NL2002216C2 - POWER LIMITER. - Google Patents

Description

P84871NL00

Title: Current limiter

The invention relates to a current limiter.

Current limiters are known in various variants. For example, the old US 3,671,810 (from 1962) describes a limiter based on the principle of a saturated magnetic core, which core can be brought out of the saturated state in the event of a short-circuit in a current collector.

Many variants of this principle have already been developed, such as superconducting variants that would offer various advantages over non-superconducting systems, see for example WO2007 / 029224.

The present invention contemplates an improved current limiter. In particular, the invention contemplates a limiter capable of limiting relatively high nominal currents, for example a current generated by a medium-voltage electricity generator, in a particularly efficient (almost loss-free) manner. A further object of the invention is to provide a relatively durable limiter which requires little maintenance and which can preferably be manufactured with relatively inexpensive means.

According to an aspect of the invention, the limiter for this purpose is characterized by the features of claim 1.

The limiter is adapted to limit three-phase alternating current, with a nominal current strength of 100 A or more, and is provided with at least 20: a first, second and third current conductor for conducting the three-phase alternating current; -a magnetic core of saturable, magnetically permeable material; A saturation unit to keep the core in a magnetically saturated state during normal use; wherein each current conductor is provided with a first flux generator to generate a respective first magnetic flux in the core, and a second flux generator to generate a second magnetic flux opposite to the respective first flux.

The current limiter according to the invention can limit particularly large nominal currents (with a current strength of at least 100 A, and preferably at least 200 A, in particular at least 400 A). That is, the limiter leaves the current substantially untouched as long as it remains within the nominal range, and limits the current as soon as the current rises significantly from the nominal range (e.g. due to a short circuit downstream of the limiter). Moreover, it appears that the present limiter consumes surprisingly little power, in particular to keep the magnetic core in the saturated state. In particular, it has been found that relatively high core masses benefit the desired efficient operation of the current limiter.

Thus, a further elaboration provides a core with a mass of more than 15 tons, in particular more than 10 tons. According to an advantageous embodiment, the said flux generators comprise coils, preferably with aluminum current conductors. In particular, the relatively heavy core can lead to a relatively low current density in the flux generators and the saturation unit, which can considerably reduce losses.

Extra advantage is an embodiment in which the coils of the first flux generators are wound in mutually the same direction, while the coils of the second flux generators are also wound in mutually the same direction.

The present limiter is durable and relatively simple, in particular by not using superconductors. The use of low-temperature coolants, with all its disadvantages, can therefore be omitted.

The saturation unit is preferably adapted to consume a maximum of 5 kW, in particular a maximum of 2 kW and more in particular a maximum of 1.5 kW, in order to keep the core in the magnetically saturated state during the normal (ie non-limiting) ) position of use. In this way, the current limiter uses very little energy to control the three-phase current.

Furthermore, it appears that surprisingly good results can be obtained when the core is large. With a particularly efficient current limiter for high nominal currents, two orthogonal dimensions of the core (for example a length and width) are each greater than approximately 1 meter, in particular even larger than approximately 2 meters. Furthermore, it appears to be advantageous if the core has a thickness of at least 40 cm, in particular at least 0.5 m. In a cross-section, the core can locally measure, for example, at least 0.4 mx 0.4 m, in in particular at least 0.5 mx 0.5 m.

The invention further provides an electricity transport system, provided with at least one electricity generator, for instance a wind-driven generator, which generator is adapted to generate three-phase alternating current, and at least one current limiter to limit the alternating current, for instance when a short circuit occurs in a downstream part of the conveyor system, wherein the current limiter is a limiter according to the invention.

The present current limiter can for example be advantageously used to control electricity supplied by windmill generators, but can also be used in combination with other types of generators. The limiter can for instance be arranged close to the generator, and can serve to protect the generator against problems (for example short-circuiting) elsewhere in the network. In view of the reliability and durability, the limiter in such a case is, for example, very advantageous in combination with a (usually remote) windmill generator.

According to a preferred embodiment, the current limiter 30 is used to limit three-phase alternating current at a relatively high nominal voltage 4 of more than 1 kV, in particular in the range of 5-36 kV. The limiter can protect such a current in a particularly reliable manner.

The current limiter can be manufactured in various ways. The invention offers a particularly advantageous method for manufacturing an additional advantageous embodiment of the current limiter. The method comprises at least: - providing an E-shaped transformer core part; arranging drums on outer legs of the E-shaped transformer core part 10, which drums are or are provided with the flux generators to generate respective first magnetic fluxes in the core; and arranging a core closure member to close the E-shaped transformer core member.

In this way a particularly solid limiter can be obtained which is considerably less complex and less expensive than known superconducting systems. Moreover, the limiter can thus be manufactured from relatively few parts. Said drums are preferably made from aluminum, and can for instance be accurately provided with the flux generators before (or after) the drums are slid onto respective legs of the core. The drums are preferably arranged not to allow loops in respective drum material; for this purpose the drums can for instance be provided with a break or an electrically insulating seam, for instance if the drums are made of aluminum. Furthermore, it is preferred that parts of said saturation unit, in particular coil parts, are also provided on the drums.

Said saturation unit (to keep the core in a magnetically saturated state) can be applied at various moments, on a suitable core part or drum part, for example before or just after the application of said closing part. Further advantageous elaborations of the invention are described in the subclaims. The invention will now be elucidated on the basis of an exemplary embodiment and the drawing. In the drawing: Figure 1 schematically shows a front view of an exemplary embodiment of the invention;

Figure 2 is a side view of the exemplary embodiment;

Figure 3 shows a top view of a part of the exemplary embodiment; Figure 4 shows schematically an electricity transport system provided with an exemplary embodiment of the invention; and

Figure 5 shows a part of a method for manufacturing the exemplary embodiment.

Equal or corresponding measures are designated in this application with the same or corresponding reference characters.

Figures 1-3 show a non-limitative exemplary embodiment of a current limiter K, which is adapted to limit three-phase alternating current, with a nominal current strength of 100 A or more, and preferably at least 400 A. Figure 5 shows a part of the limiter K, in an exploded position, in a method of assembling the limiter.

As follows, the current limiter K has a relatively simple construction, whereby the limiter can provide a particularly reliable operation, in an energy-efficient manner, without the use of superconductivity.

In particular, the limiter K is adapted to limit the three-phase alternating current at a medium voltage, at least at a nominal voltage of more than 1 kV, in particular more than 5 kV. The effective range of the present limiter K is, for example, in the range of 5-36 kV rated voltage.

6

Alternatively, the current limiter K can be used to protect three-phase current at higher voltages.

Therefore, the current limiter K can be used, for example, in an upstream part of an electricity transport system, for example to protect a medium voltage generator against short-circuiting (for example, short-circuiting of one of the phases R, S, T to ground).

Figure 4 shows an example of a system that contains the current limiter K. As Figure 4 shows, the limiter K 10 may, for example, form part of an electricity transport system provided with at least one electricity generator W, for example a wind-driven generator. The generator W is arranged to generate three-phase alternating current. The current limiter K can limit the alternating current, for example when a short circuit occurs in a downstream part D of the transport system. The limiter K can, for example, advantageously be arranged near the generator W, or be integrated therewith, however, this is not necessary. As shown in FIG. 4, for example, electricity transport means 130, usually at least provided with power cables, and furthermore, for example, with distribution stations and the like, not shown, are provided for connecting the various components W, K, D to each other.

The limiter K is provided with a first, second and third current conductor 31, 32, 33 for conducting the three-phase alternating current. The limiter K further comprises a magnetic core 5 of (magnetically) saturable, magnetically permeable material. A saturation unit 8 is provided to keep the magnetic core 5 in a magnetically saturated state during a normal use position (in particular, if said nominal current is below a certain threshold value). In addition, each current conductor 31, 32, 33 is provided with a first flux generator 1, 2, 3 to generate a respective first magnetic flux in the core 7, and a second flux generator 11, 12, 13 to generate a first flux generator 11, 12, 13 to generate flux opposite second magnetic flux in the core 5.

In particular, a first phase of said alternating current (usually indicated by R) is conducted via the first conductor 31, a second phase (usually indicated by S) via the second conductor 32 and a third phase (usually indicated by T) via the third conductor 33.

Each of the current conductors 31, 32, 33 can be designed in different ways. Each conductor 31, 32, 33 is preferably provided with a power cable, or a series of power cables or conductor parts connected to each other. The current conductors 31, 32, 33 are connected to said electricity transport means 130 during use, or form part thereof, to conduct the current to be limited. Connection between the conductors 31, 32, 33 and electricity transport means 130 can be achieved in various ways, for example using plugging means and the like.

As Figure 1 shows, each phase conductor 31, 32, 33 of the limiter K mentioned per se can, for example, be subdivided into different successive sub-conductor parts. Conductor members 31, 32, 33 are associated with the first flux generators 1, 2, 3.

Conductor members 31 ", 32", 33 "are associated with the second flux generators 11, 12, 13. Furthermore, intermediate conductor parts 31 ", 32", 33 "are provided to suitably couple the first flux generators 1, 2, 3 and second flux generators 11, 12, 13 to each other. The intermediate conductor parts 31 ", 32", 33 "can be designed in different ways, and can for instance be kept at a suitable distance from other parts of the limiter K (and from each other) by suitable spacers (not shown). In the example, each of the intermediate conductor parts 31 ", 32", 33 "is provided with earth jacket branching sleeves 45.

8

The flux generators are preferably provided with insulating material in order to make the current limiter K safe to touch. Preferably, each of said phase conductor parts consists of a suitable power cable, for example a coaxial cable, provided with a current-conducting core and an insulating sheath surrounding the core. Extra advantageous is an embodiment in which each cable further comprises at least one earthing jacket (of electrically conductive material) and a second insulating protective layer surrounding the earthing jacket.

Good results are achieved if the current-conducting cable core is made of metal and has a cross-section of more than 150 mm 2, wherein a cross-section of the cable including sheath is, for example, larger than approximately 500 mm 2.

Said cable core can for instance be manufactured from copper, however, for cost reasons and for mass reduction, the use of an aluminum cable core is preferred. In that case the cross-section of the core can be more than 500 mm 2, for example approximately 630 mm 2. A particularly advantageous embodiment for this purpose comprises the use of triple extruded cables with an aluminum core. Each cable 31, 32, 33 is preferably provided with a said conductive (aluminum) core, provided with a first insulating jacket, around which a grounding screen is arranged. An insulating top layer is provided around said grounding screen. The earthing screen can for instance be separated from the first insulating jacket by an additional intermediate layer, for instance an (electrically conductive) swelling tape. The earthing screen of each cable 31, 32, 33 may per se comprise, for example, two aluminum windings wound in the opposite direction, or may be designed in a different way. An outer layer (or layers) of the cable 31, 32, 33 provided on the earthing screen can for instance comprise one or more layers of mica, or be configured in another way.

9

Said grounding jackets of the conductors of the flux generators 1, 2, 3,11,12,13 are preferably coupled to ground E. In the example, the cables are provided with branch sleeves 45, in which branches of the earthing jackets are arranged, to connect said jackets (via suitable conductors 45) to earth. In the example, these sleeves 45 are arranged between the cable parts 31, 32, 33 of the first flux generators 1, 2, 3 and the cable parts 31 ", 32", 33 "of the second flux generators 11, 12, 13, i.e. on the intermediate cable sections 3Γ, 32 ', 33'. Preferably, the ground branch sleeves are arranged at the center of the respective intermediate cable parts 31 ", 32", 33 ".

As follows further from the drawing, the branches of the earthing sheaths of the cables 31, 32, 33 can for instance be coupled to the limiter magnet core 5, wherein said core 5 itself is grounded (by coupling to ground E). Alternatively, cable grounding jackets 15 may bite the core 5 to be coupled to ground.

The limiter magnet core

The present limiter magnet core 5 is a closed core, adapted to provide a self-closed loop of magnetically saturable core material. The core 5 is relatively bulky and heavy-duty. Preferably, the core 5 per se already has a mass of more than 5 tons, in particular more than 10 tons. According to an advantageous elaboration, the core 5 consists essentially of a suitable magnetic core material, preferably laminated steel (preferably also provided with silicon), in particular transformer can. In the example, two orthogonal dimensions X, Y of the core 5 (see Fig. 5) are each greater than approximately 1 meter, in particular larger than approximately 2 meters. The core 5 preferably has a thickness Z (see Fig. 3) of at least 0.3 m, preferably at least 0.4 m, in particular at least 0.5 m. Preferably the core 5 is on earth E coupled (to ground the core).

The core can be configured in various ways. In the example, the core 5 is mirror-symmetrical, and provided with a first leg 51 and a second leg 52. In addition, the core 5 comprises two longitudinal legs 53, 54 which connect ends of the first and second leg. The four legs 51-54 enclose an opening H. In the example, the first and second leg 51, 52 are parallel, with the (mutually parallel) longitudinal legs extending perpendicularly therebetween. Each of said legs 51-54 has in the example a substantially square cross-section. The legs 51-54 can also be shaped differently, for example with a polygonal, rectangular, octagonal, oval, round or otherwise shaped cross-section. Each of the legs 51-54 is made from said core material, for example from a laminate of transformer sheet (in particular comprising superimposed layers of magnetic core material with a layer thickness of less than 1 mm, for example approximately 0.3 mm.

A transverse width B of each of the legs 51-54 (see Fig. 5) is, for example, larger or equal to approximately 0.3 m, preferably 0.4 m. Said width B can, for example, be approximately the same (e.g. with a margin of approximately +/- 10%) to the core thickness Z.

The longitudinal legs 53, 54 are preferably adapted to provide a short-circuit path when the core 5 is brought from a said saturated state. For this purpose, the second longitudinal 54 may, for example, be provided with a central central leg 55 which extends perpendicular to said leg 54 and extends to the opposite first longitudinal 53.

Between an end face of the middle leg 55 and the first along 53 there is an air gap Q (which is part of said opening H surrounded by the core). The central leg 55 is, for example, parallel to the first and second leg 51, 52, and for example has approximately the same thickness as the longitudinal legs 53, 54 together. Said end face of the central leg 55 may, for example, extend parallel to an opposite inner side of a core leg 53.

In the example, a transverse width U of the central leg 55 is greater than said width B of the other core legs 51-54. In an advantageous embodiment, the central leg 55 has a width U of at least 0.5 m, in particular at least 0.8 m, and more in particular at least 1 m.

The space between said central leg 55 and a first and second leg 51, 52, respectively, is intended at least for placement of the flux generators 1, 2, 3.11, 12, 13 and, for example, also for placement of saturation coils 8a. A width L of a said spacing can for instance be larger than 0.2 m. According to a further elaboration, this width is in the range of approximately 20-80 cm.

The central leg 55 and the gap Q form a flux short-circuit, which flux short-circuit has a lower magnetic permeability than a permeability of the core legs 51-54.

As Figure 5 shows, the present core is provided with, for example, an E-shaped core part 51, 52, 54, 55 and a closing part 53 which connects two outer legs of the E-shaped core part. To this end, the middle leg 55, the respective one along 54 and both the first and second leg 51, 52 can be made in one piece. The other along 53 serves as a closure of the core.

In an alternative embodiment, each can be provided along with a central central leg, which central central legs reach towards each other to define a gap between them.

The flux generators 12

In the example, the flux generators comprise coils 1, 2, 3, 11, 12, 13, provided with wound power cables, each power cable being provided with an insulating jacket. Advantageous cable configurations, provided with an earthing screen, and different insulating layers / jackets, have been described above.

In particular, first cable parts 31, 32, 33 of said current conductors form part of the first flux generators 1, 2, 3 by being wound into respective coils. Second cable parts 31 ", 32", 33 "of the current conductors form part of the second flux generators 11, 12, 13 in the same way. Good results are obtained when said conductors 31, 32, 33 each comprise a current-conducting aluminum core, with a cross-section of more than 500 mm 2, and preferably at least 600 mm 2.

Each fluxop alarm clock 1, 2, 3, 11, 12, 13 is preferably provided with a relatively small number of (Nac) coil turns. Good results are obtained if each flux generator comprises no more than 100 turns, for example no more than 50 turns, and for example more than 10 turns,

A further elaboration is particularly advantageous in which the coils 20 of the first flux generators 1, 2, 3 are all wound in mutually the same direction (for example, to the left or to the right, relative to a coil axis). This provides the particularly great advantage when using the three-phase current, that with fully balanced currents (of the three phases) the magnetic fluxes 25 generated by the three first flux generators 1, 2, 3 can completely cancel each other out. Moreover, a relatively small imbalance between the three current phases (for example, a maximum of 10% of the stated nominal current) can be properly absorbed by the magnet limiter (without blocking current transmission).

13

The coils of the second ilix generators 11, 12, 13 are also all wound in the same direction (for example, to the left or to the right) to provide the same advantage.

The first flux generators 1, 2, 3 are adapted to generate respective first magnetic fluxes in the first core bone 51; the second flux generators 11, 12, 13 are arranged to generate respective second magnetic fluxes in the second core bone 52. To this end, the first core leg 51 is provided with all the said first flux generators, the second core leg 52 being provided with all the said second flux generators.

The configuration of the flux generators is here such that during normal use the flux generated in the core 5 by the first flux generator 1, associated with the first current phase (conductor 31), is opposite to a second flux which during use by the second flux generator 11 of the first current phase (conductor 31 ") in the core 5 is generated. The first and second flux generated under the influence of the first current phase (via generators 1, 11) can therefore substantially cancel each other out during normal use.

The configuration of the flux generators is furthermore such that during normal use the flux generated in the core 5 by the first flux generator 2, associated with the second flow phase (conductor 32), is opposite to a second flux which, during use, by the second flux generator 12 of the second current phase (conductor 32 ") in the core 5 is generated.

Furthermore, the configuration of the flux generators is such that a flux generated in the core 5 by the first flux generator 3 associated with the third flow phase (conductor 33) during normal use is opposite to a second flux which during use by the second flux generator 13 of the third current phase (conductor 33 ") in the core 5 is generated.

The saturation unit 14

The saturation unit 8 comprises a non-superconducting coil system 8a during use, in particular comprising one or more coils of electrically conductive windings, preferably with an aluminum core, for example wound coaxial cables.

Preferably, the cable of each saturation unit 8 is configured the same as the cables 31, 32, 33 of the flux generators, for example at least provided with an aluminum core, a first insulating jacket, an earthing screen, and an outer protective jacket.

In the example, the saturation unit 8 is provided with two coils 8a, which are arranged for example on the core 5, for example on a said longitudinal 54 (i.e., a part 54 of the core 5 is surrounded by each coil 8a). Furthermore, the unit is provided with a current source 8b for supplying the coils 8a with a direct current, for example a direct current 15 of more than 100 A, in particular more than 400 A, for example approximately 450 A. Alternatively, the coils 8a can for instance in addition to the coils of the flux generators are provided, for example on the drums 81, 82.

During normal use, the saturation unit 8 generates such a high magnetic flux in the core 5 (under the influence of said direct current) that the core 5 is in a magnetically saturated state such that the said flux generators 1, 2, 3,11, 12,13 experience no or hardly any impedance from the magnetic core. The core saturation effected by the saturation unit 8 is such that the saturation can be interrupted by a said flux generator if the current phase led via that generator exceeds, for example, a threshold value (for example, in the event of a short-circuit in the relevant current phase). In particular, the core saturation generated by saturation unit 8 is such that certain imbalances that may occur in the three-phase power network during normal use are taken into account. In other words: an imbalance mentioned does not yet lead to breaking the saturation during use.

The current limiter is preferably designed to limit the current as soon as the current phase led by a flux generator exceeds, for example, a threshold value which is 10% of said nominal current of the network. In this way the current limiter can also occur to counteract an undesirably large imbalance (of more than 10% nominal current), so that disadvantages of such an imbalance (for example stationary losses) can be prevented.

It is advantageous if the coils 8a of the saturation unit comprise relatively few turns. Good results are obtained, for example, when the total number of turns Ndc of the coils 8a of the saturation unit 8 is lower than 50, preferably lower than 20. A combined electrical resistance of the coils 8a is preferably lower than 20 πιΩ (milli-ohms) ), preferably less than 10 mils, e.g. about 7 πιΩ or less. Moreover, a cross-section of the coils 8a is relatively large (at least equal to a stated width B and / or thickness Z of the core leg 54), so that a relatively small number of direct current windings Ndc is already sufficient to achieve a suitable core saturation. Particularly good results can moreover be obtained when both the saturation unit (8) and the flux generators (1, 2, 3, 11, 12,13) comprise coils, wherein a ratio between the total number of turns Nac of the flux generators and the number of turns Ndc of the saturation unit is in the range of 1: 2-1: 4, for example about 1: 3.

25

Reel drums

It is particularly advantageous if the core 5 is provided with separate drums 81, 82, which drums comprise at least said flux generators 30. Each drum 81, 82 may, for example, be made of aluminum 16 or another non-magnetizable material. The example comprises two drums 81, 82 which are each provided with three said flux generators (i.e. respective conductor cable windings). Preferably, each drum 81, 82 is provided with optional partitions (see Fig. 5), to separate the turns of neighboring flux generators. The drums 81, 82 may, for example, each be provided with a central passage to closely receive a core leg 51, 52.

Said drums 81, 82 can for instance each be interrupted, for instance by being provided in the longitudinal direction with a slit or an electrically insulating seam. In this way, electrical currents can be prevented from circulating in the aluminum drums 81, 82 themselves.

For example, the flux generators can be accurately applied to the drums 81, 82 before the drums 81, 82 are applied to respective parts 51, 52 of the core 5. It is particularly advantageous here to provide extra cable length on the drums 81, 82, for example cable length for forming the intermediate cable parts 31 ', 32', 33 ', and possibly for supplying external connections to for example, provide network links. After mounting the drums 81, 82 on the core 5, the additional cable length 20 can, for example, be unwound from the drums 81, 82 to form the intermediate cable parts 31 ", 32", 33 "and the like.

Figure 5, for example, schematically shows a method in which a said E-shaped transformer core part is provided. The drums 81, 82 can be mounted on the outer legs 51, 52 (arrow P1).

Subsequently, the core-closing part 53 can be provided (arrow P2) to close the core 5. Said coils 8a of the saturation unit can be arranged at different moments, for example before or after the installation of the coil drums 81, 82. According to an advantageous alternative embodiment, each drum 81, 82 is or is provided with a saturation unit coil 8a, 8b.

17

As Fig. 5 also shows, end faces of the outer legs 51, 52 can, for example, engage on end faces of the closing leg 53, to position the closing leg 53 in a longitudinal direction of that part, during assembly of the closing part and the E-shaped part .

In the example, the abovementioned end edges are obliquely designed for this purpose; it will be clear that the sides of the legs 51, 52, 53 which are to be fitted on top of each other can also be formed differently in order to effect a desired positioning and / or engagement, for example with a finger joint configuration, conical engagement surfaces, integral hole-pin couplings and the like.

Use of the exemplary embodiment comprises keeping the core 5 in a magnetically saturated state by passing a high direct current through the coils 8a of the saturation unit. The three-phase alternating current is thereby passed through the respective conductors 31, 32, 33; the associated flux generators 1, 2, 3, 11, 12, 13 then experience little or no impedance from the magnetic core. Because the coils of the first flux generators 1, 2, 3 are wound in the same direction, the generated fluxes can substantially cancel each other out (as long as the three phases are balanced); the same applies to the second flux generators 11, 12, 13.

The limiter K can very rapidly, within a microsecond, limit the current through the conductors 31-33, for example when one of the phase currents, under the influence of a network error, such as short circuit (for example elsewhere in a respective transport network), exceeds a threshold value. Said threshold value can for instance comprise three times a said nominal current, preferably 2.5 times the nominal current, and more preferably twice the nominal current. The threshold value mentioned can for instance amount to more than 1000 A.

As soon as the threshold value of, for example, a phase current passed through a first conductor 31 is overwritten, the core 5 falls out of the magnetically saturated state (as a result of an increased flux counteracting the 18 saturation generated by one of the respective flux generators 1, 11 which conducting the short-circuit current), and magnetic flux is diverted via said flux short-circuit (the center 55 and the gap Q).

The disappearance of the saturated state leads directly to the limitation of the currents. In this way, the three-phase alternating current, with a high nominal current, is protected in a particularly reliable manner.

Moreover, the current current limiter K consumes surprisingly little energy. A further embodiment of the limiter K appears to require a maximum of 5 kW, in particular a maximum of 2 kW and more in particular a maximum of 1.5 kW, in order to keep the core 5 in a suitable magnetically saturated state during the normal use position (in order to protect a nominal three-phase alternating current of 400 A).

In particular, it appears that the three-phase currents of a medium or high voltage transport system are relatively well balanced, for example with respect to low-voltage networks (such as a 230 V network). An explanation for this can be that the impedance at high voltages is relatively low. An underlying idea behind the invention is that in such a case a relatively low saturation level of the core 5 is already sufficient for the limiter K to provide the desired protection. Use can herein be made of a relatively small direct current through the saturation coils 8a, for example a current in the range of approximately 400-500 A (for example approximately 450 A), with a limited number of turns in the coils 8a, which leads to a relatively low losses.

Example 19

A Saber computer simulation is performed to calculate the efficiency of a current limiter implementation. The following parameters were used for this: - core material = transformer can (silicon steel); 5-first orthogonal dimension X of the core = 206 cm; second orthogonal dimension Y of the core = 252 cm; - width B = thickness Z of core legs = 53 cm; width of intermediate leg U = 106 cm; gap width V = 90 cm; 10-gap-width L = 20 cm; - number of turns of flux generator coils Nac = 50; - number of turns of saturation coils Ndc = 15; -total mass of core = 16 tons; -cross section copper core current conductors = 180mm2; 15-total resistance flux generator inductors = 7 ηιΩ; -Nominal alternating current = 400 A; - nominal line voltage = 5.8 kV; and current strength DC flux generator coils = 450 A With this advantageous configuration, the limiter appears to deliver only a loss of approximately 0.18% of the nominal power per phase. Furthermore, it appears that in this case the saturation unit only needs 1.4 kW of power to keep said core in the appropriate saturated state, which is only 0.06% of the nominal power. The limiter therefore consumes surprisingly little energy per se, without the use of generally relatively expensive, superconducting magnets (which moreover require a lot of maintenance). The invention is thus particularly based on the idea of providing such a massive, heavy and bulky current limiter to protect three-phase alternating currents (with a high nominal current intensity), which appears to lead to a surprisingly economical limiter system.

20

It will be clear to the skilled person that the invention is not limited to the exemplary embodiments described. Various changes are possible within the scope of the invention as set forth in the following claims.

5

Claims (21)

A current limiter, wherein the limiter is adapted to limit three-phase alternating current, with a nominal current of 100 A or more, wherein the limiter is at least provided with: -a first, second and third current conductor (31, 32, 33 ) to conduct the three-phase alternating current; -a magnetic core (5) of saturable, magnetically permeable material; - a saturation unit (8) to keep the core (5) in a magnetically saturated state during a normal use position; wherein each current conductor (31, 32, 33) is provided with a first flux generator (1, 2, 3) to generate a respective first magnetic flux in the core, and a second flux generator (11, 12, 13) to to generate second magnetic flux opposite to the respective first flux. 2. Current limiter according to claim 1, wherein the core has a mass of more than 5 tons, in particular more than 10 tons. A current limiter according to claim 1 or 2, wherein said flux generators comprise coils, wherein the coils of the first flux generators (1, 2, 3) are all wound in mutually the same direction, the coils of the second flux generators (11, 12, 13 ) wound in the same direction. Current limiter according to one of the preceding claims, in which the core consists essentially of laminated steel. A current limiter according to any one of the preceding claims, wherein each saturation unit (8) comprises a non-superconducting coil 25 during use, in particular provided with an aluminum core. A current limiter according to any one of the preceding claims, wherein two orthogonal dimensions of the core (5) are each greater than approximately 1 meter, in particular larger than approximately 2 meters. Current limiter according to one of the preceding claims, wherein the core (5) has a thickness of at least 40 cm, in particular at least 0.5 m. 8. Current limiter according to one of the preceding claims, wherein said conductors (31, 32, 33) each comprise a current-conducting core with a cross-section of more than 150 mm 2, in particular at least 180 mm 2. A current limiter according to any one of the preceding claims, wherein the flux generators comprise wound power cables, wherein each power cable is provided with an insulating jacket. 10. Current limiter as claimed in any of the foregoing claims, wherein the core (5) is provided with at least one drum, which drum comprises at least two said flux generators, the drum preferably being made of aluminum. 11. Current limiter according to claim 10, provided with two drums, each of which is provided with three said flux generators. A current limiter according to any one of the preceding claims, wherein the core (5) is provided with at least a first leg (51) and a second leg (52), wherein at least two of the first flux generators (1, 2, 3) are arranged to generate respective fluxes in the first leg, wherein at least two of the second flux generators (11, 12, 13) are arranged to generate respective fluxes in the second leg. The current limiter of claim 12, wherein the first core leg is provided with all of said first flux generators, and wherein the second core leg is provided with all of said second flux generators. A current limiter according to any one of the preceding claims 12-13, wherein the core (5) comprises two longitudinal legs (53, 54) connecting ends of the first and second legs, the longitudinal legs (53, 54) preferably being arranged to provide a short circuit path when the core (5) is brought from a said saturated state. 15. A current limiter according to any one of the preceding claims, adapted to limit three-phase alternating current, with a nominal voltage of more than 1 kV, in particular more than 5 kV. 16. Current limiter as claimed in any of the foregoing claims, wherein the saturation unit (8) is adapted to consume a maximum of 5 kW, in particular a maximum of 2 kW and more in particular a maximum of 1.5 kW, around the core (5). maintain the magnetically saturated state during normal use. 17. Current limiter according to one of the preceding claims, wherein both the saturation unit (8) and the flux generators (1, 2, 3, 11, 12,13) comprise coils, wherein a ratio between the total number of turns Nac of the flux generators and the number of turns Ndc of the saturation unit is in the range of 1: 2-1: 4, for example approximately 1: 3. 18. Current limiter as claimed in any of the foregoing claims, wherein the core is provided with an E-shaped core part and a closing part which connects two outer legs of the E-shaped core part to each other, wherein a gap is present between the closing part and a central leg of the E-shaped core part. 19. Electricity transmission system, provided with at least one electricity generator, for example a wind-driven generator, which generator is adapted to generate three-phase alternating current, and at least one current limiter to limit the alternating current, for example when a short-circuit occurs in a downstream part of the transport system, wherein the current limiter is a limiter according to any one of the preceding claims. 20. A method for manufacturing a current limiter according to any one of claims 1-18, wherein the method comprises at least: - providing an E-shaped transformer core part; arranging drums on outer legs of the E-shaped transformer core part, which drums are or are provided with the flux generators (1, 2, 3,11,12,13) to generate respective first magnetic fluxes 5 in the core; and arranging a core closure member to close the E-shaped transformer core member. 21. Method as claimed in claim 20, wherein end faces of outer legs of the E-shaped transformer core part engage on end sides of the closing part to position the closing part relative to the E-shaped part in a longitudinal direction of that part, during assembly of the closing part and the E-shaped part.