Zinc oxide varistor having reduced edge current density

• US 4,451,815 A
• Filed: 09/27/1982
• Issued: 05/29/1984
• Est. Priority Date: 09/27/1982
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Kresge, James S., Sakshaug, Eugene C.
• Primary Examiner(s): Albritton, C. L.
• Application Number:
  US06/423,908
• Time in Patent Office: 610 Days
• Field of Search: 338/21, 338/20, 361/127, 29/610
• US Class Current: 338/21
• CPC Class Codes: H01C 7/102 Varistor boundary, e.g. surface layers H01C7/12 takes precedence

Abstract

A zinc oxide varistor disc is provided with one or more circumferential recesses in its rim to reduce the current density at the edges of the electrodes on the opposed disc faces, which electrodes are of a lesser diameter than the varistor disc. It has been discovered that optimum results are achieved when the diameter at the bottom of the recess is somewhat less than the diameter of the electrodes.

Claims

1. A zinc oxide varistor comprising:

a disc-shaped sintered body having opposed faces and circumferential rim;

an electrode applied to each said face, the edges of said electrodes being spaced from the edges of said body to leave circumferential marginal portions of said faces devoid of electrode material; and

at least one circumferential groove created in said rim, the depth of said groove being approximately equal to the width of said electrode-free marginal face portions.

2. The zinc oxide varistor defined in claim 1, wherein said rim is provided with a pair of circumferential grooves.

3. The zinc oxide varistor defined in claim 2, wherein the spacing between said grooves is greater than the spacing between each said groove and the face of said body most adjacent thereto.

4. The zinc oxide varistor defined in claim 1, wherein said rim is provided with a single wide groove, the width of said single groove being in excess of 50% of the height of said rim.

5. The zinc oxide varistor defined in claims 1, 2, 3, or 4, wherein the groove depth is somewhat in excess of the width of said electrode-free marginal width portions.

6. A zinc oxide varistor comprising:

a disc-shaped body having opposed faces and a circumferential rim;

an electrode applied to each said face, the edges of said electrodes being spaced from the edges of said body to leave electrode-free circumferential marginal portions of said faces; and

at least one circumferential groove created in said rim, the depth of said groove being at least equal to the width of said marginal face portions such as to limit the overload current densities in the portions of said body located adjacent the electrode edges and the bottom of said groove to tolerable levels.