MXPA99005677A - Device and method relating to protection of an object against over-currents comprising over-current reduction and current limitation - Google Patents

Abstract

This invention is related to a device and a method for protection, in an electric power plant, of an object (1) against overcurrents from a network (3) or another equipment included in the high voltage plant, the device comprising a switching device (4) in a line (2) between the object and the network/equipment. The line (2) between the object and the network/equipment is connected to an arrangement (5) reducing overcurrents towards the object (1), said arrangement (5) being activatable for overcurrent reduction with the assistance of an arrangement (11-13) detecting overcurrent conditions within a time period substantially shorter than the breaktime of the switching device (4).

Description

DEVICE AND METHOD IN RELATION TO PROTECTION OF AN OBJECT AGAINST OVERCROWDING THAT INCLUDES REDUCTION OF OVERCURRENT AND CURRENT LIMITATION FIELD OF THE INVENTION AND PREVIOUS TECHNIQUE This invention relates to a device in an electric power plant for protection of an object connected to an electrical power network or other equipment in the power plant of fault-related overcurrents, the device comprises a switching device in a line between the object y- the network / equipment. In addition, the invention includes a method for protecting the object from overcurrents. The electrical object in question is preferably formed by a rotary electric machine having a magnetic circuit, for example a generator, motor (both synchronous and asynchronous motors are included) or synchronous compensator that requires protection against fault-related overcurrents, ie in the practice of short circuit current. As will be discussed in more detail in the following, the structure of the rotary electric machine can be based on a conventional as well as non-conventional technique. The present invention is designed to be applied in relation to a medium or high voltage. According to the IS standard, an average voltage refers to 1-72.5 kV while a high voltage is > 72.5 kV. Therefore, the levels of transmission, subtransmission and distribution are included. In the previous power plants of this nature one has acquired for protection of the object in question a conventional circuit breaker (switching device) of such design that provides galvanic separation before rupture. Since this circuit breaker must be designed to be able to interrupt very high currents and voltages, you will get a comparatively bulky design with a high inertia, which reflects itself in a comparatively long interruption time. It is emphasized that the overcurrent considered mainly is the short-circuit current that occurs in connection with the protected object, for example as a consequence of faults in the electrical isolation system of the protected object. Such failures mean that the fault current (short circuit current) of the external network / equipment tends to flow through the arc generated in the object. The result can be a very large download. It can be mentioned that for the Swedish energy network, the dimensioning of a short circuit current / fault current is 63 kA. Actually, the short circuit current can constitute 40-50 kA. A problem with the circuit breaker is the extended interruption time of the circuit breaker. The sizing of the interruption time (IEC standard) for interruptions carried out completely is 150 milliseconds (ms). It is associated with difficulties to reduce this reduction time to less than 50-130 ms based on the real case. The consequence thereof is that there is a fault in the protected object, and a very high current will flow through it for all the time necessary to drive the circuit breaker to perform the interruption. During this time, the complete current failure of the external power network involves a considerable load on the protected object. In order to avoid damage and complete interruption with respect to the protected object, according to the prior art, an object must be constructed in a manner that handles, without appreciable damage, the short circuit current / fault current to which it is subjected during the interruption time of the circuit breaker. It is emphasized that a short circuit current (fault current) in the protected object can be constituted by its own object contribution to the fault current and the addition of current arising from the network / equipment. The object's own contribution to the fault current is not affected by the operation of the circuit breaker, but the contribution to the fault current from the network / equipment depends on the operation of the circuit breaker. The requirement to construct the protected object so that it can withstand a short circuit current / high fault current for a considerable period of time represents substantial disadvantages in the form of a more expensive design and reduced operation.

Current transformers and reactors are based, with respect to protection, on their own current limiting capacity, transient and inherent, as a consequence of high conductance, in addition to the function of the conventional circuit breaker described above. Although the present invention is applicable to such conventional transformers and reactors, it is applicable with special advantage over new inventive transformers or rectores, which will be discussed in greater detail in the following and which, by their own design, have lower inductance / impedance in Comparison with conventional transformers and reactors and which therefore can not constitute, to an equally high degree, an inductively current limiting unit that involves self-protection against overcurrents as well as a protection for electrical unities. located before and after, respectively, of the transformer / reactor. In such transformers the non-conventional reactors of course it is particularly important that the protection device operates quickly to delimit the damaging effect of. the mistake. In order to simplify understanding, a conventional power transformer will be explained in the following. What is established is in its entire essence also applicable with respect to reactors. The reactors can be designed as single-phase or three-phase reactors. Regarding insulation and cooling, in principle they have the same modalities as transformers. Therefore, reactors isolated by air and isolated in oil, self-cooled, refrigerated by oil under pressure, etc. are available. Although the reactors have a winding (per phase) and can be designed with or without an iron core, the following description is relevant to a large extent also for the reactors. A conventional power transformer comprises a transformer core, in the following referred to as a core, often with oriented and laminated sheets, usually iron with silicone. The core comprises many core extremities, connected by yokes which together form one or more core windows. These transformers with such a core are often referred to as core transformers. Around the core limbs there are numerous windings which are usually referred to as primary, secondary and control windings. As far as power transformers are concerned, these windings are practically always concentrically placed and distributed along the length of the core ends. The core transformer normally has circular windings as well as a tapered core end section in order to fill the coils as closely as possible. Sometimes other types of core designs are also presented, for example those which are included in the so-called shell type transformers. These have as a rule rectangular coils and a rectangular end section. The conventional energy transformers, in the lower part of the energy range in question, specifically from 1 VA up to 1000 MVA in range, sometimes designated as air cooled to carry out the inevitable inherent losses. For protection against contact, and possibly to reduce the external magnetic field of the transformer, an outer coating provided with ventilation openings is often provided. However, most conventional power transformers are cooled by air. One of the reasons therefore is that the oil has the additional function, very important, as an insulating medium. A conventional oil-cooled and oil-insulated energy transformer must therefore be surrounded by an external tank which, as will be clear from the following description, sets very high demands. The conventional energy transformers insulated with oil are also manufactured with oil water coolant. The next part of the description will refer mostly to conventional oil-filled power transformers.

The windings mentioned in the above are formed from one or more coils connected in series accumulated with a large number of turns connected in series. In addition, the coils are provided with a special device to allow switching between the terminals of the coils. Such a device can be designed for permutation with the help of screw joints or more frequently with the help of a special switch which is operable in the vicinity of the tank. In the case where the switching takes place for a transformer under voltage, the permutation switch is referred to as a lid-to-load exchanger, whereas otherwise it is referred to as a "de-energized" lid-changer. energy cooled by oil and insulated with oil in the upper energy range, the interrupter element of the lid changers in charge are placed in special oil filled containers with direct connection to the transformer tank. purely mechanical by means of a motor-driven rotary shaft and are positioned in such a way that a fast movement is obtained during switching when the contact is opened and a slower movement when the contact is to be closed. in charge as such they are placed in the current transformer tank During the operation, a tonnage and formation of spark This leads to degradation of the oil in the containers. In order to obtain fewer arcs and thus also less tartar formation and less wear on the contacts, the cover-plate changers are normally connected to the high-voltage side of the transformer. This is due to the fact that the currents which need to be interrupted and connected, respectively, are smaller on the high-voltage side than if the load-changers on the load were to be connected to the low-voltage side. Failure statistics of conventional oil-filled power transformers show that it is often the lid-top changers that give rise to faults. In the lower energy range of oil-cooled and oil-insulated energy transformers, both the load-changers and their interruption element are placed inside the tank. This means that the problems mentioned before with the degradation of the oil, due to the arcs during the operation, etc., are carried out in the entire oil system. A considerable difference between a conventional power transformer and such an unconventional power transformer designed with the invention refers to the conditions with respect to the insulation. For this reason, the reason why the insulation system is constructed as established in conventional power transformers will be described in more detail with reference to FIG.

From the point of view of applied or induced voltage, it can be said broadly that a voltage which is stationary through a winding is distributed equally in each turn of the winding. That is, the return voltage is the same in all laps. From the point of view of electrical potential, however, the situation is completely different. One end of a winding, assuming a lower end of a winding 51 according to Figure 12, is normally connected to ground. However, this means that the electric potential of each turn increases linearly from virtually zero in the turn which is closest to the ground potential, up to a potential in the turns which is at the other end of the winding, which corresponds to the applied voltage. In Figure 12, which in addition to a winding 51 comprises a core 52, a simplified and fundamental view of the equipotential lines 53 with respect to the electric field distribution for a conventional winding for a cover is shown in which the lower part of the Winding is assumed to be at ground potential. This distribution of potential determines the composition of the insulation system, since it is necessary to have sufficient insulation both between adjacent turns of the windings and between each turn and the earth. Therefore, the figure shows that the upper part of the winding is subjected to the highest insulation loads. The design and location of a winding in relation to the core in this manner is determined substantially by the distribution of electric field in the core window. The turns in an individual coil are usually joined in a coherent geometric unit, physically delimited from other coils. The distance between the coils is also determined by the dielectric voltage which can be allowed to occur between the coils. Therefore, this means that some insulation distance between the coils is also required. According to the foregoing, sufficient isolation distances are also required from the other electrically conductive objects which are within the electric field from the electrical potential that occurs locally in the coils. Therefore, it is clear from the above description that for the individual coils, the voltage difference internally between physically adjacent conductive elements is relatively low while the voltage difference externally in relation to other metal objects, including other coils, can be relatively high. The voltage difference is determined by the voltage induced by magnetic induction as well as by the capacitively distributed voltages which can arise from an external electrical system connected on the external connectors of the transformer. The types of voltage which can enter externally include, in addition to the operating voltage, lightning surges and switching overvoltages. In the current lines of the coils, additional losses arise as a result of the magnetic leakage field around the conductor. To keep these losses as low as possible, especially for power transformers in the upper power range, the conductors are normally divided into several conductor elements, often referred to as threads, which are connected in parallel during operation. These strands must be transposed according to such a pattern so that the voltage induced in each strand becomes as identical as possible so that the difference in voltage induced between each strand pair becomes as small as possible for the strand. circulation internally of current components and so that it remains low at a reasonable level from the point of view of losses. When designing transformers according to the prior art, the general objective is to have a large amount of conductive material as possible within a given area limited by what is called a transformer window, generally described as having a factor of filled as high as possible. The space available will comprise, in addition to the conductive material, also the insulating material associated with the coils, partially internally between the coils and partially to other metallic components including the magnetic core. The insulation system, partly inside a coil / coil and partly between coils / windings and other metal parts, is usually designed as a solid insulation based on cellulose or varnish closest to the individual conductor element, and outside it as a solid insulation of cellulose and liquid, and possibly also gaseous. The windings with insulation and possibly part of reinforcement, in this way represent large volumes which will be subjected to high electric field forces which arise in and around the active electromagnetic parts of the transformer. To be able to predetermine the dielectric voltages which arise and reach a good dimensioning with a minimum risk of insulation failure, a good knowledge of the properties of insulating materials is required. It is also important to obtain such surrounding environment so that it does not change or reduce the insulating properties. The current predominant insulation system for conventional high-voltage power transformers comprises a cellulose material such as solid insulation and a transformer oil as the liquid insulation. The transformer oil is based on what is called mineral oil. The transformer oil has a double function, since, in addition to the insulating function, it actively contributes to the cooling of the core, the winding, etc., by removing the heat losses of the transformer. Oil cooling requires an oil pump, an external cooling element and expansion coupling, etc. The electrical connection between the external connections of the transformer and the connected coils / windings is immediately termed as an insulator trying on a conductive connection through the tank which, in the case of power transformers filled with oil, surrounds the current transformer. The insulator is also a separate component fixed to the tank, it is designed to withstand the insulation requirements that are made, both outside and inside the tank, while at the same time it must withstand the current loads that arise and the forces of current they enter. It should be noted that the same requirements for the insulation system as described above with respect to the windings also apply to the necessary internal connections between the coils, between the insulators and the coils, the different types of permutation switches and the insulators as such. All metal components within a conventional power transformer are normally connected to a ground potential with the exception of conductors carrying current. In this way, the risk of an unwanted potential increase is avoided, and difficult to control, as a result of the distribution of voltage capacity between the current that leads to a high potential and to ground. Such an increase in unwanted potential can lead to partial discharges, called corona. The corona can be revealed during normal acceptance tests, which are partially performed, compared to nominal data, increased voltage and frequency. The crown can lead to damage during the operation. The individual coils in a transformer must have such a mechanical dimensioning that they can resist any voltage that occurs as a result of arising currents and the resultant current forces during a short circuit process. Normally, the coils are designed so that the forces arising are absorbed within each individual coil, which in turn may mean that the coil can not be optimally sized for its normal function during normal operation. Within a narrow voltage and an energy range of energy transformers filled with oil, the windings are designed in what are called leaf windings. This means that the individual conductors mentioned in the above are replaced by thin sheets. The sheet-fed power transformers are manufactured for voltages of up to 20-30 kV and powers of up to 20-30 MW.

The insulation system of conventional energy transformers within the upper energy range requires, in addition to a relatively complicated design, also special manufacturing measures to utilize the properties of the insulation system in the best way. For a good insulation to be obtained, the insulation system must have a low moisture content, the solid part of the insulation must be well impregnated with the surrounding oil and the risk of remaining "gas" packages in the solid part must be minimized . To ensure this, a special drying and impregnation procedure is carried out on a complete core with windings before they are lowered into the tank. After this drying and impregnation process, the transformer is lowered into the tank which is then sealed. Before filling it with oil, the tank with the submerged transformer must be emptied of all air. This is done in connection with a special vacuum treatment. When this is done, filling with oil takes place. In order to be able to obtain the promised service life, etc., of a conventional transformer filled with oil, it is required to pump out in almost absolute vacuum in relation to the vacuum treatment. Therefore, this presupposes that the tank which surrounds the transformer is designed for complete vacuum, which implies a considerable consumption of material and time of manufacture. If electric shocks occur in a power transformer filled with oil, or if there is a considerable local increase in temperature in any part of the transformer, the oil disintegrates and gaseous conduits in the oil are dissolved. Therefore, transformers are usually transformed with monitoring devices to detect the gas dissolved in the oil. For reasons of weight, large power transformers are transported without oil. In the on-site installation of the transformer by a customer requires, in turn, a renewed vacuum treatment. In addition, this is a process which must be repeated every time the tank is opened for some action or inspection. It is evident that these processes are time-consuming and cost-intensive and constitute a considerable part of the total for manufacturing and repair while at the same time requiring access to expensive resources. The insulating material in a conventional power transformer makes up a large part of the total volume of the transformer. For a conventional energy transformer the upper energy range, oil quantities in the order of magnitude of several tens of cubic meters of transformer oil are not rare. The oil which shows some similarity to diesel oil is a thin fluid and shows a relatively low flash point. Therefore, it is evident that the oil with the cellulose constitutes a non-negligible ignition risk in the case of unintentional heating, for example in an internal disruptive discharge, and a resulting oil spill. It is also obvious that, especially in conventional oil-filled power transformers, there is a very large transport problem. A conventional oil-filled energy transformer in the upper energy range can have a total oil volume of 40-50 cubic meters and can weigh up to 30-40 tons. For conventional transformers "of energy in the upper energy range, transport is often produced with a tank without the oil.It happens that the external design of the transformer must be adapted to the current transport profile, this is for the passage through the bridges , tunnels, etc. What follows is a brief summary of what can be described as areas of limitation and problems according to the prior art with respect to oil-filled power transformers: A conventional energy transformer filled with oil: It comprises an external tank which must house a transformer comprising a transformer core with coils, oil for insulation and cooling, mechanical reinforcement devices of various kinds, etc. Very large mechanical demands are placed on the tank, since, without oil but with a transformer, it will be able to be vacuum treated to practically fill the vacuum. The need for an external tank requires a very extensive manufacturing and testing process. In addition, the tank means that the external measurements of the transformer become much greater than what is called a "dry" transformer of the same power. The larger external measures usually also involve considerable transport problems. - normally comprises what is called pressure oil cooling. This method of cooling requires access to an oil pump, an external cooling element, an expansion vessel and an expansion coupling, etc. - comprises an electrical connection between the external connections of the transformer and the coils / windings connected immediately in the form of an insulator fixed to the tank. The insulation is designed to withstand any insulation requirement made, both with respect to the exterior and the interior of the tank. It comprises coils / windings whose conductors are divided into several conductive elements, strands, which must be transported in such a way that the voltage induced in each strand becomes as identical as possible and so that the difference in voltage induced between each pair of strands becomes as possible as possible. it comprises an insulation system, partially inside a coil / coil and partly between coils / coils and other metal parts, system which is designed as a solid or varnish-based cellulose insulation closest to the individual conductor element and, outside of this , the solid and liquid cellulose, possibly also gaseous, as insulation. In addition, it is extremely important that the insulation system shows a very low moisture content. It is understood as an integrated part in a cover-to-load exchanger surrounded by oil and normally connected to the high-voltage winding of the transformer for voltage control. - Involves a non-negligible fire risk with respect to internal partial discharges, which is called corona, sparking in lid changers under load and other failure conditions. It usually includes a monitoring device to monitor the gas dissolved in the oil, which occurs in case of electric discharges in the oil and in case of local increases in temperature. it may result, in the case of damage or accident, in oil leaks that lead to extensive environmental damage.

OBJECTIVE OF THE INVENTION The main objective of the present invention is to establish ways of designing the device and the method so as to obtain better protection for the object and, consequently, a reduced load therein, a fact which means that the object itself It must not be designed to withstand a maximum of short circuit currents / fault currents for relatively long periods of time. A secondary objective with the invention is to design the protection device and method so that adequate protection is obtained for electrical objects in the form of transformers and reactors, the design of which is based on unconventional design principles, which may mean that the design does not have the same resistance to overcurrents related to faults, internal as well as external, in comparison with current conventional transformers and reactors. However, the invention is of course also intended to be applicable in relation to conventional transformers and reactors.

BRIEF DESCRIPTION OF THE INVENTION According to the invention, the object indicated above is obtained insofar as a line between the object and the switching device is connected to an overcurrent reducing assembly, which is operable to reduce overcurrent with the help of an assembly detecting overcurrent conditions within a period of time substantially less than the interruption time of the switching device, and between the connection of the overcurrent reducing assembly to the line and the object, a current limiter is provided. Therefore, the invention is based on the principle not to be based solely on braking purposes before a switching device which finally establishes galvanic separation, but instead the use of a rapidly operating overcurrent reducing assembly which, without causing any real interruption of the overcurrent, nevertheless reduce it to such an extent that the object under protection is subjected to substantially reduced stress and, consequently, a lesser amount of damage. The reduced overcurrent / fault current means, consequently, when the switching device establishes galvanic separation, the total energy injection within the protected object will have been much smaller than in the absence of the overcurrent reduction assembly. In addition, there will be an additional reduction of the fault current flowing to (or from) the object by means of the current limiter. Furthermore, the current limiter is of such a nature that it operates rapidly to reduce current to such an extent that the voltages imposed on the object are significantly reduced without the current limiter having to carry out any such interruption of the overcurrent / current of the current. failure. According to a preferred embodiment of the invention, the overcurrent reducing assembly is designed to comprise an overcurrent diverter for overcurrent deviation to ground or to another unit having a lower potential than the network / equipment. The current limiter according to the invention is suitably based on current limitation by means of a constant or variable inductance and / or resistance or other impedance. As defined more clearly in the claims, the invention is applicable to transformers and reactors constructed by means of non-conventional technique, specifically cable technology. Under certain conditions this can become sensitive to electrical faults. Such a design can be supplied, for example, with a lower impedance than what is currently considered conventional within the field of energy. This means that the design does not have the same resistance against overcurrents related to faults, internal as well as external, in comparison with current conventional devices. If the deviceIn addition, it has been designed to start operating with an electrical voltage higher than that of a conventional current device, the voltage on the electrical insulation system in the device, caused by the resulting higher electric field, becomes, of course, higher. This means that the apparatus can be more efficient, more economical, mechanically lighter, more reliable, less expensive to produce and generally more economical than a conventional apparatus and can change without the usual connection to another electromagnetic device, such apparatus requires protection adequate electrical power to eliminate, or at least reduce the consequences of, an insulation failure in the apparatus in question. A combination of the protection device according to the invention and an apparatus designed in this way, preferably a transformer or reactor, means an optimization of the plant as a whole. The non-conventional transformer designed in the present is an energy transformer with a nominal power from a few hundred kVA up to more than 1000 kVA with a nominal voltage of 3-4 kV up to very high transmission voltages, such as 400 kV to 800 kV or higher, and which do not involve the disadvantages, problems and limitations which are associated with the oil-filled energy transformers of the prior art, in accordance with what was presented above. The invention is based on the consideration that when designing at least one winding in a transformer / reactor so as to comprise a solid insulation surrounded by an outer semiconducting layer and a potential equalizing interior, within which the inner layer of At least one conductor is placed, providing a possibility to maintain the electric field in the entire plant within the conductor. According to the invention, the electrical conductor is suitably positioned so that it has such conductive contact with the inner semiconductor layer so that no harmful potential differences can arise in the boundary layer between the innermost part of the solid insulation and the layer semiconductor located inside it. Such a power transformer shows great advantages in relation to a conventional transformer filled with oil. As mentioned by way of introduction, the invention also provides that the concept be applied in reactors both with and without a core of magnetic material. The essential difference between conventional oil-filled power transformers / reactors and the power transformer / reactor according to the invention is that the windings / windings therefore comprise a solid insulation surrounded by external and internal potentials capable as well as by minus an electrical conductor placed inside the inner potential layer, the potential layers are made of a semiconductor material. The definition of what is understood by the concept of the semiconductor will be described in the following. According to a preferred embodiment, the winding / windings are designed in the form of a flexible cable. At the high voltage levels which are required in a power transformer / reactor according to the invention, which is connected to high voltage networks with very high operating voltages, the electrical and thermal charges which may arise will impose demands extreme on the insulating material. It is known that what are called partial discharges, pd, are generally a serious problem for insulating material in high voltage installations. If cavities, pores or similar arise in the insulating layer, internal corona discharges may arise at high electrical voltages, so that the insulating material degrades gradually, which can eventually lead to a failure of electrical insulation through the insulation. It is taken into account that this can lead to a serious isolation failure, for example, of an energy transformer. The invention is based, for example, on the concept that it is of extreme importance that the layers of semiconductor material exhibit similar thermal properties and that the layers are firmly connected to the solid insulation. The thermal properties in view of the present are related to the coefficient of thermal expansion. The inner and outer semiconducting layers and the intermediate insulation, accordingly, must be well integrated, that is, in good contact with each other over substantially the entire boundary layer, independently of the temperature changes that occur at different loads. Therefore, the insulation includes the surrounding semiconducting layers which will constitute, at the temperature gradients, a monolithic part and no defects will arise caused by different temperature expansion in the insulation and the surrounding layers. The electrical charge on the material is reduced as a consequence of the fact that the semiconductor layers around the insulation will constitute equipotential surfaces and that the electric field in the insulation is therefore evenly distributed over the insulation. According to the invention, it must be ensured that the insulation is not interrupted by the phenomenon described above. This can be carried out by using a semiconductor layer insulation system and intermediate layered insulation produced in such a way as to minimize the risk of cavities and pores, for example extruded layers of a suitable plastic material such as XLPE (cross-linked polyethylene). ) and EP rubber (EP = ethylene-propylene). The insulating material is at least a low loss material with a high resistance to insulation failure. It is known that high voltage transmission cables are designed with conductors having an extruded insulation with an inner and outer semiconductor layer. In the transmission of electrical energy, for a long time it has been tried to avoid the defects in the isolation. However, in high-voltage transmission cables the electrical potential along the length of the cable does not change, but the potential, in principle, is at the same level, which means a high electrical voltage on the insulating material. The transmission cable is provided with an inner semiconductor layer and an outer layer for potential equalization. Therefore, the winding according to the invention is provided with a solid insulation and surrounding equalizing layers, so that the transformer / reactor can be obtained, in which the electric field is retained within the winding. Additional improvements can also be obtained by building the conductor for smaller isolated parts, called threads. When making these small circular strands, the magnetic field through the strands will show a constant geometry in relation to the field and the presentation of parasitic currents is minimized. According to the invention, the winding / windings in this way are manufactured in the form of a cable comprising at least one conductor comprising numerous threads and a semiconductor layer around the threads. Outside of this inner semiconducting layer is the main insulation of the cable in the form of a solid extruded insulation, and around this insulation there is an outer semiconductive layer. In certain connections the cable may have additional outer and inner layers. For example, additional potential equalizing semiconductor layers can be placed in the solid insulation between these two layers which in this specification are called "inner" and "outer". In such a case, this additional layer will be in a medium potential. According to the invention, the outer semiconductive layer will show electrical properties such that a potential equalization along the conductor is ensured. Nevertheless, the semiconductor layer may not show such conductivity properties that will induce a current in the layer, the current causes an undesired thermal load. However, the conductive properties of the layer must be sufficient to ensure that the outer layer is capable of forming an equipotential surface. The inner semiconductor layer must have sufficient electrical conductivity to be able to operate by equalizing the potential and, consequently, equalization with respect to the electric field outside the inner layer. In this respect, it is important that the layer has properties such as to equalize irregularities in the surface of the conductor and in this way the layer is capable of forming an equipotential surface with a high surface finish in the boundary layer with respect to the rigid insulation. The inner layer can be formed with a variable thickness but in order to ensure a uniform surface with respect to the conductor and solid insulation, the thickness of the layer can be between 0.5 and 1 mm. However, the inner layer may not exhibit such high electrical conductivity so that the layer contributes to voltage induction. The resistivity for the inner and outer layers may be in the range of 10"6 Ocm-100 kOcm, suitably 10" 3-100 Ocm, preferably 1-500 Ocm. Furthermore, it is preferred that the inner and outer layers each show a resistance, which per meter of cable, is in the range of 50 UO-5 MO. Therefore, such an XLPE cable or a cable with EP rubber insulation or a corresponding cable is used according to the invention in a modified mode and in a completely new field of use as a coil in a magnetic circuit. A winding comprising such a cable will involve very different conditions from the isolation point of view to those which apply to conventional transformer / reactor windings due to the electric field distribution. To utilize the advantages provided by the use of the mentioned cable, there are other possible modalities with respect to the grounding of a transformer / reactor according to the invention in a manner which is applicable to conventional oil-filled power transformers.

These methods with the aim of a separate application for patent. It is essential and necessary for a winding in an energy transformer / reactor according to the invention, that at least one of the strands of the conductor is not insulated and placed so as to obtain good electrical contact with the inner semiconductor layer. Therefore, the inner layer will always be in the driver's potential. With regard to the rest of the strands, all or some of them can be isolated, for example when varnished. The manufacture of transformer or reactor windings of a cable according to the above implies drastic differences with respect to the distribution of electric field between the conventional power transformers / reactors and the power transformer / reactor according to the invention. The decisive advantage with a wire-wound winding according to the invention is that the electric field is enclosed in the winding and that therefore, no electric field exists outside the outer semiconductive layer. The electric field that is obtained by the current-carrying conductor is essentially only in the solid main insulation. From the point of view of design as well as from the point of view of manufacture this means considerable advantages; The windings of the transformer can be formed without having to consider any electrical field distribution and the transposition of strands, mentioned under the prior art, is omitted. - A transformer core design can be formed without having to consider any electrical field distribution. No oil is needed for electrical insulation of the winding, that is, the medium surrounding the winding can be air. No special connections are required for the electrical connection between the external connections of the transformer and the coils / windings connected immediately since the electrical connection, contrary to conventional plants, is integrated with the winding. The manufacturing and testing technology which is necessary for an energy transformer according to the invention is considerably simpler than for a conventional energy transformer / reactor since the impregnation, drying and vacuum treatments described under the description of the art antecedents are no longer necessary. The advantages and additional features of the invention, in particular, with respect to the method according to the invention, are presented from the following description and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS With reference to the appended drawings, a more specific description of an example of embodiment of the invention follows. In the drawings: Figure 1 is a completely diagrammatic view illustrating the basic aspects behind the solution according to the invention, Figures 2a-2d are diagrams illustrating in a diagrammatic manner and in a comparative manner the current developments of failure and development of energy with or without the protection device according to the invention, - Figure 3 is a diagrammatic view illustrating a conceivable design of a device according to the invention; Figures 4-9 are views partially corresponding to Figure 3 of a different alternative embodiment of the invention with respect to the current limiter indicated by the number 6; Fig. 10 is a diagrammatic view illustrating a possible design of the overcurrent reducing assembly; Figure 11 is a diagrammatic view illustrating the device according to the invention applied in relation to a power plant comprising a generator, a transformer and an energy network coupled thereto; Figure 12 shows the distribution of electric field around a winding of a conventional power transformer / reactor; Figure 13 shows an example of a cable used in the windings of the power transformers / reactors according to the invention, and Figure 14 illustrates an embodiment of an energy transformer according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Figure 1 shows an electric power plant comprising a protected object 1. As described in the following, this object may consist, for example, of a transformer or reactor. This object is connected, via a line 2, to an external distribution network 3. Instead of such a network, the unit indicated with the number 3 can be formed by some other equipment contained in the power plant. The power plant involved is conceived to be of such a nature that it is the object itself which is intended primarily to protect against fault currents from the network / equipment 3 when a fault occurs in object 1 that results in a fault. fault current from the network / equipment 3 to object 1 so that the fault current will flow through the object. Such failure can consist of a short circuit that is formed in object 1. A short circuit is a driving path, which is not designed, between two or more points. The short circuit may consist, for example, of an arc. This short circuit and the resulting violent current flow can involve considerable damage and even a total insulation failure of object 1. It has already been emphasized that with at least two types of protected electrical objects 1, short circuit currents / damaging fault currents for the object in question may flow from the protected object to the network / equipment 3. Within the scope of the invention, it is intended to be used for protection purposes not only to protect the object from fault currents that emanate externally and flowing towards the object, but also internal fault currents in the object that flow in the opposite direction. This will be discussed in more detail in the following. In the following, the designation 3, to simplify the description, will always be mentioned as consisting of an external energy network. However, it must be remembered that part of the equipment may be involved instead of such a network, to the extent that such equipment causes a violent flow of current through object 1 when there is a fault. A conventional circuit breaker 4 is placed on line 2 between object 1 and network 3. This circuit breaker comprises at least one sensor of its own to detect circumstances indicative of the fact that there is an overcurrent flow in line 2. Such circumstances may be currents / voltages, but also others that indicate that a fault occurs. For example, the sensor may be an arc sensor or a sensor that records a short circuit sound, etc. When the sensor indicates that the overcurrent is above a certain level, circuit breaker 4 is activated to interrupt the connection between object 1 and network 3. However, circuit breaker 4 must interrupt the short circuit current / fault current. total. Therefore, the circuit breaker must be designed to meet high set requirements, which in practice means that it will operate at a relatively slow speed. Figure 2a illustrates a current / time diagram that when a fault occurs, for example a short circuit in object 1, at a time tfalla, the fault current in the line indicated as 2 in figure 1 quickly assumes the magnitude i ^ This fault current ix is interrupted by means of a circuit breaker 4 at t, which is at least 150 ms after tfalla. Figure 2d illustrates the diagram i2. t and, consequently, the energy developed in the protected object 1 as a consequence of the short circuit in it. The injection of energy into the object occurs as a consequence of which the short-circuit current, consequently, is represented by the total area of the outer rectangle in Figure 2d. In this regard it is emphasized that the fault current in Figures 2a-c and the currents in Figure 2d represent the envelope of an extreme value. Only polarity has been drawn in the diagrams for simplicity. The circuit breaker 4 is of such design that it establishes galvanic separation by separation of metallic contacts. In consecuense, the circuit breaker 4 comprises, as a rule, auxiliary equipment necessary for arc extinction. According to the invention, the line 2 between the object 1 and the switching device 4 is connected to an assembly which reduces the overcurrents towards the apparatus 1 and is generally indicated with the number 5. The assembly is operable for overcurrent reduction with the assistance of an overcurrent condition detector assembly within a period of time substantially less than the interruption time of the circuit breaker 4. This assembly 5, therefore, is designed so that no galvanic separation needs to be established. Therefore, conditions are generated to very quickly establish a current reduction without having to carry out any total elimination of the current flow from the network 3 to the protected object 1. Figure 2d illustrates in contrast to the case according to Figure 2a, that the overcurrent reducing assembly 5 according to the invention is activated upon presentation of a short-circuit current at the time tfalla for reduction of overcurrent at level i2 in the time t2. The time interval tfalla-t2 represents, consequently, the reaction time of the overcurrent reducing assembly 5. By the task of assembly 5 not to interrupt but only to reduce the fault current, it can cause the assembly to react extremely quickly, which will be discussed in more depth in the following. As an example, it may be mentioned that the current reduction from level i to level i2 is intended to be carried out within one or a few more minutes after unacceptable overcurrent conditions have been detected. Thus, the objective is to carry out the current reduction in a shorter time of 1 ms, and preferably more rapidly than 1 microsecond. As it appears from figure 1, the device comprises a current limiter indicated generally with the number 6 and placed on the line 2 between the connection of the assembly 5 to the line 2 and the object 1. This current limiter is adapted to operate for Current limitation mainly in one direction towards object 1, but in certain cases of failure also in one direction away from the object. The current limiter 6 can be placed to operate for current limitation as quickly or even more quickly than the overcurrent reduction assembly 5. According to an additional alternative involving less voltage on the current limiter 6, the current limiter can be designed to be activated for current limitation that the overcurrent of the network 3 towards the object 1 has been reduced by means of the assembly 5. overcurrent reducer but of course, the current limiter 6 must be activated for current limitation substantially earlier compared to the time at which interruption occurs by the circuit breaker 4. From what has been established it is evident that it is suitable for the current limiter 6 to be coupled to line 2 in such a way that the current is reduced by means of the overcurrent reducing assembly which, to an even smaller degree, will flow through the current limiter 6. Figure 2b illustrates the action of a current limiter 6. In this figure it has been chosen to indicate that the current limiter 6 starts operating for current limitation at time t3, which in the example may mean that the duration of the current i2 reduced by means of the overcurrent reduction assembly 5 has been substantially limited, specifically to the time extension t2-t3. Again it is emphasized that the representations in Figure 2 should be considered as only diagrammatic. The time t3 when the current limiter 6 is activated can be much earlier and even earlier than the time for activation of the overcurrent reduction assembly at time t2. It is evident from Fig. 2b that the fault current after time t3 is reduced to level i3. This remaining fault current i3 is finally interrupted by means of a circuit breaker 4 at a time t2. Nevertheless, the fault current i3 is comparatively so small as a consequence of the proper sizing of the current limiter 6 that the fault current in question can persist for the object in question and also for other part of the power plant. The consequence of the reduction and limitation respectively of the fault current, which the injection of energy from the network 3 caused by the fault current results in the protected object 1, is represented by the surfaces marked in figure 2d with lines oblique. It is evident that a drastic reduction of the energy injection is obtained. In this regard, it is emphasized that, since, according to a specific model, the energy increases with the square of the current, a reduction in half of the current reduces the induction of energy in a quarter. In Figure 2c it is illustrated that the fault current will tend to flow through the device 5. That part i3 of the total fault current i ± will continue to flow through the current limiter 6 after the time t3 which is also marked in figure 2c. In reality, the dimensioning of the assembly 5 and the current limiter 6 is conceived to be carried out so that the assembly 5 reduces the fault current and the voltage is restricted by means of the current limiter 6 to substantially lower levels. A realistic activation time with respect to the current limiter 6 is 1 ms, the dimensioning possibly being carried out to materialize such a current limiter 6 so that it delimits the current not until after the assembly 5 has reduced the current current flowing through limiter 6 in at least a substantial degree. As indicated, this is not a requirement but in the opposite case it is also possible. Figure 3 illustrates in more detail the manner in which the device can be carried out. It is emphasized that the invention is applicable in direct current connections (also HVDC = high voltage direct current) and alternating current connections. In a multiple phase assembly with alternating current, the line indicated by number 2 can be considered to form one of the phases in a multi-phase alternating current system. However, it should be noted that the device according to the invention can be carried out in such a way that all the phases are subjected to the protective function according to the invention in case of a detected error, or that only those phases in where fault current is obtained they are subjected to current limitation. From figure 3 it is evident that the current reducing assembly indicated generally with the number 5 comprises an overcurrent diverter 7 for diverting overcurrents to ground 8 or to a different unit in any other way having a smaller potential than the network 3. Therefore, it can be considered that the overcurrent diverter as a constituent of a current deviator which rapidly establishes a short circuit to ground or in some other way a low potential 8 with the purpose of diverting at least a substantial part of the current. current flowing in line 2, so that the current does not reach the object 1 to be protected. If there is a serious fault in the object 1, for example a short circuit, which is of the same magnitude as the short circuit that the overcurrent deviator 7 is capable of establishing, it can be said that generally speaking a reduction of the half of the current flow of the object 1 from the network 3 as a consequence of the overcurrent diverter 7 in case the fault is close to the latter. In comparison with FIG. 2b, accordingly, it appears that the current level i2 illustrated therein and that it is indicated constitutes approximately half of ± it can be said to represent the worst case. Under normal conditions, the purpose is that the overcurrent diverter 7 is capable of. establish a short circuit that has better conductivity than one corresponding to the short circuit fault in object 1 that is to be protected so that a main part of the fault current is diverted to ground or in some other way to a smaller potential by means of the overcurrent diverter 7. It seems from this that, a case of normal failure, the injection of energy into object 1 in case of a fault becomes substantially smaller than that which is indicated in figure 2d as a consequence of a lower current level i2 as well as an extension of time shorter t2-t3. - 4.2 - The overcurrent diverter 7 comprises a switching means coupled between the ground 8 or the lower potential and the line 2 between the object 1 and the network 3. This switching means comprises a control member 9 and a member 10 of switch. This switch member 10 can be formed, for example, by at least one semiconductor component, for example a thyristor, which opens in a normal state, ie isolated in relation to ground, but by means of the control member 9 can put in an active state, driver in a very short time in order to establish current reduction by deviation to ground. Figure 3 also illustrates that an overcurrent condition detection assembly may comprise at least one and preferably several sensors 11-13 suitable for detecting such overcurrent situations that require activation of the protection function. It is also evident from Figure 3 that these sensors can include the sensor indicated with the number 13 which is located in the object 1 or in its vicinity. In addition, the detector assembly comprises a sensor 11 adapted to detect overcurrent conditions in the line 2 upstream of the connection of the overcurrent reducing assembly 5 and in the line 2. As also explained in the following, it is suitable that the sensor 12 additional is provided to detect the current flowing in line 2 towards the object 1 to be protected, ie, the current which has been reduced by means of the overcurrent reducing assembly 5. Furthermore, it is emphasized that the sensor 11, as well as possibly the sensor 13, are capable of detecting the current flowing in the line 2 in a direction analogous to the object 1, for example, in cases where the energy stored magnetically in the Object 1 gives rise to a directed current away from object 1. It is emphasized that sensors 11-13 need not be constituted by only sensors that detect current and / or voltage. Within the scope of the invention, the sensors must be of a nature such that generally speaking they can detect any condition indicative of the presentation of a nature failure that requires the initiation of a protection formation. In cases where a fault occurs so that the fault current will flow in a direction away from the object 1, the device is designed so that the control unit 14 thereof will control that the switch 6 is additionally closed, in case in addition, the overcurrent reduction assembly 5 is activated so that the short-circuit current can be diverted by means of it. When, for example, object 1 is conceived to consist of a transformer, the function before the presentation of a short circuit in it must be such that the short circuit first results in a violent flow of current inside the transformer, which the activation of the assembly 5 for the purpose of current deviation is detected and results. When the current flowing to the transformer 1 has been reduced to a required degree, the current limiter 6 is caused to reduce the current but, controlled by the control unit 14, possibly not before a release time for the current is produced. the energy, in the cases in which it is produced, magnetically stored in the generator 1 so that it flows away from the generator 1 and is diverted by means of the assembly 5. Furthermore, the device comprises a control unit indicated generally with the number 14 that it is connected to the sensors 11-13, to the overcurrent reducing assembly 5 and to the current limiter 6. The operation is such that when the control unit 14 by means of one or more of the sensors 11-13 receives signals indicative of the presentation of an unacceptable fault current to the object 1, the overcurrent reducing assembly 5 is immediately controlled to Quickly provide the required current reduction. The control unit 14 can be arranged so that when the sensor 12 has detected that the voltage current has been reduced to a sufficient degree, controls the current limiter 6 to obtain operation thereof by interruption when the overcurrent is below a predetermined level. Such a design ensures that the current limiter 6 is not caused to limit the current until the current has actually been reduced to such an extent that the current limiter 6 does not provide the task of interrupting such an elevated current so that it is not suitably sized for that purpose. However, the mode may alternatively be such that the current limiter 6 is controlled to limit the current at a predetermined time after the overcurrent reduction assembly has been controlled to carry out the current reduction. The circuit breaker 4 may comprise a separate detector assembly for detecting overcurrent situations or otherwise the circuit breaker may be controlled by means of the control unit 14 based on the information from the same sensors 11-13 and also control the operation of the Overcurrent reducing assembly. In the modality illustrated in figure 3, the limiter 6 current is formed by an inductance 27 provided in line 2, such inductance is obtained by means of a coil that results in some increase in the current, and a certain electromotive force back, which counteracts the increase of current. An advantage with this mode is that it is extremely sensitive and furthermore, results in a rapid limitation, when a failure occurs, of the current flow to object 1 without the need for active control.

In the manner in which the device has been described so far, it functions as follows: in the absence of a fault, the circuit breaker closes while the switching means 10 of the overcurrent reducing assembly 5 is opened, i.e. in a non-conducting. In this situation, the switching means 10, of course, must have adequate electrical force so that it is not unintentionally placed in a conductive state. The overvoltage conditions that appear on line 2 as a result of atmospheric circumstances (lightning) or a coupling measurement, in this way, may not cause the voltage force of the closing means 10 to be exceeded in its non-conductive state. For this purpose, it is suitable to couple at least one overvoltage dissipater 22 in parallel on the switching means 10. In the example, such surge suppressors are illustrated on both sides of the switch means 10. The surge arresters, therefore, have the purpose of diverting such overvoltages which would otherwise put them at risk and would cause inadvertent interference in the switch means 10. When an overcurrent state has been registered by any of the sensors 11-13 or the own sensor of the circuit breaker 4 (of course it is understood that the sensor information of the circuit breaker 4 itself can be used as a basis for the control of the reducer assembly 5 overcurrent according to the invention) and this overcurrent state is of such a magnitude that - 4.7 - a serious fault of object 1 can be expected to occur, the interruption function is initiated with respect to circuit breaker 4. In addition, the control unit 14 controls the overcurrent reducing assembly 5 for carrying out such a reduction, and this is more closely caused by the switch means 10 in an electrically conductive state by means of the control member 9. As described in the above, this can be carried out very quickly, that is, in a fraction of time necessary for interruption by the circuit breaker 4, which is why the object to be protected is immediately released from the full current of the short circuit of the network 3 by the switching means 10 which deflects at least a significant part, and in practice the main part of the current, to ground, or in some other way at a lower potential. The current limiter 6 can also come into operation quickly to limit the current flowing on line 2 to (or possibly from) object 1. When these incidents have occurred, the interruption is carried out as a last measure by means of the circuit breaker 4. It is important to note that the overcurrent reducing assembly 5 as well as the current limiter 6 according to a first mode are designed to be able to operate repeatedly. Therefore, when it has been established by means of the sensors 11-13 that the circuit breaker 4 has a closed switch means 10, it is reset to a non-conductive state, and the current limiter 6 is ready, so that the the next time the circuit breaker 4 is closed, the protective device is in its fully operational state. According to another embodiment, the assembly 5 may require the change of one or more parts in order to operate again. Figure 4 illustrates an alternative embodiment of the current limiter 6a. This embodiment comprises an inductance 28 and a capacitor 29, which form in unison a resonance circuit, which at a resonance provides a very high impedance. The inductance and the capacitor are coupled in parallel with each other. A switch 30 and the capacitor 29 are coupled in parallel on the inductance 28 placed on the line 2. Accordingly, the switch 30 and the capacitor 29 are coupled in parallel on the inductance 28 placed on the line 2. Accordingly, the switch 30 and the capacitor 29 are placed in series one with respect to the other. The coupler 30 has one or more contacts, which by means of a suitable operating member 31 can be controlled to close or open respectively via the control unit 14. The current limiter 6a illustrated in FIG. 4 operates in the following manner: during normal operating conditions, the switch 30 is opened. The impedance of the current limiter 6a is provided by the inductance and the resistance of the inductor. In case of a fault current of sufficient magnitude, the control unit 14 will control the switching means 10 to be closed for the purpose of overcurrent deviation and further, the control unit 14 will control the switch 30 to close so that the capacitor 29 is coupled and a parallel resonance circuit is formed which can be adjusted to the energy frequency. The impedance of the current limiter 6a will be raised to resonance. It is also evident from the comparative study of FIG. 2b, that a considerable current reduction is obtained downstream of the current level i3. In Figure 5 an alternative mode of the current limiter 6b is shown, this mode is based on a resonance circuit in series comprising an inductance 32 and a capacitor 33 in series with each other and a switch 34 coupled in parallel on the capacitor 33. An operation member 35 for operating the contact or contacts of the switch 34 is under control from the control unit 14 . During normal operation, the switch 34 is opened on the capacitor 33. The coil 32 in series with the capacitor 33 in series resonance (for example at 50 Hz) has a very small impedance. Transient fault currents are blocked by coil 32. In case of a fault, the voltage on the capacitor is increased as well as the inductance. When closing the switch 34 on the capacitor, it is placed in short circuit. This involves a gastric increase in total impedance, which is why the current is limited.

As indicated in Figure 5, the inductance 32 can be made variable, for example by means of short circuits of the winding or a winding that is located on the same core. In this way it becomes possible to continuously adjust the current limiter 6b to minimize the voltage drop on the current limiter during normal load. Another modification, which is not shown in Figure 5, is to use a self-activated spark space, instead of the switch 34 on the capacitor 33. In this way, a self-activating function is obtained, ie the mode becomes passive in the sense that no particular control is required from any control unit. In the variant illustrated in Figure 6, the current limiter 6c comprises a switch 36 placed on line 2 and in parallel on this switch a capacitor 37 and a resistor 38, the capacitor and the resistor are coupled in parallel one in relation to the other. The switch 36 actually has the character of a vacuum circuit breaker provided with cross-directed coils 39 to increase the arc voltage and obtain current switching in the limiting resistor 38. The control unit 14 is arranged to control the switch 36 by means of an operation member 40. Figure 7 illustrates a current limiter 6d formed by a mechanical switch 41 having a switching element 42 consisting of a large number of arc chambers connected in series. The arc chambers are made of a resistive material, when the switch 41 is opened, the arc short-circuits the resistive arc chamber. When the arc moves inside the arc chamber, the arc is divided into many sub-arcs. In this way the arcs are of increasing length of the resistive path between the contacts and an increased resistance is obtained. As in the above, the control unit 14 is arranged to control the operation of the switch 41 by means of an operation member 43. Figure 8 illustrates a further embodiment of a current limiter 6e. The limiter comprises, in the embodiment, a fast semiconductor switch 44 and an impedance 45 current limiting in parallel and a voltage limiting element 46, for example a varistor. The semiconductor switch 44 can be formed by means of gate deactivation cristol (GTO cristores). A resistor is used as a current limiting impedance. The varistor 46 limits the overvoltage when the current is restricted. Under normal load conditions, current flows through the semiconductors 44. When a fault is detected, the semiconductor switch 44 is opened under control via the control unit 14, preferably via a suitable operating member 47, and the current is switched to resistor 45.

Finally, a current limiter 6f is illustrated in FIG. 9, this limiter comprises a coil 48 connected in line 2. The coil 48 is included in a reactor having an iron core 49. Between the iron core 49 and the reactor and the coil 48 a tubular superconductive mesh 50 is provided. Under normal condition, the superconducting 50 mesh eliminates by shielding the iron core from the coil, and therefore the inductance is relatively low. When the current exceeds a certain level, the superconduction ceases and the inductance increases drastically. Therefore, a strong current limitation is obtained. In the embodiment according to Figure 9, the shielding of the iron core from the coil occurs due to the Meissner effect. An advantage with the embodiment according to Fig. 9 is that, with respect to the current limiter 6f, a small inductance is at hand in normal operation. A disadvantage is that, in order to obtain superconducting, cooling is required at very low temperatures, for example by means of liquid nitrogen. In all the embodiments of figures 4 to 9 that have just been described, only the differences with respect to the current limiter in relation to the design according to figure 3 have been more closely described with respect to the other constituents, reference is made to the description in relation to figure 3.

Figure 10 illustrates an alternative embodiment of the overcurrent reducing assembly 5. Instead of being based on a semiconductor switch means as in Figure 3, the embodiment according to Figure 10 is designed to involve causing a medium present in a space 24 between the electrodes 23 to sink electrical conductivity by means of a member 9a of control . This control member is arranged to control the operation of the members 25 to cause or at least initiate the middle or part thereof in the space 24 in the conductive state. Member 25 in the example is arranged to cause the medium in space 24 to assume electrical conductivity by causing or at least helping to provoke the ionization / plasma medium. It is preferred that the members 25 comprise a laser, which by supply of energy to the medium in the space 24 provides the ionization. As shown in Figure 10, a mirror 26 can be used to make the necessary deviation from the laser beam group. In this regard it is emphasized that the embodiment according to Figure 10 can be such that the medium 25 does not only lead to ionization / plasma in the entire electrode space. Therefore, the intention may be that an electric field imposed on the space may contribute to the formation of ionization / plasma, only part of the medium in space is ionized by means of the member 25 so that subsequently the electric field in space It leads to the establishment of plasma in the entire space. In this regard it is emphasized that, in the electrode space, there can be not only a medium consisting of various gases or mixtures of gases but also a vacuum. In the case of vacuum, the initiation by means of a laser occurs in at least one of the electrodes which, consequently, will function as an electron and ion transmitter for the establishment of an ionized / plasma environment in the space of electrode. • Figure 11 illustrates a conventional embodiment in the sense that the generator Ib via a transformer is coupled to a power network 3a. The objects to be protected, as a result, are represented by the transformer la and the generator Ib. The overcurrent reducing assembly 5a and the current limiter 6g and the common circuit breaker 4a, as can be seen, are positioned in a manner similar to that shown in figure 1 for the case of object 1 shown therein which is conceived and The object is formed according to FIG. 11. Accordingly, reference is made in this respect to the descriptions given with respect to FIG. 1. The same is true for the protection function of the 5c overcurrent assembly and the limiter 6i of current with respect to generator Ib. In this case, accordingly, the generator Ib should be considered equivalent to the object 1 in figure 1, while the transformer should be considered equivalent to the equipment 3 in figure 1. Therefore, the assembly 5c overcurrent reducer and the current limiter 6b in combination with a conventional circuit breaker 4b, will be able to protect the generator Ib against a violent flow of current in a direction away from the transformer la. As a further aspect in Figure 11, the additional overcurrent reducing assembly 5b with the associated current limiter 6h are present. As you can see, there will be 5a and 5b overcurrent reducing mounts on both sides of the transformer la. It is further emphasized that the current limiters 6g and 6i respectively are placed in the connections between the overcurrent reducing assemblies 5a and 5b and the transformer la. The additional overcurrent reducing assembly 5b is designed to protect the transformer from the current groups to the transformer from the generator Ib. As can be seen, the circuit breaker 4b will be able to interrupt regardless of the direction in which the function is desired of protection between the objects la and Ib. With the help of FIGS. 12-14 a mode according to the invention will now be described in the form of an unconventional design of a transformer / reactor. Figure 13 shows an example of a cable which can be used in the windings which are included in the dry energy transformers / reactors according to the invention. Such a cable comprises at least one conductor 54 consisting of several strands 55 with an inner semiconducting layer 56 positioned around the strands. Outside this inner semiconducting layer is the main insulation 57 of the cable in the form of a suitably extruded insulation, solid, and surrounding this solid extruded insulation a semiconductor layer 58. As previously mentioned, the cable can be provided with additional additional layers for special purposes, for example to avoid too high electrical voltages in other regions of the transformer / reactor. From the point of view of the geometrical dimensions, the cables in question will have a conductive area which is between 80 and 3000 mm2 and an outer cable diameter which is between 20 and 250 mm. The windings of a power transformer / reactor manufactured from the cable described above can be used for three-phase or multi-phase single-phase transformers / reactors, regardless of how the core is formed. In Figure 14 a modality is shown which illustrates a three-phase laminated core transformer. The core comprises, in a conventional manner, three ends 59, 60 and 61 of the core and retention yokes 62 and 63. In J-a mode shown, both the limbs of nuscle and the yokes have a taper cross section. Consistently around the extremities, the windings formed with the cable are located. As can be seen, the embodiment shown in Fig. 14 has three twists 64, 65 and 66 of the coil winding. The innermost winding turn 64 can represent the primary winding and the other two winding turns 15 and 16 can represent secondary windings. In order not to overload the figure with too many details, the connections of the windings are not shown. Otherwise, the figure shows that, in the embodiment shown, bars 67 and 68 are placed separators with several different functions at certain points around the windings. Separating bars of insulating material designed to provide some space between the windings of the windings for cooling, reinforcement, etc. can be formed. They can also be formed of electrically conductive material in order to form part of the earthing system of the windings. It should be noted that the description presented in the foregoing should only be considered as an example for the idea of the invention, on which the invention is based. Therefore, it is evident to people familiar with the technique that detailed modifications can be made without abandoning the alsanse of the invention. As an example, it can be mentioned that it is possible to use a switching means 10 as a mechanical switch.

Claims (47)

1. A device in an electric power plant for protection of an object connected to an electrical power grid or other equipment included in the electric power plant to avoid related overcurrents are failures, the device includes a switching device in a line between the object and the network / equipment, the device is sarasterized because the line between the object and the device are routed to a redundant overcurrent assembly which is acusable for redussion of the current is a help of a settling of the sonority of the current within a period of time substantially shorter than the interruption time of the switch device, and wherein the sorptive limiter is soldered between the connection of the redustor assembly of the current to the line and the object.

2. The sonification device is claim 1, which is sarasterized because the device is formed by a circuit breaker.

3. The sonication device is claim 1 or 2, characterized in that the overcurrent reducing assembly comprises an overcurrent diverter for diverting overcurrents to ground or to another unit that otherwise has a lower potential as compared to the network / equipment.

4. The device according to claim 3, characterized in that the overcurrent diverter comprises a switching means coupled between the ground or the smaller potential and the line between the object 1 and the network / equipment.

5. The device according to claim 4, characterized in that the switchover comprises at least one semiconductor component.

6. The device according to claim 4, which is sarasterized because the switch offers an electrode space and a means for causing or at least initiating the spacing of the electrode or at least part of it so as to assume the elstric sonrocity.

7. The device according to claim 6, characterized in that the means for proving or at least initiating the electrode spasm to assume eurythmic conductivity is arranged to prevent the space or part thereof from taking the form of a plasma.

8. The compliance device is claim 7, characterized in that the members for causing or at least initiating the ellipsic space or part thereof to assume eléstrica sondustividad at least one laser.

9. The device of sonification with any presending claim, sarasterized because the current limiter comprises at least one inductance and / or a resistensia or other impedance.

10. The device according to any of the preceding claims, characterized in that the current limiter comprises an inductance and a capacitor, the sual form in unison a resonance synthase that provides high impedance to resonance.

11. The sonification device is the claim 10, sarasterized because the industansia and the sapasitor are coupled in parallel with each other.

12. The device according to claim 11, characterized in that the commutator and the layer are swirled in parallel on the inductiosia provided in the line.

13. The device according to claim 11, characterized in that the industansia and the sapasitor are swapped in series with each other.

14. The sonification device is claim 13, which is sarasterized because it is connected to a capacitor that produces a short circuit to the capacitor, parallel to the capacitor.

15. The device according to claim 14, sarasterized because the assembly that produse sorto sircuito in the sapasitor is formed by a switch.

16. The compliance device is claim 14, characterized in that the assembly that produces short sirsuite in the sapasitor is formed by a spasm of shispa.

17. The device according to claim 9, characterized in that the current limiter comprises a switch placed on the line and a capacitor and resistor coupled in parallel to the switch and each other.

18. The compliance device is claim 9, characterized in that the current limiter comprises a single-line switch and a switching assembly comprising at least one resistive arc chamber.

19. The compliance device is claim 9, characterized in that the current limiter comprises a switch placed on the line and a current limiting impedance coupled in parallel on the switch, a current limiting element that couples in parallel on the impedance.

20. The device according to claim 9, which is sarasterized because the sorptive limiter comprises a coiled coil in the line, the coil is insulated in a reactor with an iron core so that a super-hidden tubular shield is provided between the iron null reastor and the coil, the shield supersondustor shielded to the iron nusleo of the coil under normal operasión, and in this way the industansia is relatively low, while suando the sorrente exsede sierto level, the superconduction ceases and the inductance is drastically insremented.

21. The sonicity device is any of the foregoing claims, characterized in that the current limiter is placed to be astivated for limiting the current when an oversupply sonar is detected.

22. The compliance device is claim 21, characterized in that a control unit placed to activate the current limiter based on the information of the overcurrent condition detector assembly.

23. The device according to claim 22, characterized in that the control unit is adapted to activate the sorptive limiter by operation of the switch defined in accordance with claims 12, 15, 18 and 19.

24. The sonicity device is any one of the preceding claims, characterized in that the current limiter is adapted to be activated for loss of current after redussing the superethrust hasia or away from the object by means of the redustor assembly of superator but substantially musho before the sonmutador device.

25. The sonicity device is any one of claims 22 to 24, sarasterized in that the control unit is adapted to provide activation of the sorptive limiter by superating the superego to or away from the object it is indicated to be below a predetermined level by the detec- tion assembly. .

26. The sonicity device is any of the presequent claims, which is sarasterized because two redundant overcurrent assemblies are solved on both sides of the object to protect it from both sides.

27. The device according to claim 1, characterized in that it comprises a control unit connected to the overcurrent reducing assembly and to the overcurrent conditions detection assembly, the control unit is colossal to control the overcurrent reducing assembly to close it with the help of information from the assembly that detects the overcurrent conditions when it is justified for protection reasons.

28. The conformity device is claim 22, 23, 25, or 27, which is sarasterized because one and the same sontrol unit are adapted to control the superordinate redustor assembly and the current limiter based on the configuration information of the sensor array. overcurrent

29. The compliance device is any preceding claim, characterized in that the protected object is formed by an electrical device with a magnetic circuit.

30. The device according to claim 29, characterized in that the object is formed by a transformer or reactor.

31. The device according to any of claims 29 to 30, characterized in that the apparatus is supplied with a magnetic cirsuite and is designed for high voltage, suitably 72.5 kV and higher.

32. The device according to any of claims 29 to 31, characterized in that the magnetic circuit of the electrical apparatus comprises a winding formed by means of a saber.

33. The device of soundness are any of the claims 29 to 32, sarasterized because at least one winding of the apparatus comprises at least one conductor and around this conductor is an electrical insulation of a solid insulation material, where a sapa colose outside of a semi-solid material around the insulation, where the inner layer of a semi-solid material is soldered within the insulation and where at least one solder is solved within the inner layer.

34. The sounding device with claim 33, which is sarasterized, because at least one of the inner and outer layers has a thermal expansion surface substantially the same as the insulation material.

35. The sonicity device is any of the claims 33 and 34, characterized in that the inner layer is in electrical contact with at least one sonductor.

36. The sonicity device is any one of claims 33 to 35, characterized in that the outer layer essentially forms an equipotential surface.

37. The device according to any of claims 33 to 36, characterized in that the inner and outer semiconductive layers and the insulation are bonded together over substantially the entire interface.

38. The device according to claim 33, sarasterized because at least one of the strands of the cousin is not insulated and soldered so as to obtain sontasto eléstriso are the inner semisondustora sapa.

39. The sonicity device is any of the claims 33 to 38, characterized in that the cables are manufactured in a sonar area the sual is between 80 and 3000 mm2 and is an outer saber diameter the sual is between 20 and 250 mm

40. The sonicity device is any of claims 30 to 39, sarasterized in that the object is designed as an energy transformer / reactor comprising a core formed of magnetic material and consisting of core ends and yokes.

41. The device according to any of claims 29 to 40, characterized in that the power transformer / reactor is formed without a core (wind-wound).

42. The sonicity device is any of claims 29 to 41, which is sarasterized because at least two galvanically separated windings are present, the device being characterized in that the windings are concentrically wound.

43. The use of a device according to any of the preceding claims, characterized in that it is used to protect an object in the form of a transformer or reactor against overcurrents related to faults.

44. A method in an electric power plant for protection of an object connected to an electrical power grid or other equipment maintained in the power plant eléstrisa of redundant related failures, a switching device is located in a line between the object and the network / equipment, the method is sarasterized because the redustor assembly of superator current is to the line between the object and the device is shifter for redussion of superethrier suando have been deformed by an assembly for this purpose, within a period of time more sustainably than the interruption time of the switch device.

45. The method according to claim 44, characterized in that the overflows are diverted to ground or to another unit that otherwise has a lower potential than the network / equipment by means of the redundant surge assembly.

46. The method according to claim 44 or 45, characterized in that the current limiter, which is placed in the line between the connecting device and the object between the overcurrent reducing assembly and the object, is caused to interrupt not until it has reduced the overcurrent to or away from the object by means of the overcurrent reduction assembly.

47. The method according to any of claims 44 to 46, characterized in that the protection device comprises a substow reduction assembly that is blown for protrusion of an object in the form of a transformer or retractor.