MXPA99005679A - 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 in an electric power plant for protection 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 actuatable for over-current reduction with the assistance of an over-current condition detecting arrangement (11-13) within a time period substantially less than the break-time of the switching device (4).

Description

DEVICE AND METHOD IN RELATION TO PROTECTION OF AN OBJECT AGAINST OVERCURRENTS THAT INCLUDES ENVELOPE REDUCTION CURRENT 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 against 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 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, i.e. 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 will handle, 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.

The rotary electric machines proposed here comprise synchronous machines used primarily as generators for connection to distribution and transmission networks collectively indicated as power networks in the following. Synchronous machines are also used as motors and for phase compensation and voltage regulation and then as machines mechanically in vacuum. The technical field also includes double feed machines, asynchronous converter cascades, external pole machines and synchronous flow machines. The magnetic circuit referred to in this context can be wound up in the air, but can also comprise a normal or oriented laminated magnetic core of one sheet or another, for example, a material based on amorphous or powdery material, or any other action for the purpose of allowing an alternating flow, a winding, a cooling system, etc., and can be placed in the stator or rotor of the machine, or in both. According to the invention, the main intention is to protect an unconventional rotating electric machine from the direct connection of all kinds of high voltage power networks. Such a machine has its magnetic circuit designed with a threaded conductor, which is isolated with a solid isolation and in which earth has been incorporated.

In order to be able to explain and describe the non-conventional machine, a brief description of the rotary electric machine, exemplified on the basis of a synchronous machine, will first be provided. The first part of the description relates substantially to the magnetic circuit of such a machine and the manner in which it is constructed in accordance with the classical technique. Since the magnetic circuit to which most of the cases are referred is located in the stator, the magnetic circuit below will normally be described as a stator with a metal core of laminated sheet, the winding of which will be referred to as the winding of the The stator and slots arranged for the winding in the rolling core will be referred to as the stator slots or simply the slots. Many synchronous machines have a field winding in the rotor, where the main flow is generated by direct current, and an AC winding in the stator. Synchronous machines are normally of three-phase design and the invention relates mainly to such machines. Sometimes synchronous machines are designed with salient poles. However, cylindrical rotors are used for two- to four-pole turbine generators for double feed machines. The latter have an AC winding in the rotor and this can be designed for the voltage levels of the power grid.

The stator body for large synchronous machines is often manufactured from a steel sheet with a welded construction. The laminated core is usually manufactured from a varnished 0.35 or 0.5 mm electrical sheet. For radial ventilation and cooling, the laminated core is, at least for medium and large machines, divided into packages with radial or axial ventilation channels. For larger machines, the blade is punched into segments, which are attached to the stator body by wedges / dovetails. The laminated core is retained by pressure fingers and pressure plates. The winding of the stator is located in grooves in the laminated core and the grooves have, as a rule, a cross section as a rectangle or as a trapezoid. AC multi-phase windings are designed as either single-layer or two-layer windings. In the case of single layer windings, there is only one coil side per slot, and in the case of two layer coils there are two coil sides per slot. By coil side it is meant one or more conductors joined in height and / or width and which are provided with a common coil insulation, that is, an insulation designed to withstand the nominal voltage of the machine in relation to the earth. Two windings of layers are usually designed as diamond windings, while the single layer windings, which are relevant in this respect, can be designed as a diamond winding or as a flat winding. In the case of a diamond winding, only one coil extension (or possibly two coil extensions) are present, whereas the flat windings are designed as concentric windings, i.e., with a coil extension that varies greatly. By extension of coils it is meant the distance in the circular measurement between two coil sides belonging to the same coil, either in relation to the relevant pole pitch or in the number of intermediate slot passages. Usually different variants of stringing, for example fractional pitch, are used to provide the winding with the desired properties. The type of winding substantially describes the manner in which the coils are connected in the slots, that is, the sides of the coil, together outwardly of the stator, this at the ends of the coil. A typical coil side is formed by what are called Roebel rods, in which some of the rods have been made hollow for a coolant. The Roebel bar comprises a plurality of rectangular copper conductors connected in parallel, which are transposed 360 degrees along the groove. Ringland bars with 540 degree transpositions and other transpositions are also produced. Transposition is necessary to avoid circulating currents. Between each chain there is a thin insulation, for example of epoxy / glass fiber. The main insulation between the grooves and the conductors is manufactured, for example, from exopic material / fiber glass / mica and externally has a potential layer of thin semiconductor earth used to equalize the electric field. Externally to the stack of sheets, one does not have any other potential layer of semiconductor ground but an electric field control in the form of what is called corona protection varnish designed to convert a radial field into an axial field, which means that the Insulation on the coil end occurs at a high potential in relation to ground. Field control is a problem which sometimes results in a corona in the bobbin end region, which can be destructive. Normally, all large machines are designed with a two-layer winding and equally large coils. Each coil is placed with one side in one of the layers and the other side in the other layer. This means that the coils also cross each other at the coil end. If more than two layers are used, these crudes make the winding work difficult and damage the end of the coil. What has been established before can be said to belong to the classical technique when they encounter rotating electrical machines in sight. During the last decades, there have been increasing requirements for rotating electric machines for higher voltages compared to those that it has been possible to design and produce previously. The maximum voltage level, which according to the state of the art it has been possible to obtain for synchronous machines with a good performance in the coil production is approximately 25-30 kV. It is also generally known that the connection of a synchronous machine / generator to a power network must be done via a? / Y connected to what is called a step-up transformer, since the voltage of the power grid is normally at a higher level than the voltage of the rotary electric machine. Together with a synchronous machine, this transformer therefore constitutes an integrated part of a plant. The transformer constitutes an additional cost and also implies the disadvantage that the total efficiency of the system is reduced. If it were possible to manufacture machines with considerably higher voltages, in this way the elevator transformer would be omitted. Certain attempts have been described for a new approach in the design of synchronous machines, for example, in an article entitled "Water-and-oil-cooled Turbogenerator TV -300" in J. Elektrotechnika, No. 1, 1970, pp. 6-8, in US 4 429 244"Stator of generator" and in the Russian patent document CCCP patent 955369. The synchronous machine cooled with water and oil described in J. Elektrotechnika is designed for voltages of up to 20 kV. The article describes a new insulation system consisting of an oil / paper insulation, which makes it possible to immerse the stator completely in oil. Then the oil can be used as a coolant and at the same time used as an insulator. To prevent the oil in the stator from leaking out towards the rotor, a dielectric oil separation ring is provided on the inner surface of the core. The stator winding is made of conductors with a hollow oval shape provided with oil and paper insulation. The sides of the winding with its insulation are fixed in grooves made with a rectangular cross section by means of wedges. A cooling oil is used both in the hollow conductors and in the holes in the walls of the eatator. However, such cooling systems involve a large number of connections of both oil and electricity at the ends of the coil. The thick insulation also implies an increased radius of curvature of the conductors, which in turn results in an increased size of the protruding winding. The aforementioned US patent relates to the stator part of a synchronous machine which comprises a magnetic core of laminated sheet with trapezoidal grooves for the stator winding. The grooves are tapered since the need for insulation of the stator winding is less towards the inside of the rotor where that part of the winding which is located closer to the neutral point is located. In addition, the stator part comprises a dielectric oil separating cylinder closer to the inner surface of the core. This part can increase the magnetization requirement in relation to a machine without this ring. The stator winding is made of cables immersed in oil with the same diameter for each coil layer. The layers are separated from each other by means of spacers in the slots and fixed by wedges. What is special for the winding is that it comprises two of what are called semi-coils connected in series. -One of the two half-coils is located, centered inside an insulating sleeve. The stator winding conductors are cooled by surrounding oil. A disadvantage with such a large amount of oil in the system is that there is a risk of leakage and a considerable amount of cleaning work which may result from a failure condition. Those parts of the insulating sleeve which are located outside the grooves have a cylindrical part and a conical termination, the operation of which is to control the strength of the electric field in the region where the wire leaves the laminated core. From CCCP 955369 it is clear, in another attempt to increase the nominal voltage of the synchronous machine, that the oil-cooled stator winding comprises a conventional high voltage cable with the same dimension for all layers. The cable is placed in stator slots formed as radially located, circular openings, which correspond to the cross-sectional area of the cable and to the space required for fixing and for refrigerant. The radially located layers different from the windings are surrounded by and fixed in isolated tubes. The insulating separators fix the tubes in the stator slot. Due to the oil cooling, a dielectric ring is also needed here to seal the oil coolant against the internal air spaces. The structure shown has no reduction of insulation or stator slots. The structure comprises a very thin radial belt between the different stator slots, which means a large flux of slot leakage which significantly affects the magnetization requirements of the machine. The machine designs according to the pieces of literature that is considered means that the electromagnetic material in the stator is not used to the optimum. The stator teeth should be attached as closely to the cover of the sides of the coil as possible from a magnetic point of view. It is highly desirable to have a stator tooth having, at each radial level, a maximum width since the width of the tooth considerably affects the losses of the machine, and consequently, the need for magnetization. This is particularly important for machines with higher voltage since the number of conductors per slots becomes large in them.

OBJECTIVE OF THE INVENTION The main objective of the present invention is to determine ways to design the device and the method in order to obtain better protection for the object and, consequently, a reduced load therein, a fact which means that the object itself The same must not be designed to withstand a maximum of short circuit currents / fault currents during correlatively 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 rotating electrical machines, the design of which is based on conventional design principles, which may mean that the design has no the same resistance to overcurrents related to failure, internal as well as external, compared to conventional machines of today.

BRIEF DESCRIPTION OF THE INVENTION According to the invention, the objective indicated in the above is obtained in which the line between the object and the switching device is connected to an overcurrent reduction assembly, which is - actuable for overcurrent reduction with the help of an assembly for detecting overcurrent conditions within a substantially shorter period of time compared to the re-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 of not only supporting for purposes of interruption on a switching device which finally establishes a galvanic separation, but instead, use an overcurrent reducing device that operates quickly which, without effecting any actual interruption of the overcurrent, it nevertheless reduces it to such an extent that the object under protection will be subjected to substantially reduced stresses and, consequently, a lesser amount of damage. As a result, the overcurrent / reduced fault current means, compared to a switching device that establishes galvanic separation, the total energy injection in the protected object has been much lower than in the absence of the overcurrent reduction assembly. Further. There will be an additional reduction of the fault current flowing to (or from) the object by means of the current limiter. In addition, 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 will be greatly reduced without the current limiter carrying out any total interruption of the overcurrent / fault current. . According to a preferred embodiment of the invention, the overcurrent reducing assembly is designed to comprise an overcurrent diverter for diverting overcurrents to ground or to another unit in some other way that has 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 rotating electrical machines having magnetic circuits designed by means of cable technology. Under certain conditions, these machines become sensitive to electrical faults. Such a design can be provided, for example, for a lower impedance than is currently considered normal within the field of energy. This means a lower resistance against overcurrents related to failure compared to that presented by conventional machines currently. In addition, if the machines have been designed from the start to operate with a higher electrical voltage compared to today's conventional machines, the voltage on the electric insulation system of the machine, caused by the resulting higher electric field, becomes, of course, higher. This means that the machine can be more efficient, more economical, mechanically lighter, more reliable, less expensive to use and generally more economical compared to conventional machines, and the machine can operate without the usual connection to other electromagnetic machines, but such a machine establishes great demands with respect to electric protection to eliminate, or at least reduce the consequences of, an interruption in the machine in question. A combination of the protection device according to the invention and a rotating electrical machine designed in this way therefore means an optimization of the plant as a whole. The electrical machine designed primarily with the invention operates with a high total voltage so that the aforementioned connected? / Y riser transformer can be omitted, i.e. machines with a considerably higher voltage compared to the machines according to the state The technique is intended to, in order to be able to make direct connection to power grid of all types of high voltage. This means considerably lower investment costs for systems with a rotary electric machine and the overall efficiency of the system can be increased. A rotary electric machine according to the invention involves a considerably reduced thermal stress in the stator. Temporary overloads of the machine become less critical and it will be possible to drive a machine to overload for a longer period of time without risking damage. This means considerable advantages for the owners of power generation plants, who are currently obliged, in case of operational alterations, to quickly switch to other equipment in order to ensure the supply requirements established by law. With an electric-rotary machine of such design contemplated herein, maintenance costs can be significantly reduced because the transformer should not be included in the system to connect the machine to the power grid. The invention also includes a synchronous compensator connected directly to the power network. To increase the power of a rotary electric machine, it is known to try to increase the current in the AC coils. This has been obtained by optimizing the amount of conductive material, that is, by narrow packing of rectangular conductors in the rectangular rotor slots. The objective has been to manage the increase in temperature that results from this by increasing the amount of insulating material and using insulating materials that are more resistant to temperature and therefore more expensive. The high temperatures and the field load in the insulation have also caused problems with the duration of the insulation. In relatively thick wall insulating layers which are used for high voltage equipment, for example, layers impregnated with mica tape, partial discharges, pd, constitute a serious problem. When these insulating layers are manufactured, cavities, pores and the like will easily arise, in which internal corona discharges arise when the insulation is subjected to high-voltage electric field voltages. These corona discharges gradually degrade the material and can lead to electrical insulation failure through the insulation. In order to be able to increase the power of a rotary electric machine in a technically and economically justifiable way, this must be obtained by ensuring that the insulation does not fail by the phenomenon described above. This can be obtained by means of an insulation system produced in such a way that the irrigation of cavities and pores is minimal. The insulation system on which at least one conductor carrying current included in the winding in question comprises an electrically insulating layer of a solid insulating material, around which an outer layer of a semiconductor material is placed. An inner layer of semiconductor material is placed inwardly of the insulating layer, at least one conductor is placed inwardly of the inner layer. In order to obtain a good thermal resistance, it is preferred that at least one of the inner and outer layers have coefficients of thermal expansion substantially equal to the insulating material. In practice, the layers and the insulating material, both, have substantially equal thermal expansion coefficients. This in combination with the fact that the inner and outer layers are joined in relation to the insulating material along substantially all of the interface means where the insulating material as well as the inner and outer layers will form a monolithic part so that the Defects due to a different expansion temperature are not present. The electric charge on the insulation increases as a consequence of the fact that the semiconductor layers around the insulating material will form equipotential surfaces means that the electric field in the insulating material will be evenly distributed over it. The outer semiconductor layer is properly connected to the ground potential or in some other way at a low potential. This means that for such a cable, the outer layer around the insulating material can be kept in potential to ground all along the cable. The outer semiconductive layer can also be cut off at suitable positions along the length of the conductor and each trimmed partial length can be directly connected to ground potential. Other layers, coatings and the like may also be placed around the outer semiconducting layer, such as a metal shield and a protective blanket. A further improvement of the invention is obtained by manufacturing the coils and slots, in which the coils are placed, rounded instead of rectangular. When making the cross section of the rounded coils, these will be surrounded by a constant magnetic field without concentrations where magnetic separations can arise. In addition, the electric field of the coil will be evenly distributed over the cross section and the local loads of the insulation are considerably reduced. Furthermore, it is easier to place circular coils in slots in such a way that the number of coil sides per coil group can be increased and an increase in voltage can take place without having to increase the current in the conductors. Additional improvements can be obtained by composing the conductor of smaller parts, the so-called strands. The strands can be isolated from each other and only a small number of strands can be left uninsulated and in contact with the inner semiconductor layer to ensure that it is at the same potential as the conductor. The outer semiconductive layer can have such electrical properties so as to ensure a potential equalization along the conductor. However, the outer layer may not exhibit such conduction properties so that a current will be transported along the surface, which may result in losses, which in turn can cause an undesired thermal load. The inner semiconductor layer must have sufficient electrical conductivity to ensure equalization of potential and, consequently, equalization of the electric field outside the layer, but this requires, on the one hand, that the resistivity may not be too small. It is preferred that the resistivity for the inner and outer layers be in the range of 10"6 Ocm - 100 k Ocm, suitably 10 ~ 3 - 1000 Ocm, preferably 1-500 Ocm. The use of a cable of a Flexible type to form the winding means means that the winding work can be carried out by means of a screwing operation wherein the wire is screwed into the openings of the grooves in the magnetic cores, since the outer semiconductor layer is connected to the ground potential or in some other way at some relatively low potential, 'will essentially operate to enclose the electric field into the layer. The use of an insulation system comprises a solid insulation surrounded by inner and outer semiconducting layers to enclose the electric field in the insulation means a substantial improvement compared to the prior art and completely eliminates the need to resort to liquid insulation materials or gaseous In order to overcome the problems that arise with the direct connection of rotary electrical machines of all kinds to high voltage power grids, a machine according to the invention has numerous characteristics, which differs substantially compared to the prior art with respect to the classic machine technology and machine technology which has been published in recent years: - as mentioned, the winding is made of a cable having one or more solidly insulated conductors with a conductive layer around the isolation. Some typical conductors of this class are the XLPE cable (cross-linked polyethylene) or a cable with an EP rubber insulation (EP = ethylene-propylene); however, the cable must develop further in regard to the conductor strands and in regard to the semiconductor layers - the cables are preferably used with a circular cross-section. However, in order to obtain a better packing density, cable with another cross section can be used - the use of such a cable allows the magnetic core to be designed in a new and optimum manner according to the invention both with respect to the slots as well as the teeth - the winding is carried out with a trapped insulation for the best possible use of the magnetic core - the design of the slots is adapted to the cross section of the winding cable in such a way that the slots are formed as a quantity of axially and radially outwardly extending to each other in the cylindrical openings with an open waist running between the layers of the stator winding - the design of the slots is adjusted to the cable cross-section in the view - the design of the slots is adapted to the insulation trapped in the slots - the development with respect to the strands means that the winding conductor consists of numerous combined layers each other, that is, not necessarily appropriately transposed with respect to one another, from the strands, which include both uninsulated and isolated strands - the development with respect to the outer coating means that the outer coating is trimmed at suitable positions throughout of the length of the conductor and each partial trimming length is directly connected to ground potential the winding is preferably carried out as a multi-layer concentric cable winding to decrease the number of end-wound crossings.

These characteristics involve numerous advantages in relation to the machines according to the prior art: - the trapped insulation means that an almost constant tooth width can be used independently of the radial propagation the use of such a cable means that the outer semiconductive layer of the winding it can be held in potential to ground along the entire length of it - an important advantage is that the electric field is almost zero in the coil end region outside the outer semiconductor layer and that the electric field should not be controlled when the layer is in potential to ground. This means that one can not obtain any field concentration, either in the core, in the coil end regions or in the transition between them - the mixture of isolated and non-isolated combined strands and transposed strands alternately involves additional costs low.

To summarize, a rotary electric machine according to the invention means a considerable number of important advantages in relation to the corresponding machines of the prior art. First of all, the machine can be connected directly to a power network in all types of high voltage. Another important advantage is that the ground potential has been conducted consistently throughout the entire winding, which means that the coil end region can be manufactured compact and that the support means in the coil end region can be made apply to virtually the potential of land. Another important additional advantage is that oil-based insulation and cooling systems disappear. This means that no sealing problems can occur and that the aforementioned dielectric ring is not needed. An advantage is also that all the driven coolant can be manufactured with ground potential. A considerable saving of space and weight is obtained from the point of view of the installation with the rotary electric machine according to the invention, since it replaces a previous insulation design both with the machine and with a step-up transformer. The additional advantages and features of the invention, particularly with respect to the method according to the invention, appear from the following description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS With reference to the accompanying drawings, a more specific description of an exemplary embodiment of the invention follows. In the drawings: Figure 1 is a purely 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 failure developments of current and energy development with and without the protection device according to the invention; Figure 3 is a diagrammatic view illustrating the conceivable design of a device according to the invention; Figures 4-9 are views that partially correspond to Figure 3 of different alternative embodiments of the invention with respect to the current limiter indicated with the number 6; Figure 10 is a diagrammatic view illustrating a possible design of the overcurrent reducing arrangement; 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 illustrates parts contained in a cable designed to form the winding for a magnetic circuit of a rotary electric machine of a class suitable to be protected by the protection device according to the invention; and Figure 13 illustrates in an axial end view an embodiment of a sector / pole step of a magnetic circuit in an electric rotary machine, for which the protection device according to the invention is particularly suitable.

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 generator. This object is connected, by means of a line 2, to an external distribution network 3. Instead of such a network, the unit indicated with the 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 1 itself which is primarily designed to be protected against power failure from the network / equipment 3 when a fault occurs, in object 1 a fault occurs of current from the network / equipment 3 to object 1, so that the current fault flows through the object. Such failure may consist of a short circuit that has been produced 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 even a total insulation failure of object 1.

As already indicated with at least some types of protected electrical objects 1, short circuit currents / fault currents dangerous for the object in question can 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 faults of externally emanating currents flowing through the object but also from internal fault current of objects flowing in the opposite direction. This will be discussed in more detail in the following. In the following, designation 3 will always be mentioned, to simplify the description, consisting of an external energy network. However, it must be borne in mind that some other equipment may be involved instead of such a network, to the extent that such equipment causes violent current flows through the object 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 flowing on line 2. Such circumstances may be currents / voltages, but also others that indicate that a fault is approaching. For example, the sensor can be an arc sensor or a sensor that records 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 / total fault current. . Therefore, the circuit breaker must be designed to meet the established high requirements, which in practice means that it will operate relatively slowly. In figure 2a it is illustrated in a current / time diagram that when a fault occurs, for example a short circuit in object 1 at the time fai-a the fault current in the line indicated by number 2 in the figure 1 quickly assumes the magnitude ix. This fault current i is decomposed by means of the circuit breaker 4 in tL, which is at least 150 ms after tfalla. Figure 2b 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 the short circuit current which is represented, therefore, 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 the extreme value. Only the polarity in the diagram has been indicated for simplicity. The circuit breaker 4 is of such a design that it establishes a galvanic separation by separation of metallic contacts. In consecuense, the circuit breaker 4 comprises, as a rule, auxiliary equipment necessary to extinguish an arc. According to the invention, the line between the object 1 and the circuit breaker 4 is connected to an assembly that reduces overcurrents towards the apparatus 1 and which is indicated generally with the number 5. The assembly is operable for overcurrent reduction with the help of overcurrent conditions that detect the arrangement within a period of time substantially less than the break time of the circuit breaker 4. This assembly 5, therefore, is designed so that no galvanic separation should be established. Therefore, conditions are created to very quickly establish a current reduction without having to carry out any total elimination of the current flowing from the network 3 to the protected object 1. Figure 2b illustrates in contrast the case, according to Figure 2a wherein the overcurrent reducing assembly 5 according to the invention is activated upon the presentation of a short circuit current in the flat time, for reduction on current at the level i2 at time t2. The time interval tfalla-t2 represents, consequently, the reaction time of the overcurrent reducing assembly 5. The task of assembly 5 is not to interrupt but only to reduce the fault current, it can cause the assembly to react extremely quickly, which will be discussed more closely in the following. As an example, it can be mentioned that the current reduction from level i: to level i2 is intended to be carried out within a few more minutes after unacceptable overcurrent conditions have been detected. Thus, the objective is to carry out a reduction in the current in a shorter time of 1 ms, and preferably more rapidly than 1 microsecond. As is evident from Figure 1, the device comprises a current limiter indicated generally with the number 6, and placed on 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 be operated for current limitation both rapidly and even more rapidly than the overcurrent reduction assembly 5. According to a further alternative involving less voltage in the current limiter 6, the current limiter may be designed to be activated for current limitation not until the overcurrent from the network 3 to the object 1 has been reduced by means of the assembly 5 overcurrent reducer, but of course the current limiter 6 can be put into activity for current limitation substantially earlier compared to the time at which the circuit breaker performs the interruption 4. From what has been It is obvious that it is appropriate for the current limiter 6 to be coupled to line 2 in such a way that the current is reduced by means of an overcurrent reducing assembly which, even to a lesser degree, will flow through the limiter ß of current. Figure 2b illustrates the action of current limiter 6. In such figure it has been chosen to indicate that the current limiter 6 starts operating for current limitation at time t3, which in the example would mean that the duration of the current i2 is reduced by means of the overcurrent reduction assembly 5 and has substantially limited, specifically to the time extension t2-t3. Again, it is emphasized that the representations in the figure should be considered as only diagrammatic. The time t3, when the current limiter 6 is activated, can be much sooner and even sooner than the time for activation of the overcurrent reduction assembly 5 at the time t2. From Fig. 2b it is evident that a fault current after a time t3 is reduced to the level i3. This current i. of remaining fault is finally interrupted by means of a circuit breaker 4 at a time tx. Nevertheless, the fault current i3 is so comparatively small as a consequence of an adequate dimensioning of the current limiter 6, that the fault current in question can persist for the object in question and also other parts of the power plant. The consequence of the reduction and limitation respectively of the fault current, which occurs by the injection of energy from the network 3 caused by the fault current 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 should be noted 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. It is illustrated in Figure 2c that the fault current will tend to flow through device 5. Part i3 of current i, of total failure will continue to flow through current limiter 6 after time t3 which is also marked on the Figure 2c. Actually, the sizing 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 so that the voltage is restricted by means of a current limiter 6 to levels substantially inferiors A realistic activation time with respect to the current limiter 6 is 1 ms, and the dimensioning is possibly carried out to be carried out in such a way that the current limiter 6 is caused to delimit the current not only after that the assembly 5 has reduced the flow of current through the limiter 6 to at least a substantial degree. As indicated in the above, this is not a requirement, but the opposite case 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) as in alternating current connections. In a multiple phase assembly with alternating current, the line indicated by number 2 can be considered as consisting of 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 the case of a detected error or that only those phases in the that a fault current is obtained are subjected to current limitation. It is evident from Figure 3 that the overcurrent reducing assembly generally indicated by the number 5 comprises an overcurrent diverter 7 for diverting the overcurrents to ground 8 or to a different unit in some way that has a lower potential than the network 3. thus the overcurrent diverter can be considered to form a current divider which quickly establishes a short circuit to ground or in some way to some other low potential 8 for the purpose of diverting at least a substantial part of the flowing current in the line, so that the current does not reach the object 1 to be protected. If there is a fault in the object 1, for example a short circuit, which is of the same magnitude as the short circuit that is able to establish the overcurrent deviator 7, it can be said that speaking generally, a reduction of the half of the current flow to object 1 from network 3 as a consequence of overcurrent diverter 7 in case the fault is close to the latter. In comparison with Figure 2b, it appears, therefore, that the current level i illustrated therein and indicated by the amount of approximately half ii 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 having better conductivity compared to one corresponding to the short circuit fault in the object 1 that is to be protected so that consequently, a Main part of the ground fault current or in some other way to a lower potential by means of the overcurrent diverter 7. It is evident from this that, consequently, in a case of normal failure, the energy injection in object 1 in the case of a fault becomes substantially smaller than that indicated in figure 2b as a consequence of the lower current level 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 commutator member 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 that can be put into a conductive active state in a very short time in order to establish current reduction by deviation to ground. Figure 3 also illustrates that the overcurrent condition detecting device may comprise at least one and preferably several tensors 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 provide an additional sensor 12 for detecting the current flowing in the line 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 12, 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 do not necessarily have to be constructed by only sensors that detect current and / or voltage. Within the scope of the invention, the sensors can be of a nature such that, generally speaking, they can detect any conditions indicative of the presence of a nature fault that requires the start of a protection function. In cases where such failure 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 the additional circuit breaker 6 to be closed, in case it has been opened and, in addition, the overcurrent reduction assembly 5 is activated so that the short-circuit current can be diverted therefrom. When, for example, object 1 is conceived to consist of a transformer, the function on 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, the which is detected and results in activation of the assembly 5 for the purpose of current deviation. When the current flowing to the transformer 1 has been reduced to a desired degree, the current limiter 6 is caused to reduce the current but, controlled by means of the control unit 14, possibly not before the exit time for the energy , in cases where it is present, 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. This is connects 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 unacceptable fault current to the object 1, the overcurrent reducing assembly 5 is immediately controlled to Quickly provide the necessary current reduction The control unit 14 can be positioned so that when the sensor has detected that the current or voltage 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 but until the current has actually been reduced to a radius such that the current limiter 6 is not given the task of interrupting such high current in a manner that is not adequately sized for that purpose. However, the mode alternatively may also be capable of the current limiter 6 being controlled to limit the current at a certain predetermined time after the overcurrent reducing 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 a control unit 14 based on information from the same sensors 11-13 which also control the operation of the Overcurrent reducing assembly. In the embodiment illustrated in Figure 3, the current limiter 6 is formed by an inductance 27 that is provided in line 2. Such inductance is obtained by means of a coil and has the result that there is some increase in current , a return electromotive force arises which counteracts the current increase. An advantage with this mode is that it is extremely simple and also gives rise to a rapid limitation, when a failure occurs, of the current flow to object 1 without the need for active control. As the device that has been described up to now, it operates in the following manner: in the absence of a fault, the circuit breaker closes while the switch means 10 of the overcurrent reducing assembly 5 is opened, that is, in a - 4O - state non-conducting. In this situation, the switch means 10, of course, must have a suitable electrical resistance so that it is not unintentionally put in the conductive state. The overvoltage conditions that appear in line 2 as a consequence of atmospheric circumstances (rays) or coupling measures, in this way can not cause the voltage resistance of the closing means 10 to be exceeded in its non-conductive state. For this purpose, it is suitable to couple at least one parallel overvoltage dissipator 22 on the commutator means 10. In the example, such surge suppressors are illustrated on both sides of the switch means 10. Accordingly, the surge suppressors are intended to deflect the overvoltages which would otherwise put at risk of causing an inadvertent insulation failure in the switch means 10. When an overcurrent state has been recorded by any of the sensors 11-13 or the sensor itself of the circuit breaker 4 (of course it is understood that the information from the sensor itself of the circuit breaker 4 can be used as a basis for the control of the assembly. overcurrent reducer, according to the invention), and this overcurrent state is of such a magnitude that it can be expected that a severe fault of object 1 occurs, the interruption function is initiated with respect to the circuit breaker 4. In addition, the control unit 14 controls the overcurrent reducing assembly 5 to carry out such a reduction, and this is further brought t by causing the switch means 10 to be in the electrically conductive state via the control member 9. As described in the e, this can be carried out very quickly, that is, in a fraction of time necessary for the interruption of the circuit breaker 4, which is why the object to be protected is immediately released from the current of complete short circuit of network 3 by means 10 switch that diverts at least a significant part and, in practice, the main part of the current to earth or otherwise to a lower potential. The current limiter 6 can also enter the fast function to limit the current flowing within line 2 to (or possibly from) object 1. When these incidents have occurred, the fault 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 closed the switching means 10, it is readjusted to a non-conductive state, and the current limiter 6 is ready, so that the next once the circuit breaker 4 is closed, and the protective device is in a 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 mode of the current limiter ßa. This embodiment comprises an inductance 28 and a capacitor 29, which forms, in unison, a resonance circuit, which provides a very high impedance at resonance. 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 condenser 29 are placed in series with each 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 given by the inductance and the resistance of the inductor. In the case of a fault current of a sufficient magnitude, the control unit 14 will control the switch means 10 to close for the purpose of deviation from the overcurrent and further, the control unit 14 will control the switch 30 for closing the same. so that the capacitor 29 is coupled in, and a resonance circuit is formed in parallel, which must be adjusted in the energy frequency. The impedance of the current limiter 6a will be very high at resonance. As is also evident from the comparative study of Fig. 2b, a considerable downward current reduction towards the extracted current level i3 is obtained. In Figure 5 an alternative mode of the current limiter ßb is shown, this mode is based on a series resonance circuit 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 operating 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 the series resonance (for example at 50 Hz) has a very small impedance. Transient fault currents are blocked by coil 32. In the 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 drastic increase in the total impedance, which is why the current is limited. As indicated in FIG. 5, the inductance 32 can be made variable, for example, by short circuiting parts of the winding or a winding located in the same core. In this way, it becomes possible to continuously adjust the current limiter ßb to minimize the voltage drop over the current limiter during normal charging. Another modification 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, an autoactivated function is obtained, that is, 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 is a capacitor 37 and a resistor 38, the capacitor and the resistor are coupled in parallel one in relation 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 communication within the limiting resistor 38. The control unit 14 is positioned to control the switch 36 by means of an operation member 40. Figure 7 illustrates a current limiter ßd 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 forms short circuits in the rugged arc chamber. When the arch moves towards 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 improved resistance is obtained. As in the above, the control unit 14 is mounted 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. This limiter comprises, in the embodiment, a fast semiconductor switch 44 and a parallel current limiting impedance 45 and a voltage limiting element 46, for example and varistor. The semiconductor switch 44 can be formed by means of gate inactivation thyristors (GTO thyristors). A resistor is used as a current limiting impedance. Varistor 4ß limits overvoltage when 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 it is communicated to the resistor 45. Finally, a limiter ßf of current is illustrated in figure 9, this limiter comprises a coil 48 connected to the line 2. The coil 48 is included in a reactor having a core 49 of steel. Between the steel core 49 of the reactor and the coil 48 a tubular superconductive mesh 50 is provided. Under normal operation, the superconducting screen 50 removes the sol from the iron core of the coil, the inductance therefore being relatively new. When the current exceeds a certain level, the superconduction stops and the increases in inductance increase 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, with respect to the current limiter ßf, that a small inductance occurs in normal operation. One disadvantage is that in order to obtain superconducting, cooling at low and low temperatures is required, for example by liquid nitrogen. In all the embodiments of Figures 4-9 which have just been described, only the differences with respect to the current limiters in relation to the design according to Figure 3 have been more clearly 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 switching medium like in Figure 3, the embodiment according to Figure 10 is designed to cause a medium present in a space 24 between the electrodes 23 to assume an electrical conductivity by means of a control member 9a. This control member is positioned to control the operation of the members 25 to cause or at least initiate the medium or part thereof in the space 24 to the conductive state. Member 25 in this example is positioned to cause the medium in space 24 to assume electrical conductivity by causing or at least helping to cause the ionize / plasma medium. It is preferred that the members 25 comprise at least one laser, which can be an energy supply for the medium in the space 24 and provide the ionization. As shown in Figure 10, a mirror 2ß can be used for necessary deviation of the laser beam assembly. In this regard it is emphasized that the embodiment according to Figure 10 can be such that the medium 25 not only gives rise to ionization / plasma in the entire electrode space. Therefore, the intention may be that the electric field imposed on the space may contribute to the formation of ionization / plasma, only part of the medium in the space is ionized by means of the members 25 so that later in the electric field in the space leads to the establishment of plasma in the entire space. In this regard it is emphasized that there may be in the electrode space not only a medium consisting of various gases or mixtures of gases, but also of vacuum. In the case of vacuum, laser initiation occurs in at least one of the electrodes, which, consequently, will function as a transmitter of electrons and ions for the establishment of an ionized environment / a plasma in space of electrode. Figure 11 illustrates a conventional embodiment in the sense in which a generator lb is coupled via a transformer to a power network 3a. The objects to be protected are represented, as a consequence, by the transformer la and the generator lb. The overcurrent reducing assembly 5a and the current limiter ßg and the common circuit breaker 4a are placed, as can be seen, in a manner similar to that shown in figure 1 for the case in which object 1 shown therein is the object according to FIG. 11 is conceived to form the object. Accordingly, reference is made in this regard to the descriptions given with respect to FIG. 1. The same is due for the protection function of the overcurrent reducer assembly 5c and the limiter ßi of current with respect to the generator Ib. In this case, consequently, the generator Ib can be considered equivalent with the object 1 in figure 1, while the transformer can be considered equivalent to the equipment 3 in figure 1. Therefore, the assembly 5c overcurrent reducer and the current limiter ßi will be able, in combination with the conventional circuit breaker 4b, to protect the generator lb against the violent flow of current in a direction away from the transformer la.

As an additional aspect of Figure 11, the additional overcurrent reducing assembly 5b is presented with the associated current limiter 6h. As can be seen, there will be overcurrent reducing mounts 5a and 5b on both sides of the transformer la. In this way it is emphasized that the current limiters ßg and ßi respectively are placed in the connections between the overcurrent reducing assemblies 5a and 5b and the transformer la. The additional overcurrent reducer assembly 5b is designed to protect the transformer from the current flows to the transformer from the lb generator. As can be seen, the circuit breaker 4b will be able to interrupt independently of the direction, between the objects la and lb the protection function that is desired. With the help of Figures 12 and 13, we will now describe a modality which is "unconventional" in contrast to one in Figure 11 in the sense that a rotary electric machine with a magnetic circuit or high voltage is designed to be directly connectable to a high voltage 3a power network without any intermediate upstream transformer. An important condition for being able to manufacture an unconventional magnetic circuit is to use for the winding a conductive cable with a solid electrical insulation with a semiconductor layer in both the conductor and the cover. Such cables are available as standard cables - So for other fields of energy engineering use. As mentioned above, an additional developed embodiment of such a standard cable is used as a stator winding. To be able to describe a modality, a brief description of a standard cable will be made initially. A conductor carrying internal current comprises numerous non-insulated strands. Around the strands is an inner semiconducting coating. Around this semiconducting inner coating is an insulating layer of solid insulation. An example of such solid insulation is cross-linked polyethylene (XLPE), alternatively ethylene-propylene rubber (EP). This insulating layer is surrounded by an outer semiconducting layer which in turn is surrounded by a metal shield and a blanket. Such a cable will be referred to in the following as an energy cable. In Figure 12 a preferred embodiment of the further developed cable is shown. The cable 51 is described in the figure consisting of a conductor 52 carrying current which comprises transposed strands not isolated and isolated. Electromechanically transposed strands, solidly isolated, are also possible. Around the conductor there is an inner semiconducting layer or coating 53 which, in turn, is surrounded by a layer 54 of a solid insulation material. The cable used as a winding in the preferred embodiment does not have a metallic shield and an outer jacket. To avoid induced currents and losses associated therewith in the outer semiconductor layer, it is reported, preferably at the coil end, that is, in the transitions from the stack of sheets to the end windings. Then each clipped part is connected to ground, whereby the outer semiconductor layer 55 or min. Of a ground potential over the entire length of the cable will be maintained. This means that, around the solid insulated winding at the coil ends, the contactable surfaces and the surfaces which are dirty after a certain time of use, only have negligible potentials for earth and also cause negligible electric fields. To optimize a rotating electric machine, the design of the magnetic circuit with respect to the grooves and the teeth, respectively, is of decisive importance. As mentioned in the above, the slots must be connected as closely as possible to the cover of the sides of the coil. It is also desirable that the teeth at each radial level be as wide as possible. This is important to minimize losses, the magnetization requirements, etc., of the machine. With access to a conductor for the winding such as for example the cable described above, there are great possibilities of being able to optimize the laminated magnetic core from several points of view. In the following, reference is made to a magnetic circuit in the stator of a rotary electric machine. Figure 13 shows an embodiment of an axial end view of a sector / pole step 52 of a machine according to the invention. The rotor with the rotor pole is designated with the number 57. In a conventional manner, the stator is constituted by a laminated core of electric sheets composed successively of sheets formed by sectors. From a rear core portion 58 located at the radially outermost end, many teeth 59 extend inward towards the rotor. Between the teeth are the corresponding number of slots 60. The use of cables 51 in accordance with the above, among other things, allows the depth of the slots for high voltage machines to be made larger in comparison with what was possible of according to the state of the art. The grooves have a cross section which is reduced towards the rotor since the need for cable insulation becomes smaller for each winding layer towards the rotor. As is clear from the figure, the groove consists substantially of a circular cross section 62 around each layer of the winding with the narrower waist portions ß3 between the layers. With some justification, such a cross section of slots can be referred to as a "cycle chain slot". Since relatively large number of layers will be required in such a high-voltage machine and the availability of current cable dimensions with respect to insulation and outdoor semiconductors is restrictive, and in practice it can be difficult to obtain a desirable continuous reduction of insulation of cable and the stator slot, respectively. In the embodiment shown in FIG. 13, cables with three different dimensions of the cable insulation are used, arranged in three sections 54, 65 and 66 correspondingly dimensioned, that is, in practice a modified cycle chain slot will be obtained. The figure also shows that the teeth of the stator can be shaped with a practically constant radial width along the depth of the entire groove. In an alternative embodiment, the cable that is used as a winding can be a conventional power cable as described above. The ground connection of the outer semiconducting shield then takes place by stretching the metal shield and the cable jacket in suitable positions. In the scope of the invention, it accommodates a large number of alternative modalities, which depend on the available cable dimensions with regard to the insulation and the outer semiconductive layer, etc., of what is referred to as the cycle chain slot. As mentioned before, the magnetic circuit can be located in the stator and / or the rotor of the rotary electric machine. However, the design of the magnetic circuit will largely correspond to the above description, regardless of whether the magnetic circuit is located in the stator and / or the rotor. As a winding, a winding is preferably used which can be described as a multi-layer concentric cable winding. Such winding means that the number of crosses in has been minimized. The coil ends when placing all the coils within the same group radially outward from each other. This also allows a simpler method for manufacturing and winding the stator winding of the different slots. It should be noted that the description presented herein should be considered only as an example of the inventive idea, on which the invention is made. Thus, it is obvious to those 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 10.

Claims (55)

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 from 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 reducing assembly, which is operable for overcurrent reduction with the help of an overcurrent condition detector assembly within a a period of time substantially shorter than the interruption time of the switching device, and wherein the current limiter is placed between the connection of the overcurrent reducing assembly to the line and the object.

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 another unit that in some other way has a potential smaller than that of 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 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 ß, characterized in that the means for causing or at least initiating the electrode space to assume electrical conductivity is placed to cause the space or a part of it 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 that the electrode space or a part thereof assumes electrical conductivity comprises at least one laser.

9. The device according to any preceding claim, characterized in that the current limiter comprises at least one inductance and / or a resistance or other impedance.

10. The device according to any preceding claim, characterized in that the current limiter comprises an inductance and a capacitor, which in unison form a resonance circuit that provides a high impedance at resonance.

11. The device in accordance with the claim 10, characterized in that the inductance and the capacitor are coupled in parallel with each other.

12. The device in accordance with the claim 11, characterized in that a switch and the capacitor are coupled in parallel on the inductance provided in the line.

13. The device according to claim 11, characterized in that the inductance and the capacitor are coupled in series with each other.

14. The device in accordance with the claim 13, characterized in that an assembly is connected that short-circuits the capacitor, in parallel on the capacitor.

15. The device according to claim 14, characterized in that the assembly that short-circuits the capacitor is formed of a switch.

16. The device in accordance with the claim 14, characterized in that the assembly that short-circuits the capacitor is formed by a spark gap.

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 parallel to the switch and each other.

18. The device according to claim 9, characterized in that the current limiter comprises a switch placed on the line and a commutator assembly comprising at least one resistive arc chamber.

19. The device according to 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 is coupled in parallel on the impedance.

20. The device according to claim 9, characterized in that the current limiter comprises a coil coupled in line, the coil is included in a reactor with an iron core where a superconducting tubular shield is provided between the iron core of the reactor and the coil, the superconducting shield shields the coil's iron core under normal operation, and thus the inductance is relatively low, whereas when the current exceeds a certain level, the superconduction ceases and the inductance increases drastically.

21. The device according to any preceding claim, characterized in that the current limiter is arranged to be activated for current limitation when overcurrent conditions have been detected.

22. The device according to claim 21, characterized by a control unit and placed to activate the current limiter based on the information of the overcurrent conditions detection assembly.

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

24. The device according to any preceding claim, characterized in that the current limiter is adapted to be activated for current limiting after reduction of the overcurrent to or away from the object by means of an overcurrent reducing assembly but substantially long before the device switch.

25. The device according to claims 22 to 24, characterized in that the control unit is adapted to provide activation of the current limiter when it is indicated that the overcurrent to or away from the object is below a predetermined level by the detection assembly.

26. The device according to any preceding claim, characterized in that two overcurrent reducing assemblies are placed 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 detecting assembly, the control unit is arranged to control the overcurrent reducing assembly so that it is closed with the Information help from the detector assembly of overcurrent conditions when justified for protection reasons.

28. The device according to claims 22, 23, 25 or 27, characterized in that one and the same control unit is adapted to control the overcurrent reducing assembly and the current limiter based on the information from the sensor condition monitoring assembly. overcurrent

29. The device according to any preceding claim, characterized in that the protected object is formed by a rotating electric machine with magnetic circuit.

30. The device in accordance with the claim 29, characterized in that the rotary electric machine is formed by a generator, motor or synchronous compensator.

31. The device in accordance with the claim 30, characterized in that the generator is a hydrogenerator or turbogenerator.

32. The device according to any of claims 29 to 31, characterized in that the magnetic circuit of the rotary electric machine is designed for high voltage.

33. The device according to any of claims 29 to 32, characterized in that the magnetic circuit includes a winding comprising at least one conductor carrying current around which is placed an electrically insulating layer of a solid insulation material, an outer layer of a semiconductor material is provided around the insulating layer, wherein the inner layer of the semiconductor material is placed inwardly of the insulating layer and at least one conductor is placed inwardly of the inner layer.

34. The device according to claim 33, characterized in that at least one of the inner and outer layers has a coefficient of thermal expansion substantially the same as the insulating material.

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

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

37. The device according to any of claims 29 to 36, characterized in that the magnetic circuit of the rotary electric machine comprises a winding formed by means of a cable.

38. The device according to any of claims 29 to 37, characterized in that the rotary electric machine is connected directly to the electric power network which is designed for high voltages, preferably 36 kV and more.

39. The device according to any of claims 29 to 38, characterized in that the magnetic circuit comprises one or more cores having grooves for the winding.

40. The device according to claim 33, characterized in that the winding further comprises a metal shield and a blanket.

41. The device according to any of claims 29 to 40, characterized in that the magnetic circuit is placed in the stator and / or rotor of the rotary electric machine.

42. The device according to any of claims 33 to 36, characterized in that the outer semiconductor layer is connected to a potential to ground.

43. The device according to any of claims 33 to 42, characterized in that the outer semiconductor layer is cut into many parts, each of which is connected to ground potential.

44. The device according to any of claims 33 or 43, characterized in that, with the connection of the outer semiconductor layer to ground potential, the electric field of the machine outside the semiconductor layer both in. * The slots and in the region The end of the coil is close to zero.

45. The device according to any of claims 33 to 44, characterized in that when the cable comprises several conductors, these are transposed.

46. The device according to any of claims 33 to 45, characterized in that the conductor / conductors carrying current comprise both uninsulated and isolated wires, placed in strands in numerous layers.

47. The device according to any of claims 33 to 46, characterized in that the conductor / conductors carrying current comprise both uninsulated and isolated strands, transposed into numerous layers.

48. The device according to claim 39, characterized in that grooves are formed with numerous cylindrical openings separated by a narrower waist portion between the cylindrical openings.

49. The device according to claim 48, characterized in that the cross section of the cylindrical openings of the grooves, counting from a rear portion of the core, are designed to decrease continuously.

50. The device according to claim 48, characterized in that the cross section of the cylindrical openings of the grooves, counting from the rear portion of the laminated core, are designed to discontinuously decrease.

51. The use of a device according to any preceding claim, characterized in that it is used for protection of a rotary electric machine having a magnetic circuit against overcurrents related to faults.

52. A method in a power plant for protection of an object connected to a power grid or other equipment included in the power plant, of overcurrents related to failure, a switching device is placed 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 overcurrent reduction when overcurrent conditions have been detected by means of an assembly for such detection, within a period of time substantially less than the interruption time of the switching device.

53. The method according to claim 52, characterized in that the overcurrents are diverted to ground or to another unit in some other way that has a potential smaller than that of the network / equipment by means of the overcurrent reduction assembly.

54. The method according to claim 52 or 53, characterized in that the current limiter, which is placed in the line between the switching device and the object and between the overcurrent reducing assembly and the object, is operated for interruption after overcurrent. towards or away from the object that has been reduced by means of the overcurrent reduction assembly.

55. The method according to any of claims 52 to 54, characterized in that the overcurrent reducing assembly is used to protect an object in the form of a rotary electric machine having a magnetic circuit, in particular a generator, motor or synchronous compensator.