Draft Tube Surge Detection in Francis Hydroturbines Using Bispectrum Analysis

The pressure surge in the draft tube is one of the main causes of instability and power losses in hydro power plants. This fault usually happens when the turbine operates in part load. Early detection of draft tube surge helps the operators to prevent potential damages to the turbine. In this study a new method for detection of draft tube surge from vibration signals is presented. The vibration signals of turbine guide bearing, draft tube and spiral case are acquired. These signals are then processed using bispectrum analysis. Bispectrum analysis can detect the nonlinearities present in the signal. When surge in draft tube occurs, changes are observed in signal bispectrum which show the occurrence of the fault in turbine. Therefore, this technique can be used as a powerful tool for fault detection in turbines. The results of different measurement positions are also discussed and the most significant ones are presented. The results demonstrate the efficiency of this method in draft tube surge detection.