FAULT DETECTION IN INDUCTION MACHINES

• US 20150260794A1
• Filed: 02/19/2015
• Published: 09/17/2015
• Est. Priority Date: 03/11/2014
• Status: Active Grant

• Current Assignee: Rolls-Royce PLC (Rolls-Royce Holdings Plc)
• Original Assignee: Rolls-Royce PLC (Rolls-Royce Holdings Plc)
• Inventors: NADARAJAN, Sivakumar, GUPTA, Amit Kumar, ATHIKESSAVAN, Subash C., PANDA, Sanjib K.
• Granted Patent: US 10,267,860 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01R 31/343 in operation

Abstract

A method of detecting a fault in an induction machine having one or more windings arranged to draw current at a supply frequency, the method including: performing a process of judging whether a respective sideband of one or more selected harmonics of the supply frequency exists at a predetermined fault frequency in a signal in the one or more windings; and determining that a fault has occurred if the judgement is positive; wherein in the judging process each of the selected harmonics of the supply frequency is a harmonic frequency of the supply frequency other than the supply frequency itself.

Claims

1. A method of detecting a fault in an induction machine having one or more windings arranged to draw current at a supply frequency, the method comprising:

performing a process of judging whether a respective sideband of one or more selected harmonics of the supply frequency exists at a predetermined fault frequency in a signal in the one or more windings; and

determining that a fault has occurred if the judgement is positive;

wherein in the judging process each of the selected harmonics of the supply frequency is a harmonic frequency of the supply frequency other than the supply frequency itself; and

determining whether the power distribution of at least one of the selected harmonics to its sidebands is below a predetermined threshold; and

determining the fault type based on the determination.

2. A method of detecting a fault in an induction machine according to claim 1 including the step of assessing whether the magnitude of the sideband exceeds a predetermined threshold, and determining that a fault has occurred if the assessment is positive.

3. A method of detecting a fault in an induction machine according to claim 1 wherein the method includes modifying the signal to include the one or more selected harmonics as one or more probe harmonics.

4. A method of detecting a fault in an induction machine according to claim 3 wherein the judgement step includes the step of judging whether a sideband of at least one of the one or more probe harmonics exists at the predetermined fault frequency in the signal in one or more windings of the induction machine.

5. A method of detecting a fault in an induction machine according to claim 1 including the step of generating the predetermined fault frequency (f_brb) on the basis of the following equation:

f_brb=(f_h±

2ksf_s), Where k=1, 2, 3, . . .

where, f_s is the supply frequency, f_h is the frequency corresponding to the h^th order harmonic of the supply frequency, and s is the slip of the induction machine.

6. A method of detecting a fault in an induction machine according to claim 1 further including the step of acquiring the frequency spectrum of the signal in order to perform the judgement step.

7. A method of detecting a fault in an induction machine according to claim 6 including the step of calculating the slip of the induction machine on the basis of the acquired frequency spectrum.

8. A method of detecting a fault in an induction machine according to claim 1 wherein the induction machine includes a stator, the one or more windings being located on the stator.

9. A method of detecting a fault in an induction machine according to claim 1, wherein the induction machine is an induction motor, and the fault is in a rotor bar of the motor;

or wherein the induction machine is a generator, and the fault is in a damper bar of the generator.

10. A method of detecting a fault in an induction machine according to claim 1, wherein the fault type is a broken rotor bar fault when the power distribution is below the threshold and is an air gap eccentricity when the power distribution is above the threshold.

11. A fault detector for detecting a fault in an induction machine having one or more windings arranged to draw current at a supply frequency, the fault detector comprising:

a sensor for acquiring a measurement of a signal in the one or more windings, and for transmitting an output indicative of the frequency spectrum of the measured signal;

a processor arranged to receive the transmitted output, and arranged to perform the method according to claim 1.

12. A fault detector according to claim 11 further including a signal modifier arranged to modify the signal to include the one or more selected harmonics as one or more probe harmonics.

13. A fault detector according to claim 11, wherein the induction machine is an induction motor, and the fault is in a rotor bar of the motor;

or wherein the induction machine is a generator, and the fault is a damper bar of the generator.

14. A fault detector according to claim 11, wherein the one or more windings are arranged to draw the current at the supply frequency to drive rotation of a rotor.

15. A fault detector in an induction machine according to claim 11, wherein the signal is at least a component of said drawn current.