DE4341721C2 - Transformer with a frame-shaped laminated core - Google Patents

Abstract

The invention relates to a transformer having a laminated core in the form of a frame, into whose central free space windings project which are grouped as n pairs, each composed of an inner high-voltage winding and an outer low-voltage winding located above it, around two of the opposite limbs of the laminated core, in particular for parallel operation with a plurality of supplying four-quadrant controllers. When a 16 2/3 Hz AC voltage is produced from a DC voltage by means of pulsed four-quadrant controllers, interfering current harmonics occur. In order to reduce the harmonics in a simple manner - that is to say without increasing the transformer costs, the transformer volume or the transformer weight - it is proposed according to the invention that one or more cruciform intermediate yokes (8) be inserted into the central free space (7) in the laminated core (6), which yokes divide the free space (7) into windows (9) for the individual winding pairs (1/3) in which these are inserted, and that the high-voltage windings (3) be connected in series. <IMAGE>

Description

The invention relates to a transformer with a frame Sheet pack. When providing 16 2/3 Hz energy at the Traction power supply problems are known to occur when static Inverters with power semiconductors (e.g. GTO) in pulse mode be used. The high power required is generally determined by Parallel connection of several four-quadrant feeders achieved via only one such transformer mentioned above, the must be designed accordingly large.

In FIG. 5, the schematic diagram is shown of such a transformer with four feeding to separate low-voltage windings 1 four-quadrant actuators. 2 The four high-voltage windings 3 are generally connected in parallel.

The construction of such a known transformer is shown in FIG. 6. To the legs 4 and 5 of a frame-shaped lamination stack 6 while the low-voltage windings 1 and high-voltage windings 3 are each grouped into pairs and project on one side in a space enclosed by the lamination stack 6 central space. 7 The 16 2/3 Hz AC voltage is generated by pulsing power semiconductors (GTO) in four-quadrant actuators 2 from DC voltages. By pulsing, the output voltages e1, e2, e3 and e4 of the four-quadrant controller (cf. FIG. 5) are superimposed with high harmonics in accordance with FIG. 7c. These voltage harmonics cause current harmonics in the undervoltage windings 1 , as shown in FIG. 7b. To compensate for current harmonics, the individual four-quadrant actuators are clocked with an offset. As a result, the output current of the transformer i _Ges in the high-voltage winding 3 becomes sinusoidal (cf. FIG. 7a).

Additional current heat losses in the transformer and in the converters are caused by the current harmonics in the undervoltage windings 1 . In addition, the utilization of the power semiconductors (GTO) is significantly deteriorated by the current peaks. These disadvantages can be eliminated by using four separate transformers, which are connected in series on the high voltage side. As a result, however, the overall cost, volume and weight of the arrangement are greatly increased.

The object of the invention is a single transformer of the beginning mentioned type so that with it in a simple manner without substantial increase in costs, volume and weight unwanted current harmonics can be greatly reduced.

This object is achieved according to the invention by a transformer frame-shaped laminated core with arranged on its legs Pairs of windings made of wrapped upper and Undervoltage windings solved, the central clearance through cruciform intermediate yokes divided into uniform single windows is, into which respectively assigned pairs of windings project, the Cross section of the winding yokes a fraction of the cross section of the Leg is such that the scatter between the Winding pairs is increased, with particular use in static inverters with parallel connection of "n" Four quadrant actuators then "n" winding pairs are provided. Advantageous refinements can be found in the further claims.

Outside of the present field of application and The performance range already includes numerous transformer designs and interpretations became known, each of which certain Have partial characteristics and similarities, but not overall Contribute to the solution of the task.

So are already single-phase transformers with frame-shaped Sheet metal package, in which the central clearance through cruciform intermediate yokes is divided into individual windows, the Cross section of the intermediate yokes sometimes only a fraction of the Cross-section of the legs is (DE-PS 631 785).  

The primary and secondary windings are separate on the legs housed. The intermediate yokes serve there Short-circuit current limitation by increasing the leakage inductance between the primary and secondary windings. This measure enlarged the voltage drop and deteriorates the electrical properties of the transformer considerably.

From DE-AS 1 110 299 a three-phase high-voltage transformer for X-ray technology is known, in which pairs of windings are used on the legs, the upper and lower voltage windings of which - but differently - are wound around or above one another. The three-leg transformer shown in one embodiment ( FIG. 5) has a transverse yoke crossing a middle leg, which initially associates a certain similarity to cruciform intermediate yokes. However, the transverse yoke there serves a different purpose and is intended exclusively for guiding the flux difference (fundamental oscillation) caused by the star-delta connection there. The cross section of the transverse yoke is therefore only insignificantly reduced there. This version is neither useful for the magnetic separation of all pairs of windings nor a further solution to the problem.

Also known is a three-phase three-leg transformer with two Retention bars of reduced cross-section in the two windows (approx. 30% of the leg cross section), with which harmonics of the Have magnetization current largely suppressed (book by R. Küchler "The Transformers", 2nd edition 1966, Springer Verlag Berlin, p. 60). The arrangement, however, is based on transformers Star zigzag circuit is limited and can be used for larger ones Hardly use transformers in the target area.  

Based on schematic embodiments, the invention in explained in more detail below.

It shows

Fig. 1 shows the novel transformer assembly of four pairs of windings,

Fig. 2, the corresponding current and voltage waveforms,

Fig. 3 shows the novel transformer assembly for six pairs of windings,

Fig. 4 shows the transformer construction for eight pairs of windings,

Fig. 5 to 7 the state already explained art.

As shown in FIG. 1, a cross-shaped intermediate yoke 8 is integrated into the new transformer instead of the mere frame-shaped laminated core 6 which has hitherto been the case. The four winding pairs 1/3 lie in the four windows 9 thus formed (in the previous free space 7 ). The principle underlying the new design is as follows:
The magnitude of the current harmonics in the undervoltage windings 1 depends on the leakage inductance and decreases with increasing leakage inductance. In the case of transformers with a plurality of undervoltage windings 1, there are two different leakage inductances: that between the individual undervoltage windings 1 and that between the undervoltage windings 1 and the high-voltage windings 3 . While the first leakage inductance is decisive for limiting the current harmonics, the second determines the voltage drop of the transformer. In the previous transformer design (see FIG. 6), the sizes of the two leakage inductances are dependent on one another. The leakage inductance between the undervoltage windings 1 must therefore not be increased arbitrarily in order to reduce the current harmonics, since otherwise the voltage drop of the transformer is also increased, which means a deterioration in the electrical properties of the transformer.

In the new transformer design, the four low and high voltage windings are magnetically decoupled by the additional intermediate yoke 8 . The leakage inductance between the individual undervoltage windings 1 , which determines the magnitude of the current harmonics, can thus be increased as desired without influencing the other leakage inductance. That is, the current harmonics can be greatly reduced by increasing the leakage inductance without increasing the voltage drop of the transformer. In FIGS. 2a and 2b it is seen that the currents are sinusoidal by the use of the new transformer design both in the Oberspannungs- and in the low-voltage windings. Since only harmonics of the river are present in the intermediate yoke 8 , which have a very small amplitude, the intermediate yoke 8 can be dimensioned very narrow. To the current harmonics z. B. to reduce about 20 times, a cross section of the intermediate yoke 8 of about only 1/10 of the leg cross section 4 or 5 is required. For this reason, the additional intermediate yoke 8 does not make the transformer much larger and heavier.

FIGS. 3 and 4 show transformer designs for six or eight times the feed and arranged corresponding to two three or four pairs of windings twice 1/3. The transformer laminated core 6 is supplemented here by two or three adjacent cross-shaped intermediate yokes 8 which merge into one another. The principle of action is as already described.

The new transformer design can be used wherever several Four quadrant actuators are operated in parallel, e.g. B. also on locomotives, be used.

Claims (5)

1. Transformer with a frame-shaped laminated core ( 6 ) with on its legs ( 4 , 5 ) arranged pairs of windings ( 1/3 ) made of over- and undervoltage windings ( 1 and 3 ), the central free space ( 7 ) through cruciform intermediate yokes ( 8 ) is subdivided into uniform individual windows ( 9 ), into which respectively assigned pairs of windings ( 1/3 ) protrude, the cross section of the intermediate yokes ( 8 ) being a fraction of the cross section of the legs ( 4, 5 ), such that the scatter between the Winding pairs ( 1/3 ) is increased, the transformer having "n" such winding pairs ( 1/3 ), in particular when used with static converters with parallel connection of "n" four-quadrant actuators. 2. Transformer according to claim 1, characterized in that in each pair of windings ( 1/3 ) the high voltage winding ( 3 ) inside and the undervoltage winding ( 1 ) is outside. 3. Transformer according to claim 1 or 2, characterized in that for n = 4 winding pairs ( 1/3 ) a single intermediate yoke ( 8 ) is used, which forms four individual windows ( 9 ) in the free space ( 7 ). 4. Transformer according to claim 1 or 2, characterized in that for n = 6 or n = 8 winding pairs ( 1/3 ) several intermediate yokes ( 8 ) are arranged such that they form 6 or 8 individual windows ( 9 ). 5. Transformer according to claim 1 or 2, characterized in that the high-voltage windings ( 3 ) are connected in series.