Method and apparatus for measuring bearing currents in an electrical machine
View Patent ↗The present disclosure relates to a measuring bearing currents in an electrical machine. According to exemplary embodiments, radio frequency signals that are generated by electric discharges are detected by an antenna near the bearing. A synchronizing signal is combined with the origin of the bearing current and signal triggered by the synchronizing signal is measured.
1. A method for measuring a bearing current in an electrical machine, wherein electric discharges are generated, the electrical machine including a stator fixed to a frame of the electrical machine, and a rotor that is arranged to rotate around its axis and that is supported to the frame by bearings, where an electric discharge burst occurs when a voltage over a lubricating film is high and the electric discharge generates a radio frequency signal, whereby radio frequency signals are received by an antenna near a location of the electric discharge, the method comprising:
generating a synchronizing signal dependent in time on an origin of the electric discharge based on a switching frequency received from a converter that controls the electric machine;
triggering a radio frequency signal detecting equipment in response to the synchronizing signal; and
registering a radio frequency signal that matches to the synchronizing signal as a signal representing the bearing current.
2. Method according to the claim 1 , comprising:
monitoring a time-window defined on a basis of a frequency of the synchronizing signal.
3. Method according to the claim 1 , comprising:
integrating or counting plural radio frequency signals.
4. Method according to the claim 1 , wherein the converter includes a plurality of electronic switches that are controlled by high frequency pulse width modulation (PWM) pulses.
5. Method according to claim 4 , wherein the generating of the synchronizing signal comprises generating the synchronizing signal by conducting trigger signals of the switches in the converter.
6. Method according to claim 1 , wherein the generating of the synchronizing signal comprises generating the synchronizing signal based on a sensor detecting a common mode current or common mode voltage.
7. An apparatus for measuring bearing currents by monitoring an electric discharge generated in an electrical machine that includes a stator fixed to a frame of the electrical machine, and a rotor that is arranged to rotate around its axis and that is supported to the frame by bearings, whereby an electric discharge bursts over the bearing when a voltage over a lubricant film is too high and the electric discharge generates a radio frequency signal, the apparatus comprising:
an antenna for placement near a location of electric discharge for receiving the radio frequency signal;
a device for generating a synchronizing signal that is dependent in time on an origin of the electric discharge;
a detector device that is triggered based on the synchronizing signal; and
a registration component for displaying or storing a radio frequency signal that matches to the synchronizing signal,
wherein the device for generating the synchronizing signal includes an input for receiving a switching frequency from a converter that controls the machine.
8. Apparatus according to the claim 7 , comprising:
a sensor for detecting a common mode current or common mode voltage for generating the synchronizing signal.
9. Apparatus according to claim 8 , comprising:
an oscilloscope for displaying a voltage proportional to bearing current.
10. Apparatus according to claim 8 , comprising:
a pulse counter or integrator for defining a parameter proportional to a malfunction of the bearing.
11. Apparatus according to claim 7 , comprising:
an oscilloscope for displaying a voltage proportional to bearing current.
12. Apparatus according to claim 11 , comprising:
a pulse counter or integrator for defining a parameter proportional to a malfunction of the bearing.
13. Apparatus according to claim 7 , comprising:
a pulse counter or integrator for defining a parameter proportional to a malfunction of the bearing.
14. Apparatus according to claim 7 , comprising:
an oscilloscope for displaying a voltage proportional to bearing current.
15. Apparatus according to claim 7 , comprising:
a pulse counter or integrator for defining a parameter proportional to a malfunction of the bearing.
16. Apparatus according to claim 7 , in combination with an electric machine comprising:
a stator fixed to a frame of the electrical machine; and
a rotor that is arranged to rotate around its axis and that is supported to the frame by bearings, whereby an electric discharge bursts over the bearing when a voltage over a lubricant film is too high and the electric discharge generates a radio frequency signal.
17. Apparatus according to the claim 7 , wherein the converter includes a plurality of electronic switches that are controlled by high frequency pulse width modulation (PWM) pulses.
18. Apparatus according to claim 17 , wherein the device for generating the synchronizing signal is configured to generate the synchronizing signal by conducting trigger signals of the switches in the converter.
19. Apparatus according to claim 7 , wherein the device for generating the synchronizing signal is configured to generate the synchronizing signal based on a sensor detecting a common mode current or common mode voltage.