US2576574A

US2576574A - Fault indicating system for control circuits

Info

Publication number: US2576574A
Application number: US51730A
Authority: US
Inventors: Cochran Emilienne
Original assignee: Individual
Current assignee: Individual
Priority date: 1948-09-29
Filing date: 1948-09-29
Publication date: 1951-11-27
Anticipated expiration: 1968-11-27

Description

R. w. cnca-wmw FAULT INDICATING SYSTEM FOR CONTROL CIRCUITS Nam 27, 7/

Filed Sept. 29, 1948 3nventor Patented Nov. 27, 1951 t UNITED STATES PATENT OFFICE FAULT INDICATING SYSTEM FOR CONTROL CIRCUITS Russell W. Cochran, Aliquippa, Pa.; Emilienne Cochran, exccutrix of Russell W. Cochran, deceased, assignor to Emilienne Cochran, Aliquippa, Pa.

Application September 29, 1948, Serial No. 51,730

7 Claims. (Cl. 177-311) 1 2 This invention relates to electromagnet control ciator or similar device are interposed in resystems, and more particularly to a means for spective loop circuits connected respectively indicating which of a plurality of protective conaround the several series-connected contacts of tacts has opened to effect deenergization of an the protective devices. The annunciator windelectromagnetic control means for a translating 5 ings are responsive to the voltage induced in device. the winding of the contactor or relay upon open' This application is a continuation-in-part of ing of one or more of the series-connected conmy copending application Serial No. 723,697, filed tacts, and means are provided which permit cur- January '23, 1947, now abandoned. rent to pass through the annunciator winding Many electromagnetic control systems require 1 during the brief period of this induced voltage that a plurality of protective devices such as but which prevent the flow of current after the limit switches, overload relays, and the like have inductive discharge surge has subsided. When their respective normally-closed contacts conall of the contacts of the protective devices arenected in series with each other and with the closed, o cu r t ws through the onmllloioperating winding of a contactor or relay conator windings- W one f the Protective trolling the supply of voltage to the controlled tacts opens, the transient voltage induced in the device which may be, for example, an electric W of the contactor relay is added to motor. The normally-closed contacts of one or the line volta e and causes a surge current to more of the protective devices open upon occurflow r h t one f the n n l r W rence of abnormal conditions to deenergize the inss which is connected in parallel with h pr series-connected contactor or relay. The prot ot v n c that p An immediate tective devices thus are operative to disconnect H l in ic ti s th y r v to w which the motor from its source of supply when abof the several protective contacts has operated to normal conditions occur. Depending upo the cause the shut-down. Since the annunciator type of protective devices utilized, the abnorwindings are Connected in l p r i r n mal conditions may be either in the motor itthe protective contacts, it is important that the self, the motor circuit, the mechanism driven parallel circuits thus formed be incapable of conby the motor, or in a related control system, ducting current of sufiicient magnitude and duran the ease of a motor, for example, the opertion to prevent drop out of the contactor or ating winding of the main line contactor or the relay. Many irect current op r t d contactors operating winding of an under voltage relay 0r relays remain closed even though the current might have connected in series therewith the in their opera in w n has re ed to ten respective normally-closed contacts of an overp t of s normal value he ssary load relay, various field protective relays, a speed reduction in current flow is accomplished in acresponsive device, a plurality of l m t it h cordance with the present invention by connectand one or more relay the operation of which ing in series with each of the annunciator windis dependent upon the operation of related coninss a d vi e capa f u tin ur nt nly trollers. The large number of such normallyurin th n v l a h h r e vol a closed protective contacts in a control system exists and thereafter capable of pr v ntin th maybe such as to render diflicult the determinai now of current through the loop circuit. For tion' of which one has operated to cause a shutfurther safety, th l p ir uit including the down of the apparatus. This is because many of l d n ln i t r W n ing is interrupted by the normally-closed protective contacts are of Contacts Which p upon energization of the the automatic reclosing type so that after they n un ia r Win in have opened to shut down the apparatus they 4 Loop circuits for the operation of annunciators return to their normal positions and leave no mpl y n lt rna in current introduce certain indication that they have operated. Furtherdifficulties due to the matching of impedances more, the protective contacts may be spaced at which Would be q l O the other hand, considerable distances from each other, for inif direct c r e t W e e p y in such a D stance, at the top and bottom of a skip hoist annunciator circuit, a large volta e su would supplying a blast furnace or at each floor of be available and would assure an adequate voltan elevator system. Consequently, fault locaa e increas so h m t hi f imp an tors or indicators have been developed which are would become unnecessary, and in fact, due to capable of giving a visual or other indication of he l w h l -in vol a e of direc current device which of the plurality of protective contacts has the matching of impedances would be impractical. opened to cause a shut-down of the protected However, since the voltage surge requires direct device. v current and the direct current devices in turn In accordance with this invention, there is prohave a low hold-in voltage, there is introduced vidcd an improved fault indicator in which the the danger of improper ,by-passing 01' the proseveral operating windings of a suitable annunco tective contacts. In order to take advantage of ways present the danger that the contacts may close its normally-open contactsla,

operate improperly or may fail to operate. In

order to render the installation completely safe, therefore, a condenser or other current limiting or interrupting means also should be interposed in the loop circuit. The concurrent solution of all of these correlated problems is therefore necessary to assure safety of operation under all operating conditions":

It is an object of .this invention to provide an improved means for indicating which of a plurality of series-connected protective contacts has opened.

Another object is to provide a fault finder comprising an annunciator having its several operating windings connected in parallel, respectively, with the series-connected normally-closed contacts of a plurality of protective devices.

A further object is to provide a fault finder of the foregoing type usable on direct current systems. .A related object is to provide a fault finder of theforegoing type in which the resistance of the annunciator winding need not be related to the drop-out or pick-up voltage of the contactor or relay controlled by the protective contacts.

Still another object is to provide a fault finder comprising annunciator elements which operate in response to the inductive discharge voltage of an electromagnetic device when deenergized by opening of a protective contact.

Another object is to provide a-means in a circuit paralleling a protective contact and including an annunciator winding which means positively prevents the parallel circuit from conducting current after the transient produced by deenergization of an associated electromagnetic device has subsided.

Further objects and advantages of this invention will become apparent from the. following description wherein reference is made to the drawings in which: I

Fig. l is a schematic wiring diagram illustrating one embodiment of the invention applied in f a control system for an A.-C. motor and utilizing a D.-C. source for the motor control circuits.

Fig. 2 is a schematic wiring diagram of a modification and illustrates how the invention may be applied in a control system for a direct current motor.

Figs. 3.and 4 are fragmentary wiring diagrams of. further modifications, respectively; and

Fig. 5 is a schematic wiring diagram of an additional modification applied in the control of a nA.-C. motor utilizing an A.-C. source for the motor control circuit.

Referring to Fig. l, the controlled translating device is shown as a polyphase synchronous motor II] having an'armature winding Ina and a field winding IOb whichis supplied from a suitable source of direct current. Alternating current is supplied to the armature winding Illa from a suitable supply line I3 under the control of electromagnetic contactors I4'and I5. As will be explained hereinafter, the contactor I4 is operatedtoclose itsnormally-open contacts I411, Mb, andI Ic to start the fm'otor on reduced voltage taken from intermediate taps on ,thewindingsof auto trahsformers I6. Other meanssuch as resisters or reactors may, be used if desired to obtain the reduced starting voltage. The contactor I5 is the running contactor and, after the motor has accelerated to a predetermined speed and the contactor I4 has opened, is operated to I51), and I5c to continue the operation of the motor ID on the full voltage of the supply line I3.

The contactors I4 and I5 are of well-known construction having operating windings NW and I5w, respectively. These windings are adapted to be energized from a'suitable direct current supply line H. The circuits for windings I4w and I5w illustrated in Fig. 1 have been reduced to bare essentials for clarity of explanation. It will be understood that the circuits of an actual controller would include many other features not shown. In the. elementary control system shown in Fig. l, the winding I4w of the starting contactor I4 is controlled by a normally-open pushbutton I8. The circuit for the winding I4w also includes normally-closed contacts I9 of a speedresponsive device 20 which serves to transfer the motor ID from starting to running voltage and also to interlock the windings I41 and I5w to prevent simultaneous energization thereof The winding I5w of the running contactor I5 has connected in series therewith a plurality of normally-closed contacts 2I, 22, and 23 of a plurality of protective devices. The contacts 2I, 22, and 23 may, for example, be the contacts of such protective devices, not shown, as an overload relay, a field-failure relay, and an over-speed mechanism. Whatever the nature of the protective devices controlling or including the normallyclosed contacts 2I, 22, and 23, their function is to deenergize the winding I5w of the running contactor I5 in order to disconnect the armature winding Illa from the supply line I3 upon occurrence of one or more abnormal conditions. The circuit of the winding I5w also includes normally-open contacts 24 of the speed-responsive device 20 and a normally-closed push button 25.

The circuits so far described represent standard practice and form no part of my invention. In the operation of the motor control system of Fig. 1, starting of the motor I0 is initiated by closing thepush button I8 to energize the winding I4w of the starting contactor. I4 from the direct current supply line H. The contactor. I4 thereupon moves to its operated position and the motor In starts due to the impressiongof'a reduced alternating voltage on its armature winding la and accelerates toward a predetermined speed. The push button I8 must be held closed until the motor Ill has accelerated sufiiciently to permit full voltage to be applied. When the motor. I0 reaches the speed desired for voltage transfer, the speed responsive device 20 operates to open its contacts I9 and to close its contacts 24. The winding I4w is thus deenergized to effect opening the contacts I4a, I41), and Me. Concurrently, the winding I5w is energized and the contactor I5 closes its contacts I5a, I5b,

and I to apply full voltage to the motor IIl if all of the protective contacts 2|, 22, and 23 are closed. I f

Under normal conditions, the contacts 2I, 22, and 23 remain closed and the motor continues in operation until the pushbutton 25 is opened. Opening of the push button 25 deenergizes the winding I510 and causes the contactorI5 toopen its contacts thereby to'eifect deenergization of the motor Ill, The occurrence of abnormal, conditions in the motor It or equipment driven by it causes one or more of the protective contacts 2|, 22, and 23 to open and similarly disconnects the motor from the source of supply.

In order to provide an immediate and readily observable indication as to which of. the protective devices has operated to disconnect the motor ID from the supply line I3, a plurality of loop circuits 26, 27, and 28 are connected around the normally-closed protective contacts 2|, 22, and 23, respectively. The

loop circuits

2E, 21, and 28 include operating windings 29w, 3020, and 31w, respectively, of a suitable annunciator which are connected in series, in the respective loop circuits, with a plurality of current blocking means such as

condensers

32, 33, and 34, respectively. As will be explained hereinafter, the condensers prevent the flow of current through the loop circuits around their associated protective contacts to the winding w after the inductive discharge voltage oi the winding 15w has subsided. The loop circuits and 21 have a common portion including normally-closed contacts 29a, the loop circuits 2! and 28 have a common portion including normally closed contacts a, and the loop circuit 28 is completed by normally-closed contacts 3la.

Preferably the annunciator is of rugged construction and is one in which the indicating means is retained in indicating position after its associated operating winding has been deenergized. As illustrated, the annunciator is of the drop type and the operating windings 2910, 3020, and 3lw are magnetically associated with suitable indicating mechanisms, respectively, comprising clapper-type magnetic armatures 29b, 30b, and 3|?) which, when moved to their energized position, effect opening of the

normallyclosed contacts

29a, 38a, and 31a, respectively. Since the several mechanisms are identical, a detailed description of only one is suflicient. The armature 29b is arranged to retain an indicating flag member 290 in a normal non-indicating position as shown. The flag member 290 is suspended from one end portion of a centrally-pivoted link 1 29d having its other end portion normally retained in a lower position by latching engagement with the armature 2972. Upon energization of the winding 29w, the armature 2% moves to its attracted position releasing the link 29d and permitting the flag member 290 to drop to an observable indicating position. Concurrently, the contacts 29a are opened. The contacts 29c can be reclosed and the flag 29c raised to nonindicating position only by manually re-engaging the link 29d with the armature 2912.

Upon opening of any one of the contacts 2|, 22, or 23, the current decreases and eventually ceases to flow through the winding l5w. As a result of the relatively high inductance of the winding I5w, a large transient voltage surge or inductive kick results from the collapsing lines of the magnetic force through the core of the winding cutting the turns of the latter. This transient voltage is added to the line voltage and causes a current impulse to flow through the loop circuit around the protective contact that has opened. Normally the series connected annunciator winding, the condenser, and the associated interlock contact in this loop circuit are by-passed by the respective contact 2%, 22, or 23, and no voltage is impressed upon the winding in the loop. When the protective contact opens, however, the associated loop circuit is effectively connected in series with the winding l5w across the source H. The

voltage induced in the winding l'5w is much higher than the line voltage and causes a transient charging current to flow through the one of the

loop circuits

25, 21, or 28 which is connected around the opened one of the protective contacts. This transient current causes the dropping of the proper one of the several flag members giving an immediate visible indication as to which protective contact has opened. The flag members are preferably coded as by numbering in accordance with similar numbers on its associated protective contacts. With this immediate indication as to which protective contact has opened, no time is lost in determining the source of the fault which caused the motor I 6 to shut down. All that is required in order to restore the indicating system for further operation is to reset the armature and link mechanism which operated to indicate the fault.

The operation of the control system of Fig. 1 will be explained more specifically with the assumption that the protective contacts 21 have opened. Opening of the contacts 2! causes the discharge voltage of the winding lbw to be added to that of the line and the combined voltage forces a current through the loop circuit 26 including the series connected condenser 32, the winding 2910, and the normally-closed contacts 29a. This momentary surge of current is willcient to cause the armature 29b to be moved to its attracted position by the winding 29w. When the armature 23b reaches its attracted position the link 29d is released and the flag 29c drops to an observable position. Concurrently, the contacts 29a open to interrupt the only remaining low impedance circuit to the winding l5w. This impulse of current through the shunt circuit also starts to charge the condenser 32 which, if the contacts 29a had for any reason failed to open, would have reached a charged condition preventing the further flow of current to the winding i520. Consequently, it is seen that the protective contacts are by-passed by shunt circuits each of which includes two separate means to prevent the continued flow of current through the shunt circuit to the controlled winding after one of the protective contacts has opened. Each of the other protective contacts and associated shunt circuits operates in a similar manner as outlined above.

After the fault has been corrected and the protective contact which opened has returned to its normal position, the motor It] may be reaccelerated by operation of the push button la in the same manner as described hereinbefore.

Referring now to Fig. 2, a direct current motor 35 is arranged to be connected for energization from a suitable supply line 39 through a suitable current-limiting acceleration and speed control means 3'! when a knife switch 38 and an electromagnetic contactor 39 are both in their closed positions. The motor 35 has an armature winding 35a and may have a series field winding 35b and a shunt field winding 350 the latter of which i is supplied from a suitable source of direct current as indicated. The contactor 39 has an operating winding 39w and also has normally-open main contacts 33a. and 39b in series with the motor armature 35a. A master switch 40 has stationary contacts 4! and 42 adapted to be bridged by a contact segment 43 in its on position and stationary contacts 44 and 45 adapted to be bridged by the segment 43 in its operative or on position. The master switch s9 is arranged to control the energization of an under voltage relay 46 having an operating winding 46w and normally-open contacts 46a and in turn controls the operation of the contactor 39. It will be understood that the master switch 4|! may have many more contacts and segments and be used to control also the acceleration and speed control means 31. Connected in series with each other and in series with the winding 4510 are the plurality of normally-closed series connected protective contacts 2|, 22, and 23 of Fig. 1. When the master switch 40 is in its off position, an operating circuit for the winding 4520 is from one side of the line 36 through the knife switch 38, the contact 4|, the segment 43, the contact 42, the contacts 2!, 22, and 23, the winding 4611), and the knife switch 38 to the other side of the line 36. After the relay 46 has operated, the portion of the above traced operating circuit through the masterswitch 4!: between the contacts 4! and 42 is by-passed by the now closed contacts 48a through the conductors 5|. It is apparent that the relay 46 may be deenergized at any time by the opening of one of the contacts 2!, 22, and 23.

A plurality of

loop circuits

52, 53, and 54 include the

operating windings

29w, 3520, and 3 lw, respectively, of the annunciator of Fig. 1 and also include in series With these windings the plurality of

condensers

32, 33, and 34, respectively. The

loop circuits

52, 53, and 54 also include, respectively, the normally-closed

contacts

29a, 30a, and 3m of the annunciator as indicated. In the operation of Fig. 2, closure of the knife switch 38 with the master switch 4!! in its off position and the contacts 2 I, 22, and 23 all closed completes the previously traced operating circuit for the winding 46w and the under voltage relay 46 moves to its operated position. The motor is started by moving the segment 43' into bridging engagement withthe contacts .44 and which completes an obvious energizing circuit for the winding 39w through the conductors 5! and the now closed contacts 46a. In response to energization of its winding 3910, the contactor 39 closes its contacts 39a and 39b to supply voltage to the motor 35 and the acceleration control means 31 functions in a well-known manner to control the rate of acceleration of the motor 35.

lf any one of the contacts 2|, 22, and 23,

opens, the winding 45w is deenergized and the contacts 416a opento interrupt the energizing circuit for the winding 39w causing the contactor 39 to open and the motor 35 to be deenergized. Upon opening of any of the protective contacts,

the surge voltage produced by the winding 46w causes energization of the annunciator winding connected in parallel with the protective contact that has opened. This energized annunciator winding functions as described in cpnnectionwith Fig. 1 to provide an indication as to which protective contact has opened and also to interrupt the by-pass circuit around the open protective contact. It is to be noted that the arrangement of the

contacts

29a, 30a, and 3| a in Fig. 2 is such that the opening of any one of them While its associated protective contact is open positively disconnects the winding 45w from the supply source. The condenser in the loop circuit around the open protective contact alsoserves to insure that no current continues to flowqfrom the line 36 to the winding 4611). After one of the protective contacts has opened to dropout the relay 4'6, the relay 45 cannot be reclosed to 'permit energization of the contactor 39 until the master switch 40 has returned to its off position and all of the protective con-'- tacts are reclosed. Thus, even if the protective contacts reclose upon deenergization of the motor, the motor cannot automatically restart. In any event, a visible indication as to which protective contact has opened is provided at the annunciator which may be mounted remote from the contacts.

The modification illustrated in Fig. 3 shows the use of a unidirectional conducting device instead of a condenser in a loop circuit of the type shown in Figs. 1 and 2. Only the series connected protective contact 2| is shown in Fig. 3 and it is by-passed by a loop circuit 58 including a suitable rectifier 59, the winding 29w of the annunciator, and the normally-closed contacts 28a connected in series. The rectifier 59 is preferably of the dry type and has a definite reverse voltage break-down value. It is of rugged construction and is so poled with respect to the supply line I! or 36 that current flow through the winding 2910 is normally blocked. Upon opening of the contacts 2|, however, the discharge voltage of the winding I5w or 4610 when added to that of the line voltage is sufiicient to break down the normal blocking action of the rectifier 59 and a surge of current passes through the winding 29w. This current is sumcient to operate the annunciator elements associated with the winding 2921; and to cause opening of the contacts 29a. When the surge voltage has decreased the normal blocking action of the rectifier 59 is restored so that if the contacts 29a should have failed to open, no current can flow through the rectifier 59 to prevent the drop-out of thecontactor or relay. Since rectifiers currently available have a tendency to deteriorate when subjected to excess reverse voltage, this modification is not preferred in those instances in which the annunciator may be called upon to operate frequently.

Fig. 4 illustrates a further modification in which an electronic tube 60 is used instead of the condensers of Figs. 1 and 2 and the rectifier of Fig. 3.- The electronic tube 60 is of a well-known type having but two electrodes mounted in a gaseous filled envelope and has a predetermined breakdown voltage. If the voltage impressed on the electrodes of the tube 60 isbelow the breakdown voltage, the tube 60 conducts nocurrent. However, if the voltage is above the breakdown value, the tube 60 conducts current and has but a very low impedance. The breakdown voltage of the tube 60 should be materially above the normal voltage of the supply lines and materially below the abnormal voltage produced when the line contactor or under-voltage relay is deenergized. The tube 60 thus constitutes a means responsive to an excess voltage which permits current to flow through the winding 29w upon opening of the contact 2| and which prevents current from flowing in this circuit after the inductive discharge has subsided. It will be understood that other devices having suitable operating characteristics may be used instead of the condenser, rectifier, and tube. For example, so-called thyrite type resistors may be used if desired, these having the property of conducting current only when high voltage is impressed thereon. p The foregoing description and explanation apply to direct current control systems. Ifalternating current is used for the control circuits, reliance cannot be placed for obvious reasons upon the inductive kick of the contactor orrelay.

Thecircuits of. Figs. 1 and 2 may, however, be used in alternating current systems provided that the impedance of the annunciator windings is large enough to prevent the flow of current of operative magnitude to the contactor or relay when one of the protective contacts is open. In Fig. 1, for example, when the contacts 2i open, the winding 2%; is immediately energized by current flowing through it and the condenser in series therewith. Thus operation of the annunciator would be caused by the voltage normally existing between the lines I! instead of by the surge voltage as in the case of the direct current system. The winding 2911) and the condenser 32, however, must have a low enough impedance to permit the desired current flow to operate the annunciator but must have suflicient impedance to limit the current through the winding 15w to a value helow the drop-out value of the contactor 15. This requires a very delicate balance of impedances. Because of this delicate balance, the contacts such as 29a, 30a, and am should be included for safety.

Preferably, for alternating current service, the condensers are omitted and external resistors are used instead. As shown in Fig. 5, resistors 59 and .10 limit the current that can flow to a winding Hw. of a main line contactor H for an alternating current motor 72 supplied from a suitable supply line H through a knife switch 75. The 'contactor 'II is provided with nornially-open auxiliary contacts lid. The motor control circuit of Fig. 5 also includes a normally-closed push button 76 and a normally-open push button 18. Only two protective contacts 2| and 22 are shown in Fig. 5 and are by-passed by loop circuits I9 and 80 including respectively the resistors E9 and 70, the annunciator windings 29w and 36w, and the contacts 29a and 33a.

In the operation of Fig. 5, closure of the ,push button 18 energizes the winding 'llw by completing a circuit through the contacts 2! and 22 from a single-phase of the supply line 74. Operation of the contactor H in response to the energization of its winding 'Hw closes its main contacts to energize the motor 12 and closes its auxiliary contacts Ha to complete a holding circuit for the winding 'Hw around the push button 18 and through the push button It. Thus the motor 12 may be deenergized at any time after the push button 18 has been released by operation of the push button '16.

The motor l2is also deenergized when either of the contacts 2! and-'22 opens. Upon opening of either one of the protective contacts, the circuit to the winding 'Hw remains completed for an instant through the loop circuit around the opened contact. Current flowing through the loop circuit energizes the winding therein and an indication is made of its energization. Concurrently, the contacts operated by the annunciator winding open and interrupt the only remaining circuit to the winding N20. The contacto-r 1| thereupon drops out to deenergize the motor i2 and an indication is left as to which protective contact opened to cause the shut down.

Preferably the impedance .of the loop circuit is .sufiicient to reduce the current in the winding 11w below the drop-out value even though the

contacts

29a or 30a should fail to open. By using these contacts the applicant assures reasonable safety without the necessity of such precise impedance matching.

However, the D.-C. operated control circuit is preferred because of the large inductive kick and,

10 when such circuit includes the additional means for interrupting the loop circuits, proper and safe operation of the control without the accompanying danger of a protective contact being improperly by-passed by the loop circuits is obtained.

Thus the loop circuits around protective contacts can be introduced for indicating while eliminating the hazards normally accompanying the use of such loop circuits.

Instead of employing an annunciator as the indicating device, I may use an operation recorder of known construction or signal lamps which are energized or deenergized by appropriate relays on the opening of an interlock contact. The operation recorder has the advantage in that it indicates the nature of the fault, the time of occurrence, and length of time it existed.

It will be evident that, since the protective contacts, which remain closed upon the occurrence of a fault, shunt the annunciator coils other than the one connected across the protective contact which has opened, a false indication is impossible. The invention thus has the advantage of certainty in operation and indication. In addition, the apparatus involved is simple and inexpensive and does not introduce any complications into the design or operation of the control circuit itself. Since the only moving parts are the annunciator armature and link,'a minimum of maintenance is required. The annunciator or other indicating means operates immediately upon the opening of one of the protective interlocks, and thus no delay is involved in determining which one has opened. The investigation necessary to determine the cause of the existing abnormality may therefore be directed immediately toward the most likely sources of trouble.

A further advantage of the invention is that the high voltage of the inductive kick is absorbed in sending current through the indicator circuit. This prevents burning of the protective contacts upon opening thereof, reduces the voltage stress on the insulation of the conductors in the main control circuit, and tends to prevent temporary short or sneak circuits which might otherwise result from insulation failure and cause faulty operation of or damage to other current-carrying apparatus connected to the circuit.

A further advantage of the invention is that,

in event the control bus itself is disconnected automatically in response to operation of one of the protective contacts, the inductive kick causes such a rapid and large surge of current that the indicating means is certain to operate either during the short interval required for the contacts in the control bus to open or during the arcing interval incident to the opening of the control bus contacts. 1

Although I have illustrated and described preferred embodiments of the invention, it will be recognized that changes in the details of construction and arrangement may be made without departing from the spirit of the invention or the scope of the appended claims.

I claim:

1. A fault indicating system comprising, an electromagnetic device having an operating winding, a supply circuit for said winding, a plurality of normally-closed protective contacts connected in said supply circuit and in series with each other and in series with said one of said contacts, and means respective to said circuits and each being operative, after actuation of said indicating means, in response to the flow of current in its associated one of said loop circuits for preventing the flow of "current, and in its said associated loop circuit.

each of said last named means including a voltage responsive means in series with a contact means and in series with the one of said actuating windings, in its associated loop circuit, and said contact means being operated by its associated one of said actuating windings.

2. A fault indicating system comprising, an

electromagnetic device having an operating winding, a supply circuit for said winding, a plurality of normally-closed contacts connected in series in said supply circuit and in series with said winding, loop circuits connected around said contacts, respectively, an indicating means having a plurality of actuating windings which are connected in said loop circuits, respectively, and each of which actuating windings has an impedance so related to the impedance of said operating winding that when one of said actuating windings is connected in series with said operating winding in said supply circuit said electromagnetic device remains in a predetermined operated position, and voltage responsive means in said loop circuits, respectively, each voltage responsive means being operative to permit a surge of current to flow through its assoated loop circuit consequent upon opening of the associated one of said contacts and thereafter preventing the flow of current in its loop circuit, the actuating winding in said last mentioned loop circuit being adapted to become operatively energized by said surge to actuate said indicating means.

' 3'. In a fault indicating system, the combination with an electromagnetic device having an operating winding, a supply circuit for said winding, a plurality of normally-closed protective contacts connected in said supply circuit in series with each other and in series with said winding, loop circuits connected around said contacts, respectively, and indicating means having actuating windings connected in said loop circuits, respectively, and thereby in parallel with the contacts thereof, and each actuating winding being adapted to become operatively energized, upon opening of the one of said contacts in parallel therewith, to actuate said indicating means, of

two current flow preventing means in each of vent flow of current in the loop circuit containing its said associated actuating winding.

4. A fault indicating system in accordance-with claim 3 characterized in that one of said current flow preventing means in each loop circuit is a condenser, which by accumulating a charge revents the continued fiow of current in its associated loop circuit.

1 5. A fault indicating system in accordance with claim 3 characterized in that one of said current flow preventing means in each loop circuit is a condenser and the other of the current flow preventing means in each loop circuit is an electromagnetically operated switch contact.

6. In a fault indicating system, the combination with an electromagnetic device having an operating winding, a supply circuit for said winding, a plurality of normally-closed protective contacts connected in said supply circuit in series with each other and in series with said winding, loop circuits connected around said contacts, respectively, and indicating means having actuating windings connected in said loop circuits, respectively, and thereby in parallel with the contacts thereof, and each actuating winding being adapted to become operatively energized, upon ings and each, consequent upon opening of its associated one of said normally-closed contacts and after energization of its associated one of said actuating windings and resultant actuation of the said indicating means thereby, being operative to prevent the flow of current in the loop circuit containing its said associated actuated winding.

'7. In a fault indicating system, the combination with an electromagnetic device having an operating winding, a supply circuit for said winding, a plurality of normally-closed protective contacts connected in said supply circuit in series with each other and in series with said winding, loop circuits connected around said contacts, respectively, and indicating means having actuat ing windings connected in said loop circuits, respectively, and thereby in parallel with the contacts thereof, and each actuating winding being adapted to become operatively energized, upon opening of the one of said contacts in parallel therewith, to actuate said indicating means, of means connected in said loop circuits, respectively, in series with the actuating windings and each, consequent upon opening of its associated one of said normally-closed contacts and after energization of its associated one of said actuating windings and resultant actuation of the said indicating means thereby, being operative to prevent the fiow of current in the loop circuit containing its said associated actuated winding, each of said last named means being operative in response to the abnormal voltage which occurs upon opening of its associated normally-closed contact.

RUSSELL W. COCHRAN.

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

UNITED STATES PATENTS Number Name Date 1,537,211 Wootton May 12, 1925 1,901,628 Brainard Mar. 14, 1933 2,127,343 Parlett Aug. 16, 1933 2,168,805 Pelican Aug. 8, 1939 FOREIGN PATENTS Number Country Date 545,982 England June 22, 1942