CONTACTORS TYPE CN

CONTACTORS FOR CAPACITORS TYPE CN UP TO 3000V 50-250Hz

The switching of the usual three-phase power factor correction capacitors for motor or lines, is normally exploited by the standard type N contactors in the version with poles type V or S for voltage up to 1000V.
Special care must be taken for switching the capacitors (single-phase) used for power factor correction and current balancing of induction furnaces where high frequency of operation and remarkable presence of harmonics is expected.
The contactors CN are properly designed to withstand the increased thermal stresses due to harmonics exsting in the circuits feeding the capacitors, and to withstand for a great number of operations the highest overcurrents that may occur when connecting a capacitor.
According to the figured diagram (fig.1), for limiting the above mentioned transient current peaks, the contactor, wher provided in the plant, connects the capacitor through a proper limiting resistor, which, after a very short delay, is by-passed by the main pole that connects the capacitor directly to the line.
Moreover the contactor, when opening, can connect the capacitor across a discharge resistor by a proper contact.
The above metioned resistances, thet on request can be supplied with the contactor, must be carefully designed according to the performances of the contactor itself and in function of the number of operations per hour required.
For voltages up to 500V the contactors are fitted with poles without magnetic blowers or arc-chutes. For voltages over 500V the arcing poles are always of the magnetic blowed type with arc-chutes.
Moreover, for voltages over 1000V, two or more arcing poles connected in series are provided.

I = arcing pole
C = main pole
S = discharge resistance connecting contact

RI = limiting resistance
RS = discharge resistance

For reactive power higher than 0,5 KVAR, a discharge resistor must be always provided