US1241505A - Multiphase rectifying system. - Google Patents

Description

C. LE G. FORTESCUE. MULTIPHASE RECTIFYING SYSTEM.

APPLICATION FILED MAR. 30, 1914. 1,241,505. I Patented Oct. 2, 1917.

2 SHEETS-SHEET I.

INVENTOR ATTORNEY C. LE G. FORTESCUE.

MULTIPHASE RECTIFYING SYSTEM.

APPLICATION FILED MAR. 30. I914.

Patented Oct. 2, 1917,

2 SHEETS-SHEET 2.

I Be it known that I, CHARLES UNITED STATES PATENT OFFICE.

' CHARLES LE G. FORTESCUE, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOB TO WEST- TNGHOUSE ELECTRIC AND MANUFACTUBDHG- COMPANY, A CORPORATION 01 PENN- SYLVANIA.

MULTIPHASE BECTIFYING SYSTEKL To all whom it may concern:

L G. FonnscUn, subject of the King of Great Britain, and a resident of Pittsburgh, 1n the county of Allegheny and State of Pennsylvania, have invented a new and useful limprovement in, Multiphase Rectlfying Systems, of which the following is a specification. I

My invention relates to systems for the rectification of alternating currents.'

. The object of my invention is the connection of rectifying units in such a manner that they may be used at their highest elliciency to insure a high power factor in the system and a resultant direct current of nearly uniform value... I q By the use of my invention ll am enabled under certain conditions, to place a portion 'of my asymmetric conductors in each of several containers without the necessity of providing separate maintenance for each of said containers. I

Referring to the accompanying drawing, Figure 1 is a diagrammatic View of my sys 'tem as applied to a six-phase star interconnected source of alternating currents which are rectified by means of two three-phase mercury arc rectifiers; Fig. 2 is a wave diagram of the potentials in Fig. 1; Fig. 3 is a diagrammatic view of my system as applied to an interconnected quarter-phase source of alternating currents, the rectification being by asymmetric conductors of the electrolytic type; Fig. 4 is a wave diagram of the potentials in thecircuit of Fig. 3; and Fig. 5 is a diagrammatic view of a modification of the system shown in Fig. 1.

In the rectification of alternating currents, it is frequently desirable to connect the secondaries of a pair of three-phase transformers as shown at 1, 2, 3 and 1, 2 and 3 in Fig. 1. This forms a source of six-phase alternating currents which, when rectified, make'up a practically uniform direct current. For mechanical reasons, it is extremely difiicult to place more than. three anodes of the heavy current type in a single mercury vapor arc rectifier. Accordingly, I have provided two containers 4: and 5, preferably of metal, andhaveplaced therein method of connection which would be fol:

lowed by one who had studied the prior art. wouldbe to connect the two cathodes by a anode 7 in the .same container, the current 110 Specification of Letters Patent.

Patented Oct. 2, 1917.

Application filed larch 30, 1914, Serial No. 828,216

.- bond, thus forming the electricalv equivalent of g a single container having six anodes. The direct current load 15 .would be con:

nected between this bond and the neutral point 16 of the transformer. The diagram of Fig. 2 shows that, under these conditions, current will be flowing from each anode and obtained from each transformer winding for this system of connections would operate to produce a direct current, represented by a line 17, 1 18, 2, l9, 2*, 20, the system would be extremely ineificient in its use of the transformers, since each separate winding is n action for only one-sixth of the time, and it would also have an exceedingly poor pcwer factor. Furthermore, the rectifiers 4 and 5 would not be self-maintaining, as is the case with an ordinary three;phase rectifier, because of the fact that the ripple 17, 18, would fiow in container 5, ripple 18, 19 in container 4, ripple 19, 20 in container 5, etc. Thus, in each container there is an arc during only every other sixth of a cycle, giving ample-opportunityfor the negative electrode reluctance to reestablish itself and necessitating expensive and cumbersome maintaining devices.

l obviate all the above objectionable features of a direct bond between cathodes 12 and 14 by inserting in the connection between these electrodes an inductive winding 24 which may, for the purpom of this case, be considered as an auto-transformer. I connect a direct-current load between an intermediate pointv of this auto-transformer and the neutral point 16 of the alternatmg-current source. The point of connection to winding 24 is preierably themid pointizhereof. The operation'of the system is asiollows: wave 1 will flow from anode 6 and will not be extinguished at int 1'? by the rise of potential of; anode 9 ut will continue to flow until the int 21 is reached, when, because of the potential of flow will be transferred thereto. This feature, that each anode carries current until another anode in the same container comes into action, causes each rectifier to be selfmaintaining. The two ends of auto-transformer 24 will alternate in potential, and the mid point 25 will always assume an intermediate potential which may be plotted as an undulatory line 26, 17, 27 etc., having a maximum potential point slightly less than the maximum potential of the supply. The back electromotive force of the load is shown by a line 28-29.

By the use of the auto-transforming device 24, each transformer winding and each anode is active for one third of each cycle rather than for a sixth thereof, a much better power factor for the system is secured; and the resultant direct-current wave form is as good as, or better than, that derived from a direct bond between cathodes. The auto-transformer 24 may be made extremely compact, since it operates at six times thefrequency of the source, and the difference of potential "across it is only about five per cent-of the voltage of the directcurrent system.

Referring to Figs. 3 and 4; 30, 31, 32., 33 is a quarter-phase interconnected source of alternating currents, having 'a neutral point 34. Comiected to each winding is an asymmetric conductor of the electrolytic type, shown at 35, 36, 37 and 38. Each electrolytic device comprises an aluminum containerwhich is the active electrode and to which is attached the connection from the transformer; and a central electrode of some inactive material, such, for example, as iron or carbon. Asymmetric conductors of this type are so common and well known in the art as to need no further detailed description. Electrolytic devices 35 and 36 have their inactive electrodes connected by a bond 39, and electrolytic devices 37 and 38 have their inactive electrodes connected by a bond 40. Connecting the bonds 39 and 40 is an inductive device 41 corresponding to the auto-transformer 24 in Fig. 1, the intermediate point 42 thereof being connected through a load 66 with the neutral point 34 of the alternating current source.

Referring to Fig. 4, the waves from windings 30 and 32 are represented as 30 and 32, respectively, and those from windings 31 and 33 as 31 and 33, respectively. The back electromotive force of the load is shown by a line 5l52. Without the device 41, wave 31 would cease to deliver current at the oint 44, wave 32 at point 45, etc.; and the directcurrent wave form would be shown by a.

' line 31, 44, 32. 45, etc. With the device 41 use, however, wave 31 will continue to deliver current to the point 49, wave 32 to the point 53, etc. On a pure resistance load, wave 31 will continue to deliver current up to point 57 wave 32 up to point 58, etc. Thus, it is seen that, without device 41, each transformer winding is in use but one-fourth of the time on any type of load; with the device in use and a load having a back electromotive force, each windin is in use between one-fourth and one-hal thetime; and with device 41 and a resistance load, each winding is in use for one-half the time. The resultant wave form on a load of back electromotive force 5152 is shown by a line 43, 59, 44, 60, 45, etc., and on a pure resistance load by a line 43, .62, 44, 63, etc., having ripples of four times the frequency of the source.

The auto transformer may be placed beattached the other terminal of the load 63.

In operation, the two neutral points alternate in polarity to the same extent as do the cathodes in the system of Fig. 1, with resultant variations in the potential difference impressed upon the rectifiers. Inconsequence, each alternating-current wave will flow for one third of a cycle as in the s stem of Fig. 1, rather than for one-sixth of a cycle.

What I claim is:

1. The combination with a source of mu1- tiphase alternating currents provided with a neutral point, of two groups of asymmetric conductors, a connection from each phase of the source to a terminal of one of said asymmetric conductors, all such termi-' na-ls being of like polarity, successive phases being connected alternatively to asymmetric conductors of each group, and all the terminals of the other polarity in each of the groups of asymmetric conductors being in electrical connection with each other, a conductor containing an inductive winding connecting each of said groups of common terminals, and a circuit between an intermediate point of said inductive winding and the neutral point of the source of alternating currents.

2. The combination with a poly hase source of alternating currents provided with a neutral point and having an even number of phases, of two groups of asymmetric conductors, a connection from each of one half of said phases to a terminal of an asymmetric conductor of one of said groups, a connection from each of the remaining phases to a terminal of an asymmetric conductor of the other of said groups, said terminals all beall ing of like polarity, and all the terminals of the other polarity in each group bein in electrical connection, a connection inclu 'ng an impedance device between the common terminals, and a load circuit connecting an intermediate point of the impedance device and the neutral point of the source of alternating currents.

3. The combination with two polyphase sources of alternating currents having the same phase angle anddiflering. from each other in phase by one-half the common phase angle, each of said sources being provided with a neutral point, of two groups of asymmetric conductors, there being as many asymmetric conductors in each group as there are phases in each source, a connection from each phase of one source to a terminal of an asymmetric conductor in one group a connection from each phase of the other source to a terminal of an asetric conductor of the other group, all of said terminals being of the same polarity, all of the teals of the other polarity in each group being in electrical connection, a connection including an impedance device between said common terminals, and a directcurrent load circuit between an intermediate point of the impedance and the neutral points of the two sources. 4

4a The combination with two sources of three-phase alternating currents having a common neutral point and differing from each other by a phase angle of substantially 60, of two three-phase rectifying devices, a connection between each phase of one source and a terminal of one of the rectifying devices, a connection between each phase of the other source and a terminal of the other rectifying device, all of said terminals being of the same polarity, all the terminals of the opposite polarity in each rectifying device bemg in electrical connection, a concurrent load circuit between an intermediate point in said auto-transformer and the common neutral point of the two sources.

5. T he combination with two sources of three-phase alternating currents having a common neutral point and difiering from each other by a phase angle of 60; of two three-phase mercury arc rectifiers, a connection between each phase of one source and an anode of one rectifier, a connection between each phase of the other source and an anode of the other rectifier, a connection between the cathodes of the rectifiers including an auto-transformer, and a direct-current load circuit between the mid point of said auto-transformer and the coon neutral point of the two sources of alternating currents.

6. The combination with two sources of alternating currents having the sal ne phase angle and diflering from each other in phase by one-half the coon phase angle, of two groups of asymmetric conductors, there being as many asymmetric conductors in each group as there are phases in each source, a connection from each phase of one source to a terminal of an aetric conductor or" one group, a connection from each phase of the other source to a terminal of an asymmetric conductor of the other group, all of said terminals being of the same polarity, and means whereby there will be working current flowing in each group of asymmetnic conductors at all times.

In testimony whereof, I have hereunto subscribed myname this 23rd day of March, 1914. 5

CHARLES LE G. FORTESCUE,

Witnesses:

W. M. MCGONAHY, B. B. Hmns.

Images