Three-phase electric motor in a single-phase network. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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To use a three-phase electric motor in a single-phase network, the third winding of the electric motor is connected through a phase-shifting capacitor. The operation of electric motors with a phase-shifting capacitor has some features. When the electric motor is running at idle or with underload, the current flowing through the winding fed through the capacitor is 20-40% more than the nominal current. If there are two identical or similar electric motors in power, one of them can be used as a "shifted" phase generator.
The electrical circuit for switching on electric motors is shown in the figure.
The start of the electric motor M1 is carried out by the magnetic starter KM1. When you press the SB2 ("Start") button, contacts 1, 2 turn on the KM1 starter, and contacts 3, 4 break the power circuit of the KM2 starter. The electric motor M1 is started using the starting capacitor C1. After starting the motor M1, the SB2 button is released. Voltage is applied to the KM2 magnetic starter, contacts KM2.1 and KM2.2 turn on voltage to two windings of the M2 electric motor, and a voltage shifted in phase by 90 ° is applied to the third winding. The M2 motor starts easily, and the KM2.3 contacts turn off the starting capacitor C1. Electric motors are used as both working or electric motor M1 as a motor-generator, and M2 as a working one. Stopping both electric motors with the SB1 button.
Electrolytic capacitor C1 for a voltage of 450 V. The capacity of the starting capacitor depends on the power of the electric motor and is determined by the formula
Cp=7000I/U, where I is the motor current; U - network voltage.
For an electric motor with a power of 1 kW C1 300 mx450 V. Buttons SB1 and SB2 type KE011U3 version 1 and version 2 or VK14-21.
Author: V.F. Yakovlev
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