Method of improving strip paper for electrical insulation

Claim 1

A method of treating a sheet of electrical paper insulation to remove conductive impurities from said sheet of a preselected diameter smaller than the thickness of said sheet comprising the steps of passing said paper sheet containing said conductive impurities betWeen a pair of directly confronting opposed conductive electrodes at least one of which has a plurality of probes spaced apart both longitudinally and transversely of said sheet so that said electrodes directly engage opposite surfaces of said sheet, connecting an adjustable electrical circuit across said pair of electrodes and adjusting said circuit to apply a predetermined voltage of sufficient magnitude across said electrodes so that a discharge current is triggered by the presence between said electrodes of a conductive impurity in said sheet of said preselected diameter smaller than the thickness of said sheet, said predetermined voltage being in the range from 50 percent to 150 percent of the one minute dielectric strength in air of said sheet of paper insulation, adjusting said circuit independently of said voltage-adjusting step so that said discharge current is of sufficient magnitude and flows between said electrodes for a sufficient interval of time to remove said impurity and form a controlled perforation in said sheet without charring and tracking of said sheet, and impregnating said sheet with high dielectric strength oil to fill said perforations and form a solid wall of insulation.

Claim 2

A method of treating a sheet of electrical paper insulation to remove conductive impurities from said sheet of a preselected diameter smaller than the thickness of said sheet comprising the steps of passing said paper sheet containing said conductive impurities betWeen a pair of directly confronting opposed conductive electrodes at least one of which has a plurality of probes spaced apart both longitudinally and transversely of said sheet so that said electrodes directly engage opposite surfaces of said sheet, connecting an adjustable electrical circuit across said pair of electrodes and adjusting said circuit to apply a predetermined voltage of sufficient magnitude across said electrodes so that a discharge current is triggered by the presence between said electrodes of a conductive impurity in said sheet of said preselected diameter smaller than the thickness of said sheet, said predetermined voltage being in the range from 50 percent to 150 percent of the one minute dielectric strength in air of said sheet of paper insulation, adjusting said circuit independently of said voltage-adjusting step so that said discharge current is of sufficient magnitude and flows between said electrodes for a sufficient interval of time to remove said impurity and form a controlled perforation in said sheet without charring and tracking of said sheet, and impregnating said sheet with high dielectric strength oil to fill said perforations and form a solid wall of insulation.

Claim 5

A method of treating electrical paper insulation sheet to remove conductive particles therein larger than a preselected diameter, which diameter is smaller than the thickness of said sheet, comprising the steps of passing said paper insulation sheet between directly confronting opposed conductive electrodes directly engaging opposite sides of said sheet to scan the surface of said sheet, at least one of said electrodes having a plurality of probes spaced apart both longitudinally and transversely of said sheet, connecting across said pair of electrodes an electrical circuit adjustable in both voltage and in the magnitude of current which will flow between said electrodes when a discharge is formed between said electrodes, adjusting said circuit to apply across said electrodes a predetermined voltage slightly below the desired average dielectric strength of said sheet and of sufficient magnitude to detect a conductive particle in said sheet of said preselected diameter smaller than the thickness of said sheet as it passes between said electrodes and trigger a discharge between said electrodes, adjusting said electrical circuit independently of said voltage-adjusting step so that said discharge current between said electrodes is of sufficient magnitude to remove said particle and form a clean perforation in said sheet without charring and tracking of said sheet, and impregnating said sheet with high dielectric strength liquid to fill said perforations and form a solid wall of insulation.

Claim 6

A method of treating electrical paper insulation sheet to remove conductive particles therein larger than a preselected diameter, which diameter is smaller than the thickness of said sheet, comprising the steps of passing said paper insulation sheet between directly confronting opposed conductive electrodes directly engaging opposite sides of said sheet to scan the surface of said sheet, at least one of said electrodes having a plurality of probes spaced apart both longitudinally and transversely of said sheet, connecting across said pair of electrodes an electrical circuit adjustable in both voltage and in the magnitude of current which will flow between said electrodes when a discharge is formed between said electrodes, adjusting said circuit to apply across said electrodes a predetermined voltage slightly below the desired average dielectric strength of said sheet and of sufficient magnitude to detect a conductive particle in said sheet of said preselected diameter smaller than the thickness of said sheet as it passes between said electrodes and trigger a discharge between said electrodes, adjusting said electrical circuit independently of said voltage-adjusting step so that said discharge current between said electrodes is of sufficient magnitude to remove said particle and form a clean perforation in said sheet without charring and tracking of said sheet, and impregnating said sheet with high dielectric strength liquid to fill said perforations and form a solid wall of insulation.

Claim 7

A method of treating a sheet of electrical insulation paper to remove conductive particles therein of a preselected diameter smaller than the thickness of said paper sheet, comprising the steps of passing said paper sheet between a pair of directly confronting opposed conductive electrodes at least one of which has a plurality of probes spaced apart both longitudinally and transversely of said sheet so that said electrodes directly engage opposite surfaces of said sheet, connecting an adjustable electrical circuit across said electrodes and adjusting said circuit to apply a predetermined voltage of sufficient magnitude across said electrodes to trigger a discharge current between said electrodes when a conductive particle in said sheet of said preselected diameter smaller than the thickness of said paper sheet appears between said electrodes, adjusting, independently of said voltage-adjusting step, both the magnitude of discharge current from said electrical circuit across said electrodes and the time of said discharge so that a sufficient magnitude of current flows for sufficient time to remove from said sheet said conductive particle of said preselected diameter smaller than the thickness of said sheet and form a clean perforation of controlled size therein without charring and tracking of said paper sheet, and impregnating said sheet with high dielectric strength oil to fill said perforations and form a solid wall of insulation.

Claim 8

A method of treating a sheet of electrical insulation paper to remove conductive particles therein of a preselected diameter smaller than the thickness of said paper sheet, comprising the steps of passing said paper sheet between a pair of directly confronting opposed conductive electrodes at least one of which has a plurality of probes spaced apart both longitudinally and transversely of said sheet so that said electrodes directly engage opposite surfaces of said sheet, connecting an adjustable electrical circuit across said electrodes and adjusting said circuit to apply a predetermined voltage of sufficient magnitude across said electrodes to trigger a discharge current between said electrodes when a conductive particle in said sheet of said preselected diameter smaller than the thickness of said paper sheet appears between said electrodes, adjusting, independently of said voltage-adjusting step, both the magnitude of discharge current from said electrical circuit across said electrodes and the time of said discharge so that a sufficient magnitude of current flows for sufficient time to remove from said sheet said conductive particle of said preselected diameter smaller than the thickness of said sheet and form a clean perforation of controlled size therein without charring and tracking of said paper sheet, and impregnating said sheet with high dielectric strength oil to fill said perforations and form a solid wall of insulation.