When switched on, a capacitor can function as a short-circuit element. The capacitor inrush or charging current magnitude depends on AC voltage at turn-on and on the impedance of connection cables and a power supply transformer.
In case of individual capacitor load, charging current peaks that are 30-time greater than rated capacitor current can occur. In case of a multi-stage capacitor the inrush current can exceed 180-time rated capacitor current.
Such a strong current can flow through a contactor from the beginning when inrush current occurs from power supply network and the capacitor is already connected. Such inrush current is undesirable since main contacts of standard duty contactors are likely to weld.
A new capacitor duty contactor is designed to meet the requirements of capacitor duty applications. Contactors are fitted with a block of three auxiliary contacts connected in series with six quick discharge damping resistors, two per each phase. Peak current is limited to the value within the contactor making
Three-pole contactors from 10 kVAr to 60 kVAr are available in seven ratings complying with the IEC 60070 and IEC 60830 standards. They have the UL certificate.