EP0932168B1 - Coaxial transformer - Google Patents

Description

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

A coaxial transformer has compared to a conventional transformer with tube or disc windings a good insulation between Primärund Secondary winding due to the electric field symmetry between inner and Outer conductor of the coaxial cable. Another advantage is the relatively low influence due to the current displacement effect even with larger conductor cross sections Reason for the magnetic field symmetry in the cylindrical conductor layers of the Coaxial cable. Another advantage is the low and reproducible leakage inductance, because the stray field only between inner and outer conductor and the conductors even occurs. Finally, a high power density and cost-effective Assembly given.

As a result, for example, the application of the transformer in a soft switching power converter with a switching frequency of, for example, 20 kHz and larger transmissible power (far more than 100 kW) at the same time high Currents and high isolation requirements (up to, e.g., 50 kV). It is conceivable but also an application at mains frequency.

From K.W. Klontz, D. Divan, D. Novotny; "To 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, p.1257-1263 is a soft switching power converter known in which a coaxial transformer on the one hand is used for potential separation 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 except the otherwise possible transmission ratio of 1: 1 also other integer ratios can be adjusted. It However, it is obvious that in view of a desired high insulation strength the segmentation on the one hand requires a complicated special cable, as the individual conductor segments already during the manufacturing process without inclusion must be isolated from each other by air cavities. On the other hand requires the frontal interconnection of the individual conductor segments special constructive Measures, one wants in addition to a high isolation ability in particular At high currents and consequently high conductor cross-sections a low-loss Achieve construction with small geometric dimensions. The in the cited reference cited embodiment of the coaxial transformer is therefore at the same time for high transmittable powers (e.g., 500 kW) high insulation resistance no longer suitable.

For many industrial applications (such as converters in process, industrial and traction technology) is but especially at relatively high potential differences and at the same time high power to be transmitted a permanently good electrical insulation between the primary and secondary terminals of the transformer of great importance. Only then can you, for example, leakage currents and permanently prevent glare and the proper functioning of the power converter over a long period of time.

US-A-3 717 808 describes a coaxial cable transformer with a Coaxial cable enclosing a core in one turn. The coaxial cable has three conductors, of which two conductors are the primary winding and the Form secondary winding. The document describes the Coaxial transformer based on an equivalent circuit diagram, the actual constructive structure of the transformer, in particular the design of the Connections, however, is not described.

The invention has for its object to provide a coaxial transformer of the above mentioned type with very good electrical isolation between primary and Secondary connection, which is suitable for very high performance, a low Has volume and is inexpensive to produce.

This object is achieved by a coaxial transformer with a Solved primary and secondary winding coaxial cable, at least one Core of suitable material encloses the windings and each end of the coaxial cable is provided with a cable termination, which is the two conductors of Connect a coaxial cable to a primary terminal and a secondary terminal, ensure electrical insulation and control the electric field.

The achievable with the present invention consist in particular that the proposed, for power over 1 MW suitable transformer very high insulation requirements for example, 50 kV with high power density filled with solid insulating material. The high power density leads to a cost-effective, relatively light and requiring only small space transformer. The dispersion of the transformer is very low and exactly defined, so that they Even with series production without additional effort is very accurate reproducible. This is particularly true when operated at a constant switching frequency resonant converters Of great importance as the reactive elements of the resonant circuit then allowed to have only small tolerances.

To ensure a high insulation resistance, it is advantageous that the high Potential only on a single side, the connection side, is open. This facilitates the electrical insulation and helps to create a transformer with very little 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 very easy to separate what the desired very low leakage inductance and low-impedance connection to the adjacent power semiconductors guaranteed. Due to the design of the transformer as a plurality of modules existing matrix transformer can be by appropriate interconnection of Primary and secondary connections of the individual modules also different gear ratios set as 1: 1 between primary and secondary winding. To this Way, the modularity of the concept is ensured 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 will be explained below with reference to the embodiments illustrated in the drawings. Show it:

Fig. 1

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

Fig. 2

a coaxial transformer according to FIG. 1 with mounting device,

Fig. 3

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

Fig. 4

the possibility of a modular construction of the coaxial transformer shown in Figure 2 in detail with voltage arrows and an electrical equivalent circuit diagram to illustrate the voltage conditions,

Fig. 5

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

In Fig. 1, a first variant of the coaxial transformer is shown. 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 an electrically insulating material to recognize, which with recesses for Guiding the individual turns of the winding and the core is provided. The Windings (primary winding, secondary winding) are through a coaxial cable 17th formed, which encloses the winding block 16 with a plurality of turns. there For example, the winding may be single-layered or multi-layered, with the advantage the precisely defined and thus reproducible inductance or scattering also at multilayer windings is given.

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

The dielectric 19 is preferably for defined control of the electric field on its two cylinder jacket surfaces with an electrically semiconducting Material 27 connected. This allows air cavities between the primary and secondary side even with large temperature fluctuations and heavy load fluctuations be avoided altogether. The outer conductor 20 is of an electrically insulating and mechanically protective jacket 7 covered. Advantageously, a standard manufactured and therefore inexpensive coaxial cable used become.

Each of the two ends of the coaxial cable 17 is provided with a cable end closure 8 Provided. The completely maintenance-free cable terminations 8 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 terminal, the control of the electric field and the electrical insulation. The inner conductor 18 of the coaxial cable 17 preferably forms the primary winding of the Transformers and is connected at each end to a primary terminal 9. 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 terminal 10 connected. The fixation of 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 other coaxial cables, not shown be connected, which the other electrical wiring within a Plant, for example, within an electric rail vehicle accomplish.

As can be appreciated, auxiliary windings can be wrapped around by the coaxial cable formed winding to be wound. This is due to the exception of the connection side at no point open winding completely problem-free.

The winding formed from the coaxial cable 17 preferably has in this embodiment the shape of an oval hollow cylinder. This can be the minimum allowed Bending radius of the cable can be ensured. The two are directly opposite straight sections of this oval hollow cylinder are each from a Core 12 of suitable core material (e.g., iron ribbon or ferrite) enclosed. Each of the two halves of the core 12 can easily consist of several individual Cores which are magnetically connected in parallel, are manufactured. So one simple assembly of the core / winding arrangement is possible, the cores are preferably cut to use. In this way can also reproducibility the main inductance of the transformer by the introduction of a Air gap can be ensured. The split cores 12 become, for example compressed by means along the outer jacket extending steel straps.

Advantageously, the core 12 easily to any potential, for example be set to ground potential.

In Fig. 2 (side view in the upper section and top view in the lower section) is additionally a mounting device for the variant shown in Fig. 1 of the coaxial transformer shown. There are in turn the winding frame 16 with the wound coaxial cable 17, the core 12 and the two serving for the connection To detect cable terminations 8. At the winding frame 16 are at both End plates 13 provided, which for vibration-proof and space-saving attachment of the transformer within a housing are suitable.

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

The inner conductor 18 of the coaxial cable 17 is in forced cooling for guiding the Coolant (for example, water or compressed air) used. It serves, for example the one primary connection as coolant inlet and the other primary connection of the Coaxial cable as coolant drain. By circulation of the coolant along the entire inner conductor of the coaxial cable 17 are during operation in the Coaxial cable 17 itself produced heat losses to the outside to an external Recooler drained.

For cooling the core, the transformer can at least in the region of the core be partially filled with a good thermal conductivity casting, which the Core 12 partially surrounds and run in which Kuhlmittelkanäle or radiator are introduced.

In Fig. 3 (in the left section, a view from above, in the lower section of a Side view and in the middle section a view on the front side) is the possibility of the modular construction of the coaxial transformer of Figure 2 in mechanical Illustration shown. By primary-side and / or secondary-side rows and / or Parallel connection of several, each with a winding of FIG. 1/2 provided modules are in principle any transformer ratios adjustable at the same time easy handling of the insulation resistance.

In the example shown, a total of six modules 1 to 6 (the coaxial transformer according to Figure 2 represents such a module is) connected so that a transformer with a gear ratio of 1: 3 results. All primary connections 9 with The modules marked 1 to 6 are connected via connecting bridges 28 in FIG Series switched. The terminal 21 thus provides the outer formed thereby Primary-side main connection of the modular transformer. Secondary side are the terminals 10 of the modules 1 to 3 and the terminals 10 of the modules. 4 to 6 connected via connecting bridges 29 each in parallel. Subsequently, the Once again, two new winding connections are connected in series. Terminal 22 represents the outer secondary side formed thereby Main connection of the modular transformer.

Fig. 4 shows for clarity the adjusting primary and secondary voltage conditions in the upper section on the basis of a detailed representation of the mechanical arrangement of Figure 3 and in the lower section on the basis of an electrical equivalent circuit diagram. In each case, the outer primary voltage with u _P (t), the outer secondary voltage with u _S (t), the primary voltages of the modules 1 to 6 with u _P1 (t) to u _P6 (t) and the secondary voltages of the modules 1 to 6 with u _S1 (t) to u _S6 (t).

Through this elementary type of interconnection, the amount of transferable power even with the use of n modules also n-fold compared to the transferable Performance of a module can be increased. Symmetrization (uniform voltage and power distribution for all n modules) is not a problem, since-like already mentioned at the beginning - the electrical parameters such as scattering and main inductance can be reproduced very well with every single module. This is the first thing - in transformers with tube or Disc windings rather critical - parallel winding 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 the individual in parallel switched windings can occur are avoided.

To a low-inductive and low-loss interconnection of the individual modules themselves to be able to guarantee at higher operating frequencies (eg 20 kHz) is - as in Figure 3 shown - a large-scale busbar of the connecting lines (see the connecting bridges 28, 29) advantageous. The busbar should be made in this way, that in the parallel conductor pieces (connecting bridges) adjusting Currents are oppositely directed and equal in magnitude. This is always satisfied with the busbar shown in Figure 3. The contacting of the individual modules can always be in the proposed type of busbar in the same way. In Figure 3, this is through the terminal contacts 23rd (secondary side) and 24 (primary side).

From Figure 3 also shows that by the selected busbar (connecting bridges) no additional isolation problem arises. Primary and secondary side Winding connections remain, as already with the use of only a module, locally always equidistant from each other. The same applies also for the cooling, in the example shown by a loop 30th (Series connection of the cooling connections of all six modules 1 to 6) is constructed. The coolant is introduced through the port 25. By connection 26 leaves the coolant finally returns to the cooling circuit. Of course, but also a parallel connection of all cooling connection pairs or a combination of Reihenund Parallel connection possible.

FIG. 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, in particular also for a modular construction with e.g. a big one common core 12 is suitable for all modules. In this type of modular Aufbaues the individual modules are simply on the common core 12 mounted and e.g. by crosses into corresponding holes of the winding block 16 Screw connections 31 fixed. An assembly device (plates 13), as in FIG. 3 shown is not essential.

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-inductance Modul Verschiebenung as in the example shown above according to FIG 3 met are. Furthermore, to the shape of all modules common core 12th No special claims made, since in principle the arrangement of the modules to each other can be arbitrary. However, the space-saving design would be advantageous of the core 12 as a UU core or Ul core.

Claims (5)

1. Coaxial transformer, having a coaxial cable (17) which forms a primary winding and a secondary winding, having two conductors (18, 20), with at least one core (12) surrounding the windings, and the two conductors (18, 20) being connected at each end of the coaxial cable to a primary connection (9) and to a secondary connection (10), characterized in that the coaxial cable (17) is provided at each end with a cable termination (8), which cable terminations (8) connect the two conductors (18, 20) of the coaxial cable to the primary connection (9) and to the secondary connection (10), which ensure electrical isolation and control the electrical field.
2. Coaxial transformer according to Claim 1, characterized in that a winding block (16) is used to guide the coaxial cable (17).
3. Coaxial transformer according to Claim 1 and/or 2, characterized in that the tubular inner conductor (18) of the coaxial cable (17) is used for circulation of a coolant.
4. Coaxial transformer according to one of the preceding Claims 1 to 3, characterized in that a number of windings are provided, which each form a primary winding and a secondary winding and are provided with cable terminations (8), in which case the individual primary windings and/or secondary windings are connected in series and/or in parallel by means of connecting links (28, 29), and forms a common outer primary connection (21) and outer secondary connection (22) of the module arrangement.
5. Coaxial transformer according to Claim 4, characterized by a common core for all the windings in the module arrangement.

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