US1849485A - Transformer - Google Patents

Description

March 15, 1932.

TRANSFORMER Y J. B. GIBBS ET AL Filed Feb. 15, 1930 INVENTORS Jesse B.Gz'bb6 and Alberl M. Wz'yl'n's I ATTdRNE ,UNITE'D. STATES.

PATENT OFFICE JESSE B. GIBBS AND ALBERT M. WIGGINS, OI SHARON, PENNSYLVANIA, ASSIGNORS TO WESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY, A: CORPORATION 01' PENNSYLVANIA rnnnsronmnn Application filed February 5,1930. Serial No. 428,621.

, Our invention relates to transformers and it has particular relation to means for obtaining any desired ratio of transformation.

In electricaltranslating devices, such as transformers, having two windings disposed on an iron core, both being interlinked by the magnetic flux passing through the magnetic circuit formed by the iron core, the ampere turns in one winding would be equal'to theampere turns in the other winding, andthe ratio of secondary current to primary current would be inversely as the ratio of the number of turns in the windings were it not for the exciting current of the transformer.

In practice, however, the ratio of secondary current to primary current varies from the theoretical or inverse turn ratio. This variation in the actual transformation ratio from the theoretical value is inherent in all transformers and is caused by the exciting 7 current that supplies the iron losses and sets up the magnetic flux in the transformer core.

The error in the transformation ratio may be compensatedfor by adding one or more turns to the primary winding, or subtracting one or more turns from the secondary winding; Such compensation, however, may be only approximate since the addition or subtraction of a full turn may not give the exact compensation required.

In transformers employed in connection with measuring instruments, the variation of theactual ratio of transformation from the inverse turn ratio is of prime importance because it affects the accuracy'of the measurement and, therefore, the transformer must be compensated accurately for this variation in transformation ratio.

In certain types of instrument transformers, for example, current transformers, er-

- 'rors in the ratio of transformation are compensated for by'using fewer than the theoretically-correctnumber of turns in the second-. ary winding. In transformers having a few turns in the secondary winding, it is difiic ult to obtain the exact compensation required because thecompensation necessary in most cases does not correspond to integral turns. Thus, ifin a' transformer having fifty secondary turns, a compensation of 1 is desired, it is diflicult to obtain this compensat1on as each turn represents 2% of the total wmding and droppmg oneturn would pro- JHStlIlg' the fractional turn. ratio after the transformer has been assembled.

We have elected to illustrate our invention as applied to a current transformer, but it will be obvious that it is not limited to this application.

Our invention may be best understood by reference to the following description and to the accompanying drawings, in which,

Figure 1 is a perspective view of a transformer constructed 'in accordance with our invention.

Fig. 2 is a side elevational view, with parts removed, of the transformer illustrated in Fig. 1.

Fig. 3 is an end view of a transformer showing a modified form of our invention.

Referring to Figs, 1 and 2 of the drawings,

'our invention comprises, in general, a transformer core 2 and a plurality of windings 3 and 4 inductively related thereto.

The core 2 maybe divided into a plurality of core sections, but is here illustrated as comprising two apertured core sections 5 and 6 having equal apertures but unequal lengths and unequal cross sections of flux paths. v The core sections 5 and 6 comprise aplurality of apertured laminations 7 having their apertures 8 in alignment, each section being sepa rated from the next section by a non-magnetic spacing member 9.

The windings 3 and 4 encompass all the sections of the core 2 and extend through the apertures 8. All the turns of winding 4 encompass all the core sections, while only some the larger core'section 6. v Portions of the spacer 9 are removed to permit turns of the windings 3 to encircle the smaller core 5, only.

When one turn encircles the smaller core section 5, theturns compensation is equal to where A and B are the lengths of thecore sections 5* and 6, respectively. For example, ifone-quarter turn compensation 1s requlred, the dimension A must be one-third of the dimension. B with one turn encircling. the smaller core section. To secure one-half turn compensation, two turns around the smaller core section 5 are necessary or one turn around a core section twice as long as the core section 5. v p

We have found with this construction that fractional turn compensation may be attained to any desired degree, and that more exact predetermination of the necessary compensation is possible. I

.It will be noted that the construction of the transformer is extremely simple and the number of turns linking the small core section 5 may be easily changed, which makes possible a change in the number of turns linking the smaller core member 5 after the transformer has been built and tested. "-The laminations 7 may be moved from one core member to the other, thus varying the relative lengths of the core members. These adjustments are particularly advantageous on account of the difficulty in some cases of predetermining the exact compensation required.

Referring to Fig. 3 of the drawings, one core section 11 is disposed within the other core section 12. Most of the turns of winding .3 encompass both core sections 11 and 12' and relatively few turns of the winding 3 encompass one core section only, which may be either core section 11 or 12.

It will be evident from the above descrip tion that we have provided a transformer in which-accurate fractional turn compensation may be secured by using a single conductor for each winding, and one that is simple in construction and in which the required compensation may readily be effected.

Since many changes may be made in the form and relation of the core members 5 and 6, and in the disposition of the winding 3 thereon without departing from the spirit and scope of our. invention, we do not wish to be limited otherwise than as set forth in the appended claims.

We claim as our invention:

1. A transformer comprising a plurality of core members each having uniform cross sections-of flux paths and a winding disposed on the core members, .a portion of said winding interlinking all core members and another portion of said windinginterlinking less than all core members.

2. In an instrument transformer, a'core comprising a plurality of core members each having a substantially constant cross-sectional area throughout the length of its magnetic path, primary and secondary windings inter linking all of said core members, at least one turn of one of said windings interlinking less than all the core members.

1,3. A transformer comprising two core members each having a substantially constant cross-sectional area throughout the length of'its' magnetic path, the cross section of flux path of one member being a fractional part of that of the other member, a winding disposed on the core members, said winding having a plurality of turns thereof encircling the two core .members and a relatively few of said winding linkingboth core members and at least one turn linking only onecore member.

, 5. In an instrument transformer, a core comprising two apertured core members formed from similarly shaped laminations,

the cross section of flux path of one member being a fractional part of that of the other,

the core members being separated by nonmagnetic material and having their apertures in alignment, two windings of unequal turns disposed on said core, the majority of turns of the winding having the greater number of turns linking both core members and extending through their apertures, at least one turn of the winding having the greater ligumber of turns linking only one core mem- 6. An instrument transformer comprising two core members each formed from a plurality of apertured laminations of the same shape and size and having their apertures in alignment, a winding interlinking said core members and extending throughtheir apertures, the majority of the turns of said winding encircling both core members and at least one turn encircling only one core member.

7. An instrument transformer comprising a core consisting of two apertured core members having equal apertures and each having a constant cross sectional area throughout the length of its magnetic path, one core member having a smaller cross section of flux path than the other, azwindin'g interlinkinfi said core members and extending throng their apertures, nearly all the turns of the winding encircling both core members and at least one turn encircling one core member 8. A current transformer, comprising a core structure consisting of aplurality of core members each comprising separate r groups'of magnetic laminations having 1;, equal cross sections of flux paths, primary and secondary windings disposed on said core, the majority of turns of the secondary winding interlinln'n the plurality of core sections and relative y few turns of the seczo ondary winding interlinking less than the plurality of core sections to produce fractional turn ratios between primary and secondarg windings.

9. current transformer, comprising a core structure consisting of two core members formed from two stacks of similar laminations, the stack comprising the flux path of one core member being much smaller than the stack comprising the flux path of the other core member, primary and secondary windin s disposed on the core, most of the turns 0% the secondary winding interlinking both core members and at least one turn interlinln'ng only the core member having the small flux path to produce fractional turn ratios between primary and secondary windm s. ln testimony whereof, we have hereunto subscribed our names this 6th day of Febru- 40 ary, 1930. JESSE B, GIBBS.

ALBERT WIGGIN S.

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