US2539786A - Rectifying system - Google Patents

Description

Jan.- 30, 1951 A. Lyssa/IAN 2,539,786

' RECTIFYING SYTEM Filed May 27, 1946 POWER SUPPLY VOLTAGES COMMUTAT & N 6

V0 LTAG ES Patented Jan. 30, 1951 RECTIFYING SYSTEM Marcel A. Lissman, Cambridge. Mass., assignor to Raytheon Manufacturing Company, Newton, Mass, a corporation of Delaware Application May 27, 1946, Serial No. 672,468

2 Claims.

This invention relates to rectifying systems for multi-phase, alternating-current power supplies, and more particularly to rectifying systems of the general character indicated which include gridcontrolled, gaseous-discharge tubes, commonly known as thyratrons.

An object of the present invention is to provide such rectifying systems with simple and efficient means for obtaining a continuously variable output voltage.

Another object of the present invention is to provide such rectifying systems with means for protecting the same against possible .damage by the inverse voltages of the power supply.

These and other objects of the present invention, which will become more apparent as the detailed description thereof progresses, are attained, briefly, in the following manner:

The system contemplates the provision of a plurality of gaseous-discharge tubes each of which includes a cathode, an anode, and a control grid, said tubes having their anode-cathode and grid-cathode circuits so connected, in phase opposition, to a multi-phase, alternating-current power supply to be rectified as to be initially non-conducting. A load impedance is connected in series with the potential difierence applied between the anodes and cathodes of said gaseousdischarge tubes, and means are provided for shifting the initial phase of the potential difierence applied between the control grids and cathodes of said tubes, whereby said tubes become successively conducting, each for a time interval, the duration of which is a function of the magnitude of said phase shift. The conducting state of each of said gaseous-discharge tubes causes a current to flow through said load impedance. and the average potential developed across said load impedance is a function of the duration of said time interval. Thus, by adjusting the magnitude of said phase shift, the magnitude of the output voltage can be controlled between zero and the maximum of which the system is capable.

The system also contemplates the provision of a second group of gaseous-discharge tubes, each of which includes a cathode and an anode, this second group of tubes being connected, respectively, in series with the tubes of the first abovementioned group. The arrangement is such that the anodes of said first-named gaseous-discharge tu es. c n n v r so s neg tiv with respect o their corresponding cathodes as to subject said tubes to damaging inverse voltages.

In the accompanying specification there shall be described, and in the annexed drawings shown,

an illustrative embodiment of the rectifying system of the present invention. It is, however, to be clearly understood that the present invention is not to be limited to the details herein shown and described for purposes of illustration only, inasmuch as changes therein may be made without the exercise of invention, and within the true spirit and scope of the claims hereto appended.

In said drawing, Fig. l is a circuit diagram of a rectifying system assembled in accordance with the principles of the present invention; and

Fig. 2 shows the relationships between the various voltages applied to the system from the power supply.

Referring now more in detail to the aforesaid illustrative embodiment of the present invention, with particular reference to Fig. 1 of the drawing, the numerals i5, H and I2 generally designate gaseous-discharge tubes, known a thyratrons, and including, respectively, cathodes l3, l4 and I5, anodes l6, l1 and I8, and control grids I9, 20 and 2|.

The anodes I6, I? and I8 of said tubes I0, II and I2 are connected, respectively. to the outer terminals of secondary windings 22, 23 and 24 of a multi-phase power transformer 25, the inner terminals of said windings being connected together and constituting a neutral reference point 25.

Said transformer 25 additionally includes primary windings 21, 2B and 29 connected to lines 30, 3| and 32 of a three-phase, alternating-current, commercial power source, and another group of secondary windings 33, 34 and 35 connected together at their inner terminals, as at a neutral reference point 355, said first and secondnamed secondary windings being so disposed with respect to each other that the voltages developed thereacross are in phase opposition.

The anodes l6, ii and [8 of the tubes H], H and I2 are also connected, respectively, to cathodes 31, 38 and 39 of additional gaseous-discharge tubes 45, i! and 42, said last-named tubes including anodes d3, 44 and 45 connected to ground, as at 46, and, through a load resistor 41, lay-passed by a capacitor 58, to the cathodes l3, l4 and 15, of said first-named gaseous-discharge tubes.

Said cathodes I3, I41 and i5 of said tubes III, II and 12 are also connected, through a bias resistor 49, by-passed by a capacitor 50, to the neutral point 35 of the second above-mentioned secondary windings 33, 34 and 35, and, through contacts 5| and 52 of a ganged switch 53, and a resistor 54 and relay 55, to ground, as at 56. The

3 r eglay 55 controls contacts in the lines 30, an and I) The outer terminals of the secondary windings 33, 3d and 35 are connected, respectively, through resistors 57, 50 and 59, to one of the end terminals 50, 65 and 62 of potentio-meters 63, 05 and t5, the remaining end terminals 65, 6? and 68 of said potentiometers being connected respectively, through resistors 59, i and H, to the outer terminals of the secondary windings 34, 35 and 33. The resistance between the end terminals of each of the potentiometers 63, 64 and is centertapped, respectively, as at l2, l3 and M, whereby said potentiometers comprise, respectively, pairs of resistors l5 and '16, TI and i8, and 19 and 00. The center taps l2, l3 and M are connected, respectively, to the outer terminals of the secondary windings 35, 33 and 34. V

By means of the potent ometer connections just described, two phases of the power su ply are applied to each potentiometer, and, as will hereinafter be further described, phase shifts of up to substantially 240 may be obtained.

The potentiometers 63, 64 and 65 include, respectively, adjustable arms 8!, 82 and 83 which are ganged together, as indicated by the broken lines, and said adjustable arms are connected, respectively, through pairs of series-connected resistors 051 and 05, 85 and 81, and 88 and 89, to the control grids I9, 20 and 2! of the gaseousdischarge tubes 50, l l and H2. The junctions between the pairs of series-connected resistors just described are connected, respectively, to contacts 90, st and 92 included in the switch 53. Additional contacts 03, 94 and 05, cooperable, respect vely, with the contacts 90, 9! and 92, are connected, respectively, to the end terminals 50, 6! and 62 of the potentiometers 53, 54 and 65.

The grids i0, 20 and 2! of the tubes l0, H and i2 are also c nnected, respectively, through capacitors 96, 91 and 98, to the cathodes I3, M- and lliof said tubes.

This completes the descr t on of the aforesaid illustrative embodiment of the invention and the mode of operation thereof will now be described, for which purpose reference is made to Fig 2 of the drawing as well as to Fig. l.

. In said Fig. 2 of the drawing, there are shown three main voltages A, B, and C corresponding,

to the three phases, spaced 120 apart, of the. commerc al power lines 30, 3! and 32, and three commutating voltages A, B and C, likew se spaced 120 apart, but in phase opposition, respectivelv, to said voltages A, B and C.

It will be assumed, for the purposes of this s ecification, that the main voltages A, B and C, which appear across the secondarv windings 22, 23 and 24, have a peak value of about 5,000 volts, and that the commutating voltages A, B and C, which a pear across the secondary windings 33, 3d and 35, have a peak value of about 150 volts.

Consider the time 251, at which the main voltage A is somewhat greater than one-half its positive peak, for example, 2,550 volts; the main voltage B is somewhat less than its negative peak, for example, 4,950 volts; and the main voltage C is somewhat less than one-half its positive peak, for example 2,450 volts, all with respect to the neutral reference point 26. At the same time, the commutating voltage A is somewhat greater than one-half its negative peak, for example, 130

volts, all with respect to the neutral reference point 36,

Under these circumstances, the cathode 3'! of the gaseous-discharge tube 40 will be positive with respect to the anode 03 of said tube, and said tube will be non-conducting. The cathode 39 of the gaseous-discharge tube 32 will be positive with respect to the anode 5 of said tube, and said tube will also be non-conducting. However, the cathode 38 of the gaseous-discharge tube ii will be negative with respect to the anode M of said tube, and said tube will be conducting.

Hence, there appears upon the anode E0 of the gaseous-discharge tube ill a voltage which is 7,500 volts positive (the sum of voltages across the windings 22 and 23) with respect to the oathode iii of said tube, and the latter, if it were not for the fact that the instantaneous voltage on its control grid it? was 130 volts negative with respect to its cathode it, would be conducting.

There appears upon the anode iii of the gaseous-discharge tube l2 a voltage which is 7,400

' volts positive (the sum of the voltages across the windings 23 and 2:3) with respect to the cathode 55 of said tube. but the control grid 2d of. the latter is 120 volts negative with respect to the oath ode 5, and therefore, said tube, too, is non-con n ducting.

' ter is non-conducting, even though its control volts: the commutating voltage B is somewhat.

l ss than its positive peak, for example, 145 'voltsj grid 20 is 145 volts positive with respect to its cathode l4.

Thus, at the time t1, none of the gaseous-discharge tubes :10, ii and i 2 is conducting, and consideration of the voltage relationships at any time within the 360 illustrated in Fig. 2 of the drawing will reveal the same non-conducting conditions, these conditions obtaining as long as the commutating voltages A. B and C are maintained 180 out of phase with the main voltages A, B and C. The potentiometers 63, M and 65, and the var-- ious re istors between sa d potentiometers and the ga eous-d charge tubes In, H and i2 and the secondary wind ngs and 35, preferably, are of such values that when the adjustable arms at. 82 and 83 of said potentiometers are in their extreme counter-clockwise positions, the out-ofphase relation h ps above referred to exists.

Now, assume that the adjustable arms 0!, 02 and 83 of the potentiometers E3. 6 and 65 are moved, in a clockwise d rection. to advance the pha e of the commutating voltages, each, Further assume that the commutating voltages are now represented by the sine waves A, B

and C" in Fig. 2 of the drawing, and consider the time t2.

At said time 152. the main voltage A is at its po itive peak, 5.000 volts: and the main voltages B and C are each at one-half their negative peak, 2,500 volts, the former becoming less negative, and the latter becoming more negative. At the same instant. the commutating voltage A is zero, but starting on its positive alternation; the" commutating voltage B" is somewhat less than its negative peak. for example, volts; and' the commutating voltage C is somewhat less than po itive peak, for example, '145 volts.

Under these circumstances, the cathode s! or the gaseous-discharge tube 40 is positive -with respect to the anode 33 of said tube, and said tube will be non-conducting. The cathode 3B of the gaseous-discharge tube M will, until the point of the cross-over between the main voltages B and C is reached, be negative with respect to the anode M of said tube, and until said cross-over point is reached, said tube will be conducting. As soon as said cross-over point is passed, the cathode 3g of the tube 4! will be positive with respect to the anode 4c of said tube, and said tube will no longer conduct. The cathode 39 of the gaseous-discharge tube 42 will, until the above-referred to cross-over point is reached, be positive with respect to the anode A5 of said tube, and until said cross-over point is reached, said tube will be non-conducting. As soon as said cross-over point is passed, the cathode 39 of the tube 42 will be negative with respect to the anode 45 of said tube, and said tube will begin to conduct.

Hence, there appears upon the anode 15 of the gaseous-discharge tube It! a voltage which is '7 500 volts po itive (the sum of the voltages across the windings 22 and 24) with respect to the oathode [3 of said tube, and inasmuch as the commutating voltage A is, at the instant under consideration, going positive, said tube ID will begin to conduct.

Now, during the periods that no one of the tubes il I! and i2 is conducting, the potential of the cathodes 13, M and 15 of said tubes follows the lower envelope of the voltages A, B and C, but as soon as any one of said tubes becomes conducting, said cathodes attain a potential equal to the potential of the anode of the instantaneously conducting tube minus the small drop wi hin said conducting tube itself.

Therefore, as soon as the tube ll) becomes conducting as aforesaid, there appears upon the anode i! of the gaseous-discharge tube H a voltage which is somewhat less than 7,504 volts negative with respect to the cathode M of said tube i l, and said tube will not conduct. Actually, the control grid 28 of said tube I! is, at this instant, about 145 volts negatve with respect to the cathode H thereof.

There appears upon the anode !8 of the gaseons-discharge tube [2 a voltage which is, at the instant under consideration. somewhat more than 7,590 volts negative with respect to the cathode 15 of said tube, and therefore, even though the control grid 2i of said tube is about 145 volts positive with re pect to said cathode 55, said tube 52 will not conduct.

Now, once the tube H] is conducting, it will continue to conduct until its anode potential goes negative with respect to its cathode. This would not occur until time 253 were reached if it were not for the capacitor 48. The residual voltage across said capacitor 48 causes this to occur, actually, at some short time before the time is.

At that time, the anode and control grid volttages of the gaseous-discharge tube i I will be the same as the anode and control grid voltages of gaseous-discharge tube ll! were at the time t2. Therefore, the tube I! will start to conduct, the cathodes l3, :4 and 15 will jump almost to the tial of the anode ll of said tube H, and in 3h this potential is positive with respect to anode Hi of the tube 55, the latter will cease conducting.

i. he same sort of commutation will occur shortly before time 154, when the gaseous-discharge tube if: will start to conduct and the gaseous-discharge tube it will stop conducting.

As each tube !0, II and i2 conducts, current will flow through the load resistor 41, said current producing the output voltage of the system.

With a phase shift of such as has been under consideration in the foregoing description, tubes i9, 5 I and 12 will conduct for the periods indicated by the shaded portions, respectively, from left to right, superimposed on the sine waves A, B and C. As indicated in earlier portions of this specification, the magnitude of the phase shift introduced by adjustment of the ganged potentiometer arms 8!, 32 and 83 will control the duration of the conducting intervals of the tubes H3, Ii and I2, and, in turn, the duration of said time intervals will control the average output voltage developed across the load resistor 48.

The ganged switch 53 enables the output voltage to be tuned. on and off without regard to the magnitude thereof, and the relay 55 is utilized to automatically open the power lines in the event said switch 53, when closed, fails to reduce the output voltage substantially to zero.

This completes the description of the mode of operation of the aforesaid illustrative embodiment of the present invention.

It will be noted from all of the foregoing that the present invention provides a rectifying system for a multi-phase, alternating-current power supply, especially, a rectifying system which includes thyratrons, in which there is incorporated a simple and efficient means for obtaining continuously variable output voltage. It will further be noted that the rectifying system of the present invention is so designed as to prevent the same from being damaged by excessive inverse voltages of the power supply.

Other objects and advantages of the present invention will readily occur to those skilled in the art to which the same relates.

What is claimed is:

l. A rectifying system for a multi-phase, altermating-current power supply comprising: a plurality of gaseous-discharge tubes each of which includes a cathode, an anode, and a control grid; a plurality of additional gaseous-discharge tubes each of which includes a cathode and an anode; said first and second-named gaseous-discharge tubes being connected, respectively, in series with each other; means adapted to be energized from said power supply, for applying such potential differences between the anodes and cathodes, and the control grids and cathodes of said first-named gaseous-discharge tubes, and between the anodes and cathodes of said second-named gaseous-discharge tubes as to maintain said first-named tubes initially non-conducting; a load impedance connected across said series-connected, first and second-named gaseous-discharge tubes; resistance networks connected in series with the potential difference applied between the control grids and cathodes of said first-named gaseous-discharge tubes, for so shifting the phase of said potential difference as to render said gaseous-discharge tubes successively conducting, each for a time interval which is a function of the magnitude of said phase shift; and means across which control-grid rectification develops a bias sufficient to maintain all but one of said first-named gaseous-discharge tubes. non-conducting; the current flowing as a result of the conducting state of each of said first-named gaseous-discharge "ubes developing an average potential across said load impedance the magnitude of which is a function of the duration of said time interval.

2. A rectifying system for a multi-phase, alterhating-current power supply comprising: a plurality of gaseous-discharge tubes each of which includes a cathode, an anode, and a control grid; a plurality of additional gaseous-discharge tubes each of which includes a cathode and an anode; said first and second-named gaseous-discharge tubes being connected, respectively, in series with each other; means, adapted to be energized from said power supply, for applying such potential differences between the anodes and cathodes, and the control grids and cathodes of said firstnamed gaseous-discharge tubes, and between the anodes and cathodes of said second-named gasecue-discharge tubes as to maintain said firstnarned tubes initially non-conducting; a load impedance connected across said series-connected, first and second-named gaseous-discharge tubes; resistance networks connected in series with the potential diiference applied between the control grids and cathodes of said first-named gaseousdischarge tubes, for so shifting the phase of said potential difference as to render said gaseousdischarge tubes successively conducting, each for a time interval which is a function of the magnitude of said phase shift; and a resistance capacitance network across which control-grid REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,829,254 Asch Oct. 27, 1931 1,874,840 Williamson Aug. 30, 1932 2,037,567 Ehrensperger et al. Apr. 14:, 1936 2,085,940 Armstrong July 6, 1937 2,093,329 Lord Sept. 14, 1937 2,103,996 Bedford Dec. 28, 1937 2,137,126 Bedford Nov. 15, 1938 2,288,338 Willis June 30, 1942

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