They are electromagnetic switches which open their closed contacts when the coil is energized, close their open contacts and can be controlled by an electrical signal.
As it is known, capacitors cause high currents between 1 and 15 kHz at the first start-up and up to 150 times the rated current. To limit these currents, a pre-resistance can be added to all three phases to which the capacitor is connected. Capacitor contactor designed for this purpose is used because this process is normally difficult.