US1749388A - Transformer - Google Patents

Description

March 4, 1930. AAAAAAAAA Ns 1,749,388

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, inw uur mmm@ uvl 2 Patented Mar. 4, 1930 UNITED STATES AUGUST DIEYER'IANS, OF ENNETBADEN, Fs"

raar o'tr'itl VTZERLAND, ASSGNOR T0 A. Gr. BROVJLT BOVERI & CE., OF BADEN, SWITZERLAND, A FUENTE-STOCK COMANY OF SWTZER- LAND Application Afiled Gctoser $5, i922?, Serial No. 228,596, and in Germany and Switzerland November 8, 1926.

This invention relates to improvements in transformers.

The production of extremely high voltages has hitherto been realized by employing two or more insulated single-phase transformers connected in cascade, each transformer having a low-tension primary winding and a high-tension secondary winding, to which is added a third winding usually of low voltage which serves to supply the primary of a second and similar transformer forming part of the cascade. The secondary winding of this transformer which produces the nent higher stage of voltage is connected in series with the secondary of the leading transformer and its third winding is similarly used to supply a further member of the cascade. The diliculty with these combinations of transformers lies in the insulation between the windings themselves and between the windings and the cores, since with transformers of ordinary design the voltage differences between adjacent winding sections and between windings and core may be very high. Attempts were therefore made to impress a series of potentials such as would result in the smallest possible potential difference between adjacent parts of the transformer. This impressed distribution of voltage was effected by the use of conducting connections between certain parts of the traneformer and suitable points on the hightension winding, of which one pole was earthed. Although the potential of these controlled parts was chosen midway between the potentials of the adjacent parts. this method of controlling the distribution of potential had very great drawbacks. There is no objection to the inter-connection oi'i single points in two separate electrical circuits which are insulated from one another, since the current loading of the transformer windings is not increased thereby. The case is otherwise, however, in the event of a breakdown of the insulation between the two circuits at some other point. The aforcsa'd connection would then act as a direct shortcircuit on the transformer which would be burnt out and the whole plant thereby endangered. The control of potential by means of connections between isolated circuits of the transformer should therefore be avoided as far as possible, and is at the best an unsatisfactory solution to the problem under consideration.

One of the objects of the present invention is the provision of means for effecting a satisfactory distribution of potential without the disadvantages mentioned above. F or this purpose use is made of a phenomenon depending on trie capacitive relationship between any insulated body and its surroundings. lf one insulated body be placed ivicinity of a. number of other bodies at ferent poten 'ials, it will asnne a poten various pien! il which is mean of the which would be produced by each of neighboring bodies acting separately. The body in question is then in state of cquilibrium under the action of the various potentials simultaneously imposed upon it, and its resulting potential is the mean of these` rThe magnitude or this resultant potential varies with the position of the body relative to the surrounding bodies, and in every ca e it is possible to find a position in which ne difference between this potential and those of the surrounding bodies is a minin This conception may be utilized in arra` the various windings of the transf( Thus, an arrangement of the .vindi with regard to one another and gard to the iron cores is chosen si. .a capacitive reactions o the vari n, duce the desired distribution of potential such as has hitherto been obtained by the inipressed voltage method referred to above.

Other objects and advantages will hereinafter appear.

ln accordance with the present invention. a single-phase transformer is mounted insulated from earth and forms part of a car'- cade, the transformer being provided with a plurality of windings (at least three), nainely, a low-voltage primary winding, a high voltage secondary winding, and a tertiary winding usually of low voltage which serres to supply the primary of a second similarly constructed transformer forming part ofthe cascade. The secondary of this latter transformer gives a further step-up to the voltage and is connected in series with the secondary of the first or leading transformer, the tertiary of the second transformer serving to supply a third transformer of the cascade, as described. According to the invention the various windings of the transformer are so arranged that by capacitive action alone between the windings themselves and between the windings and iron core the parts in question assume such potentials that the potential difference between adjacent vwindings and between windings and cores is everywhere a minimum. By this means the dielectric stresses in the insulation of the transformers approach the lowest values attainable.

For the purpose of illustrating the present invention, several embodiments thereof are shown in the drawings, wherein Figure 1 is a schematic view illustrating the manner in which the various parts of the improved transformer are related and connected, and the manner in which a number of such transformers might be connected in cascade; and

Fig. 2 is a. view similar to Fig. 1, illustrating a modification.

The transformers are mounted insulated, and hence the potential of the iron cores may be controlled.

Referring more particularly to Fig. 1, the two transformers 10 and 11 are identical in all respects and comprise, respectively, the cores 12 and 13 having the axes of symmetry 14 and 15, equal portions of the core legs 16, 17 and 18, 19 being disposed on opposite sides of the axes 14 and 15 which accordingly pass through the centers 20, 21 and 22. 23 of the core legs as shown. The first or leading transformer 10 is provided with the low-voltage primary winding 24, the high-voltage secondary Winding 25, and the low-voltage tertiary winding 26, while the second or following transformer 11 is provided with the low-voltage primary winding 27, the highvoltage secondary winding 28, and the lowvoltage tertiary winding 29. It is assumed that the low-voltage tertiary windings 26 and 29 have the same number of turns as the respective associated primary windings 24 and 27 but of course this relation may vary with different conditions.

The cores 12 and 13 are connected as shown at the points 30 and 31 to the mid-points of the secondary windings 25 and 28.

The primary energy is supplied to the winding 24, and from thence is transmitted in part to the secondary winding portions 32 and 33, and in part to the winding 26. The winding 26 feeds the primary 27 of the transformer 11, and the energy is transmitted by primary 27 to the secondary winding portions 34 and 35 and, if there are further l transformers in the cascade, to the next of the series through winding 29. The two secondary winding portions 32 and 33 of transformer 10 are connected in parallel, as shown, and their ends lie on the axis of symmetry 14. In order to ensure perfect symmetry a out the aforesaid axis, the winding portions 32 and 33 are wound in opposite directions, as indicated. Moreover, they are equally distributed over both core legs 16 and 17 of the transformer, as shown, and therefore the voltage mid-point of the secondary 25 is situated in the connecting wires 36 and 37. Similarly, the two secondary winding portions 34 and 35 of transformer 11 are connected in parallel, as shown. their' ends lying on the axis of symmetry 15. The winding portions 34 and 35, also, are wound in opposite directions, as indicated, to ensure perfect symmetry about axis 15. Furthermore, they are equally distributed over both core legs 18 and 19 of thc transformer, as shown, so that the voltage mid-point of the secondary 28 is situated in the connecting wires 38 and 39. The secondary windings 25 and 28 of the two transformers are connected in series by means of the wire 40. The beginning 41 of the secondary winding 25 is earthed. The voltage above earth of the end 42 of the secondary winding 28 is therefore double the secondary voltage of 011e transformer, the two tra-nsformers being identical in all respects. The potential of the intermediate circuit 26, 27 is, in accordance with the invention, determined by its capacitive relationship with the other windings, and the potential of the cores 12 and 13 is fixed by the conductive connections between the points 30, 31 and 36, 38 respectively. The core 12 is therefore at the same potential as the mid-point of the winding 25, and the core 13 is at the same potential as the mid-point of winding 28. The symmetrical arrangement of the three windings with respect to the axes 14 and 15 results in the potential being distributed as follows.

(1) The winding 24 is in close-coupled capacitive relationship with the adjacent turns of theassociated secondary winding portions 32 and 33 which, since 41 is carthed, are both at earth potential. The principal factor governing the potential of primary 24 is, however, the primary mains system which itself is at nearly earth potential. It is evident, therefore. that the potential assumed by primary 24 cannot be widely different from that of the associated secondary winding portions 32 and 33.

(2) The circuit containing the windings 26 and 27 is closely coupled with the end turns of the associated secondary winding portions 32 and 33 and the beginning turns of secondary winding portions 34 and 35. rlhe potential of all these windings will correspond to the secondary voltage of the transformer 10 and will consequently impress this voltage on the circuit aforesaid.

Between the winding 26 and the core 12, and between the winding 27 and the core 18, however, a much closer coupling exists. The core l2 is at the potential of the mid-point of the secondary 25, and the core 18 is at the potential of the mid-point of secondary 28, and since the first potential aforesaid is half the secondary voltage of a transformer and the second potential aforesaid is one and a half times the said secondary voltage, it will be evident that the circuit 26-27' will assume a potential midway between these two, that is to say, a potential corresponding to the secondary voltage of one transformer. 'lhe capacitive interlinlring of the secondary windings 25, 28 and the iron cores l2, 'i3 with the circuit 26-27 iXes the potential of the latter at a value corresponding to the secondary voltage of one of the transformers.

f, The potential difference between the said circuit and adjacent winding sections is thus Zero, and the potential to the iron core is equal to half the value of the secondary voltage, as was also the case, approximately, with primary winding 24.

(3) The winding 29 is capacitively interlinled with the end turns of the secondary winding portions 34, 85 and with the iron core 13, and will therefore assume a potential to earth which is larger than one and a half times but smaller than twice the seondary voltage of one of the transformers. The potential difference between the winding 29 and either the iron core g3 or the secondary winding portions 34, 85 is therefore less than half the secondary voltage of a single transformer. In the event of the winding 29 being used to feed a further primary winding 43 of a third transformer (not shown), the potential of the circuit will be fixed by the final secondary voltage of the transformer ll in the same way as the potential of the circuit 2l-2 is ii d by the final secondary voltage of the transformer l0.

lt will be evident from the above that by he arrangement of the windings alone, and

under the influence of their capacitive relationships, the potentials of the various windings adjust themselves in such a manner that between no two adjacent parts of the transformer is the potential difference greater than half the secondary voltage of the said transformer. Hitherto such a result has only been obtained by the use of conducting links between the controlled circuits and points on the grounded high-voltage secondary winding.

A further development of the arrangement of Fig. l is provided by the quaternary winding shown in Fig. 2 of the drawing. The reference characters in Fig. 2 bear the same significance as in Fig. l. The windings 24, 26, 27 and 29 are arranged as concentra windings in the middle of their respec.

core legs, each being symmetrical with regard to the axes of symmetry 14 and l5. Moreover, each of these windings, as in Fig. l, is flanked on either side by the parallelconnected secondary winding portions 32, 33 and 34, 35 of the associated secondary windings 25 and 28. Upposite these secondary winding portions, and uniformly distributed over the whole of the respective core legs as shown, are the halves 44, and 46, 4i of Quaternary windings, such halves being connected shown and providing for neutralization of the leakage fields of the other three windings. ln addition to neutralizing the leakage fields, these quaternary windings relieve the associated secondary windings and 28 from the duty of transmitting the power supplied from the respective primary windings 24 and 22' to the corresponding tertiary windings 26 and 29. is a result of their symmetrical arrangement on the tra sformer cores, as shown, the potentials of thes fourth or Quaternary windings automatically assume values equal to that of the respective cores with which they are associated. This will be readily understood from the close capacitive interlinliage of these windings with the secondaries, since this capacitive intcrlinlrage is present equally in each transformer having secondary turns of low, medium and high potential, so that the resultant potential of the fourth winding is an a *orage value which is equal to that obtaining at the mid-point of the associated secondary winding. rlhis is also the potential of the iron core of the transformer considered.

rllhe examples given do not exhaust the number of possible arrangements of windings incorporating the invention. Thus. instead of concentrated windings, distributed windings may be employed, and the number of windings per transformer is not limited three or four. ln every case, the arrangement and symmetrical disposition of the wind 'n gs with resp et to an axis of symmetry passing through the center of the core legs and the effect of the capacitive reactions between the various components of the 'transformer results in a self-adjustment of the potential differences of acent parts to the lowest possible values.

rihe invention claimed is: l. ln a transformer, a core having an axis symmetry and legs with substantially o, al portions thereof disposed on opposite sides of said axis, a primary winding disposed on one of said legs at said axis, a second winding` similar to -said primary windino' disposed on the other of said legs at said axis for providing a supply source for a second transformer, and parallel-connected secondary windings symmetrical with respect to said anis and disposed respectively on the leg portions of said core on opposite sides of i-is lll)

said axis, the points of connection of said secondary windings with each other being disposed substantially on said axis.

2. In a transformer, a core having an axis of symmetry and legs with substantially equal portions thereof disposed on opposite sides of said axis, a primary winding disposed on one of said legs at said axis, a second winding similar to said primary winding disposed on the other of said legs at said axis for providing a supply source for a second transformer, and parallel-connected secondary windings symmetrical with respect to said axis and disposed respectively on the leg portions of said core on opposite sides of said axis, the points of connection of said secondary windings with each other being disposed substantially on said axis, said core being connected to said secondary winding at substantially the point of mid-potential thereof.

3. In a transformer, a core having an axis of symmetry and legs with substantially equal portions thereof disposed on opposite sides of said axis, a primary winding, a secondary winding, and a third winding providing a supply source for the primary of a second transformer, each of said windings being disposed on said core symmetrically with respect to said axis, said secondary winding comprising two oppositely wound parallel-connected sections disposed on opposite sides of said axis, the points of connection of said sections with each other being substantially on said axis, each of said sections being disposed over both portions of the core legs on the same side of said axis as said section.

4. In a transformer, a core having an axis of symmetry and leds with substantially equal portions thereof5 disposed on opposite sides of said axis, a primary winding disposed on one of the core legs, a secondary winding, and a third winding disposed on the other of the core legs and providing a supply source for the primary of a second transformer, each of said windings being disposed on said core symmetrically with respect to said axis, said secondary winding comprising two oppositely wound parallelconnected sections disposed on opposite sides of said axis, the points of connection of said sections with each other being substantially on said axis, each of said sections being disposed over both portions of the core legs on the same side of said axis as said section.

5. In a transformer, a core having an axis of symmetry and legs with substantially equal portions thereof disposed on opposite sides of said axis, a primary winding disposed on one of said legs at said axis, a secondary winding, a third winding disposed on the other of said legs at said axis and providing a supply source for the primary of a second transformer, said secondary winding AUGUST MEYERHANS.

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