System for protecting bearings and seals of refrigerant compressor

Abstract

To protect the bearings, lubricant and seals of a refrigerant compressor, the compressor includes one or more inductors for mitigating a high frequency common mode current that produces a high frequency shaft voltage. Each inductor is a ring of magnetic material encircling three insulated cables that convey three-phase power from an adjustable frequency drive to the compressor's motor. Without the inductors, the high frequency shaft voltage can become damagingly high due to the length of a cast iron housing that can be particularly long if the housing contains both a motor and several centrifugal impellers. The high frequency shaft voltage is just one component of a composite adverse shaft voltage. Another component, known as an operationally induced shaft voltage, can be reduced by a grounding contact, so instead of using just an inductor or just a contact, both can be used to provide a total solution to the problem.

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         39 . A method of retrofitting a compressor system, wherein the compressor system comprises a housing; a sight glass supported by the housing in an aperture; a motor that includes a rotor, a shaft extending from the rotor, a stator winding disposed within the housing in proximity with the rotor, and a bearing supporting the shaft and the rotor within the housing; a compressing element disposed within the housing and being coupled to the rotor such that rotation of the rotor motivates the compressing element to compress a refrigerant; an adjustable frequency drive that provides the stator winding with three-phase electrical power to rotate the rotor; and three conductors electrically coupling the adjustable frequency drive to the stator winding such that the three conductors can convey the three-phase electrical power to the stator winding; the method comprising:
 removing the sight glass from the aperture; and   inserting a grounding contact device into the aperture such that the grounding contact device is in electrical contact with the shaft.   
     
     
         40 . The method of  claim 39 , further comprising encircling the three conductors with an inductor made of a magnetic material. 
     
     
         41 . The method of  claim 39  wherein the compressor system includes a ground return path conductor extending between the adjustable frequency drive and the housing, the ground return path conductor is made of an electrically conductive material that has greater electrical conductivity than an iron-based material of which the housing is made, the method further comprising encircling the three conductors with an inductor made of a magnetic material while leaving the ground return path conductor lie outside the inductor, whereby the inductor does not encircle the ground return path conductor. 
     
     
         42 . A method of retrofitting a functional compressor system, wherein the functional compressor system comprises a housing; a motor that includes a rotor, a shaft extending from the rotor, a stator winding disposed within the housing in proximity with the rotor, and a bearing supporting the shaft and the rotor within the housing; a compressing element disposed within the housing and being coupled to the rotor such that rotation of the rotor motivates the compressing element to compress a refrigerant; an adjustable frequency drive that provides the stator winding with three-phase electrical power to rotate the rotor; and three conductors electrically coupling the adjustable frequency drive to the stator winding such that the three conductors can convey the three-phase electrical power to the stator winding; the method comprising:
 temporarily disabling the functional compressor system;   temporarily disconnecting the three conductors;   inserting the three conductors through an annular inductor;   reconnecting the three conductors; and   restoring operation to the functional compressor system.   
     
     
         43 . The method of  claim 42 , further comprising:
 operating the functional compressor system without the annular inductor;   prior to temporarily disconnecting the three conductors, generating a first high frequency common mode voltage that drives a first high frequency common mode current through the housing; and   after reconnecting the three conductors and restoring operation to the functional compressor system, generating a second high frequency common mode voltage that drives a second high frequency common mode current through the housing, wherein a voltage ratio of the first high frequency common mode voltage to the second high frequency common mode voltage may not be the same as a current ratio of the first high frequency common mode current to the second high frequency common mode current.   
     
     
         44 . The method of  claim 42 , further comprising:
 prior to temporarily disconnecting the three conductors, operating the functional compressor system without the annular inductor and generating a first high frequency common mode voltage that drives a first high frequency common mode current through the housing; and   after reconnecting the three conductors and restoring operation to the functional compressor system, operating the functional compressor system with the annular inductor and generating a second high frequency common mode voltage that drives a second high frequency common mode current through the housing, wherein:   a) the first high frequency common mode voltage is at a first frequency,   b) the second high frequency common mode voltage is at a second frequency,   c) the first high frequency common mode current is at a third frequency,   d) the second high frequency common mode current is at a fourth frequency, and   e) a first ratio of the first frequency to the second frequency may not be the same as a second ratio of the third frequency to the fourth frequency.   
     
     
         45 . The method of  claim 42  wherein the compressor system includes a ground return path conductor extending between the adjustable frequency drive and the housing, the ground return path conductor is made of an electrically conductive material that has greater electrical conductivity than an iron-based material of which the housing is made, the method further comprising leaving the ground return path conductor lying outside the annular inductor, whereby the annular inductor does not encircle the ground return path conductor. 
     
     
         46 . The method of  claim 42  wherein the inserting step comprises the further steps of: selecting the annular inductor from a ring of magnetic material that is selectively configurable to an open position and a closed position; positioning the ring of magnetic material adjacent to the three conductors while the ring of magnetic material is in the open position; and reconfiguring the ring of magnetic material to the closed position so that the ring of magnetic material encircles the three conductors, thereby installing the annular inductor. 
     
     
         47 . The method of  claim 46  further including the steps of: removing a sight glass from an aperture in the housing; and adding a grounding contact device to the aperture such that the grounding contact device is in electrical contact with the shaft. 
     
     
         48 . The method of  claim 46  wherein the inductor selecting step includes forming the inductor from a number of inductors such that the number of inductors is sufficient to reduce the common mode current.