US2434595A - Magnetizing-inrush tripping suppressor - Google Patents

Description

Jan. 13, 1948. w, ISQNNEMANN ETAL 2,434,595

MAGNETI Z ING- INRUSH TRIPPING-SUPPRESSORS Filed Nov. 6, 1943 A INVENTO R5 M'l/iam Senna/nan v and Myron I? ZaJ/n/aK.

ATTORNEY Patented Jan. 13, 1948 UNITED STATES PATENT OFFICE MAGNETIZING-INRUSH TRIPPING SUPPRESSOR Application November 6, 1943, Serial No. 509,242

15 Claims. 1

Our invention relates to differential relays for the protection of transformer-banks or other alternating-current electrical apparatus of a type which is subject to aninrush of magnetizing current, or other transient fault-simulating conditions, when the apparatus is first energized. More particularly, our invention relates to ratiodifferential relays, which respond to the ratio between the difference-current and the throughcurrent, rather than responding simply to a predetermined magnitude of the difference-current alone, the difierence-current being the difference between the input and output currents of the protected apparatus, or the sum of all of the currents entering the apparatus, whereas the through current is the sum of the input and output currents, or any load-current, or combination of load-currents, of the protected apparatus, Our invention is more particularly related to these ratio-(inferential relays, because such relays can be, and are, set much more sensitively than straight dihferential relays, thus introducing the danger of faulty tripping, on the magnetizingcurrent inruslrnecessitating some form of magnetizing-inrush tripping-suppresson Several different forms of magnetizing-inrush tripping-suppressors have been devised, in the past, but all of these previous devices have involved difficulties in one form or another. Such difficulties may include a race between getting the suppressor-relay contacts open and the differential-relay contacts closed, or the introduction of undesirable delays in the tripping-time in the event of faults, either a permanent retardation of the tripping-time, or a delay which is introduced under certain fault-conditions.

An object of our present invention is to provide a magnetizing-inrush tripping-suppressor which takes advantage of the well-known fact that the magnetizing inrush-current of a transformer always a pronounced asymmetrical component, or a direct-current component which is superimposed upon the alternating-current component of the current which is first fed into the powertransiormer when the latter is first energized,

this asymmetrical component being of a transient nature which dies out in a certain length of time, which may be of the order of 1 to 5 seconds, more or less, depending upon the size and characteristics of the power-transformer to be protected the system connected thereto.

According to our present invention, we sort out this direct-current component, at least partially segregating it from the alternating-current component of the transformer-current, and we provide a device which is selectively responsive to this direct-current component for rendering the differential fault-responsive protective-relay relatively ineffective, or for preventing said rotective-relay from producing a tripping-operation while the direct-current component is present in a predetermined degree or magnitude. Thus, We prevent the faulty tripping'or opening of the circuit-breakers which are connected in the input and output leads of the protected transformer, during the magnetizing-current inrush.

This magnetizing-inrush tripping-suppressor may take the form either of an extra or auxiliary restraining winding or other restraint-torque.

, means which is incorporated in the differential protective-relay itself, or the suppressor may take the form of a separate suppressor-relay having its operating-coil energized selectively responsively to the alternating-current component of a relaying current which is derived from the protected transformer, and having a restraining coil which is energized selectively responsively to any direct-current component which may be present in the same relaying current. When We refer to differential protective-relays, in this connection, we mean to include either straight differential relays or ratio-differential relays.

An asymmetrical-current-responsive suppressor, of the nature just mentioned, will introduce a time-delay during which it is impossible to trip or open the circuit-breakers protecting the protected transformer, throughout the duration of the asymmetrical or direct-current component of the transformer-current. This will introduce a slight delay in the tripping-time in the event of bona fide internal fault in the protected transformer, in all cases except where such faults are symmetrical or substantially symmetrical, the time-delay depending also upon the degree of asymmetry and the time-constant of the directcurrent transient. However, the direct-current transient of an internal fault will always have a very much shorter time-constant than the directcurrent transient of the inrush-current, in any bank of power-transformers which are large enough to justify the use of a differential protective relay.

A further object of our invention, however, is directed to auxiliary means which may be utilized for distinguishing between asymmetrical components which are obtained during magnetizing-current inrush, and asymmetrical components which are obtained as a result of asymmetrical faults occurring within the protected transformer while it is in service. To this end, we may provide a relatively slowly responsive remembrance-relay means, which is responsive to an energized condition of the protected apparatus, or any suitable fault-detecting means, for rendering said suppressor-means inoperative.

In the case of the remembrance-relay means, th slowness of its response is such that the differential protective-relay operates without any suppressor, if an apparent fault-current occurs when the protected transformer has been operating under normal voltage-conditions, and so that the diiferential protective-relay is under the con trol of the suppressor whenever a direct-current component appears after a period of deenergization, or substantial deenergization, of the protected transformer. This slowly responsive means may take the form of a fault-responsive fau1tdetector, or relay-means, energized responsively to a. voltage of the protected apparatus. This voltage may either be the several single-phase voltages of the transformer-bank, either delta-voltages or star-voltages, or it may be a phase-sequence component of the transformer-voltage, or any combination of phase-sequence components.

In this way, our tripping-suppressor apparatus becomes effective, only for asymmetrical currentcomponents which appear either during the initial magnetizing-current inrush which occurs when voltage is first applied to a previously unenergized transformer-bank, or the voltage-responsive adjustment may be such that the suppressor also operates during the recovery-voltage period when the transformer-voltage is recovering, or being restored to full value, after the clearing of an external fault somewhere on the electrical system to which the protected transformer is connected.

With the foregoing and other objects in view, our invention consists in the relays, elements, combinations, systems, and methods, hereinafter described and claimed, and illustrated in the accompanying drawing, the four figures of which are diagrammatic views of apparatus and connections which illustrate our invention in four difa bank of power-transformers PT in a three-phase line, the power-transformer bank being protected by means of oil circuit-breakers CB which are provided with trip-coils TC. Three differential relays are provided, one for each phase, as indicated at RDA, RDB and BBC, and each relay is provided with a differential-current operating-winding Ill, and two through-current restraint-windings H and I2, one for each of the terminals or windings of the protected power-transformer PT, so that one of the restraint-windings II or !2 responds to the input-currents of the protected transformer, While the other is energized in response to the output-currents of the protected transformer.

We have illustrated our invention in connection with high-speed or instantaneous ratio-differential relays of the balanced-beam type, as indicated at l3, but we Wish it to be undnerstood that our invention is also susceptible of application to slow-speed differential relays, and we furtherwish it to be understood that our invention is also susceptible of application, not only to ratiotype diiferential relays, having the through-current restraining-means I l l2, but that it is also applicable to straight differential relays which 4 omit the through-current restraining means The differential relays RDA, BBB and RDC are provided, in a known manner, with tripping-contacts l4 and I5, which are utilize to energize the trip-coils TC of the two circuit-breakers CB which are connected to the primary and secondary terminal-leads of the protected transformer PT.

In accordance with our present invention, we utilize what is known as a transient shunt, for at least partially segregating the alternating-current component and the direct-current component of some relaying electrical quantity which is derived, or obtained in some manner, from the protected transformer. This transient shunt takes the form of two parallel-connected relaying-circuits 2i and 22, the first circuit having a low ratio of inductance to resistance, as obtained by the use of a serially-connected resistor 23, while the second circuit has a high ratio of inductance to resistance, as is obtained by the use of a serially-connected coil 24 having such a high ratio. As a result of this divided-circuit connection, the direct-current component passes freely through the coil 24, and is impeded by the resistance 23 in the other circuit, while the alternating-current component divides between the two circuits in a manner inversely proportional to the respective impedances of the two circuits. The second relaying circuit 22 is thus selectively responsive to the direct-current component, while the first relaying circuit 2| is selectively responsive to the alternating-current component of the current in the common or undivided portion, 25, of the relaying circuit.

We utilize a magnetizing-inrush tripping-suppressor, which is suitably responsive to the directcurrent component in the second relaying circuit 22, for suppressing or preventing tlipping-opera tions produced by the differential relays RDA, BBB and RDC. This tripping-suppressor may either take the form of an auxiliary restraintmeans or winding 26, which is placed on, or associated with, the differential relay, as shown in Figs. 1, 2 and 3, or the tripping-suppressor may take the form of a separate relay TS, as shown in Fig. 4, having tripping-contacts 27 in series with the tripping-contacts l4 and 15 of the differential relay. This separate tripping-suppressor relay TS has an operating winding 28, which is included in the alternating-current-selective relaying-circuit 2|, and a restraining winding 29 which is in the direct-current-responsive relaying-circuit 22.

The tripping-suppressor, in either form of embodiment, may be responsive to the direct-current component of any function of any alternating electrical quantity of the protected apparatus PT, whether it is an apparatus-current or an apparatus-voltage, or any combination of these. For simplicity, however, we have illustrated our invention in the manner in which we at present prefer to utilize it, in which the differential current, which is utilized for operating the differential protective relays RDA, RDB and RDC, is subdivided, by means of the transient-shunt connection, so as to sort out, or partially sort out, the alternating-current component in the relaying-circuit 2|, and the asymmetrical or directcurrent component in the relaying-circuit 22. The operating coil in of the differential relay is included in the alternating-current branch 2| of the relaying-circuit 25, while the inrush-suppressor coil 26 of Figs. 1, 2 and 3, or the coil 29 of 1 5 Fig. 4, is connected in thedirect-current branch 22 of the' common relaying-circuit 25..

In most applications ofour inventiomwe prefer to supplement the suppressor-coil 26 or" 29 with additional means for making the suppressor-coil operative only when there is no fault on the system, or for rendering the suppressor-coil inoperative, or. relatively inefiectual, when normal voltage-conditions appear on the powertransformer bank PT, and for a. short moment of time after the removal or discontinuance of such normal voltage-conditions; while permitting the suppressor-coil to be fully operative when no voltage, or a, predeterminedly low voltage, appears on the protected transformer, and for a moment of time after normal voltage is first applied to the protected transformer. This suppressor-controlling apparatus can take a number ofv difierent forms of embodiment, several of'which are illustrated in Figs. 1, 2, 3and 4.

In Fig. 1, the suppressor-controlling apparatus takes the form of three delayed-action single-phase under-voltage relays A, B and C, which are energized from potential-transformers 3i] which are connected across one of the polyphase terminals of the power-transformer PT whichis being protected. These voltage-responsive relays A, B and C have. bath -contacts 3|, 32 and 33, which are connectedinseries with the respec tive direct-current branches 22 of the several differential-current relaying-circuits 25. These voltage-relays A, B and C may be connected to respond to different phase-voltages of the polyphase line, these phase-voltages'being either delta or star connected. While we have illustrated these voltage-relays A, B and CY as having backcontacts 3|, 32 and 33 which are connected in series with the several suppressor-windings 25 of Fig. 1, it is obvious that we are not limited to this particular connectiomand, that wezmay utilize any form of connection which will make the suppressor-winding inefiectlve when. the corresponding one of the three voltage-relaysA, B and C is in its actuated or responsive position,

while makin all'ofthe suppressor-windings 26" effective, to perform their suppressing-function, whenever all of the voltage-relays A, B and C are in their deenergized positions.

In Figs. 2 and 3, a single polyphase-responsiv voltage-relay 34', or 35, is utilized, in place of the three singleephase suppressor-controlling relays A, B and C of Fig. 1. In Fig. 2, the suppressorcontrolling relay 34 is a time-delayed undewolt age positive-sequence relay which is energized from the positive phase-sequence component. E1 oithe polyphase transformer-voltage, as obtained from a phase-sequence network 36. This undervoltage-relay 34 has three back-contacts31 which are included in. the respective direct-current-segregatingbranches 2'2 oiithe transient shunts.

In Fig. 3,. the suppressoracontrolling relay 35 is an instantaneously. operating undervoltageinegative-phasewequence relay which is energized.

from the negativeephase-sequence voltage-com,-

ponent E2, as; obtained from a phase-sequence H is: normally energized, even when the circuitbreakers CB are open, the undervoltage relaysv A, B and C are: normally energized, so as to close their respective make-contacts 42, although the relays areillustrated in their deenergized po indicated diagrammatically, in the drawing, by

means of dashpots 5|, which are associated with the suppressor controlling relays A, B and C and 34. This representation of dashpots 5| is intended tobe symbolic of any means, or arrangements, or types of apparatus; which will make the suppressor-controlling relays slower, in either responding or dropping out, than the fault-responsive or differential relays RDA, RDB and BBC.

In operation, when the protected power-transformer PT is in thenon-energized condition, the suppressor-supervisory relays A, B, C, 34 and 35 of Figs. 1, 2 and 3 are in their. illustrated. deenergized or drop-out positions; When polyphase voltage is first. applied to the protected transformer PT by the closure of one of its circuitbreakers CB, voltage will be applied to these voltage-responsive suppressor-controlling relays, and these will begin to pick up, except in the case of the negative-sequence relay 35. However, the pick-up operating-time of the single-phase voltage-relays A, B and C, or of the positive-phasesequence'voltage-relay 34, is longer than the time during which the magnetizing inrush-current of the power-transformer PT will create an artificial difference-current tending to produce a faulty operation of the protective differential relays RDA, RDB and RDC, During this time, the

direct-current component of the magnetizing in-- rush-current of the power-transformer flows selectively through the restraint-winding 26' or 29, and presents a. faulty tripping-operation of the circuit-breakers CB.

In the case of the forms of embodiment shown in Figs. 1, 2 and 3, the restraint is placed directly upon the differential or protective relays RDA, RDBand RDC, whereas, in the form ofembodiment shown in Fig. 4, the restraint is applied to a separate tripping-suppressor relay TS, which has its make-contacts 2'! in the tripping-circuit, in series with the tripping-contacts l4 and I5 of the differential or fault-responsive relay. In this latter case, the restraint-winding 29 is so strong that it preventsa picking up of. the. auxiliary tripping-suppressor relay TS, under the influence of its operating coil 28, until. the direct-current component ofthe line-current has subsided to a predetermined fraction of the alterhating-current component of the same. current,- during, which. time the magnetizing-current in.-' rushwill have subsided suificlently so that the quicker-acting difierential' relays-RDA, RDB and RDC will. have reset themselves to their normal, non-actuated positions, withtheir tripping-con.- tacts I4 and I5 open. In this manner, weeffectually avoi-da faulty tripping-operation as a result of a difierential-relay response during the magnetizing-current inrush-period;

In. the event that a'bona fide fault should occur within the protected transformer PT. while the latter is in operation, if the fault is symmetrical,

there will not be any direct-current component of the fault-current, and hence there will not, in any event, be any effective restraint or inhibition against an immediate tripping-operation. Even though the fault should be asymmetrical (which is the usual case), the duration of its direct-current transient will be, in any event, much shorter than the direct-current transient of the magnetizing inrush-current, and hence the direct-current component would not long delay tripping, even though the operation of the tripping-suppressor means were not restrained by the voltage-responsive supervisory relays A, B, C, 34, 35, A, B or However, as previously pointed out, we prefer to utilize voltage-responsive relays or fault-responsive relays, for looking out the tripping-suppressor means, or rendering it ineffective, in the event of an actual fault within the protected transformer PT, or in the event that such fault occurs when the transformer is in operation, with voltage applied thereto previous to the development of the fault-condition.

Thus, in Fig. 1, any fault which develops within the protected transformer PT at a time when the transformer is already energized will occur at a time when all three of the voltage-responsive relays A, B, and C will be energized, so that their back-contacts 3|, 32 and 33 will be opened. Hence, the direct-current-responsive restraint- Winding 26 of each of the differential relays RDA, RDB and RDC will be deenergized. If a fault should occur on the protected transformer PT, one or more of the voltage-relays A, B and C will start to drop out, but their drop-out time will be far longer than the time required for the differential relay RDA, RDB or RDC to effect a tripping operation. Hence the tripping operation will be performed by one or more of the differential relays RDA, RDB or RDC, without any hindrance whatsoever from the auxiliary restraining-Winding 25 which is energized selectively responsively to the direct-current component of the differential transformer-current whenever its relayingcircuit 22 is energized.

In Fig. 2, the positive-sequence voltage-relay 3e performs a function similar to that of the three single-phase relays A, B and C in Fig. 1. When the protected transformer PT is first energized, the phase-sequence voltage-relay 34 starts from its deenergized position, with its contact 3! closed, and it starts to open its contact, but it requires so long to accomplish this opening-movement that the magnetizing-current inrush will have subsided sufficiently so that there is no danger of an erroneous response of the differential relays RDA, RDB or RDC, by the time that the voltage-relay contact 3'! finally opens. Meanwhile, the direct-current component of the magnetizing inrush-current will have been sufficiently strong to prevent the faulty operation of any of the differential relays while the magnetizing-ourrent inrush lasted. 'When a fault occurs in the protected transformer PT after it has once been energized, it will likewise be observed that the voltage-relay 34 will start from its energized position, with its back-contact 3'! open, so that the restraint-winding 26 will be open-circuited, permitting the appropriate differential relay RDA, RDB or RDC, or any number of them, to respond to the faulty condition within the protected transformer.

In Fig. 3, we have illustrated the general use of any suitable fault-detector, and specifically a negative-phase-sequence voltage-response faultdetector 35, for supervising the operation of the restraint-winding 28 which is responsive to the direct-current component. In this case, the neg ative-sequence voltage-relay 35 responds sensitively to any fault except a well-balanced threephase fault, and it looks out, or prevents the effective operation of, the direct-current-responsive restraining-means 25, only when there is an actual fault on the system, permitting this restraint to be efiective for blocking the operation of the differential relays at all other times whenever there is a direct-current component in the alternating-current wave of the protected transformer. Since the relay 35 responds only to faults, there is no necessity for making it slow in its action, and it will preferably be an instantaneously responsive relay, which responds, without any intentional time-delay, to those faultconditions to which it is adapted to respond. This will provide instantaneous tripping for all faults within the protected transformer, except a very well-balanced three-phase fault suddenly appearing across all three phases of the protected transformer; and if such a balanced fault should occur, its tripping, by the differential protective relays, will be delayed by any direct-current component which may be present in the current-wave of the transformer.

In Fig. 4, the fault-detectors A, B and C replace the remembrance relays A, B and C of Fig. 1. These fault-detectors are normally energized, even before the protected power-transformer PT is energized. Hence, our direct-current-responsive magnetizing-inrush circuits 22 are in service at the first moment of energization of the power-transformer PT, thus preventing faulty tripping of the circuit-breakers CB as a result of the magnetizing inrush-current. If a fault should occur within the protected transformer PT while the transformer is in service, the voltage applied to at least one of the undervoltage relays A, B or C will be reduced sufficiently to drop out said relay, thus opening the appropriate repressor-circuit 22 and permitting quick tripping by at least one of the differential relays RDA, RDB or DRC. It is desirable for the speed of operation of the fault-detectors A, B and C' to be faster than that of the differential relays RDA, RDB and BBC, in Fig, 4, so that, when a fault on the line (not in the transformer PT) is cleared, the fault-detector which had dropped out on undervoltage will reclose its contact 42 before a faulty tripping operation is caused by the differential relays in response to the magnetizing inrush due to the recovery-voltage.

In all of the forms of embodiment of our invention, it is to be understood that the directcurrent-responsive restraining-means 26 and 29 are interchangeable, in any of the figures of the drawing, in the sense that the restraint 2G or 29 can either be imposed directly on the fault-responsive relays RDA, RDB or RDC which are to be supervised, or a separate supervising-relay may be provided, with said restraint imposed-on the separate supervisory-relay, with relay-circuit connections which require a response of both the fault-responsive relay and the supervisory-relay (such as the relay TS in Fig. 4), in order to obtain a tripping-operation. These and many other variations of our invention may be incorporated by those skilled in the art, without in the least departing from the essential principles of our basic invention. We desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their language.

We claim as our invention: 4

1.- Protective relay equipment for an alternating-current electrical apparatus of a type which is subject to transient fault-simulating conditions when the apparatus is unfaulted, said relaying equipment comprising the combination, with the protected apparatus, of a relay having an operating winding and a restraining winding, means for obtaining a relaying electrical quantity from the protected apparatus, means for at least partially segregating the alternating-current component and the direct-current component of said relaying electrical quantity, means energized from said segregating-means for energizing said operating winding so as to be selectively responsive to said alternating-current component, and-means energized from said segregating-means for energizing said restraining winding so as to be selectively responsive to said direct-current component.

2. Protective relaying equipment for an alterhating-current electrical apparatus of a type which is subject to transient fault-simulating conditions when the apparatus is unfaulted, said relaying equipment comprising the combination, with the protected apparatus, of a fault-responsive relay having electrical energizing-means for rendering it responsive to a fault-condition in the protected apparatus, a transient-responsive relay having an operating winding and a restraining winding, means for obtaining a relaying electrical quantity from the protected apparatus, means for at least partially segregating the alternating-current component and the ,direct-current component of said relaying electrical quantity. means energized from said segregatingemeans for energizing the operating winding of said transient-responsive relay so as to be selectively responsive to said alternating-current component, means energized from said segregating-means for energizing the restraining winding of said transient-responsive relay so as to 'be' selectively responsive to said direct-current component, and means for obtaining a, relaying response to a joint response of said fault-responsive relay and said transient-responsive relay.

3. Protective relaying equipment for an alterhating-current electrical apparatus of a type which is subject to transient fault-simulating conditions when the apparatus is unfaulted, said relaying equipment comprising the combination, with the protected apparatus, of a relay having an operating winding and a restraining winding, means for obtaining a relaying current which is responsive to the difference between the input and output currents of'the protected apparatus, means for atleast'partially segregating the alternating-current component and the direct-current component of said relaying current, means energized from said segregrating-means for energizing said operating winding so as to be selectively responsive to said alternating-current component, and means energized from said segregating-means for energizing said restraining winding :so as to be selectively responsive to said direct-current component.

"4. "Protective relaying equipment for an alterhating-current electrical apparatus of a type which'is subject .to transient fault-simulating conditions when the apparatus 'is unfaulted, said relaying equipment comprising the combination, with-the protected apparatus, of a difierential relay having :operatingemeans which :is responsive to the diiference l between the input :and output currents f :the :protected apparatus, a transientresponsive :relay having :an. :operating winding and a restraining winding, means for obtaining a relaying electrical quantity from the protected apparatus, means for at least partially segregating the alternating-current component and the direct-current component of said relaying electrical quantity, means energized from said segregating-means for energizing the operating winding of said transient-responsive relay so as to be selectively responsive to said alternating-current component, means energized from said segregating-means for energizing the restraining winding of said transient-responsive relay so as to be selectively responsive to said direct-current component, and means for obtaining a relaying response to a joint response of said difierential relay and said transient-responsive relay.

'5. Protective relaying equipment for an alternating-current electrical apparatus of a type which is subject to transient fault-simulating conditions when the apparatus is unfaulted, said relaying equipment comprising the combination, with the protected apparatus, of a ratio-differentia'l relay comprising operating-means and restraint-means, means for obtaining a differential relaying current which is responsive to the difierence between the input .and output currents of the protected apparatus, means for at least par tiailly segregating-the alternating-current com.- ponent and the direct-current component of said differential relaying current, :means energized from said se regating-means for energizing said operating-means 550 as to ice selectively responsiveto sai alterna in -cu rent component, and means for energizing said restraint-means so as to :be responsive "to a throughscurrent passing throu h the protected apparatus.

16. Protective relaying equipment for an alternetting-current electrical apparatus of a type which is subjectfito transient fault-simulating conditions when the apparatus is unfaulted, said r la ing q ipmentcomprising the combination, with the protected apparatus, ofa ratioPdi-fferential relay comprising operating means and restraint-means, transiently operative suppress0rmeans for rendering said ratio-difierential relay relatively :inefi'ective, means for obtaining a differential relaying current which :is responsive to the difference between the input and output currents of the'iprotected apparatus, means for at least partially. segregating the alternating-cunrent component and :the direct-current component of .saiddifieren'tial relaying current, means energized from said segregating-means for energizing said :operatingsmeans so as to be selectively responsive to said alternating-current component, means -energized-from said segregating-means for energizing said suppressor-means, and means for energizing said restraint-means so as to be responsive to a through-current passing through the protectediapparatus.

'17. Protective relaying equipment for an alternating current electrical apparatus of a type which is subject to transient fault-simulating conditions when the apparatus is unfaulted, said relaying equipment comprising the combination, with the protected apparatus, of a ratio-differential relay comprising differential-current -operat ing means, through-current restraint-means,

11 'means for energizing said first and second relaying circuits in parallel to each other in response to the difference between the input and output currents of the protected apparatus.

8. Protective relaying equipment for an alternating-current electrical apparatus of a type which is subject to transient fault-simulating conditions when the apparatus is unfaulted, said relaying equipment comprising the combination, with the protected apparatus, of a faultresponsive relay having electrical energizingmeans for rendering it responsive to a faultcondition in the protected apparatus, transiently operative suppressor-means for rendering said fault-responsive relay relatively ineffective, said suppressor means including means for selectively responding to any direct-current component existing in an alternating electrical quantity of the protected apparatus, and relatively slowly responsive means, responsive to an energized condition of the protected apparatus, for rendering said suppressor-means inoperative.

9. Protective relaying equipment for an alternating-current electrical apparatus of a type which is subject to transient fault-simulating conditions when the apparatus is uniaulted, said relaying equipment comprising the combination, with the protected apparatus, of a faultresponsive relay having electrical energizingmeans for rendering it responsive to a faultcondition in the protected apparatus, transiently operative suppressor-means for rendering said fault-responsive relay relatively ineffective, said suppressor means including means for selectively responding to any direct-current component existing in an alternating electrical quantity of the protected apparatus, and fault-detector-means for rendering said suppressor-means inoperative in response to a fault-condition on the line to which the protected apparatus is connected.

10. Protective relaying equipment for an alternating-current electrical apparatus of a type which is subject to transient fault-simulating conditions when the apparatus is unfaulted, said relaying equipment comprising the combination, with the protected apparatus, of a faultresponsive relay having electrical energizingmeans for rendering it responsive to a faultcondition in the protected apparatus, transiently operative suppressor-means for rendering said fault-responsive relay relatively ineffective, said suppressor means including means for selectively responding to any direct-current component existing in an alternating electrical quantity of the protected apparatus, and fault-responsive voltage-relay means for rendering said suppressormeans inoperative in response to a fault-condition on the line to which the protected apparatus is connected.

11. Protective relaying equipment for an alternating-current electrical apparatus of a type which is subject to transient fault-simulating conditions when the apparatus is unfaulted, said re aying equipment comprising the combination, with the protected apparatus, of a faultresponsive relay having electrical energizingmeans for rendering it responsive to a faultcondition in the protected apparatus, transiently operative suppressor-means for rendering said fault-responsive relay relatively ineffective, said suppressor means including means for selectively responding to any direct-current component existing in an alternating electrical quantity of the protected apparatus, and a relay-means, ener- 12 gized responsively to a voltage or the protected apparatus, for at times rendering said suppressor-means inoperative.

12. Protective relaying equipment for an alter hating-current electrical apparatus of a type which is subject to transient fault-simulating conditions when the apparatus is uniaulted, said relaying equipment comprising the combination, with the protected apparatus, of a faultresponsive relay having electrical energizingmeans for rendering it responsive to a fault condition in the protected apparatus, transiently operative suppressor-means for rendering said fault-responsive relay relatively ineffective, said suppressor means including means for selectively responding to any direct-current component existing in an alternating electrical quantity of the protected apparatus, and a relay-means, energized responsively to a voltage of the protected apparatus, for rendering said suppressor-means inoperative when said protected apparatus is in normal service.

13. Protective relaying equipment for a polyphase electrical apparatus of a type which is subject to transient fault-simulating conditions when the apparatus is unfaulted, said relaying equipment comprising the combination, with the protected apparatus, of a fault-responsive relay having electrical energizing-means for rendering it responsive to a fault-condition in the protected apparatus, transiently operative suppressormeans for rendering said fault-responsive relay relatively inefiective, said suppressor-means lncluding means for selectively responding to any direct-current component existing in an alternating electrical quantity of the protected apparatus, and a plurality of relay-means, energized responsively to a plurality of diflerent phases oi the protected apparatus, for at times rendering said suppressor-means inoperative.

14. Protective relaying equipment for a polyphase electrical apparatus of a type which is subject to transient fault-simulating conditions when the apparatus is unfaulted, said relaying equipment comprising the combination, with the protected apparatus, of a fault-responsive relay having electrical energizing-means for rendering it responsive to a fault-condition in the protected apparatus, transiently operative suppressormeans for rendering said Iault-responsive relay relatively ineffective, said suppressor-means including means for selectively responding to any direct-current component existing in an alternating electrical quantity of the protected apparatus, and a plurality of relay-means, energized reponsively to a plurality of difierent phases of the protected apparatus, for rendering said suppressor-means inoperative when normal voltage appears in all of said plurality of phases.

15. Protective relaying equipment for a polyphase electrical apparatus of a typewhich is subject to transient fault-simulating conditions when the apparatus is unfaulted, said relaying equipment comprising the combination, with the protected apparatus, of a fault-responsive relay having electrical energizing-means for rendering it responsive to a fault-condition in the protected apparatus, transiently operative suppressormeans for rendering said fault-responsive relay relatively inefiective, said suppressor-means including means for selectively responding to any direct-current component existing in an alternating electrical quantity of the'protected apparatus, and a relay-means, energized responsively. to a WILLIAM KNOX SONNEMANN. 5 MYRON A. BOSTWICK.

REFERENCES CITED The following references are of record in the 10 file of this patent:

Number UNITED STATES PATENTS Name Date Golds-borough Sept. 13, 1932 Crichton Aug. 29, 1933 Lewis July 17, 1934 Fallou Sept, 19, 1933 Gutmann July 14, 1942 Goldsborough May 15, 1934 Le Vesconte et a1. Oct. 12, 1937 Ratz May 22, 1945

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