What are the hazards of inter-turn short circuit in flying shear motor?

1. Electrical performance
1. Abnormal increase in current
When inter-turn short circuit occurs, the closed loop formed by the short-circuited turns is equivalent to a low-impedance branch. According to Ohm's law, when the applied voltage of the motor remains unchanged, the short-circuited turns reduce the overall equivalent impedance of the winding, which will cause the current to increase.
This current increase may exceed the rated current of the motor. On the one hand, it will cause a sharp increase in the copper loss of the motor and waste of electric energy; on the other hand, excessive current will cause overload pressure on other electrical components of the motor (such as fuses, contactors, etc.), which may cause these components to be damaged prematurely.
2. Three-phase current imbalance
For three-phase flying shear motors, inter-turn short circuits usually do not occur symmetrically in the three-phase windings at the same time. Once an inter-turn short circuit occurs in a phase winding, the impedance of the phase will be different from that of the other two phases, resulting in unbalanced three-phase current.
The unbalanced three-phase current will cause the motor to generate a negative sequence magnetic field, which will interact with the positive sequence magnetic field of the motor to generate additional torque and loss. At the same time, unbalanced current may also cause vibration and increased noise of the motor, affecting the normal operation of the motor.
2. Magnetic field and torque
1. Magnetic field distortion
Turning short circuit will change the magnetomotive force distribution of the motor winding. Under normal circumstances, the magnetic field generated by the stator winding of the motor is evenly distributed and used to drive the rotor to rotate. When a turning short circuit occurs, the direction of the current in the short-circuited turn is opposite to the direction of the current in the normal turn, which will weaken the magnetic field strength in some areas, resulting in uneven magnetic field distribution and magnetic field distortion.
Magnetic field distortion will affect the electromagnetic torque generation mechanism of the motor. Electromagnetic torque is related to the interaction between magnetic field and current. Uneven magnetic field will make the electromagnetic torque generated by the motor unstable. Torque fluctuations may occur during operation, affecting the precise drive of the flying shear motor to the flying shear equipment, thereby affecting the shearing accuracy and efficiency of the flying shear.
2. Torque reduction
Due to the magnetic field distortion and current abnormality caused by turning short circuit, the effective electromagnetic torque of the motor will decrease. When the flying shear is working, sufficient torque is required to overcome the shearing force to complete the shearing action. The decrease in torque may make the flying shear motor unable to provide sufficient power, resulting in the flying shear failing to cut normally, shearing failure or the length of the cut material not meeting the requirements.
3. Heat generation and insulation
1. Local overheating
The short circuit between turns will cause the current in the short-circuited turns to increase sharply. According to Joule's law (), these short-circuited turns will generate a lot of heat. Since the heat is mainly concentrated in the short-circuited turns and their surrounding areas, local overheating will occur.
Local overheating will further accelerate the aging and damage of the insulating material, causing the insulation performance to decline faster. If not handled in time, it may cause more serious phase-to-phase short circuit or ground short circuit faults, and even burn the motor.
2. Insulation damage is aggravated
Factors such as local overheating, increased current, and electromagnetic force generated by magnetic field distortion will put greater pressure on the insulation of the motor. Under the action of high temperature, strong electric field and electromagnetic force, the molecular structure of the insulating material is easily destroyed, and the insulation performance is gradually lost.
Once the insulation is damaged, the reliability and safety of the motor will be seriously threatened, leakage may occur, endangering the safety of the operator, and the motor needs to be repaired or replaced on a large scale.
IV. Operation stability
1. Increased vibration and noise
As mentioned above, problems such as three-phase current imbalance, magnetic field distortion and torque fluctuation caused by inter-turn short circuit will lead to increased vibration and noise during motor operation.
Excessive vibration and noise will not only affect the comfort of the working environment, but may also indicate that there are serious hidden faults inside the motor. If the vibration is too large, it may also cause the mechanical parts of the motor (such as bearings, couplings, etc.) to loosen and wear more, further reducing the service life and operational reliability of the motor.
2. Shortened service life
Due to a series of problems such as increased current, heat, magnetic field distortion, vibration, etc. caused by inter-turn short circuit, various parts of the motor (electrical parts, mechanical parts, insulation parts, etc.) will be cumulatively damaged.
This damage will accelerate the aging process of the motor, making it unable to reach the normal design service life, and failure will occur in advance, increasing the company's equipment maintenance costs and downtime costs.