US1680910A - Earthing choking coil or voltage transformer for high voltages - Google Patents

Description

Aug. 14,l 192s.

ET PFIFFNER EARTHING CHOKNG COIL 0R VOLTAGE TRANSFORMER FOR HIGH VOLTAGES Filed June 9, 1925 2 Sheets-Sheet ,i O l1-Ilm@ 4 ffl'unwm A i211/ u @z2/o@ l Pf ffii/er ?7% Aug.14,192s. y' 1,680,910

E. PFIF'FNER EARTHING CHOKING COIL OR VOLTAGE i'IRANSFORMER I FOR HIGH VOLTAGESlv JIJ ff? el Patented Aug. 14, 1928.

UNITED STATES EMIL PFIFFNEB, OF FRYBOURG, SWITZERLAND.

EARTHING CHOKING COIL OR VOLTAGE TRANSFORMEB FOR HIGH VOLTAGES.

Application led .Tune 9. `19215. Serial No. 85,997.

This invention relates to improvements in earthing choking coils or voltage transformers for high voltages and essentially consists in the particular construction of a compound or cascade transformer, which renders possible not only the carrying-off of continuous current charges of the network, but also the connection of measuring devices, such as voltmeters and output-meters.

One mode of carr ing out the present 1n- Vention is illustrate by way of example on the accompanying sheets of drawings in which Figs. l and 2 show a compound transformer in sectional elevation, the section being taken at 90 degrees with respect to one'another. A

Figs. 3, 4 and 5 illustrate diagrammatically detail views, and t l Fig. 6 shows the magnetization-lines of the individual transformers of which the compound transformer is composed.

Figs. 1 and 2 illustrate a compound or cascade transformer composed of three superposed transformers 1, 2 and 3, each individual transformer being in the shape of a shell transformer provided with cores 4 and yokes 5. The cores 4 as well as the yokes v5 are furnished with adjustable air-gaps 6. The primary windings 7 and the secondary windings 8a, 8", 8c, 8d, 8e and 8f, connected in series are disposed around the cores 4. Further a compensating windin 9, in the form of a longitudinally slotte copper cyl1nder, is located round the core, and an .insulating sleeve 10 is arranged between the said cylinder and the primary and secondary windings. Copper-sheets 11 are arranged b etween the coils of the primary winding 7, 1n order to improve the carrying-off of heat, the copper-sheets extending through the fillin material l2 to the inner wall of the porce ain casing 13. The ends of the coppersheets 11 are turned up, in order to provide a better conduction of heat from the said copper-sheets to the inner wall of the porcelain casing 13. The individual porcelain casings of the compound transformer are connected with each other by means of the armature- rings 14 and 15 cemented to the corresponding porcelain casings and screwed toetlier, the said rings being also employed or electrically connecting the transformers 1, 2 and 2, 3 respectively. A second electric connection is established by means of a platespring 18 cooperating with hoods 16 and 17,

which are cemented centrally to the porcelain casings. The secondary winding 8Z of the transformer 3 is employed for feeding the measuring devices. In order to protect o0 this winding against static charges, the same is connected with a grounded metallic coil member 19 and with the cast-iron support 20 of the transformer. A terminal 22 and an insulated terminal 2l are attached to the o5 in Fig. 4. The winding 25 is a part of the 70 choking coil winding 24, 25 and is connected to the coil 8 of the next transformer. This connection serves for establishing a certain ratio between the field of the choking coil andthe field of the first transformer. Fig.

3l shows an arrangement of the choking coil 2,4Lwithout the compensating coil. Also. this iron core is provided with an adjustable air-gap 27. The choking coil is not embedded in a filling material, but is air insulated andA protected by a metallic hood 28, which carries a supply terminal 29. In order to properly distribute the electrostaticfield outside the transformer, conducting rain covers 30 or tubular rain covers 30 are clamped 85 between the armature- rings 14 and 15.

For the operation as a voltage transformer it is of importance, that in case of an increase or drop of the primary voltage the terminal voltage of the secondary winding always is varied in proportion with the variation of the primary voltage. According to the present invention this condition is satisfied in that the individual transformers are provided with different magnetizationg5 The degree of saturation in the adrf" lines. mission transformer l is greater than in the transformer 2, and in the latter greater than in the transformer 3, this being accomplished by varying the cross-sectional areas of the iron in the individual transformers and by providing adjustable air-gaps in the magnetic circuit of these transformers. The number of air-gaps of a transformer depends on the desired kind of cliaracteristic of this transformer. A comparison between the magnetization-lines of the three transformersis illustrated in Fig. 6 of the drawings. At an ordinary working voltage the decrease of voltage in the first transformer is larger thanin the last transformer owing t0 this distribution of field. In case the primary voltage is increasing the decrease of voltage of this transformer will be more rapid than corresponds to the increase of the primary voltage, in consequence of the smaller saturation of the transformer 3. However owing to the greater primary voltage and the increased charging rate called for by this, the decreases of voltage have also mounted up in consequence of leakage and resistance, and therefore the observation of the correct secondary voltage is rendered possible.

A connection is employed to distribute in the desired manner the primary high voltage to the individual transformers. In the diagrammatic View shown in Fig. 3 two successive transformers 1 and 2, and 2 and 3 respectively are coupled with each other by the coils 8", 8 and 8, 8 respectively. These coils form a part of the' beginning and end of the primary winding 7 of each transformer. The connection of these coils 8, 8, 81 and 8 is such, that the voltages induced in the same yby the alternating field of the transformers are eliminated if the fields are alike, e. g. of the same strength. In case a difference in the fields arises owing to the dissimilarity of the magnetic resistances, a current passes through the said coils, the said current supplying ampereturns to re-establish the field-similarity. But these windings alone and the primary Winding would result in a considerable leakage. In order to avoid this, a compensating winding is arranged within each individual transformer. In Fig. 3, the reference characters 31, 31, 31", 31, 31d and 31 designate these windings of the three transformers. Each compensating winding consists of two coils arranged at the ends of the core. These coils are connected with each other in such a manner, that in case of similarity of the fields at the end of each core no current is passing. A short-circuit current is produced which effects an equaliza tion of field,'in case of dissimilarity in the field of a core, which is caused in consequence of leakage between the said windings 31 and the winding 7. As shown in Fig. 5, a longitudinally slotted solid cylinder 9 of copper may be substituted for the winding 31. This cylinder prevents not only the leakage between the primary winding 7 and ywindings 8, but also the leakage within the primary winding. The copper cylinder, disposed around the core, serves not only as a cover of the core, but also acts as awinding and therefore has to consist of a well conducting material. In case a pulsating magnetic iuX passes through the said cylinder, the tensions produced in the cylinder are eliminated only in case the strength of the magnetic field within the cylinder is alike at all places. In case the field within the cylinder is not alike at all In order to produce satisfactory condiy tions of insulation between the Winding and core, each iron core is brought to the medium potential of the corresponding de-y crease of voltage by means of the connection 32, 32" and 32 attached to the middle of itsprimary winding. The end of the primary winding of the last transformer 3 is grounded. In order to avoid the coil 8', supplying the measuring instrument, from being charged with dangerous voltages by the static induction of the iron core, this coil is wound upon a conducting coil casing, which is connected with the earth connection of the transformer. In front of the first transformer is conductively mounted a choking coil 24 (Fig. 3), which protects the compound transformer against jumping waves. This choking coil is not embedded in insulating material in order that it can be removedl easily in case of defects. choking coil cany be usedl for correcting the transformation ratio and any inaccuraciesof the voltage transformer. For this object the choking coil is provided with adjustable air-gaps in the magnetic circuit and with tapping places 33 (Fig. 4) for attachment to he primary terminal 29. The tension of t e transformer can be reduced by providing the choking coil with a larger number of windings. The tension of the The loir

transformer and thus also of the measuring instrument can be increased by reducing the number of windings of the choking coil. The correct number of windings is determined at the time of Calibrating the transformer by connection to the convenient tapping place of the choking coil winding. The last turns 25 of the choking coil are connected with the first compensation coil 82l of the first transformer for the purpose of magnetic connection or coupling.

1. A voltage transformer comprising in combination a plurality of sections, each section having a magnetic circuit provided with an air gap, a primary winding on each section and a compensating winding on each section connected in series with said primary winding, said compensating winding of each section being connected with the windings of the adjacent sections.

2. A voltage transformer comprising in combination a plurality of sections, each section having a. magnetic circuit provided with an air gap, a primary winding on each section, a compensating winding on each section connected in series with said primar winding, said compensating winding of eac section beingconnected with the windings of adjacent sections.

4. A transformer comprising' in combination, a plurality of sections, each section' having a magnetic circuit provided with an air gap, a plurality of coils in each section I magnetically'connecting said magnetic circuits and a slotted metallic cylinder arranged on the core of each magnetic circuit.

5. A transformer comprising in combination a plurality of sections, each section having a magnetic circuit provided with an' air gap, a plurality ofcoils in each section magnetically connecting said magnetic circuits, a slotted metallic cylinder arranged on the core of each magnetic circuit, a. primary winding on each sectionk and an electric connection between the core of each sectionvand the middle of said primary winding.

6. A transformer comprising in combination a plurality of sections, each section having a magnetic circuit provided 'with an air gap, a plurality of coils in each section magnetically connecting said magnetic circuits a slotted `metallic cylinder arranged on t e.

core of each magnetic circuit, av primary winding on each section, an electric connection between the core of each section and the middle of said winding, a measuring coil onthe last magneticcircuit, and a grounded conductive coil-casing on `which the said' measuring coil is wound. v

7. A voltagev transformer comprising `in combination a plurality of sections, each secs tion having a magnetic circuit provided with an air gap, a primary Winding on eachsec'- tion, a compensating winding onl each sec-- tion connectedin series'with said primar winding, said compensating winding of eac section beingconnected with the windings of the adjacent sections, an electric connection between the core of each section and the yconductive coil-casinv an lair gap, a primary winding on each section, a compensating winding on each section connected in series with said primar windin said compensating winding of eac sectioneing connected with the windings of thev adjacent sections, an electric connection between the core of each section and the middle of said primary winding, a grounded conductive coil-casing on the last section, a measuring coil wound on. said casin a choking coil disposed in front of all o the magnetic circuits and arranged in series therewith, and an adjustable air gap provided in the said choking coil.

A9. A voltage transformer comprising in combination a plurality of sections, each section having a ma etic circuit provided with an air gap, a primary winding on each section, a compensatin winding on each sec tion connected in series with said primar winding, said compensating winding of eac section being connected with the windings `of the adjacent sections, an electric connection between the core of each section andthe middle of said primary winding,a grounded conductive coil-casin on'l the lastsection, a measurin .coil woun on said casing, a choking-coil disposed in front of all of the magnetic'. circuits and arranged in series therewith, an adjustable .air lgap provided in the said choking coil, and a plurality of taps on thewinding of said cholnng coil.

. .10. A transformer comprising in -combination a pluralityof sections, each section having a ma etic circuit ofy different iron cross 'sectiona -area with respect to the other ma etic circuits, an air gap provided in eac' of the said circuits, and a-separate`insulting casing enclosing each magnetic circui In testimony whereof I aix my signature.

EMIL PFIFFNER..

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