing and other more specific objects of the invention are 
achieved will be evident in the description of the illustrative 
embodiments of the invention which will now be set forth in reference to 
the drawing.

DESCRIPTION OF A PREFERRED EMBODIMENT 
FIG. 1 depicts an X-ray tube casing 10 to which two insulated and 
metallically sheathed high voltage electric cables 11 and 12 may be 
connected by means of the new connector design which is to be described. 
In FIG. 1, the cable connectors are disposed within parts of the X-ray 
tube casing which are called horns 13 and 14. Each cable goes through an 
insulating strain relief sleeve such as those marked 15 and 16. 
The preferred embodiment of the new cable connecting means is illustrated 
in FIG. 2. In this figure one of the casing horns is marked 13 as it is in 
FIG. 1. The casing is provided with a counterbore 17 which terminates in a 
shoulder 18 and has an internal thread 19 running from its open end 20 
toward shoulder 18. The shoulder has an annular recess for accommodating 
an elastic o-ring 21 which is required because X-ray tube casing 10 is 
filled with dielectric fluid. A female receptacle 22 comprised of solid 
insulating material extends through an opening 23 in casing 13. This 
receptacle has a hollow cylindrical body 24 which has one end 25 closed 
and its opposite end open similar to a cup. Said opposite end has an 
integral radially outwardly extending flange 26 whose one face interfaces 
with and compresses o-ring 21 to effect a seal with the oil filled casing 
13 when the parts of the connector are pressed together as will be 
explained. 
The insulating male cable terminal member or sleeve which fits into 
insulating receptacle 22 is generally designated by the reference numeral 
27. Sleeve 27 has an internal bore 28 into which the insulated and 
unsheathed end 29 of a high voltage cable is inserted. Sleeve 27 has a 
radially extending flange 27' molded integrally with one of its ends. A 
typical wire 30 extending from the end of the cable is fastened in a male 
connector pin, a typical pin being marked 31. The male pin connectors 
extend into female connectors 32 which are assembled and sealed into the 
closed end 25 of outer receptacle 22. Connectors 32 have threaded ends 33 
for facilitating making electrical connections between them and whatever 
device, such as an X-ray tube, is being supplied from the cable. The space 
34 around the cable in bore 28 is customarily filled with a self-setting 
insulating and sealing compound, not shown. The male terminal member or 
sleeve 27 can be and has been molded or potted directly on insulated cable 
end 29 in one connector style, not shown, In such case, space 34 is not 
created and a compound in this space is unnecessary. Term "sleeve" is used 
herein as inclusive of a male terminal member that is molded on the cable 
as well as one that is not. 
It should be noted that there is a small clearance space or annular gap 35 
defined between the outer periphery of male cable terminating sleeve 27 
and the inner cylindrical surface of female receptacle 22. This clearance 
space is filled with a fluid dielectric medium to reduce the likelihood of 
an electrical breakdown between the cable connectors in the receptacle and 
the casing 13 in which it is mounted. As will be explained subsequently, 
the connector assembly described herein has a unique capability for 
accommodating expansion and contraction of the dielectric fluid medium in 
this clearance space, for maintaining effective seals against dielectric 
fluid leaking from the connector assembly and for eliminating vacuum or 
air pockets or cavities in the dielectric medium. Thus, in the present 
case, thin dielectric oil or synthetic dielectric liquid or a low 
viscosity material with a relatively low melting temperature such as 
certain silicone compounds and petroleum jelly may now be used as the 
dielectric medium in preference to conventional more viscous dielectrics. 
Being able to use a thin or relatively nonviscous dielectric medium 
facilitates inserting the male cable sleeve 27 into female receptacle 22 
without having air pockets or cavities develop during assembly as well. It 
is only necessary to partially fill the receptacle 22 with the thin and 
flowable dielectric medium and let it ooze back along clearance gap 35 
when male sleeve 27 is inserted in female receptacle 22. By way of example 
and not limitation, annular clearance space 35 between the receptacle and 
male sleeve is on the order of 10 to 12 thousandths of an inch in a 
commercial embodiment and the cylindrical part of the male sleeve is about 
five inches long. 
For controlled expansion and contraction of the dielectric, it is desirable 
but not necessary for the receptacle 22 and sleeve 27 to have compatible 
thermal expansion properties. Thus, in a preferred commercial embodiment, 
female receptacle 22 and the sleeve 27 are made of an identical or similar 
molding compound. 
In FIG. 2, the cable end 29 is shown extending into bore 28 of the male 
sleeve 27 but the braided metallic sheath 40 on the cable is flared out 
and soldered, in the region marked 41, to an annular conical metal ring 42 
which is crimped around the outer periphery of the flange 27' extending 
from male cable terminating sleeve 27. Another ring or metal shield 43 is 
crimped over ring 42 and provides a gap in which the end of the outer 
plastic insulating sleeve 44 of the cable is squeezed and held. As 
mentioned in connection with FIG. 1, the cable passes through a rigid 
strain relief 15 which is also shown in FIG. 2. It has a flange 45 
surrounded by a crimped-on ring 46 which provides a metal-to-metal bearing 
surface where it interferes with shield ring 43. An externally threaded 
ring nut 47 is turnable into the thread 19 within counterbore 17 in X-ray 
tube casing 10 for the purpose of clamping the male cable terminating 
sleeve 27 into female receptacle 22 as is evident from inspection of FIG. 
2. 
The flange 27' on male sleeve 27 and the flange 26 on female receptacle 22 
are axially spaced from each other when the sleeve is inserted as far as 
it will go into the receptacle as is evident in FIG. 2. In accordance with 
this embodiment of the invention, the space between the interfacing 
surfaces of the flanges 27' and 26 has a ring element, generally 
designated by the reference numeral 50, disposed in it. Ring element 50 
has a peripheral or external thread which turns into female thread 19 in 
tube casing counterbore 17 and acts to clamp the female receptacle 22 in 
the tube casing 13. The recesses in the ring element for enabling it to be 
tightened in with a spanner wrench are not shown. In the FIG. 2 
embodiment, ring element 50 has grooves on its opposite end faces which 
are occupied by commercially available quad rings 51 and 52, which effect 
seals between the interfacing surfaces of the receptacle flange and sleeve 
flange, respectively. Ordinary o-rings could, of course, be used instead 
of quad rings. The quad rings may be neoprene rubber. They are efficient 
low pressure seals. Ring element 50 is also provided with an open-sided 
groove or chamber 53 which, in accordance with the invention, accommodates 
an element which yields or compresses when exposed to fluid pressure and 
tends to restore to its original volume as pressure is relieved. The 
compressible self-restoring element in the preferred FIG. 2 embodiment is 
a toroidal bellows 54 whose inside is contiguous with an annular cavity 55 
which places the bellows in fluid exchange communication with dielectric 
medium filled clearance gap or space 35 between male sleeve 27 and female 
receptacle 22. 
A magnified cross section through one side of annular or toroidal bellows 
54 is shown in FIG. 3. Here it may be seen to comprise serpentine-shaped 
inner and outer rings 56 and 57 to which flat end plates 58 and 59 are 
brazed or welded. In a commercial embodiment, the bellows end plates 58 
and 59 are made of stainless steel and the serpentine bellows walls are 
made of nickel. The bellows assembly as used in FIG. 2 is not required to 
perform any sealing function. It simply compresses when the dielectric 
medium in clearance space 35 becomes hot and expands and it expands to 
make up for contraction of the fluid when the fluid gets cooler to thereby 
prevent formation of air or vacuum cavities in the fluid. The bellows 54 
may fit loosely in groove or chamber 53. In a commercial embodiment, the 
annular bellows 54 is not preloaded or precompressed and its interior is 
at atmospheric pressure when cold. When ring member 50 is turned in 
tightly, quad ring seal 51 becomes slightly compressed to effect a seal. 
When clamping ring nut 47 is screwed in, the other quad ring 52 becomes 
slightly compressed to effect a seal. Thus, all the volume change of the 
dielectric medium with temperature is accommodated exclusively by the 
bellows in this embodiment. 
It should be evident that ring member 50 performs the multiple functions of 
retaining seals 51 and 52, clamping receptacle 22 and providing for 
development of the annular space or chamber 53 which is subject to the 
pressure of fluid in clearance space 35 and is occupied by compressible 
element 54. The arrangement permits using preexisting flanged female 
receptacles 22 and male sleeves 27 without modification. However, the 
chamber 53 does not have to be in clamping and seal retaining ring member 
50. The annular space or chamber for accommodating compressible element 54 
may be formed in the flange on female receptacle 22, for example, or it 
may be formed within the bore of the female receptacle or even as a groove 
in the outside of the sleeve. The requirements are that the dielectric 
fluid in the clearance space between the receptacle and the sleeve must be 
able to enter the chamber, the chamber should be internal to the 
receptacle and the chamber should be occupied by a compressible element. 
The thermal expansion characteristics of the materials used for receptacle 
22 and sleeve 27 should be chosen so the expansion of the sleeve will 
track expansion of the receptacle as the two components become warmer. If 
the sleeve expands at a higher rate, the volume of the fluid filled 
clearance space 35 decreases and pressures could build up which are higher 
than would be predicted if only the increase in temperature of the 
dielectric fluid itself were considered. Such high pressure, if they were 
allowed to occur, could cause the limits of the compressibility of the 
compressible element to be reached. By way of example, tests with a 
premanufacturing prototype revealed that pressures of the dielectric fluid 
at the highest operating temperatures expected in an X-ray tube casing 
environment reached a maximum of forty pounds per square inch whereas 
pressures were even higher in a prototype in which the sleeve expanded 
more than the receptacle. 
Now that the preferred embodiment has been described in detail in 
connection with FIG. 2, alternative embodiments of the connector assembly 
will be described which use an annular resilient or compressible or 
yieldable element other than a bellows for accommodating volume changes in 
the dielectric medium. 
In the FIG. 4 embodiment, components which are similar to those shown in 
FIG. 2 are given the same reference numerals. Thus, there is a casing 13 
having a counterbore 17 which has an internal thread 19 and defines a 
shoulder 18 which provides for capturing an o-ring seal 21 between the 
shoulder and one face of the flange 26 on outer female insulating 
receptacle 22. It is assumed that the casing 13 is filled with oil which 
also surrounds receptacle 22. Shields such as the one marked 43 are 
crimped on the flange of inner male cable terminal sleeve 27. A clamping 
nut 47 is also provided for securing the sleeve in the receptacle. 
In the FIG. 4 embodiment, flange 26 on the female receptacle 22 and flange 
27' on male cable terminating sleeve 27 are axially spaced from each other 
when the sleeve is inserted as far as it will go into the receptacle. A 
metal ring member 57 has an external thread for turning it into internal 
thread 19 of the counterbore to secure the receptacle 22 in the tube 
casing 13. This ring member 57 provides on its axially opposite faces 
reaction surfaces for engaging a resilient sealing element which is 
generally designated by the reference numeral 58 and serves as a yieldable 
or compressible diaphragm and a sealing device. Element 58 may be any 
rubber-like material which is compatible with the dielectric medium used 
between the sleeve and receptacle. The annular resilient fluid expansion 
and contraction accommodating diaphragm or element 58 has a generally 
U-shaped cross sectional shape and its rims terminate in integral annular 
rings 59 and 60 which serve as o-ring seals. One may see that when 
externally threaded metal ring member 57 is screwed tightly into the 
internal thread 19 of the tube casing counterbore 17, o-ring portion 59 
will be compressed to effect a seal between ring member 57 and the end 
face of the flange 26 on receptacle 22. Also, when clamping nut 47 is 
turned in, the flange 27' on receptacle 27 will compress o-ring portion 60 
of u-shaped element 58 to effect a seal between the flange 27' and the 
metal ring member 57. The u-shaped configuration of resilient element 58 
allows for a free but sealed off space 61 to be created between the inside 
of the annular u-shaped resilient element 58 and the threaded metal ring 
member 57. The air-filled space 61 reduces in volume when resilient 
element 58 is subjected to fluid pressure on its outside surface 62 which 
is interfaced with and subject to any pressure developed in the dielectric 
fluid that resides in clearance space 35. Dielectric fluid volume changes 
are accommodated by flexing of the resilient u-shaped diaphragm 58. When 
the outside surface 62 of the diaphragm is subjected to pressure, the 
captured air in space 61 reduces in volume and attains a pressure that is 
always in equilibrium with the externally applied fluid pressure. When the 
dielectric medium cools and contracts, expansion of the diaphragm and the 
compressed air makes up for the loss in volume which would otherwise occur 
due to contraction to thereby prevent formation of any air or vacuum 
cavities in the dielectric fluid. 
FIG. 5 illustrates another embodiment of the new connector assembly. Parts 
which are substantially the same as in the previously described 
embodiments are given the same reference numerals. In FIG. 5, the flange 
of female receptacle 22 is pressed against a shoulder on apparatus casing 
13 and an o-ring forms a seal between these two parts to prevent leakage 
of dielectric oil from the apparatus casing. Radially extending flange 27' 
on the male sleeve is axially spaced from the flange 26 on the receptacle 
22. Tightening of threaded locking ring 47 into casing 13 presses the 
flange 27' of sleeve 27 toward the flange 26 of receptacle 22. An 
externally threaded metal ring 65 is interposed between the two flanges. 
It secures receptacle 22 in the tube casing 13. The bore of ring 65 has 
another metal ring 66 within it. The two concentric rings form a chamber 
67 in which there is a quad ring 68 that is exposed on one side to the 
dielectric medium in clearance space 35 between male sleeve 27 and female 
receptacle 22. Quad ring 68 is composed of a resilient rubber-like 
material. The four rims or projections from the quad ring form seals. An 
o-ring 69 forms a seal between interfacing surfaces on ring 65 and the 
flange on receptacle 22. 
The quad ring 68 is yieldable for accommodating volume changes in the 
dielectric medium in space 35 between sleeve 27 and receptacle. A circular 
spring 70 with a wavy or otherwise formed cross section as shown in FIG. 6 
is interposed between flange 27' of sleeve 26 and inside axially yieldable 
ring 66 to accommodate volume changes in chamber 67. When the dielectric 
medium expands, quad ring 68 and metal ring 66 slide a little bit axially 
and load wave spring 70 slightly. When the dielectric medium cools and 
contracts, the stored energy in wave spring 70 forces ring 66 and quad 
ring 68 axially to thereby keep the dielectric medium under compression so 
that no vacuum or air cavities will form in the medium. It should be 
evident that an o-ring, not shown, could be used in place of the quad ring 
seal 68. 
Although the preferred FIG. 2 embodiment uses a bellows 54 in an annular 
chamber or cavity 55 which leads to the fluid filled clearance space 35, 
it should be understood that resilient or compressible elements other than 
a bellows may be used to compensate for dielectric fluid volume changes 
with temperature. For instance, a sealed tubular ring of elastic material, 
not illustrated, may be used in place of the bellows. A ring composed of 
compressible sponge may also be used but care must be exercised in 
choosing a sponge material that does not have a propensity to take on a 
permanent set when it is compressed and subjected to heat from the 
dielectric fluid and the surroundings at the same time. 
Although several embodiments of the new anticavitation high voltage cable 
connector have been shown and described in considerable detail, such 
description is intended to be illustrative rather than limiting, for the 
invention may be variously embodied and is to be limited only by 
interpretation of the claims which follow.