Abstract:
Pressurized rotary machine comprising a canned or sleeved assembly of which the electrical connections are connected to the outside of the machine by an electric supply duct, the electrical connections passing from the canned or sleeved assembly to the outside via the electric supply duct by passing in succession through first, second and third hermetically sealed bushings, none of these hermetically sealed bushings through which the electrical connections pass being exposed to a pressurized gas.

Description:
FIELD OF THE INVENTION 
       [0001]    The subject of the present invention is a pressurized machine equipped with a rotor in contact with a particle-laden, acidic or corrosive liquid or gaseous atmosphere and relates more specifically to a pressurized rotary machine equipped with sleeved magnetic bearings, with sleeved detectors for magnetic bearings and/or with a canned electric motor. 
       PRIOR ART 
       [0002]    Sleeved magnetic bearings are generally used in pressurized rotary machines, commonly in a high-pressure gas environment. A sleeved magnetic bearing consists of a stator part comprised of wound cores placed in a protective metal enclosure consisting of an armature, of a thin sleeve and of a hermetically sealed passage, and filled with a filler which may serve to support the thin sleeve. 
         [0003]      FIG. 3  depicts one example of a sleeved magnetic bearing  10  positioned inside a machine  12  containing pressurized gas. A connection socket  14  equipped with a hermetically sealed or fluidtight bushing  14   a  is installed on a protective metal enclosure  16  of the sleeved magnetic bearing  10  so that electrical connections can be led out. A flexible duct  18  equipped at one end with a connector  20  also provided with a hermetically sealed or fluidtight bushing  20   a  allows the electrical connections  22  of the sleeved magnetic bearing  10  to be connected to the outside of the machine via a further socket  24  provided with a hermetically sealed or fluidtight bushing  24   a.    
         [0004]    As shown by the enlarged detail of this figure, these hermetically sealed bushings are generally conductive passages crimped onto a metal wall by means of beads of glass in order to form either a connection socket or a mobile connector plug or simply a fluidtight electrical passage. The assembly is then welded or fixed hermetically to the wall using seals, welding, etc. 
         [0005]    To prevent it from being crushed under the pressure of the ambient gas, the flexible duct is filled with oil or some other liquid so that the internal pressure inside the duct differs only very little from the gas pressure in the machine. Likewise, the duct is flexible enough to cope with the thermal expansion of the liquid. An access  26  communicating with the outside of the machine may allow the flexible duct to be filled with liquid. 
         [0006]    The space between the two hermetically sealed bushings  14   a  and  20   a  is left in communication with the gas present in the machine if the quality of the gas is compatible with the nature of the electrical contacts or is hermetically sealed if the gas presents a risk to these contacts. 
         [0007]    The disadvantage of a setup such as this is that there may be significant pressure differences between the gaseous media present and therefore it displays great sensitivity to the quality of the leak rates of each of the hermetic sealing barriers. 
         [0008]    Hence, it is very difficult to achieve bushings  14   a ,  20   a  of the connection socket  14  of the magnetic bearing and of the connector  20  of the flexible duct  18  which have excellent leak rates, that is to say leak rates better than 1E-8 mbar.l/s (rates measured under helium at 1 bar gauge), just as it is very difficult reliably to achieve connection sockets and hermetically sealed connectors that have leak rates of this order. The standard orders of magnitude for the leak rates of such sockets are actually typically of the order of 1E-6 mbar.l/s. Very careful manufacture or sorting during the manufacturing process makes it possible to obtain hermetically sealed bushings with leak rates of the desired order of magnitude (&lt;10E-8 mbar.l/s). However, these components are excessively fragile both in terms of fitting and in terms of durability, and their cost is very high. In addition, when the enclosure of the sleeved magnetic bearing has to be equipped with several bushings, the overall leak rate is the sum of the leak rates. The operations of fitting (soldering the wires to the rear of the bushing, welding the bushing to the protective enclosure, etc.) apply thermal or mechanical stresses to the glass beads which then lose some of their quality. The original leak rate is thereby adversely affected. 
         [0009]    It therefore follows that, via residual leakages, ambient gas from inside the machine migrates into the magnetic bearing or into the canned or sleeved assembly through the various connections. As these leaks build up, they are liable to create an environment that is dangerous (corrosive, explosive, harmful, polluting, etc.) to or detracts from the life of the canned or sleeved assembly. Should the machine become depressurized, the internal pressure inside the canned or sleeved assembly may then exceed the ambient pressure, which then causes the enclosure to distend at the thin sleeve to the extent that the thin sleeve may be destroyed either through plastic deformation or through contact with the rotor armatures  28  of the rotor  30  as in the case of the sleeved axial magnetic bearing illustrated in  FIG. 3 . This is all the more dangerous if the gas is corrosive because the bearing can then also be destroyed by corrosion. 
         [0010]    Typically, the pressure inside the sleeved bearing is of the order of one bar absolute (manufacturing pressure of the sleeved bearing) whereas the pressure of the gas inside the machine may be 100 to 200 bar. At this pressure, even if the space between the two bushings  14   a  and  20   a  is isolated by sealing gaskets  32 , the gas pressure rapidly reaches it through the leak rate of these seals. Thereafter, the hermetically sealed bushing  14   a  of the connection socket  14  of the sleeved magnetic bearing  10  is subjected to a differential gas pressure substantially equal to the pressure of the machine. If this bushing does not have an excellent leak rate (far better than 1E-8 mbar.l/s), the pressure inside the sleeved magnetic bearing increases and this may lead to its destruction as explained hereinabove. 
       DEFINITION AND OBJECT OF THE INVENTION 
       [0011]    The present invention sets out to overcome the aforementioned disadvantages and in particular to limit the leak rate of the hermetically sealed bushings so that there is no need to fear any migration of gas into the magnetic bearing or the canned or sleeved assembly. 
         [0012]    These objects are achieved, according to the invention, by a pressurized rotary machine comprising a canned or sleeved assembly of which the electrical connections are connected to the outside of the said machine by an electric supply duct, the said electrical connections passing from the said canned or sleeved assembly to the outside via the said electric supply duct by passing in succession through first, second and third hermetically sealed bushings, characterized in that none of the said hermetically sealed bushings through which the said electrical connections pass is exposed to a pressurized gas. 
         [0013]    Thus, by preventing each of the hermetically sealed bushings from experiencing a substantial gas pressure on one of its faces, it is no longer possible for gas to migrate and the fluidtightness of the connection is preserved. The volume of gas passing through the various sealing gaskets of the connection (which may then have a standard leak rate of the order of 1E-6 mbar.l/s) is then negligible. A raised liquid pressure on one of the faces presents no danger because a standard leak rate of the order of 1E-6 mbar.l/s under helium does not allow liquid to pass. 
         [0014]    The said electric supply duct may be a rigid duct or alternatively a flexible duct, depending on the envisaged embodiment. 
         [0015]    Advantageously, the said supply duct is filled with a liquid filler so as to keep the internal pressure inside the said electric supply duct identical to the internal pressure inside the machine. The said liquid filler may be a dielectric insulator. 
         [0016]    A pressure compensating balloon may be added to keep the internal pressure inside the said electric supply duct identical to the internal pressure inside the machine. 
         [0017]    As a preference, a valve is positioned or a drilling created across the said second hermetically sealed bushing so that the external pressure applied to the said first hermetically sealed bushing is created by the said liquid filler. 
         [0018]    The invention is equally applicable to a sleeved magnetic bearing as it is to a sleeved detector for a magnetic bearing or to a canned electric motor. The medium external to the machine may be liquid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Further features and advantages of the invention will become apparent from reading the following description of some particular embodiments of the invention, which have been given by way of example with reference to the attached drawings in which: 
           [0020]      FIG. 1  is a schematic view of a first embodiment of the electrical connections connecting a sleeved magnetic bearing to the external wall of a rotary machine according to the invention, 
           [0021]      FIG. 2  is a schematic view of a second embodiment of the electrical connections connecting a sleeved magnetic bearing to the external wall of a rotary machine according to the invention, and 
           [0022]      FIG. 3  is a schematic view of the electrical connections connecting a sleeved magnetic bearing to the external wall of a rotary machine according to the prior art. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0023]      FIG. 1  illustrates a first example, according to the invention, of how the electrical connection of a sleeved magnetic bearing  100  positioned inside a machine  102  containing pressurized gas is led to the outside (the ringed references I and II respectively denote the inside and the outside of the machine). As shown in greater detail in the enlarged detail of this figure, a connection socket  104  equipped with a hermetically sealed or fluidtight bushing  104   a  is installed on a protective metal enclosure  106  of the sleeved magnetic bearing  100 , so as to lead out the electrical connections  108  needed to supply the windings  110  of the sleeved magnetic bearing. A flexible duct  112  equipped at one end with a connector  114 , also equipped with a hermetically sealed or fluidtight bushing  114   a , allows the electrical connections  108  to be connected to a connector (not depicted) external to the machine via a connection socket  116  at its other end which is likewise equipped with a hermetically sealed or fluidtight bushing  116   a  and mounted on a cover plate  118  of this machine. The mechanical connection between the connection socket  104  and the connector  114  is achieved by means of a nut  120  which also compresses an isolating gasket  122  positioned at the interface between these two elements and isolating the space  124  contained between the two hermetically sealed bushings  104   a  and  114   a.    
         [0024]    The flexible duct  112  is filled with oil or any other liquid such that its internal pressure differs only very little from the pressure of the gases in the machine, and is flexible enough to be compatible with the thermal expansion of the liquid. As a preference, a pressure compensating balloon  126  is installed on the cover plate  118  which also comprises an orifice  128  for communicating with the outside of the machine so that the flexible duct  112  can be filled with liquid. 
         [0025]    According to the invention, the bushing  114   a  is made permeable to the liquid flowing through the flexible duct  112  so that the liquid fills the empty space  124  present between the bushings  104   a  and  114   a . This liquid filler may be a dielectric insulator. 
         [0026]    Because the pressure of the liquid is very nearly equal to the pressure of the gas inside the machine thanks to the flexibility of the duct  112  and/or the pressure compensating balloon  126 , the sealing gasket  122  is subjected, on one side, to the gas and, on the other side, to the liquid, with a very small pressure difference that does not allow the gas to migrate into the empty space  124 . 
         [0027]    Further, the pressure across the bushing  104   a  is, on one side, a high liquid pressure from the flexible duct  112  and, on the other side, the internal pressure inside the sleeved bearing, typically equal to 1 bar. A bushing of standard manufacture (leak rate under helium of 1E-6 mbar.l/s) is therefore completely hermetically sealed against the liquid and there is no need to fear any migration into the sleeved magnetic bearing. In the first exemplary embodiment illustrated in  FIG. 1 , the connector  114  comprises, for example at its middle, a valve  130  of which the opening, at the instant that the two elements  104  and  114  are assembled, places the internal volume of the duct  112  in communication with the space  124  between the bushings  104   a  and  114   a.    
         [0028]    When the flexible duct is connected to the connection socket  104  of the sleeved magnetic bearing, a small quantity of liquid comes to fill the space  124  between the hermetically sealed bushing of the socket which is situated on the sleeved magnetic bearing and the bushing of the connector of the flexible duct. The pressure compensating balloon  126  may assist with equalizing the internal pressure inside the duct with the ambient pressure. This balloon is needed only if the flexible duct is not supple enough (or is even rigid) to perform this role. 
         [0029]    At the critical points of the connection socket  104   a  of the sleeved magnetic bearing there is then, on one side, a pressure of the order of one bar and, on the other side, the presence of pressurized oil. Bearing in mind the standard leak rate of the bushings (1E-6 mbar.l/s under 1 bar of helium) this represents a perfect hermetic seal against liquid and there is therefore absolutely no need to resort to special manufacture in order to obtain better leak rates. 
         [0030]    Likewise, the hermetic sealing  114   a  of the bushing of the connector  114  fitted to the flexible duct  112  plays no further part in normal operation and is merely an aid to assembly to prevent the liquid from running out at the time of fitting. 
         [0031]    Because the pressure in the space  124  between the bushings  104   a  and  114   a  is substantially equal to the internal pressure inside the machine, there is only a negligible pressure difference across the sealing gasket  122 , making the migration of gas equally negligible with “standard” leak rates. 
         [0032]    In another exemplary embodiment that has not been depicted, the bushing  104   a  is simply pierced. Of course, that entails not filling the duct  112  with liquid until after the elements  104  and  114  have been connected, using the filling orifice  128 . 
         [0033]    As a preference, the duct  112  is symmetric and the hermetically sealed bushing  116   a  installed on the cover plate  118  of the machine is similar to the hermetically sealed bushing  114   a . It may be noted that when a pressure compensating balloon is provided, the duct  112  can then be less flexible, to the point of being rigid, it being possible for one and the same balloon to be used to equalize the pressure in several ducts. 
         [0034]      FIG. 2  illustrates a second example, according to the invention, of how the electrical connection of a sleeved magnetic bearing  100  placed inside a machine  102  containing pressurized gas is led to the outside. 
         [0035]    In this example, the connection socket  104  equipped with a hermetically sealed or fluidtight bushing  104   a  is installed not on the protective metal enclosure  106  but at the opposite end of the flexible duct  112  where it engages with a connector  114  likewise fitted with a hermetically sealed or fluidtight bushing  114   a  secured to the cover plate of the machine  118  and therefore allowing the electrical connections  108  to be connected to an external connection plug  142 . 
         [0036]    The mechanical connection between the connecting socket  104  and the connector  114  is, as before, achieved by way of a nut  120  which also compresses an isolating gasket  122  positioned at the interface between these two elements and isolating the space  124  between the two hermetically sealed bushings  104   a  and  114   a.    
         [0037]    The electrical connections  108  needed for supplying the windings  110  of the sleeved magnetic bearing are, for their part, now led out in a connecting part that adopts the form of a short rigid duct  140  as far as a bushing hermetically sealed against the liquid  116   a  which provides the connection with the electrical connections of the flexible duct to the end of which this short rigid duct is secured. 
         [0038]    Thus, because the hermetically sealed bushing  116   a  serves no further function in normal operation, the pressure on one side of the canned or sleeved assembly is of the order of one bar and pressurized oil is present on the other side. Bearing in mind the standard leak rate of the bushings (1E-6 mbar.l/s under 1 bar of helium), that represents a perfect seal against the liquid and there is then absolutely no need to resort to special manufactures in order to obtain better leak rates. 
         [0039]    The flexible duct  112  is filled with oil or any other liquid prior to assembly. Once assembly has been performed, the internal pressure inside the duct then differs only very slightly from the pressure of the gas in the machine, the duct being flexible enough to be compatible with the thermal expansion of the liquid. As a preference, a pressure compensating balloon  126  is also present but this time installed on the short rigid duct  140  that it crosses downstream of the hermetically sealed bushing  116   a  in order to communicate with the inside of the flexible duct  112 . 
         [0040]    Because of the presence of the valve  130 , the bushing  114   a  is rendered permeable to the liquid flowing through the flexible duct  112  such that the liquid fills the empty space  124  present between the bushings  104   a  and  114   a.    
         [0041]    Because the pressure of the liquid is very nearly equal to the pressure of the gas inside the machine thanks to the flexibility of the duct  112  and/or the pressure compensating balloon  126 , the sealing gasket  122  is subjected on one side to the gas and on the other side to the liquid with a very small pressure difference that does not allow the gas to migrate into the empty space  124 . 
         [0042]    Furthermore, the pressure across the bushing  104   a  is, on one side, a high liquid pressure from the flexible duct  112 , and, on the other side, atmospheric pressure from the outside, typically equal to 1 bar. A bushing of standard manufacture (leak rate under helium of 1E-6 mbar.l/s) is therefore completely hermetically sealed against the liquid and there is no need to fear any migration to the outside.