Method for on-line detection of incipient cracks in turbine-generator rotors
First Claim
1. A method for detecting incipient cracks in the rotor of a turbine-generator while the turbine-generator is in operation at running speed, comprising the steps of:
- (a) sensing mechanical vibrations of the rotor at at least one location thereof to produce at least one time-dependent vibration signal;
(b) providing at least one enhanced background vibration signal prior to development of a crack in the rotor, said signal being obtained and processed by(b1) collecting an integral number of time segments of said vibration signal, each time segment corresponding to one revolution of the rotor;
(b2) generating said enhanced background signal by summing together all such collected time segments of said vibration signal by superposing each on the other;
(b3) storing said enhanced background signal;
(c) providing at least one enhanced foreground signal by(c1) collecting an integral number of time segments of said vibration signal equal to the number collected in (b1), each time segment corresponding to one revolution of the rotor;
(c2) generating said enhanced foreground signal by summing together all such collected time segments of said vibration signal by superposing each on the other;
(d) providing a difference signal by subtracting said enhanced background signal from said enhanced foreground signal by superposing one on the other; and
(e) determining the spectral content of said difference signal, the presence and relative amplitude of higher harmonics of the running speed being indicative of the presence and size of a rotor crack.
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Abstract
A method is disclosed for detecting incipient cracks in the rotor of a turbine-generator while the turbine-generator is on-line operating under normal conditions. Vibration signature analysis is performed on a set of difference signals produced by superposing and subtracting corresponding enhanced background and foreground vibration signals. Each enhanced vibration signal is created by superposing and summing an integral number of vibration signal segments, each segment corresponding to one revolution of the rotor. An incipient crack is manifested principally by the appearance and increase in relative amplitude of signal harmonics at twice the rotational speed of the rotor. The method of the invention is sufficiently sensitive to detect cracks having a depth on the order of less than one-percent the diameter of the rotor.
97 Citations
7 Claims
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1. A method for detecting incipient cracks in the rotor of a turbine-generator while the turbine-generator is in operation at running speed, comprising the steps of:
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(a) sensing mechanical vibrations of the rotor at at least one location thereof to produce at least one time-dependent vibration signal; (b) providing at least one enhanced background vibration signal prior to development of a crack in the rotor, said signal being obtained and processed by (b1) collecting an integral number of time segments of said vibration signal, each time segment corresponding to one revolution of the rotor; (b2) generating said enhanced background signal by summing together all such collected time segments of said vibration signal by superposing each on the other; (b3) storing said enhanced background signal; (c) providing at least one enhanced foreground signal by (c1) collecting an integral number of time segments of said vibration signal equal to the number collected in (b1), each time segment corresponding to one revolution of the rotor; (c2) generating said enhanced foreground signal by summing together all such collected time segments of said vibration signal by superposing each on the other; (d) providing a difference signal by subtracting said enhanced background signal from said enhanced foreground signal by superposing one on the other; and (e) determining the spectral content of said difference signal, the presence and relative amplitude of higher harmonics of the running speed being indicative of the presence and size of a rotor crack. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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Specification