Integral motor pump or turbine with sensorless monitoring of axial bearing wear
Axial bearing wear of a directly driven, axial, integral motor pump (IMP) or integral motor turbine (IMT) is monitored without use of sensors by estimating an axial rotor-stator gap according to a known dependence of the back EMF on the impeller rotation rate and the rotor-stator gap. The back EMF can be directly measured, for example between impulses of a variable frequency drive (VFD), or inferred from measurements of voltage applied to IMP stator coils and the resulting current. The rotation rate of an IMT impeller can be determined from a modulation frequency of the EMF. The rotation rate of an IMP impeller can be inferred due to its synchronicity with the applied, amplitude modulated power. A controller can record and report rotor-stator gap estimates over time, and can halt operation of the module if the estimated rotor-stator gap falls outside of a specified range.
1. A bearing wear monitoring system for an integral motor pump (IMP) or integral motor turbine (IMT), the system comprising:
a module including:
a module housing configured to enable a fluid to pass from an input of the module housing to an output of the module housing;
a stator housing fixed within the module housing;
a shaft extending axially from the stator housing;
an impeller;
a bearing fixed to the impeller so as to enable the impeller to rotate about the shaft;
a plurality of induction coils or permanent magnets fixed to the impeller so as to pass in proximity to the stator housing when the impeller rotates about the shaft;
a plurality of stator coils fixed within the stator housing so as to be proximate the plurality of induction coils or permanent magnets as the plurality of induction coils or permanent magnets passes in proximity to the stator housing, the plurality of induction coils or permanent magnets and the plurality of stator coils facing each other so as to define an axial rotor-stator gap as the plurality of induction coils or permanent magnets passes in proximity to the plurality of stator coils;
a magnetic thrust limiter fixed to the stator housing so as to resist an axial magnetic thrust of the plurality of induction coils or permanent magnets toward the plurality of stator coils by applying an opposing mechanical force to the bearing, the magnetic thrust limiter thereby maintaining the rotor-stator gap when the magnetic thrust is greater than an axial hydraulic thrust of the impeller; and
a power source or power load electrically cooperative with the plurality of stator coils; and
a controller configured to:
determine a magnitude of a back electro-motive force (EMF) generated as the plurality of induction coils or permanent magnets passes in proximity to the plurality of stator coils;
determine a rotation rate of the impeller;
estimate a magnitude of the rotor-stator gap based on the rotation rate of the impeller and the magnitude of the back EMF;
estimate a wear status of the magnetic thrust limiter based on the estimated magnitude of the rotor-stator gap when the magnetic thrust is greater than the hydraulic thrust; and
at least one of:
communicate the estimated magnitude of the rotor-stator gap to a user; and
cause the module to cease operation when the estimated magnitude of the rotor-stator gap falls below a specified threshold.
2. The system of claim 1 , wherein the shaft is fixed to the stator housing.
3. The system of claim 1 , wherein the magnetic thrust limiter resists the axial magnetic thrust by contacting the bearing.
4. The system of claim 1 , wherein the determining of the magnitude of the back EMF includes directly measuring the back EMF.
5. The system of claim 4 , wherein:
the module is an IMP module including the power source;
the power source is a variable frequency drive (VFD); and
the back EMF is directly measured during intervals between power impulses emitted by the VFD.
6. The system of claim 1 , wherein:
the module is an IMP module including the power source; and
the determining of the magnitude of the back EMF includes calculating the back EMF based on a voltage applied to the plurality of stator coils by the power source and a current flowing through the plurality of stator coils.
7. The system of claim 1 , wherein:
the module is an IMT module including the power load; and
the determining of the rotation rate of the impeller includes directly measuring the back EMF and determining a periodicity of an amplitude modulation of the back EMF.
8. The system of claim 1 , wherein:
the module is an IMP module including the power source;
the rotation of the impeller is synchronous with an amplitude modulation of a voltage applied to the plurality of stator coils by the power source; and
the determining of the rotation rate of the impeller includes deducing the rotation rate based on a modulation frequency of the amplitude modulation.
9. The system of claim 1 , wherein the module further includes a hydraulic thrust limiter fixed to the shaft so as to resist the hydraulic thrust of the impeller by applying an opposing mechanical force to the bearing, the hydraulic thrust limiter thereby maintaining the rotor-stator gap when the hydraulic thrust is greater than the magnetic thrust.
10. The system of claim 9 , wherein the controller is further configured to:
estimate, based on the rotation rate of the impeller and the magnitude of the back EMF, a minimum magnitude of the rotor-stator gap when the magnetic thrust is greater than the hydraulic thrust, and a maximum magnitude of the rotor-stator gap when the hydraulic thrust is greater than the magnetic thrust;
estimate the wear status of the magnetic thrust limiter based on the estimated magnitude of the rotor-stator gap when the magnetic thrust is greater than the hydraulic thrust; and
estimate a wear status of the hydraulic thrust limiter based on the estimated magnitude of the rotor-stator gap when the hydraulic thrust is greater than the magnetic thrust.
11. The system of claim 1 , wherein the controller is further configured to cause the module to cease operation when the estimated magnitude of the rotor-stator gap falls below the specified threshold.
12. A method of monitoring bearing wear of an integral motor pump (IMP) or integral motor turbine (IMT), the method comprising:
providing a module including:
a module housing configured to enable a fluid to pass from an input of the module housing to an output of the module housing;
a stator housing fixed within the module housing;
a shaft extending axially from the stator housing;
an impeller;
a bearing fixed to the impeller so as to enable the impeller to rotate about the shaft;
a plurality of induction coils or permanent magnets fixed to the impeller so as to pass in proximity to the stator housing when the impeller rotates about the shaft;
a plurality of stator coils fixed within the stator housing so as to be proximate the plurality of induction coils or permanent magnets as the plurality of induction coils or permanent magnets passes in proximity to the stator housing, the plurality of induction coils or permanent magnets and the plurality of stator coils facing each other so as to define an axial rotor-stator gap as the plurality of induction coils or permanent magnets passes in proximity to the plurality of stator coils; and
a magnetic thrust limiter fixed to the stator housing so as to resist an axial magnetic thrust of the impeller by applying an opposing force to the bearing, the magnetic thrust limiter thereby maintaining the rotor-stator gap when the magnetic thrust is greater than an axial hydraulic thrust of the impeller;
determining a magnitude of a back electro-motive force (EMF) generated as the plurality of induction coils or permanent magnets passes in proximity to the plurality of stator coils;
determining a rotation rate of the impeller;
estimating a magnitude of the rotor-stator gap based on the rotation rate of the impeller and the magnitude of the back EMF;
estimating a wear status of the magnetic thrust limiter based on the estimated magnitude of the rotor-stator gap when the magnetic thrust is greater than the hydraulic thrust; and
at least one of:
communicating the estimated magnitude of the rotor-stator gap to a user; and
causing the module to cease operation when the estimated magnitude of the rotor-stator gap falls below a specified threshold.
13. The method of claim 12 , wherein the determining of the magnitude of the back EMF includes directly measuring the back EMF.
14. The method of claim 13 , wherein:
the module is an IMP module which further includes a power source configured as a variable frequency drive (VFD); and
the determining of the magnitude of the back EMF includes directly measuring the magnitude of the back EMF during intervals between power impulses emitted by the VFD.
15. The method of claim 12 , wherein:
the module is an IMP module; and
the determining of the magnitude of the back EMF includes calculating the back EMF based on a voltage applied to the plurality of stator coils and a current flowing through the plurality of stator coils.
16. The method of claim 12 , wherein:
the module is an IMT module; and
the determining of the rotation rate of the impeller includes directly measuring the back EMF and determining a periodicity of an amplitude modulation of the back EMF.
17. The method of claim 12 , wherein:
the module is an IMP module;
the rotation of the impeller is synchronous with an amplitude modulation of a voltage applied to the plurality of stator coils; and
the determining of the rotation rate of the impeller includes deducing the rotation rate based on a modulation frequency of the amplitude modulation.
18. The method of claim 12 , wherein:
the module further includes a hydraulic thrust limiter fixed to the shaft so as to resist the hydraulic thrust of the impeller by applying an opposing mechanical force to the bearing, the hydraulic thrust limiter thereby maintaining the rotor-stator gap when the hydraulic thrust is greater than the magnetic thrust; and
the method further comprises:
estimating the magnitude of the rotor-stator gap based on the rotation rate of the impeller and the magnitude of the back EMF when the hydraulic thrust is greater than the magnetic thrust; and
estimating a wear status of the hydraulic thrust limiter based on the estimated magnitude of the rotor-stator gap when the hydraulic thrust is greater than the magnetic thrust.
19. The method of claim 12 , wherein the communicating of the estimated magnitude of the rotor-stator gap to the user includes at least one of:
visually displaying the estimated magnitude of the rotor-stator gap;
transmitting the estimated magnitude of the rotor-stator gap to a device that is accessible to the user; and
recording the estimated magnitude of the rotor-stator gap on non-transient media that is accessible to the user.
20. The method of claim 12 , wherein the method includes the causing of the module to cease operation when the estimated magnitude of the rotor-stator gap falls below the specified threshold.