First, it is very common to make clear that themotor thermal protector does not guarantee that the motor will not burn. The motor thermal protector can only protect the action under the condition of the motor over current, and the action delay is relatively long. At some point, the protector has not had time to protect the motor. So what are the reasons for the motor burning?

Over-current operation for a long time will cause high heat in the winding of the motor, and the motor can not normally dissipate heat. After the internal overheating of the motor, the insulation level will be reduced, resulting in the ground or an interphase short circuit causing the motor to burn out. Each motor has a rated working voltage. If the voltage is too high, the stator winding magnetomotive force will be enhanced, the rotor induced current will increase, and the thermal effect of the rotor current will be enhanced, which will cause the internal overheating of the motor to burn out the motor. The three-phase voltage imbalance will cause the asymmetry of the magnetomotive force generated by the stator winding of the motor, resulting in additional loss and heating of the rotor, and the overall or local temperature rise of the motor, resulting in the motor burning down. These problems are not installed motor thermal protector can avoid motor burning.

In addition, the large fit gap between the stator and rotor causes the increase of reluctance, the increase of excitation loss, the increase of motor excitation current, the small easy to cause the increase of air gap harmonic magnetic field, and easy to cause friction, the occurrence of the phenomenon of sweeping. The terminal is loose, causing the terminal to burn off the wiring nose, which will seriously cause the motor to run out of phase and burn the motor. According to experience, it is necessary to check and tighten the circuit when the newly installed motor runs for about one month.

So it is not the installation of themotor thermal protectorthat can ensure that the motor will not be burned, if the motor is burned out more frequently, it is recommended to find the cause of the motor burn, in addition to the installation of a thermal protector recommended installation phase sequence protector and circuit breaker.