Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
2000-05-30
2003-01-14
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C324S076220
Reexamination Certificate
active
06507797
ABSTRACT:
BACKGROUND
The invention relates generally to direct current machines and more particularly to direct current machine monitoring systems.
A degraded commutator of a direct current (dc) machine will show excessive sparking as brushes bounce over the rough surface and the conduction period for a particular segment ends prematurely or as a winding remains shorted for too long by a spark region which extends between segments. Ultimately a short circuit will develop, through an extended spark region over the commutator bars, between opposite-polarity brushes. This “flashover” is often severe enough to destroy the machine. Sparking can additionally be caused by factors such as worn down brushes, improper brush positioning, or load or supply problems, for example.
On-line monitoring of commutation quality degradation as a measure of brush and/or commutator degradation or wear, for example, or as a precursor to flashover in dc machines can provide a significant advantage in steel mill, paper mill, and locomotive applications, for example, wherein visual inspection during operation is unsafe or otherwise impractical. As described in Michael P. Treanor and Gerald B. Kliman, “INCIPIENT FAULT DETECTION IN LOCOMOTIVE DC TRACTION MOTORS,” Proceedings of the 49
th
Meeting of the Society for Machinery Failure Prevention Technology, Virginia Beach, Va., April 1995, pp. 221-230, machine condition monitoring for poor commutation can be achieved by frequency-domain analysis of machine current at the frequency of bar passing. The bar-passing frequency can be determined by multiplying the number of commutator bars by the speed (rotation frequency) of the motor. The magnitude of the peak at the bar-passing frequency increased by a factor of at least two when the commutation quality was degraded by incorrectly aligning the brushes. To provide an unambiguous determination of the bar passing frequency, the speed of the motor needs to be obtained with sufficient certainty and precision.
Additionally, once an assessment of commutation quality has been made, it would further be advantageous to assess whether the cause of any degradation resulted from commutator roughness or distortion as compared with non-commutator factors such as brush wear, improper positioning of brushes, or load or supply problems. By identifying the cause, proper maintenance and/or repair can be initiated.
BRIEF SUMMARY
Briefly, in accordance with one embodiment of the present invention, a system for determining a rotation frequency of a direct current machine comprises (a) a sensor for monitoring load current of the machine; and (b) a computer for (i) obtaining a first power spectrum of the load current, (ii) identifying significant peaks of the power spectrum, (iii) identifying one of the significant peaks as indicative of rotation frequency, and (iv) identifying a frequency of the identified peak as the rotation frequency.
In accordance with another embodiment of the present invention, a direct current machine monitoring system comprises (a) a current sensor for monitoring load current of the machine; and (b) a computer for (i) obtaining a power spectrum in a range including a machine trait-passing frequency, (ii) determining a magnitude of a maximum peak in the power spectrum in a range including the trait-passing frequency plus or minus an uncertainty frequency, and (iii) evaluating the magnitude of the maximum peak to assess a condition of the machine.
In accordance with another embodiment of the present invention, a direct current machine monitoring system comprises (a) a current sensor for monitoring load current of the machine; and (b) a computer for (i) obtaining a low frequency power spectrum of the load current, (ii) obtaining at least one magnitude of a component of the power spectrum at a respective predicted frequency, and (iii) evaluating the at least one magnitude of the component to assess a condition of th machine.
REFERENCES:
patent: 4761703 (1988-08-01), Kliman et al.
patent: 5365787 (1994-11-01), Hernandez et al.
patent: 5729145 (1998-03-01), Blades
patent: 5816122 (1998-10-01), Benning et al.
patent: 6199019 (2001-03-01), Iino et al.
H. Bishop, et al, Determination of the Quality of Commutation in a D.C. Machine, 2ndInternational Conference on Electrical Machines Design and Applications, Sep. 1985, Pub. No. 254, pp. 275-279.
B. Plyushch, et al “Measurement of Sparking Intensity in D.C. Motors”, Izvestiya Vysshikh Uchebnykh Zavedenii Elektromekhanika Journal, No. 4, 1969, pp. 385-390.
S. Desai, “Sensing Poor Commutation to Detect Impending Failures in DC Machines”, 1stInternational Machinery Monitoring and Diagnostic Conference, pp. 683-689.
M. Treanor, et al, “Incipient Fault Detection in Locomotive DC Traction Motors”, Proceedings of the 49thMeeting of the Society for Machinery Failure Prevention Technology, 1995, pp. 221-230.
A. Still, “Elements of Electrical Design”, McGraw-Hill Book Co, Inc., 1932, pp. 208-214.
M. Treanor, et al, “Commutation Monitoring in Locomotive DC Traction Motors”, Report of the Diesel Electrical Maintenance Committee, Proceedings of the 57thAnnual Meeting, Chicago, 1995, pp. 152-157.
D. Steeples, “On-Line Commutation Monitoring of Locomotive DC Traction Motors in Service”, Proceedings of the 8thInternational Congress on Condition Monitoring and Diagnostic Engineering Management, vol. 2, 1995, pp. 709-713.
G. Kliman, et al, “Noninvasive Detection of Broker Rotor Bars in Operating Induction Motors”, IEEE Trans of Energy Conversion, vol. 3, No. 4, Dec. 1988, pp. 873-879.
M. Steele, et al, “Applications of an Electrical Method for Condition Monitoring of Motors”, Motorcon Sep. 1982 Proceedings, pp. 321-335.
D. Steeples, et al, “On-Line Commutation Monitoring of Locomotive DC Traction Motors in Service”, Proceedings of the 49thMeeting of the Society for Machinery Failure Prevention Technology, 1995, pp. 709-713.
M. Steele, et al, “An Electrical Method for Condition Monitoring of Motors”, IEE Conference on Electrical Machines—Design and Applications, PUB 213, Jul. 1982, pp. 231-235.
Barton Richard Kenneth
Hokanson Paul Robert
Kliman Gerald Burt
Koegl Rudolph Alfred Albert
Treanor Michael Paul
Agosti Ann M.
Hoff Marc S.
Patnode Patrick K.
Raymond Edward
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