EP0342468B1 - Rail winding - Google Patents

Abstract

A coil winding consisting of an electrical conductor (1) provided with an insulation is monitored using an optical waveguide (2) for the purpose of a distributed temperature measurement. The electrical conductor (1) has a longitudinal groove (3) on one inner side below the insulation. The optical waveguide (2) lies loosely in the longitudinal groove (3). In addition, the optical waveguide (2) is longer than the electrical conductor (1) by an amount which is sufficient to ensure that it is protected from excessive elongation in the event of a large degree of thermal expansion of the electrical conductor (1). In a method for manufacturing the coil winding, the conductor combination of electrical conductor (1) and optical waveguide (2) is first wound on an auxiliary drum (5). The coil winding is then wound in an opposing winding direction. <IMAGE>

Description

Technical field

The invention relates to a coil winding made of an electrical conductor provided with insulation, which is monitored with an optical waveguide for the purpose of a distributed temperature measurement.

State of the art

It is generally recognized today (see, for example, AJ Wakeling, Colloquium on Power Transformers, CIGRE SC 12, 1985) that the service life of a power transformer is determined by the so-called hotspot temperature. For some time, transformers have been monitored with temperature sensors which are attached to the suspected hotspots in the transformer (W. Lampe et al, In. Conf. Large high voltage electric systems 12-02, 1984). A glass fiber with an optical sensor at its end is brought into the best possible thermal contact with the suspected (and determined by computer simulation) hotspots. It is now the case that the suspected hotspot is not necessarily an actual one. This discrepancy leaves be overcome by a per se known DTS system (D istributed T emperature S ensor). If the sensor fiber along which the temperature is measured is brought into the turns of the transformer, then the actual hotspot can be determined.

To measure the temperature profiles of transformer or choke coils, not only is a suitable measuring system necessary (DTS), but the temperature sensor must also be inserted into the coil in a suitable manner. It is not sufficient to wind the optical fiber around the coil afterwards, but you have to integrate it directly into the electrical conductor in the form of a combination of optical fibers and electrical conductors and then use them to produce the coil. However, because of its sensitivity to pressure and bending, the optical waveguide must be well protected from mechanical loads and must also be integrated so that it can withstand the inevitable thermal expansion of the electrical conductor during operation.

Presentation of the invention

The object of the invention is to provide a coil winding from an electrical conductor provided with insulation, which is monitored with an optical waveguide for the purpose of a distributed temperature measurement, in which coil winding there is good thermal contact between the two conductors, the temperature distribution in the coil winding is accurate can be measured and the optical waveguide is protected against mechanical overload.

Furthermore, it is an object of the invention to provide a method for producing such a coil winding.

According to the invention, the solution is that the electrical conductor has a longitudinal groove under the insulation on the side facing the center of the coil winding, and that the optical waveguide is loose lies in the longitudinal groove and that the optical waveguide has an excess length in relation to the electrical conductor, which is sufficient to protect it from excessive expansion in the event of strong thermal expansion of the electrical conductor.

In a method according to the invention for producing such a coil winding, the optical waveguide is first loosely inserted into the longitudinal groove of the electrical conductor, then the electrical conductor is wound onto an auxiliary drum with a drum radius r _T such that the longitudinal groove with the inserted optical waveguide comes to lie on the outside and finally the electrical conductor is wound up from the auxiliary drum to the coil winding in such a way that the longitudinal groove comes to lie on the inside of the electrical conductor.

The essence of the invention is to be seen in the fact that the optical waveguide is connected to the electrical conductor to form a conductor combination in which the optical waveguide has an excess length compared to the electrical conductor at room temperature, with which it compensates for the large thermal expansion of the electrical conductor at the working temperature can.

Preferred embodiments of the invention result from the dependent patent claims.

Brief description of the drawings

• Fig. 1a, b, c einen Ausschnitt aus einer erfindungsgemässen Spulenwicklung und
• Fig. 2a, b eine schematische Darstellung von Verfahrensschritten zum Herstellen einer erfindungsgemässen Spulenwicklung.

The invention is to be explained in more detail below on the basis of exemplary embodiments and in connection with the drawings. Show it:

• 1a, b, c a section of a coil winding according to the invention and
• 2a, b show a schematic representation of method steps for producing a coil winding according to the invention.

Ways of Carrying Out the Invention

1a shows a plan view, FIG. 1b shows a cross section and FIG. 1c shows a longitudinal section of a section of a coil winding according to the invention. In the three figures, identical parts are provided with the same reference symbols.

One starts from a band-shaped electrical conductor 1, e.g. a copper tape with a thickness of approx. 2.5 mm and a width of approx. 12 mm. The electrical conductor 1 has a longitudinal groove 3 in which an optical waveguide 2, e.g. an Allsilica fiber. According to a preferred embodiment, the electrical conductor 1 and the optical waveguide 2 lying in the longitudinal groove 3 are wrapped with paper insulation 4.

1c that the electrical conductor 1, which is part of a coil winding, is curved. It lies on a circle with a radius r _S (coil radius). The coil radius r _S is measured from a center of the coil winding up to a central plane M of the band-shaped electrical conductor 1. The longitudinal groove 3 lies on an inside of the electrical conductor 1 or the coil winding.

The optical waveguide 2 lies loosely in the longitudinal groove 3. In addition, it has an excess length in relation to the electrical conductor 1, ie it does not lie on a straight line in the longitudinal groove 3, but on a serpentine line. In other words, if one cut out a full turn of the coil winding, stretched the electrical conductor 1 and the optical waveguide 2, then the optical waveguide 2 would be an excess length Δ L longer than the electrical conductor 1.

The dimensions of the longitudinal groove 3 are of central importance.

A first important point is that it is arranged asymmetrically with respect to the center plane M of the electrical conductor 1. That is, it does not penetrate substantially beyond the center plane M. The aim of the condition mentioned is that an axis A of an optical waveguide 2 lying in the longitudinal groove 3 has a minimum distance d from the central plane M.

According to a preferred embodiment, the longitudinal groove 3 penetrates straight to the central plane M, so that the distance d corresponds to just half the diameter of the optical waveguide 2.

A second important point is that the straight longitudinal groove 3 has transverse dimensions which make it possible to accommodate the excess length of the optical waveguide 2 in the form of a serpentine line. Therefore, it should preferably be two to five times as wide as the diameter of the optical waveguide 2. In the same sense, it should be about one to two times as deep as the diameter of the optical waveguide 2. In any case, it must be ensured that the optical waveguide 2 can be freely moved in the longitudinal groove 3 and that it is not clamped in any way (e.g. by the insulation).

1a to c, the paper insulation 4 ensures that the optical waveguide 2 cannot come out of the longitudinal groove 3. Even if the optical waveguide 2 is not in surface contact with the electrical conductor 1, there is thermal contact between the two conductors, whether because the optical waveguide 2 is surrounded on three sides by the electrical conductor 1 or because of the coil winding is immersed in an oil bath.

The relative excess length which is necessary in order to protect the optical waveguide against mechanical stress given the large thermal expansion of the electrical conductor can be determined as follows.

Quarzglas

0.19 10⁻³

Kupfer

5.2 10⁻³

Aluminium

7.7 10⁻³

Tabelle I: Thermische Ausdehnung von Quarzglas, Kupfer und Aluminium zwischen 0 - 300 °C.Table I shows typical materials and their expansion when the temperature rises from 0 to 300 ° C:

Quartz glass

0.19 10⁻³

copper

5.2 10⁻³

aluminum

7.7 10⁻³

Table I: Thermal expansion of quartz glass, copper and aluminum between 0 - 300 ° C.

mindestens ca. 0.001, vorzugsweise ca. 0.005 betragen sollte.It follows that a relative excess length $\frac{\text{ΔL}}{\text{L}}$

should be at least about 0.001, preferably about 0.005.

Since the excess length leads to a meandering of the optical waveguide 2, if the excess length is too large, the local curvature (micro-macrobending) of the optical waveguide 2 may be so great that bending-related damping occurs, i.e. that light is coupled out.

In a test, a coil winding according to the invention was produced from a copper strip 2.5 mm thick and 12 mm wide. The longitudinal groove 3, which was attached to the inside of the copper tape, was 1.2 mm wide and just as deep. The longitudinal groove 3 thus just penetrated up to the central plane M. The glass fiber lying loosely in the longitudinal groove had a diameter of approximately 0.6 mm. The copper tape was wrapped with paper insulation. The entire coil winding was immersed in an oil bath.

The effective temperature along the copper strip was measured with a DTS measurement. It was clearly the first time see how periodically the temperature profile rises and falls with the turns. It was also possible to see how the mean value of the temperature profile rose slightly from the turns in the oil bath to the top.

A method according to the invention for producing the coil winding is described below.

It essentially comprises two steps: first, winding the conductor combination (electrical conductor + fiber optic cable) onto an auxiliary drum and second, winding the conductor combination from the auxiliary drum onto the coil winding.

2a shows the first method step. The electrical conductor 1 is already provided with a longitudinal groove according to the invention. In this first loose, i.e. without tension, the optical fiber 2 inserted. The electrical conductor 1 and the optical waveguide 2 are then wrapped with paper insulation 4. This conductor combination is now wound onto an auxiliary drum in such a way that the longitudinal groove 3 comes to lie outwards.

Since the axis A of the optical waveguide 2 lies further outwards from the central plane M by a distance d, the optical waveguide lies on a somewhat larger circle than the electrical conductor.

2b shows the second method step. The conductor combination is unwound from the auxiliary drum 5 and wound to the coil winding 6. The winding sense must be inverted, ie the coil winding 6 is wound so that the longitudinal groove 3 of the electrical conductor 1, which was on the outside of the auxiliary drum 5, comes to lie on the inside of the coil winding 6.

On the auxiliary drum 5, the optical waveguide 2 lies on a straight line in the longitudinal groove 3. When the auxiliary drum 5 is unwound, an excess length is created for the first time and when the coil winding is wound, an excess length is produced for the second time. The excess length is determined solely by the asymmetrical longitudinal groove 3, i.e. created the distance d.

von $$\frac{\text{ΔL}}{\text{L}}\text{= d (}\frac{\text{1}}{{\text{r}}_{\text{S}}}\text{+}\frac{\text{1}}{{\text{r}}_{\text{T}}}\text{)}$$

Provided that the central plane M of the electrical conductor 1 is the neutral plane when it is bent, the method according to the invention results in a relative excess length $\frac{\text{ΔL}}{\text{L}}$

from $$\frac{\text{ΔL}}{\text{L}}\text{= d (}\frac{\text{1}}{{\text{r}}_{\text{S}}}\text{+}\frac{\text{1}}{{\text{r}}_{\text{T}}}\text{)}$$

ist definiert durch eine Längendifferenz L zwischen Lichtwellenleiter und elektrischem Leiter 1 bezogen auf eine Länge L des elektrischen Leiters 1. Die Distanz d wurde im Zusammenhang mit Fig. 1b definiert. r_T bezeichnet den Trommelradius und r_S den Spulenradius.The relative excess length $\frac{\text{L}}{\text{L}}$

is defined by a length difference L between the optical waveguide and the electrical conductor 1 in relation to a length L of the electrical conductor 1. The distance d was defined in connection with FIG. 1b. r _T denotes the drum radius and r _S the coil radius.

≅ 0.005. Die Breite von 1.2 mm der Längsnut 3 reicht aus, um eine relative Ueberlänge von bis zu 0.02 aufzunehmen, ohne eine merkliche zusätzliche Dämpfung durch Micro- resp. Macrobending zu verursachen.In the experiment described above, r _T = 0.3 m and r _S = 0.2 m. With the distance d = 0.6 mm, the relative excess length of $\frac{\text{ΔL}}{\text{L}}$

≅ 0.005. The width of 1.2 mm of the longitudinal groove 3 is sufficient to accommodate a relative excess length of up to 0.02 without a noticeable additional damping by micro resp. To cause macrobending.

It goes without saying that, in the method according to the invention, the electrical conductor 1 does not first have to be completely wound onto the auxiliary drum 5 before it can be wound into a coil. It is generally sufficient to guide it over deflection drums that have a suitable radius of curvature. In any case, it must be ensured that the desired first excess length is created after the deflecting drums and is also retained.

An additional excess length can also be achieved by an increased meandering of the optical waveguide 2 in the longitudinal groove. This can be enforced by auxiliary knobs which are attached in the longitudinal slot before the optical waveguide 1 is inserted and which dissolve during operation of the coil winding.

For example, 3 knobs made of wax can be attached in the longitudinal groove, between which the optical waveguide 2 meanders. After winding the coil, they are thermally destroyed or dissolved in the impregnating oil of the oil bath.

In conclusion, it can be said that the invention creates the conditions for using DTS in coil windings, e.g. To be able to use choke coils and transformers.

Claims (9)

1. Coil winding made from an electric conductor (1) provided with insulation (4), which winding is monitored by means of an optical fibre (2) for the purpose of a distributed temperature measurement, characterised in that

   a) on its side facing the centre of the coil winding the electric conductor (1) has a longitudinal groove (3) under the insulation,

   b) the optical fibre (2) lies loosely in the longitudinal groove (3), and

   c) the optical fibre (2) has an excess length with respect to the electric conductor (1) which suffices to protect it against excessive strain in the event of strong thermal expansion of the electric conductor (1).
2. Coil winding according to Claim 1, characterised in that the longitudinal groove (3) penetrates no deeper than up to the flexurally neutral central plane (M) of the electric conductor (1), so that the longitudinal axis (A) of the optical fibre (2) is displaced towards the center of the coil winding by a distance d with respect to the central plane (M).
3. Coil winding according to Claim 2, characterised in that the longitudinal groove is 1 - 2 times as deep and 2 - 5 times as wide as the diameter of the optical fibre (2).
4. Coil winding according to Claim 2, characterised in that the relative excess length $$\frac{\text{(ΔL)}}{\text{L}}$$

   

   of the optical is greater than 0.001.
5. Coil winding according to Claim 4, characterised in that the relative excess length (ΔL/L) is greater than 0.005.
6. Coil winding according to Claim 3, characterised in that the insulation is paper insulation (4) which retains the optical fibre (2) in the longitudinal groove in a laterally displaceable fashion.
7. Method for producing a coil winding according to Claim 1, characterised in that

   a) the optical fibre (2) is loosely inserted in the longitudinal groove (3) of the electric conductor (1),

   b) the electric conductor (1) is wound up on to an auxiliary drum (5) having a drum radius of r_T in such a way that the longitudinal groove (3) with the inserted optical fibre (2) comes to lie outside, and

   c) the electric conductor (1) is thereafter wound up by the auxiliary drum (5) to form the coil winding (6) in such a way that the longitudinal groove (3) comes to lie on the inside of the electric conductor (1).
8. Method according to Claim 7, characterised in that for the purpose of fixing the optical fibre (2) in the longitudinal groove (3) the electric conductor (1) is wrapped with paper insulation (4) after insertion of the optical fibre (2).
9. Method according to Claim 7, characterised in that the distance d, drum radius r_T and coil radius r_S are selected in such a way that the relative excess length ΔL/L is given by the formula $$\frac{\text{ΔL}}{\text{L}}\text{= d}\frac{\text{( 1 )}}{{\text{r}}_{\text{S}}}\text{+}\frac{\text{1 )}}{{\text{r}}_{\text{S}}}$$

   

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