US2568003A - Switch choke coil - Google Patents

Description

Sept. 18, 1951 HQ HARTMANN SWITCH cHoKE COIL Filed, Feb. 25. 1949 Patented Sept. 18, 1951 2,568,003 SWITCH oHoKE'ooIL Hans Hartmann, Baden, Switzerland, assigner to Aktiengesellschaft Brown, Boveri & Cie, Baden, Switzerland, a joint-stock company Application February 25, 1949, Serial No. 78,436 In Switzerland March 6, 1948 6 Claims. l

This invention relates to so-called switch choke coils employed in high voltage converters and inverters of the mechanical switching type.

'I'he purpose of a switch choke coil is to widen out or prolong the period during which the current through the switch contacts is approximately zero, i. e. to produce a weak current interval of a given time duration, dt, for spark-free `opening of the contacts of a mechanical switch at the end of the current-carrying period of the contacts. An equation for computing the weak current time interval dt is:

where e is the number of turns of the choke coil windings; F is the cross-section of the active iron of the core; U is the direct current voltage; and dB is the changes in induction available according to the magnetization curve.

Good design practice for the iron requires that the iron core of the choke coils be wound as an annular core. The practice has been to form the high voltage winding in a plurality of sections connected in parallel and each suitably dimensioned to carry a part of the choke coil current. The conductor sections were wound by hand on the annular core in the form of disk coils, and this process was exceedingly time-consuming.,A In view of the necessity of subdividing the winding and the diiculty of winding the coil sections, a relatively large space was necessarily provided inside the core. The prior practice therefore yielded a. poor factor of fllling the core opening, and resulted in a large mass of material of poor magnetic characteristics. The relatively great width of the disk coils moreover led to undesired air fields which detrimentally affected the operation of the choke coils.

An object of the invention is to provide switch choke coils for high voltage converter and inverter systems, the windings and cores being of novel design and arrangement to afford compact and highly eicient constructions. More specically, an object is to provide switch choke coils in which the winding consists of tubular conductors in coaxial telescoped arrangement, and the annular iron core is wound upon and carried by the outer conductor.

These and other objects and the advantages of the invention will be apparent from the following specification when taken with the accompanying drawing in which:

Fig. 1 is a fragmentary longitudinal section through a choke coil embodying the invention; and

Fig. 2 is a transverse section on line 2-2 of Fig. 1.

In the drawing, the reference characters ai to as identify a plurality of tubular conductors arranged in two groups of coaxially telescoped conductors, the axes of the two groups being in parallel physical relation and the conductors of the respective groups being electrically connected to each other in alternation by conductor straps b1 to bv to form the single series-circuit winding of the choke coil. Sleeves or strips i of insulation are arranged between the telescoped conductors of each group to provide a rigid mechanical assembly of the several parts of the winding.

The innermost conductor a1 of one group and the outermost conductor as of the other group serve as the terminals of the winding. The conductor a1 is preferably extended through an insulator I carried by the cover C of a tank T, for connection into the external circuit network, but the outer conductor as can not be similarly extended in View of the conductor straps b2, b4 and b. A part of the conductor as could be cut away to clear the conductor straps but preferably, as shown, the connection to the exterior of the tank T is by way of a connecting strap s and a terminal rod or tube t supported in a second insulator bushing I. v

The conductors of each group are preferably stepped or varied in length in order that the connecting straps b1 to bi may be parallel to each "other, Connector b1 joins the lower ends of conductors a1 and a2, and connector b2 connects the upper ends of conductors a2 and a3. In like manner, the remaining connectors are applied to connect the several tubular conductors in series.

Annular cores c1 and c2 are wound directly upon the outer tubular conductors ai and as of the two groups, and the cores assume the potential of the portions of the conductors to which they are applied. Each core may consist of a single sheet of soft iron but preferably, as illustrated, the cores are formed as a plurality of windings of iron bands of relatively small axial length. The total axial length or height of a core is approximately equal to the length of the conductor upon which it is wound. Disks d of insulating material are arranged between the lower ends of the cores c1, .c2 and the adjacent connecting straps b1, and strips i of insulation are preferably arranged transversely between adjacent pairs of connecting straps to space and strengthen the same. The connecting straps may be of any desired type and, as illustrated, are in the form of rectangular plates with spaced circular openings into which the ends of a pair of tubular conductors are snugly tted and soldered or welded.

The lower ends of the innermost conductors a1 and a2 ,extendinto .cylindrical openings in sa cylindrical openings into which,conductorsf,a1.,..az are stepped to permit a circulation-oi 1the., .insu.

lating oil through the tubular conductors `for cooling. The upper end of thevconductorai is provided with transverse openings o to permit this oil circulation when, as illustrated, `the conductor a1 extends to the exterior of the tankY 'I1 The number of concentric tubes of each of theparallelfgroups isin generalequalto the number of turns of the choke coil winding. as this-conditicn locates the.winding terminaison different groups.

The*describedvconstruction has numerpusadyantages over. the priorY switchV ,chokeY coils. The annularcores arewound directly` upon vrtheoutermost conductors andthis construction is par- -ticularlyffavorable with respect tothe quantity of :material required and. to, the ...magnetic char.-

acteristics of the assembly. .An exceedinglyhsatisfactory .iillingniactor .of the .core opening is thus; assuredfwith ,minimum core dimensions, The..optimumutilization.ofthe core opening yresuits in.a..maximumA crossfsectional area F of the .core with. v a minimum mass .orweight of`- the core. '.Thereare no airpathsfortheinagnetic ilux. inparalleb with the. ironipath since the iran corel closely enclosesthe Winding,.and thev space between. .the parallel groups., o,f1coaxial1y tele scoped-conductors .can `be filled..practicallymcpmf pletelylv by iron. thereby vsubstantially .COmpletely excluding', an.- air pathfor the flux. Furthermore, the eddy current losses yare reduced, tmaininimumbythe conductor arrangement.

.'Iheiank Tv isfilled with an insulating oil`not Shownr according ,to` current? practice,: and the insulation i .between telescoped conductorsmay provide longitudinal passages. forl thermosyphonic cooling of the choke coil.

4 fall within the spirit and scope of the invention as set forth in the following claims.

I claim:

1. In a choke coil for use with high current rectilers and inverters with mechanical switching and of the type comprising a multi-turn wind-ing threaded through a.ringform iron core; two groups of coaxially t'elescoped conductors in parallel physical relation, conductor straps connecting the conductors of the respective groups ytogetheruin alternation to form a single seriescircuit winding, and an annular iron core survrounding the outermost conductor of each ..g1'0l.1l3,-

Ai?. In achoke coil, the invention as recited y in claim 1, wherein each core comprises a spiral Itis to be,understood.thatl the, invention is notl :limited to the :particular vconstrnotions herein shown .and described since` variations which. mayv .occur v to ,those `familiar .with the art windngwound directly upon and in electrical contact with the associated conductor.

v3. In a choke coil, the invention as recited in claim 1, wherein the conductors of each group are. stepped as to length, and said ,conductor strapsare. in. parallell physical relation .to each other. Y

l:4.Inpa chokecoil, the invention as, .recited in Iclaim 1, wherein. ,theaxial length of an anriular.v core isapproximately equal to, vthe r length of ythe vcuterinost.,conductor'which itsurrouncls. l. Ina choke ..coil, .the invention asrecited .in claim.`.1,. .wherein.each annular core ycoinp'yriscs aplu rality .of axially, superposed windings". of bands. eachpf] relatively shfrt. axial .,leng'th. y

6. In a choke coil, the-ijnvention1asrecitedin claim 5, wherein each of said core bands is wound directly upon-and in electrical contact with the outermost, ,conductor which it surrounds.

HANSHARTMANN REFERENCES CITED 'The :following referencesare-oi recnrcigm the le of this ,.patent;

UNITED STATES PATENTS

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