EP0932168A2 - Coaxial transformer - Google Patents

Abstract

The transformer has a coaxial cable forming a primary- and a secondary winding, and at least one core (12) enveloping the windings. Each end of the cable is provided with a cable termination (8) which provides an electric insulation and controls the electric field, and which connects both conductors of the cable with a primary connection (9) and a secondary connection (10).

Description

The invention relates to a coaxial transformer, for example for Electrical isolation of converters in various industrial applications and can be used in traction technology. Under a coaxial transformer is generally understood to be a transformer in which inner and outer conductors of a coaxial cable wound around a magnetic core, the primary winding or form the secondary winding.

A coaxial transformer shows compared to a conventional transformer with tube or disc windings, good insulation ability between primary and secondary winding due to the electrical field symmetry between indoor and outer conductor of the coaxial cable. The relatively small influence is also advantageous due to the current displacement effect even with larger conductor cross sections Because of the magnetic field symmetry in the cylindrical conductor layers of the Coaxial cable. Another advantage is the low and reproducible leakage inductance, since the stray field is only between the inner and outer conductors and the conductors itself occurs. After all, there is also a high power density and inexpensive Given assembly.

This makes the application of the transformer, for example, soft switching converter with a switching frequency of, for example, 20 kHz and larger transmissible powers (far more than 100 kW) with high at the same time Currents and high insulation requirements (up to e.g. 50 kV). Is conceivable but also an application at mains frequency.

From K.W. Klontz, D. Divan, D. Novotny; "An Actively Cooled 120-kW Coaxial Winding Transformer for Fast Charging of Electric Vehicles "; IEEE Transactions on Industry Applications, Vol. 31, No. 6, November / December 1995, pp. 1257-1263 is a known soft switching converter in which a coaxial transformer on the one hand is used for electrical isolation and on the other hand for voltage adjustment. At this embodiment is at least one of the two conductors of the coaxial cable segmented so that in addition to the otherwise possible gear ratio of 1: 1 other integer ratios can also be set. It However, it is obvious that in view of a desired high insulation strength the segmentation on the one hand requires a complex special cable, because the individual conductor segments during the manufacturing process without inclusion must be isolated from air voids. On the other hand, requires the frontal connection of the individual conductor segments is particularly constructive In addition to a high level of insulation, measures are particularly important with high currents and consequently large conductor cross sections, a low power dissipation Achieve construction with small geometric dimensions. The In the embodiment of the coaxial transformer specified in the above-cited literature reference is therefore for high transferable powers (e.g. 500 kW) at the same time high insulation strength no longer suitable.

For many industrial applications (e.g. for converters in process, industrial and traction technology) is especially in the case of relatively high potential differences and at the same time high performance to be transmitted a permanently good one electrical insulation between the primary connection and the secondary connection of the transformer of great importance. Only then you can, for example, leakage currents and permanently prevent glowing and the perfect functioning of the converter ensure over a long period of time.

The invention has for its object a coaxial transformer of the beginning mentioned type with very good electrical insulation ability between primary and Specify secondary connection that is suitable for very high outputs, a low one Has volume and is inexpensive to manufacture.

This object is achieved by a coaxial transformer with a Solved primary and secondary winding coaxial cable, at least one Appropriate material core that wraps around the windings and each end of the coaxial cable is provided with a cable end closure, which the two conductors of the Connect the coaxial cable to a primary connection and a secondary connection, ensure electrical insulation and control the electrical field.

The advantages that can be achieved with the invention are, in particular, that the proposed transformer, suitable for outputs over 1 MW, very high insulation requirements of, for example, 50 kV with a high power density at the same time met with solid insulating material. The high power density leads to an inexpensive, relatively light and requiring little space transformer. The spread of the transformer is very small and precisely defined, so that it can be reproduced very precisely even in series production without additional effort. This is particularly the case with resonant converters operated at a constant switching frequency of great importance since the reactive elements of the resonant circuit then only have small tolerances.

To ensure high insulation strength, it is advantageous that the high Potential is only open on one side, the connection side. This makes it easier the electrical insulation and helps make a transformer with very low To create dimensions. In addition, the electrical connections for the primary and secondary side directly next to each other and can be through the cable terminations separate very easily what is the desired very low leakage inductance and low-impedance connection to the neighboring power semiconductors. By designing the transformer as consisting of several modules Existing matrix transformers can be connected appropriately Primary and secondary connections of the individual modules also other gear ratios Set as 1: 1 between primary and secondary winding. To this In this way, the modularity of the concept is guaranteed in a wide range.

Fig. 1

eine erste Variante eines Koaxialtransformators in zweilagiger Wicklungsausführung bei Verwendung von zwei Kernhälften mit Querschnittsdarstellungen,

Fig. 2

einen Koaxialtransformator gemäß Fig. 1 mit Montagevorrichtung,

Fig. 3

die Möglichkeit eines modularen Aufbaues des in Figur 2 dargestellten Koaxialtransformators in mechanischer Darstellung,

Fig. 4

die Möglichkeit eines modularen Aufbaues des in Figur 2 dargestellten Koaxialtransformators in Detaildarstellung mit Spannungspfeilen sowie ein elektrisches Ersatzschaltbild zur Verdeutlichung der sich einstellenden Spannungsverhältnisse,

Fig. 5

eine zweite Variante eines Koaxialtransformators bei Verwendung von einem einzigen Kern für modularen Aufbau.

The invention is explained below with reference to the embodiments shown in the drawing. Show it:

Fig. 1

a first variant of a coaxial transformer in two-layer winding design when using two core halves with cross-sectional representations,

Fig. 2

1 with a mounting device,

Fig. 3

the possibility of a modular construction of the coaxial transformer shown in FIG. 2 in a mechanical representation,

Fig. 4

the possibility of a modular structure of the coaxial transformer shown in FIG. 2 in detail with voltage arrows and an electrical equivalent circuit diagram to clarify the voltage relationships that arise,

Fig. 5

a second variant of a coaxial transformer when using a single core for modular construction.

1 shows a first variant of the coaxial transformer. In the upper section (Side view) and in the lower section (view from above with in the upper Section marked section A) of the figure is a central winding block 16 to recognize an electrically insulating material which with recesses for Guide the individual turns of the winding and the core is provided. The Windings (primary winding, secondary winding) are by a coaxial cable 17th formed, which surrounds the winding block 16 with several turns. Here the winding can be formed in one or more layers, the advantage the precisely defined and thus reproducible inductance or scattering multilayer windings is given.

As the cross section shown in the left section of FIG. 1 shows, the coaxial cable 17 on a hollow-walled cylindrical inner conductor 18, which by means of a Dielectric 19 is also separated from the cylindrical outer conductor 20.

The dielectric 19 is preferred for the defined control of the electrical field on its two cylindrical surfaces with an electrically semiconducting Material 27 connected. This can create air voids between the primary and secondary side even with large temperature fluctuations and strong load fluctuations to be avoided entirely. The outer conductor 20 is of an electrically insulating type and mechanically protective jacket 7 covered. One can be advantageous standard manufactured and therefore inexpensive coaxial cable used become.

Each of the two ends of the coaxial cable 17 is with a cable end closure 8 Mistake. The completely maintenance-free cable terminations 17 serve the current-carrying Connection between the one conductor of the coaxial cable and the primary connection and between the other conductor of the coaxial cable and the secondary connection, the control of the electrical field and the electrical insulation. The inner conductor 18 of the coaxial cable 17 preferably forms the primary winding of the Transformer and is connected to a primary terminal 9 at each end. Of the Outer conductor 20 of the coaxial cable 17 forms the secondary winding of the transformer and is at each end with a preferably large-area secondary connection 10 connected. Fixing the coaxial cable for the purpose of parallel Design of the winding connections is made possible by a spacer 11.

Both the two primary connections and the two secondary connections can in a simple and expedient manner with further coaxial cables, not shown be connected, which the further electrical wiring within a System, for example within an electric rail vehicle.

As is easy to see, auxiliary windings can be wrapped around the coaxial cable formed winding are wound. This is due to the exception of the connection side nowhere open winding without any problems.

The winding formed from the coaxial cable 17 preferably has in this embodiment the shape of an oval hollow cylinder. This allows the minimum allowed Bending radius of the cable can be guaranteed. The two directly opposite each other straight sections of this oval hollow cylinder are each one Core 12 enclosed in a suitable core material (e.g. iron band or ferrite). Each of the two halves of the core 12 can easily consist of several individual ones Cores that are magnetically connected in parallel are manufactured. So that one simple assembly of the core / winding arrangement is possible, the cores are preferred cut to use. In this way, reproducibility the main inductance of the transformer by introducing a Air gap can be guaranteed. The split cores 12, for example pressed together by means of steel strips running along the outer shell.

Advantageously, the core 12 can easily reach any potential, for example be "laid" on ground potential.

In Fig. 2 (side view in the upper section and top view in the lower section) is also a mounting device for the variant shown in Fig. 1 of the coaxial transformer shown. There are again the winding block 16 with the wound coaxial cable 17, the core 12 and the two serving for connection Cable terminations 8 can be seen. On the winding block 16 are on both Face plates 13 are provided, which for vibration-proof and space-saving attachment of the transformer are suitable within a housing.

In terms of heating and thus also cooling technology, the winding and core are almost complete decoupled. For winding and core are therefore depending on the prevailing environmental conditions and the load conditions also different cooling combinations (various combinations with self-cooling, forced air cooling, Water cooling) possible.

The inner conductor 3 of the coaxial cable 2 is with forced cooling to guide the Coolant (e.g. water or compressed air). It serves, for example one primary connection as coolant inlet 14 and the other primary connection of the Coaxial cable as coolant drain 15. By circulating the coolant along the entire inner conductor of the coaxial cable 2 are the during operation in Coaxial cable 2 self-generated heat losses to the outside to an external Recooler removed.

To cool the core, the transformer can at least in the area of the core partially filled with a thermally conductive potting, which the Core 12 partially encloses and in which coolant channels run or cooler are introduced.

3 (in the left section a view from above, in the lower section one Side view and in the middle section a view of the front) is the possibility of the modular structure of the coaxial transformer according to Figure 2 in mechanical Representation shown. Through primary and / or secondary side row and / or parallel connection of several, each with a winding according to FIG. In principle, 1/2 provided modules are arbitrary transformer ratios adjustable with simple handling of the insulation strength.

In the example shown, a total of six modules 1 to 6 (the coaxial transformer according to Figure 2 represents such a module) connected so that a transformer with a gear ratio of 1: 3 results. All primary connections 9 with the numbers 1 to 6 marked modules are via connecting bridges 28 in Series connected. The terminal 21 thus represents the outer formed thereby primary connection of the modular transformer. Secondary side are the connections 10 of the modules 1 to 3 and the connections 10 of the modules 4 to 6 each connected in parallel via connecting bridges 29. Then the two new winding connections that are set up in this way. Terminal 22 represents the outer secondary side formed thereby Main connection of the modular transformer.

For clarification, FIG. 4 shows the primary and secondary voltage relationships that arise in the upper section using a detailed representation of the mechanical arrangement according to FIG. 3 and in the lower section using an electrical equivalent circuit diagram. The external primary voltage with u _P (t), the external secondary voltage with u _S (t), the primary voltages of modules 1 to 6 with u _P1 (t) to u _P6 (t) and the secondary voltages of modules 1 to 6 denoted by u _S1 (t) to u _S6 (t).

Through this elementary type of connection, the amount of the transferable power even when using n modules, n times compared to the transferable Performance of a module can be increased. The symmetry (uniform voltage and power distribution for all n modules) is not a problem because - As already mentioned at the beginning - the electrical parameters such as scattering and main inductance can be reproduced very well with every single module. In this way it is the first - for transformers with tubes or Disc windings rather critical - parallel connection of windings in the higher Performance range possible. Internal circulating currents, as in the parallel connection of Tube or disc windings due to different induced voltages and different electrical transformer parameters in each parallel switched windings can occur are avoided.

A low-inductance and low-loss connection of the individual modules themselves To be able to guarantee at higher operating frequencies (e.g. 20 kHz) is - as in Figure 3 shown - a large-area railing of the connecting lines (see the connecting bridges 28, 29) advantageous. The splint should be done so that the resulting in the parallel conductor pieces (connecting bridges) Currents are directed in opposite directions and are of equal magnitude. This is always fulfilled with the railing shown in FIG. 3. Contacting the individual modules can always be in the proposed type of splinting done in the same way. In FIG. 3, this is shown by the connection contacts 23 (secondary side) and 24 (primary side) clarified.

FIG. 3 also shows that the selected busbars (connecting bridges) no additional insulation problem arises. Primary and secondary sides Winding connections remain, as when using only one module, always at the same distance from each other. The same applies also for cooling, which in the example shown by a ring line 30 (Series connection of the cooling connections of all six modules 1 to 6) is set up. The coolant is introduced through the connection 25. Leaves through port 26 the coolant finally returns to the cooling circuit. Of course it is also a parallel connection of all cooling connection pairs or a combination of series and parallel connection possible.

Figure 5 (in the upper section a side view and in the lower section a view from above) shows a second variant of the proposed transformer design, which in particular also for a modular structure with z. B. a large one common core 12 is suitable for all modules. With this type of modular The individual modules are simply set up on the common core 12 assembled and e.g. by reaching into corresponding bores of the winding block 16 Screw connections 31 fixed. A mounting device (plates 13), as in Figure 3 shown is not absolutely necessary.

It is obvious that for this simple modular concept according to FIG. 5, of course the same simple wiring rules and embodiments of the low inductive Module railing as in the example shown above shown in Figure 3 fulfilled are. Furthermore, the shape of the core 12 common to all modules is no special demands were made, since in principle the arrangement of the modules is mutually exclusive can be any. However, the space-saving design would be advantageous of the core 12 as a UU core or Ul core.

Claims (5)

Coaxial transformer with a primary and secondary winding Coaxial cable (2), at least one core (12) enclosing the windings and each end of the coaxial cable is provided with a cable end closure (8) which the two conductors (3, 5) of the coaxial cable with a primary connection (9) and Connect a secondary connection (10), ensure electrical insulation and control the electric field. Coaxial transformer according to claim 1, characterized in that a Winding block (1) is used to guide the coaxial cable (2). Coaxial transformer according to claim 1 and / or 2, characterized in that the tubular inner conductor (3) of the coaxial cable (2) for the circulation of a Coolant. Coaxial transformer according to one of the preceding claims 1 to 3, characterized in that several primary and secondary windings each and windings provided with cable terminations (8) are provided, whereby a series and / or parallel connection is made by means of connecting bridges (28, 29) of the individual primary windings and / or secondary windings takes place and one common outer primary connection (21) and outer secondary connection (22) Module arrangement forms. Coaxial transformer according to claim 4, characterized by a common one Core for all windings of the module arrangement.

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