Structure of asynchronous motors

Asynchronous motors are usually made into three-phase, which facilitates the establishment of a rotating magnetic field. The three phase asynchronous motors shown are small and large to medium-sized, which are composed of the stator, rotor, and other accessories.

1) Stator: The stator is composed of a stator core and a stator winding. In order to reduce hysteresis and eddy current losses, the annular stator core is composed of silicon steel sheets with grooves. The stator three-phase winding is embedded in the iron core slot, and the six output terminals of the three-phase winding are fixed in the junction box of the machine base casing. The terminal markings of each phase winding are marked next to the terminal terminals. The three-phase winding can be connected as a star () or a triangle（ Δ）。

2) Rotor: The rotor core is stacked with silicon steel sheets and pressed onto the shaft, with evenly distributed grooves punched on the silicon steel sheets, and the rotor winding is embedded in the grooves. The rotor can be divided into two types according to its winding structure: squirrel cage rotor and wound rotor. The rotor winding of a squirrel cage type asynchronous motor is a copper strip without insulation placed in the rotor slot, and the two ends of the copper strip are welded together with short-circuit rings, resembling a squirrel cage. In recent years, small and medium-sized electric motors have been produced, with no insulation paint applied between the rotor blades. The conductors in the rotor slot and the short circuit rings at both ends, along with the fan blades, are cast into a whole with aluminum. In order to improve starting performance, squirrel cage rotors generally adopt a inclined slot structure. In addition, there are also double squirrel cage and deep groove structures. The double squirrel cage rotor has two inner and outer squirrel cages. The outer cage conductor uses brass bars with higher resistivity, while the inner cage conductor uses red copper bars with lower resistivity. Deep slot rotor winding utilizes narrow and long conductors to generate skin effect and improve starting performance. The wound rotor winding is similar to the stator winding and is a three-phase winding made of insulated wires. The number of phases and pole pairs of the rotor winding are the same as those of the stator winding. The three-phase rotor winding is generally connected in a star shape, with three outgoing wires connected to three sliding rings fixed on the shaft. A set of brushes supported on the end cover connects the sliding rings to external circuits (such as starting or speed regulating resistors).

3) Other accessories: including base, end cover, fan, etc. The base is made of cast iron or steel plate to support components such as the stator and end cover, and to withstand and transmit torque. The end cover is made of cast iron or steel plate, and a bearing is installed in its center hole to support the rotor. The ventilation and cooling methods for electric motors include self cooling, self fan cooling, tube side ventilation, and external coolers.