Three phase asynchronous motors overload causes can be divided into the following cases.
① caused by the drag of mechanical equipment. Such as irrigation and drainage machinery waterway obstruction, shaft different heart, resulting in motor load is too large, or even locked.
② due to poor quality of the power supply network, such as voltage is too low, three-phase imbalance caused by the increase in motor current and so on.
③ due to the poor working conditions of the motor itself caused. Such as poor ventilation, the ambient temperature is too high, part of the motor and mechanical failure caused by the motor overheating, lower insulation levels. Even short circuit.
According to the three-phase asynchronous motors rotor structure
Can be divided into squirrel-cage motor and winding motor.
2, according to the three-phase asynchronous motors protection type
Can be divided into open (IP11) three-phase asynchronous motors, protective three-phase asynchronous motors (IP22 and IP23), closed three-phase asynchronous motors (IP44), explosion-proof three-phase asynchronous motors.
Open type (IP11): cheap, the best heat dissipation conditions, because the rotor and winding exposed to the air, can only be used for dry, little dust and no corrosive and explosive gas environment.
Protection (IP22 and IP23): ventilation and cooling conditions are better, to prevent water droplets, iron and other external debris into the motor inside, only for more dry and dusty and no corrosive and explosive gas environment.
Closed (IP44): for wet, dusty, vulnerable to wind and rain erosion, corrosive gases and other harsh working environment, the most common application.