Paper Capacitors

02 Sep.,2022


metalized paper

Transient suppression / X- and Y-capacitors

In the group of RFI capacitors that shall protect against Radio Frequency Interference so called X- and Y-capacitors are included. They are connected to the mains according to Figure Connecting of X- and Y-capacitors. There they also serve another important purpose. Transients strike namely every live mains relatively often. They may come from the ”outside” but may also be generated by our own equipment.

Between 80 and 90 % of all transients from the mains last between 1 and 10 μs, are higher than 1000 V, have voltage rise times of 200 to 2000 V/μs and are occurring at least 10 times a day. We realize that their damage must be eliminated. It is done by the X-capacitors which thus are connected between the lines of the mains.

The Y-capacitors represent another type of transient suppression. They are connected between either of the power lines and the grounded cover of electric equipment. Here we require an extra high safety against short-circuits in order to prevent the equipment being put under tension and thus causing serious personal injuries. Besides, the Y-capacitor shall have a limited capacitance in order not to bring about harmfully high currents through the human body in case of a possible open circuit in the ground wire (see Figure Connecting of X- and Y-capacitors).