Description

Contactors for Capacitor Switching With Insertion Of Damping Resistors

When choosing switching contactors for capacitors used to compensate the reactive power present in the network, you should bear several aspects in mind

• On being energized the capacitor is connected in parallel to the inductive network and the oscillating circuit produced by connecting the capacitor to the network will result in the passage of a high-frequency current (from 3 to 15 kHz), which may be 160 times greater than the In current for 1 or 2 ms
•  The presence of harmonic currents and the tolerance with respect to mains voltage determine the continuous passage, within the circuit, of a current whose value is around 1.3 times greater than the rated current In of the capacitor
• Because of the tolerances allowed by the manufacturer, the exact power of a capacitor may be 1.10 times greater than the rated power.

The contactor must be capable of working with:

• An elevated, albeit transient, peak current during the closing phase.
• A closing current that may be 1.43 times greater than the rated current of the capacitor

The contactors offered by DUCATI Energia are specifically engineered to work in these conditions. Select the type of contactor based on the working voltage and effective power (in kVAr) of the capacitor bank to be controlled.

Contactors within banked or group PFC systems are typically in close proximity to low-impedance capacitors that are already charged. The short wire lengths add little impedance to the charge path letting charged, low-impedance capacitors combine with the power source to produce inrush currents that exceed the ratings of normal contactors.