ES2580042T3 - Surge arrester provided with a device that signals a degradation situation - Google Patents

Abstract

A surge arrester consisting of a first and a second terminal (1, 2) for connection to the active conductors of a power plant, between which a protective element (3) is inserted, provided with a pair of electrodes (4) electrically connected to said connection terminals, said protection element (3) being degradable with temperature depending on the weather, and between said first terminal (1) and an electrode (4) of the protection element (3) is provided a disconnector, characterized in that it additionally comprises a signaling device (30-39) of the state of degradation of said protection element (3), comprising at least mobile means (30, 33), having a pressure element (30a ), which is loaded by an elastic means (35) against a cushion (H) made of material of variable viscosity with temperature, signaling means (36) connected to said mobile means, whose signaling means ón (36) show the level of degradation depending on the displacement thereof caused by the sinking of said pressure element (30a) of said mobile means (30) within said cushion (H).

Description

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DESCRIPTION

Surge arrester provided with a device that signals a degradation situation Scope of the invention

The present invention relates to an improved structure of a surge arrester, also defined as a surge arrester or, to synthesize, SPD (Surge Protection Device). With these terms, reference is made to those electrical or electronic devices, connected between the active terminals of the power plant and ground, that discharge surge peaks to the ground - such as those generated by atmospheric rays and switching maneuvers - that may, on the other mode, cause serious damage to the power plant and its appliances.

Prior art

Direct atmospheric phenomena are the main cause of the devastating destructive effects on power plants; Indirect discharges and switching surges are also a source of corn flakes, whose origin is not easy to identify, but whose effects are equally harmful to sensitive plants, in which it is essential that there is continuity in their operation. The duration of these phenomena varies between a few microseconds to a few hundred milliseconds, but in this short period of time they concentrate an extremely high energy content. These phenomena must be properly intercepted to protect the plants connected to the network and thus guarantee their integrity and operation. At present, with the increasing use of electrical and electronic equipment and with the exponential increase in the level of semiconductor integration, it is necessary to pay increasing attention to this matter, compared to the past. The awareness that transient overvoltages represent a relevant factor in the characteristic "average time between avenues" (MTBF) of a plant or apparatus, has raised the need for greater and more effective safety measures.

All this has led to the increasing attention of the sector, which has generated, on the one hand, an effort on the part of the manufacturers in the development of equipment more efficient than ever and, on the other hand an effort on the part of the standardizing organisms in the definition of more precise national and international requirements and standards that must be met by technological developments.

The present invention relates to the manufacture of devices for surge protection - devices referred to below as arresters - the application of which is regulated, for example, in IEC standards EN 62305-1 / 4, Ed. 2 (2011-02), IEC 60364-4-44-443 Ed. 2 (2007) and CLC / TS 50539-12 (2010-03) for protection against lightning and surges due to switching. The requirements and test methods refer to IEC 61643-11 Ed. 1 (2011-03) and IEC EN 50539-11 (2013-02).

In particular, in this context, the arresters will be treated according to the most recent technique, which includes a varistor and specific protection element for BT plants (low voltage, that is, nominal voltage of up to 1000 V AC and 1500 V DC ) and photovoltaic plants (AC side and DC side).

The varistor used in the arresters is a well known component; its behavior is the same as that of a variable (nonlinear) resistance in the voltage / current relationship. Once the reference voltage has been exceeded, for example when a short duration surge occurs, the varistor abruptly reduces the resistance, so that the current peak can be easily discharged to ground and does not continue to other parts of greater resistance of the plant. A varistor usually consists of a mass of semiconductor material (for example, ZnO), inserted as a sandwich between two opposite metal surfaces, which make up the electrodes to which the terminal contacts are electrically connected for connection with the arrester .

In the internal circuit of the arrester, in series with the protection element in the form of a varistor, a “disconnector” is normally supplied, which is a complex release device, with protective functions in case of failure of the protection element.

EP 14160969.3 describes an example of a particularly effective disconnector in the name of the same Applicant.

Under normal conditions, that is, in the absence of overvoltages, the protection element has such a high impedance that it represents an interruption of the ground circuit and the current flowing inside the arrester is insignificant. Therefore, no current flows to the ground that can generate dangerous conditions for the safety of people. This system, widely known, works highly effectively as long as the protection element (for example, the varistor) is fully operational.

After several overloads due to large transient currents discharged to ground, an excessive number of operations or abnormal conditions of the supply network, the protection element (normally the varistor) undergoes an aging and degradation process after which it gradually begins to reduce your

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impedance and, therefore, to discharge to ground, even in the absence of surges, increasing values of currents and increasingly significant. As low as the impedance reduction is, the value of the ground discharge current will also be small, and the operation of the arrester will still be acceptable, but above certain values, the arrester becomes unusable and dangerous for users. At this point it must necessarily be disconnected from the plant.

Since the degradation of the arrester does not follow a linear trend, a device that quickly disconnects it from the plant must be supplied, in the event that the values of the current discharged to the ground suddenly become high. Said device is the aforementioned disconnect.

However, this type of device works independently of the ability to identify in advance the actual state of degradation of the arrester. It should be considered in any case that an early indication of the level of degradation is, on the contrary, beneficial and desirable to be able to prepare in a timely manner the replacement of the operating arrester, before its functionality is finally affected. This previous activity, as it is logical, is of all desirable point to be able to always have the plant in optimal operating conditions.

It should not be forgotten that a arrester that operates in degraded conditions cannot effectively carry out its protective function when it is damaged by the maximum transient currents for which it has been designed and installed. This is a particularly pernicious situation because the current legal requirements establish a series of rules related to the installation of security, but do not refer at all to a sensitive issue such as the ability to guarantee the function of protection against surges in the presence of situations of reduced efficiency. In other words, if the protection function is not carried out effectively, the rules only provide, subsequently, the obligation to replace the component, but does not establish anything related to precautionary measures.

On the other hand, there is no doubt that the life of a arrester cannot be determined beforehand, since multiple factors affect it, fundamentally the number and intensity of the current discharges that circulate through it and that progressively cause the deterioration of the impedance internal: in fact, it is known that the deterioration of a arrester is always associated with a Joule heating, which increases over time, caused by small leakage currents that run through it (in a new one, they are below 1 mA, under conditions of deterioration the magnitude is a few mA).

For a timely verification, in Teona such currents can be measured, but it is difficult to perform it in practice in technical and economic terms given the application and existing spaces. Also, the detection of temperature, as an indicator of the state of degradation, will be a viable and more direct solution, but it will be necessary to measure the complex amount "temperature in relation to time". In fact, in the processes of transient discharge the temperature of the varistor rises sharply but the subsequent cooling process begins immediately: a powerful thermal fatigue therefore operates for a short period of time; on the contrary, a degradation process occurs from less intense thermal fatigue, which, however, continues indefinitely in time. Supervising such magnitudes over time is a technically difficult and expensive task.

In some installations, it has been proposed to count the number of transient discharges, as an approximate indicator of the potential degradation of the arrester, but the result is not fully reliable, so spare elements should be provided at a very early stage with respect to the functionality that the downloader could guarantee.

Document US 2008/019073 A1 describes a surge arrester comprising a degradation state signaling device, for example, of the electrical connection of a varistor to a terminal and signaling means mechanically associated with said disconnector and capable of presenting on the screen, for example, two different electrical connection / disconnection situations.

The Applicant has addressed this issue, considering that the correct indicators of the degradation of an arrester cannot be other than the leakage current and the corresponding heating that act over time, paying attention to the number of repeated transient phenomena that trigger the degradation.

Summary of the invention

The problem at the foundation of the invention is therefore to propose a downloader structure that overcomes the difficulties mentioned above and that allows to provide a reliable and realistic indication, in real time, of the state of the actual degradation of the arrester. These objectives are achieved by means of a surge arrester according to claim 1. The embodiments of the invention are embodied by means of the features set forth in the essential terms in the appended claims.

In particular, according to a first aspect of the invention, there is provided a surge arrester comprising a first and a second terminal for connecting to the active points of an electric plant between which a protection element is inserted, equipped with a pair of electrodes electrically connected to said connection terminals, said protection element being degradable by temperature depending on the

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time, and between said first terminal and an electrode of the protection element a disconnector is provided, which further comprises a device for signaling the state of degradation of said protection element, which comprises at least one mobile means, which has an element of pressure loaded by elastic means against a pad made of viscous material variable with temperature, and which has signaling means connected to said mobile means, said signaling means showing the level of degradation as a function of its displacement caused by the sinking of said pressure element of said mobile means within said cushion. In particular, said mobile means is a mobile slider. Preferably, said mobile slider is in the form of a rigid rod, sliding along its longitudinal axis under the preload of said elastic means, and said signaling means having the form of a visible signaling strip through a window from the window. outside the surge arrester housing.

According to a preferred aspect of the invention, the arrester is also provided with a contrast plate hidden from view, through said window, by the end of said signaling strip and which becomes progressively visible as a function of the displacement of said signaling strip.

Preferably, said signaling means comprises a micro-switch capable of triggering a warning signal and that is activated when said mobile means performs a pre-set displacement.

According to another aspect, said pad is placed between said pressure element of the mobile means and a support integrated in a surge arrester housing.

According to a preferred aspect, said pad is made of heat meltable resin. In particular, said hot melt resin has a softening temperature ranging from 90 ° C to 140 ° C.

According to one aspect of the invention, said pad (H) is obtained in situ by means of the injection of mass of heat meltable resin in a fluid state, which is made to solidify while maintaining said elastic medium in a preload state.

Brief description of the drawings

Other advantages and disadvantages of the invention are in any case evident from the following detailed description of a preferred embodiment, given merely by way of non-limiting example and illustrated in the accompanying drawings, in which:

Figure 1 is a schematic side elevation view, with certain parts removed, of the structure of a arrester equipped with a degradation signaling device according to the invention; shown the unloader in operational conditions and with a new degradation signaling device;

Figure 2 is a view similar to that of Figure 1, but with the degradation signaling device in medium condition; Y

Figure 3 is a view similar to that of Figure 1, but with the degradation signaling device in a final state (device to be replaced).

Detailed description of a preferred embodiment

The different side views of the devices attached in this document represent a downloader which, in its general configuration, corresponds to that described in the aforementioned application EP14160969.3. It consists of a body similar to a box or module C, of dimensions such as to be housed in a single standardized module and wired inside a switching plate for low voltage power plants.

In this module C two opposite terminals are housed - a first terminal 1 for the connection of the phase terminal and a second terminal 2 for the connection of the neutral or protection terminal - between which a protection element (usually a varistor) is mounted , schematized by a plate 3, on whose opposite surfaces respective conductive electrodes are provided (only one electrode 4 is shown in the drawings; the other being on the opposite side cannot be seen in the drawing).

The electrode 4 is electrically connected to the phase 1 terminal, while the opposite electrode is connected to ground or to the neutral terminal 2. The connection between the electrode 4 and the phase 1 terminal is made by a conductive means forming an element of the disconnector .

In particular, such a conductive means of the disconnector has the form of a flexible sheet 5, which is elastically preloaded and connected to the electrode 4 by means of a suitable welding of low melting temperature at the point marked 5d.

The material used to perform low melting point welding typically belongs to the group of tin, lead, bismuth, binary or ternary indium base, eutectic and non-eutectic formulations, with melting temperatures ranging between 120 ° C and 180 ° C .

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In the example configuration illustrated in the drawings, the disconnector sheet 5 is generally folded in a U-shaped So.

During normal operation (standby position of the disconnector), this configuration ensures the electrical continuity between the connection terminal 1 and the electrode 4 of the varistor, by means of the lamina 5.

In module C a gma 6 is further formed along which a slider, loaded and pushed by elastic preload means, for example a pre-compressed spring, can be moved longitudinally, for the interruption function of the electric circuit better described in the Application cited EP14160969.3.

With this assembly, in the condition of rest of the disconnector, when the foot 5d is welded to the electrode 4, the slider is retained in its initial position, against the precompression load of the spring. This is the normal condition of the arrester (also shown in Figure 1).

When, due to the slow degradation of the protection element in the varistor form, the current begins to flow (even at low intensity but continuously) through the disconnector sheet 5, said current eventually heats the welding point between the electrode 4 and foot 5d, until the welded material melts and consequently interrupts the restriction. This triggers the action of the disconnect, in accordance with the manner widely described in the application EP14160969.3.

According to the invention, very close to the assembly of the disconnect, an indicator of the degradation is provided, based on materials whose viscosity depends on the temperature.

In particular, the degradation indicator according to the invention consists of a sliding, mobile-like signaling means, which is loaded by elastic means against a resin-made pad, whose viscosity depends on the temperature, in particular a family resin called "heat meltable resins".

These resins, already known and used (with specific formulations) in hot bonding processes, are solid at room temperature, but progressively acquire a less viscous behavior as the temperature increases, until a complete fluidization.

Appropriate heat-meltable resins are thermoplastic polymers consisting of a polymer base added with a wide variety of additives (pigments, stabilizers, plasticizers, ...). The polymer base normally consists of polymers such as copolymers of ethyl vinyl acetate (EVA), ethylene acrylate, polyolefins (PO) and amorphous polyolefins (APO, APAO), polyethylene (LDPE, HOPE), polypropylene (PP, APP), polybutene-1 and copolymers thereof, polyamides, polyester, polyurethane (PUR), thermoplastic polyurethane (TPU), styrene-based copolymers (SBC, SBS, SIS, SEBS, SEP), polycarbonates and fluoropolymers.

Normally the thermoplastic joints within these resins are reversible, unless they are subjected to curing processes: therefore, after suffering a sufficient thermal load, they tend to soften and become liquid, losing cohesion and greatly reducing this viscosity, even after a first solidification.

The application temperatures of heat-meltable resins are typically in the range 160 ° C and 220 ° C, within which the corresponding viscosity drops rapidly from 3000 mPa to less than 2000 mPa. A fundamental feature of these materials, especially with reference to the context of the present application, is the softening point (softening point), at which the material viscosity begins to decay significantly.

Surge arresters are arranged to work at maximum outside temperatures not exceeding 120 ° C, but, at the same time, they must be able to be maintained at a temperature of around 80 ° C without altering: therefore, according to the invention, Variable viscosity materials (heat meltable resins) are chosen so that the softening temperature (i.e., the temperature above which the viscosity falls below predetermined values, established by agreement) is in the range between 90 ° C-140 ° C.

Returning to the specific configuration of interest for the invention, it should be noted that the penetration resistance, which a pad of heat-meltable resin offers to an elastically charged, sliding type mobile medium, is therefore inversely proportional to the temperature at which Said cushion is exposed: the slider progressively sinks into the cushion, the more the lower the viscosity of the cushion and the longer the exposure time, thus carrying out a stroke or displacement proportional to the temperature and the exposure time to said temperature.

Taking advantage of this behavior, the solution proposed by the present invention is the assembly of a heat-meltable resin pad between a part of the electrical circuit exposed to be heated by the dispersion currents and a mobile equipment exposed to the action of charging means that they push it against said resin pad.

Referring now to the accompanying drawings, a preferred embodiment is illustrated, in which the degradation signaling device consists of a slider 30, which slides in a gma ring 31, integrated in turn with a conductive terminal 32 of the arrester . For this purpose, the terminal 32 has a hole through which the slider 30 passes, preferably being formed in the form of a circular section rod.

5 On the slider 30 a round nut 34 or other stop element is fastened, against which a first end of a spiral spring 35, whose other end is supported on the ring 31, which is the terminal 32 acting as a fixed support element. Due to this assembly of the spring 35, the slider 30 is elastically loaded in the direction of the free end 33 thereof, that is, downwards in the drawing of Figure 1.

According to the invention, between a pressure element 30a integrated in the slider 30 and a fixed part of 10 support, for example the same terminal 32, a temperature-dependent viscosity resin pad, usually meltable resin, is provided by hot. The bearing H, when in its solid state, keeps the pressure element 33a of the slider 30 separated apart from the fixed support 32, against the load caused by the spring 35. This separating function, against the action of the spring 35, is performed provided that the heat-meltable resin pad has a solidification or viscosity sufficient to prevent the pressure element 30a from penetrating into the resin.

The pressure element 30a, for example, has the shape of a short arm that protrudes transversely from the slider 30.

The mass of the pad H preferably extends over a volume of at least 400 mm 3, so as to determine a sliding intervention stroke of at least 6 mm.

20 The pad H can be constructed separately and then installed on the body plate C in the solid phase, after bringing the spring 35 to a preload situation. Alternatively, the pad H can be manufactured in situ: initially, the pressure element 30a of the slider 30 is made to move backwards, compressing the spring 35 and then a mass of molten heat-melted resin is directly injected into its seat inside the seat. body C, for example, by means of a glue dosing gun. Once the mass of 25 cushion H has been injected, it is expected that the resin cools and solidifies at which time the slider 30 can be released, so that the spring 35 compresses the pressure element 30a in the support on The solidified bearing.

The mass of the pad H can also surround part of the slider 30, which must however be free to slide through.

According to another embodiment, it can be provided that the resin mass H is enclosed in a suitable cover whose volume is varied by the movement of the pressure element 30a, which therefore acts as a plunger. In such a case, the cover additionally has a calibrated flow outlet opening, through which the viscous mass of resin H can exit: hence the displacement of the slider 30 can be further controlled by acting both on the resin composition and on the size and conformation of the opening of the outflow.

Preferably, in a position opposite to the most distant end 33 of the slider 30, a fixed limit switch support 33a is provided: advantageously, a micro switch can be provided at the limit switch 33a, for the function illustrated more Go ahead with detail.

At the nearest end of the slider 30, opposite the most distant end, a signaling strip 40 36 is fastened, which consists for example of a flexible thin sheet, which travels along a first segment,

oriented substantially in accordance with the axis of the slider 30, and then oriented along a second segment, perpendicular to the first, until it corresponds to a signaling window 37.

The signaling strip 36 preferably has the form of a polycarbonate sheet, for example, colored green.

45 The signaling window 37 is substantially an opening or an cleared area in the housing of the body C, so as to make the underlying portion of the device visible from the outside.

The terminal part of the signaling strip 36 is located behind the window 37 and conceals an underlying contrast plate or tape that looks very different from that of the signaling strip 36, for example orange. Under normal working conditions, only the signaling strip 36 is visible through the window 37, for example of green color, which completely covers the underlying contrast tape 38. When, following the displacement of the slider 30, also the end of the marking strip 36 is dragged and displaced with respect to the window 37, at least part of the tape / contrast plate 38 is uncovered by the strip and becomes visible, in a possibly orange color.

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The elongation of the contrast tape / plate 38 that is visible from the outside, through the window 37, gives an indication of the extent of the displacement made by the slider 30 and, as a last analysis, of the degradation experienced by the device .

During operation, the signaling device according to the invention has the following operating mode.

Whenever the unloading device experiences overheating, especially if it is a significant duration in time, the mass of heat-meltable resin of the H-bearing reduces its viscosity and facilitates a certain penetration of the sliding element 30a of the slider, which results in the corresponding displacement of the slider 30 and therefore of the stroke of the signaling strip 36. Repeated heating cycles of this type produce a displacement of the signaling tape 36 sufficient to make the phenomenon visible from the outside, by means of the appearance of the tape / contrast plate 38 through the window 37, more clearly the more the heating of the softening of the H-pad (and consequently the degradation of the device) has caused the heating.

In an initial phase of degradation, this displacement of the tape is moderate and therefore the green part of the tape 36 is still, at least partially visible through the window 37. However, the orange color of the plate 38 It is - at least in part - already visible. This is clearly shown in Figure 2 and indicates that degradation has begun.

It is evident that the user of the system can intervene in the replacement of the apparatus as soon as the part colored in orange becomes of dominant importance through the window 37.

Figure 3 finally shows the final arrangement of the signaling device, that is, when the signaling tape 36 has been completely displaced and the only orange contrast tape 38 has been made completely visible. Under that condition, the replacement of the apparatus is mandatory .

In this terminal phase of the signaling process, the end 33 of the slider 30 ends its movement against the fixed end-of-stroke support 33a. The support 33a must be provided with a micro switch, so it is also possible to generate an electrical signal that can activate a remote warning of total degradation (in addition to the evidence obtained locally in the window 37 of the unloading device).

As is evident, the advantage of the described arrangement is given by the fact that the displacement of the signaling tape 36 is progressive depending on the amount of heat developed by the system over time; Therefore, in other words, it not only depends on the temperature reached by the underlying heating in absolute values, but also depends on the time elapsed in the various heating conditions.

This displacement is also connected to visual signaling means, which indicate, according to various means, the degradation achieved and therefore the need to replace the arrester before its natural life limit. This signaling resides temporarily between the two signals provided by the rules, that is, the regular operation and the fault.

However, it will be understood that the invention cannot be considered limited to the special assembly illustrated above, which only attempts to exemplify an embodiment thereof, but that different variants are possible, which may be internal or external with respect to the SPD, all within of the scope of persons skilled in the art, without departing from the scope of the invention, as defined by the following claims.

For example, although the mobile medium is described in the drawings as a slider, it can have a different shape, such as a pivoting lever or a vaiven or other signal.

Claims (9)

5 10 fifteen twenty 25 30 35 1. A surge arrester consisting of a first and a second terminal (1, 2) for connection to the active conductors of a power plant, between which a protection element (3) is inserted, provided with a pair of electrodes (4) electrically connected to said connection terminals, said protection element (3) being degradable with the temperature depending on the time, and between said first terminal (1) and an electrode (4) of the protection element (3) a disconnector is provided, characterized in that it further comprises a signaling device (30-39) of the state of degradation of said protection element (3), which comprises at least mobile means (30, 33), having a pressure element (30a), which is loaded by an elastic means (35) against a cushion (H) made of material of variable viscosity with temperature, signaling means (36) connected to said mobile means, whose signaling means (36) evidences n the level of degradation depending on the displacement thereof caused by the sinking of said pressure element (30a) of said mobile means (30) within said cushion (H). 2. Surge arrester according to claim 1, wherein said mobile means is a mobile slider. 3. Surge arrester according to claim 2, wherein said mobile slider is in the form of a rigid rod (30), slidable along its longitudinal axis under the preload of said elastic means (35), and in wherein said signaling means are in the form of a signaling strip (36) visible from the outside of a housing (C) of the surge arrester through the window (37). 4. Surge arrester according to claims 2 or 3, which is additionally provided with a contrast plate (38) hidden from view, through said window (37), by the end of said signaling strip (36 ) and that it becomes progressively visible depending on the displacement of said signaling strip (36). 5. Surge arrester according to any of the preceding claims, wherein said signaling means (36) consists of a micro switch capable of triggering an alarm signal and which is activated when said mobile means (30) has made a default offset. 6. Surge arrester according to any of the preceding claims, wherein said bearing (H) rests between said pressure element (30a) of the mobile means (30) and a fixed support (32) integrated in a housing (C ) of the surge arrester 7. Surge arrester according to any of the preceding claims, wherein said pad (H) is made of a heat meltable resin. 8. Surge arrester according to claim 7, wherein said heat meltable resin has a softening temperature in the range between 90 ° C and 140 ° C. 9. Surge arrester according to claim 7 or claim 8, wherein said pad (H) is obtained in situ by injecting a mass of heat meltable resin in a fluid state to which it is solidifies while maintaining said elastic means (35) in a preload state.