SI23040A - Varistor with defined weak spot within its structure - Google Patents

Abstract

The invention refers to varistors featuring a deliberately and position defined weak spot on the structure of varistors and inside of them with the basic purpose of upgrading the varistor featuring a thermal disconnector in surge protection modules. The varistor with the deliberately integrated weak spot inside the structure according to requirement number 1 is characterised in that inside the varistor body (1) there is a weak spot (2) of circular shape with depth (2a) and the spot on the body (1) can be selected randomly considering the varistor size. The varistor despite the weak spot (2) where the local overheating of the body (1) takes place does not negatively affect the energy absorption of the varistor. Upon the passing of the current through the varistor regardless of the reason for such a current, there is always a slightly higher current running through the weak spot (2) of the varistor body (1) compared to the remaining structure. Upon the process of adequate current distribution inside the varistor this can be triggered at the defined integrated weak spot (2) of the varistor and the process of local heating is started which due to the high conductive factor quickly spreads across the complete varistor body (1). In the case of high but short power overloads the temperature is quickly transferred from the weak spot (2) to the whole varistor body (1), while in the case of longer overloads the deliberately integrated weak spot (2) acts as a relatively constant source of temperature which enables the upgraded thermal disconnecting system to perform the adequate reaction and to physically disconnect from the system.

Description

VARISTOR WITH DEFINED WEAK POINT IN STRUCTURE

The field of technology

The invention relates to a varistor with a purpose-defined and positionally defined weak point on and in the structure of the varistors for the primary purpose of upgrading the varistor by thermal disconnection in overvoltage protection modules.

A technical problem

The technical problem that the invention solves is the structural solution of the varistor, which will have a purpose-defined and positionally determined weak point. In combination with thermal disconnection, a purpose-defined and positionally defined weak point will enable precisely defined, fast, efficient and safe disconnection of protection modules and their protection against complete destruction in the event of excessive electrical overload. The invention solves the positioning of a purpose-built weak point and defining its effect for that minimum required displacement that is greater than some natural inhomogeneity of the structure, which at the same time does not weaken the general defined energy absorption of the varistor.

The prior art

Varistors are passive components that are preferably made of a ceramic material such as zinc oxide with the addition of other metal oxides. They have a specific non-linear U / l characteristic, which is very similar to the dual Zener diode characteristic, but with significantly higher current absorption. They are mainly used in surge protectors. As limiting elements, in the case of electrical overloads in the form of surges or surges, they must absorb the resulting energy and limit the voltage to a non-hazardous level that is no longer detrimental to the components, devices or systems protecting them.

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For varistors, therefore, in addition to voltage limitation, one of their most important characteristics is their ability to absorb energy. This is the energy that the varistor can still absorb before complete destruction. It is measured and given in the form of current absorption in [kA] for short-term pulse shapes, or as temporary overvoltage in [V] in the case of defects in the infrastructure systems to which they are installed. For all electrical overloads, regardless of the cause of their formation, the received energy is converted into thermal energy, and depending on the varistor structure it depends on the temperature distribution in the structure itself. The flow through the varistor body is generally distributed unevenly and undefined as a result of a technological process.

According to the state of the art, all the solutions we know are directed to the ideal varistor structure both at the level of material preparation and in the manufacturing process. There are quite a few solutions for material defects detection and solutions aimed at controlling the manufacturing process with the aim of preventively eliminating all risks associated with potential defects in the structure of the varistor body. However, since certain natural anomalies always occur during the fabrication process, the ideal homogeneity of the structure cannot be achieved in any case, resulting in uneven current distribution and local overheating.

In the available documents, we have not found a solution to deliberately create weaknesses or other anomalies in the structure of the varistor body at predetermined points on the surface or inside the varistor body, and related solutions to the effective definition of a weak or hot spot.

Description of the solution

The point of a varistor with a defined weak point in the structure is that the local overheating has a predetermined location at the exact location of the varistor body, which at the same time does not impair the energy absorption of the varistor. A built-in weak point in the structure of a varistor body may have a circular, rectangular or any other geometric shape. The number of purpose-built weak points can be arbitrary. When there are several weak points in one body structure of a varistor, • these are the same geometric shapes or a combination of different geometric shapes.

A varistor with a defined weak point in the structure will be described below with the help of pictures showing:

Figure 1 - View of various forms of purpose-built weak points in the varistor body of the invention

Figure 2 - Temperature gradient (5) in a purpose-built weak point in the varistor body compared to the course of the average temperature (6) of the varistor body upon absorption of a current impact

A varistor with a defined weak point in the structure is characterized in that in the varistor body 1, the weak point 2 is in a circular shape with a depth of 2a. The spot on the body can be arbitrarily selected according to the size of the varistor. Despite the weak point 2 where the local overheating of the varistor body takes place, the varistor does not impair the energy absorption of the varistor. The varistor of the present invention achieves the basic goal of passing a slightly larger current through the weak point 2 of the body 1 of the varistor when passing the current through the varistor than through the rest of the structure. When this process of proper current division is triggered at the varistor's defined built-in weak point 2, the process of adequate local heating begins, which, due to its large coefficient of conduction, rapidly spreads to the entire body of the varistor. In the case of large but short-lived electrical overloads, the temperature is very quickly transferred from the site of the purpose-built weak point 2 to the whole body of the varistor, while in the case of long-term overloads, the purpose-built weak point 2 acts as a relatively constant source of temperature, which allows the upgraded thermocouple system to adequately reaction and physical exclusion from the system.

The weak point representing the hot spot is the exact location of the selected site (s) on the surface or depth of the varistor, where in the case of electrical overloads

the varistor temperature rises significantly faster than in the rest of the varistor and is above the average of between 10% and 40%.

Purpose-defined weak point 2 is located on any part of body 1 and is circular in shape, 1 mm in diameter to 15 mm or 0.05% to 60% of the total body surface 1. Depth 2a of point 2 is 0.1 mm to 1 mm or 0.1% to 30% of the total body thickness of 1 varistor.

The material for item 2 is similar to the basic constituent of varistor material, most commonly ZnO and the corresponding dopants, and is incorporated into the basic varistor ceramics during the technological process.

From a technological standpoint, a weak or hot spot is a deliberately defined anomaly with respect to the standard or typified forms of varistors that are now known in the art. A controlled anomaly can be defined as any change in the surface relative to the normal plane in depth or in height relative to the reference (typed) plane.

The varistor according to the invention includes a method for introducing a purpose-defined varistor weak point on the surface, or inside the varistor, or a combination of the two, at a specific location that is technologically determined and allows the prediction of a weak point in electrical overloads. Since, at this point, electrical overloads result in more intense heating than the rest of the body of the varistor, we also call this point a hot spot.

A varistor with a defined weak point in the structure of variant I is characterized in that in the varistor body 1, the weak point 3 is of rectangular shape with depth 3a and the surface of the purpose-built weak point 3 on the surface of the varistor body 1 is in the range 0.05% to 60 % of total varistor area.

A varistor with a defined weak point in structure according to variant II is characterized in that the weak point 4 is a foreign body which is embedded in the body 1. A foreign body is formed by inserting a substance of organic or inorganic origin into the depth of the varistor at any part of the body of the varistor in similar geometric proportions as in varistor variant I.

The characteristics of a varistor with a purpose-built weak point in the structure according to the invention as well as a varistor according to variants I and II is that at a site with a purpose-built weak point, the temperature in the case of electrical overload increases by 10% to 40% faster than in other parts of the varistor body .

A varistor with a purpose-built weak point in the structure is characterized by the fact that the surface of the purpose-built weak point on the surface of the varistor body is in the range 0.05% to 60% of the total surface of the varistor.

A varistor with a purpose-built weak point in the structure is characterized in that a purpose-built weak point is inserted at a depth of 0.1 to 1 mm or 0.1% to

30% of varistor body thickness.

A varistor with a purpose-built weakness in the structure can have any number of purpose-built weaknesses.

A varistor with a purpose-built weak point in the structure can have a purpose-built weakness in any geometric shape. Defined embedded weak points are created on the surface where they can have a circle shape or some other geometric shape. Deliberately installed weak points, anomalies include any variations in the surface of the varistor body that deviate from the requirements of good industrial practice principles for homogeneous material, free of foreign matter and bubbles.

Claims (9)

PATENT APPLICATIONS 1. A varistor with a purpose-built weak point in a structure comprising ZnO base material and suitable dopants is characterized in that it has a purpose-built weak point that may lie on the surface or inside the body of the varistor. A varistor with a purpose-built weak point in the structure according to claim 1, characterized in that in the varistor body (1) there is a weak point (2) in circular shape with a depth (2a) that the position on the body (1) can be arbitrary chosen with respect to the size of the varistor, that despite the weak point (2) where the local overheating of the body (1) takes place, the varistor does not impair the energy absorption of the varistor, that when passing the current through the varistor it flows through the weak point (2) of the body (1) of the varistor is increasing slightly more than through the rest of the structure, in order to initiate the process of proper local heating which, due to the process of proper division of the current through the varistor, initiates it at the defined built-in weak point (2) of the varistor. the large conductivity coefficient is rapidly extended to the whole body (1) of the varistor, so that in the case of large but short-lived electrical overloads, the temperature is very rapidly transferred from the location of the weak point (2) to the whole body (1) of the varistor, d. when, in the case of prolonged overloads, a purpose-built weak point (2) acts as a relatively constant source of temperature, which enables the upgraded thermocouple system to react appropriately and physically disconnect from the system. A varistor with a purpose-built weak point in the structure according to claims 1 and 2, characterized in that at the site with a purpose-built weak point, the temperature in the case of electrical overload rises by 10% to 40% faster than in other parts of the varistor body. A varistor with a purpose-built weak point in the structure according to claims 1 and 2, characterized in that a weak point (2) of circular shape with a depth (2a) is deliberately mounted on the surface of the varistor body, that the surface of the point (2) is ) in the range of 0.05% to 60% «· the total surface area of the varistor body (1), that the depth (2a) is 0.1 to 1 mm or 0.1% to 30% of the varistor body thickness (1). 5. A varistor with a purpose-built weak point in the structure according to claims 1 and 2, characterized in that a weak point (3) of a rectangular shape with a depth (3a) is deliberately mounted on the surface of the varistor body (3a) such that the surface of the point ( 3) in the range of 0.05% to 60% of the total surface area of the varistor body (1), that the depth (3a) is 0.1 to 1 mm, or 0.1% to 30% of body thickness (1) of varistor. 10 A varistor with a purpose-built weak point in the structure according to claim 1, characterized in that the purpose-built weak point (4) at the depth of the body (1) of the varistor is made by inserting substances of organic or inorganic origin that cause the local heating effect according to the claim 3. 15 A varistor with a purpose-built weak point in the structure according to any one of claims 1 to 6, characterized in that the purpose-built weak points are any number. A varistor with a purpose-built weak point in the structure according to any one of claims 1 to 6, characterized in that it is a purpose-built weak point in any 20 geometric shape. A varistor with a purpose-built weak point in the structure according to any one of claims 1 to 8, characterized in that it is purpose-built weak points of different geometric shapes.