CN1272215A - Magnetic tap changer - Google Patents

Abstract

An induction-controlled voltage regulator mainly used for high-voltage regulation, comprising a magnetic circuit based on a magnetic core (1) with one or more magnetic flux paths or legs (2), the paths or legs The legs are surrounded by high and low voltage windings (3, 15). The leg (2) is divided into at least two branches (2A, 2B), at least one of which (2B) is provided with adjustment means for a zone (5) of variable magnetic permeability. The magnetic permeability can be changed by moving a magnetic rod (4) into and out of a zone (5) forming an air gap. Another embodiment for such a modification involves the use of regulator windings acting on the flux passing through the leg branch (2B). A compensator winding can be arranged around the leg branch (2B) comprising the zone of variable permeability (5). The compensator winding is electrically connected in series with the capacitor arrangement. At least one of the windings is wound by a high voltage cable comprising a conductor surrounded by an inner semiconductor, an insulator layer and an outer semiconductor.

Description

magnetic tap changer

The present invention relates generally to inductively controlled voltage regulators, and more particularly to such an inductive regulation as defined in the preamble of claim 1 by means of an electrical transformer or reactor arrangement. The invention also relates to a regulator winding for use with such an inductively controlled voltage regulator as defined in claim 10, and to a voltage control as defined in claim 13 for use in electrical lines and for Method for reactive power control in power plant equipment.

Conventional induction-controlled voltage regulators for lower voltage ranges are arranged by using inductors with coils rotating or moving relative to each other, as for example by I.L.Ia Cour and K.Faye-Hansen in the book "Drehtransformator und Schubtransformator, Die Wechselstromtechnik Bd.2, Die Transformatoren", Verlag von Julius Springer, Berlin, Germany, 1936, pp. 586-598, as described in the literature. In addition, such an inductive control cannot be performed at reasonable cost for high voltages. Insulation construction is a severe design constraint.

Another technique is known from US-A-4 206 434, in which the flux between the different legs of an induction-controlled voltage regulator is described as being redistributed by variable DC magnetization. For this purpose, a variable DC source is required.

Thus, electrical high voltage control is mostly performed by an electrical transformer comprising one or more windings wound on one or more legs of a transformer core. The windings include taps that make it possible to supply different voltage levels from the transformer. Current power transformers and distribution transformers, as described above and used in voltage mains, include tap changers for voltage regulation. They are susceptible to mechanical wear and electrophysical corrosion due to electrical discharges between the contacts. Regulation can only be segmented. Thus, stepwise voltage regulation and movable contacts are required for connection to different taps.

The disadvantages of prior art voltage regulation are avoided by the inductively controlled voltage regulator according to the invention. The characteristic property to be found is that the flux path or the short length of the leg of the magnetic circuit surrounded by the high and low voltage windings is divided into at least two branches, at least one of which comprises an adjustment of a zone with a variable permeability device.

A preferred embodiment of the regulator of the present invention has the high voltage winding wound as far as possible to contain all of the core flux. The low voltage winding of the regulator is then divided into at least two winding sections, one of which comprises the majority of the turns and is wound within the high voltage winding. Other winding portions comprising smaller portions of turns are wound around at least one leg branch having a region of variable permeability. The number of turns in the leg branch depends on the required voltage regulation range.

The division of the necessary magnetic flux division between the different leg branches is obtained by varying the reluctance in the different leg branches, which is achieved by regions of variable magnetic permeability. Different embodiments are possible within the field of the invention. The presently preferred embodiment comprises either a magnetic rod movable in and out of the region forming an air gap, or a regulator winding wound on a separate magnetic core forming a lateral path. The regulator winding is supplied with a control voltage which affects the flux through the leg branch.

The higher reluctance at the air gap can be compensated by compensator windings surrounding the area of the region and electrically connected in series with a capacitor in a separate closed circuit.

Such a compensator winding incorporating a capacitor forms a negative reluctance R _c =-n ² ω ² C. The number of winding turns n and the capacitor capacitance C can be chosen in such a way as to correspond to a positive reluctance _RL = 1/Aμ ₀ where

l is the (effective) length of the air gap,

A is the cross-sectional area of the core, and

μ ₀ is the magnetic permeability of air.

Typical values for capacitance C are on the order of a few microfarads to millifarads for a voltage of 1 kV.

An important condition that makes possible the regulation of such a high voltage, i.e. 36 kV up to 800 kV, is that at least part of any of the above-mentioned windings is constructed from a high-voltage cable comprising a conductor, an inner semi-conductor, an insulator , and an outer semiconductor. Thus, the transformer/reactor is a so-called dry type. The use of such a designed high voltage cable makes it possible to "trap" the electric field inside the cable insulation. This means that it is possible to design inductively controlled voltage regulators for high voltage applications.

Another advantage is that the layers are arranged to adhere to each other even when the cable is bent. Thus, good contact is achieved between the layers throughout the life of the cable.

For those skilled in the art, various uses lie within the field. Thus, it is possible, for example, to use the invention for single-phase induction-controlled voltage regulators. It is also possible to implement on-load tap changer devices, i.e. single-phase induction-controlled voltage regulators integrated in the transformer. Furthermore, by means of individual phase control as well as by means of common phase control, a multi-phase inductively controlled voltage regulator can be made.

These and other features and advantages of the present invention will become more apparent from the following detailed description of exemplary embodiments thereof as illustrated in the accompanying drawings, in which:

Figure 1 is a cross-sectional view of a part of a transformer core according to the present invention,

2 is a side view of a shorter portion of a transformer core, partly in cross-section, in accordance with one embodiment of the invention,

Figure 3 is a side view similar to Figure 2 but showing another embodiment of the invention, and

Figure 4 is a cross-sectional view of a high voltage cable used in a regulating winding according to the invention.

The invention will now be described in detail with reference to some preferred embodiments, the principles of which are illustrated in the included drawings. Like reference numbers used in the various figures refer to similar or other devices having corresponding functions. 1 to 2 show only the parts of the voltage regulator that are important to the invention.

Figure 1 shows a view of a transformer core 1 with a core flux path or leg 2, half of which splits into two branches 2A and 2B. A high-voltage winding 3 surrounds the undivided half of the leg 2 in the outer position, within which a first part 15A of a low-voltage winding is wound around the leg 2 . The windings are shown in cross section. A first part 15A of the low voltage winding comprises the main part of the winding turns and is electrically connected in series with a second part 15B of the low voltage winding. A second part 15B with a smaller part of the winding turns surrounds one 2B of the leg branches.

The voltage regulation of the transformer is based on the principle of changing the flux Φ leakage in the transformer by controlling the reluctance in the different core leg branches 2A, 2B. For this purpose, one or both of the core leg branches may comprise regions 4 whose magnetic permeability is reduced and/or increased by a control device.

Figure 2 shows a preferred embodiment of the invention in which, upstream of the point where the leg divides into two branches 2A and 2B, one leg 2 of the transformer core 1 is formed by a high voltage winding 3 and a low voltage winding The (main) first part 15A surrounds. As in the embodiment shown in FIG. 1 , the second part 15B of the low voltage winding is wound around the leg branch 2B. The leg branch 2B includes an air gap 5 in which a magnetic rod 4 is arranged. The rod 4 can be moved out and into the air gap 5 indicated by the double arrow A. The movement of the magnetic rod 4 can be controlled manually by suitable mechanical means or by any electrical drive means. As a result of the movement of the magnetic rod 4, the magnetic flux in the low voltage winding second part 15B can vary between zero and full core branch flux. The number of winding turns in the low voltage winding second portion 15B will limit the regulation area.

As indicated by dashed lines in FIG. 2 , the other leg branch 2A may also comprise an air gap with a movable rod 4 . The use of such a movable rod 4 in both leg branches 2A, 2B gives a finer adjustment of the reluctance in the magnetic core 1 . Movement of the rods 4 can be performed in combination with each other and towards or away from each other. The initial position of the rod 4 in the air gap 5 can be different, for example the rod in the leg branch 2B completely fills the air gap (as shown in FIG. 2 ), while the rod in the leg branch 2A More or less in a position outside the corresponding air gap.

Another embodiment of the invention is shown in Figure 3, where the mechanical rod or air gap has been replaced by an external magnetic field. Such an external magnetic field can be obtained by means of a separate magnetic core 9 whose axis lies transversely to the axis of the leg branch 2B. The core 9 can be a premagnetized section or, preferably, a core surrounded by a regulator winding 6 . An external magnetic field generated by the regulator winding 6 and/or the separate magnetic core 9 more or less cancels the magnetic flux through the leg branch depending on the control voltage applied to the regulator winding 6 . The control voltage can be an AC voltage in phase with the high voltage to be regulated, or preferably a DC voltage. By this embodiment, the same induced control voltage of the transformer or reactor arrangement is obtained as by those shown in FIGS. 1 and 2 .

As shown in FIG. 2 , a compensator winding 7 is wound around the flux path or leg 2 of the transformer core 1 . The compensator winding 7 forms a closed circuit comprising a capacitor arrangement 8 .

In the embodiment shown in Fig. 3, the compensator circuit now described can also be implemented.

In order to make it possible to obtain regulation of high voltages, i.e. in fields of about 36 to 800 kV, by using a high voltage cable 61 of the type shown as an example in FIG. 4, winding windings 3, 6, 7, 15A and 15B at least one of, or a part of any of them.

The cables used in the present invention are flexible and of the kind described in more detail in WO 97/45919 and WO 97/45847. Additional descriptions of cables can be found in WO97/45918, WO97/45930 and WO97/45931.

Thus, the windings in the device according to the invention are preferably of the type corresponding to cables with solid, extruded insulation, of the type now used for power distribution, such as XLPE cables or cables with EPR insulation . Such a cable comprises an inner conductor consisting of one or more strands, an inner semiconducting layer surrounding the conductor, a solid insulating layer surrounding the layer, and an outer semiconducting layer surrounding the insulating layer . Such cables are bendable, which is an important property in this context, since the technology used for the device according to the invention is mainly based on winding systems in which the windings are formed by cables that flex during assembly. The flexibility of an XLPE cable generally corresponds to a bending radius of about 20 cm for a cable diameter of 30 mm, and about 65 cm for a cable diameter of 80 mm. In this application, the term "bendable" is used to denote a winding that is bendable for bend radii of the order of four cable diameters, preferably eight to twelve times the cable diameter.

A winding should be constructed to retain its properties even when it is bent and when it is subjected to thermal or mechanical stress during operation. What is important in this context is that the layers maintain their adhesion to each other. The material properties of the layers, especially their elasticity and relative thermal expansion coefficients, are decisive here. In XLPE cables, for example, the insulating layer comprises cross-linked, low-density polyethylene, while the semiconducting layers consist of polyethylene in which carbon black and metal particles are mixed. Changes in volume as a result of temperature fluctuations are completely absorbed as changes in cable radius, and radial expansion can occur without loss between the layers due to relatively slight differences in the thermal expansion coefficients in the layers with respect to the elasticity of the materials. of bonding.

The above material combinations should be considered as examples only. Other combinations of fulfilling the specified conditions, and also being a semiconductor, i.e. having a resistivity in the range of 10 ⁻¹ to 10 ⁶ ohm-cm, for example 1-500 ohm-cm, or 10-200 ohm-cm, naturally also fall within the scope of the present invention.

For example, the insulating layer may be composed of materials such as low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polybutylene (PB), polymethylpentene ("TPX") Solid thermoplastic materials such as cross-linked polyethylene (XLPE), or rubbers such as ethylene-propylene-diene rubber (EPR) or silicone rubber.

The inner and outer semiconducting layers may be of the same base material, but with particles of conductive material such as carbon black or metal powder mixed therein.

The mechanical properties of these materials, in particular their coefficient of thermal expansion, are less affected by whether carbon black or metal powder is mixed therein - at least in the proportions required to achieve the electrical conductivity necessary according to the invention. The insulating layer and the semiconducting layer thus have substantially the same coefficient of thermal expansion.

Ethylene vinyl acetate copolymer/nitrile rubber (EVA/NBR), butyl grafted polyethylene, ethylene butyl acrylate copolymer (EBA) and ethylene ethyl acrylate copolymer (EEA) can also constitute suitable polymers for semiconducting layers things.

Even when different types of materials are used as the basis in the layers, it is desirable that their coefficients of thermal expansion be substantially the same. This is the case with the material combinations listed above.

The materials listed above have relatively good elasticity, with an E modulus of E < 500 MPa, preferably < 200 MPa. The elasticity is sufficient for any small differences between the coefficients of thermal expansion of the materials in the layers to be absorbed in the radial direction of the elasticity so that no cracks, or other damage, occur and thus the layers do not separate from each other. The material in the layers is elastic and the bond between the layers is at least as great as the weakest of the materials.

The conductivity of the two semiconducting layers is sufficient to substantially equalize the potential along each layer. The conductivity of the outer semiconducting layer is high enough to contain the electric field within the cable and low enough not to cause significant losses due to currents induced in the longitudinal direction of the layer.

Thus, each of the two semiconducting layers substantially constitutes an equipotential surface, and these layers will substantially surround the electric field between them.

Of course, nothing prevents one or more auxiliary semiconductor layers from being arranged in the insulating layer.

Such a high voltage cable 61 may comprise one or more electrical conductors 631 . The cable embodiment shown in Figure 4 comprises an insulation and the conductor 631 is directly connected to the first layer 632 having semiconducting properties. The first layer 632 is in turn surrounded by a solid insulating layer 633 which is then surrounded by a second layer 634 having semiconducting properties.

In Figure 4, which shows details of the invention in relation to the cable, three layers 632, 633, 634 are arranged so as to adhere to each other even when the cable is bent. The cables shown are flexible and will maintain this performance throughout the life of the cable.

Layers 632, 633, 634 are preferably made of the same plastic material or other material with the same coefficient of expansion. An important advantage resulting from this is that defects, cracks etc. are avoided at the point of thermal movement in the winding. The plastic material of the first and second layers 632, 634 has conductive material added thereto.

Although the invention has been described above with reference to transformers or reactors shown in the figures as single-phase forms, it is obvious that it can also be applied to multi-phase transformers and similar devices, as used in autotransformers and in step-up transformers .

Claims (17)

1. induction controlled voltage regulator, particularly a kind of transformer or a kind of reactor device, comprise a magnetic circuit that comprises an iron core (1), (1) unshakable in one's determination has at least one by high and low pressure winding (3,15) circumjacent magnetic flux path or supporting leg (2), described adjuster is characterised in that: a short length of described at least one supporting leg (2) is divided at least two branch road (2A, 2B), wherein its at least one have the adjusting device (4 or 6) in a district (5) that comprises variable magnetic permeability, and at least one circle of all circles of high pressure winding (3) is twined by a high-tension cable (61), and cable (61) comprises a conductor (631), an interior semiconductor (632), an insulator (633), an and outer semiconductor (634).

2. adjuster according to claim 1, and its feature also is: described high pressure winding (3) is wound into farthest to comprise all magnetic fluxs unshakable in one's determination, and low pressure winding (15) is divided at least two winding parts (15A, 15B), one of them winding part (15A) comprises the major part of all circles, and be wrapped in the high pressure winding (3), comprise that another winding part (15B) of all circle smaller portions is twined around described at least one leg branch (2B) in the described district (5) with variable permeability.

3. according to claim 1 or the described adjuster of claim 2, and its feature also is: the described district (5) of variable permeability comprises a magnetic bar (4) but shift-in and shift out the district (5) that forms an air gap.

4. according to claim 1 or the described adjuster of claim 2, and its feature also is: the described district (5) of variable permeability comprises a regulator winding (6), regulator winding (6) is wound into for described at least one leg branch (2B) and forms on the separation magnetic core (9) of a transverse path, and confession is useful on the control voltage of the controlled change of the magnetic flux that passes described at least one leg branch (2B).

5. according to the described adjuster of each above claim, and its feature also is: a compensator winding (7) is around the area in the described district (5) with variable permeability, and connects with a capacitor device (8) and to be electrically connected.

6. according to the described adjuster of each above claim, and its feature also is: at least one of other winding (6,7,15A, 15B) also twined by a high-tension cable (61), and cable (61) comprises a conductor (631), an interior semiconductor (632), an insulator (633), an and outer semiconductor (634).

7. according to the described adjuster of each above claim, and its feature also is: described adjuster is a polyphase transformer, and described at least one leg branch (2B) of every phase comprises an adjusting device (4 or 6) that is used for the independent regulation of every phase.

8. according to each described adjuster of claim 1 to 6, and its feature also is: described adjuster is a polyphase transformer, and described at least one leg branch (2B) of every phase comprises one for having the adjusting device (4 or 6) that the contact adjusting connects.

9. according to each described adjuster of claim 1 to 6, and its feature also is: described adjuster is an autotransformer or a step-up transformer.

10. according to the described adjuster of each above claim, and its feature also is: described layer (632,633,634) is even be arranged to when the cable bending also bonded to one another.

11. one kind is used for according to each described induction controlled voltage regulator of above claim, the transformer or the reactor device that particularly comprise a high pressure winding (3) and low pressure winding (15A, 15B), regulator winding (6), it is characterized in that: any part of at least one of described winding (3,6,15A, 15B) or its is twined by a high-tension cable (61), and cable (61) comprises a conductor (631), an interior semiconductor (632), an insulator (633), an and outer semiconductor (634).

12. winding according to claim 11, its feature also is: described semiconductor (632,634) and described insulator (633) have substantially the same thermal coefficient of expansion.

13. according to claim 11 or 12 described windings, its feature also is: described semiconductor (632,634) is made by identical plastic material with described insulator (633), and the semiconductor plastic material has the electric conducting material of interpolation.

14. one kind is used in the voltage control of electric wire and/or is used for the method for the Reactive Power Control of electric power factory equipment, this electric power factory equipment comprises at least one transformer or reactor, this transformer or reactor make any part of at least one or its of its winding, according to each described high-tension cable type of above claim, wherein voltage control realizes in such a way by the flux leakage that the induction adjusting changes in the winding, thereby changes the magnetic resistance of the different leg branch of described transformer/reactor.

15. method according to claim 14 is characterized in that:, obtain described induction and regulate by a magnetic bar being shifted out or moves into the air gap at least one of described different leg branch.

16. method according to claim 14 is characterized in that:, obtain described induction and regulate by supplying to the variation of regulating the regulation voltage on the winding that supporting leg twines around one of described transformer/reactor.

17. method according to claim 16 is characterized in that:, obtain the variation of described regulation voltage by controlling a capacitor with may command electric capacity.

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