Hermetic motor cooling and control

Abstract

An apparatus and method for cooling a compressor motor ( 152 ) having a motor stator ( 162 ) and cooling a rotor ( 166 ) in a refrigerant system ( 100 ). The method cools the rotor and the stator, electromagnetic bearings ( 160 ) located within a compressor housing by providing refrigerant liquid to the stator internal channels, the channels being in fluid communication with a rotor passageway ( 172 ), and a flow-control device ( 168 ) controlling refrigerant flow into the stator. A temperature monitoring device ( 176 ) in communication with a controller ( 140 ) monitors motor temperature. The controller ( 140 ) evaluates the motor temperature and adjusts refrigerant flow through the flow control device ( 168 ), maintaining the motor ( 152 ) within a predetermined temperature range.

What is claimed is: 
     
         1 . A compressor assembly comprising:
 a compressor housing;   a compressor ( 100 ) positioned within the housing;   a compressor inlet, to input refrigerant gas to the compressor ( 100 );   a motor ( 152 ), the motor comprising
 a motor housing, 
 a stator ( 162 ) positioned within the motor housing, the stator having windings and cooling channels ( 164 ), 
 a rotor ( 166 ) positioned within the stator ( 162 ), the rotor having a shaft having a first end connected to an impeller ( 102 ) the compressor and a second end, 
 wherein when electrical current is applied to the stator windings, the rotor ( 166 ) rotates, causing the compressor ( 100 ) to operate; 
 electromagnetic bearings ( 160 ) positioned at both ends of the rotor ( 166 ) to support the rotor when current is applied to the stator windings; 
   the motor ( 152 ) further including
 a temperature monitoring device ( 176 ) positioned within the stator; 
 a stator inlet ( 186 ) and a stator outlet ( 190 ), the stator inlet receiving liquid refrigerant for cooling the stator ( 162 ), 
 a rotor inlet ( 192 ), a rotor liquid ( 170 ) drain and a rotor gas vent ( 174 ), the rotor inlet receiving refrigerant from the stator outlet ( 190 ); 
 a flow control device ( 168 ) positioned to control the flow of refrigerant within the stator ( 162 ) in response to the temperature of the stator ( 162 ) and the rotor ( 166 ) as provided by the temperature monitoring device ( 176 ). 
   
     
     
         2 . The compressor assembly of  claim 1  wherein the compressor ( 100 ) is a centrifugal compressor having an impeller ( 102 ) connected to the rotor shaft and positioned within the compressor housing. 
     
     
         3 . The compressor assembly of  claim 1  wherein the stator temperature monitoring device ( 176 ) is a thermistor. 
     
     
         4 . The compressor assembly of  claim 2  wherein electromagnetic bearings ( 160 ) are positioned at both ends of the rotor ( 166 ) to support the rotor. 
     
     
         5 . The compressor assembly of  claim 1  wherein the liquid refrigerant to cool the motor ( 152 ) is provided from a subcooler ( 124 ). 
     
     
         6 . The compressor assembly of  claim 1  further including a controller ( 140 ) to regulate the flow of liquid refrigerant through the flow control device ( 168 ) in response to the temperature of the stator ( 162 ) as provided by the temperature monitoring device ( 176 ). 
     
     
         7 . The compressor assembly of  claim 6  further including a rotor temperature monitoring device ( 178 ) positioned within the rotor ( 166 ) to provide the rotor temperature to the controller to regulate the flow of liquid refrigerant through the flow control device ( 168 ) in response to the temperature of the stator ( 162 ) and the rotor ( 166 ). 
     
     
         8 . The compressor assembly of  claim 7  wherein the rotor temperature monitoring device ( 178 ) is positioned adjacent a rotor gap ( 172 ). 
     
     
         9 . The compressor assembly of  claim 7  wherein the rotor temperature monitoring device ( 178 ) is a thermistor. 
     
     
         10 . The compressor assembly of  claim 1  wherein the flow control device ( 168 ) is an expansion valve. 
     
     
         11 . A method for cooling a compressor motor ( 152 ) in a refrigeration system comprising the steps of:
 providing a compressor motor ( 152 ) having a stator ( 162 ) and a rotor ( 166 ), the rotor having a shaft, and the compressor motor in fluid communication with a source of high pressure subcooled, refrigerant liquid;   providing a flow of high pressure refrigerant liquid to the stator;   monitoring the temperature of the stator;   circulating the refrigerant liquid through the stator to remove heat from the stator to maintain the temperature of the stator within a predetermined range;   lowering the pressure of the high pressure refrigerant prior to providing the refrigerant to the rotor;   providing the refrigerant to the rotor;   circulating the refrigerant through the rotor to remove heat from the rotor;   adjusting a flow of refrigerant to the stator to maintain the temperature of the stator within the predetermined range;   returning liquid refrigerant exiting the stator and not entering the rotor to an evaporator; and   returning refrigerant exiting the rotor to the evaporator.   
     
     
         12 . The method of  claim 11  further including the steps of
 monitoring the temperature of the rotor; and 
 circulating the refrigerant through the rotor to remove heat from the rotor to maintain the temperature of the rotor within a predetermined range. 
 
     
     
         13 . The method of  claim 11  wherein the step of maintaining the temperature of the stator within a predetermined range includes maintaining the temperature of the stator above a dew point of the ambient atmosphere and below a safety device activation temperature. 
     
     
         14 . The method of  claim 13  further including the steps of
 providing a controller ( 140 ); 
 providing a flow control device ( 168 ) in communication with the controller; 
 providing a stator temperature monitoring device ( 176 ) in communication with the controller ( 140 ); 
 providing a rotor temperature monitoring device ( 178 ) in communication with the controller ( 140 ); and 
 wherein the step of adjusting the flow of refrigerant further includes providing a signal from the stator temperature monitoring device ( 176 ) to the controller ( 140 ) indicative of the stator temperature, providing a signal from the rotor temperature monitoring device ( 178 ) to the controller ( 140 ) indicative of the rotor temperature, the controller determining whether the stator temperature is within a predetermined temperature range an whether the rotor temperature is within a predetermined temperature range, the controller sending a signal to the flow control device ( 168 ) to adjust the flow of refrigerant when the stator temperature or the rotor temperature is not within the predetermined temperature range. 
 
     
     
         15 . The method of  claim 11  further including the step of providing a subcooler ( 124 ) in fluid communication with a condenser ( 116 ) and the stator ( 162 ), the subcooler providing high pressure subcooled refrigerant liquid to the stator.