Parameters and Classification of Capacitors(II)

3. Rated voltage (U R). At any temperature between the lower class temperature and the rated temperature, the maximum DC voltage or the maximum AC voltage RMS or the peak pulse voltage may be continuously applied to the capacitor. When capacitors are applied in high voltage fields, the effect of corona must be paid attention to. Corona is due to the existence of a gap between the dielectric / electrode layer, which can produce parasitic signals of damaged equipment, but also lead to dielectric breakdown of capacitors. Under alternating or pulsating conditions, corona is particularly easy to occur. For all capacitors, the sum of the DC voltage and the AC peak voltage shall not exceed the rated voltage of the capacitor in use.

4. Loss angle tangent (TG δ). The loss power of the capacitor is divided by the reactive power of the capacitor as the loss angle tangent under the sinusoidal voltage of the specified frequency. In the practical application, the capacitor is not a pure capacitor, it has internal equivalent resistance, its simplified equivalent circuit is shown in the drawings. For electronic equipment, the smaller required R S is better, that is to say, the loss power and the angle between the power and the capacitance should be small.

5. Temperature characteristics of capacitors. It is usually expressed as a percentage of the capacitance of the reference temperature of 20 ℃ and the capacitance of the temperature concerned.

6. Service life. The service life of the capacitor decreases with the increase of temperature. The main reason is that temperature accelerates the chemical reaction and causes the medium to degenerate with time.

7. Insulation resistance. Because the temperature rise causes the electronic activity to increase, therefore the temperature rise will cause the insulation resistance to reduce.

Capacitors include fixed capacitors and variable capacitors. The fixed capacitors can be classified into mica capacitors, ceramic capacitors and paper / plastic film capacitors according to their dielectric materials.