Fuses with improved cooling

Abstract

 A new type of fuse with improved cooling is provided for use in single-phase or three-phase electrical installations which include high breaking capacity fuses, fast fuses, general purpose fuses, except miniature fuses, during normal operating conditions and/or overloads.
At a traditional fuse (SF) attaches one or more aluminum heat sink (R) with different geometrical fin shapes (A), on one, two or three lateral sides of the ceramic body of the fuse (SF). Thermal contact between the surfaces of the aluminum heat sink (R) and ceramic body is achieved through a silicon paste/compound with high thermal conductivity. Using a small fan (V) mounted on the heat sink (R), a forced cooling is obtained.

Description

[0001] The present invention relates to a new type of electric fuse with an improved cooling in comparison with traditional one.

[0002] Fuses have been produced over 100 years and there are now an extremely large number in use throughout the world. They incorporate one or more current-carrying elements, depending on their current ratings, and melting of these followed by arcing, occurs when excessive overcurrents flow through them. Fuses can be designed to interrupt safely the very highest fault currents that may be encountered in service, and, because of the rapidity of their operation in these circumstances, they limit the energy dissipated during fault periods. This enables the fuses to be of relatively small overall dimensions and may also lead to economies in the cost and size of the protected equipment. From fuse beginnings, first scientific reference by Sir. Edward Nairne during 1773 and first official US fuse patent of Thomas Edison by 1880, the main improvements have been aimed to use of better materials, to extend the current and voltage application ranges, and towards the development of faster and cheaper construction techniques.

[0003] Fuses are basically simple and relatively cheap devices, although their behaviour is somewhat more complex than may be generally realised. Surprisingly, the arcing process which occurs when they are interrupting current is still not fully understood. Research is continuing on this topic with the object of producing fuses capable of meeting the ever-increasing performance demands made on them. In this connection the advent and rapid growth of semiconductor devices, with their limited overload capacities, has introduced particularly stringent requirements, especially from the cooling point of view during normal operation conditions.

[0004] US 3287526 describes a fusible element which is of ribbon-form and comprises a plurality of regions of reduced cross-section located at spaced-apart locations along its length. Each region of reduced cross-section comprises a pair of notches in the opposed edges of the ribbon and a hole between the notches forming a pair of spaced-apart restricted necks at opposite sides of the hole between the hole and the notches. Integrally attached to the ribbon at an edge of the hole located between the necks is a tab that serves to cool the necks. US 4839625 provides a fuse comprising a body encapsulating a fuse element, said body including a baseplate formed from a material having good thermal conductivity. The baseplate forming part of the fuse construction acts as a heat sink but the fuse may also be mounted upon a heat sink which already forms part of the electrical equipment which is to be fused. US 5214565 describes a bracket for fuse holders which includes heat sink fins for cooling the fuse holders. The bracket has a main body conforming to the shape of the fuse holders and mounting members or feet which can be attached, using self-clinching nuts, to a printed circuit board on which the fuse holders are mounted. The heat sink is formed of fins attached to the main body. In US 4050045 is presented a fuse holder of the type having a heat sink consisting of a plurality of specially spaced and constructed vertically extending fins located in the area where the heat generated by the fuse and/or the heat generated in the material of a wire connector or block itself is dissipated between the fuse and the location where the electrical wires enter the connector or block.

[0005] The present invention seeks to provide an improved cooling for high breaking capacity fuses, fast fuses, general using fuses, except miniature fuses, during normal operating conditions and/or overloads.

[0006] According to the present invention there is provided an electric fuse with improved cooling which has mounted on one, two or three lateral sides of its ceramic body, aluminum heat sinks of different geometrical shapes and different types of the fins. In order to achieve a good thermal transfer between the external surface of the ceramic body of the electric fuse and the aluminum heat sink, it uses silicone pastes/compounds. To get the necessary contact force between the aluminum heat sink and the external surfaces of the cermanic body there is used a prestressed stainless wire which is mounted through the fins of the heat sink and the opposite side of the ceramic body of the electric fuse.

[0007] With the aim to improve the fuse cooling a small fan can be used which can be supplied in dc or ac voltage using a rectifier. The fan is mounted on the upper side of the aluminum heat sink through small screws.

[0008] Hence, the electric fuse may have natural cooling when only aluminum heat sinks are used or forced cooling when besides aluinum heat sinks a small fan is used.

[0009] The new type of fuse with improved cooling can be used both in single-phase and three-phase electrical installations and can be applied to all type of electric fuses with rectangular ceramic body. In the case of fuses with cylindrical ceramic body, the monting baseplate of the heat sinks has to be also with a cylindrical shape.

[0010] Embodiments of the present invention with now be described, by way of example, with reference to the accompanying drawings in which:

Figure 1 is a three dimensional view of an embodiment of a fuse with improved cooling with heat sinks mounted in the horizontal position, according to the present invention;

Figure 2 is a three dimensional view of an embodiment of a fuse with improved cooling with heat sinks mounted in the vertical position, according to the present invention;

Figure 3 is a three dimensional view of an embodiment of a fuse with improved cooling with heat sinks mounted on three lateral sides of the ceramic body, according to the present invention;

Figure 4 is a three dimensional view of an embodiment of a fuse with improved cooling with heat sink and small fan, according to the present invention; and

Figure 5 is a three dimensional view of an alternative embodiment of this invention.

[0011] For the purpose of illustration, this invention will be described with reference to rectangular ceramic body of the electric fuses, but is applicable to other type of ceramic body such as cylindrical one. In that case, the heat sink to be mount on the external surface of the cyclindrical ceramic body, has to be with an adequate baseplate, a cylindrical one, or with a specific curved surface.

[0012] Figure 1 is the new type of electric fuse with improved cooling made from a high breaking capacity fuse SF, with knife terminal contacts and the aluminum heat sink R, mounted on one of the external surface of the ceramic body of the fuse. The aluminum heat sink R, has actually only one horizontal baseplate P, in contact with the external surface of the cermaic body and to its ends in order to enhance the thermal transfer from the ceramic body of the fuse to the environment, there are fins A. Hence, the surface for thermal transfer to the environment is increased very much. The aluminum heat sink is pressed on the external side of the ceramic body of the fuse using a prestressed stainless wire S, which is mounted through the fins A, of the heat sink R, and the opposite side of the ceramic body of the electric fuse.

[0013] With the aim to save space in horizontal plane, when three fuses are used in a three-phase electrical installation, for instance, the assembly from figure 2 can be used. On two lateral sides of the ceramic body of the electric fuse SF, two aluminum heat sink R, are mounted in vertical plane. Like in previous case, the heat sink in contact on the external surface of the ceramic body is made only by a simple baseplate P, with a specific thickness. As shown in figure 2, at one of the end of the aluminum heat sinks R, there are also the fins A, in order to increase the thermal exchange surface to the environment.

[0014] In the case of the fuses with many fuse links mounted in parallel inside the ceramic body, in order to increase the efficiency of the fuse cooling, the power assembly from figure 3 can be used. It observes that on three lateral sides of the ceramic body of the fuse SF, an aluminum heat sink R, is mounted provided with a series of fins A.

[0015] With the aim to increse the cooling efficiency of the electric fuse, besides the aluminum heat sink R, with fins A, mounted on one of the lateral side of the ceramic body of the fuse SF, there is possibility to use a small fan V, as shown in figure 4. The fan is made from plastic as ones used to cool the microprocessors or microcontrollers from computers. It can be supplied on 5V direct current or alternative current through a simple rectifier.

[0016] At fuses with high rated current and important power loss value, the structure shown in figure 5 can be used. The aluminum heat sink R, with long fins A, is mounted on the external surface of the ceramic body of the fuse SF, and on this heat sink is mounted the small fan V, in order to get a forced cooling of the electric fuse.

Claims

1. Fuse with improved cooling characterised in that said an aluminum heat sink (R) with fins (A) to increase the surface of thermal transfer to the environment, is mounted on one of the lateral sides of the ceramic body of the fuse (SF).

2. Fuse with improved cooling according to claim 1, wherein said to achieve a good thermal contact between external surface of the cermaic body of the fuse (SF) and the aluminum heat sink (R), a silicon paste/compound with high thermal conductivity is used.

3. Fuse with improved cooling according to claim 1, wherein said to save space in the case of three phase electrical installations, the aluminum heat sinks (R) with fins (A) can be mounted in vertical position on two lateral sides of the ceramic body of the fuse (SF).

4. Fuse with improved cooling according to claim 1, wherein said at fuses (SF) with high rated current, three aluminum heat sink (R) with a series of fins (A) can be mounted on three lateral sides of the ceramic body of the fuse (SF).

5. Fuse with improved cooling according to claim 1, wherein said to increase the cooling efficiency besides the aluminum heat sink (R) with fins (A) mounted on the ceramic body of the fuse (SF), there is a small fan (V) made from plastic and mounted on the top of the aluminum heat sink (R), supplied with 5V direct current.

6. Fuse with improved cooling according to claim 5, wherein said the small fan (V) mounted on the top of the aluminum heat sink (R), is supplied in alternative current through a rectifier.

Drawing