Metal oxide varistors having thermal protection

• US 6,252,488 B1
• Filed: 09/01/1999
• Issued: 06/26/2001
• Est. Priority Date: 09/01/1999
• Status: Expired due to Fees

• Current Assignee: Leviton Manufacturing Company Incorporated
• Original Assignee: Leviton Manufacturing Company Incorporated
• Inventors: Ziegler, William R., Campolo, Steve
• Primary Examiner(s): Picard, Leo P.
• Assistant Examiner(s): Vortman, Anatoly
• Application Number:
  US09/388,821
• Time in Patent Office: 664 Days
• Field of Search: 337/182, 337/114, 337/120, 337/403, 337/404, 337/405, 337/407, 337/2-6, 337/121, 337/123, 337/139, 337/140, 337/388, 337/401, 337/406, 361/117-119, 361/124-127, 361/103, 361/121, 361/56, 361/111, 361/91, 361/104-106, 361/93
• US Class Current: 337/5
• CPC Class Codes: H01C 7/102 Varistor boundary, e.g. surface layers H01C7/12 takes precedence
• CPC Class Codes: H01C 7/12 Overvoltage protection resistors series resistors structurally associated with spark gaps H01T1/16

Abstract

A layer of thermal fusible material is placed on one surface of a metal oxide varistor (MOV) to monitor the heating of the MOV due to applied voltage spikes. The thermal fusible material is part of the electrical circuit which includes the MOV and melts at a predetermined temperature. In the presence of a severe or a number of voltage spikes the MOV heats up and the heat transferred to the thermal fusible material causes it to open the electrical circuit to the MOV to prevent overheating and thermal runaway. In another form, the MOV is separated into two halves and the thermal fusible material layer is placed between the ends of the MOV halves.

Claims

1. A thermal protection device for a metal oxide varistor (MOV) to prevent thermal runaway of said MOV comprising:

a) a first segment MOV element defined by a first straight side surface and a first outer side surface;

b) a second segment MOV element defined by a second straight side surface and a second outer side surface;

c) said first segment and said second segment generally describing a MOV where said first straight side surface is held parallel with said second straight side surface;

d) said first segment MOV element and said second segment MOV element heat up when exposed to voltage spikes;

e) said first segment having a first front surface and a first rear surface, said second segment having a second front surface and a second rear surface;

f) a thermal fusible material layer extending between said first segment first straight side surface and said second segment second straight side surface, said thermal fusible material layer capable of conducting current therethrough and having a predetermined temperature at which it melts and interrupts any flow of current through said thermal fusible material layer;

g) a first conductor having a first end and a second end, said first end coupled to one of said first front and first rear surfaces of said first segment, and

h) a second conductor having a third end and a fourth end, said third end coupled to one of said second front and rear surfaces of said second segment, whereby current is permitted to flow through said first conductor, said first segment, said thermal fusible material layer, said second segment and said second conductor when said thermal fusible material layer is held below said predetermined temperature and current flow is interrupted when said thermal fusible material layer goes above said predetermined temperature and melts due to the heat provided by said first and second MOV.

2. A thermal protection device, as defined in claim 1, further comprising:

a) a layer of insulation surrounding said first front surface, said first outer side surface, said first rear surface, a rear surface of said thermal fusible material layer, said second rear surface, said second outer side surface, said second front surface and a front surface of said thermal fusible material layer.

3. A thermal protection device, as defined in claim 2, wherein said layer of insulation has a top surface and a bottom surface.

4. A thermal protection device, as defined in claim 3, further comprising:

a) an air gap extending from said layer of insulation top surface to said bottom surface along one side of said thermal fusible material layer.