Temperature Coefficient and Capacitance Retrace of Polypropylene Film Capacitors

For want of better electrical insulators in general and capacitor insulations in particular, especially in the realm of extra high voltage stress areas, work has been done by many pioneers toward this end, first in the materials provided by nature and then in the field of synthetics limited only by man's imagination. One of the newest and seemingly most practical glimpses of light, especially in the field of capacitor dielectrics, is the use of polypropylene films. A considerable amount of work has been done. The work involved is directed only to the particular interest of capacitor engineering and application. It was limited to the area of two most important requirements for capacitors used in the communication and control industries, namely, temperature coefficient and capacitance stability or retrace under temperature variation and cycling. Several types of construction and treatment are reviewed and results are presented for general evaluation. The main purpose of this paper is, of course, to reveal some pertinent experimental data and to limit the comment to a minimum. No claim is laid as to the ultimate superiority of polypropylene film capacitors, but the facts are presented and can be judged by their own merit. Some apparent highlights, such as the exceptionally good retrace, of course, have been pointed out, but in general the paper is intended to be an unbiased evaluation.