Sigma Capacitor contactors are specifially designed to handle the unique application requirements for single or group PFC. The resistors work in conjuction with a special early-make auxiliary contact to pre-charge the capacitors so the main contacts do not see the peak inrush. After the pre-charge , the main contacts then close after a time lag and conduct continious current. In case of individual capacitor load, charging current peaks that are 30- time greater than rated capacitor current can ocur.
In case of a multi stage capacitor the inrush current can exceed 180 times 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 capacitors 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.peack current is limited to value within the contactor making capacity.