US2405397A - Electric circuits - Google Patents

Description

Bu D. BEDFORD ELECTRIC CIRCUIT Aug. 6, 1946.

Filed Feb. 12, 1945 5 Sheets-Sheet 1 m @uw Mb H His @Iter-neg.

23mg. 6, "19460 E., n. BEDFQR@ 294652397 l ELECTRIC CIRCUIT Filed Feb. 12', 19345 3 sheetsfsheet 2.

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Burnice D. Bedford, b9 //My MIM-1 His Attorney.

Auvg. 6, 1946. B. D. BEDFORD 2,405,397

l ELECTRIC CIRCUIT Filed Febr 12, 194s s sheets-sheet ls Fig.

Inventor: Burnce D. Bedford,

b5 ,JW

Hi8 Attorneg.

Patented Aug. 6, 1,946

ELECTRIC CIRCUITS Burnice D. Bedford, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application February 12, 1943, Serial No. 475,645

13 Claims. 1

My invention relates to electric control and indicating circuits particularly adapted for use in connection with electric valve means for indieating abnormal operation thereof.

Electrical apparatus employing electric valves of the type utilizing an ionizable medium has been extensively used in industrial applications. These electric valves, which normally conduct in one direction only, sometimes conduct in the reverse direction. The reverse current is usually many times larger than the normal forward current and has caused considerable operating difculty in systems of this type. From the standpoint of the operator, it is desirable to know which valve arcs back first in order that it may be removed from the system and reconditioned in the event that it fails persistently. From the standpoint of design, it is desirable to know in addition the time in the anode-cathode voltage wave that the arc-back occurs since this information is of assistance in determining the' cause of the arc-back and the features of design which may be modified to eliminate the fault. In accordance with the teachings of my invention, I provide new and improved electric circuits for indicating which one of a number of transients, such as those caused by arc-back of an electric valve means occurs rst' and further for indicating the time in the cycle of the anode-cathode voltage of the valve means at which the arcback occurs.

It is an object of my invention to provide a new and improved electric circuit for indicating the rst of a plurality of transient conditions.

It is another object of my invention to provide a new and improved electric indicating circuit for indicating the instant in the anode-cathode voltage wave that an electric valve conducts in the reverse direction.

It is another object of my inventio-n to provide an improved electric circuit for indicating the rst of a plurality of electric valves to conduct in a reverse direction and to record the time in the anode-cathode voltage of the valve that reverse conduction is initiated. I

In accordance with the illustrated embodiments of my invention, an improved electromagnetic device is associated with each of the anode conductors of an electric valve system to produce an impulse of voltage upon the occurrence of an arc-back in the associated electric valve. An indicating circuit having a controlled electric valve and an indicating device in series for each electric valve of the power system is provided and each of the controlled electric valves is energized in accordance with the voltage produced by the electromagnetic device associated with a corresponding one of the main electric valves. When any one of the controlled valves conducts in response to an arc-back in the corresponding main valve, the remainder of the controlled electric valves are prevented from operating. An auxiliary circuit associated with each of the main electric valves and controlled in response to conduction of any one of the controlled electric valves of the indicator circuit provides means for indicating the time in the anode-cathode voltage wave at which the arc-back occurs. In

' accordance with another illustrated embodiment one of the electromagnetic devices employed inA the embodiment illustrated in Fig. 1, Fig. 3 represents certain operating characteristics of the circuit illustrated in Fig. l, and Figs. 4 and 5 are schematic diagrams of other embodiments of my invention.

Referring now to Fig. 1 of the drawings, I have shown my invention embodied in an indicating circuit applied to an electric valve translating apparatus connected between a polyphase alternating-current circuit li) and a direct-current circuit comprising conductors Il and l2. In the following description it will be assumed that the electric valve apparatus is operating as a rectier, in which case, the circuit H3 is the supply circuit and the conductors Il and I2 constitute the load circuit. lIhe translating apparatus includes a transformer i3 having groups of electrically displaced secondary windings I4 and I5 having neutral connections interconnected by an interphase transformer If. The phase terminals of the windings I4 and i5 are connected with the direct-current conductor I2 through electric valves il to 22, inclusive. A midpointon the interphase transformer i6 is connected with the other direct-current conductor il. Each of the electric valves, as illustrated, comprises an anode `23, a cathode 2i, and an immersion-ignitor control member 2R. In order to simplify the drawings, no energizing circuits for control member have been illustrated and it will be understood that any of the types of control known. in the' art may be used, if desired.

I provide an indicating circuit including a plurality of parallel electric paths, the number ci paths corresponding to the number of electric valves in the rectifier system. lllhe electric paths are energized in parallel across conductors 26 and 21 and each comprises an indicating device such as an electric lamp 2S and a controlled electric valve. The valves, as indicated by the dot within the envelope, are of the gaseous type and are designated by numerals 29 to til, inclusive, and correspond respectively to the main electric valves ll to 22, inclusive. The other valves of the various illustrated embodiments which are of the gaseous type are similarly indicated. As a means for energizing the conductors 26 and 27, I provide a full-wave rectier energized from a transformer 3c having the primary winding 3l thereof connected with the alternating-current supply circuit it. The output of the rectiner is filtered by a se ies reactor 33 and parallel capacitor and impresse on Voltage-dividing resistors eil and ll through a manual switch e2. The conductor 26 is connected with one terminal of the resistor fill and the conductor 2l is connected with the common terminal of resistors Ml and ll through a resistor 0,3 and a manual switch 43.

In order to provide a source ci control voltage for the electric valves 29 to 30, dependent upon an arc-back condition in the electric valves il to 22, respectively, I provide a plurality-of electromagnetic devices illustrated generally by the numeral lit, and one of which is associated with the anode conductor of each of the electric valves, Referring briefly to Fig. 2, each of the electromagnetic devices comprises a closed magnetic circuit Alli including oppositely disposed legs Il@ and il of smaller cross section than the connecting end portions of the core. Control windings 43 and 49 are Wound on the legs it and dll, respectively, and direct-current saturating windings 50 and 5l are positioned on the legs l and It? on the outside of the control windings l and 139. As illustrated in the drawings, the directcurrent coils lill and 5l of each device Ml are connected in series. Referring again to Fig. 1, it will be noted that the direct-current windings of the devices M associated with the anode conductors of all of the electric valves are connected in series and energized from a source of direct current which may be derived from the transformer winding 36 by means of a full-wave rectier 52. The control windings i8 and t9 are connected in parallel and one common. terminal thereof is connected to the control member of the corresponding electric valve 23 through a resistor 53. The other common terminal of the control winding is connected to the negative terminal of voltage-dividing resistor Il! which provides a source oi negative bias for the electric valve 29 and, as previously mentioned, is connected to the cathode thereof through switch t3 and resistor dit. A capacitor 5e is connected between the control member and cathode of each. of the electric valves 29 to The control windings of the device it associated with main electric valve ll are the only ones that have shown connected in the drawings, It will be understood that the control windings of the remaining devices associated with valves i3 to are d similarly connected in the control-to-cathode circuit of electric valves 3@ to 3e.

Before describing the operation of the indicating circuit, the arrangement provided in Fig. l for indicating the time in the anode-cathode voltage cycle of each of the electric valves ll to 22 at which an arc-back occurs will be described. Associated with the valves il to inclusive, are the control circuits to ll respectively. These circuits are identical and the same reference numerals will be employed to designate the corresponding parts and only one will be described. Referring to the circuit i a resistance a nonlinear and a portion of resistance which provi es a source` of unidirectional voltage are connected in series across the anode-cathode circuit of th electric valve il, The resista-nce elements preferably of the type having a negative-current impedance characteristic so that the voltage across the terminals thereof is maintained substantially constant. These resistance elements may be formed of a material disclosed. and claimed in United States Patent 1,822,742, granted September 8, 1931, of Karl B. McEachron and assigned to the assignee of the present invention.. The voltage appearing across the nonlinear resistance element 62 is utilized for charging a capacitance Elf through a resistance Gli in accordance with the inverse voltage of the electric Valve ll. An electric valve d5, an inductive element El', and a capacitance til are connected in series across the capacitor te. The electric valve lid is of the type employing an ionizable medium, as indicated by the dot within the envelope, and is provided with a control member its which is energized by a secondary winding l@ of the transformer il to render the electric valve conductive at the instant one of the main electric valves arcs back. This is accomplished by energizing the primary winding l2 of the transformer in accordance with the voltage appearing across resistor da which, as will be brought out in more detail at a later point in the specification, impresses a transient voltage on the winding 'l2 at the time that the first one of these electricl valves t9 to becomes conductive. A capacitor i3, connected in series with Winding l2, prevents steady-state direct current from flowing in the primary winding l2. The voltage drop appearing across the upper portion of resistor (i3 is adjusted by the slider le so as to be equal substantially to the normal arc drop of the electric valve El' and the electric valve et, The voltage for energizing the resistor Eis may be obtained in any suitable manner and is derived from the output of a rectifier bridge l5 energized from a transformer lt which may, in turn, be energized from any suitable source of alternating current, such as the supply circuit it. A capacitor 'll' connected in parallel with resistor 33 provides a lowimpedance path for transient voltages and mits the rapid discharge oi the condenser t`=l during conduction of the valve il through a path which includes the resistor di and the anodecathode circuit of the valve il. A unilateraly conducting device 'lis is connected in parallel with resistor and is poled to provide a second discharge path -for capacitor fill during the conducting pericd of the electric valve il. As will become more apparent after a description of the operation of the system described above, the magnitude of the charge on the condenser Et after an arc back will be an indication of the time in the anode-cathode voltage wave of the associated main electric valve at which the arcback occurred. In order to measure this voltage, I provide a measuring instrument, such as a galvanometer 19, which may be selectively connected in circuit with the capacitor 68 of circuits 55 to 60 by means of manual switches 85 to 85, respectively.

A better understanding of the features and advantages of my invention may be had by a brief consideration of the operation of the system as a whole. Let it be assumed that the electric valves I1 to 22 are operating normally as a. double three-phase rectifier to supply unidirectional current to the conductors Il and l2. The electromagnetic devices 44 associated with the anode leads of the electric valves l1 to 22 are saturated suiciently as a result of the unidirectional current owing in the windings 5i! and 5I so that the decay of current through the associated electric valves during normal operation induces only a small voltage in the control windings 48 and 49. The negative biasesl impressed on the electric valves 29 to 34 by resistor 4I together with the time constant of the circuit including resistor 53 and capacitor 54 cooperate to maintain the valve nonconductive during this operation. If electric valve I1, for example, conducts current in a reverse direction, the change in iiux in the core 45 will be many times that occasioned by the normal decay of current through the electric valve l1 when it becomes nonconducting. A relatively large impulse of voltage is induced in the windings 43 and 49 and this is impressed on the control member of electric valve 29 and the associated indicating lamp 28 is energized. From an inspection of the drawings, it will be noted that conduction of any one of the valves 29 to 34 will increase the negative bias impressed on the control members of the remaining valves by resistor 4l and resistor 43 and, assuming that resistor 43 is substantially smaller than resistor 45, will simultaneously decrease the anode-cathode voltage of these valves appearing between conductors 26 and 21. This increase -in negative bias and decrease in anodecathode voltage is suiicient to prevent more than one of the electric valves 29 to 34 from becoming conductive regardless of the number of main electric valves which arc back. Thus, only the rst arc back to occur is indicated.

In the above discussion, it was pointed out that all of the direct-current windings are connected in series and the control windings are located on opposite legs of the device 44 and connected in parallel. This arrangement of windings has numerous advantages. With the control windings connected directly in parallel, there is etsablished a low-impedance closed circuit including these two coils so that any tendency for there to be a change in iiux in one leg without a corresponding change in flux in the same direction in the other leg is opposed by a circulating current in the low-impedance circuit which substantially prevents any quick change in flux in the two legs in opposite directions due to stray flux from other phases of the system. This arrangement of windings and the relatively large cross section of the core legs between the winding legs prevents false operation of the indicating system due to stray flux not symmetrically located with respect to the coils. The series connection of the direct-current windings provides considerable impedance in the direct-current circuit and minimizes the effect of transient voltages in this circuit.

When the electric valves l1 to 22 are operating normally, the capacitor 64 is periodically charged during the inverse-voltage cycle and discharged quickly at the end of this voltage cycle. The voltage across resistor 63 is employed to insure an initial charge on the capacitor 64 at the beginning of the inverse-voltage cycle corresponding to the break-down voltage of the electric valve 65. Referring particularly to Fig. 3, the inverse voltage of electric valve l1 is illustrated by curve A. Curve B illustrates the voltage across the nonlinear resistance 62 with the initial negative voltage being determined by the setting of the slider 14 on resistor 63. curve C illustrates the voltage of the capacitor 64, which may be operated over such a range that the increase in voltage is substantially linear. At the end of the inverse-voltage cycle. the voltage on the condenser is rapidly discharged as illustrated at D through the unilaterally conducting device 18. In the event that an arcback occurs in electric valve l1 at any time during the inverse-voltage cycle, the electric valve 2'9 is rendered conductive and a transient voltage appears across resistor 43. This voltage through transformer 1| renders each of the electric valves 66 of circuits 55 to 60, inclusive, conductive and the charges on capacitors 64 are transferred to the corresponding capacitors 68 through the anode-cathode circuits of the associated valves 66. The inductance 61 renders the discharge circuit of capacitor 64 oscillatory to insure reversal of the anode-cathode voltage of valve 6E a termination of its conduction. The capacitor 68 having no discharge circuit established for it will hold its charge for a cornparatively long period of time. The operator, upon observing from the lamps 28 that one of the electric valves has arced back may close one of the switch B to S5 corresponding to the first valve to arc back and read the deflection of the galvanometer 19 to determine the time during the inverse-voitage cycle that the arc-back occurred. It is apparent that calibration charts may be made for any given voltage of the system so that the deflection of the galvanometer may be converted to a phase position of the arc back. In order to reset the system for a subsequent operation, the control electric valves 28 to 3L! may all be rendered nonconducting by opening switch 42 or 43 to remove the anode-cathode voltage and the capacitors 68 may be completely discharged by temporarily closing the manual switches 8i) to 85, inclusive.

In Fig. 4, I have illustrated a modioation of my .invention in which a different arrangement for recording the time in the inverse-voltage cycle at which the arc-back occurred is provided. The system for indicating which one of the various 'phases arc-s back iirst is the same as that de.-

scribed in connection with'Fig. l and corresponding parts have been designated by the same reference numerals. In the arrangement shown in Fig. 4, the time in the inverse-voltage cycle at which the arc-back occurs is recorded on a disk by means of an electrical impulse which is produced when the arc-back occurs. This disk is rotated synchronously with the voltage of the supply circuit in the sense that the Cycles of operation of the disk and the alternations of the voltage of the supply circuit bear a timed relation to each other. Referring now to Fig. 4. a rotating disk 86 is mounted on the shaft or a synchronous motor 81 which is energized from the alternating-current supply circuit I5 through The dotted a transformer 88. The disk is preferably of good conducting material and is provided with a central hub 89 which is electrically connected with one terminal of the transformer winding 99a by means of a brush contact 91. The other terminal of the winding a is connected through a resistor 92 with a recording electrode 93 which is held in proximity to the rotating disk by any suitable means not shown. An impulse is produced in the Winding sila upon the occurrence of an arc-back in any one of the electric valves Il to 21?. by means of a circuit illustrated generally by the numeral Iifi. The circuit .fili includes an electric discharge device 95 which is connected in series with the primary winding iib of the transformer Sti and across the voltage-dividing resistor I0 through manual switches 95 and Ii'I. A resistor 98 is also connected in this circuit. An energy-storage capacitor .'Ii is connected across the electric valve 95 and the series connected transformer winding glib to be charged from the resistor All through resistor 9B. The control member of the electric valve Q is connected with the cathode thereof through the resistor 98, a capacitor Ii, and resistor EIII. The common terminal of capacitor le@ and resistor I @i is connected through manual switch I32 with the negative terminal of resistor i I. With this arrangement, the control member of the electric valve is maintained at the poten-- tial of the negative terminal cf resistor II when the electric valve system including valves I'I to is operating normally. The capacitor SQ is charged to the full voltage appearing across resistor di). A5 pointed out in connection with the operation of the arrangement of Fig, 1, the voltage across resistor Il is reduced and the voltage across resistor 4I is increased at the instant any of the electric valves 29 to 34 are rendered conductive in response to an arc-back in a corresponding one of the main electric valves I'I to 22. This momentarily renders the control member oi' the valve 95 positive with respect to the cathode thereof and eifects discharge of capacitor Sii through the transformer winding 9% and, as a result, causes a spark to jump from the electrode 93 the disk 33 and, in this way, forms a hole in the paper chart IIlS which is secured on the face of the disk 36 in any desired manner.

In order that the hole in the paper will indicate the time in the inverse-voltage cycle that the arc-back occurs, I provide means for synchronizing the disk 88 with the inverse-voltage cycle of the electric valves Il to 22. As illustrated in the drawings, the disk is provided near the edge thereof with an opening les behind which is mounted a lamp m5, which may be supported in any suitable manner, and which is energized in accordance with the voltage across a resistor H255. The resistor IE5 is connected in series with parallel connected resistor lIi'i capacitor ISS and across the anode-cathode circuit of the electric valve Il. The constants of the circuit including resistors IBS and IQ'I and the capacitor I t8 are so chosen that the lamp is illuminated only during the rapid change of voltage across the electric valve Il occurring at the beginning of the inverse-voltage cycle. In this way, the lamp is made to iiash at the beginning of the inverse-voltage cycle and, by adjusting the disk on the shaft of the motor or adjusting the phase of the voltage impressed on the motor windings, a definite reference or zero position of the disk may be established. Inasmuch as the phase relation of the voltages of all of the electric valves is known with respect to the voltages of the valve I'I, the instant of arc-back in the inverse-voltage cycle of any of the valves may readily be determined.

In Fig. 5, I have illustrated another embodiment of my invention in which the occurrence of an arc-back in any one of the main electric valves is recorded and in which means are provided for indicating which of the valves arcs back first. In Fig. 5, the power system is the same as that described and illustrated in Fig. 1 and the same reference numerals have been used to designate corresponding parts. In the arrangement shown in Fig. 5, the electromagnetic devices associated with the anode conductors of each of the elec-tric valves may be the same as those described in connection with Fig. 1. However, as illustrated in Fig. 5, these devices, designated by the numerals |89 to I I4, each includes only a single control winding I I5 and a single saturating winding Il. One terminal of each of the contro-l windings is connected to a common conductor Ill which is, in turn, connected with the hub I It of a rotating disk I I9 through a brush contact i223. The other terminals of the windings I I5 are connected with recording electrodes I2! to IZB, inclusive, through suitable current-limiting resistors I2'I. An additional electrode I28 is connected with the conductor I I'I through the secondary winding |529 of a transformer I 3u, the primary winding ISI of which is energized only upon the occurrence of the first arc-back by a control -circ it illustrated generally by the numeral I 32.

'I'he saturating winding Il@ of the devices I to lis, inclusive, are connected in series and for energization from the conductors |33 and |34'.

which are energized by direct current from the output terminals cf a rectifier bridge |35. The bridge E35 may be energized from the alternating-current supply circuit Iii through the transformer I which also provides a source of power for the motor I3? which drives the recording disk IIS. Across the terminals of each of the saturating windings III is connected a resistance element |33 so that, upon the occurrence of an arc-back in any one of the main electric valves Il' to 22, the transient voltage produced across one of the resistors is impressed on the conductors ist and i3d through a noninductive circuit. This impulse of voltage is impressed on the primary winding Ide of a transformer Iii@ through a capacitor is! to render conductive an electric valve MZ. The valve M2 has the control member thereof connected with the secondary winding I I3 of the transformer winding IM! through a suitable current-limiting resistor Ilili and the anode-cathode circuit thereof connected in series with the primary winding I SI of transformer Ifiii and a capacitor Ii which has been charged through resistors I dii and l-II'I from the directcurrent supply conductors IEE and Lili.

The operation of the embodiment of my invention illustrated in Fig. 5-may be briey described as follows. When the electric valves Il to Z2 are operating normally, the voltages induced in the windings of devices It to IIIi, inclusive, are relatively small and no sparks are caused to jump from the recording electrodes to the rotating disk. Upon the occurrence of an arc-back, a Voltage impulse of large magnitudeI is induced in the winding I I5 of the electromagnetic device associated with the valve which has failed and a spark is caused tor pass from the corresponding electrode to the rotating disk IIII. At they same instant, the voltage impulse induced in the saturating winding IIS is impressed on the transformer Winding |39 and renders electric Valve |42 conductive to discharge condenser |45 through the transformer |30 and thereby to cause a spark to jump from the electrode |28 to the revolving disk ||9. Inasmuch as all of the recording electrodes are supported in alignment on a radius of the disk ||9, there will be tvvo holes in the record paper upon the occurrence of the iirst arc-back and only one hole for each arc-back occurring thereafter, if the disk |I9 is rotated at a relatively slow speed, it may be lpossible to record all the arc-backs occurring in one sequence before the chart makes a complete revolution. It will be readily appreciated that the arrangement shown in Fig. may be operated to indicate or record the time in the inverse voltage cycle at which the arc-back occurs by synchronizing the position of the disk I9 with the inverse voltage cycle of one of the main electric valve means l1 to 22 in the same manner as described in detail in connection with Fig. 4.

Although resistors 33 have been shown connected across windings H6, it will be obvious to those skilled in the art that rectiiiers suitably poled may replace such resistors Without departing from my invention.

While I have shown and described particular embodiments of my invention, it Will be obvious to those skilled in the art that changes and modifications may be made Without departing from my invention in its broader aspects, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of Vthe United States is:

l. In combination, an electric valve means, means for rendering said electric valve means conducting and nonconducting during predetermined intervals ancl for subjecting said valve means to an inverse voltage cycle during each of the normally nonconductingV intervals, said electric valve means being subject to an arcback during said inverse voltage cycle, an energy storage device, means for supplying electric energy to said energy storage device, means including an electric discharge device connected to be rendered conductive in response to the occurrence of an arc-back in said electric valve means for releasing the energy ofsaid energy storage device, and means connected to be energized in accordance with the release of energy of said energy storage device for determining the instant in the inverse voltage cycle that an arc-back in said electric valve means occurs.

2. In combination, an electric valve means, means for rendering said electric Valve means conducting and nonconducting during predetermined intervals and for subjecting said valve means to an inverse voltage cycle during each of the normally nonconducting intervals, said electric valve means being subject to an arcback during said inverse voltage cycle, means including an energy storage device for producing an electric quantity which varies progressively in accordance with the duration of the inverse voltage cycle, means responsive to the magnitude of said electric quantity at the instant of an arcback for indicating the time in the inverse voltage cycle that the arc-back occurs.

3. In combination, an electric valve means, means for rendering said electric valve means conducting and nonconducting during predetermined intervals and for subjecting said valve means to an inverse voltage cycle during each of the normally nonconducting intervals, a capacitor, means for charging said capacitor in accordance with the inverse voltage cycle, and means responsive to the condition of charge of said capacitor upon the occurrence of an arcback for indicating the time in the inverse voltage cycle that the arc-back occurs.

4. In combination, an electric valve means, means for rendering said electric valve means conducting and nonconducting during predetermined intervals and for subjecting said valve means to an inverse Voltage cycle during each or" the normally nonconducting intervals, a capacitor, means for charging said capacitor in accordance with the inverse voltage cycle impressed on said valve means, a second capacitor, means for transferring the charge from said first capacitor to said second capacitor upon the occurrence of an arc-back, and means for measuring the vcharge on said second capacitor to indicate the time in the inverse voltage cycle that the arcback occurs.

5. In combination, a plurality of electric valve means, means for energizing said electric valve means to render said valve means alternately conducting and nonconducting in a predetermined sequence and for subjecting each of said valve means to an inverse voltage cycle during the normally nonconducting periods thereof, each of said electric valve means being subject to arcback during said inverse voltage cycle, capacitance means associated with each of said plurality of electric valve means and having a charge and discharge circuit, current supply means connected to said charge circuit for charging said capacitance means, means including an electric discharge device interposed in the discharge circuit of said capacitance means and connected to be rendered conductive in response to the occurrence of an arc-back in said electric valve means for discharging said capacitance means, and means connected to be energized in accordance with an electrical condition o the discharge circuit of said capacitance means for determining the instant in the inverse voltage cycle 0I" the faulty electric valve means at Which arc-back occurs.

6, In combination, an electric valve means, means for rendering said electric valve means conducting and nonconducting during predetermined intervals and for subjecting said valve eans to an inverse voltage cycle during each of the normally nonconducting intervals, said electric valve means being subject to an abnormal operating connection during said inverse Voltage cycle, a capacitor, means for charging said capacitor between predetermined limits during each inverse voltage cycle, means for discharging said capacitor upon the occurrence of said abnormal operating condition, and means responsive to the charge on said capacitor at the instant that an abnormal operating condition of said valve means occurs for indicating the time in the inverse voltage cycle that said abnormal condition occurs.

7. In combination, an electric valve means, means for rendering said electric valve means conducting and nonconducting during predetermined intervals and for subjecting said Valve means to an inverse vo-ltage cycle during each of the normally nonconducting intervals, a capacitor, means for charging said capacitor in accordance with the inverse voltage cycle impressed on said Valve means, a second capacitor, an electric valve including a control member interconl ll necting said capacitors, means for rendering said electric valve conductive upon the occurrence of an abnormal condition of said electric valve means for transferring the charge from said rst capacitor to said second capacitor upon the occurrence of said abnormal condition, and means for measuring the charge of said second capacitor to indicate the time in the inverse voltage cycle that the abnormal condition occurs.

8. In combination, an electric valve means, means for rendering said valve means conductive and nonconductive during predetermined intervals and for subjecting said valve means to an inverse voltage cycle during each of the normally nonconducting intervals, a record chart, means for moving said chart at a predetermined speed relative to the frequency of the voltage applied to said valve means, means operatively associated with said record chart for indicating a reference point for said chart corresponding to the instant of initiation of inverse voltage cycle, and means for recording on said chart the instant that an arc-back in said valve means occurs relative to said reference point.

9. In combination, an electric valve means, means for rendering said electric valve means conducting and nonconducting during predetermined intervals and for subjecting said valve means to an inverse voltage cycle during each of the normally nonoonducting intervals, a record chart, means for moving said record chart at a predetermined speed relative to the frequency of the Voltage applied to said valve means, means operatively associated with said record chart for indicating a reference point for said chart corresponding to the instant of initiation of said inverse voltage cycle of said electric valve means, and means including means for producing a voltage impulse upon the occurrence of an abnormal condition in said electric valve means for indicating o-n said chart the instant in the inverse voltage cycle relative to said reference point that said abnormal condition occurs.

l0. In combination, a plurality of electric Valve means, means including an alternating-current circut for energizing said electric valve means to render said valve means alternately conduct'- ing and nonconducting in a predetermined sequence, a record chart, means for moving said record chart in a predetermined timed relation with the frequency of said alternating-current circuit, means associated with said chart for indicating on said chart the instant that any of said Valve means arcs back, and additional means for recording on said chart the instant of initiation of said inverse cycle so as to establish a point of reference on said chart for determining the nrst electric valve means to arc back.

1l. In combination, a plurality of electric valve means, means inclucing an alternating-current circuit for energizing said electric valve means to render said valve means alternately conducting and nonconducting in a predetermined sequence, a record chart, means for moving said record chart in a predetermined timed relation with the frequency of said alternating-current circuit, a plurality of electrodes associated with said char", means for impressing an impulse of Voltage on a predetermined one of said electrodes when a corresponding one of said electric valve means arcs back, an additional electrode, and means for impressing an impulse of voltage on said additional electrode only when the first of said electric valve means arcs back.

12. In combination, an electromagnetic device having a closed core of substantially rectangular shape with tivo oppositely located legs of substantially smaller cross section than the remaining two oppositely disposed legs, a Winding on each of said legs of smaller cross section, means for energizing said windings with unidirectional current to produce substantial saturation of said legs of smaller cross section, a second windon each of said legs ci smaller cross section, means for connecting said second windings in parallel, and means responsive to said parallel connected windings for indicating a transient electrical condition in a cond ctor symmetrically located with respect to said legs of smaller cross section, said legs of larger rro-ss section and said parallel connected windings operating to'prevent operation of said transient-indicating means in response to stray magnetomotive forces not symmetrically located with respect to said legs of smaller cross section.

13. In combination, a plurality of circuits normally subjected to a cyclically recurring electrical condition, a plurality of electromagnetic devices arranged one with each of said circuits and each electromagnetic device including a core structure and a first winding on each of said core structures and each Winding being coupled with one of said circuits, a plurality of indicating means each individual to one of said circuits, means connecting rst windings respectively With said indicating means, a second winding on each of said core structures, a direct-current supply means, means connecting said second windings in series and for energization from said direct-current supply means, and means responsive to a transient voltage in the series direct current circuit of said second windings resulting from a voltage induced in one of said second windings in response to a transient voltage in one ci said circuits for indicating the rst transient voltage to occur in one of said circuits.

BURNICE D. BEDFORD.

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