US2432927A - Ignitron control system for circuit breakers - Google Patents

Description

Dec. 16, 1947. w. E. PAKALA IGNITRON CONTROL SYSTEM FOR CIRCUIT BREAKERS Filed Oct. 30, 1942 EL HIIF 4 75' iNVENTOR William E. Paka la.

WITNESSES; fill M25 ATTORNE Patented Dec. 16, 1947 IGNITRON CONTROL SYSTEM FOR CIRCUIT BREAKERS William E. Pakala, Forest Hills, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application October 30, 1942, Serial No. 463,924

10 Claims.

1 My invention relates to arrangements for controlling the opening and closure of circuit interrupters and in particular to control of current flow to solenoids of electrically actuated circuit solenoid of a circuit interrupter which shall insure that accidental ionization of the discharge space in an electrical discharge devic shall not result in unexpected closure of the circuit interrupter.

interrupters. 5' Other objects of my invention will become ap- One of the most widely used arrangements for parent when reading the accompanying descripactuating the mechanism of circuit interrupters tion when taken in connection with the drawing, to move them to their closed-circuit position comin which: prises a magnetic core which is attracted by an Figure 1 is a diagrammatic showing of the cirelectrically energized solenoid to move the circuit for energizing the closing-solenoid of a circuit interrupter against a spring or other bias to cuit interrupter from a direct-current supplyits closed-circuit position. Such a, solenoid is, source and which employs electrical discharge ofv course, energized by current flow only during tubes of the ignitron type; the comparatively infrequent intervals when the Fig. 2 is a schematic diagram of a. circuit for circuit breaker is actually being moved to closed energizing the closing solenoid of a circuit breaker circuit position. It is also the usual practice to from an alternating current supply-source and provide such circuit breakers with overload relays using electrical discharge devices of the ignitr-on which operate, when an overload occurs on the type; circuit governed by the breaker to upset a toggle Fig. 3- is a schematic diagram of a circuit for thereby permitting the above-mentioned bias energizing the closing solenoid of a circuit breaker to move the circuit breaker to open-circuit posifrom an alternating current source and which tion. employs a, single electrical discharge tube of After the circuit breaker has thuszbeen opened the ignitron type provided with a shield-el ct ode; by the overload relay an attendant usually closes and a manually operated switchwhich sends current Fig. 4 is a schematic diagram of a circuit for from a supply source through the above-mencontrolling current flow to a closing solenoid-for tioned closing-solenoid thereby reclosing the cira circuit breaker from. a direct-current So e cuit' breaker; Ii now the overload condition on and using only a single electrical discharge tube the line governed by the circuit breaker still pertherein. sists, the overload relay will again trip the circuit Referring in detail to Fig. 1, a circuit breaker breaker to open-circuit position If the attend- I which may be of conventional type but is here ant still holds the above-mentioned manual shown for sake of simplicity as of the single-pole switch closed, the solenoid will again close the cirtype controls current flow through an alternatcui-t interrupter, and this cycle of periodic opening-current power line 2. The bridging member ings and closings. will continuefor some time with of the circuit breaker l is biased to open cirwear, overheating and other injurious efiects to cuit position by any suitable means such as a the circuit: breaker mechanism. Such repeated spring 3 and is moved to closed circuit breaker Operations are? Wn' in t art s pumping. position by energization of a solenoid 4 enclosing One. object of my invention is to: provide a cira magnetic core 5 by current flow from a. directcuit for-energizing theclosing solenoid oia circuit 40 current supply line 8-1. Current flow through breaker which Will p -pu p n the solenoid 4 takes place from the line B through Another object of my invention is to provide a pair of. serially connected electrical discharge an. arrangement in which. electrical discharge detubes 8--8 which are. preferably of the ignitron vices are employed to control. current flow to the type embodying respectively anodes l I--l2, cathclosing coil of a circuit breaker in such a way odes l3--l4 and igniter electrodes 1 c5110 prevent P p trical discharge devices of the ig yp l Electrical. discharge tubes. sometimes become referred to remain non-conductive notwith- 3 wnductivcbyionization, which pr ably standing the impression across their anodes and an electrical breakdown phenonmena, in their cathodes of a voltage of e Order Of that of the discharge spaces even when the only voltage imsource 6-! as long as their igniter electrodes pressed across their terminals is: one supposedly too: low' to render them conductive.

Still another object of my invention is to pro vide a: circuit employing electrical discharge devicesi-or controlling energization. of th closing lE-lli are not energized by current flow. However, when a suiiicient current flows through their igniter electrodes even for a very short time, the path between the anodes. and cathodes of tubes such as 8 and 9 are ionized and rendered conductive so that current will flow through them from such a supply-line as 6-'I, and will continue to flow even after cessation of current through the igniter electrodes until it is interrupted by reducing the voltage between their anodes and cathodes to a value below a certain critical minimum. Thus in the present case the tubes 89 are supposed to remain non-conductive since, as will now be explained their igniter electrodes are not energized; and to be rendered conductive when it is desired to close the circuit breaker I by manually energizing their igniter electrodes.

A pair of equal resistors I'II8 are respectively bridged in shunt with the tubes 8-S, their resistances being of a high value, and their purpose being to insure an equal division of voltage of the line 6? between the tubes 89 when they are in their normal, nominally non-conductive, condition.

The igniter electrodes I6 are respectively connected to the cathode I3 of the tube 8 through a manually operated switch I9, and the igniter electrode I5 of the tube 8 is connected through a second switch 2I which moves simultaneously with the switch I9 to the common terminal of a resistor 22 and a capacitor 23 which are bridged in and serves to maintain the capacitor 23 charged to the full voltage of the supply line 61 as long as the switches I9-2I remain open. When it is desired to energize the solenoid 4 to move the circuit breaker 4 from its open to its closed position, the common handle of the switches I92I is moved against the bias of their spring 24 to close them.

The capacitor 23 is bridged by a switch 25 which is open while the circuit breaker I is opened and closed when the latter is closed. When the circuit breaker I is closed the switch 25 short circuits the capacitor 23 and insures that it is maintained in a discharged condition thereby insuring that the capacitor 23 cannot discharge sufiicient current to energize the ignitrons 8 and 9 to maintain current flow through the solenoid 4 even should the switches I9 and 2! be accidentally closed while the circuit breaker I is in its closed circuit position. The resistor 22 is preferably made large enough in value so that the current flowing through it and switch 25 from the line 6-1 while the circuit breaker I is closed does not represent a substantial loss of energy, but is made small enough so as to charge the capacitor 23, when switch 25 and circuit breaker I are open, in a time which is small compared with the period elapsing while the mechanism of the circuit breaker I is moving at from open to closed position.

As has previously been stated, current would continue to flow through the closing solenoid 4 and the ignitrons 8 and 9 from the source 6-? for an indefinite period, even though the switches I9 and 2I were released to open position if the circuit contained only the elements so far described. In order to interrupt current fiow through the solenoid 4 and the ignitrons 89 as soon as the circuit breaker I has moved to its closed circuit position, I provide a capacitor 25 which is connected between the anode II of the ignitron 8 and the common terminal of a pair of resistors 2'l--28 which are serially connected across the supply line 6'! through a switch 29 which is opened while the circuit breaker I is opened and closed while it is closed. The capacitor 25 is normally maintained in a substantially discharged condition while the circuit breaker I is either standing open or standing closed by reason of the fact that the ignitrons 8 and 9 are non-conductive and there is no voltage drop across the terminals of the solenoid 4. When, however, the ignitrons 8 and 9 are energized to close the circuit breaker I, current can flow through the resistor 2! through capacitor 26 and ignitrons 8 and 9 to charge capacitor 28 substantially up to the full voltage of the line 6-7, its lower plate being charged positively relative to its upper plate. This condition continues until the circuit breaker I closes at which time the switch 29 closes, bridging the capacitor 26 across the two ignitrons 89 with such a polarity as to tend to send a current in the reverse direction through them than that which they are already conducting through the solenoid 4. This reduces the voltage drop between their anodes and cathodes far below the critical value which is necessary to maintain current flow through them and their arcs are immediately extinguished and they are rendered non-conductive. They thus remain non-conductive until they are ionized by energization of their igniter electrodes I5I6 by manual closure of the switches I9-2I.

The circuit interrupter I is provided with an overload relay 3| which upon suflicient energizations by current flow through the line 2 closes a switch 32 which is connected in series with a solenoid 33 which magnetically operates a latch 34. The latch 34 normally holds the circuit breaker I in its closed circuit position, once it has been moved thereto by current flow through solenoid 4. Closure of the contacts 32 upon flow of an overload current in the lines 2 energizes the solenoid 33 to trip the latch 34 and permit the circuit breaker I to be moved to its open circuit position under the edge of its bias 3. The latch 34 is only symbolical and may be replaced by an overset toggle or other devices commonly employed for similar purposes in the circuit breaker art.

It will be noted that if an overload still exists on the line 2 after the circuit breaker I has been reclosed by manual closure of the switch 2I, the solenoid 33 will again cause reopening of that circuit breaker. If now the switch 2| is still held in its closed position, there will be no reenergization of the closing coil 4 for the reason that the condenser 23 is virtually short-circuited by the current path through the igniter electrodes and the current flowing through the high resistance 22 is unable to charge the condenser 23 to a substantial voltage. It is only when the switch 2| has been reopened that the condenser 23 can charge up to substantially the line voltage and thereby become capable of igniting the tubes 8 and 9 when it discharges through their electrodes I5 and I6. Under these conditions, it is obviously impossible for the solenoid 4 to cause a second reclosure of the circuit interrupter I until the manual switch 2I has been reopened. This prevents the repeated reclosures and reopenings known as pumping.

It will be noted that the source 6! impresses voltage at all times between the anode and the cathode of each of the ignitrons 8-9, and although such electrical discharge tubes are supposedly to remain non-conductive as long as no current flows through their igniter electrodes, it is found in actual practice that in long intervals for some causes which are difficult to explain they tend to acquire conductivity which, unless followed up by substantial current flow, persists for only an extremely brief instant. If only a single acquisltionby this singleigni tren' tor conductivity to: evensueh a brieiinstant wou d! be renewed bycurrent flow from t source S- I and the circuit interrupted w ch might he closed xpectedly Without operation of the manual switches, such as "I 9 or 21 in the i gniter While'such random and brief acquisitions of conductivity lay the ipmitrons occur only at very long intervals. it is often desired that a circuit ter- "mister shall remain open for days at a time and the occurrence of one of these i 'andom brief intervals at any time within that ldh'g perio'd would unexpectedly close the circuit breaker, with nossibie disastrous results to men working on the line :2. when, in accordance with my invention, two ig n-itrons connecte series with each other are used, the acquisition of conductivity iior a brief interval by one will :be incapable of causing substantial current flow through :the solenoid 4 because of the last that the other ignition will be non 'conductive. The latter fact will also prevent maintenance of conductivity in the firstmentione'd ig nitron by substantial current flow through the solenoid 4 and *will permit the random conditions to cause reacquisition of the non-conductive state after an extremely brief interva'l.

The probability that the brief random conductive state will occur simultaneously in the two ignitrons is so extremely small as to be utterly negligible. Hence by employing two vig'nit-rons in series, I insure against any accidental closure of the circuit breaker 'l while the m'anually'opei'ated switches 19 and 2! remain open.

Referring now to the modification of my vinve-ntion shown in Fig. 2, the source of supply-0f energizing current for the circuit breaker closing-solehold 4 is an alternating current line iii-42. AS in the case :of .Fig. 1, the closing solenoid disconnected tothe line 41-42 through-a pair of serially connected ig-ni-trons 8 9. and in this case these aignitrons rectify the alternating voltage across the lines 41-42 so that the cur-rent flowing through the solenoid 4 .is pulsating direct current. 'I he ignitrons =89 are bridged by resistors 11-48, the same as in 1, and the igniter electrode 6 of tube 9 is connected to its anode through a switch 9 as in the case of Fig. :1. The igniter electrode 15 of tube -8, however, is likewise connected through a switch 2] as in Fig. '1 but in this case the other terminal of the switch 2l is connected through a pair of similarly poled .rectifiers 43-44 to the line 42 to which the cathode IQ of the .ignitron 9 is connected. It will be observed that the rectifier 43 is so poledt-hat current flows into the cathode 13 of tube '8 from its :ign-iter electrode 1 5 in the same direction :as currentilo us into that cathode-from its associated anode 41-.

The common terminal of the rectifiers 43 is connected through a, switch 45 which is manually operated in synchronism with the switches l9--'2l and thence through :a second switch 45 which is closed while the circuit breaker El is ope-n and is open while the circuit breaker l is closed, i

thence through the secondary winding M5 of a transformer and a current limiting resistor 49 back to the supply line 42 -A primary winding "51 connected across the supply lines ii- 5 2 cooperates with the secondary windingyA-S. Thercircuit breaker l is provided, with a latch 34 and an overload relay 3:! which are the same as th'o'se in Fig. 1.

The mode of operation of the device in Fig; .2 is as follows.

As long as the manually operated il 9-?2- -l- 45 'riemains cpen no current'iiows through'the igniter electrodes ii -4% o: ignitrons "B -9 and the solenoid t remains nn'ener- ?gized. When the manually :nperated switches f9-2 i 45 are closed, current can flow fromthe secondary winding 48 thnius'h the contacts 46 are closed because circuit breaker i is open) through the switch 45, rectifier #3., switch 21, i'gniter electrode [5, switch 19., iigni'ter "electrode 16, line 42 and current limiting resistor 19. The voltage of secondary winding 48 and current limiting resistor 19 are so proportioned that the current thus flowing is suillcient to energize i 'ghi ter' electrodes 5--l'6 to render .i gnitrons 8 and 9 conductive. once the 'i'gnitron's 8- 9 are rendered conductive current can flow from line II to line &2 through solenoid 1i andthe two ignitrons. HOWEVER, this current now 'Will continue *fbi only one-hal fbyc1e 0f this alternating voltage onlines li -4'2. the reversal of this voltage stopping all current'llow through the ignitroi-l's fl il. The current ilow through ignitrons 8--9 and solenoid'll will, however, be resumed on the next hal f cycle e f-voltage provided the manually operated switch 1 9- 2145 remains closed and half-cycle of ouri'en t'will thus flow through solenoid 4 until circuit breaker '-l' "is moved to circuit closing posit-ion. When' this happens switch -4-6 opens and cuts oif current flow th-roi-lgh the 'igniter electrodes "-l'5 l 6 from the secondary winding 4 8. This condition "persists as long as latch 3 4 maintains -'oi-rcuit nreai-ker ciosed even thoughthe manual-1y o erated switch N di -4 5 is held closed.

It will be noted that the rectifier -44 permits current to flow in the opposite direction through secondary winding '48 from that half cycle which has already been described as flowing through secondary winding 18 and rectifier *43. Since alternate 'h'al'f cycles of current "canfiow through the secondary winding -48, no saturation results therein such would occur if rectifier 4'3 alone were used in the circuit.

It will be noted that the presence of two ignitrons "8-"9 in the Fig, 2 arrangement acts to prevent accidental closure of th "circuithreaker 'l resultingfro'm random ionization of one i'gnitron lor'abriefinterval in the same way as has already 'g e'en described in the case of "ignitrcns 8- 9 in 'ig. '1.

Fig. 3 shows how a single tube can be arranged to perform thee a'me functions as the two 'ignitrons 2 and "9 were employed for in the case of Figs. 1 and 2. This figure shows the arrangement using an alternating current supply line similar to that in Fig. '1. The circuit bre'a-ker closing solenoid 4 is "connected :irom one sub'pily line to the other through a single :i'g'nitron tube 6-! which is pro- 'vided with an anode 62, a cathode 6 3 and an ig'n'iter electrode "61, and a shield electrode 65. The ign'i ter electrode :54 is connected through a air of similarly poled rectifiers *66B to the alternating current supply line 42 which is connected to the cathode 63 of the .ig ni-tron 64 The common terminal of the rectifier -66-51 is connected through a manually operated switch Mar-1d a, switch 4-6 which :is closed while the circuit breaker l is-opened and isopehed while ithe' circuit breaker :l is closed to the primary winding #8 of a transformer, the other terminal of which is con ':nected through a current limiting resistor 4'9 'to the line 42. The secondary winding 48 is e'n'e i :g-i'zed i-from a primary winding 54 which is con- :nected across the lines 4l-42 i he'shi elecerode '55 is connected to one te'i mmal -of asmtitch 69 which is closed simultaneously with switch 68 and thence through a resistor 'II to line 42. The shield electrode 65 is likewise connected through a switch I2 which is closed while switch 69 is open and is open while switch 69 is closed to one terminal of a capacitor I3, the other terminal of which is connected to the line 42. The capacitor I3 is bridged by a resistor I4 in series with a bias source 15 which tends to make the shield electrode 65 negative relative to its cathode 63,

The circuit breaker I is provided with a latch 34, an overload relay 3| in the case of Figs. 1 and 2.

When the circuit breaker I stands in open circuit position, the manually operated switches 68 and 69 are opened and the switches 12 and 46 are closed. The switch 68 prevents current flow from the secondary winding 48 to the igniter electrodes 64 until the manually operated switch is moved to closed circuit position, Hence the ignitron 6I is non-conductive and no current can fiow through the solenoid 4. To move the circuit breaker I to its closed circuit position the manually operated switches 6869 are closed and current then flows from the secondary winding 48 through closed switches 46-66, rectifier 66, and igniter electrode 64 thereby rendering the ignitron 6| conductive. Current then flows through solenoid 4 and closes circuit breaker I whereupon switch 46 is opened and ignitron 6| is deenergized in accordance with the description of ignitrons 8 and 9 in Fig. 2. It will be noted that switch I2 connects shield electrode 65 through bias battery I to the cathode 63 as long as manually operated switch I2 is closed thereby imposing a strong negative bias on the shield 65 which is sufiicient to insure against the appearance of an such random brief intervals of conductivity in the space between the anode and cathode of the discharge tube 6|. Thus while only a single ignitron is used in this system, none of the difficulties which made it necessary to employ to ignitrons in series, as described in Fig. 2, will be met with. When the manual switches 68 and 69 are closed to energize the igniter electrode 64, this negative bias on the shield electrode 65 is removed by the opening of switch "I2. It will be observed that when the manually operated switch 68-69-42 is actuated to close circuit breaker I, switch 69 connects the shield electrode 65 to the line 4| which is nearest in potential to the anode of tube 6I, thereby removing any negative bias from shield electrode 65 and insuring free conduction in ignitron 6 I.

It will be noted that the circuit 13, I4, 15, I2, 69, II which is connected to the shield electrode 65 is merely connected across the supply line 4I42 while the circuit 66, 6?, 68, 46, 48, 49 is the means for energizing the igniter electrode 63, and that these two circuits are entirely separate from each other. It is accordingly possible to employ the circuit comprising elements I3, 74, 15, I2, 69 and shield electrode 65 connected across a direct-current supply line such as that shown in Fig. 1 in just the same way as it is employed across the supply line 4I-42 in Fig. 3. On the other hand, the control circuit for the igniter electrode 64 may have substituted for it an igniter electrode control circuit such as is shown in Fig, 4 with the result that a single igniter tube may be employed with a direct-current supply source.

Referring in detail to Fig. 4, a circuit breaker I is provided with a closing solenoid 4 which is supplied with current from direct-current line 6'I through a single electrical discharge tube 6i which is preferably of the ignitron type provided with a shield electrode similar to that described in connection with Fig. 3. The shield electrode is connected through a switch 69 which is normally open and through a resistor II with the positive side of the supply line 6-1 to which one terminal of the solenoid 4 is likewise attached. The shield electrode is likewise connected through a switch I2 which is closed while the switch 69 is open and is open when the switch 69 is closed to one terminal of a capacitor I3 01 which the other terminal is connected to the negative supply line 'I. The capacitor 13 is bridged by a resistor I4 and a bias source I5 having its positive terminal connected to the supply line I. It will be seen upon examination that the connections so far recited for the shield electrode 65 are the same as the connections for the shield electrode 65 in Fig. 3.

The igniter electrode 64 of the ignitron H is connected through a resistor I6 to one terminal of a switch 2I which is operated in synchronism with the above-mentioned switch 69 and is open when the latter is open. The other terminal of the switch 2| is connected to the common terminal of a resistor 22 and a capacitor 23 which are serially connected with each other across the supply line 6-'I. The capacitor 23 is bridged by a switch 25 which is connected to the circuit breaker I and is open when the latter is opened and closed when the latter is closed.

The anode 62 of the ignitron BI is connected through a capacitor 26 to the common terminal of a pair of resistors 21-28 which are connected in series with a switch 29 to the cathode of the tube 6|. The switch 29 is connected to the circuit breaker I too but open when the latter is opened and closed when the latter is closed. The circuit breaker I is likewise provided with a latch 34 under control of an overload relay the same as the circuit breaker described in Fig. 1.

When the circuit breaker I is open and it is desired to close it, the manually operated switches 69, 2I which are normally held in open circuit position are closed, thereby opening the switch I2. Openin the switch I2 disconnects the shield electrode 65 from the bias source I5 which normally maintains it at a potential sufliciently highly negative relative to its cathode 63 that there is no danger of spontaneous and random ionization of the space between the anodes 62 and 63. Closure of the switch 69 connects the shield electrode 65 to the positive line wire 6 and causes the capacitor 23 to discharge through the igniter electrode 64 and ionize the tube 6I in the same manner as discharge of the capacitor 23 in Fig. 1, has already been described as energizing the igniter electrodes of the tubes therein. In consequence of this alternation the potentials of its igniter and shield electrode tube BI is rendered conductive and current flows from the line 6 through the solenoid 4 and ignitron 6I to line I. The circuit breaker is thereby moved to closed circuit position thereby in turn closing the switch 25 to shunt circuit capacitor 23 and closing the switch 29 to discharge capacitor 26 in reverse direction through ignitron 6I just as capacitor 26 has already been described as discharging through, and quenching, the ignitrons 8 and 9 in Fig. 1. No further detailed description of Fig. 4 is believed to be necessary in view of the similarity of its elements to those already described in Fig. 1.

I claim as my invention:

1. In combination with a circuit interrupter, a closing solenoid having one terminal connected to a supply line and its other terminal connected through a pair of serially connected electrical discharge tubes, to the other side of said supply line, said discharge tubes being each provided with a starting electrode, and auxiliary means including switch ng means for rendering both said discharge tubes conductive.

2. In combination with a circuit interrupter, a closing solenoid having one terminal connected to a supply line and its other terminal connected through a pair of serially connected electrical discharge tubes, to the other side of said supply line, said discharge tubes being each provided with a starting electrode, and auxiliary switch ng means for discharging a condenser through said starting electrodes to render said discharge tubes conductive.

3. In combination with a circuit interrupter, a closing solenoid having one terminal connected to a supply line and its other terminal connected through a pair of serially connected electrical discharge tubes, to the other side of said supply line, a pair of similar impedances respectively connected in multiple with said discharge tubes, said discharge tubes being each provided with a starting electrode, and auxiliary means including switching means for energizing said control electrodes to render both said discharge tubes conductive.

4. In comb nation with a circuit interrupter, a closing solenoid having one terminal connected to a supply line and its other terminal connected through a pair of serially connected electrical discharge tubes, to the other side of said supply line, a pair of sim lar impedances respectively connected in multiple with said discharge tubes, said discharge tubes being each provided with a starting electrode, and auxiliary switching means for discharging a condenser through said starting electrodes to render said discharge tubes conductive.

5. In combination with a circuit interrupter, a closing solenoid having one terminal connected to a supply line and its other terminal connected through a pair of serially connected ignitrons to the other side of said supply line, said ignitrons being each provided with a discharge electrode, and auxiliary means including switching means for discharging a condenser through said discharge electrodes to render said ignitrons con.- ductive.

6. In combination with a circuit interrupter, a closing solenoid having one terminal connected to a supply line and its other terminal connected through a pair of serially connected ignitrons to the other side of said supply line, said ignitrons being each provided with a discharge electrode, and manually operated means for discharging a condenser through said starting electrodes to render said ignitrons conductive.

7. In combination with an electrical supply line, a circuit-breaker having an operating solenoid, said solenod having one terminal connected to one side of said supply line and its other terminal connected through a pair of serially connected ignitrons, to the other side of said supply line, said ignitrons being each provided with a starting electrode, and auxiliary means including switching means for energizing said control electrodes to render both said ignitrons conductive.

8. In combination with a circuit interrupter, a closing solenoid connected across a supply line in serial relation with two serially connected ignitrons each having a starting electrode, a resistance which is high compared with the sum of the resistances of said starting electrodes connected in series with a condenser across a voltage source,

and a circuit including switching means for connecting said condenser in serial relation with both said starting electrodes.

9. In combination with an electrical load connected across a supply line in serial relationship with two serially connected ignitrons each having a starting electrode, a resistance which is high compared with the sum of the resistances of said starting electrodes connected in series with a condenser across a voltage source, and switching means for connecting said condenser in serial relation with both said starting electrodes.

10. In combination with a circuit interrupter, a closing solenoid connected across a supply line in serial relation with an ignitron having a starting electrode, a res stor connected in series with a condenser across a voltage source, and a switching means for connecting said condenser and said discharge electrode in serial relationship, said resistor having a resistance which is high compared with that of said circuit.

WILLIAM E. PAKALAi REFERENCES CETED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,093,310 Currier Sept. 14, 1937 2,215,804 West Sept. 24, 1940 978,959 Thomas Dec. 20, 1910 1,840,055 Rentschler Jan. 5, 1932 2,303,453 Gulliksen Dec. 1, 1942 2,248,968 Dawson July 15, 1941 2,250,708 Herz July 29, 1941 2,008,730 Smede July 23, 1935 2,085,100 Knowles June 29, 1937 2,147,472 Ulrey Feb. 14, 1939 2,190,759 Alexanderson Feb. 20, 1940 2,021,034 Thompson Nov, 12, 1935 2,391,812 Winograd Dec. 25, 1945 2,043,515 Mulder et al June 9, 1936 2,008,409 Wensley July 16, 1935 2,299,561 Bivens Oct. 20, 1942

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