EP2221834B1 - Load resistor with defined short circuit protection - Google Patents

Abstract

The power resistance (1) has at least one resistance element (5) as a spiral (6) with two electrical connections (13,14) at the power line (15,16). A short circuit protection (2) has two electrodes (24,25) in a common housing (20), electrically linked to the connections, forming a spark gap (26) between them. They form a short circuit when a voltage overload breaches a threshold.

Description

The invention relates to a load resistor, comprising at least one provided with two electrical terminals resistance element in the form of two at least partially parallel helical strands having resistance coil whose terminals are each connected to a load line and which is arranged in a metal sheath, wherein the helical strands against each other and are electrically insulated against the metal sheath.

Load resistors of the generic type have been known for some time from the prior art. Such load resistors are used in electrical systems, in particular for the "destruction" of excess electrical energy. Such excess electrical energy arises, for example, during idle or overrun operation of machines which are operated by electric motors. The electric motors generate electrical energy as generators in this coasting or idle mode. In order to destroy this electrical energy harmless, it is converted by the load resistance into heat, which is released in a suitable manner to the environment. In this case, such load resistors consist of at least one resistance element provided with two electrical connections, which can be designed in particular in the form of a resistance coil. The resistance coil of the resistance element can be a single or at least two at least partially parallel form mutually extending helical strands, which are arranged in a metal housing. This resistance element is connected via corresponding connections with load lines. In order to effect a corresponding switching or loading of such a load resistor, corresponding controls or arrangements are provided for this purpose, which establishes the connection via the load lines to the resistance element, for example, in the "switching" of an electric motor in the generator mode. The load of the load resistor is usually pulse-like, to avoid overloading the load resistance. An overloading of the load resistance can occur on the one hand, in rarer cases, by occurrence of an "overvoltage" and in the majority of cases by the concern of a permanent load due to a defect of the control or regulation. In particular, a continuous load of a load resistor with a closed metal jacket and in an insulating material and / or an insulating material embedded resistance element leads to an overheating of the load resistance, so that its Isolierstoffpackung and / or insulating material is electrically conductive or, so that an uncontrolled flashover, in particular to the metal jacket out can be done.

In this case, such load resistors can be configured in various ways. It is exemplary here on the DE 20 2007 014 360 U1 directed. This load resistor is a so-called aluminum load resistor, which is characterized in that the actual load resistor with its metal jacket is arranged in a cooling body provided with cooling fins, in particular made of aluminum. At the subject of DE 20 2007 014 360 U1 the resistance element is arranged in the form of a resistance coil in a metal jacket, which is inserted into a corresponding bore of the heat sink is and is in contact with this area. As a result, the best possible heat dissipation is achieved to the outside.

Further shows EP 1 748 679 a load resistance in the form of a heating cartridge with the features of the preamble of claim 1.

Furthermore, load resistors are also known, in which the resistance element is designed in the form of an "open" resistance spiral, which is secured against access, for example, by means of a shut-off grid or the like.

As already mentioned above, such a load resistance, in particular in the case of faulty circuits of the control electronics or of the control electronics, can be partially "overloaded" by an overvoltage or else by a continuous load over a relatively long period of time. In the case of a load designed as a DC voltage, this can in turn lead to a voltage flashover, in particular with respect to this metal jacket. For aluminum load resistors of the type briefly described above, this voltage flashover can also be done to the heat sink, so that it is destroyed due to the extremely high energy. In particular, an explosive evaporation of the aluminum can occur here. This is extremely dangerous especially for the operator who is in the immediate vicinity of such a load resistor. If such load resistances in the environment of an explosive atmosphere, such as e.g. used in paint shops, an outwardly directed, uncontrolled discharge in unfavorable cases can also lead to explosions.

The invention is accordingly an object of the invention to design a load resistor of the generic type such that such uncontrolled discharge processes are safely excluded.

The object is achieved in that a short circuit fuse is provided, which has two mutually parallel Heizwendelabschnitte having a spark gap form and cause a short circuit by a voltage flashover on reaching a predetermined by the load resistance limit load. The short circuit according to the invention takes place innocuous exactly at a predetermined location.

Due to the inventive design of the short circuit fuse is in case of error, d. H. when a limit load of the load resistance is exceeded, causes a predefined short circuit. In particular, an uncontrolled discharge between the resistance element and the metal shell and in particular a possibly envisaged heat sink is safely excluded, so that a threat to the surrounding area is reliably avoided. For this purpose, the short circuit fuse on two mutually parallel Heizwendelabschnitte, which form a spark gap. If an overload occurs, in particular in the form of an energy exceeding the limit load (overvoltage and / or continuous load) at the terminals of the resistive element, then this is reduced by a voltage flashover defined with appropriate design and arrangement of the two Heizwendelabschnitte and / or their mutual isolation. In this case, the Heizwendelabschnitte form a kind of spark gap whose size is set depending on the determined by the load resistance limit load. This voltage flashover causes a short circuit at the same time, so that the assigned control or regulation is either switched off or destroyed. In particular, voltage flashovers can not be uncontrolled at the load resistance to the metal housing, because the safe removal of the "overload" via the short-circuit fuse is defined. Consequently, a risk of persons staying in the surrounding area of the load resistance is also reliably excluded.

Furthermore, by using the Heizwendelabschnitte as "spark gap" until the onset of a voltage flashover, an additional energy reduction is achieved because the Heizwendelabschnitte be heated when concerns a degraded electrical load also.

Further advantageous embodiments of the invention can be found in the further subclaims.

Thus it can be provided according to claim 2, that the electrodes are arranged in a separate from the load resistor, common protective housing. Due to this configuration, the short circuit fuse can also be retrofitted to an existing load resistor in a simple manner without further modification to the control or regulation. This separate training of the short-circuit fuse, a destruction of the load resistance itself is additionally avoided because the flashover occurs externally in the short circuit fuse.

According to claim 3, the Heizwendelabschnitte may each be connected in series with one of the load lines of the resistive element. In this case, starting from the Heizwendelabschnitten from the protective housing two leads are led out, which are each electrically contacted with one of the terminals of the resistance element. The two Heizwendelabschnitte form here with their lying within the protective housing ends a corresponding spark gap. The energy supply to the load resistor takes place in this embodiment of the load lines on the two Heizwendelabschnitte, so that they also reduce the overload by a short circuit when a surplus energy exceeds the energy with a relatively short reaction time by a flashover.

Furthermore, it can be provided according to claim 4 that the distance between the two Heizwendelabschnitte is smaller than the distance of the respective Heizwendelabschnittes to the protective housing. This means that the Heizwendelabschnitte are integrated into the load lines and thus with the resistive element of the load resistor are connected in series. Due to a relatively small distance between these two Heizwendelabschnitten, which is smaller than the distance to the protective housing, it is ensured that a voltage flashover is mandatory between the Heizwendelabschnitten and not between one of the Heizwendelabschnitte and the protective housing.

The use of the heating coil sections in turn has a heating of the short circuit fuse result. Thus, it can be provided according to claim 5 that the Heizwendelabschnitte are accommodated in a housing arranged in the protective, consisting of a ceramic, electrically insulating material receiving body. This ceramic material is selected according to claim 5 such that it is or becomes electrically conductive above a predetermined temperature. This means that when a "overload" occurs, the short circuit fuse first heats up until the ceramic material reaches its electrical conductivity. At the time in which this insulating material of the receiving body is electrically conductive, then the voltage flashover between the Heizwendelabschnitten takes place. In this case, provision is made in particular for the heating coil sections to have a smaller spacing from one another than to the protective housing surrounding the receiving body. This ensures that the material of the receiving body between the Heizwendelabschnitten heats up faster than the areas to the protective housing out, so as to ensure that a flashover is actually done safely between the Heizwendeabschnitten. This refinement has the further advantage, in particular due to the initial heating of the short-circuit fuse, that a flashover does not take place immediately with an overload occurring only briefly, but only after a certain "waiting time", which is determined by the time-delayed heating of the short-circuit fuse ,

It can be further provided according to claim 6, that the receiving body forms a two Heizwendelabschnitte insulating partition and that the dielectric strength of the partition is less than the dielectric strength of the receiving body together with this surrounding the protective housing towards Isolierstoffpackung. This can be achieved by a correspondingly small distance between the Heizwendelabschnitte each other and a correspondingly larger, outer wall thickness of the receiving body together with the Isolierstoffpackung. Also, the Isolierstoffpackung can have a significantly higher dielectric strength than the partition wall of the receiving body. This embodiment also ensures that a voltage flashover can occur only within the short circuit fuse. A danger to the outside is thus safely excluded.

This insulating material package can also be compressed according to claim 7, whereby an increased "dielectric strength" is achieved in particular with respect to the outer protective housing.

Furthermore, it can be provided according to claim 8, that the protective housing consists of a cylinder jacket whose end faces are sealed by two inserted sealing plug. If the short-circuit fuse according to claim 7 is also compressed, an extremely firm hold in particular of the sealing plug in the cylinder jacket is achieved. This ensures that due to the voltage flashover within the short-circuit fuse no external effect, in particular no explosion or the like. More may occur.

Furthermore, it can be provided according to claim 9, that the resistance coil of the load resistor has a lower power density than the two Heizwendelabschnitte the short circuit fuse. This configuration ensures in particular that the voltage flashover exclusively in the short-circuit protection and not in the load resistor. Due to the higher power density of the two Heizwendelabschnitte the short circuit fuse ensures that the short circuit fuse heats up faster than the load resistance when exceeding the limit load of the load resistance, so that in particular the receiving body becomes electrically conductive at an earlier date.

Additionally or alternatively, the metal shell of the load resistor can also be arranged in a matched both in its cross-section and in terms of its length to the dimensions of the metal shell cavity of an existing aluminum alloy heat sink and are in thermal contact with this surface area. This embodiment of the load resistor allows optimal heat dissipation, wherein the heating of the load resistance defined slower than a heating of the short-circuit fuse, so that energy dissipation takes place by voltage flashover safely only in the short circuit fuse.

It can further be provided according to claim 10, that the resistance coil of the load resistor has a lower power density than the two Heizwendelabschnitte the short circuit fuse and that the Heizwendelabschnitte are accommodated in a ceramic, electrically insulating material existing receiving body and that the ceramic material above a predetermined temperature is electrically conductive and that the receiving body is arranged integrated in the load resistor. This configuration results in an extremely compact design of the load resistance. Due to the integrated arrangement and the lower power density of the resistance coil (s) of the load resistance compared to the power density of the Heizwendelabschnitte the short circuit fuse finds a locally and temporally defined discharge within the load resistance instead, so that an external effect of any kind is safely excluded. In particular, a hazard (of whatever kind) is safely excluded by persons staying in the vicinity of the load resistance.

If the Heizwendelabschnitte the short-circuit fuse according to the embodiment of claim 10 provided with its own protective housing, it may be included replaceable in the load resistance, so that it can be renewed after an overload and possibly associated destruction of the short-circuit fuse.

For such a load resistor integrated arrangement of the short-circuit fuse, the Heizwendelabschnitte may also be formed by the helical strands of the load resistor or its resistance element itself according to claim 11. For this purpose, it is further provided according to claim 11 that the Heizwendelabschnitte are arranged side by side extending in the metal shell and that the Heizwendelabschnitte are accommodated in a Isolierstoffpackung and that the Heizwendelabschnitte have a smaller distance from each other than their respective distance from the metal shell. This embodiment provides an extremely simple and cost-effective design of the load resistor with "integrated" short-circuit protection.

It can further be provided according to claim 12 that the helical strands of the load resistor in the region of their connection to the terminals over a portion of their length form the two Heizwendelabschnitte the short circuit fuse and that the Heizwendelabschnitte in this area have a smaller distance from each other than the "remaining "Spiral strands of each other and in particular as the" remaining "coil strands to the metal shell of the load resistance. This configuration also ensures that the smallest possible construction possible Voltage flashover when exceeding the limit load occurs only within the load resistance and no external effect occurs. It is also important for this purpose that the heating coil sections which form the short-circuit fuse are arranged in the immediate vicinity of the connection points of the connections, since the highest voltage potential is located in this area.

Next can be provided for an integrated arrangement of the short circuit fuse in the load resistor according to claim 13, the coil strands of the load resistor form the two Heizwendelabschnitte the short circuit fuse and that the Heizwendelabschnitte are arranged side by side extending in the metal shell and that the Heizwendelabschnitte in a particular from a ceramic, electrically insulating material existing receiving body are received and are electrically insulated from each other by a partition of the receiving body and that the partition is electrically conductive when reaching a certain temperature, so that between the Heizwendelabschnitten a voltage flashover occurs. By the receiving body, in particular, we ensure that the short-circuit fuse and thus the Heizwendelabschnitte forming helical strands of the resistance coil of the load resistor are positioned accurately positioned during production in the metal shell and remain.

In a further alternative embodiment may be provided according to claim 14, the helical strands of the load resistor form the two Heizwendelabschnitte the short circuit fuse and that the Heizwendelabschnitte are arranged side by side extending in the metal shell and that the Heizwendelabschnitte existing by a ceramic, electrically insulating material Partition are separated from each other and that the partition electrically when it reaches a certain temperature becomes conductive, so that between the Heizwendelabschnitten a voltage flashover occurs. Due to the thermal electrical properties of the partition is also ensured by this configuration that takes place only between the Heizwendelabschnitten the short circuit fuse when exceeding the limit load, a flashover. The entire arrangement of the Heizwendelabschnitte forming helical strands together with the partition is preferably embedded in an insulating material whose insulating properties ensures sufficient electrical insulation of the Heizwendelabschnitte to enveloping metal shell even at higher temperatures.

The embodiment according to the invention of a load resistor with short-circuit protection thus achieves, in particular, considerably improved personal protection of persons staying in the vicinity of the load resistance. If the short-circuit fuse is arranged as an external component outside the load resistor, destruction or damage to the load resistor itself is additionally excluded. With such a separate "design", the short-circuit fuse can also be retrofitted to a load resistor with appropriate design.

It should be noted that the inclusion of the or resistive elements (s) and / or Heizwendelabschnitte in the metal shell and / or in the separate protective housing can be done in a non-compressed or a compacted Isolierstoffpackung. Also, a separate Isolierstoffkörper with corresponding mounting holes for the helical strands of the resistor element and / or the Heizwendelabschnitte the short circuit fuse conceivable. Also, a combination of insulating material and Isolierstoffpackung be provided. In this case, for example, the insulating material completely surround the entire arrangement, while the compressed or uncompressed Isolierstoffpackung "only" is provided in the receiving bores. In this case, however, the Heizwendelabschnitte the short-circuit fuse are to be arranged in the smallest possible distance from each other, which must be smaller in any case than their distance from the enclosing protective housing or metal shell. Alternatively, the receiving body may be wrapped with an insulating material, wherein the receiving holes can be filled with Isolierstoffmasse. In order to ensure a voltage flashover exclusively in the area of the heating coil sections of the respective short-circuit fuse, either the distance of the heating coil sections from one another must be selected such that a voltage flashover to the protective housing or (in the case of an integrated arrangement in the metal jacket) to the metal jacket is reliably precluded. This can be done additionally or alternatively by the choice of material and shape of the insulating material and the possibly provided, electrically insulating receiving body.

Fig. 1

eine Schnittdarstellung eines Lastwiderstandes zusammen mit einer als externes Bauelement ausgebildeten Kur- schluss-Sicherung, welche eine Funkenstrecke bildende Heizwendelabschnitte ausweist;

Fig. 2

einen Schnitt II-II durch die Kurzschluss-Sicherung aus Fig. 1;

Fig. 3

eine Ausführungsvariante eines Lastwiderstandes im Schnitt, bei welcher die Kurzschluss-Sicherung integriert im Lastwiderstand angeordnet ist

Fig. 4

eine Schnittdarstellung eines Lastwiderstandes mit integ- rierter Kurzschluss-Sicherung, bei welche die Funkenstre- cke durch Heizwendelabschnitte gebildet sind, welche aus den Wendelsträngen der Widerstandswendel des Widerstand- elementes bestehen;

Fig. 5

eine Schnittdarstellung des Lastwiderstandes aus Fig. 4 mit einer elektrisch isolierenden Trennwand, durch welche die Heizwendelabschnitte und somit die Wendelstränge der Widerstandswendel voneinander getrennt sind;

Fig. 6

den Lastwiderstand aus Fig. 4 mit integrierter Kurz- schluss-Sicherung bei welcher die von den Wendelstränge der Widerstandwendel gebildeten Heizwendelabschnitte im Bereich ihrer Verbindung zu den Anschlüssen einen gerin- geren Abstand voneinander aufweisen als die "restlichen" Bereiche der Wendelstränge der Widerstandswendel des Wi- derstandelementes;

Fig. 7

beispielhaft eine Ausführungsvariante eines Lastwiderstandes, bei welchem die die Kurzschlusssicherung bildenden Heizwendelabschnitte durch die Wendelstränge der Widerstandswendel des Widerstandselementes gebildet werden.

Reference to the drawings, the invention is explained in more detail below in some embodiments. It shows:

Fig. 1

a sectional view of a load resistor together with a designed as an external device circuit fuse, which identifies a spark gap forming Heizwendelabschnitte;

Fig. 2

a section II-II through the short circuit fuse Fig. 1 ;

Fig. 3

an embodiment of a load resistor in section, in which the short circuit fuse is integrated in the load resistor is arranged

Fig. 4

a sectional view of a load resistor with integrated short circuit fuse, in which the spark gap are formed by Heizwendelabschnitte, which aus consist of the helical strands of the resistance coil of the resistance element;

Fig. 5

a sectional view of the load resistor Fig. 4 with an electrically insulating partition, by which the Heizwendelabschnitte and thus the helical strands of the resistance coil are separated from each other;

Fig. 6

the load resistance Fig. 4 with integrated short-circuit fuse in which the Heizwendelabschnitte formed by the coil strands of the resistance coil in the region of their connection to the terminals have a lesser distance from each other than the "remaining" areas of the coil strands of the resistance coil of the resistance element;

Fig. 7

By way of example, a variant of a load resistor, in which the Heizwendelabschnitte forming the short-circuit protection are formed by the helical strands of the resistance coil of the resistance element.

Fig. 1 shows a basic design possibility of a load resistor 1 together with an "external" short-circuit fuse 40 in section. The load resistor 1, in the present embodiment, an outer metal shell 3, which is closed with a bottom part 4. The metal shell 3 may be tubular and have a circular cross-section. Within the metal shell 3, a resistance element 5 is arranged in the form of a resistance coil 6. This resistance coil 6 is arranged in the metal shell 3 extending in a U-shape and forms two helical strands 7 and 8, which in the illustrated embodiment - apart from the arcuate connecting region - parallel to each other. There is the possibility, the resistance coil without further notice 6 in several U-loops with meandering course to arrange.

In its bottom portion 4 opposite end portion of the metal shell 3 is closed with an inserted cap 9. Furthermore, it is off Fig. 1 seen that the resistance coil 6 is embedded with their helical strands 7 and 8 in an insulating material 10. In this case, this Isolierstoffpackung 10 may be compressed, for example, by a radial compression of the metal shell 3. By a radial compression of the metal shell 3, an extremely tight fit of the closure lid 9 in the metal shell 3 can also be achieved.

Furthermore, it is off Fig. 1 it can be seen that of the two helical strands 7 and 8 each have a connecting line 11 and 12 is guided through the closure cover 9 to the outside. These two connecting lines 11 and 12 each form a terminal 13 or 14, which is connected via a connecting wire 50 and 51 with a short-circuit fuse 40 in connection. The Isolierstoffpackung 10 may, as is known, consist of magnesium oxide, silica, quartz sand or a similar, electrically insulating material. This load resistor 1 is used in operation to "destroy" excess electrical energy, especially DC energy, which may be incurred in various electrical systems of various kinds.

Thus, it is known, for example, that electric motors can serve the same except for driving, for example, an elevator, for braking. In the case of switching over this electric motor into the generator operation, which is brought about via a control or regulation, the generated electrical energy, in particular DC energy, must be "destroyed". For this purpose, the load resistor 1 is provided with its trained resistance element 5 in the form of the resistance coil 6. This excess electrical energy is clocked in normal operation, ie pulsed, supplied via the two terminals 13 and 14 and the connecting lines 11 and 12 of the resistance coil 6 and converted into heat. In this case, for a particularly good heat dissipation to the outside of the insulating material 10 and the metal shell 3 be provided. It is also known from the prior art to use this load resistor 1 with its metal jacket 3, for example in a heat sink in the form of an aluminum housing, which in turn may be provided with cooling fins for optimal heat dissipation (not shown in the drawing).

The load resistor 1 with its resistance coil 6 is designed for the purely mathematically resulting electrical loads. However, in particular in the case of faulty circuits, for example the control or regulation, it may happen that the limit load for which the load resistor 1 is designed with its resistance coil 6 is exceeded not only for a short time but permanently or over a longer (impermissible) period. The degraded electrical energy is normally impulsively and relatively briefly transmitted to the load resistor 1, so that it can optimally convert this load into heat. In case of faulty circuits, however, it may happen that the load does not act in a pulse-like manner on the load resistance, but acts as a continuous load, whereby a predetermined limit load of the load resistor 1 is exceeded. Also or in addition, although occurring infrequently in practice, an electrical overvoltage can lead to exceeding the limit load. In any case, exceeding the limit load would normally lead to a voltage flashover from the resistance coil 6 to the metal jacket 3, in particular in the case of an "overheating" of the insulating material packing 10. Such a flashover, in particular to the metal jacket 3 and to further voltage flashovers, can lead to an aluminum heat sink arranged around this metal shell 3 (not shown in the drawing), which can cause destruction or explosive evaporation of the aluminum material. This would be extremely dangerous, especially for people who are in the immediate vicinity of the load resistor 1 with his not shown in the drawing heat sink are. It is therefore important to avert this danger safely.

In order to prevent such an uncontrolled "discharge", the short circuit fuse 40 is provided. In this case, the short-circuit protection can be configured in different variants.

In the embodiment of Fig. 1 is the load resistor 1, the external short-circuit fuse 40 assigned. From this short-circuit fuse 40 shows Fig. 2 a sectional view along the section line II - II off Fig. 1 ,

In the short circuit fuse 40 two Heizwendelabschnitte 41 and 42 are provided, which define a spark gap between them. The two Heizwendelabschnitte 41 and 42 are arranged in the present embodiment in receiving bores 43 and 44 of a receiving body 45 and accordingly by a "partition" 45/1 isolated from each other electrical. This receiving body 45 in turn is in turn embedded in an insulating material 46, which may be compressed. This Isolierstoffpackung 46 may also be provided in the receiving bores 43 and 44 (not shown in the drawing), so that the two Heizwendelabschnitte 41 and 42 defined after compression in the receiving bores 43 and 44 are added. The whole is arranged in a protective housing 47, which is closed at both ends by means of two sealing plugs 48 and 49. Through the sealing plug 48, connecting wires 50 and 51 are led to the terminals 13 and 14 of the load resistor 1 starting from the two heating coil sections 41 and 42. On the opposite side lead two more connecting wires 52 and 53 through the plug 49 of the protective housing 47 through to the outside and are connected via corresponding terminals 54 and 55 with two load lines 15 and 16.

In this embodiment of the short-circuit fuse 40, the two heating coil sections 41 and 42 are connected in series with the resistance coil 6 of the load resistor 1.

The peculiarity of this short circuit fuse 40 off Fig. 1 and 2 It now consists in that, in particular in case of overloading or exceeding the limit load for the load resistor 1, heating of the receiving body 45 takes place. Normally, the load resistor 1 clocked with a pulse-like load is applied, so that it can be easily broken down by alternately cooling and heating by the load resistor 1. However, if the load resistor 1 is subjected to a continuous load in the event of a faulty switching of the control or regulation, this will be "overheated" due to the permanent heating. This "overheating" leads in particular to the fact that, starting at a specific, material-dependent "limit temperature", the insulating compound 10 becomes conductive. This in turn leads to an uncontrolled voltage flashover between the two helical strands 7 and 8 of the resistance coil 6 or between the resistance coil 6 and the metal shell 3. If the metal shell 3 is still surrounded by a heat sink, as indicated in the introduction, then a dangerous voltage flashover after step outside. To counteract this, the special design of the short circuit fuse 40 is provided.

The receiving body 45 of the short-circuit fuse 40 may consist of a ceramic material which becomes electrically conductive upon reaching or exceeding a certain temperature. The two Heizwendelabschnitte 41 and 42 in this case have a higher power density than the resistance coil 6 of the load resistor 1. This causes the short-circuit fuse 40 heats up much faster than the load resistor is at an applied overload, in particular in the sense of a continuous load above a certain temperature (limit temperature) the material of the receiving housing 45 conductive, so there is a voltage flashover between the two Heizwendelabschnitten 41 and 42 through the partition wall 45/1, which also leads to a short circuit. The two Heizwendelabschnitte 41 and 42 thus form a kind of spark gap, which is effective when reaching a certain limit temperature.

An advantage of this embodiment of the short circuit fuse 40 is that a certain time delay occurs until the onset of the voltage flashover. In other words, this short-circuit fuse 40 only reacts after a certain period of time, for example if an overload occurs, over a period of, for example, 10 to 12 seconds. This means that only short-term overloads which can still be withstood without damage by the load resistor 1 do not immediately lead to a short circuit.

Also, the middle partition 45/1 between the two Heizwendelabschnitten 41 and 42 have a small wall thickness, so that even before reaching the limit temperature, a voltage flashover through the partition 45/1 takes place between the two Heizwendelabschnitten 41 and 52. This also an overvoltage protection for short-term "overload" for the load resistor 1 by the short-circuit fuse 40 can be achieved. this should be necessary for certain applications. In particular, a voltage flashover can certainly not occur between the resistance coil 6 and the metal shell 3 or between the Heizdrahtwendeln 41, 42 and the protective housing 47, so that a danger to the outside is safely excluded.

Fig. 3 shows a further embodiment of a load resistor 60, which also has a metal shell 3 and a resistance coil arranged therein 6 with two helical strands 7 and 8. These resistance coil 6 with its helical strands 7 and 8 is in an insulating material 10 within arranged the metal shell 3. The bottom part 4 of the metal shell 3 opposite the metal shell 3 is also closed with a closure lid 9, which is inserted into the metal shell 3. In contrast to the embodiment of load resistors 1 described above, in the case of the load resistor 60, the short-circuit fuse 40 is integrated in the load resistor 60. In this case, a closure plug 61 may be provided in the closure lid 9, via which the short-circuit fuse 40 can be inserted into the load resistor 60. The embodiment according to Fig. 3 thus represents an extremely compact design of a load resistor 60 with integrated short-circuit fuse 40. Otherwise, the operation of the short-circuit fuse 40 is identical to the short-circuit fuse 40 from the Fig. 1 and 2 ,

Since the two Heizwendelabschnitte 41 and 42 and in the embodiment of the Fig. 3 can be absorbed in the receiving body 45, can also be dispensed with the protective housing 47. In this case, the receiving body 45 is embedded directly in the insulating material package 10 of the load resistor 60. Such a configuration is provided in particular when it is dispensed with interchangeability of the short circuit fuse 40.

Should or can be dispensed with a replaceability of the short-circuit fuse, it can also be designed as an integral part of the load resistor 1 easier.

So shows Fig. 4 a variant of a load resistor 20, which also has a metal shell 3, in which a resistance element 5 is provided. This resistance element 5 is also formed in the form of a resistance coil 6, which forms two mutually parallel helical strands 7 and 8. The metal shell 3 may be cylindrical here and has, as already to Fig. 1 described, also a bottom part 4. In the opposite area of this floor part 4, the load resistor 20 is closed with a closure lid 9, from which two pin-shaped terminals 13 and 14 are led out. Each spiral strand 7, 8 is connected with its end facing the closure lid 9 electrically connected to one of the terminals 13 and 14, respectively. In the region of the bottom part 4, the two helical strands 7 and 8 are electrically connected via a connecting wire 21, so that the two helical strands 7 and 8 are electrically connected in series.

At the in Fig. 4 illustrated embodiment, the two helical strands 7 and 8 form a "spark gap" over their entire length, so that they are to be referred to as Heizwendelabschnitt 22 and 23 at the same time. These Heizwendelabschnitte 22 and 23 or accordingly the helical strands 7 and 8 thus form the actual short circuit fuse 25. In the illustrated embodiment of Fig. 4 the metal shell 3 is filled with an insulating material packing 10, which may be compressed, so that the spiral strands 7 and 8 or the heating coil sections 41 and 42 are accommodated precisely positioned in the metal casing 3.

In this embodiment shown, in which the load resistor 20 with its helical strands 7 and 8 itself forms the short circuit fuse 25, the distance a of the helical strands 7, 8 or the Heizwendelabschnitte 22 and 23 from each other considerably smaller than the distance A of the helical strands. 7 and 8 or the Heizwendelabschnitte 22 and 23 to the metal shell 3 out. As a result, it is certainly ensured that, in the event of exceeding a limit load, a voltage flashover occurs exclusively between the heating coil sections 22 and 23 and thus no external effect occurs. In particular, in the event that this load resistor 20 is also used in a heat sink in the form of an aluminum housing with cooling fins, a risk to the environment is thus reliably avoided.

This in turn means that this embodiment of the load resistor 20, which in principle itself forms the short-circuit fuse 25, considerable advantages in terms of energy dissipation and in particular the size of such a load resistor 20 exist.

In a further embodiment according to Fig. 5 is also the load resistor 20 itself designed as a short-circuit fuse 25. In particular, with regard to the configuration of the resistance element 5, this load resistor 20 differs Fig. 5 not from the load resistor 20 Fig. 4 Thus, the above description in this regard also on the load resistor 20 from Fig. 5 is readable. In that regard, are in Fig. 5 also for the same components the same reference numerals.

The load resistor 20 off Fig. 5 differs from the load resistor 20 Fig. 4 in that between the two spiral strands 7 and 8 there is provided a dividing wall 27 which is made in particular of a ceramic, electrically insulating material. In the present embodiment, the partition 27 is provided in the region of the bottom part 4 with an opening 29 through which the connecting wire 21 of the resistance coil 6 is passed between the two helical strands 7 and 8. The ceramic material, such as micanite, the partition 27 is chosen so that their dielectric strength or their electrical resistance decreases very strongly with increasing temperature of the load resistance. Upon reaching a certain limit temperature, the partition wall 27 is thus conductive, so that it is ensured that a voltage flashover always takes place exclusively in the region of the heating coil sections 22 and 23 resting essentially on the partition wall 27. Since the Heizwendelabschnitte 22 and 23 or this forming helical strands 7 and 8 of the resistance coil 6 of the resistance element 5 out to the metal sheath 3 out in the electrically insulating Isolierstoffpackung 10 are embedded and this does not lose its high-resistance electrically insulating properties when reaching or exceeding the above limit temperature, a voltage flashover to the metal shell is safely excluded.

To ensure that this voltage flashover also takes place precisely in the region of this breakthrough 28, the Heizwendelabschnitte 22 and 23 in the connecting region between the Heizwendelabschnitte forming helical strands 7 and 8 also have a smaller distance from each other than the "remaining" helical strands 7, 8 as it for the embodiment of the Fig. 6 is shown. The arrangement in this connection region also ensures a voltage flashover between the heating coil sections 22 and 23, if only because the greatest voltage potential is present in this connection region during operation.

Fig. 7 shows further exemplary embodiment variant of a load resistor 20, in which also the short-circuit fuse 25 forming Heizwendelabschnitte 22 and 23 are formed by the helical strands 7 and 8 of the resistance coil 6 of the resistor element 5. These Heizwendelabschnitte are added in this embodiment in a consisting of a ceramic, electrically insulating material receiving body 30. The helical strands 7, 8 and thus the Heizwendelabschnitte 22, 23 are received in receiving bore 31 and 32 of the receiving body 30. The Heizwendelabschnitte 22 and 23 are separated by a fairly thin partition 33 of the receiving body 30 from each other. Similar to the variant of the Fig. 5 Also, the receiving body 30 is made of a ceramic material, such as micanite, which becomes conductive from a certain limit temperature. When this limit temperature is exceeded, a voltage flashover thus takes place between the heating coil sections 22 and 23. , so that also an external effect is excluded. Since the receiving body 30 is embedded to the outside of the metal shell 3 in an electrically insulating insulating material 10 and this does not lose their high-resistance electrically insulating properties when reaching or exceeding the above limit temperature, a flashover to the metal shell is safely excluded.

In addition, it must therefore be stated that, in particular, a danger to the outside is reliably precluded by the short-circuit fuses 25 or 40 by means of a defined flashover. Due to the provided a kind of spark gap forming Heizwendelabschnitte 22, 23 and 41, 42 an "internal" voltage flashover at overload of the load resistor 1 and 20 is guaranteed safe.

To ensure this "internal" voltage flashover can, as explained above, on the one hand be provided by a "relatively small" distance of the Heizwendelabschnitte 22, 23 and 41, 42 in relation to the distance to the outer metal shell 3 or to the protective housing 7. The choice of the material of the insulating material pack 10 or 46, e.g. MgO, or the receiving body 45 or 30, e.g. Mikanit, can take on its own or in addition to ensure such an internal flashover. In this case, 45 and 30 different variants are conceivable with respect to the arrangement and shaping of such a receiving body. Thus, the inventive design of the load resistors 1, 20 and 60 with their short-circuit fuses 25 and 40 a risk to the environment by a voltage flashover to the metal shell 3 and the protective housing 47 safely excluded.

Ie. in summary, that the load resistor 1, 60 and 20 is formed with its short-circuit fuse 40 and 25 such that the Heizwendelabschnitte 41 and 42 or 22 and 23 through the these mutually insulating layer, partition and / or Isolierstoffpackung are electrically insulated from each other so that the dielectric strength between the Heizwendelabschnitten 41 and 42 and 22 and 23 defined is lower (or with increasing temperature) than the dielectric strength between these Heizwendelabschnitten 41, 42 and 22, 23 to the protective housing 47 and in particular to the outer metal jacket 3 of the load resistor 1, 20 and 60, respectively.

To Fig. 6 It should be noted here that instead of the smaller distance of the Heizwendelabschnitte 22 and 23, these can be arranged to extend, approximately centrally relative to the axial length of an extremely small distance between these Heizwendelabschnitten 22 and 23 is set. This ensures a safe voltage flashover in this area of the smallest distance of the Heizwendelabschnitte 22 and 23 also by this measure.

The range of Heizwendelabschnitte can, as exemplified above, additionally protected, encased, compacted, potted or otherwise enclosed, so that as a result of the overload occurring short circuit by flashover no explosion, no arc, no fire and also no smoke can escape to the outside. In an external embodiment of the short-circuit fuse, the load resistor, as described above for the embodiments, be designed as a closed load resistor or even with resistance coils exposed to air. The illustrated embodiments have in common that a threat to a person in the vicinity of the load resistance - when the fault occurs when exceeding the limit load - is safely excluded.

Furthermore, with external arrangement of the short-circuit fuse 40 outside the load resistor 1, the actual one Load resistor 1 or its resistance element 5 or resistance coil 6 secured against overloading and destruction.

According to the invention, the short circuit takes place harmlessly precisely at a predetermined location or "point", which leads to a considerable improvement in the safety, in particular of persons staying in the vicinity of the load resistance.

Claims (14)

1. A load resistor (1, 20, 60), comprising at least one resistor element (5) provided with electrical terminals (13, 14) and in the form of at least one resistor coil (6) which has at least two coil strands (7, 8) extending parallel to each other at least locally, wherein the terminals (13, 14) are connected in each case to a load line (15, 16) and wherein the resistor element (5) is arranged in a metallic casing (3) and wherein the coil strands (7, 8) are insulated electrically with respect to each other and with respect to the metallic casing (3), characterized in that a short circuit protection (25, 40) is provided which has two heating coil portions (22, 23, 41, 42) which extend parallel to each other and which form a spark gap and which when a limit load pre-determined by the load resistor (1, 20, 60) is reached cause a short circuit by a voltage flashover, so that the short circuit occurs precisely at a pre-determined location.
2. A load resistor according to claim 1, characterized in that the heating coil portions (41, 42) are arranged in a common protective housing (47) separated from the load resistor (1).
3. A load resistor according to claim 2, characterized in that the heating coil portions (41, 42) are connected in series in each case to one of the load lines (15, 16) of the resistor element (5), and, starting from the heating coil portions (41, 42), two terminal wires (50, 51) which are contacted electrically by one of the terminals (13, 14) of the resistor element (5) in each case are brought out of the protective housing (47), and the heating coil portions (41, 42) situated inside the protective housing (47) form the spark gap.
4. A load resistor according to claim 3, characterized in that the distance of the heating coil portions (41, 42) from each other is smaller than the distance of the respective heating coil portion (41, 42) from the protective housing (47).
5. A load resistor according to claim 4 or 5 [sic], characterized in that the heating coil portions (41, 42) are received in a receiving member (45) which is arranged in the protective housing (47) and consists of a ceramic, electrically insulating material and which electrically insulates the heating coil portions (41, 42), and the ceramic material is electrically conductive above a pre-determined temperature.
6. A load resistor according to claim 5, characterized in that the receiving member (45) is embedded in the protective housing (47) in an insulator packing (46) consisting of MgO, SiO₂ or quartz sand or a similar electrically insulating material, and the receiving member (45) forms a partition wall (45/1) insulating the two heating coil portions (41, 42), and the dielectric strength of the partition wall (45/1) is lower than the dielectric strength of the receiving member (45) together with the insulator packing (46) surrounding the protective housing (47).
7. A load resistor according to claim 6, characterized in that the insulator packing (46) is compressed.
8. A load resistor according to any one of claims 2 to 7, characterized in that the protective housing (47) comprises a cylinder casing, the end faces of which are closed tight by two inserted closure plugs (48, 49).
9. A load resistor according to any one of claims 5 to 8, characterized in that the resistor coil (6) of the load resistor (1, 60) has a lower power density than the two heating coil portions (41, 42) of the short circuit protection (40).
10. A load resistor according to claim 1, characterized in that the resistor coil (6) of the load resistor (60) has a lower power density than the two heating coil portions (41, 42) of the short circuit protection (40), and the heating coil portions (41, 42) are received in a receiving member (45) consisting of a ceramic, electrically insulating material, and the ceramic material is electrically conductive above a pre-determined temperature, and the receiving member (45) is arranged integrated in the load resistor (60).
11. A load resistor according to claim 1, characterized in that the coil strands (7, 9) of the load resistor (20) form the two heating coil portions (22, 23) of the short circuit protection (25), and the heating coil portions (22, 23) are arranged extending adjacent to each other in the metallic casing (3), and the heating coil portions (22, 23) are received in an insulator packing (10), and the heating coil portions (22, 23) are at a shorter distance (a) from each other than the respective distance (A) thereof from the metallic casing (3).
12. A load resistor according to claim 1, characterized in that in the region of the connection of the coil strands (7, 9) of the load resistor (20) to the terminals (13, 14) over part of the length thereof these coil strands (7, 9) form the two heating coil portions (22, 23) of the short circuit protection (25), and the heating coil portions (22, 23) in this region are at a shorter distance from each other than the "remaining" coil strands (7, 8) from each other and, in particular, from the "remaining" coil strands from the metallic casing (3) of the load resistor (20).
13. A load resistor according to claim 1, characterized in that the coil strands (7, 9) of the load resistor (20) form the two heating coil portions (22, 23) of the short circuit protection (25), and the heating coil portions (22, 23) are arranged extending adjacent to each other in the metallic casing (3), and the heating coil portions (22, 23) are received in a receiving member (30) consisting, in particular, of a ceramic, electrically insulating material and are electrically insulated from each other by a partition wall (33) of the receiving member (30), and when a pre-determined temperature is reached at least the partition wall (33) becomes electrically conductive so that a voltage flashover occurs between the heating coil portions (22, 23).
14. A load resistor according to claim 13, characterized in that the coil strands (7, 9) of the load resistor (20) form the two heating coil portions (22, 23) of the short circuit protection (25), and the heating coil portions (22, 23) are arranged extending adjacent to each other in the metallic casing (3), and the heating coil portions (22, 23) are separated from each other by a partition wall consisting of a ceramic, electrically insulating material, and when a pre-determined temperature is reached the partition wall (33) becomes electrically conductive so that a voltage flashover occurs between the heating coil portions (22, 23).

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