US1747528A - Arrangement for reducing the stray reactance of cascade transformers - Google Patents

Description

Feb. E8, 393%. E. PFIFFNER ARRANGEMENT FOR REDUCING THE STRAY REACTANCE OF CASCADE TRANSFORMERS 2 Sheets-Sheet 1 Filed NOV. 26, 1923 imveiizzzr 5 hm.) $046k Fb. 1, 193@. PFIFFNER 1 747 528 ARRANGEMENT FOR REDUCING THE STRAY REACTANCE OF CASCADE TRANSFORMERS Filed Nov, 26, 1923 2 Sheets-Sheet 2 Patented Feb. 18, 1930 UNITED STATES PATENT OFFICE EMIL PFIFFNER, OF BUDAPEST, HUNGARY Application filed November 26, 1923, Serial No. 677,114, and in Germany November 28, 1922.

I This invention relates to improvements in arrangements for reducing the leakage reactance of compound or cascade transformers.

and essentially consists in the provision of 6 compensating windings which convey and improve the electromagnetic interlinking between the primary and secondary windings and the coupling windings respectively.

With the above object in view the-invention consists of certain noveldetails of construction hereinafter fully described and claimed. I

Several modes of carrying out the present invention are illustrated by way of example on the accompanying sheets of drawings in which Fig. 1 shows diagrammatically a compound or cascade transformer constructed accord- I in to the present invention.

igs. 2 and 3 illustrate the constructive arrangement of compensating or equalizing windings. U

Figs. 4 and 5'illustrate in sectional el'evation and plan view respectively a compound or cascade transformer constructed according to the present invention.

As shown in Fig. l the compound or cascade transformer comprises a number of individual transformers connected in series.

By placing a number of such transformers one-on the other a transformer for any voltage can be constructed. It is well known that such an arrangement has the advantage of simplification of manufacture by using the same coil elements for construction of apparatus for the most varied voltages.

There is, however, the disadvantage that owing to differences in the magnetic resistance of the separate cores and the reaction of the secondary windings in the coils of the diiferent cores different voltages are induced which affects the accuracy of the secondary windings.

Owing to the magnetic leakage at the ends of the core inequalities occur in the magnetic flux of the iron core; this is very undesirable.

The object of this invention is to overcome these objections by means of compensating coils which are connected up in opposition to each other and compensate any variation in the magnetic flux occurring in the coils.

The other undesirable objection of inequalities in the magnetic flux of the iron core is overcome by the arrangement ofa further compensating winding. This winding comprises two coils connected in opposition to each other, and arranged at the points of the magnetic circuits which are to be mutually compensated.

Owing to the better electric insulation cascade transformers are employed as hightension transformers particularly voltagetransformers, the said cascade transformers comprising a number of individual trans formers connected in series, each of the latter being constructed and insulated for a part of the voltage. Each of these individual transformers is provided with a high-tension winding W W "W through which the respective individual voltage is adapted to pass and which is in series with the other individual transformers. The beginning of winding of the first individual transformer is connected to the respective high-tension line and the end of winding is grounded. In order to attain the smallest insulation-stress, the iron members of the individual transformers are constructively connected with the centre of winding of the respective part-members. T e grounded secondarywindings 8 lies next to the hightension coil which is grounded.

The voltage drop between the individual transformers is increased uniformly and therefore the secondary winding, whose volt also the electromagnetic reaction of the secondary current has to be transferred to all individualtransformers. This cannot be ac complished by series connection of all secondary windings, as otherwise all individual high-tension windings would require to be I the high-tension windings.

entirely insulated against earth connection and thus the entire compound or cascade arrangement would be ofno use. Moreover the transfer of the secondary reaction has to be accomplished by means of coupling windings, which. electromagnetically couple the upper end of one member with the lower end of the adjacent member. I

As shown in Fig. 1, W W W designate the transformer are connected to the iron cores f f f by means of connections U U and U Thecoupling windings K and K and. K and K respectively are connected in opposition. 7 Their efiects result therefrom, that f the secondary windings s of the flux in the iron-core f is weakened, whereby a smaller tension is induced than in the winding K so that a compensating or equalizing current will be produced from the windings K to the winding K which hasthe tendency to increase the flux in the iron core f and to reduce the flux in the iron-core f The weakening in the iron-core f will produce the same effect in the iron-core f over the coupling windings K and K and thus the reaction of the secondary current is transferred to all members.

From the above it is clear, that the principle of construction of these compound or cascade transformers will lead to an axially displaced arrangement of primary and secondary windings, thus toa construction which does not produce a good electromagnetic interlinking of these windings but a large leakage resistance. Therefore in practice the arrangement diagrammatically illustrated in Fig. 1 is of no use, as during a secondary stress it will yield voltage drops which are far too large. These reactive drops produce an unsymmetricaldistribution of the magnetic flux in the magnetic iron in such a manner that-the flux is reduced in the direction of current along the axis of magnetic cores.

The arrangement hereinafter described reduces the leakage to a tolerable degree by arranging on the iron-core a compensating or equalizing winding a, a", which by means of a direct electrical connection with the same is brought to the same electrical potential and which is disposed concentrically with respect to the primary and secondary winding as diagrammatically shown in Fig. 2.

The said compensating or equalizing winding consists of two coils which are. connected in opposition and try to prevent the unsymmetrical field distribution produced by the able degree and the cascade arrangement may be used for measuring purposes.

Fig. 3 illustrates diagrammatically the constructive arrangement of the compensating or equalizing winding a, a". The iron-core 7 may be used as one of the two connections of the coils a, a.

In the arrangement illustrated in Fig.3 the best possible electromagnetic interlinking of the three windings is conclusive for the arrangement of the three windings with respect to one another.

Fig. 4 shows in longitudinal section 'a two stage cascade transformer provided with the various windings above described. Fig. 5 is a cross-sectional view of the transformer shown in Fig. 4 and illustrates the arrangement of the windings W and the iron-core W and W designate the two series-connected high-tension windings to which are coaxially coupled the oppositely connected coupling windings k and k The coupling winding k of the top unit is disposed at the bottom end of the winding 'w while the coupling windings 7: of the bottom unit is located at the top. end of the winding 'w The secondary winding .9 is disposed at the bottom end of the winding w These windings are insulated by an insulating sleeve from the concentrically ar ranged compensating or equalizing windings a and a" of the bottom unit and a and a," of the top unit. The said compensating windings possess small induced tensions only and therefore need to be slightly insulated only with respect to the iron-cores f and f, respectively, so that the latter can be used as electric return line connection.

The centres of the high-tension windings W and W are connected with the iron-cores f and f, by means of connections u and M in order to determine the maximum tension of the insulatingsleeve between the high-tension windings and the iron-cores.

The operative parts of the two series-connected units are mounted in insulating cases 6 and 6 which are cemented to the sleeves k. The bottom unit rests on an earthed base 9 in which are mounted secondary terminals. A hood 0 provided with a terminal (1 for the high tension line, is mounted on the top unit.

Fig. 5 shows the relative arrangement of the iron-core f and the winding W in the insulating case 6 I claim:

1. In a cascade transformer, a plurality of iron cores, a plurality of series connected high tension primary windings inductively wound with said cores, each being electrically connected to the middle point of its respective core, a secondary winding, coupling windings axially displaced with respect to one another to efi'ect an equalization of the magnetic flux in said cores and compensating windings each consisting of two coils arranged on the-same iron core acting in opposite directions and connected in oppositionwhereby the leakage reaatance of said transformer is reduced.

2. In a cascade transformer, a plurality of iron cores, a plurality of series connected high tension primary windings inductively wound with said cores each being electrically connected to the middle oint of its respective core,asecondary win ing, coupling windings axially displaced with respect to one another to effect an equalization of the magnetic flux in said cores and compensating windings comprising a pair of oppositely Wound coils on the same iron, said iron core forming a connecting link between said coils, whereby the leakage reactance of said transformer is reduced.

In testimony whereof I hereunto afiix my signature.

EMIL PFIFFNER.

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