EP2259271A2 - High voltage rotary current system and shielded single wire rotary current cable for the system - Google Patents

Abstract

The arrangement has a metal shield (20) radially enclosing a single-conductor electrical cable and arranged above the cable. An uninterrupted tooth banding (22) made of high-permeable material encloses the metal shield. The metal shield comprises a contact unit at ends of the shield for contacting the shield. The metal shield is formed with enlarged electrical conductance value to reduce electrical leakage at the metal shield, so that shield current is induced. The shield current is same as conductor current of a cable conductor (12) during marginal case.

Description

The invention relates to a high-voltage three-phase current system and one-wire electric cable with integrated electromagnetic shielding for the high-voltage three-phase system.

To reduce the external magnetic field of three-phase cables at 50 or 60 Hz different shielding measures can be used. A summary of measures has recently been published by CIGRE (Paris, 2008): CIGRE TF C4.204; "Mitigation techniques of power-frequency magnetic fields originated from electric power systems", technical brochure. Depending on the requirement, such measures can be carried out with relatively little effort, such as the use of compensation conductors (eg P. Maioli, E. Zaccone, "Passive Loops Technique for Electromagnetic Field Mitigation, Applications and Theoretical Considerations" in Jicable-Conf. 2007, Versailles, pp. 231-236 ). In some cases, however, the effort can also be described as significant - as with the shielding of cables with a steel pipe or in a steel box ( WO 2004/034539 ; EP 1598911 A1 ) - and with adverse effects on additional losses and ampacity.

It has already been proposed to provide a flexible cable with a braided copper screen, wherein - for the purpose of magnetic shielding - particles of high permeability are pressed into the braid or the particles are glued to the braid ( DE 19807527 A1 ). The construction is especially designed for drag chain cables, since the flexibility of the line is in the foreground. A quantitative estimate of the shielding effect is not stated in the document. Furthermore, other magnetic shielding arrangements using films or ribbons of high permeability material are known. For example, a three-conductor cable is guided in a tube which is lined with said material ( WO03-003382 A1 ). Another design is to provide the leads of a three-conductor cable with a sheath of high permeability material directly ( DE 102006013553 B3 ). The said constructions have the disadvantage that either the transmission power of the cable is limited and / or high electrical additional losses are present.

It is in the case of very high demands on the magnetic shielding of a power cable system, the object of the invention to present a variant in which a highly effective electromagnetic shield is integrated into the construction, the loss contribution is greatly reduced, while maintaining effective magnetic shielding.

The solution of the problem can be found in the features of the independent claims. Advantageous developments are formulated in subclaims.

The construction according to the invention for reducing the electrical loss contribution in the metal shield of a single conductor cable is that instead of a cable shield with 'usual' cross section a much larger cross section, preferably selected from good electrically conductive material for the metal shield, thus the conductance of the cable shield compared to the otherwise in Cables usual values is increased, the metal sheds have at their ends contact means for contacting the metal shades with each other. With a metal screen, which has an increased electrical conductance compared to conventional cables, screen currents are inducible, which lie in the limit in the amount of cable conductor current. An upper limit provides at most the technical limit of the current carrying capacity of the cable.

The metal screen is arranged radially above the single conductor cable and has a corresponding electrical conductance or a corresponding conductor cross section, so that shield currents of the stated order of magnitude can be induced. Thus, instead of the electrical conductance mentioned as an inventive feature, the metal screen cross-section may also be considered. Conductance and conductor cross-section are proportional physical quantities. Equivalent are thus statements in which either increased screen cross-section or increased conductance of the metal screen is spoken.

The metal screen can also be designed in the form of a reinforcement. As a material for the metal shield are conductor metals such as copper or aluminum in question. The metal screen can be contacted - either inside or outside - with a formed as a film or tape winding metallic contact layer, preferably made of aluminum. The contact layer serves on the one hand as a cross-connector which balances the conductivity between the elements of the metal screen and on the other hand as a water vapor barrier.

Depending on the economic aspects or requirements of magnetic shielding regulations, one choice may be made at the upper limit or rather at the lower limit of said area of the metal screen. For example, by exchanging costly lead metals for low-cost metals (e.g., copper vs. aluminum), cross-sectional differences are 1.6 times, which is the difference in conductivities of the two metals. Using a material with high electrical conductivity would limit the mass of the metal screen.

As a supplement or particular embodiment of the invention, the following details are listed. These details may be implemented individually or collectively.

The electrical conductivity of the metal screen may be in the range 80% to 150% of the electrical conductivity of the cable ladder. The electrical conductivity of the metal screen can also be selected equal to the electrical conductivity of the cable ladder.

The metal screen may consist of metallic single wires or of a metal layer, wherein a layer structure is formed as a tube. The individual wires forming a metal screen may be applied with impact or consist of a mesh of the individual wires.

On the plastic insulation of each single conductor cable, the metal shield with increased conductance can be arranged as a reinforcement, or it can be arranged on a support tube, the metal shield, in each of which a single conductor cable is retracted with plastic insulation. A support tube construction could have approximately the following dimensions: Diameter of a tube made of plastic about 25 cm for pulling a cable core; Forming the metal screen made of aluminum either as a wire mesh or as a cylindrical layer on the pipe with a thickness that exceeds the conductor cross-section of the cable ladder (for example, 2500 mm ² aluminum) (cross section depending on the targeted loss contribution reduction 3000 to 4000 mm ² aluminum).

The principle of ferromagnetic shielding in the embodiment carrier tube here consists of a plastic tube for laying or drawing of three-phase cable cores with a conductive layer (also reinforcement) of large cross-section and with overlying magnetically permeable, preferably highly permeable material. Extremely high shielding factors can be achieved, which can be used to meet particularly stringent magnetic field restrictions.

The inventively constructed metal screen is wrapped with a high-permeability harness seamlessly. For the harness is preferably used: overlapping wound, thin bands of a special steel, which have a relative permeability of some 10,000. In addition to their high magnetic shielding effect, these bands are characterized by low eddy current and magnetic reversal losses. The harness should be protected against corrosion, so be covered with a corrosion protection layer.

Irrespective of the axis spacing of the cables, this type of cable allows extremely high shielding factors to be achieved, with which all conceivable conditions for limiting the magnetic field can be met. This makes the use of such cables in the case of extreme magnetic field restrictions (values around 0.2 μT) interesting and is superior to other solutions, such as shielding with steel pipes or steel channels, with very considerable advantages in terms of current carrying capacity.

In addition, the structures of the invention provide in areas where the guiding of the cables in a steel pipe is mandatory - such as when crossing under train facilities - a way to lay the individual cable core in a steel pipe, which without this construction due to the then extreme power heat losses is inadmissible.

Thus, the three-phase high-voltage three-phase system according to the invention consists of three single-conductor cables, preferably in a single-plane arrangement, with the three metal sheds (either the single-core cables or the support tubes) being short-circuited at both ends. By short-circuiting the three metal sheds at both ends, currents are induced in them which are (nearly) opposite to the respective conductor currents and whose size approaches the conductor current (asymptotically) with increasing cross-section or increasing conductance of the metal screen.

Fig. 1A und 1B:

Aufbau in einem Kabel oder in einem Verlegerohr,

Fig. 2:

Schirmverlustfaktor y₁ als Funktion des Querschnitts des Metallschirms aus Kupfer;

Fig. 3:

Abhängigkeit der drei Schirmströme vom Metallschirmquerschnitt aus Kupfer 'ohne' und 'mit' magnetischer Bebänderung;

Fig. 4:

ergänzend zu Fig. 3: Schirmverlustfaktoren in Abhängigkeit des Metallschirmquerschnitts;

Fig. 5:

horizontale Verteilung der magnetischen Induktion oberhalb Erdoberfläche;

Fig. 6:

maximale magnetische Induktion oberhalb der Erdoberfläche in Abhängigkeit vom Metall- schirmquerschnitt und

Fig. 7:

Strombelastbarkeit als Funktion des Achsabstands s der Kabel in Einebenen-Anordnung.

The invention is illustrated in drawings, the figures show in detail

FIGS. 1A and 1B:

Construction in a cable or in a laying pipe,

Fig. 2:

Screen loss factor y ₁ as a function of the cross section of the metal screen made of copper;

3:

Dependence of the three screen currents on the metal screen cross-section of copper 'without' and 'with' magnetic harness;

4:

in addition to Fig. 3 : Screen loss factors depending on the metal screen cross section;

Fig. 5:

horizontal distribution of magnetic induction above ground;

Fig. 6:

maximum magnetic induction above the earth's surface as a function of the metal screen cross-section and

Fig. 7:

Current carrying capacity as a function of the center distance s of the cables in a single-level arrangement.

The Figures 1A and 1B illustrate the structure of the invention: a cable conductor 12 is a plastic insulation 14 with inner and outer conductive layer. Instead of a normal screen (made of copper or aluminum) with cross sections between about 50 mm ² and 200 mm ² , a metal screen 20 with a much larger conductance, or cross-section (made of copper or aluminum) is used. In the cable construction of the metal shield 20 corresponds to the usual reinforcement or reinforcement.

The metal screen, which is preferably formed from wires, is contacted, either inside or outside, with a contact layer 18, preferably made of aluminum, in the form of a film or tape winding. The contact layer serves on the one hand as a water vapor barrier and on the other hand as a cross-connector which balances the conductivity between the elements of the metal screen. The metal screen 20 is wrapped with a high permeability harness 22. Such electrical bands as used in transformer and electrical engineering are made of low silicon silicon steel sheet and are made in a thickness of 0.02 to 0.04 mm. Outwardly, the construction becomes finished with a protective jacket 24, in particular with corrosion protection. The insulation of the cable ladder is preferably made of VPE, wherein an inner and an outer conductive layer - as usual - is present.

In Fig. 1B is a laying or support tube 15 is shown, in each of which a single conductor cable is drawn without metal shield. The reference numerals used correspond to the same parts as in FIG Fig. 1A , This embodiment is particularly suitable for shorter laying lines, where the support tube is laid in advance, and the cable is retracted later. The metal screen 20 and the harness 22 on the support tube 15 are therefore here at a small distance from the cable and not directly on the cable insulation.

The two features used for magnetic shielding according to the invention are thus a metal screen with a large conductor cross-section and a strapping applied from high-permeability material. With such a construction, regardless of the pitch of the cable cores, extremely high shielding factors can be achieved.

For the installation of a high-voltage three-phase system, three such single conductor cables are preferably laid in a horizontal single-level arrangement, with the ends of the metal sheds being connected to one another in each case.

For the influence of the conductance-increased metal screen, three three-phase single-conductor cables are considered in a horizontal one-plane arrangement. After making the short-circuit loop between the three metal sheds 20 (reinforcement), currents are induced in them which are (nearly) opposite to the respective conductor currents and whose size approaches the phase current with increasing screen cross-section. This results in a range of copper screen cross-sections up to about 500 mm ² to a dependence of the shielding losses (here: relative to screen loss factor y ₁ on the conductor losses), as shown in the Fig. 2 for a 110 kV XLPE cable with an aluminum conductor cross-section of 2500 mm ² . The starting point was a laying depth of 1.2 m and a horizontal center distance s of the cable wires of s = 0.5 m.

• bei einem Schirmquerschnitt A _S von etwa 100...200 mm² ein Maximum der Schirmverluste mit mehr als dem Sechsfachen der Leiterverluste auftritt und
• dass jenseits dieses Maximums bei weiterer Steigerung des Schirmquerschnitts (bzw. des Leitwerts) die Schirmverluste wieder abnehmen.

The Fig. 2 shows the screen loss factor y ₁ (middle cable core) as a function of the cross section A _{S of} the copper shields in a 110 kV single conductor cable with 2500 mm ² aluminum conductors and a horizontal wire spacing s = 0.5 m. With this figure it is clarified that in this laying arrangement

• at a screen cross section A _S of about 100 ... 200 mm ^2, a maximum of screen losses with more than six times the conductor losses occurs and
• that beyond this maximum, the screen losses decrease again as the screen cross section (or conductance) is further increased.

This behavior can be explained by the fact that initially - with small screen cross sections - with increasing cross section, the screen currents grow rapidly and approach the phase current. This is in the Fig. 3 with the three characteristics 'without' reproduced. The figure shows the dependence of the three screen currents on the cross section A _{S of} the copper screens 'without' and 'with' magnetic harness; in a horizontal single-level arrangement with wire spacing s = 0.5 m; the conductor current is I _c = 1108 A.

Out Fig. 3 It can also be seen that the three screen currents are different. In a screen cross-sectional area of 500... 1000 mm ² (Cu), the size of the conductor current is assumed to be approximately such that a further increase in cross-section no longer results in an increase in current, but only a corresponding decrease in shielding losses.

For a cross-sectional area of A _S > 400 mm ² are in Fig. 4 these screen loss factors y ₁ falling with increasing screen cross section A _{S are} reproduced. In the present example, shielding factors SF of less than 40% can be achieved with correspondingly large screen cross-sections of> 2500 mm ² . Shielding factor SF is the ratio of the magnetic induction (just above the surface of the earth) of the unshielded cable to the shielded cable.

The magnetic inductors that adjust for a symmetrical phase current of 1108 A are in the Fig. 5 horizontal distribution of the magnetic induction in 0.2 m above the earth surface 'without' and 'with' magnetic harness (x = 0 m is the coordinate of the middle cable core).

Of the Fig. 5 (a and b) shows the distribution of the magnetic induction given without shield currents: it reaches close (0.2 m) above the earth's surface and directly above the cables with approx. 120 μT noticeably above the statutory limit of 100 μT. Also, in Fig. 5 the distributions for screen cross-sections of A _S = 400 mm ² (a) and for A _S = 2500 mm ² (b) are given (note the axis labels differing by a factor of 30!).

In addition are in the Fig. 6 the maximum magnetic inductions occurring directly above the cables are compiled in 0.2 m above the earth's surface as a function of the screen cross-section A _S 'without' and 'with' magnetic banding.

To Fig. 5 and Fig. 6 the highest magnetic induction for a screen cross section of 400 mm ^{2 is} still more than 25 μT and of 2500 mm ² more than 4 μT. In view of the high constructive Effort and high additional losses, the shielding effect does not appear to be very satisfactory.

Used for the high-permeability harness, overlapping wound thin strips of special steel. Their relative permeability should be around 10,000. The effect of this applied above the copper screen bands are the FIGS. 3 to 6 refer to:

To Fig. 3 The highly permeable layer in the cables already forces shield currents at small screen cross-sections, which almost reach the size of the conductor current. With sufficiently large screen cross-sections of> 400 mm ² , where this is also the case with the cables without harness, will be after Fig. 4 the losses of the cables with and without harness comparable. This is because the additional losses in the magnetic layer remain negligibly less than 1 W / m.

Unlike other magnetic-coated cables, e.g. in tubular steel cables, the present design does not increase the conductor overhead losses due to field concentration within the magnetic sheath.

To FIGS. 5 and 6 is achieved with a screen cross-section of A _s = 400 mm ² an extremely high shielding effect; However, in such a screen cross-section also extremely high screen losses of more than twice the conductor losses occur, cf. Fig. 4 ,

If the screen cross-section is increased to A _S = 2500 mm ² , the magnetic induction directly above the cables becomes extremely low: after FIGS. 5 and 6 For example, an extreme limit of 0.2 μT, as required for example in some regions of Italy, is maintained with great certainty just above the surface of the earth. The occurring screen loss factor is below 40%. Table: Shielding factors SF with increasing screen cross-sections <i> A </ i><sub> S </ sub> 'without' magnetic harness 'with' magnetic harness Shield cross-section A _S in mm ² SF SF 400 5 280 1200 14 750 2500 28 1350

In the table, the shielding factors as a function of the screen cross section A _S are plotted for the landing point at 0.2 m above the ground, directly above the horizontal cable system in a single plane arrangement, without and with a high permeability layer above the copper screen. Without magnetic harness, shielding factors of up to around 30 are achieved, depending on the screen cross-section. If, in addition, a highly permeable layer is applied above the copper screen, extremely high shielding factors result, which reach up to about 1400.

Furthermore, it is discussed to what extent requirements for magnetic field limitation and the subsequent shielding measures according to the preceding considerations affect the current carrying capacity of the cables. For this purpose, the already discussed 110 kV VPE single-conductor cable in a laying depth of 1.2 m at a load factor of m = 0.85 is assumed again. The cable trench is thermally stabilized.

In the Fig. 7 the current carrying capacity is shown as a function of the wire spacing s of the cables in a single-level arrangement.
dashed line: cables with crossed shields with screen cross section of 50 mm ²
strong line: single conductor cable according to the invention with screen cross section 2500 mm ²
Parameter: magnetic field restriction (thin characteristic: without restriction)

In this figure, first the thin and the dashed characteristic show the current carrying capacity of the cable with a "normal" screen cross-section of 50 mm ² with cyclic cross-bonding of the screens, as a function of the wire spacing of the cables in the horizontal single-level arrangement. While the thin characteristic does not take into account any magnetic field restriction, the thick dashed characteristic at distances of about s > 0.25 m shows the required current reduction in the event that a maximum magnetic induction of 100 μT is set at a height of 0.2 m above the earth's surface , A favorable thermal expansion distance of the cable in this case leads to a reduction of the maximum current.

The black dot in Fig. 7 returns the load capacity of this cable in the case of an extreme magnetic field restriction of 0.2 μT, assuming a tight laying of the cables in a steel pipe. In this case, not only the thermally unfavorable arrangement, but also the additional losses of the steel pipe in the order of 20% and the additional losses caused by the steel pipe in the cable have a decreasing load-bearing effect.

The thick characteristic in Fig. 7 shows the current-carrying capacity of the present single conductor cable, which depends on the wire spacing, here with a copper screen cross section of 2500 mm ² . To Fig. 5b does this Cable even with large wire distances a maximum magnetic induction of less than 0.1 .mu.T, so that a case distinction with respect to the magnetic field restriction is unnecessary.

To Fig. 7 For a magnetic field restriction of 100 μT, the current carrying capacity of the single-core cable of the present application exceeds that of a 'normal' cable for wire distances of more than 1 m, however, the required effort (construction, trench width) is comparatively large.

reference numeral

12

cable conductor

14

Insulation (plastic, VPE)

15

Support tube, laying pipe

18

metallic contact layer (cross connector, accompanying winding)

20

Metal screen (reinforcement), made of copper or aluminum

22

Strap (foil) made of highly permeable material

24

Corrosion protection and / or cable sheath

A _S

Cross section of metal screen (mostly copper)

y ₁

loss factor

s

Core distance

Claims (12)

Magnetic shielding arrangement for single conductor electrical cables in a high voltage three phase system, having the following structure: Wherein each single conductor cable comprises a cable conductor (12) and a plastic insulation (14) with inner and outer conductive layer, and the shielding arrangement respectively for a single conductor cable • from a above the single conductor cable arranged the single conductor cable radially surrounded metal screen (20), and A continuous band (22) of high-permeability material surrounding the metal shield (20), characterized in that the metal sheds (20) have contact means at their ends for contacting the metal shades with each other, and
in that, in order to reduce the electrical loss contribution in the metal screen (20), the metal screen (20) is formed with an increased electrical conductance, so that screen currents are inducible, which in the limit case are equal to the conductor current of the cable conductor (12). Magnetic shielding arrangement according to claim 1, characterized in that for recording induced shield currents of the electrical conductivity of the metal shield (20) in the range 80% to 150% of the electrical conductivity of the cable conductor (12). Magnetic shielding arrangement according to claim 1 or 2, characterized in that the electrical conductance of the metal screen (20) is equal to the electrical conductance of the cable conductor (12). Magnetic shielding arrangement according to one of the preceding claims, characterized in that the metal screen (20) is surrounded by a metallic contact layer (18) formed as a foil or strip in a contacting manner. Magnetic shielding arrangement according to one of the preceding claims, characterized in that the harness (22) of overlapping wound thin bands consists of special steel with a relative permeability of some 10,000. Magnetic shielding arrangement according to one of the preceding claims, characterized in that the harness (22) is covered with a corrosion protection layer. Magnetic shielding arrangement according to one of the preceding claims, characterized in that the metal screen (20) consists of copper or of aluminum. Magnetic shielding arrangement according to claim 7, characterized in that the metal screen (20) consists of metallic single wires or of a metal layer. Magnetic shielding arrangement according to claim 8, characterized in that the metal screen (20) consists of a mesh. Magnetic shielding arrangement according to one of the preceding claims, characterized in that on the plastic insulation (14) of each single conductor cable of the metal screen (20) is arranged as a reinforcement. Magnetic shielding arrangement according to one of claims 1 to 9, characterized in that the metal shield (20) of the shielding arrangement is arranged on a carrier tube (15) into which in each case a single-core cable with plastic insulation (14) is drawn. High-voltage three-phase current system consisting of three single-conductor cables, preferably in a single-plane arrangement according to one of the preceding claims, characterized in that the three metal sheds (20) of the single-core cables or the three metal sheds (20) arranged on the support tubes (15) are short-circuited at both ends.

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