Summary:...
The rotor temperature is too high, the centrifugal load is too large, and the defects in the rotor manufacturing process (clearance and bubbles, and unqualified casting and metal welding technology) will all cause the rotor to fail. Excessive centrifugal load is the most common in the start-up process of induction motors, and manufacturing defects can lead to excessive conductor resistance, which can lead to overheating.
The failure of the
planetary gear motor body is generally manifested as: shaft bending, unbalance, shaft cracks, misalignment and eccentricity. When the rotor is unbalanced, the rotor mass will be eccentric, which will generate periodic excitation force at the same rotation frequency, which will increase the vibration of the motor. The scars left by the motor rotor during the machining process will crack during operation, and in severe cases, it will lead to catastrophic failure of the rotor fracture. Eccentricity is divided into static eccentricity, dynamic eccentricity and mixed eccentricity. When the rotor eccentricity fails, it will produce unbalanced magnetic pulling force, which will cause vibration. When the rotor temperature is unevenly distributed, when the rotor is thermally bent, the vibration will increase, which will cause friction between the stator and the rotor, which will eventually damage the induction motor.
Failure analysis of broken rotor bars
After the broken rotor bar fault occurs, the stator and rotor currents are asymmetrical, the torque of the induction motor is unbalanced, and its pulsation component also increases. The impedance of the broken bar is infinite, the current of the bar is zero, the total torque of the motor will be reduced and the magnetic field of the asymmetric rotor current air gap will change, forming a reverse-rotating magnetic field, so the electromagnetic torque is also reversed. , The positive and negative torques cancel each other out, and the effective torque of the induction motor is reduced accordingly. This kind of fault will cause the oscillation of current and electromagnetic torque. When the moment of inertia is large (constant speed), the fault phenomenon is more noticeable.
When the rotational inertia is small, the oscillation occurs on the mechanical speed and the amplitude of the stator current. After the broken bar occurs, the start-up time is significantly prolonged after the current is applied. As the number of broken bars increases, the torque decreases, the pulsation component increases, and the volatility becomes larger. After the rotor fails, if the motor continues to run, the current of the cage bar adjacent to the broken bar and the conductor bar symmetrical to the broken bar will suddenly increase, and the temperature of the bar will rise sharply. Larger stresses are easier to break. After the bar is broken, many electrical quantities change more or less accordingly. The motor starting time becomes longer, the effective torque is reduced, the slip becomes larger, the vibration and noise of the induction motor increase, the stator current fluctuates, and the motor locally heats up.
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