DE4341721A1 - 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 Laminated core as defined in the preamble of claim 1.

Such transformers are used for. B. to provide 16 2/3 Hz energy traction power supply via static converters with power semiconductors used. The high power required is achieved by connecting in parallel several four-quadrant feeders using just one Transformer reached.

In FIG. 5, the schematic diagram is shown of such a transformer with four-feeding to separate low-voltage windings 1 four-quadrant controller 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 the space enclosed by the lamination stack 6 central space. 7

The 16 2/3 Hz AC voltage is generated by pulsing power semiconductors (GTOs) in four-quadrant actuators 2 from DC voltages. By pulsing the output voltages e₁, e₂, e₃ and e₄ of the four-quadrant actuator (see. Fig. 5) corresponding to Fig. 7c with high harmonics. These voltage harmonics further 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 iGes 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 (GTOs) 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. However, this greatly increases the cost, volume and weight of the transformer.

The object of the invention is to design a transformer so that simple way, without significantly increasing the transformer costs, the Transformer volume and weight the unwanted Current harmonics can be greatly reduced.

This object is achieved according to the invention by the characterizing features of claim 1 solved. Advantageous configurations are the subclaims removable.

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

Show it:

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 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. This means that 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 by 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 (4)

1.Transformer with a frame-shaped laminated core, in the central free space of which windings protrude, which are grouped as n-pairs, each consisting of an inner high-voltage winding and an outer low-voltage winding above it, around two of the opposite legs of the laminated core, in particular for parallel operation with several four-quadrant actuators feeding in, characterized in that that the laminated core (6) in the central free space (7) one or more cross-shaped intermediate yokes (8) are inserted, which divide the free space (7) in the window (9) for the individual pairs of windings (1/3), in which einliegen this and that the high-voltage windings ( 3 ) are connected in series. 2. Transformer according to claim 1, characterized in that the intermediate yokes ( 8 ) are narrowly dimensioned and have only a fraction of the cross section of the legs ( 4 or 5 ). 3. Transformer according to claim 1 or 2, characterized in that for n = 4 pairs of windings ( 1/3 ) an intermediate yoke ( 8 ) is used which forms four windows ( 9 ) in the free space ( 7 ). 4. Transformer according to claim 1 or 2, characterized in that for n = 6 or n = 8 pairs of windings form two or three adjacent or overlapping and merging intermediate yokes 6 or 8 individual windows ( 9 ).