US2535499A

US2535499A - Control system for ignitron tubes

Info

Publication number: US2535499A
Application number: US101992A
Authority: US
Inventors: George J Lexa
Original assignee: Cutler Hammer Inc
Current assignee: Cutler Hammer Inc
Priority date: 1949-06-29
Filing date: 1949-06-29
Publication date: 1950-12-26
Anticipated expiration: 1967-12-26

Description

Dec. 26, 1950 G, J. ,LEXA 2,535,499

' CONTROL SYSTEM FORIGNITRON TUBES Filed June 29,1949

If 1 p T lo Patented Dec. 26, 1950 i 2,535,499 CONTROL SYSTEM FOR IGNITRON TUBES George J. Lexa, Wauwatosa, Wis., assignor to Cutler-Hammer, Inc., Milwaukee, Wis., a, corporation of Delaware Application June 29, 1949, Serial No. 101,992

5 Claims.

, This invention relates to a control system for ignitron tubes.

In certain control systems for ignitron tubes, the ignition voltage for energizing the ignition electrode thereof is supplied by energy stored in a capacitor. The capacitor is charged with alternating voltage through a rectifier from a source of alternating current and the energy stored therein is discharged through the ignition electrode and cathode of the ignitron to initiate its conduction. Charging of the capacitor is usually effected during non-conducting periods of the ignitrons and discharged during the conducting periods thereof. In certain applications of ignitrons the moment of initiation of conduction thereof will vary widely. Under certain load conditions it is necessary tc initiate conduction of the ignitrons just prior to the end of the conducting half cycles of voltage impressed on said ignitron, whereas under extreme load conr ditions, the ignitron is made conducting at, or just after the beginning, of the conducting half cycles of voltage impressed theeron. Regardless of the condition of loading the capacitor supplying the ignition energy is charged to a potential such that it will discharge during substan-' tially the entire conducting half cycle of voltage impressed on said ignitron. Thus under the extreme conditions of loading aforementioned,

while the capacitor in discharging decreases in potential, the charging voltage impressed thereon is such as to recharge it during the periods of its discharge. This causes the flow of unnecessary high current through the ignition electrode and cathode of the ignitron, such current ex- ,ceeding considerably in amount that required maximum value has. been reached, so as a conse- Lq'uence thereof the energy discharged through' the, ignition electrode and cathode of the ignitron "is substantially only that stored in' said capacitor prior to the moment the ignitron is rendered conducting.

An object or the present invention is to pro 'yide an energizing system for ignitron tubes reistricting to a minimum the required ignition energy; and

j Another object is to provide a system of the 2 aforementioned type which afl'ords a substantially constant amount of ignition energy regardless of the loading on the ignitron tube.

Other objects and advantages of the invention will hereinafter appear.

The accompanying drawing illustrates one embodiment of the invention which will now be described, it being understood that the embodiment shown is susceptible of modification in re spect of its details without departing from the scope of the appended claims.

In the drawing: I r

.Figure 1 illustrates, partly diagrammatically and partly schematically, a control system for a polyphase alternating current motor.

Fig. 2 illustrates the relationship of voltage existing between certain components of the control system of Fig. 1 under one operating condition, and

Fig. 3 is similar to Fig. 2 but illustrates the relationship of voltages under another operating condition. 1

Referring to Fig. 1; it shows a three phase alternating current induction motor I 0 having a primary winding w and a secondary winding lo Winding Ill is providedwith three terminals T T and T Terminals T and T are directly connected to the bus bars L and L of a three phasealternating supply circuit. A pair of ignitron tubes H and 22 are connected between bus bar L of the current suppl circuit and terminal T of the motor primary in an inverse parallel relation. More particularly cathode ll of tube I! and anode H of tube !2 are connected to terminal 'I while anode H of tube H and cathode iZ of tube l2 are connected to bus bar L Ignitron tubes II and 12 are provided with .ignitor electrodes H and 12 respectively, which when suitably energized initiate conduction of the respective tubes.

The circuit arrangement of the main electrodes of tubes II and 12 in the power supply to the motor It is like that shown and described in the Elliot Patent 2,448,256, issued August 31, 1948. The purpose of the tubes II' and I2 when the conduction thereof is suitably controlled-by the control system to be described hereinafter in detail, is that described in the aforementioned patent. Although in the aforementioned patent the motor corresponding to motor it is shown as having secondary resistance which is controlled,

such is dispensed with in the present application as it forms no part of the present invention.

through a resistor 31.

disclosed in the aforementioned patent may be incorporated with the secondary winding lil of the motor Iii if desired.

A preferred system for controlling the conduction of ignitrons ii and I2 will now be described.

A transformer 13, schematically depicted in Fig. l, is provided with a laminated core 83 and a primary winding 53 having one end terminal connected to bus bar L and its other end terminal connected to bus bar L through a winding M which is wound on a laminated core M of an inductive reactor M, which is also schematically depicted in Fig. 1. Transformer i3 has a secondary winding I3 having endterminals l5 and I6. End terminal 15 of winding l3 is connected to an anode li of a thyratron tube I! through a half-wave rectifier l8 and resistors l9 and 20.

The end terminal E6 of winding I3 is connected.

to the cathode H of ignitron i l. A capacitor 2| is connected at one ofits terminals to a common point between the resistors 59 and 2B and its'other terminal is connected to a point common to terminal is of winding l3 and cathode II" of ignitron ll. Cathode ['1 of thyratron H is connected to the ignitron electrode H' of ignitron H. Thyratron l! is also provided with a control electrode ll which is connected to the cathode li through a smoothing capacitor 22.

Transformer I3 is also provided with another secondary winding l3 having

end terminals

23 and 24. End terminal 23 of winding 13 is connected to anode 22.5 of a thyratron tube 25 through a half-wave rectifi'er26 and

resistors

21 and 28. End terminal 24 of'winding' 13 is connected to the cathode [2 of ignitron i2. Acapacitor 29 is connected at one terminal to a point common to the

resistors

21 and 28 and is connected at its other terminal to a point. common to end terminal 2 of winding 13 and cathode iz 'of ignitron l2. Cathode 25 of thyratron 25 is connected to the ignitor electrode l2 of ignitron IZ. Thyratron 25 is also provided with a control electrode 25 which is connected to the cathode 25 thereof througha smoothing capacitor30.

A transformer 31 is provided with a primary winding 3 l having one of'its terminals connected to bus bar L and its other end terminal connected to bus bar L Transformer 3! also has a secondary winding 3| having

end terminals

32 and 33 and a mid-point terminal 34. End terminal 33 is connected to the terminal 34 through a variable inductance 35 and a primary winding 33 of a transformer 36. End terminal 32 is connected to a point common to the inductance 35 and the winding 36 of transformer 36 Transformer 36 is also provided with a secondary winding 36 having end terminals38 and 39 andanother secondary winding it having end terminals 40v and. 4|. The terminal 39 of winding 36 is connected to control electrode 1'! of thyratron H' through a resistor 42 and the terminall38 or; said winding is connected to a point common to. the cathode ill of'thyratron ll and the capacitor 22-. The terminal 4B of'winding 36 is connected'to control electrode 25' of thyratron25 through a resistor 43 and the terminal 4! ofsaid' windingis' connected to a' point common to the cathode 25 of thyratron 25 and the capacitor 30.

As will be understood by thoseskilled in the art, transformer 3!, variable inductance 35, and resistor 31 constitutes a phase shift network of a well known type. The output of such network is impressed on the control electrodes 1'! and 25 of thyratron I! and 25 respectively, through the medium of the secondary windings 3t and 36 of transformer 36. Any other suitable adjustable phase shift network may be used in the place of the one herein shown and described. In the aforementioned patent there is shown a phase shift network which is particularly suitable when it is desired to automatically afiord adjustments thereof according to variations in operating conditions of the motor.

It has been found in connection with the present control system that for best operation when the phase shift network is adjusted for maximum phase shift, the voltage impressed on the control electrode I! should lag the voltage impressed on the anode ll 'of ignitron H not less than 30 and similarly the same relation should exist between the voltages impressed on the control electrode 25 of thyratron 25 and on the anode (2 of ignitron II.

It has also been found that for best operation of the present control system, under no load conditions, the voltages induced in the secondary winding la should lead the voltage impressed on the anode li of ignitron H by and similarly that the same relation should exist between the voltages induced in secondary winding l3 of transformer 93 and that impressed on the anode [2 of ignitron 52.

To best understand the advantages of the present control system, its operation will be first considered as if the reactor M were not'included in the power connections to the primary winding il of transformer i3 and then its operation will be considered with such reactor included as here inbeforeshown and described.

In the first case the voltage induced in the secondary winding l3 will have the usual sinusoidal wave form as depicted by the dotted line curve A in Fig. 2. When the polarity of the voltage at the terminal 55 is positive with respect to that at the terminal is in winding I3 current Will flow through the rectifier l8, resistor l9, capacitor 2| to terminal l6 thereby charging capacitor 2: to the potential depicted by the straight line B in Fig. 2. At the moment the charge on capacitor 2! has reached the potential B, the voltage impressed on the anode li of ignitron H becomes positive; the voltage impressed on the anode li being depicted by the curve C in Fig. 2. Assuming that the aforedescribed phase shift network is adjusted for maximum phase shift, then the voltage impressed on the control electrode li of thyratron Il may be that depicted by the curve D in Fig. 2. When the voltage impressed on control electrode ll exceeds the critical potential of thyratron [1, which is represented by the straight line E in Fig: 2, thyratron I? will conduct. As a result of thyratron I1 becoming conducting, capacitor 2| discharges through a path including resistor 20, thyratron H, the ignitor H and cathode H of ignitron ll, thereby initiating conduction of the'latter which remains conducting for the remainder'of the half cycle of anode voltage depicted by the curve C; the moment of initiation of conduction of ignitron I! being depicted by the vertical line F in Fig. 2.

Although capacitor 2! may be such that when charged to the potential B and discharged as aforedescribed to initiate conduction of ignitron H, current in excess of that supplied from the capacitor will also flow through the discharge path aforementioned. At the moment thyratron IT is rendered conducting the polarity of the enemas voltage at terminal f of winding 13 is still positive with respect to terminal l=6 andsof such magnitude that current flows. through rectifier -t'8gresistor I 9 supplementing the current flowing through the discharge path from capacitor 21'. Such excess current is proportional to the "area under the curve A to the right of vertical line F. As such excess current is not needed for initiating conduction of ignitron ll, its only effect is to shorten the life of ignitor electrode I I. As the phase shift networkxis adjusted more towarda condition of minimum phase shift, such 'as depicted by the relationship of voltages shown in Fig. 3, the amount of such excess current decreases, and at the condition of phase "shift depicted, no excess current will flow through the discharge path of capacitor 2|. found-that the average current "supplied to the It has been lgnitor of ignitron tube l'l under 'a condition of maximum phase shift is 5 to 6 times that supplied under a condition of minimum phase shift.

Now considering the present control system as it actually exists with the reactor l4 connected .in the power connections to the primary winding 13 of transformer l3, the relationship of the instantaneous voltages induced in the winding l3, when terminal 15 thereof is positive with respect to its terminal 16, is not of sinusoidal wave form but is of the high peaked forms to zero rapidly and attains a zero value before the anode voltage of ignitron H is of sufficient magnitude to render the latter conducting.

Therefore the only current supplied through the aforementioned discharge path of capicitor 2! is that stored in the latter, there being no excess current supplied from the winding l3. When the phase shift network is adjusted to provide a condition near minimum phase shift net, depicted by Fig. 3, the wave form of the voltage induced in winding I3 changes somewhat to that depicted by curve G and leads the anode voltage of ignitron II by substantially 90. It has been found that when the voltage induced in winding l3 has the wave forms depicted by curves G and G under the conditions of phase shift depicted by Figs. 2 and 3, the average ignitor current is the same for both conditions, and the same for other conditions of phase shift therebetween. Thus with the present control system the ignitor ll is supplied with only that amount of energy as is necessary to initiate conduction of ignitron H and the life of the latter is thereby materially enhanced.

The wave form of the voltages induced in winding I? will also be like that depicted by curves G and G of Figs. 2 and respectively. Thus ignit-ron 12, which is controlled in exactly the same manner as ignitron II during positive half cycles of the voltage impressed on its anode [2 will likewise be supplied with only that amount of energy needed to initiate its conduction.

It has been found by experiment that by using an inductive reactor having acore formed of electrical sheet steel laminations describing a closed magnetic path and with its inductance winding connected in the power connections to the primary winding as hereinbefore described, voltages will be induced in the secondary windings of the transformer having wave .forms generally similar to those depicted by curves G and G in Figs. 2 and 3 respectively. In one particular embodiment of the present control system, wave forms of the voltages induced in the secondary windings of the transformer 13 were obtained which were substantially like that depicted by curves G and G using the following combination of a transformer and inductive reactor connected as aforedescribed to a 215 volt alternating supply source: Transformer:

Rating-335 volt amperes Primary winding-240 turns of #IQDCwire Secondary winding-316 turns (each) of #24DC wire Coreformed of electrical sheet steel laminations describing closed magnetic path Inductive reactor:

Inductance winding-430 turns of #HI'ZE wire I Core-formed of electrical sheet steel laminations describing a closed magnetic path suitable for a volt-ampere transformer As will be understood by those skilled in the art, the combinations of transformers and reactors that will provide induced voltages having wave forms substantially like the wave forms depicted by curves G and G depends upon a number of variables. Generally considered, when the primary Winding of the transformer and the inductance winding are connected in circuit as hereinbefore described and the secondary windings of the transformer are open circuited, the measured voltage drops across the primary winding of the transformer and across the inductance winding of the reactor should be substantially equal.

1 claim:

1. In combination, an alternatin current supply source, an ignitron tube which through its main electrodes conducts energy from said source and which has an ignitor electrode. means, including a capacitor, supplying energy stored in said capacitor to said ignition electrode in timed relation to the voltage cycles of said source, transforming and rectifyiue means in energy supplying relation to the first mentioned means includin said capacitor, and a primary circuit for said transforming means supplied from said source and having reectance affording peaking of the voltage pulses in the secondary of said transforming means restricting transfer of en ergv to said ignitor electrode from said source substantially to only the energy stored in said capacitor.

2. In combination, an alternating current supply source, an ignitron tube which through its main electrodes conducts energy from said source and which has an ignitor electrode, means, including a capacitor, supplying energy stored in said capacitor to said ignition electrode in timed relation to the voltage cycles of said source, an inductive reactor, a rectifier, a transformer having its primary winding connected to said source through the winding of said reactor and having its secondary winding connected to said capacitor through said rectifier, said transformer and said reactor in association affording peaking of the voltage pulses in the secondary winding of said 7 transformer for restricting transfer of energy to said ignitor electrode from said source substantially to only the energy stored in said capacitor;

3. In combination, an alternating current supply source, an ignitron tube which through its main electrodes conducts energy from said source and which has an ignitor electrode, means, including a capacitor, supplying energy stored in said capacitor to said ignition electrode in timed relation to the voltage c cles of said source, an inductive reactor having a core formed of a low reluctance material and describing a closed mag-- netic path upon which its winding is wound, a rectifier, a transformer having its primary winding connected to said source through the Winding of said reactor and having its primary winding connected across said capacitor through said rectifier, said transformer and said reactor in association aifording peaking or the voltage pulses in said transformer secondary winding for restricting transfer of energy to said ignitor electrode from said source substantially to only the energy stored in said capacitor.

4. In combination, a polyphase alternating current supply source, a translating device connected to said source for deriving energy therefrom, an ignitron tube having its main electrode connected in a power connection to said device and having an ignitor electrode, means, including a capacitor, supplying energy stored in said capacitor to said ignitor electrode, means limiting the supply of energy to said ignitor electrode in a timed relation to conducting half cycles of voltage of said ignitron tube, an inductive reactor having a core formed of a low reluctance material and describing a closed magnetic path upon which its winding is wound, a rectifier, and a transformer having its primary winding connected across one phase of said source through the windin of said reactor and having its sec ondary Winding connected across said capacitor through said rectifier, said transformer and said reactor in association affording peaking of the voltage pulses in the transformer secondary winding for restricting transfer of energy to said ignitor electrode from said source substantially to only the energy stored in said capacitor.

5. In combination, a polyphase alternating current supply source, a translating device connected to said source for deriving energy therefrom, an ignitron tube having its main electrodes connected in a power connection to said device and having an i-gnitor electrode, a capacitor, a normally non-conducting second electron tube having its main electrodes connected across said capacitor through said ignitor electrode and the cathode of said ignitron tube and having a control electrode, an inductive reactor having a core formed of a low reluctance material and forming a closed magnetic path upon which its winding is Wound, a rectifier, a transformer having its primary winding connected across one phas of said source through the winding of said reactor and having its secondary winding connected across said capacitor through said rectifier for charging said capacitor during the non-conducting periods of said ignitron tube, and means deriving energy from said source of supply to said control electrode and limiting to the conducting half cycles of voltage of said ignitron tube the supply of energy to initiate discharge of said capacitor through said second tube for energizing said ignitor electrode, said transformer and said reactor in association affording peaking of the voltage pulses in said transformer secondary winding for restricting the transfer of energy to said ignitor electrode from said source to substantially only the energy stored in said capacitor.

GEORGE J. LEXA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,306,230 Somerville Dec. 22, 1942 2,422,575 Marsh et al June 17, 1947 2,444,921 Dawson et al. July 13, 1948 2,{i48,256 Elliot Aug. 31, 1948