STRESS CASCADE-GRADED CABLE TERMINATION

• US 3,644,662 A
• Filed: 01/11/1971
• Issued: 02/22/1972
• Est. Priority Date: 01/11/1971
• Status: Expired due to Term

• Current Assignee: Vulkor, Inc. (Therm-O-Link, Inc.)
• Original Assignee: Hooshang Salahshourian
• Inventors: Salahshourian, Hooshang
• Primary Examiner(s): Askin, Laramie E.
• Application Number:
  US05/105,198
• Time in Patent Office: 407 Days
• Field of Search: 174/73R,73SC,127 310/196 324/54
• US Class Current: 174/73.1
• CPC Class Codes: H02G 15/068 connected to the cable shield only H02G15/072 takes precedence
• CPC Class Codes: Y10S 174/28 Plural semiconductive layers
• CPC Class Codes: Y10S 174/31 having a shield or metallic layer

Abstract

Electric cable terminating means for substantially inhibiting ionization at the termini in which semiconductive coatings each having a nonlinear current characteristic are applied in a cascade arrangement, relative to resistance per square, onto the insulation layer for a predetermined length between the highvoltage output end and to the ground shielding means. Each semiconductive coating has a predetermined resistance per square different in value from an adjacent coating, or coatings, and cascaded progressively upward in value from the ground shielding means so that the semiconductive coating adjacent the shielding means has the lowermost value. A conductive coating is applied at opposite ends of the cascade onto the insulation layer to and in contact with the high-voltage output end and in contact with the ground shielding means to establish electrical contact. The cascaded semiconductive coatings have sufficient resistivity so that upon application of voltage the electrical stress at the surface for said length does not exceed the ionization start level of the cable.

Claims

1. Electric cable terminating means for substantially inhibiting ionization at the termini of said cable comprising an insulation layer surrounding a conductor and a ground shielding means concentrically disposed over said insulation layer, said cable having a voltage rating of not less than about 15,000 volts, the improvement which comprises:

a plurality of semiconductive coatings applied in a cascade arrangement onto said insulation layer extending for a predetermined length at each terminus between said shielding means and said high voltage output end, said semiconductive coatings having a substantially nonlinear current characteristic upon application of voltage, each of said semiconductive coatings having a predetermined resistance per square different in value from an adjacent semiconductive coating and cascaded progressively upward in value from said shielding means so that the coating adjacent said shielding means has the lowermost value, a conductive coating applied at opposite ends of said cascade arrangement onto said insulation layer to and in contact with said shielding means and said high-voltage output end to establish electrical contact, the resulting cascaded coatings having sufficient resistivity such that upon the application of voltage the electrical stress at the surface for said length does not exceed the ionization level of the cable.

2. Electric cable according to claim 1 wherein the semiconductive coatings provide a stress along the termination length of 3 to 5 volts per mil.

3. Electric cable according to claim 1 wherein the semiconductive coating of highest resistivity has a resistance of about 108 to 109 ohms per square.

4. Electric cable according to claim 1 wherein said termination length is cascaded in two sections each of about equal length and the semiconductive coating of highest resistivity comprises particulated silicon carbide and has a resistance of about 108 to 109 ohms per square.

5. Electric cable according to claim 1 wherein said termination length is cascaded in three sections of about equal length and the semiconductive coatings have a resistance per square of about 108 ohms, 106 ohms and 104 ohms per square.

6. A method for testing cable by high-voltage time test, said cable comprising an insulation layer surrounding a conductor and a ground shielding means concentrically disposed over said insulation layer and having a voltage rating of not less than about 15,000 volts, which comprises:

applying a plurality of semiconductive coatings in a cascade arrangement onto said insulation layer for a predetermined length at each terminus between said shielding means and said high-voltage output end, said semiconductive coatings having a substantially nonlinear current characteristic upon application of voltage, each of said semiconductive coatings having a predetermined resistance per square different in value from an adjacent semiconductive coating and cascaded progressively upward in value from said shielding means so that the coating adjacent said shielding means has the lowermost value, applying a conductive coating at opposite ends of said cascade arrangemenT onto said insulation layer to and in contact with said shielding means and said high-voltage output end to establish electrical contact, the resulting cascaded coatings having sufficient resistivity such that upon the application of voltage the electrical stress at the surface for said length does not exceed the ionization level of the cable, and subsequently applying voltage to said cable to test for failure in the cable.

7. A method according to claim 6 wherein the semiconductive coatings provide a stress along the termination length of 3 to 5 volts per mil.

8. A method according to claim 6 wherein the semiconductive coating of highest resistivity has a resistance of about 108 to 109 ohms per square.

9. A method according to claim 6 wherein said termination length is cascaded in two sections each of about equal length and the semiconductive coating of highest resistivity comprises particulated silicon carbide and has a resistance of about 108 to 109 ohms per square.

10. A method according to claim 6 wherein said termination length is cascaded in three sections of about equal length and the semiconductive coatings have a resistance per square of about 108 ohms, 106 ohms and 104 ohms per square.