The capacitors making up the POWER-9 series Heavy Duty Capacitor are used for static power factor correction of a wide range of motors and transformers. This series share the same internal configuration, with three capacitor elements wired internally in a delta connection. The overpressure protection system is specifically dimensioned so as to constantly ensure maximum safety in terms of ground protection and protection against the risk of arcing, even in conditions where there is a high energy density. In these series HEAVY DUTY of resin-impregnated capacitors, the three elements are housed in a plastic container which, together with the impregnating agents, assures dual insulation between the wound cores and metal enclosure. To guarantee perfect filling during the resin impregnation process, the process itself is carried out prior to the elements being placed in the enclosure; in this way the distribution and uniformity of the impregnation can be subjected to a complete visual and dimensional inspection.