Capacitors for high-frequency induction-heating circuits

Increased military production has accelerated the application of high-frequency heating where accurate control of temperature for short intervals is fundamentally important. The heating of metals by induction has been widely applied. The present paper describes the development of a new type of dielectric liquid called Lectronol. Capacitors containing this liquid are particularly well adapted for use in the tank circuit of electronic heaters used in induction heating. The capacitor is water-cooled and is housed in a hermetically sealed completely filled nonmagnetic container so constructed as to provide sufficient flexibility to take care of the liquid expansion due to thermal changes. The capacitor is noteworthy because of the absence of cellulose sheet insulation, satisfactory operation being entirely dependent on the superior insulating properties of the Lectronol. Capacitors containing this liquid are characterized by low dielectric loss and high dielectric strength over the frequency range utilized in power oscillators. The capacity per unit volume is approximately twice that obtained with mineral oil. The electrical characteristics of the capacitor are stable under severe conditions of use.