Asynchronous motor: construction and device

A three-phase asynchronous electric motor with a squirrel-cage rotor was invented in far 1889, on March 8, by the famous Russian scientist and engineer Mikhail Osipovich Dolivo-Dobrovolsky. And already literally a year later, on December 15, 1890, an engine with a phase rotor was invented and patented.

The three-phase asynchronous electric motor is one of the most common electrical devices in the industry. It is simple in operation, reliable and has a fairly low price. Asynchronous electric motor occupies ninety percent of the total number of engines around the world. It can be found almost everywhere - from the design of a conventional washing machine, ending with huge industrial shops, not to mention power plants. He made a significant technical revolution in the world industry.

An asynchronous electric motor is a machine that is designed to convert electrical energy into mechanical energy. "Asynchronous" means simply "not simultaneous." It is understood that in such a machine, the frequency with which the magnetic field generated by the stator rotates will always be greater than the frequency with which the moving part of the motor rotates - the rotor.

The asynchronous motor consists of a stationary part - a stator, and a movable rotating part - a rotor.

The stator is assembled from sheets of pressed electrical steel and usually has the shape of a cylinder. In the special grooves of the core, there is a stator winding made of winding wire. The stator has several windings. The axes of these windings are usually shifted by an angle of 120 degrees relative to each other. The ends of these windings can be connected by a star or a triangle (depending on what voltage is applied).

The rotors of a machine such as an asynchronous electric motor are short-circuited and phase-locked.

The first type (squirrel-cage rotor) is the core, which is recruited from copper or aluminum rods with winding wrapped in them. The rods are connected by end rings, and their appearance resembles a squirrel cage. By the way, that's why this type of rotor is often called "squirrel cage". The rotor in this case is again collected from sheets of electrical steel, pressed and poured with aluminum.

The phase rotor is also often called a rotor with contact rings. It has a three-phase winding, which actually does not differ at all from the stator windings. In general, the ends of the windings of such a rotor with contact rings (phase) are connected to a star. Free ends are brought to these very contact rings. In the winding circuit, an additional resistor is often added due to the presence of special brushes connected to the rings. Such a resistor increases the active resistance in the electrical circuit of the rotor, which contributes to a more smooth start-up and a decrease in the starting current - this is very important for machines such as three-phase asynchronous motors.