Plastic capacitors
AssigneeImperial Chemical Industries PLC
InventorColin Williams
Life of this patent
Estimating the term…
Abstract
A wound electrical capacitor having a thermoplastic film dielectric spacer with specified thermal shrinkage characteristics and provided with a shrinkable sleeve which contracts during thermal stabilization of the capacitor to expel air and moisture from the capacitor winding to reduce capacitance loss on accelerated life testing.
Claims10
A wound, thermally stabilized electrical capacitor comprising at least a pair of electrically conductive electrodes, an insulating dielectric spacer disposed therebetween, the electrodes and spacer being wound together to form the capacitor winding, and a constrictive sleeve enveloping the winding, wherein
- a. the spacer comprises a longitudinal thermoplastic polymeric film strip having (1) a thermal shrinkage in the longitudinal direction of from 5.0 to 10 percent, and (2) a ratio of thermal shrinkage in the longitudinal direction to that in a direction at right angles thereto of from 1.7:1 to 10:1, and
- b. the sleeve (1) extends over at least 75 percent of the exposed surface area of the capacitor winding, and (2) is of a material having a thermal shrinkage in the longitudinal direction at least 1.02 times that of the spacer,
- said thermal shrinkages being determined at the thermal stabilizing temperature.
A method of forming a wound electric capacitor comprising winding together at least a pair of electrically conductive electrodes with a dielectric spacer disposed therebetween, the electrodes and spacer together constituting the capacitor winding, enveloping the winding in a thermally shrinkable sleeve, and thermally stabilizing the sleeved winding, wherein
- a. the spacer comprises a longitudinal thermoplastic polymeric film strip having (1) a thermal shrinkage in the longitudinal direction of from 5.0 to 10 percent, and (2) a ratio of thermal shrinkage in the longitudinal direction to that in a direction at right angles thereto of from 1.7:1 to 10:1, and
- b. the sleeve (1) extends over at least 75 percent of the exposed surface area of the winding, and (2) has a thermal shrinkage in the longitudinal direction at least 1.02 times that of the spacer,
- said thermal shrinkages being determined at the thermal stabilizing temperature.
Dependencies are inferred from the claim text.