Shaft shear detection through shaft oscillation
There is described a shaft shear event detection method. The method comprises obtaining a demodulated waveform of a shaft oscillation wave superimposed on a shaft rotational speed signal, comparing the amplitude to an amplitude threshold, detecting oscillation when the amplitude threshold is exceeded for a plurality of samples, and detecting a shaft shear when oscillation continues for a predetermined time limit.
1. A method for detecting a shear of a rotating shaft of a gas turbine engine, the shaft positioned between a source and a load, the method comprising:
receiving a speed sensor signal from a speed sensing device;
determining, from the speed sensor signal, a demodulated waveform of a shaft oscillation wave superimposed on a shaft rotational speed signal, the waveform having an amplitude and a frequency;
comparing the amplitude of the waveform to an amplitude threshold;
detecting an oscillation of the shaft when the amplitude threshold is exceeded for a plurality of samples;
detecting a shear of the rotating shaft when oscillation continues for a predetermined time limit; and
in response to detecting the shear of the rotating shaft, commanding a fuel shutoff of the gas turbine engine.
2. The method of claim 1 , wherein the amplitude threshold comprises a lower amplitude threshold and an upper amplitude threshold.
3. The method of claim 1 , wherein the demodulated waveform is obtained through amplitude demodulation.
4. The method of claim 1 , wherein the demodulated waveform is obtained through frequency demodulation.
5. The method of claim 1 , wherein the speed sensing device comprises a phonic wheel sensing assembly; and wherein the speed sensor signal is received from the phonic wheel sensing assembly.
6. The method of claim 1 , wherein the predetermined time limit is measured as a function of a period of the waveform.
7. A system for detecting a shear of a rotating shaft of a gas turbine engine, the shaft positioned between a source and a load, the system comprising:
a processing unit; and
a non-transitory computer-readable memory having stored thereon program instructions executable by the processing unit for:
receiving a speed sensor signal from a speed sensing device;
determining, from the speed sensor signal, a demodulated waveform of a shaft oscillation wave superimposed on a shaft rotational speed signal, the waveform having an amplitude and a frequency;
comparing the amplitude of the waveform to an amplitude threshold;
detecting an oscillation of the shaft when the amplitude threshold is exceeded for a plurality of samples;
detecting a shear of the rotating shaft when oscillation continues for a predetermined time limit; and
in response to detecting the shear of the rotating shaft, commanding a fuel shutoff of the gas turbine engine.
8. The system of claim 7 , wherein the amplitude threshold comprises a lower amplitude threshold and an upper amplitude threshold.
9. The system of claim 7 , wherein the demodulated waveform is obtained through amplitude demodulation.
10. The system of claim 7 , wherein the demodulated waveform is obtained through frequency demodulation.
11. The system of claim 7 , wherein the speed sensing device comprises a phonic wheel sensing assembly; and wherein the speed sensor signal is received from the phonic wheel sensing assembly.
12. The system of claim 7 , wherein the predetermined time limit is measured as a function of a period of the waveform.
13. A non-transitory computer-readable medium having stored thereon program instructions for detecting a shear of a rotating shaft of a gas turbine engine, the shaft positioned between a source and a load, the program instructions executable by a processing unit for:
receiving a speed sensor signal from a speed sensing device;
determining, from the speed sensor signal, a demodulated waveform of a shaft oscillation wave superimposed on a shaft rotational speed signal, the waveform having an amplitude and a frequency;
comparing the amplitude of the waveform to an amplitude threshold;
detecting an oscillation of the shaft when the amplitude threshold is exceeded for a plurality of samples;
detecting a shear of the rotating shaft when oscillation continues for a predetermined time limit; and
in response to detecting the shear of the rotating shaft, commanding a fuel shutoff of the gas turbine engine.