MONITORING METHOD FOR INDUCTION MOTOR

• US 20150168495A1
• Filed: 06/08/2012
• Published: 06/18/2015
• Est. Priority Date: 06/08/2012
• Status: Active Grant

• Current Assignee: Schneider Electric USA, Inc. (Schneider Electric SE)
• Original Assignee: Schneider Electric USA, Inc. (Schneider Electric SE)
• Inventors: Bickel, Jon A.
• Granted Patent: US 10,718,813 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01R 31/34 Testing dynamo-electric machines
• CPC Class Codes: G01R 31/343 in operation

Abstract

A method of automatically identifying an anomalous condition of an induction motor by normalizing the voltage measured across its terminals relative to the power flow to the motor or the motor'"'"'s impedance. The starting and/or run current and associated voltage of the motor is measured, and a voltage variation between the measured voltage and the motor'"'"'s rated voltage is determined. The power flow or impedance at the voltage variation is calculated to determine an expected power flow or impedance at the measured voltage variation. The actual power flow or impedance is compared against a nominal or expected power flow or impedance or a statistical comparison is carried out on a historical set of power flow or impedance values within an expected range at the voltage variation. When the measured values deviate from the expected ones, an alarm is triggered to indicate a potential anomaly with the motor or external thereto.

Claims

1. A method of automatically determining an anomalous condition of an induction motor, comprising the steps of:

receiving, by an intelligent electronic device, a measured inrush or starting current flowing into an induction motor during a startup period of the induction motor;

receiving, by the intelligent electronic device, a voltage measured across power terminals of the induction motor during the startup period;

determining, using a controller, a voltage variation by comparing the voltage measured across the power terminals with a rated voltage of the induction motor;

calculating, using the controller or another controller, a characteristic function that includes the voltage measured across the power terminals and the inrush or starting current;

comparing, using the controller or another controller, the characteristic function with a baseline using the voltage variation to determine whether a criterion is satisfied; and

responsive to the criterion being satisfied, providing, using the controller or another controller, an indication of an anomalous operation of the induction motor.

2. The method of claim 1, wherein the baseline is a theoretical function that includes a rated inrush or locked-rotor current and the rated voltage, and the comparing includes determining whether the characteristic function deviates from the theoretical function at the same voltage variation.

3. The method of claim 2, wherein the theoretical function is a theoretical impedance of the induction motor operating under rated conditions, the theoretical impedance being calculated using a rated inrush or locked-rotor current and the rated voltage, and wherein the characteristic function is an impedance of the induction motor calculated using the measured current and the voltage measured across the power terminals.

4. The method of claim 2, wherein the theoretical function is a theoretical power flow to the induction motor operating under rated conditions, the theoretical power flow being calculated using a rated inrush current or locked-rotor current and the rated voltage, and wherein the characteristic function is a power flow to the induction motor using the measured current and the voltage measured across the power terminals.

5. The method of claim 4, wherein the power flow to the induction motor is real power, reactive power, or apparent power.

6. The method of claim 1, wherein the baseline is a theoretical function that includes a rated inrush or locked-rotor current and the rated voltage, and the comparing includes a statistical comparison of the characteristic function and historical characteristic functions including historical values of voltage measured across the power terminals and inrush or starting current supplied to the induction motor.

7. The method of claim 1, wherein the measured inrush or starting current and the voltage measured across the power terminals are received responsive to the measured inrush or starting current being applied to the induction motor for energizing the induction motor transitioning the induction motor from a stopped to a starting operating condition.

8. The method of claim 1, wherein the characteristic function is an impedance of the induction motor, and wherein the baseline is a theoretical impedance of the induction motor operating under rated conditions, the theoretical impedance being calculated using a rated inrush or locked-rotor current and the rated voltage.

9. The method of claim 8, wherein the comparing includes determining whether the impedance at the voltage variation deviates from the theoretical impedance at the same voltage variation by more than a threshold, and if so, determining that the criterion is satisfied, wherein the threshold is a fixed threshold, a relative threshold, or a statistical threshold.

10. The method of claim 8, wherein the comparing includes a statistical comparison of the impedance at the voltage variation and a historical impedance value that includes a historical value of a voltage measured across the power terminals and an inrush or starting current supplied to the induction motor prior to the receiving the current.

11. The method of claim 1, wherein the characteristic function is a power flow to the induction motor, and wherein the baseline is a theoretical power flow to the induction motor operating under rated conditions, the theoretical power flow being calculated using a rated inrush or locked-rotor current and the rated voltage, the power flow being calculated using the measured current and the voltage measured across the power terminals.

12. The method of claim 11, wherein the comparing includes determining whether the power flow at the voltage variation deviates from the theoretical power flow at the same voltage variation by more than a threshold, and if so, determining that the criterion is satisfied, wherein the threshold is a fixed threshold, a relative threshold, or a statistical threshold.

13. The method of claim 11, wherein the comparing includes a statistical comparison of the power flow at the voltage variation and a historical power flow value at the same voltage variation, the historical power flow value including a historical value of a voltage measured across the power terminals and an inrush or starting current supplied to the induction motor prior to the receiving the current.

14. The method of claim 1, wherein the indication of the anomaly includes an alarm indicating the amount by which the voltage measured across the power terminals or the measured current deviates from the rated voltage or a rated locked-rotor current of the induction motor.

15. The method of claim 1, wherein the indication of the anomaly includes whether an impedance of the induction motor at the voltage variation during the startup period is above or below an expected impedance of the induction motor at the voltage variation, the impedance being calculated using the measured current and the voltage measured across the power terminals, and the expected impedance at the voltage variation being calculated or derived based on a rated inrush or locked-rotor current of the induction motor and the rated voltage including the voltage variation.

16. The method of claim 15, wherein, responsive to the impedance exceeding the expected impedance, the anomaly indicates potential damage to a rotor or a rotor bar of the induction motor, a potential poor connection relative to one or both power terminals of the induction motor or to a stator winding of the induction motor.

17. The method of claim 15, wherein, responsive to the impedance being below the expected impedance, the anomaly indicates a potential short-circuit in a winding of a coil around a pole of the induction motor or between adjacent coils of the induction motor or a potential insulation breakdown in the induction motor.

18. The method of claim 1, further comprising:

receiving, by the intelligent electronic device, a measured steady-state current flowing into the induction motor during a steady-state operation of the induction motor;

receiving, by the intelligent electronic device, a second steady-state voltage measured across the power terminals during the steady-state operation;

determining, using the controller or another controller, a steady-state voltage variation by comparing the measured steady-state voltage with the rated voltage;

calculating, using the controller or another controller, a second characteristic function that includes the measured steady-state voltage and the measured steady-state current;

comparing, using the controller or another controller, the second characteristic function with a second baseline using the steady-state voltage variation to determine whether a steady-state criterion is satisfied; and

responsive to the steady-state criterion being satisfied, providing, using the controller or another controller, the indication of the anomaly.

19. A non-transitory computer-readable medium encoded with instructions to cause one or more controllers to implement a method, the method comprising:

receiving a measured inrush or starting current flowing into an induction motor during a startup period of the induction motor;

receiving a voltage measured across power terminals of the induction motor during the startup period;

determining a voltage variation by comparing the voltage measured across the power terminals with a rated voltage of the induction motor;

calculating a characteristic function that includes the voltage measured across the power terminals and the inrush or starting current;

comparing the characteristic function with a baseline using the voltage variation to determine whether a criterion is satisfied; and

responsive to the criterion being satisfied, providing an indication of an anomaly of the induction motor.

20. A method of automatically determining an anomalous condition of an induction motor, comprising the steps of:

receiving, by an intelligent electronic device, an inrush or starting current flowing into and a voltage measured across power terminals of an induction motor at an initial startup period of the induction motor;

comparing, by the intelligent electronic device, the received voltage with a rated voltage of the induction motor to produce a voltage variation;

calculating, using a controller, a characteristic function that includes the received voltage and the inrush or starting current;

comparing, using the controller or another controller, the characteristic function with a baseline using the voltage variation to determine whether a first criterion is satisfied;

receiving, by the intelligent electronic device, a steady-state current flowing into and a second voltage measured across the power terminals during a steady-state operation of the induction motor;

comparing, using the controller or another controller, the second received voltage with the rated voltage to produce a second voltage variation;

calculating, using the controller or another controller, a second characteristic function that includes the second received voltage and the steady-state current;

comparing, using the controller or another controller, the second characteristic function with a second baseline using the second voltage variation to determine whether a second criterion is satisfied; and

responsive to the first criterion or the second criterion being satisfied, providing, using the controller or another controller, an indication of an anomalous condition of the induction motor.