A three-phase asynchronous electric motor with a squirrel-cage rotor 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, the phase rotor motor was invented and patented.
The three-phase asynchronous electric motor is one of the most common electrical devices in the industry. It is easy to use, reliable and has a fairly low price. The asynchronous electric motor is actually ninety percent of the total number of motors around the world. It can be found almost everywhere - from the design of an ordinary washing machine to huge industrial workshops, not to mention power plants. He made a significant technological revolution in the world industry.
Asynchronous motor is a machine that is designed to convert electrical energy into mechanical energy. "Asynchronous" simply means "not simultaneous". This means that for 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 engine rotates - the rotor.
An asynchronous electric motor consists of a fixed part - the stator, and a moving rotating part - the rotor.
The stator is assembled from pressed electrical steel sheets and is usually cylindrical. A stator winding made of a winding wire is laid in special grooves of the core. 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 in a star or a delta (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 a core made 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 a "squirrel cage". The rotor in this case is again assembled from sheets of electrical steel, pressed and filled with aluminum.
The phase rotor is often called a slip ring rotor. It has a three-phase winding, which in fact does not differ at all from the stator windings. Basically, the ends of the windings of such a rotor with contactrings (phase) are connected in a star. The free ends are brought to these slip 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 electrical circuit of the rotor, which contributes to a smoother start and a decrease in the values of the starting current - this is very important for machines such as three-phase asynchronous motors.
