US2001454A - Three-phase rectifier transformer - Google Patents

Description

Ma 1 4, 1935. R. L. DAVIS 2,601,454

THREE PHASE RECTIFIER TRANSFORMER Filea June 27, 1955 4 Sheets-Sheet 1 M 3 k le-1040M a? Lo a;

Load

WITNESSES:

INVENTOR v fir Roberf L. Dar/'5 BY W,

IATTZDRNEY May 14, 1935.

WITNESSES R L. DAVIS THREE-PHASE RECTIFIER TRANSFORMER Filed June 27, 1933 4 Sheets-Sheet 2 INVENTOR Haber? L. 00 W5 ATTORN Mayl4, 1935. R. L. DAVIS 2,001,454

THREE-PHASE RECTIFIER TRANSFORMER Filed June 27, 1933 4 Sheets-Sheet 3 mWITNE SES I INVENTOR W Z Robe/"f Dav/'5 Patented May 14, 1935 UNITED STATES PATENT OFFICE 2,001,454 THREE -PHASE RECTIFIER TRANSFORMER Application June 27, 1933, Serial No. 677,839

'1 Claims.

My invention relates to energy-transferring systems and particularly to an arrangement of transformers and rectiflers for supplying a direct current load from a polyphase power source. Various arrangements of transformers and rectifiers have been devised with the intention of minimizing the saturating effect of the direct current on the iron but, heretofore, at least as many transformers were believed necessary as there were phases in the supply line.

I have discovered that by using a T-connection for the transformers, it is possible to use fewer transformers than there are phases and still avoid the saturation of the iron by the effect of the direct current.

in previous arrangements.

It costs less in proportion to the size to build a large transformer than a small one.

Therefore, although the individual transformers must be larger when designed for the T combination, there is a saving in cost on the whole system of approximately 15 to 20%. There is a similar saving in space and weight.

' It is an object of my invention to provide a rectifier system using T-connected transformers and to thereby obtain the advantages outlined above.

It is a further object of my invention to obtain said advantages in a system for translating between a direct-current circuit and a polyphase circuit regardless of which circuit power to the other.

is supplying The advantages which may be obtained by T-connected transformers are to be obtained whether inverters.

the system uses rectifiers or Other objects of my invention and details construction proposed will be evident from the following description and the accompanying drawings, in which:

Figure 1 illustrates one form of my invention, Fig. 2 illustrates a second form of my invention in which two rectifiers are used in connection with each phase,

Fig. 3 illustrates one method for connecting in parallel two units like that illustrated in Fig. 2,

Fig. 4 illustrates a system connecting in series two units like that illustrated in Fig. 2, and

Fig. 5 illustrates an application of my invention to a system providing four-phase from a three-phase source.

rectification In Fig. l, the supply line I is connected to any source of three-phase current, not shown. A transformer primary 2 is connected across two of the line wires and another transformer primary 3 is connected from the remaining line wire to the midpoint of the primary 2. The secondary 4, associated with the primary 2, has its midpoint connected to one terminal of the secondary 5, associated with the primary 3.

Three rectifiers II, I! and I3 are provided, one for each phase. Although these rectiflers may be of any convenient kind, I have chosen for illustration rectifiers equipped with hot cathodes, and cathode heating transformers l4, l5 and I6, one for each rectifier, are energized from the three phases of the line I. It is not necessary that the cathodes be energized in this way, but, if filaments heated by currents act as cathodes, it is desirable although not essential that the heating current be out of phase with the space current and preferably in quadrature therewith. This prolongs the life of the filament.

The anode of the rectifier II is connected to one terminal of the secondary 4 the anode of the rectifier I2 is connected to the other terminal of the secondary 4 and the anode of the rectifier I3 is connected to that terminal of the secondary 5 which is remote from the secondary 4. The several cathodes are connected together by a lead H which constitutes the positive terminal of the system. This is indicated on Fig. 1 by showing the conductor I1 connected to the positive terminal of the direct-current load.

The negative terminal of this load is connected to the neutral point I8 of the transformer system, which ordinarily is two-thirds of the length of the secondary 5 from the end thereof connected to the anode, for the three-phase connection shown. A load terminal connected at an intermediate point of the secondary dividing it in a different ratio may be of use with other systems, for a different number of rectifier phases say.

In the application of my invention illustrated in Fig. 2, the line i and the transformer windings 2 to 5 inclusive are related in the way explained in connection with Fig. 1. For each of the phases, there are a pair of rectifiers instead of the single rectifier illustrated in Fig. l. The cathodes are each heated by its own transformer in order to avoid any unintentional interconnection thereof. Thus, the tubes 2| and 24, similar to the single rectifier ll, shown in Fig. l, have their cathode-heating transformer primaries connected in parallel to one phase of the line I, not the phase connected to the primary 2. The tubes 22 and 25 have their cathodes energized through a pair of transformers having their primaries connected in parallel to another phase of the line and the tubes 23 and 26 have their cathodes energized from two transformers having their primaries connected in parallel to the third phase of the line.

The three rectifiers 2!, 22 and 23 have their cathodes connected together by a common conductor 2'1 and they may, if desired be heated from a single filament transformer instead of the three illustrated. The conductor 27 is connected to the positive terminal of the direct-current load. The three anodes of the rectifiers 24, 25 and 26 are connected together by a conductor 28 and, through a switch if desired, to the negative side of a direct-current load.

Each pair of rectifiers is associated together by a connection from the mid-tap of the cathode heating transformer of one to the anode'ofthe other. Thus, for one phase, a conductor 3! con nects the mid-tap of the cathode heating transformer of the rectifier 24 to the anode of the rectifier i. Similarly, for another phase, a conductor 32 connects the mid-tap of the cathode heating transformer of the rectifier 25 with the anode of the rectifier 22 and for the remaining phase a conductor 33 connects the mid-tap of the cathode heating transformer of the rectifier 26 to the anode of the rectifier 23.

The connections from the several secondary terminals of the plate transformer are to the connections just described which associate the tubes in pairs. The conductor 3i is connected to the lower end of the secondary 4, the conductor to the upper end of said secondary 4, and the conductor 33 to that end of the secondary which is distant from the mid-point of the secondary 4.

The negative end of the direct-current load in this application of my invention is connected to the conductor 28 and so to three anodes. It is not connected immediately to any terminal of the transformer system. The neutral point of the transformer system, namely the point IS in the secondary 5, which is one-third of the length of this secondary from the end connected to the mid point of the secondary 4, can be utilized as a terminal for direct current. The difierence of potential between this point and the cathodes united by the conductor 28 is approximately half as great as the potential difierence between conductors and 28.

A connection between this neutral point and either of said conductors can thus be used as means for supplying direct current at half the potential provided by the whole system. I

In the more usual use of such a rectifier system, there will be two distinct loads, one requiring a greater voltage than the other and I have illustrated this use.

Fig. 3 illustrates a system in which two sets of six rectifiers, each set connected as illustrated in Fig. 2, are connected in parallel. The transformer primaries 2 and 3 are connected to the line I in the same way as in Figs. 1 and 2. Each primary is, however, supplied with two secondaries connected respectfully as explained in connection with Fig. l. The secondary 34, associated with the primary and the secondary 35, associated with the primary 3, are related to the tubes 2| to 26 in the same way as the secondaries 4 and 5 of Fig. 2 are related to the similarly numbered tubes in that figure. The secondaries 54 and 55 associated with primaries 2 and 3 respectively are related to the tubes 4| to 46, inclusive, in a. strictly similar way. The structures in the left-hand part of Fig. 3 analogous to numbered structures in the right-hand part are indicated by reference numerals greater by than those for the struc tures in the right-hand part.

To provide the parallel connections of the sets, the neutral point on the secondary 35 is connected with the neutral point of the secondary 54, this connection including a balance coil 60. The anodes of the rectifiers 24, and 26 are connected together by a common conductor 23 which is connected through a balance coil 6! to a common conductor 48 uniting the anodes of the rcctifiers 44, 45 and 46.

Also, the conductor 21, uniting the cathodes of rectifiers 2|, 22 and 23, is connected to the conductor 41, uniting the cathodes of rectifiers 4|, 42 and 43. The conductor 2|41 constitutes the positive terminal of the system and is illustrated as connected to the positive terminal of a directcurrent load 62. The negative terminal of this load is connected to the mid-point of the balance coil 6!. i A half potential is secured by making a connection 63 from the mid-point of the balance coil Silto the positive end of a direct current load 64 the negative end of which is connected to the mid-point of the balance coil 61. Switches for connecting different loads to the one half on full voltage terminals are illustrated;

In Fig. 4 a similar pair of groups of tubes, six tubes in each group, is shown, the pair of groups being connected in series. Like reference characters in Figs. 3 and 4 indicate analogous structures. 21 of one group of six tubes is connected to'the positive terminal of a direct current load 62. The conductor 23 of the samegroup is not con nected to a balance coil, but is connected to the conductor 41 of the other group, and the conductor 48 of this group is connected to the negative terminal of the direct current load 62. v

Partial voltages are provided by connections to the neutral points and to the lead 284T. Thus from the neutral point of the secondary 54 to the conductor 48 gives a quarter of the full voltage, as illustrated by the connections to load 65, and a connection from the neutral point of the transformer to the conductor 48 will give threequarters of the full voltage as illustrated by the connections to load 66, while a connection between the conductor 2841 and the conductor 48 will give half of the full voltage, as illustrated by the connectionto load 61. Half-voltage could be obtained by connecting the load between the neutral point of secondary 35 and the neutral point of secondary 54, but it is more convenient to have the negative end of the load connected, in each instance to the most negative terminal of the system. This terminal may then be grounded; as shown at 10. v

Switches have been shown for connecting each of these partial potentials to its own load and the full potential to another load. If it is desired to connect one load to any of several difierent potentials, switches for doing so are easily provided.

In the system illustrated in Fig. 5, the primaries 2 and 3 and the secondaries 4 and 5 are related in the way explained in connection with the other figures. The terminals of the secondary 4 are connected respectively to the anodes of two tubes H and 12, the cathodes of which are connected together. The connection 73 of these cathodes is connected to the midpoint of the sec- For the connection in series the conductor ondary 5 and the terminals of this secondary are connected respectively to the anodes of twotubes i4 and 15. The cathodes or the two last-mentioned tubes are connected together and. this connection I6 constitutes the positive terminal for the direct-current circuit. This is illustrated by connecting these cathodes to the positive side of the direct-current load. a The negative side of the direct-current load is connected to the midpoint of the secondary 4.

The cathodes of the four tubes are heated by transformers connected in the way which has already been explained. Since each pair of tubes have their cathodes connected, a single transformer may be used for the two cathodes in each case ii desired. I

In the operation of the device, as illustrated in Figure i, consider the moment at which the secondary 5 is delivering current toward the left. This current flows through the tube l8 and along the conductor H to the positive terminal of the load. It does not pass from the conductor l1 into either tube l I or l2 because the potential is in the wrong direction through these tubes. From the negative terminal of the load, the current returns to the point l8. That portion of the secondary of the transformer 3 between the point 18 in the lefthand terminal is the source of electromotive force for the current just traced.

A third of a cycle later, the right-hand portion of the coil 5 and the lower half of the coil 4 are cooperating, the voltage being the resultant of the change in flux in both cores, which resultant is oblique to the vectors representing the change in either core. The resultant voltage is of substantially the same magnitude as the voltage which was produced by the left-hand portion of the coil 5 at the moment first considered. The current produced by the resultant voltage just described flows through the tube l I to the conductor I! through the load to the point l8 and over the right-hand portion of the coil 5 and the lower portion of the core 4 which portions thus cooperate to provide the electromotive force for this current.

Still later, the effective voltage is provided by the cooperation of the right-hand portion of the coil 5 and the upper portion of the coil 4. At this time the current is through the tube l2 and returns over the conductor l1 and the load to the point l8 and over the right-hand portion of 0011 I8 and the upper portion of coil 4.

The magneto-motive force in the core of the transformer 3-5 is in one direction during the time that the current is over the first of the three paths traced above. During the time when the current is over either of the other two paths, the magneto-motive force in the core of the transformer 3-5 is in the opposite direction. It thus appears that the flux in this core is reversed twice in each cycle. motive force must first overcome the coercive force. The maximum intensity to which the flux rises is, therefore, smaller than it would be if the magneto-motive force were unidirectional and varied only in amount. The saturation effect of the direct current upon the core of the transformer 3-5 is thus minimized.

Similarly, in the core of the transformer 24, the magneto-motive force produced by the direct current is in one direction when the upper half of the coil 4 is delivering current and in the opposite direction when the lower half of the coil 4 is delivering current. The flux, therefore, re-

;verses twice in each cycle and, for the reason al- At each reversal, the magneto readyexplained, the direct current produces less saturation effect than it would if the flux were unidirectional;

In the system illustrated in Fig. 2, when the left-hand portion of the coil 5 is delivering current, the path of this current is through the tube 23 over the conductor 21 to the positive terminal of the load, through the load to the conductor 28 and through one of the tubes 24 and 25 to one or the other terminal of the coil 4 thence through of the coil 4 and from the middle point thereof to part l8 of transformer 3. Through which tube, .24 or 25, the current will pass, depends upon the potential impressed across these tubes. As soon as the potential across the non-conducting one of these tubes exceeds that across the conducting one, the current will shift from one tube to the other. Consider the time in the cycle during which the left-hand part of the coil 5 is delivering current through tube 23 which returns through the tube 24; the return over the wire 3| is to the lower terminal of the coil 4. The voltages induced by the primaries in the lower half of the coil 4 and in the left-hand part of the coil 5 are at this time additively related.

During the time when the upper portion of the coil 4 is delivering current, the current will flow through the tube 22, over the wire 21, and through the load to the wire 28, from whence it will pass through tube 24 or 26, returning either to the lower terminal of the coil 4 or to the lefthand terminal of the coil 5. At one of these two moments, the electromotive force in the two halves of the coil 4 are in additive relation. During the other portion of the time, when the upper half of the coil 4 is delivering current, this half coil and the left-hand part of the coil 5 exert electromotive forces in additive relation.

The reversals of magnetomotive force of the direct current in the coils of the transformers may be explained in this system in the same way as for Fig. 1, and the minimization of the saturation effect results in this system also.

If the load connected to the point H! be considered, during one portion of the cycle the lefthand part of the coil 5 is acting without assistance of any other coil and only one tube is carrying current. During the portion of the cycle during which the lower half of the coil 4 is delivering current, the tube 2| is conducting and the return from the point l8 to the middle of the secondary 4 includes a portion of coil 5. These two sources of electromotive force act to produce a resultant voltage, the phase of which is oblique to the change in flux in either core, as was explained in connection with Fig. 1. The voltage delivered to the load under these circumstances, being produced by a smaller portion of the transformer secondaries, will be of smaller amount than that between conductors 21 and 28.

The application of the foregoing explanations to Fig. 3 should be evident and need not be repeated in detail. The conductor 21 is the positive terminal for the right-hand set of six tubes as explained in connection with Fig. 2 and the negative terminal of the same set of tubes is the conductor 28. In the same way the conductor 41 is the positive terminal and the conductor 48 is the negative terminal for the left-hand set of six tubes. It will be clear that two positive terminals have been connected together and two negative terminals have heen connected together and the load is between these two connections. The balance coil 6| prevents any change in the ratio between the current delivered by one set of tubes and that delivered by the other set. If, for example, the righhhand. set of six tubes were to deliver an increasing current, the flux established in the. right-hand portion ofcoil 6.1 would be increasing. and would produce in the left-hand portion of. coil 6|, an electromotive force tending to oppose this increase. That is, tending to assist the delivery of. current by the left-hand set of six tubes. An increase in current from the one set of tubes will, therefore, be accomplished by an increase in current from the other set, and similarly with a diminution. No change in the ratio between two currents can, therefore, occur.

The neutral point uponthe secondary 54, like the neutral point lain Fig, 2, is a pointof intermediate potential. Similarly, the neutral point on the coil 35. is like the point l8 in Fig. 2. The connection between these two. points, therefore, will serve as the connection between the two positivepoles for.v the use of the systemto supplydi rect current to a direct current load requiring.

half-voltage and the. coil 60 operates, in the way explained in connection with thecoil 6|, to prevent change in the ratio between the two currents supplied to the half voltage load.

In the system shown in Fig. 4, the negative terminal for the left-hand set of six tubes is the.

wire 48 and is connected to ground because it is the most negative portion of the apparatus. Passing from this wire 48 through the left-hand set of six tubes, regarded asa source of electromotive force, we arrive at the wire 41, which, in.

order that the two units may be connected in series, is connected to the negative terminal of the other set of tubes, which is the wire 28. Passing through this set of tubes, regarded as a source of electromotive force, we arrive at the wire 21, which. is, therefore, the most positive point of the wholesystem, andso. is connected to the positive terminal of the direct current load. It is thought that the connections for the smaller differences of potential will be evident from the explanations already given.

The system shown in Fig. produces four phases of potential from thethree-phase source I. Consider that moment in the cycle during which current is being delivered by the lower. half of the secondary 6. This current is through tube H to the midpoint of the secondary 5. It will then travel in that direction which accords with the potential in this secondary at the moment, which we assume, for the purpose. of definite illustration to be toward the left.. The left-hand half of the coil 5 is then additively related to the lower half of the coil 4 andthe current. passes through the second tube i5, arriving at the positive terminal of the direct-current load with a voltage derived from two portions of the secondaries. Similarly, when the lower half of the coil is delivering current and the right-hand half of the coil 5 is ad'ditively related thereto, 'current is through the tube to the middle of coil 5, from the right-hand end thereof to the tube 14 and from this tube to the load. Comparison of these two paths shows that there has been a reversal of flux in the core of the transformer 3-5. If the analysis were repeatedfdr the two remaining quarter-cycles, when the upper portion of the coil 4 is delivering current, it will be.

Since each secondary in this system full-wave rectification, each tube will carry ourrentthrough a. full halfcycle.

It is believed that the application of my invention to inverse-rectifier systems can be made in the light of the foregoing explanation by any skilledelectrical engineer and the connections for such an application need not be discussed.

Many. variations in the application of the principle of. my invention to different circumstances will be apparent to those skilled in the art, and that. only a few cases are specifically described and illustrated is not intended to be construed as a limitation of my invention. No limitation is intended except that required by the prior art or recitedin the accompanying claims.

I claim as my invention:

1. In a system for transferring power between a direct current circuit and a three-phase circuit, means including transformers with primaries T- connected to said three-phase circuit and their secondaries T-connected to at least one threephase rectifier for supplying current from one circuit to the other.

2. In a power supply system, a source of polyphase current, a plurality of groups of transformers and rectifiers, each group including pairs of rectifiers, one pair for each phase, each group having two conductors, one conductor uniting the cathodes of one member of each pair, the other conductor uniting the anodes of the other member of each pair, said two conductors constituting the direct-current terminals of their group, means connected to said conductors for uniting said groups into a cooperative system for delivering direct-current power, the transformers in each of said groups being T-connected and thereby affording neutral points and means connected to said neutral points for cooperating with said first-named means for delivering direct-current power at voltages less than the full voltage of the system.

3; A system for transferring power between an alternating-current line and a direct-current line, comprising means including a plurality of asymmetrically conducting devices for providing a plurality of paths each for direct current of the same average magnitude, said means also including transformers having their primaries con nected into a network and their secondaries connected into another network, one of said net works having winding terminals connected to the alternatingecurrent line, the other network having winding terminals connected to the asymmetrically conducting devices and both networks each having at least one winding terminal connected to a point on another winding of the same network part way between the terminals of said winding.

4'. In combination, a polyphase line, a directcurrent line, and means for transferring power between said lines, said means including a plurality of asymmetrically conducting devices at least as many as there are phases and a plurality of transformers, the primary windings of said transformers being connected into a network and the secondary windings thereof into another network, one of said networks having at least as many winding terminals connected to said polyphase line as there are phases, the other of said networks having at least as many winding terminals connected to asymmetrically conducting devices :as there are phases and each of said networks having at least one winding terminal connected. to another winding of the same network at a point intermediate the terminals of said lastnamed winding.

5. In combination with an alternating-current supply and a neutral connection-point therefor, a pair of rectifiers for'each phase of said supply, one oi. each of said pairs having its cathode and the other of each of said pairs its anode connected to said phase, means for connecting the free anode terminals of the respective rectiflers of said pairs together to one terminal of a load circuit, means for connecting the free cathode terminals of the respective rectifiers of said pairs together to the other terminal of said load circuit, means for connecting one'terminal of a second load to one terminal of said first load, and means for connecting the other terminal of said second load to said neutral connection-point.

6. In combination with a polyphase alternatlng-current supply and a neutral connectionpoint therefor, a pair of rectifiers for each phase of said supply, one of each of said pairs having its cathode and the other of each of said pairs its anode connected to said phase, means for connecting the tree anode terminals of the respective rectifiers of said pairs together to one terminal of a load circuit, means for connecting the free cathode terminals of the respective rectifiers of said pairs together to the other terminal of said load circuit, and a second load having one terminal connected to a terminal of said first load and its other terminal connected to said neutral connection-point.

7. In combination with two rectifier groups, each comprising a polyphase alternating-current supply and means for obtaining a neutral connection-point thereto, and a rectifier for each phase thereof, the rectifiers in each said group having a common junction for their like terminals, a load connected to a said common junction from both of said groups, a connection between the other terminal of said load and said neutral connection-points of both said rectifier groups, one of said two last-named connections being through the midpoint of an impedance which interconnects homologous points in said rectifier groups.

ROBERT L. DAVIS.

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