US2843816A - Rectifier transformer having means for obtaining forming voltages without additionalwindings - Google Patents

Description

y 1958 D. R. VERNER ET AL 2,843,816

RECTIFIER TRANSFORMER HAVING MEANS FOR OBTAINING FORMING VOLTAGES WITHOUT ADDITIONAL WINDINGS Filed Aug. 2, 1955 2 Sheets-Sheet 1 y 5, 1958 D. R. VERNER ETAL 2,843,816

RECTIFIER TRANSFORMER HAVING MEANS FOR OBTAINING FORMING VOLTAGES WITHOUT ADDITIONAL WINDINGS Filed Aug; 2, 1955 2 Sheets-Sheet 2 HOD 0H0 IF {i 12 I )6 3 /6 I I L3 /6 1? I 4 I w a? i /a.' I15 7:

United States Patent RECTIFIER TRANSFORMER HAVING, MEANS EOR OBTAINING FORMING VOLTAGES WITHOUT ADDITIONAL WINDINGS Dalton R. Verner and Lawrence M. Stoakes, Pittsburgh,

Pa., assignors to Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

Application August z, 1955, Serial No. 525,848

4 Claims. (Cl. 321-8) This invention relates in general to an electric current conversion system having an alternating current circuit, a rectifying transformer, a plurality of electric valves, and a direct current circuit. The invention relates in particular to an improved arrangement of the windings on the rectifier transformer and the connection of the windings to the valves so that the transformer is operable to selectively supply operating voltages to the valves or forming voltages to the valves to simultaneously bake out all the valves.

In electrical current conversion systems which employ ionic valves such as mercury arc rectifiers to translate energy from a supply circuit to aload circuit, means must be provided to supply reduced voltages to the anodes of each valve in addition to supplying normal operating voltages. This is because when the valves are to be initially energized or have been deenergized for a period of time, the reduced voltage is employed to drive off occluded gases in the valve prior to energizing the conversion system with operating voltages. This reduced voltage is often referred to as a forming voltage and the period during which it is applied to the valves is referred to as the bakeout period.

Various transformer winding arrangements have been suggested in the prior art which are operable to selectively supply either normal operating voltage or forming voltage to the anodes of the valve. However, these prior art-transformer arrangements are expensive to build because of their construction and usually have one or more disadvantages in operation. In some instances the windings of the transformers are tapped to provide the two different volt'ages. Such a winding is more difficult and more expensive to build than a winding without taps. Several other suggested arrangements involve altering the taps .on one or the other of the windings of the transformer to provide the forming voltage. In other instances extra windings are provided on the transformer which operate solely during the baking out period.

It has been found that the disadvantages of the systems embodying the teachings of the prior art may be avoided by the present invention. The present invention provides a winding arrangement for the transformer in which groups of windings may be selectively connected in one manner to supply normal operating voltage to the anodes of the valves, or connected in another manner to supply forming voltages simultaneously to all the anodes to simultaneously bake out all the valves.

It is therefore an object of the present invention to provide in an electrical conversion system employing ionic valves, an improved transformer winding arrangement for selectively supplying operating voltages to the valves or .for supplying forming voltages to the valves to simultaneously bake them out.

Another object of the present invention is to provide in a current conversion system including an alternating cur rent circuit and a plurality of ionic valves, an improved transformer winding arrangement for connecting the anodes of the valves to the supply circuit to supply either operating or forming voltages to the valves without the ice direct current of the conversion system affecting the per formance of the rectifier transformer.

A further object of the present invention is to provide a rectifying transformer having windings which do not require taps in order to selectively supply both operating and forming voltages to ionic valves in a current conversion system.

A still further object of the present invention is to provide in a Current conversion system a rectifying transformer having windings which are used to supply both operating voltages and forming voltages to the ionic valves. v

Objects and advantages other than those mentioned above will be apparent from the following description when read in connection with drawings in which:

Fig. l is a diagrammatic view of the current conversion system embodying the improved transformer connected to supply forming voltages to the valves;

Fig. 2 is a diagrammatic view similar to that shown in Fig. 1 with the transformer arrangement connected to supply operating voltages to the valves; and

Fig. 3 is a schematic illustration of the transformer shown in Fig. 1.

Referring to the drawings, the system illustrated in Fig. 1 comprises generally an alternating current supply circuit 11, a direct current load circuit 12, a plurality of electric valves 13, and the improved rectifying transformer 14 for connecting the anodes 16 of the valves 13 to the A. C. supply circuit 11.

Each ionic valve 13 comprises an anode 16, a cathode of the self-reconstructing type such as a mercury pool cathode 17, and a grid member 18. Inasmuch as the grid voltage supply circuit forms no part of the present invention and since any of the various grid voltage supply circuits suggested in the prior art may be used, a discussion and a showing of that portion of the rectifying sys tem has been omitted.

The transformer winding arrangement as shown comprises a three phase core, three primary windings and twelve separate but related secondary windings. The primary and secondary windings of the transformer are represented by lines whose lengths and directions correspond to the magnitude and phases of the voltages in them according to the usual convention. The three primary windirigs 21 of the transformer as shown are conne ted in delta to the three phase alternating supply circuit 11 but if desired the primary windings may be connected in star to supply circuit 11. The secondary windings are connected in a double star arrangement to the valves 13. The neutrals of the double star arrangement are connected to opposite ends of an interphase transformer having a midtap connected to one conductor of the load circuit 12. The cathodes 17 of all the valves are connected to a cominon bus which in turn is connected to the other conductor of the load circuit.

The three phases of the transformer winding arrangement are similar so only one is described in detail. Each phase'comprises a primary winding 21, a first group of windings 22 and a second group of windings 23 which are disposed electrically degrees from the first group. Each group of windings comprises a main winding designated by reference character a and an auxiliary winding designated by reference character b, the main windings a of each group having a like number of turns and the auxiliary windings b of each group a like number of turns. However, the number of turns for the auxiliary windings b are less than those of the main windings a. The first groups of secondary windings are disposed to define one of the star arrangements by connecting the first ends 26 of the main windings 22a to the neutral point of that star. The second groups of secondary windings are similarly disposed to define the other star arrangement by connecting the first ends 27 of the main windings 23a to the neutral point of that star.

The transformer arrangement also includes means for connecting the four secondary windings of each phase of the transformer so that the secondary windings may selectively supply both forming and operating voltages to the anodes of the valves associated with their respective phases.

The means for connecting the four secondary windings of each of the three phases to their associate valves is similar and a detailed description with respect to one phase is considered suflicient. One end 29 of each auxiliary winding is connected to a diflierent valve 13 associated with that phase. As shown, the means for interconnecting the ends of the main and auxiliary windings between the two associated valves and the respective neutrals of the star arrangements comprises a switch 36 having four contacts and a pair of bridging members adapted to bridge separate pairs of contacts. The contacts of the switch are arranged so that the main winding 22a and the auxiliary winding 22b may be connected together in substractive series relationship and also so that the main and auxiliary winding 23a and 23b may be connected together in subtractive series relationship to cause separate forming voltages displaced 180 degrees from each other to be supplied simultaneously to the two valves 13 associated with that phase of the system.

As shown, this is accomplished by connecting the second ends 37 of the two windings 22a and 22b to contacts 38 of the switch 36 which may be connected together by a bridging member 39. Likewise, the second ends 42 of the two windings 23a and 23b are connected to contacts 41 on the switch 36 which may be connected together by a second bridging member 43.

The secondary windings associated with the remaining two phases of the system are similarly connected to like switches so that with the switches 36 in the position as shown in Fig. l, the system is in condition when energized to simultaneously supply forming voltages to all the anodes to bake out all the valves at the same time.

After the required bakeout period the switches 36 may be moved to another position as shown in Fig. 2 to supply normal operating voltages to the valves.

For example, as shown in Fig. 2 the bridging members 39 and 43 of each switch may be positioned to bridge a pair of contacts different from those used for the forming voltages so that for each phase the main winding a of each group is connected in additive series circuit with the auxiliary winding b of a different group. As shown in Fig. 2 the bridging member 39 is in position to bridge contacts 38 and 41 which connect the second end 37 of the main winding 22a of the first group to the second end 42 of the auxiliary winding 23b of the second group causing these windings to be in additive series circuit to supply normal operating voltage to the anode of one of the valves 13 associated with that phase. Similarly, the other bridging member 43 is positioned to bridge contacts 38 and 41 which connect the second end 42 of the main winding 23a of the second group to the second end 37 of the auxiliary winding 22b of the first group causing these windings to be in additive series relationship to supply a normal operating voltage to the anode of the other valve associated with that phase.

It will be seen that with the improved transformer, forming voltages and operating voltages are selectively supplied to the valves by merely moving a switch from one position to another. The need for tapped windings is eliminated resulting in considerable saving of time and labor in manufacturing the transformer. Also, the bakeout period is considerably reduced in that forming voltages are supplied simultaneously to all the valves.

While the preferred embodiment of the present invention is shown having four position dial type switches associated with each phase, it will be readily seen by those skilled in the art that other type switches may be employed to etfect the results obtained by the dial switches without changing the operation of the system.

It will also be seen by referring to Fig. 3 that the windings are arranged on the transformer core so that the direct current of the conversion system does not affect the operation of the rectifier transformer. As shown in Fig. 3, the primary winding 21 and the four secondary windings 22a, 22b, 23a and 23b associated with the primary winding 21 are disposed on a single winding leg 50 of core 57 and the windings of the other two phases are similarly disposed on the remaining two legs 52 and 53 of the core. With the windings so arranged on the core the current in the load circuit does not affect the operation of the transformer.

While only one embodiment of the present invention has been illustrated and described it will be apparent to those skilled in the art that modifications may be made therein without departing from the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. An electric current conversion system comprising an alternating current circuit, a direct current circuit, a plurality of ionic valves, three phase transformer means comprising three primary windings connected to said alternating current circuit and secondary windings connected in double star arrangement to said valves to selectively supply operating and forming voltages to said valves, each phase of said transformer means comprising one of said primary windings, four of said secondary windings inductively related to said one primary winding, and switch means, said four secondary windings comprising first and second groups of windings displaced electrically degrees with respect to each other, each said group of windings comprising a main winding and an auxiliary winding having fewer number of turns than said main winding, a first end of each of said main windings connected to the neutral of a different star of said double star arrangement, a first end of each of said auxiliary windings connected to separate ones of said plurality of valves, and means connecting the second ends of said windings in said first and second groups to said switch means to cause said switch in one position to connect said main and auxiliary windings of different groups in additive series relationship to supply operating voltages to said separate valves, and to cause said switch in a second position to connect the main and auxiliary windings of the same group in subtractive series relationship to supply forming voltages simultaneously to said separate valves.

2. An electric current conversion system comprising an alternating current supply circuit, a direct current load circuit, a plurality of ionic valves, three phase transformer means connected in delta to double star arrangement between said supply circuit and said valves to selectively supply operating and forming voltages to said valves, each phase of said transformer means comprising a primary winding, four secondary windings inductively related to said primary winding, and switch means comprising four contacts and a pair of bridging members operable to bridge different pairs of said contacts, said four secondary windings comprising first and second groups of windings displaced electrically 180 degrees with respect to each other, each said group of windings comprising a main winding and an auxiliary winding having fewer number of turns than said main winding, a first end of each of said main windings connected to the neutral of a different star of said delta to double star arrangement, a first end of each of said auxiliary windings connected to separate ones of said plurality of valves, means connecting the second ends of said windings in said first and second groups to different ones of said contacts, said bridging members being operable to cause said switch in one position to connect said main and auxiliary windings of different groups in additive series relationship to supply operating voltages to said separate valves, and to cause said switch in a second position to connect the main and auxiliary windings of the same group in subtractive series relationship to supply forming voltages simultaneously to said separate valves.

3. An electric current conversion system comprising an alternating current supply circuit, a direct current load circuit, a plurality of mercury arc rectifiers, three phase transformer means connected to delta to double star arrangement between said supply circuit and said rectifiers to selectively supply operating and forming voltages to said rectifiers, each phase of said transformer means comprising a primary winding, four secondary windings inductively related to said primary Winding, and switch means comprising four contacts and a pair of bridging members arranged to bridge different pairs of said contacts, said four secondary windings comprising first and second groups of windings displaced electrically 180 degrees with respect to each other, each said group of windings comprising a main winding and an auxiliary winding having fewer number of turns than said main winding, 21 first end of each of said main windings connected to the neutral of a difierent star of said delta to double star arrangement, a first end of each of said auxiliary windings connected to separate ones of said plurality of rectifiers, means connecting the second ends of said windings in said first and second groups to different ones of said contacts, said bridging members being operable to cause said switch in one position to connect said main and auxiliary windings of difierent groups in additive series relationship to supply operating voltages to said separate rectifiers, and to cause said switch in a second position to connect the main and auxiliary windings of the same group in subtractive series relationship to supply forming voltages simultaneously to said separate rectifiers.

4. In combination a three phase rectifying transformer having its windings arranged to be connected in a delta to double star between an alternating current circuit and a plurality of mercury arc rectifiers, each phase of said transformer comprising a primary winding and four secondary windings inductively related to said primary winding, said four secondary windings defining first and second groups of windings displaced electrically degrees with respect to each other, each said group of windings comprising a main winding and an auxiliary winding having fewer number of turns than said main winding, a first end of each said main winding connected to a neutral of a different star of said delta to double star arrangement, a first end of each said auxiliary winding connected to separate ones of said rectifiers, and switch means comprising a first pair of contacts connected to the second ends of said main windings, a second pair of contacts connected to the second ends of said auxiliary windings, and a pair of bridging members, said bridging members in a first position of said switch arranged with respect to said pairs of contacts to connect said main winding of said first group to said auxiliary winding of said second group in additive series relationship, and said main winding of said second group to said auxiliary winding of said first group in additive series relationship, and in a second position of said switch arranged with respect to said pair of contacts to connect said windings of said first group in subtractive series relationship and said wind ings of said second group in subtractive series relationship.

References Cited in the file of this patent UNITED STATES PATENTS 1,804,614 Hill May 12, 1931 1,912,151 Leuthold May 30, 1933 2,206,701 Klemperer July 2, 1940

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