Patent Application
20140077665
The invention is directed to pressurized gas cooled motors which directly drive a centrifugal compressor and, more particularly, to a wound stator design for such motors that can be removed from the motor enclosure (pressure vessel). The invention further involves a stator arrangement that facilitates removal of the stator and rotor, simultaneously.
Removable stators have been proposed for conventional motor designs. For example, it is known to axially position a removable stator using chamfered centering rings provided in the stator and clamped between mating chamfered shoulders provided in the motor casing and a clamping ring. In addition to requiring accurate centering, such an arrangement does not provide a significant allowance for relative thermal expansion that occurs in pressurized gas cooled motor assemblies.
It has also been proposed to position a removable stator axially and retain the stator in position both angularly and elastically using a wave spring. Such an arrangement includes centering and clamping by using centering rings provided in the stator in addition to a series of offset recesses in the casing used for angular positioning by engaging the spring. As such this arrangement also does not provide a significant allowance for relative thermal expansion that occurs in pressurized gas cooled motor assemblies.
It is desirable to have the ability to replace a wound stator in an integrated compressor assembly without disconnecting high pressure piping from the motor enclosure or pressure vessel. In such high pressure, integrated compressor assemblies it would be advantageous to be able to provide spare stators for easy replacement of failed stators.
In the exemplary embodiments disclosed in detail hereafter it is now proposed to use a pressurized gas cooled integrated motor-compressor unit which allows for removal of the stator core alone or simultaneously with the rotor without the need to disconnect the high pressure piping. The wound stator fits to the pressure vessel utilizing a small diametrical clearance which facilitates assembly and disassembly.
In an exemplary embodiment, an original spring loaded axial retention mechanism is disposed within a concentric groove made for this purpose in the thick-walled pressure vessel that serves as a motor enclosure. Mechanisms for the positioning and retention of the removable stator include: a shoulder provided in the pressure vessel for axial positioning and a key system for angular positioning and retention which are suitably sized to bear the torque.
More particularly, the wound stator is located axially by the shoulder in the pressure vessel. The spring loaded axial retention mechanism produces an axial force sufficient to restrain the stator from movement under operational and fault torques, and further serves to restrain the stator during transport. The spring loaded mechanism has enough axial movement to accommodate the differential thermal growth of the stator with respect to the pressure vessel during operation.
The key system maintains the angular location of the wound stator within the pressure vessel so that it does not turn or rotate through any appreciable angle within the pressure vessel during transport or under operating conditions.
The diametrical clearance is selected to minimize the eccentricity of the stator to the rotor and, therefore, limit unbalanced magnetic forces. The diametrical clearance is sufficiently large to prevent the thermal expansion of the stator from imposing excessive stresses on the pressure vessel. Tooling is provided to assist in the assembly and disassembly of the wound stator (and rotor) to and from the pressure vessel.
In accordance with the exemplary embodiments described herein the wound stator of an electric motor can be removed from the pressure vessel for service or replacement. Should an original wound stator require service, a spare wound stator can replace the original and allow the customer to keep the motor/compressor assembly in service and production.
After the rotor and stator are moved into position by tooling 31, the banding is removed. The carrier assemblies 62 then move radially into pressure vessel groove 35, as shown in
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
