Peter J. Unsworth

Fuzzy logic system to detect pump faults from motor current spectra

Faults in pumping systems can be caused through the changes in flow regimes, such as cavitation, that lead to impeller degradation or corruption of pumped material, and ultimately to the deterioration and breakdown of pumps themselves. Results are presented of experiments using spectral analysis of motor current to diagnose and predict specific failures in pumps. Fault signatures were established by relating spectral features to individual faults, and by analysing their behaviour in the presence of faults. Faults investigated were cavitation, blockage and impeller damage. A fuzzy logic system was built as a final decision making module.

Induction motor fault detection by space vector angular fluctuation

A new method of obtaining diagnostic data from induction motors, derived from space vector angular fluctuation, is presented in this paper. It obtains data from stator current by exploring the position of the current space vector in the space vector plane. Variations of the phase angle of the vector are subjected to Fourier transformation and analysed in the frequency domain. The method has been tested on laboratory induction motors with simulated stator faults, rotor resistance unbalance, supply voltage unbalance, as well as with computer simulation. The Goertzel algorithm is employed as a tool for real-time fault monitoring of the frequency domain. In the case of a stator fault, which can develop rapidly, this allows diagnosis within a few cycles. As well as providing a new tool in motor diagnostics, this method is able to detect both stator and rotor faults, and gives a good basis for an integrated induction motor condition monitor.

Sensorless speed measurement of induction machines using Short Time Fourier Transformation

Sensorless speed measurement of induction machines using short time Fourier transformation (STFT) is presented in this paper. The sensorless speed information of induction motors was derived from space vector angular fluctuation which is obtained from stator current by exploring the position of the current space vector in the space vector plane. By applying STFT to the space vector angular fluctuation signals, the eccentricity associated motor speed information can be extracted. Interpolation technique has been used to improve the accuracy of the STFT. The method has been verified on an ABB 2-pole squirrel-cage induction motor in laboratory in the case of motor starting; very good agreement has been achieved between the estimated speed and the actually measured speed.

Effect of second phase on single phase flow meters in steam quality measurement

This paper presents results from an investigation of the two phase flow, especially liquid ingas phase, in most mainly used flow meter in steam industry namely differential pressuremeter is investigated. As in general, a flowmeter is designed and employed to measure flowrate of single phase fluid. There are many types of meter available in the market characterizeby their working principles, installed conditions and measured fluid. All meters representtheir accuracies under the single phase flow condition. However, when they are working inunusual conditions especially under multiphase flow, most meters lose their accuraciessignificantly even there is small amount of second phase introduced into the system. Tounderstand the deteriorated performance of the meter under two phase flow, additional studyon the effect the second phase on the meter is required.The laboratory experiment is set up to simulate the wet steam by flowing compressed airin the 2 inch pipe. Water droplet is generated by pressurized water flowing through a nozzleand then spayed into the system in range of 25% maximum by mass fraction. The signal fromeach flowmeter is collected by digital computer and analyzed using FFT and power spectrumdensity. The results show that the presence of the second phase in the system causes highfrequency fluctuation and causes significant error on meter reading. Flow manufacturersalways add low-pass filter circuit to remove this high frequency signal, however, this papershows that the high frequency signal in specific region is useful as it can be use to estimatedthe percentage of the second phase in the main phase system.

Current space vector amplitude fluctuation based sensorless speed measurement of induction machines using Short Time Fourier Transformation

A novel method of obtaining sensorless speed information of induction motors, derived from current space vector amplitude fluctuation (SVAF), is presented in this paper. The space vector amplitude fluctuation associated with the eccentricity harmonics is first demodulated using Park transformation in space vector plane. Short Time Fourier Transformation (STFT) is then carried out to estimate the speed of an induction machine running under transient conditions phase such as motor starting. The method has been tested and verified on an ABB 2-pole induction machine in laboratory; excellent agreement has been achieved between the estimated speed using the proposed scheme and the measured speed using an actual speed sensor. The advantage of the proposed method is that it is more effective to estimate the motor speed running with high acceleration rate during motor starting.

Induction Motor Sensorless Speed Estimation by Space Vector Angular Fluctuation

A novel method of obtaining sensorless speed information of induction motors, derived from space vector angular fluctuation, is presented in this paper. It obtains data from stator current by exploring the position of the current space vector in the space vector plane. The space vector signal and variations of the phase angle of the vector are subjected to Short Time Fourier Transformation (STFT) and analyzed in the time-frequency domain. High-resolution spectrum technique is adopted to modify spectrum of FFT. The method has been tested on laboratory induction motors, as well as by computer simulation. In the case of motor starting, when motor speed can change rapidly, this allows speed estimation within a few cycles.