Classification of Dielectric Materials

Dielectric materials fall into two classes Class I used for linear capacitors and Class II used for non-linear capacitors. In general. Class I materials are natural dielectrics such as glass and mica and have capacitances within the range of a couple to several hundred picofarads. When capacitors use Class I materials, the capacitance will not change with a dynamic operating voltage and frequency. Class I dielectric materials are more costly. 

Typical Class II materials are ferrodielectric ceramics and polymer electrolytes with high dielectric constants. They are used to develop high capacitance capacitors. For example, metalized polymer foils can achieve a few thousand picofarads to a few microfarads an electrolytic capacitor can offer a capacitance in the range of a few to several thousand microfarads some 

Paper Inexpensive, applicable for high voltage use Hygroscopic, degradation of insulation and quality factor over time 

Polyester Low moisture absorption, inexpensive, high operating voltage (60,000 V) Low operating temperature (125 °C) and poor stability dielectric heats quickly, thus limiting use to low frequency AC applications 

Polyimide Similar advantages to polyester, with increased operating temperature (250°C) Less temperature stability than paper yielding an increase in power factor, higher cost than polyester 

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