A three-phase squirrel-cage induction motor was invented back in 1889, on March 8, by the famous Russian scientist and engineer Mikhail Osipovich Dolivo-Dobrovolsky. And just a year later, on December 15, 1890, an engine with a phase rotor was invented and patented.
Three-phase asynchronous electric motor is one of the most common electric devices in the industry. It is easy to operate, reliable and has a fairly low price. An asynchronous electric motor accounts for almost ninety percent of the total number of motors around the world. It can be found almost everywhere - from the design of a conventional washing machine, ending with huge industrial workshops, not to mention power plants. He made a significant technical revolution in world industry.
An asynchronous electric motor is a machine that is designed to convert electrical energy into mechanical energy. Asynchronous simply means not simultaneous. This means that in such a machine the frequency with which the magnetic field created by the stator rotates will always be greater than the frequency with which the moving part of the motor rotates - the rotor.
An asynchronous electric motor consists of a fixed part - a stator, and a moving rotating part - a rotor.
The stator is assembled from sheets of pressed electrical steel and is usually in the form of a cylinder. The stator winding made of a winding wire is laid in special grooves of the core. There are several windings at the stator. The axes of these windings are usually offset 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.
The first type (squirrel-cage rotor) is the core, which is composed of copper or aluminum rods with a winding laid in them. The rods are connected by end rings, and their appearance resembles a squirrel cage. By the way, that is why this type of rotor is often called the "squirrel cage." In this case, the rotor is again assembled from sheets of electrical steel, pressed and cast with aluminum.
The phase rotor is often called the slip ring rotor. It has a three-phase winding, which actually does not differ completely from the stator windings. Basically, the ends of the windings of such a rotor with slip rings (phase) are connected to a star. The free ends are connected to these very contact rings. An additional resistor is often added to the winding circuit due to the presence of special brushes connected to the rings. Such a resistor increases the active resistance in the electric circuit of the rotor, which contributes to a smoother start and a decrease in the inrush current - this is very important for machines such as three-phase asynchronous motors.