Wound capacitor having a thermal disconnect at a hot spot

Abstract

A capacitor having a large current carrying capacity includes a hollow core formed by a non-conducting tubular section, and a capacitor winding wrapped around the tubular section. A thermal cutoff device is disposed within the hollow core. The thermal cutoff device is configured to sense a predetermined temperature level within the hollow core and disable the current carrying capacity of the capacitor. The thermal cutoff device is disposed at a geometric center of the capacitor winding, which is also the hot spot of the capacitor winding. The thermal cutoff device includes first and second conductors electrically connected to each other with a predetermined solder alloy. The first conductor includes a cross-sectional portion that is attached to the second conductor. The cross-sectional portion is subjected to a springing force in a lateral direction away from the second conductor. Upon melting of the solder alloy, the springing force moves the cross-sectional portion away from the second conductor, thereby disabling the current carrying capacity of the capacitor.

Description

BRIEF DESCRIPTION OF THE DRAWING

The invention is best understood from the following detailed description when read in connection with the accompany drawings. Included in the drawings are the following figures:

FIG. 1 is a cross sectional view of a wound film capacitor including a thermal cutoff device in accordance with an embodiment of the present invention;

FIG. 2 is a side view of the wound film capacitor shown in FIG. 1, with the thermal cutoff device having been removed;

FIG. 3 is a perspective view of the wound film capacitor shown in FIG. 1, with the thermal cutoff device having been removed;

FIGS. 4A and 4B show an embodiment of the thermal cutoff device of FIG. 1, including two conductors disposed on a non-conducting base which are in an open state or a rest state, in accordance with an embodiment of the present invention;

FIGS. 5A and 5B show the thermal cutoff device of FIGS. 4A and 4B in a closed state or a non-resting state, in accordance with an embodiment of the present invention;

FIG. 6 shows another thermal cutoff device that includes a curved conductor end portion, which is different from the straight conductor end portion shown in FIG. 4B, in accordance with an embodiment of the present invention;

FIG. 7 shows a top view of a non-conducting base of a thermal cutoff device for receiving the two conductors (not shown), in accordance with an embodiment of the present invention;

FIG. 8 is a cross sectional view of a wound film capacitor including a thermal cutoff device, in accordance with another embodiment of the present invention;

FIGS. 9A and 9B show another embodiment of the thermal cutoff device of FIG. 1, including two conductors, one conductor disposed on a non-conducting base and the other conductor disposed on a spring, which are in an open state or a rest state, in accordance with an embodiment of the present invention; and

FIGS. 10A and 10B show the thermal cutoff device of FIGS. 9A and 9B in a closed state or a non-resting state, in accordance with another embodiment of the present invention.

Claims

1. A capacitor having a large current carrying capacity comprising a hollow core formed by a non-conducting tubular section,a capacitor winding wrapped around the tubular section, anda thermal cutoff device disposed within the hollow core,wherein the thermal cutoff device is configured to sense a predetermined temperature level within the hollow core and disable the current carrying capacity of the capacitor.

2. The capacitor of claim 1 wherein the thermal cutoff device is disposed at a geometric center of the capacitor winding.

3. The capacitor of claim 1 wherein the thermal cutoff device is disposed at a hot spot of the capacitor winding, the hot spot defined as a location of a high thermal energy within the capacitor winding.

4. The capacitor of claim 1 wherein the thermal cutoff device is disposed at a hot spot of the capacitor winding, the hot spot defined as a location of highest thermal energy within the capacitor winding.

5. The capacitor of claim 1 wherein the thermal cutoff device includes first and second conductors electrically connected to each other with a predetermined solder alloy.

6. The capacitor of claim 5 wherein the predetermined solder alloy includes a composition of one or more substances, the substances selected in proportion to each other for causing the solder alloy to melt at the predetermined temperature level.

7. The capacitor of claim 5 wherein the first conductor includes a cross-sectional portion attached to the second conductor, and the cross-sectional portion is subjected to a springing force in a lateral direction away from the second conductor.

8. The capacitor of claim 7 wherein the solder alloy includes a composition of one or more substances selected to melt at the predetermined temperature level, andupon melting of the solder alloy, the springing force moves the cross-sectional portion away from the second conductor.

9. The capacitor of claim 8 wherein the composition of the solder alloy and an amount of the springing force are selected for moving the first conductor away from the second conductor at the predetermined temperature level.

10. The capacitor of claim 7 wherein the solder alloy is disposed at the cross-sectional portion.

11. The capacitor of claim 7 wherein the capacitor winding includes a metallized film wound around the tubular section and metallic opposing ends coupled to respective ends of the metallized film,the first and second conductors are coupled to respective wire leads,one of the wire leads is connected, at a location external to the hollow core, to one of the metallic opposing ends, and the other wire lead is extended beyond the hollow core for attachment to a terminal, andlengths of the respective wire leads are adjusted to place the thermal cutoff device at the geometric center of the capacitor winding.

12. The capacitor of claim 7 wherein the thermal cutoff device includes a non-conducting base for fastening the first and second conductors thereon.

13. The capacitor of claim 7 wherein the first conductor includes a rest state that occurs after being subjected to the springing force in the lateral direction away from the second conductor,the cross-sectional portion forms an angle of A degrees with respect to the second conductor during the rest state, andthe angle A is selected based on a desired level of the springing force.

14. A method for thermally protecting a large current carrying capacitor comprising the steps of: (a) wrapping a capacitor winding around a non-conducting tubular section;(b) sensing a predetermined temperature level within a hollow core of the tubular section, using a thermal cutoff device; and(c) disabling current flow in the capacitor upon sensing the predetermined temperature level.

15. The method of claim 14 wherein step (b) includes sensing the temperature level at a geometric center of the capacitor winding.

16. The method of claim 14 wherein sensing the temperature level includes sensing a hot spot of the capacitor winding, the hot spot being the hottest spot of the capacitor winding.

17. The method of claim 14 wherein step (b) includes placing the thermal cutoff device at a geometric center of the capacitor winding.

18. The method of claim 14 including the step of connecting first and second conductors using a solder alloy composition to form the thermal cutoff device; andwherein step (b) includes sensing the temperature level based on a melting temperature of the solder alloy composition.

19. The method of claim 18 including the step of bending one end portion of the first conductor in a direction away from the second conductor, prior to connecting the first and second conductors using the solder alloy composition.

20. The method of claim 19 wherein step (c) includes moving the one end portion of the first conductor away from the second conductor, upon sensing of the temperature level based on the melting of the solder alloy composition.