| Squirrel-cage induction motors are used most widely in the process of energy conversion in industry. It is important to keep them in reliable and safe operation. The fault of broken bars is an ordinary fault which can not be easily avoided and is difficult to examine. Therefore, it plays an important part in preventing accidents and insuring safe operation to study the influence of broken bars on the motor's operation.Firstly, according to electromagnetic field theory, the 2-dimensional (2-D) mathematical model of a three phase squirrel-cage Y802-2 induction motor is developed. Then general equations can be deduced from finite element discrete and functional analysis. The motor's 2D solving region of electromagnetic field is given based on the boundary conditions and assumption conditions of the squirrel-cage induction motor. Through finite element mothod (FEM) and inner–outer convergence method, magnetic field distributions and magnetic forces of bars can be calculated in following rotor conditions: health rotor, one single broken bar, two adjacent broken bars, two broken bars with one good interval, two broken bars with two good interval and four adjacent broken bars. In order to consider the influence of skewed slots on the motor's performances, the multi-slice EFM is used to calculate currents of bars with the above mentioned conditions. Secondly, according to the time-step finite element method, the equations of time-step FEM coupling field and circuit in the solving region were established, and the starting performances of squirrel-cage induction motor with rated load are simulated and analyzed. In addition, the A phase stator current is analyzed using FFT, some valuable conclusions are obtained by comparing the side frequency component. In the procedure of finishing this paper, some experiments are done under conditions such as health rotor, one bar broken and two adjacent bars broken. Theoretical approach and experimental results confirm the validity of the proposed method and offer theoretical support for diagnosing broken bars technology. |
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