In amateur and repair practice, it becomes necessary to use three-phase electric motors for the power drive. To power them, it is not at all necessary to have a three-phase network. The most effective way to start an induction motor is to connect its third winding through a phase-shifting capacitor.
Necessary
asynchronous motor, capacitors
Instructions
Step 1
Take an induction motor and a capacitor. Usually, the motor has the ability to switch the windings on the block from the "star" (380V) to the "triangle" (220V), and can operate in 380/220 V, as well as 220/127 V. Calculate the capacitance of the capacitor using the formula Cp = 2800 * I / U, when connecting the windings "star" or Cp = 4800 * I / U, if the connection is "delta". For normal operation of the motor with a capacitor start, the capacitance of the capacitor must change depending on the number of revolutions. Since this condition is difficult to fulfill, in practice, two-stage motor control is used. Turn on the motor with the starting capacitor capacity, and then, after accelerating it, turn it off, leaving it running. The disconnection of the capacitor is done manually by a switch.
Step 2
Connect the capacitor to the induction motor connection circuit. It is necessary that the capacity of the starting capacitor is 1.5-2 times the capacity of the working one. Its voltage should be 1.5 times higher than the mains voltage, it is also necessary that it be paper type MBGP, MBGO, etc. An electric motor with a capacitor start has a simple reversing circuit. By switching the switch to one or the other power cable, the motor changes the direction of rotation. When operating motors with capacitor start, some peculiarities should be taken into account. During idle operation of the electric motor, a current flows 20-40% more than the nominal current through the winding, which is powered through a capacitor. Therefore, it is necessary to reduce the working capacity when the engine is running under load.
In the event of an overload, the motor may stall. To restart it, turn on the starting capacitor again. You also need to know that with such a connection, the power of the electric motor is 50-70% of the nominal value. Any three-phase electric motor can be included in the rotor, they work poorly in it, asynchronous electric motors of the A, AO, AO2, D, AOL, APN, UAD series, with the correct selection of capacitors, it is quite successful.
