EP0095405A1 - Thermal protection for electrical installations and apparatuses - Google Patents

Abstract

1. A temperature fuse to be connected in series in a phase conductor of the feed circuit of an installation to be protected against an ambient temperature greater than that which would risk making it unsuitable for functioning or would risk damaging it (the critical temperature), of the type which consists of two metal tips (5, 6) in the form of caps mounted, respectively, at the two ends of an insulator (1), as well as an electrically conductive, mobile element (16), capable of adopting a first position, in which it forms a connection between the two caps, and a second position, in which it breaks the electrical connection between the two caps as soon as the temperature reaches and exceeds the critical temperature, said mobile element (16) being held, against a resilient force (20), in said first position by means of a spacing-member (21) made from, or connected to said mobile element by, a material, the state of which is capable of changing after an increase in temperature above said critical temperature so as to allow said mobile element to adopt said second position, characterized in that said mobile element is formed as a tubular piston (16) in the shape of an elongated socket guided on a ceramic stop (18) which rests on, or is an integral part of, the tip (6) adjacent the open side of the socket, said resilient force being provided by a driving spring (20) which is spring between the base (17) of said tubular piston (16) and said stop (18).

Description

To protect electrical and electronic installations and equipment against an overcurrent, fuses in the form of a cartridge made with an insulating material, such as ceramic, are very commonly used, capped at its two ends by metal tips between which s 'extends a fusible wire intended to melt for a given specific intensity, the cartridge being filled with a powder of a neutral material.

Such a cartridge is mounted in one or more phases of the supply current and operates by the Joule effect, that is to say by melting the melting wire when an unacceptable overcurrent appears.

However, in certain application cases, it is desirable to ensure the protection of an installation or of electrical and electronic devices not against an overcurrent, but against an increase in the ambient temperature above a threshold, beyond which the destruction of the installation and / or electrical equipment could take place. Such protection can be provided using thermal protection.

Such a thermal protector is known which is intended to be mounted in series in a phase wire of the supply circuit of an apparatus to be protected against an ambient temperature higher than that which would risk making it unfit to function or damaging it ( critical temperature), of the type comprising, according to the preamble of claim 1, two metal end pieces in the form of hoods mounted respectively at the two ends of an insulating body, as well as a mobile element, electrically conductive, and capable of assuming a first position in which it establishes contact between the two hoods and a second position in which it interrupts the electrical connection between the two covers as soon as the temperature reaches and / or exceeds the critical temperature.

A fuse sensitive to the surrounding temperature and having a spacer element made with a material capable of melting at the critical temperature for which it must cut is described, for example, in patent GB 1,557,911. However, this fuse is of a different kind from that defined in the preamble of the claim and is not of a nature to allow, what the invention seeks, to cut out in a very low volume chamber, this which is favorable to non-ionization with the result that the cut-off axis is laminated and is quickly extinguished.

To solve this problem, the thermal protector according to the invention is essentially characterized in that said movable element is held, against an elastic force, in the first position by means of a spacer made or linked to said element. mobile with a material whose state is likely to change so as to allow said mobile element to assume said second position when the ambient temperature reaches or exceeds the critical temperature.

According to a first embodiment of the thermal protector according to the invention, said movable element, electrically conductive, is constituted by a hollow metal piston in the form of an elongated sleeve, guided on a stop made with an insulating material, preferably a ceramic resting on an integral with the end piece adjacent to the open side of the sleeve, a spring working at the extrusion being armed between the bottom of the hollow piston and said stop.

Advantageously, the hollow piston passes axially, with a peripheral clearance, the body ceramic insulator, and its axial guidance is ensured by two contact pieces each having the shape of a prism with a polygonal base, preferably based on an equilateral triangle, split along an edge and made with a metal to very high conductivity spring, each prism being mounted between the bottom of a nozzle and the neighboring face of the ceramic insulating body.

To ensure good mechanical and electrical contact, the hollow piston is tangent to all the interior sides of the two triangular prisms, and these are offset between them by 180 °, which provides good guidance of the hollow piston at the same time as an electrical contact such that the operation of the thermal protector is independent of the intensity of the current flowing through it, provided that this intensity is not greater than the maximum rated current for which the thermal protector is designed. There will be, for example, protectors designed for maximum intensities of 1 A, others of 2 A, then others for 5 A, etc.

In order to ensure a good break when passing from the first to the second position, without risk of forming an electric arc when the hollow piston assumes its second position, the length of the piston is at most equal, preferably less than the length of a triangular contact increased by the length of the insulating body.

To facilitate the passage of the piston from its first to its second position, the bottom of the piston is provided with a central bore, and the spacer is constituted by a solid spacer or by a sleeve centered on the bore.

According to a variant, the bottom of the piston is provided with a central bore and the spacer is constituted by a rod, one end of which is engaged in this bore and is welded to the bottom of the piston and the other end of which bears against the neighboring end-piece.

According to another embodiment, the bottom of the piston is provided with a central bore closed by a washer made with a material as indicated above, while between this washer and the neighboring end piece is provided a stop having a tail passing through the washer and said bore.

• La figure 1 est une coupe axiale d'un protecteur thermique de l'invention, selon une première forme de réalisation.
• La figure 2 est une coupe de la figure 1 le long de la ligne de coupe II-II.
• La figure 3 représente la protection thermique de la figure 1, avec le piston dans sa seconde position.
• Les figures 4, 5 et 6 représentent trois variantes possibles pour l'entretoise servant à maintenir le piston dans sa première position.

By way of example, various embodiments of a thermal protector according to the invention have been described below and shown in the accompanying drawing.

• Figure 1 is an axial section of a thermal protector of the invention, according to a first embodiment.
• Figure 2 is a section of Figure 1 along the section line II-II.
• Figure 3 shows the thermal protection of Figure 1, with the piston in its second position.
• Figures 4, 5 and 6 show three possible variants for the spacer used to maintain the piston in its first position.

The thermal protector of FIG. 1 comprises a median insulating body 1, preferably made of ceramic, provided with a central bore 2. On the end portions 3 and 4, of smaller diameter than that of the median portion, are engaged the metal end pieces 5 and 6 which abut against the shoulders 7 and 8. Between the front face 9 of the insulating body 1 and the bottom 10 of the end piece 6 is arranged a contact piece 11 having the form of a prism with triangular base, split in 12 along one of its edges and produced with a spring metal of very high conductivity. Between the front face 13 of the insulating body 1 and the bottom 14 of the end piece 5 is provided a contact piece 15 identical to the contact piece 11, these two contact pieces being offset between them by 180 °.

The bore 2 of the insulating body 1 is traversed by a hollow piston 16 which is a good current conductor and whose bottom is designated by 17, said piston being engaged on a ceramic stop 18.

Between the bottom 17 of the piston 16 and the face 19 of the ceramic stopper 18 is armed a spring 20 working at extension, spring held in its armed position by means of a spacer 21 which is made of a material whose characteristics, and in particular the mechanical characteristics are such that it maintains the piston in the position shown in FIG. 1 (first position). In this position, and when the thermal protector is mounted in one phase of the circuit to be protected, the current flows from one of the end pieces, for example from the end piece 6 to the end piece 5 passing through the contact piece 6, by the cylinder 16 and by the contact piece 15, it being noted that the contact between the end pieces 5, 6 and the prismatic contact pieces 11 and 15 is made along the edges of the latter while the contact between the contact pieces prismatic 11, 15 and the tips 5 and 6 is done along generators thereof, as shown in Figure 2 for elements 6, 11 and 6 for the lower part of Figure 1. The arrangement is similar for elements 5, 15 and 16, but with the difference that the contact generator between the positions 16 and the prismatic contact piece 15 is offset by 180 ° relative to the contact generator between the cylinder 16 and the prismatic contact piece 11, which ensures perfect guiding of the cylinder 16 when it passes from its first position to its second position.

This, shown in Figure 3, is reached upon triggering due to a surrounding temperature equal to or greater than the critical temperature. In this case, the spacer 21 changes state and authorizes the displacement of the piston 16 in the position shown in FIG. 3, under the action of the spring 20 which relaxes, so that the bottom 17 of the piston abuts against the bottom 14 of the nozzle 5, the central opening 22 formed in the bottom 14 facilitating this movement and authorizing the passage through the cylinder of the material constituting the spacer 21 if the latter is made with a material melting at the triggering temperature .

In the triggered state as shown in Figure 3, the piston 16 is completely disengaged from the prismatic contact 11 and its free end is located at a distance large enough from the latter so that there is a high-value isolation between the tips 5 and 6. if an electric arc tends to be established between the two ends of the piston 16 and the prismatic contact 6, it will be stretched and driven by the axial movement of the piston in space cylin- dri ^q ue located between the insulating body 1 and cylinder 16, resulting in the rolling and rapid extinction of this electric arc.

In fact, the phenomena of extinction and residual isolation after cutting are very favored by the very design of the thermal protector which makes it possible to laminate and draw the arc in a cylindrical space whose walls are formed by ceramic which, among the known materials, has the strongest resistance to the path of the electric arc (outer wall of the stop 18 discovered by the translation of the hollow piston 16 and inner wall of the body 1).

The rod 23 is made with a material stable at the critical temperature, while the weld melts at this temperature, allowing the spring 20 to push the piston 16 against the bottom 14 of the end piece 6, in a position similar to that of the figure 3.

According to a variant, the rod 23 can be glued with a material which will be chosen according to the thermal characteristics of the glued joint.

In FIG. 5, the spacer is constituted by a bush centered on the opening 22 of the bottom 17 of the cylinder 16 and mounted between this bottom 17 and the bottom 14 of the end piece 5, this cylinder being produced with a material whose physical or mechanical characteristics change at the critical temperature so as to allow the spring 22 to discharge the piston 16 into the position shown in FIG. 3.

Finally, in the case of FIG. 6, a washer 25 made with a material as just indicated is placed externally on the bottom 14 of the piston 16, and it is held in place by a ceramic stop 26 whose the tail passes through a central hole in the washer 25 and through the hole 22 in the bottom 17 of the piston 16.

At the critical temperature, the washer changes state, for example it melts and the piston 16 is driven back into the position shown in FIG. 3, it being understood that for this purpose the diameter of the spacer 26 is less that of the opening. 22.

Claims (8)

1. Thermal protector intended to be mounted in series in a phase wire of the supply circuit of an apparatus to be protected against an ambient temperature higher than that which would risk making it unfit to function or deteriorating it (critical temperature), of the type comprising two metal end pieces in the form of cowls mounted respectively at the two ends of an insulating body, as well as an electrically conductive movable element capable of assuming a first position in which it establishes contact between the two cowls and a second position in which it interrupts the electrical connection between the two covers as soon as the temperature reaches and exceeds the critical temperature, characterized in that said movable element (16) is held, against an elastic force, in said first position by means of a spacer (21) made or linked to said movable element with a material whose state is liable to change so as to allow said movable element to assume said second position. 2. Thermal protector according to claim 1, characterized in that said movable element is constituted by a hollow piston (16) in the form of an elongated sleeve guided on a stop (18) made with an insulating material, preferably a ceramic resting on or integral with the end piece (10) adjacent to the open side of the socket, a spring (20) working at the extension being reinforced between the bottom (17) of the hollow piston (16) and said stop (21). 3. Thermal protector according to either of Claims 1 or 2, characterized in that the hollow piston (16) passes with a peripheral clearance (2) axially through the ceramic insulating body (1) and its guide axial is ensured by two contact pieces (11, 15) each having the shape of a prism with a polygonal base, preferably based on an equilateral triangle, split along an edge and made with a spring metal of very high conductivity, each prism being mounted between the bottom of a nozzle (10, 14) and the adjacent face of the insulating ceramic body (1). 4. Thermal protector according to claim 3, characterized in that the hollow piston (16) is tangent to all the interior sides of the two triangular prisms (11, 15), and these are offset from one another by 180 °. 5. Thermal protector according to any one of claims 1 to 4, characterized in that the length of the piston (16) is at most equal to the length of a triangular contact (11, 15), increased by the length of the insulating body (1). 6. Thermal protector according to any one of claims 2 to 5, characterized in that the bottom (17) of the piston (16) is provided with a central bore (22), and that the spacer (21) is constituted by a solid part (21, 23) or by a socket (24) centered on the bore (22). 7. Thermal protector according to ^q uelcon- that of claims 2 to 6, characterized in fact that the bottom of the piston (17) is provided with a central bore (22) and that the spacer consists of a rod (23) one end of which is engaged in this bore and is welded to the bottom of the piston (17) and the other end of which bears against the neighboring end piece (14). 8. A thermal protector according to any one of claims 2 to 5, characterized in that the bottom of the piston is provided with a central bore (17) closed by a washer (25) made with a material as indicated in claim 1, and that between this washer (25) and the adjacent end piece (14) is provided a stop (26) having a shank passing through the washer and said bore, the diameter of the washer (25) being greater than that of said bore (17).

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