Interference-Suppression Capacitors

In general, interference-suppression capacitors have low inductances. These capacitors can be separated into two classes depending on their use Class X and Class Y. Class X types are used in applications with lower safety requirements, for example, where a collapse would not pose a danger. Class Y types are used in environments or applications that have strict safety requirements. These two classes have different test conditions. For example, an 1100 V test voltage is used for testing Class X capacitors such as a 4 pF/250 V capacitor a 

2250 V test is used for testing Class Y capacitors. Both types are used in high (ceramic) and low (polymer) radio frequency and automotive applications. 

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Depending on the dielectric materials and applications, various types of capacitors have been designed, fabricated, and commercialized. These capacitors are categorized as fixed, variable, power, high voltage, interference suppression, ferrodielectric, polar polymer dielectric, linear, and nonlinear capacitors [7]. The following sections will briefly discuss each type. 

When the main arc has been struck in the low-pressure mercury vapour, the current is limited by the choke. The capacitor across the mains supply provides power-factor correction and the capacitor across the starter switch contact is for radio interference suppression. 

Polystyrene capacitors have exceptionally low tan S values (< 10 q, making them well suited for frequency-selective circuits in telecommunications equipment. Polymer capacitors are widely used for power-factor correction in fluorescent lighting units, and in start/run circuitry for medium-type electric motors used in washing machines, tumble-dryers and copying machines for example. They are also used in filter circuits to suppress radio frequencies transmitted along main leads. Such interference noise may originate from mechanical switches, furnace controllers and switch mode power supplies it not only spoils radio and television reception but can also cause serious faults in data-processing and computer equipment. 

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