IEC 60940-2015 pdf Guidance information on the application of capacitors, resistors, inductors and complete filter units for electromagnetic interference suppression

During operation, the capacitors are subjected to the supply mains voltage with a superimposed radio interference voltage. In many cases, the extra load caused by the radio- frequency voltage is not important, but in other cases an appreciable radio-frequency current through the capacitor may occur or high voltage peaks may be present. This must be taken into account when choosing the capacitor and a check should be made with the capacitor under its working conditions to make sure that its ratings are not exceeded. The presence of inductance in the supply circuits in series with the capacitor may cause the voltage at power frequency applied to the capacitor to exceed the supply voltage. For inductors using ferromagnetic cores, it is important to be aware of the possible loss of suppression caused by saturation of the core causing decrease of inductance. This saturation may be caused by peaks of load current or interference current, or continuous excessive load current. Unbalance of winding in current-compensated inductors will also contribute to the effect. The effectiveness of interference suppression is a function of suppression component construction, mounting of the component in the machine or apparatus, the radio-frequency voltage spectrum generated by the machine or apparatus and of characteristics of the external circuit. Due to the complexity of the problem it is not possible to estimate with sufficient accuracy from the radio-frequency characteristics of a component how effective it will be under various conditions. On the other hand, components for use under similar conditions can be compared on the basis of their radio-frequency characteristics. For this purpose the resonance frequency measured under given conditions and the radio-frequency resistive at resonance may be of use. For these reasons it is not required that the radio-frequency characteristics be marked on the components nor has it been attempted to standardize certain values for these characteristics.