Magnetic bearing compressor protection

Abstract

A vapor compression system and method for operating the vapor compression system are provided. The vapor compression system includes a first compressor, a second compressor, a condenser, and at least one check valve disposed between the first compressor and the condenser. The method provides for the transmitting of a shutdown command to at least one of the first compressor and the second compressor, at least one of the first compressor and the second compressor including a rotating shaft and a magnetic bearing, the magnetic bearing having an active mode and an inactive mode, the magnetic bearing levitating the rotating shaft in the active mode. The method further provides for the monitoring of at least one of a rotational speed of the rotating shaft and a differential pressure over the check valve for a preset time, wherein the magnetic bearing remains in the active mode at least during the preset time.

What is claimed is: 
     
         1 . A method of operating a vapor compression system comprising a first compressor, a second compressor, a condenser, at least one check valve disposed between the first compressor and the condenser, and an isolation valve positioned between an evaporator and the first compressor, the method comprising:
 transmitting a shutdown command to at least one of the first compressor and the second compressor, at least one of the first compressor and second compressor comprising a rotating shaft and a magnetic bearing, the magnetic bearing comprising an active mode and an inactive mode, the magnetic bearing levitating the rotating shaft in the active mode;   monitoring at least one of a rotational speed of the rotating shaft and a differential pressure over the check valve for a preset time, wherein the magnetic bearing remains in the active mode at least during the preset time; and   closing the isolation valve when the rotational speed of the rotating shaft of the first compressor does not reach the acceptable threshold within the preset time.   
     
     
         2 . The method of  claim 1 , wherein the preset time is less than ten minutes after the shutdown command is transmitted. 
     
     
         3 . The method of  claim 1 , further comprising switching the magnetic bearing from the active mode to the inactive mode when the rotational speed reaches an acceptable threshold. 
     
     
         4 . The method of  claim 3 , wherein the acceptable threshold is less than 50 RPMs. 
     
     
         5 . The method of  claim 1 , further comprising transmitting a shutdown command to the other of the first compressor or the second compressor when the rotational speed does not reach an acceptable threshold within the preset time. 
     
     
         6 . The method of  claim 1 , further comprising activating an alarm when the rotational speed does not reach an acceptable threshold within the preset time.