US1559295A - Frequency converter - Google Patents

Description

H. M. STOLLER FREQUENCY CONVERTER Filed Sept. 20, 1916 n iii /n ven for: Ha qh M. SIM/er.

Patented Oct. 27, 1925.

UNITED STATES 1,559,295 PATENT OFFICE.

HUGH M. STOLLER, OF NEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRIC COMPANY, INGORPORATEJLOF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

FREQUENCY CONVERTER.

Application filed September 20, 1916. Serial No. 121,171.

To all whom it may concern:

Be it known that I, HUGH M. STOLLER, a citizen of the United States, residing at New York, in the county of New York and State of New York, have invented certain new and useful Improvements in Frequency Converters, of which the following is a full, clear, concise, and exact description.

This invention relates to frequency converters, and more particularly to a static or transformer type of converter, the object of which is to raise or lower the periodicity of a given generated alternating current without resorting to the use of rapidly moving mechanisms.

This invention therefore comprises a static transformer having polyphase low frequency windings arranged according to the practice common in induction motor design to produce a rotating magnetic field. By an un equal distribution of the low frequency windingswith respect to the winding space which they occupy, this rotating field is made to set up an electromotive force of higher frequency in a secondary circuit which has several reversals in the direction of winding so that each element of the magnetic field, during a complete rotation of the field as a whole, has several effective reversals of direction with respect to the secondary circuit. One revolution of the magnetic field may therefore produce several reversals of currents in the high frequency winding, and an arrangement is available whereby a primary current of given periodicity may induce a secondary current whose periodicity may be made greater or less than the primary periodicity depending on the ratio of primary to secondary poles.

The invention will be more clearly understood by reference to the accompanying drawings in which Fig. 1 illustrates the transformer of this invention in assembled from; Figs. 2, 3 and 4 illustrate the relative geometrical relations of the different phases of a three-phase primary winding; Figs. 5, 6 and 7 illustrate a geometrical arrangement of secondary windings for 1producing a three-phase secondary current aving a frequency three times that of the primary current: Fig. 8 illustrates a winding arrangement for one of the rimary phase windings of Figs. 2, 3 or 4; Fig. 9 illustrates diagrammatically a lap winding arrangement for the windings of Figs. 5, 6 and 7; and Figs. 10 and 11 illustrate the preferred connection for the primary'and secondary phase windings respectively.

In the particular embodiment of this invention herein illustrated, a ring sha ed magnetic core 1 is provided with a pluraiity of projecting teeth 2 and intervening winding slots 3. Each of the primary windings 4, 5 and 6 has a section on opposite halves of the core 1, the two sections being wound in opposition, as illustrated in Figs. 2, 3 and 4, respectively. Each of these primary sections' is of the tapered type, by which is meant a winding in which the number of turns per unit length of winding space is greatest at the middle of the winding space and decreases in order as the end of the winding space is approached. Center line A-A of Fig. 2 indicates the general direction of the flux set up in the space included within the ring by current in the primary winding 4, and the line about which the flux is symmetrically disposed.

It is well known that a substantially uniform rotatingmagnetic field may be established by polyphase current supplied to corresponding polyphase windings arranged about a core consisting of an iron ring or toroid. If the individual windings are each wound according to a sinusoidal distribution and the points at which the windings are most concentrated are equally displaced angularly about the core, the effect of the tapered windings of the type shown in Fig. 8, acting alone, is to produce a substantlally uniform rotating field throughout the space within the ring 1. With respect to the effective lines of force cutting a conductor element of the secondary winding, the field may be viewed at any instant as a unidirectional field extending in the same direction as the diameter of the rin passing through the conductor element. fins unidirectional field would normaly be of uniform flux density. A core of magnetic material within the ring, due to its lower reluctance, may modify the flux distribution in a. manner depending upon the form and size of the core. If there is a comparatively large air-gap, the part of the air-gap cut off by a tangent to the core parallel to the direction of the field will have a less dense flux, while the remainder or central portion of the field will have a more concentrated flux. The larger the air-gap, the greater is the proportional constriction of the effective field, although any size of air-gap, or in fact any other'ex edient, which will tend to make the uni irectional effective field non-uniform across the diameter, whether causing it to be constricted toward, or dispersed from the center, will give a series of electromotive force components in each winding, having a summatlon or resultant electromotive force changing in direction as the resultant field reverses its direction of motion with respect'to the secondary winding, that is, every 180 electrical degrees of the secondary.

If a sinusoidal distribution of secondary winding similar to that of the primary winding were employed, each magnetic line of force rotating at a uniform angular rate would induce an electromotive force of sine wave form in the secondary Winding since the product of flux and number of conductors would be a function of the sine of the angle traversed. The summation of a series of such electromotive force components differing in phase such as would be produced by the successive lines of a band of flux would also be a sine wave of the frequency of its com onents. Sinceflthe single line'of force in t e case of a secondary winding having six reversals changes its effective direction six times during a single revolution, there will be an electromotive force of triple frequency induced in the secondary winding. In the case of a uniformly distributed winding, such as illustrated in Figs. 5, 6 and 7 of the drawing, each line of force will generate a uare-topped .wave, but the sum of a series (if such square-topped waves will be a periodic wave departing to some extent from sine wave form, but still of triple frequency.

The primaries are preferably ring wound, as shown in Fig. 8, whereas a lap winding arrangement is better suited to the requirements of the secondary. Such an arrangement for a three-phase secondary applied to a core having thirty-six winding slots is shown in Fig. 9. This disposition of windings will produce a secondary frequency of three times the primary frequency. Figs. 5, 6 and 7 show an equivalent ring winding arrangement of the three secondary phases 7, 8 and 9. Here it will be noted that each secondary phase winding has six sections, three on each half of the core, and that adjacent sections are wound in opposite directions. It will further be noted that opposite sections are wound in opposite directions so that a diametric field rotating within the core 1 will produce additive effects in the diametrically opposed sections. Furthermore, for each complete rotation of the field three reversals of current will result in each secondary phase winding, thus producing a tripling of the primary frequency.

It is obvious that by employing a greater number of secondary winding sections a greater increase in frequency could be effected. Such increase is subject to the limitation imposed by the difliculty of constricting the effective rotating field to a suflicient- 1y narrow path. The effective width of the rotating field should, in fact, be comparable to the pole width ofthe sec dary winding. Where a greater increase in requency is desired, it will in general be found more practicable to connect a number of small ratio converters in tandem.

A central core member 10, is shown in Fig. 1 as located within the core member 1. This core member 10 is preferably made of laminae of transformer iron and serves the obvious purpose of decreasing the reluctance of the path transversed by the rotating flux. It is separated from the teeth 2 by an air gap 11. The width of the air gap will vary in different transformers. The use of a wide air gap will cause a low primary power factor whereas a small air gap will cause a large secondary reactive drop.

In general, the air gap used will be large as compared with that used in dynamo-electric machinery for it here serves as a means for a disturbing the uniform distribution of the effective field and for rendering negligible the reactive drop due to the secondary current.

Figs. 10 and 11 illustrate the connections for the primary and secondary windings, respectively. The disposition of the terminal portions of adjacent sections of the windings indicates a reversal of the directions of winding, going from one section to an electrically adjacent section.

While in the embodiment of the invention herein illustrated and described both the primary and secondary windings are shown as applied to the core member 1, it will readily appear to those versed in the art that these windings might. so far as theoretical I10 considerations are concerned, be equally well applied to the core member 10, or in fact one set of windings might be applied to one core member and the other set of windings to the other core member without departing from the spirit and scope of the invention.

What is claimed is:

1. A frequency converter having two concentric core members separated by an air gap, tapered polyphase primary windings on one of said members for producing a rotating magnetic field across said gap, means for supplying alternating current to said primary windings and a multipolar secondary winding in the path of said rotating field, said secondary winding servin when alternating current is supplied to said pri mary winding, as a source of alternating current of a frequency which is a multiple of that supplied to said primary winding.

2. A frequency com'erter comprising a magnetic core, polyphase primary windings and niultipolar secondary windings on said core. said primary windings being unequally distributed and means to produce a nonuniform rotating magnetic iield when polyphase current is supplied to said primary windings.

3. A frequency converter comprising a closed magnetic core, polyphase primary windings on said core, each phase winding having two sections oppositely wound on opposite halves of said core, the number of turns per unit of core length being greatest at the middle point of said core halves. and a secondary winding on said core, the number of poles in said secondary winding being a multiple of the primary poles.

4. In a static frequency transformer having means for producing a rotary magnetic field and windings inductively subjected to the influence of said magnetic field, means for rendering negligible the reactive drop due to currents generated in said windings and a magnetic core associated with said windings and separated therefrom by a nonmagnetic gap.

5. A static frequency converter comprising a primary winding excited by current of a given frequency for producing a rotating non-uniform magnetic field, and a secondary winding associated with said primary winding wound in successively opposed portions whereby an electromotive force of a fre-v quency other than that used in exciting the primary is induced therein by said rotating field.

6. In a static transformer, means for producing a non-uniform magnetic field which rotates, said means comprising a plurality of tapered windings and a magnetic device having a large air-gap associated therewith.

7. The combination of two concentric core members stationary with respect to each other and separated by an air gap, polyphase primary windings on one of said members for producing a rotating magnetic field across said gap, and a secondary winding in the path of said rotating field, the number of poles of said secondary winding being a multiple of the number of poles of the primary winding.

8. In a static frequency transformer, an annular ring, a multi-phase primary winding arranged thereon to produce a rotating field within said ring, a secondary winding associated with said ring and having a plurality of poles across which said rotating field successively sweeps. and a core member within said ring spaced therefrom by a nonmagnetic gap, the numbers of poles of said secondary and primary windings having a multiple relation with each other.

9. In a static frequency converter, means for producing a rotating non-uniform magnetic field comprising a primary winding, anda secondary winding associated therewith, the number of poles on one of said primary or secondary windings having a multiple relation with respect to the number on the other.

In witness whereof, I hereunto subscribe my name this 19thday of September, A. D. 1916.

HUGH M. STOLLER.

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