Special Tests for Cage Rotors


With R-Test it is possible to identify the following types of faults:

  • Broken or Interrupted rotor bars
  • Missing material in the rotor bar (incomplete injection)
  • Missing connection to the end rings
  • Deviation of the rotor bar angle relevant to the axis (skew)
  • Changes in the consistency of the aluminium alloy and/or the iron core
  • Short circuits between two or more rotor bars (soldering) 
  • Asymmetry distance of the bars in comparison with the shaft (Axial Error) 
  • Inclination of the stack due to some impurity between some dice (Symmetry error). 

      In case the rotor is tested before shaft insertion and turning operation, imperfection of the external surface can be detected as rotor problem. The system has the possibility with digital filter to reduce this influence. Of course, cleaner is the external surface more efficient is the default detection. By the mechanical support (designed on the Customer’s requirement and range of products), connected to the drive motor, the rotor under test is rotated within a magnetic field. A special probe then detects an electrical signal. Several analyses are then performed in the time domain as well as in the frequency domain by a Fast Fourier Transform (FFT) analysis. The use of FFT spectrum analysis allows easy identification of different defects giving each of these a measured value. Different programmable limits can be applied to these values.

      In particular the following measurements are acquired:

      1. Efficiency: The aluminium quality.

      2. Bar Error: The symmetry between one bar and the next.

      3. Axial Error: The asymmetry of the rotor shaft compared to the ideal centre.

      4. Simm Error: Measurement of the rotor inclination error.

      5. RQF: The ROTOR QUALITY FACTOR which is an indication bars with porosity, missing material, blowholes, …