MXPA99005678A

MXPA99005678A - Device and method relating to protection of an object against over-currents comprising over-current reduction

Info

Publication number: MXPA99005678A
Application number: MXPA/A/1999/005678A
Authority: MX
Inventors: Leijon Mats; Berggren Bertil; Bergkvist Mikael; Bernhoff Hans; Ekberg Mikael; Isberg Jan; Ming Li; Sunesson Anders; Windmar Dan
Original assignee: Asea Brown Boveri Ab; Berggren Bertil; Bergkvist Mikael; Bernhoff Hans; Ekberg Mats; Isberg Jan; Leijon Mats; Ming Li; Sunesson Anders; Windmar Dan
Priority date: 1996-12-17
Filing date: 1999-06-17
Publication date: 2000-01-21

Abstract

This invention is related to a device and a method for protection, in an electric power plant, of an object (1) against over-currents 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 over-currents towards the object (1), said arrangement (5) being activatable for over-current reduction with the assistance of an arrangement (11-13) detecting over-current 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 OVERCURRENTS THAT INCLUDES REDUCTION OF OVERCURRENT 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 and 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 an apparatus having a magnetic circuit that requires protection against overcurrents related to faults, that is, in practice short circuit currents. As an example, the object can be a transformer or reactor. 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 the protection, in its own current limiting capacity, transient and inherent, as a consequence of the 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 equal degree of high, an inductively current limiting unit that involves its own protection against overcurrents as well as a protection for electrical units located before and after, respectively , of the transformer / reactor. In such transformers non-conventional reactors of course it is particularly important that the protection device operate quickly to delimit the damaging effect of the fault. 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, cooled 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 of 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. further, 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, while otherwise referred to as a de-energized lid changer. Regarding oil-cooled energy transformers and insulated with oil in the upper energy range, the interrupter element of the lid changers in charge are placed in containers filled with special oil with direct connection to the transformer tank. The interrupting elements are operated in a purely mechanical manner by means of a motor-driven rotary shaft and are positioned so that a rapid movement is obtained during switching when the contact is opened and a slower movement when the device is to be closed. Contact. However, the on-load cap changer as such is placed in the current transformer tank. During the operation, an arching and spark formation occurs. 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 6, which in addition to a coil 27 comprises a core 28, a simplified and fundamental view of the equipotential lines 29 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 available space 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 sizing 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, and difficult to control, is avoided as a result of the distribution of voltage capacity between the current leading 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 performed partially, in comparison with 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 power transformers filled with oil, the windings are designed in what is 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 oil with cellulose constitutes a non-negligible fire risk in the case of unintentional heating, for example in an internal disruptive discharge, and a resulting spill of oil. 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 energy transformers in the upper energy range, transport often occurs with a tank without the oil. It happens that the external design of the transformer must be adapted to the current transport profile, that is to pass through 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 energy transformers filled with oil: A conventional energy transformer filled with oil: - comprises an outer 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 measurements usually also involve considerable transport problems. normally it 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. It 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. - 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 cellulose insulation or based on varnish closest to the individual conductive element and, apart from this, solid and liquid cellulose, possibly also gaseous, as insulation. Furthermore, it is extremely important that the insulation system shows a very low moisture content, comprising 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. it involves a non-negligible fire risk with respect to internal partial discharges, which is called corona, sparking in cover 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. - 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 in such a way that the 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 a detector assembly overcurrent conditions within a period of time substantially less than the interruption time of the switching device. 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 carrying out any actual interruption of the overcurrent, nevertheless reduce it to such an extent that the object under protection is subjected to substantially reduced stresses 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. 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. According to a particularly preferred embodiment of the invention, measures have been taken to obtain a reduction of the period of time during which the current already reduced by means of the overcurrent reducing assembly can flow inside the protected object. For this purpose the device comprises an additional switch placed in line between the circuit breaker and the object, the additional switch is designed to interrupt the lower voltage and current compared to the switching device and therefore can be designed with a timeout shorter compared to the switching device as a consequence of a lower need for movement and a lower contact weight or movable contacts of the switch, the switch is also placed to interrupt but until a time when the overcurrent to or away from the object protected has been reduced by means of the overcurrent reduction assembly. More specifically, the necessary movement of the contact or movable contacts of the additional switch is smaller due to the lower voltage, while the weight of the contact or contacts can be kept low due to the fact that the lower current does not require such large contact areas. . As defined more clearly in the claims, the invention is applicable to transformers and reactors constructed by means of unconventional 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 device has also been designed to start operating with an electrical voltage higher than that of a conventional current device, the voltage on the electrical isolation 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 "interior" and "exterior". 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 as to ensure a potential equalization along the conductor. However, 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 can 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 show each 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. In order to utilize the advantages provided by the use of the mentioned cable, there are other possible modalities with respect to the ground connection 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 fashion 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; Figure 4 is a diagrammatic view illustrating a possible design of the overcurrent reducing assembly, - Figure 5 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 to it; Figure 6 shows the distribution of electric field around a winding of a conventional power transformer / reactor; Figure 7 shows an example of a cable used in the windings of the power transformers / reactors according to the invention, and Figure 8 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 failure 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 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 can 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, in a time tfalla, the fault current in the line indicated as 2 in figure 1 quickly sums up the magnitude ±±. This fault current ± is interrupted by means of a circuit breaker 4 at t17 which is at least 150 ms after tripping. 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 the 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. Accordingly, the circuit breaker 4 comprises, as a rule, auxiliary equipment necessary for arc extinction. According to the invention, line 2 between the object 1 and the switching device 4 is connected to an assembly which reduces the overcurrents to the apparatus 1 and is generally indicated by the number 5. The assembly is operable for overcurrent reduction with the aid 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, consequently, is designed so that no galvanic separation is necessary. 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 can be mentioned that the current reduction from level ix 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 is evident from Figure 1, the device comprises an additional switch indicated generally with the number 6 and placed on line 2 between the circuit breaker 4 and object 1. This additional switch is designed to interrupt a lower voltage and currents compared to the circuit breaker 4, and as a consequence of the same, it can be designed to operate with shorter interruption times in comparison with the circuit breaker. The additional switch 6 is placed to interrupt until the overcurrent has been reduced from the network 3 to the object 1, by means of the overcurrent reducing assembly 5, but substantially before the circuit breaker 4. From what has been established, it is it is evident that the additional switch 6 must be coupled to the line 2 in such a way that the current is reduced by means of the overcurrent reduction assembly 5 which will flow through the additional switch and which, consequently, will be interrupted by means of the same.

Figure 2b illustrates the action of the additional switch 6. This switch is designed, more specifically, to interrupt at time t3, which means that the duration of the current i2 reduced by means of the overcurrent reducing assembly 5 is substantially delimited, specifically to the period of time t2-t3. The consequence is that the injection of energy into the protected object 1 caused by a fault current from the network 3 is represented by the surfaces marked with oblique lines in Figure 2d. 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 to half the current reduces the injection of energy to a quarter. The manner in which the mesh current flows through assembly 5 is illustrated in Figure 2c. The sizing of the assembly 5 and the additional switch 6 is conceived to be carried out so that the assembly 5 reduces the fault current and the voltage is decomposed by means of the additional switch 6 to substantially lower levels. A realistic interruption time with respect to the additional switch 6 is 1 ms. Nevertheless, the sizing must be performed so that the switch 6 is caused to interrupt but until after the assembly 5 has reduced the current flowing through the switch 6 to at least a substantial degree.

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, as well as in alternating current connections.) In the latter case, the line indicated with number 2 can be considered to form one of the However, it should be remembered that the device according to the invention can be manufactured in such a way that all the phases are subjected to the protection function according to the invention in case of a single phase. failure detected or that only that phase or those phases where the fault current occurs which are subject to current reduction From figure 3 it is evident that the current reducer assembly indicated generally with the number 5 comprises a diverter 7 overcurrent to divert overcurrents to ground 8 or to a different unit in any other way that has a lower potential than the network 3. Therefore, thus, the overcurrent diverter can be considered as constituting 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 that it flows on 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 able to establish a short circuit that has better conductivity than one corresponding to the short circuit fault in the object 1 to be protected so that consequently a main part of the fault current is diverted to ground or in some other way to a lower potential by means of the overcurrent diverter 7. It seems from this that, in a case of normal failure, the energy injection in object 1 in case of a fault becomes substantially smaller than that which is indicated in figure 2d as a consequence of a lower level of current i2 as well as a shorter time extension t2-t3. 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 switch member 10. 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 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 line 2 upstream of the connection of the overcurrent reducing assembly 5 and in line 2. As also explained in the following, it is suitable that the additional sensor 12 is provided to detect the current flowing in line 2 towards the object 1 to be protected, i.e., 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 on the line 2 in a direction away from the object 1, for example, in cases where the energy stored magnetically in the object 1 results in a directed current moving away from the object 1. It is emphasized that the 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, the overcurrent reducing assembly 5 and the additional switch 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, it 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 of the same sensors 11-13 and also control the operation of the mounts and overcurrent reducer. In Figure 3 it is illustrated that the additional switch 3 comprises a switch 15 having metal contacts. This switch 15 is operable between the interruption and closure positions by means of an operation member 16, which in turn is controlled by the control unit 14. A shunt line 17 is connected in parallel on this switch 15, such shunt line comprising one or more components 18 designed to avoid arcs before the separation of the contacts of the switch 15 by causing the shunt line 17 to travel on the pipeline of current from the contacts. These components are designed so that they can interrupt or restrict the current. Therefore, the purpose is that the components 18 should normally be maintained in the conduction path in the interrupted branch line 17, but close the branch line when the switch 15 is to be opened so that the current is consequently derived by passing the switch 15 and in this way arcs are not produced or possibly arcs are produced that are efficiently extinguished. The components 18 comprise one or more associated control members 19 connected to the control unit 14 for control purposes. According to one embodiment of the invention, the components 18 are controllable semiconductor components, for example GTO thyristors having the necessary overvoltage dissipators 30. A disconnect 20 for galvanic separation is placed in the current conduction path generated by means of the shunt line 17 to the object 1 to be protected, in series, with one or more of the components 18. This disconnect 20 is controlled via an operation member 21 by the control unit 14. Figure 3 illustrates the disconnector 20 placed on the branch line 17 itself. Of course, this is not necessary. The disconnector 20 can also be placed on line 2 insofar as it ensures a real galvanic separation, by series coupled with one or more components 18, in the established driving path by means of series couplings so that, consequently , there is no possibility that the current flows through the components 18. The device described so far operates in the following manner: in the absence of a fault, the circuit breaker 4 is closed in the same manner as the circuit breaker 4. Switch 15 of additional switch 6. The components 18 on the shunt line 17 are in a non-conductive state. The disconnector 20 is closed. Finally, the switch means 10 of the overcurrent reducing assembly 5 is opened, ie they are in a non-conductive state. In this situation, the switching means 10, of course, must have a suitable electrical resistance so that it does not inadvertently get into a conductive state. The overvoltage conditions that occur in line 2 as a result of atmospheric circumstances (lightning) or coupling measures, consequently, may not involve exceeding the resistance of the voltage of the switching means 10 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 a serious failure of the object 1 can be expected to occur, the interruption function is initiated with respect to the circuit breaker 4. In addition, the unit 14 control unit controls the overcurrent reducer assembly 5 to carry out such reduction, and this is more closely caused by the switch means 10 in an electrically conductive state by means of the control member 9 the switch means 10 in an electrically conductive state. 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. As soon as the current, which flows into the object 1 via the additional switch 6, has been reduced to a necessary degree, which can be established in a simple time base by a time difference between the activation of the switching medium 10. and the operation of the switch 6 or by the detection of the current flowing in the line 2 by means of, for example, the sensor 12, the operating member 16 or the switch 15 are controlled, via the control unit 14 to open the contacts of the switch 15. To extinguish or avoid arcs, the components 18, for example GTO thyristors or gas switches, are controlled via the control members 19, to establish conductivity of the bypass line 17. When the switch 15 has been opened and galvanic separation has been provided in this way, the component 18 is again controlled to place the bypass line 17 in a non-conductive state. In this way, the current from the network 3 to the object 1 has been efficiently interrupted. After the bypass line 17 has been placed in a non-conductive state, galvanic separation can be further carried out by means of the disconnect 20 by controlling the operation member 21 thereof from the control unit 14. When all these incidents have occurred, the interruption occurs by means of the circuit breaker 4 as the last incident. It is important to note that the overcurrent reducing assembly as well as the overcurrent reducer as well as the additional switch 6 according to a first mode, can be operated repeatedly. Thus, when it has been established by means of the sensors 11-13 that the circuit breaker 4 has been inactivated, the switch means 10 is reset to a non-conductive state and the switch 15 and the disconnector 20 are closed again so that when the circuit breaker 4 is closed the next time, the protection device is fully operable. According to another embodiment, however, it is contemplated that the overcurrent reducing assembly 5 may require exchange of one or more parts in order to operate again. It is emphasized that according to an alternative embodiment of the invention, the component or components 18 must be placed in a conducting state as soon as the overcurrent reducing assembly 5 has been brought into a closed state and this is regardless of whether the switch 15 it may not open later. Thus, the control of the components 18 occurs, as described above, by means of the control unit 14, or alternatively, by means of a control function that involves a dependency after the closure of the assembly 5. Figure 4 illustrates an alternative embodiment of the overcurrent reducing assembly 5. Instead of being based on semiconductor switch means as in Figure 3, the embodiment according to Figure 4 is designed to involve causing a medium present in a space 24 between the electrodes 23 to assume electrical conductivity by means of a control member 9a . This control member is arranged to control the operation of the members 25 to cause or at least initiate the medium or a part thereof in the space 24 to a conducting state. Such 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 cause the medium to ionize / plasma. It is preferred that members 25 comprise at least one laser, which by means of supplying energy to the medium in space 24 provides the ionization. As is evident from Figure 4, a mirror 26 can be used to necessarily deflect the laser beam assembly. In this regard it is emphasized that the embodiment according to Figure 4 can be such that the medium will 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 a part of the space medium is ionized by means of the members 25 so that subsequently the electric field in the space It leads to the establishment of plasma in the entire space. In this regard it is emphasized that there can be in the electrode space not only a medium consisting of various gases or gas mixtures but also a vacuum. In the case of vacuum, the initiation by means of laser occurs in at least one of the electrodes, which consequently will function as an electron and ion transmitter for establishing an ionized environment / a plasma in the electrode space. Figure 5 illustrates a conventional embodiment, in the sense that the generator lb via a transformer is coupled to a power network 3a. Consequently, the objects to be protected are represented by the transformer a and the generator lb. The overcurrent reducing assembly 5a and the additional switch 6a and the common circuit breaker 4a are placed, as can be seen, similar to what appears in figure 1 in the case where the object 1 shown therein is conceived to form the object according to FIG. 5. Accordingly, the reference in this respect is made to the descriptions given with respect to FIG. 1. The same is true for the protection function of the 5c overcurrent assembly and the additional switch 6c with respect to the generator lb. In this case, the transformer can be considered the equivalent, therefore, with the object in Figure 1, while the generator lb can be considered equivalent to the equipment 3 in Figure 1. Therefore, the 5c overcurrent reducer assembly and the additional switch 6c, in combination with the conventional circuit breaker 4b will be able to protect the transformer 1 against the violent flow of current in a direction away from the generator Ib. As a further aspect in Figure 5, the additional overcurrent reducing assembly 5b with associated additional switches 6b are present. As can be seen, there will be overcurrent reducing mounts 5a and 5b on both sides of the transformer la. It is then emphasized that the additional switches 6a and 6b 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 intended to protect the transformer from the current flowing to the transformer from the generator lb. As can be seen, the circuit breaker 4b will be able to interrupt independently of the direction, between the objects la and lb of which a protection function is desired. With the help of FIGS. 6-8, a mode according to the invention will now be described in the form of an unconventional design of a transformer / reducer. Figure 7 shows an example of a cable which can be used in the windings which are included in dry powder transformers / reactors, according to the invention. Such a cable comprises at least one conductor 30 consisting of several strands 31 with an inner semiconducting layer 32 positioned around the strands. Outside this inner semiconducting layer is the main insulation 33 of the cable in the form of a solid, the insulation extruded suitably and surrounding this solid excluded insulation a semiconductor layer 34. As previously mentioned, the cable can be provided with 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 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 less than 20 and 250 mm. The windings of a power transformer / reactor manufactured from the cable described above can be used for single-phase transformers / reactors. three-phase and multi-phase, regardless of how the core is conformed. In Figure 8 a modality is shown which illustrates a three-phase laminated core transformer. The core comprises, in conventional manner, three core ends 35, 36 and 37 and retention yokes 38 and 39. In the embodiment shown, both the core tips and the yokes have a tapered cross section. Concentrically around the core ends, the windings formed with the cable are located. The modality shown in Figure 8, as can be seen, has three concentric windings 40, 41 and 42. The innermost winding turn 40 may represent the primary winding and the other two winding turns 41 and 42 may 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 mode shown, bars 43 and 44 separators are placed with several different functions at certain points around the windings. The separation bars can be formed of insulating material designed to provide some space between the concentric windings for cooling, reinforcement, etc. They can also be formed of electrically conductive material in order to form part of the grounded system of the windings.

It should be noted that the description presented in this document should only be considered as an example for the idea of the invention, on which the invention is constructed. Therefore, it is obvious to a person familiar with the art that detailed modifications can be made without departing from the scope of the invention. As an example, it can be mentioned that it is possible to use a mechanical switch as a switch means.

Claims

1. A device in a power plant for protection of an object connected to a power grid or other equipment included in the power plant to prevent overcurrents related to faults, the device comprises a switching device in a line between the object and the network / equipment, the device is characterized in that the line between the object and the switching device is connected to an overcurrent reduction assembly, which is operable for overcurrent reduction with the help of an overcurrent condition detector assembly within a period of time substantially shorter than the interruption time of the switching device.

2. The device according to claim 1, characterized in that the switching device is formed by a circuit breaker.

3. The device according to claim 1 or 2, characterized in that the overcurrent reducing assembly comprises an overcurrent diverter for diverting the overcurrents to ground or to a different unit in some other way that has a lower potential than the network / equipment.

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

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

6. The device according to claim 4, characterized in that the switch comprises an electrode space and a means for causing or at least initiating the electrode space or at least part thereof to assume electrical conductivity.

7. The device according to claim 6, characterized in that the means for causing or at least initiating the electrical space to assume electrical conductivity is arranged to cause the space or part thereof to assume the shape of a plasma.

8. The device according to claim 7, characterized in that the members for causing or at least initiating the electrode space or part thereof to assume electrical conductivity comprises at least one laser.

9. The device according to any of the preceding claims, characterized in that it comprises an additional switch placed in line between the switching device and the object, the additional switch is placed between the overcurrent reduction assembly and the object and is adapted to interrupt minor voltages and current compared to the switch device and therefore is able to perform a shorter interruption time compared to the switch device and wherein the additional switch is adapted for interruption when the overcurrent has been reduced towards or away from the object, by means of of the overcurrent reducing assembly, but substantially before the switching device.

10. The device according to claim 9, characterized in that it comprises a control unit connected to the detection assembly and to the additional switch in order to obtain activation of the additional switch for interruption purpose when overcurrent is indicated towards or away from the object, by means of of the detection assembly, which is under a predetermined level.

11. The device according to any of claims 9-10, characterized in that an additional separator comprises a switch on which a bypass line is coupled having one or more components to avoid arcs before the separation of the switch contacts causing the branch line is taken over the current conduit from the contacts.

12. The device according to claim 11, characterized in that one or more of the components in the branch line can be closed in conduction by means of a control via the control unit.

13. The device according to claim 11 or 12, characterized in that one or more components are formed by controllable semiconductor components.

14. The device according to any of claims 11-13, characterized in that one or more of the components is provided with at least one overvoltage dissipater.

15. The device according to any of claims 11 to 14, characterized in that a disconnector is placed for galvanic separation in series with one or more components.

16. The device according to claim 15, characterized in that the disconnector is coupled to the control unit to be controlled by it for opening after the switch has been controlled to be closed and one or more components have been placed in a condition for interrupt the derivation line.

17. The device according to any of the preceding claims, characterized in that at least one overvoltage dissipator is coupled parallel with the overcurrent reducing assembly.

18. The device according to any of the preceding claims, characterized in that two overcurrent reducing assemblies are placed on both sides of the object to protect it from both sides.

19. The device according to claim 1, characterized in that it comprises a control unit connected to the overcurrent reducing assembly and to the overcurrent condition detector assembly, the control unit is positioned to control the overcurrent reducing assembly to close it based on the Information from the assembly detector of overcurrent conditions when required for protection reasons.

20. The device according to claim 19 and one or more of claims 10, 12 and 16, characterized in that one and the same control unit are placed to control, based on the information of the overcurrent condition detector assembly, the assembly Overcurrent reducer and additional switch.

21. The device according to any of the preceding claims, characterized in that the protected object is formed by an electrical device with a magnetic circuit.

22. The device according to claim 21, characterized in that the object is formed by a transformer or reactor.

23. The device according to any of claims 21 to 22, characterized in that the electrical apparatus provided with a magnetic circuit is designed for high voltage, suitably 72.5 kV and higher.

24. The device according to any of claims 29 to 23, characterized in that the magnetic circuit of the electrical apparatus comprises a winding formed by means of a cable.

25. The device according to any of claims 21 to 24, characterized in that at least one winding of the apparatus comprises at least one conductor and around this conductor an electrical insulator of a solid insulation material, wherein an outer layer of the material The semiconductor is placed around the insulation, wherein an inner layer of a semiconductor material is placed inside the insulation and where at least one conductor is placed inwardly of the inner layer.

26. The device according to claim 25, characterized in that at least one of the inner and outer layers has a coefficient of thermal expansion substantially equal to the insulation material.

27. The device according to any of claims 25 and 26, characterized in that the inner layer is in electrical contact with at least one conductor.

28. The device according to any of claims 25 to 27 characterized in that the outer layer essentially forms an equipotential surface.

29. The device according to any of claims 25 to 28, characterized in that the inner and outer semiconductive layers and the insulation are bonded together over substantially the entire interface.

30. The device according to claim 25, characterized in that at least one of the strands of the conductor is not insulated and placed so as to obtain an electrical contact with the inner semiconductor layer.

31. The device according to claims 25 to 30, characterized in that the cables are manufactured with a conductive area which is between 80 and 3000 mm2 and with an outer cable diameter which is between 20 and 250 mm.

32. The device according to any of claims 22 to 31, characterized in that the object is designed as an energy transformer / reactor and comprises a core formed by magnetic material and consisting of core and yokes.

33. The device according to any of claims 21 to 32, characterized in that the power transformer / reactor is formed without a core (air winding).

34. The device according to any of claims 21 to 33, characterized in that it comprises at least two galvanically separated windings, characterized in that the windings are wrapped concentrically.

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

36. A method in an electric power plant for protection of an object connected to a power grid or other equipment contained in the power plant of fault-related overcurrents, a switching device that is located on a line between the object and the network / equipment, the method is characterized in that the overcurrent reducing assembly connected to the line between the object and the switching device is activated for reduction on current when overcurrent conditions have been detected by means of an assembly for this purpose, within a a period of time substantially shorter than the interruption time of the switching device.

37. The method according to claim 36, characterized in that the overcurrents are diverted to ground or to another unit that otherwise has a lower potential in comparison with the network / equipment, by means of an overcurrent reducing assembly.

38. The method according to claim 36 or 37, characterized in that a switch, which is placed on the line between the switching device and the object and between the overcurrent reducing assembly and the object, is caused to be interrupted until that the overcurrent towards or away from the object has been reduced by means of the overcurrent reduction assembly.

39. The method according to any of claims 36 to 38, characterized in that the protection device comprises the overcurrent reducing assembly that is coupled to protect an object in the form of a transformer or reactor.