US2329096A - Fault-current neutralizer - Google Patents

Description

Patented Sept. 7, 1943 FAULT CURRENT NEUTRALIZER Raymond L. Witzke, Edgewood, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application October 30, 1942, Serial No. 463,971

19 Claims.

My present invention relates primarily to polyphase transmission-lines of a type employing single-pole or single-phase switching and relaying means for disconnecting both ends of the faulted line-conductor, in the event of a singleline-to-ground arcing-fault, and for promptly effecting a reclosing operation re-energizing the aforesaid line-conductor, the time-interval during which the aforesaid line-conductor is de-energized being quite short, but yet sufiiciently long for the grounding arc to extinguish itself, and for the arcing path to become sufiiciently de-energized so that it will not be likely to restrike again when voltage is again applied to the line-conductor in question. My invention has particular relation to such transmission-lines, or line-sections, which are of such high interphase capacitance and such high Voltage that the charging-current of the interphase capacitance, flowing in the grounding arc during the moment of disconnection of the grounded phase-conductor of the line, would tend to be so large as to prevent the are from extinguishing itself at all, or to make its extinction too slow for the allowable time-interval between the breaker-opening and breakerclosing operations.

The principal object of my invention is to provide means for sufficiently neutralizing or reducing the ground-fault current, in such lines, to cause the prompt extinction of the ground-fault are upon the de-energization of the faulted conductor, without having to go to the expense of installing a sufficient number of switching-stations to make each sectionalized line-section so short that the charging-current between the faulted line-conductor and the charged or energized capacity-coupled sound phase-conductors will be too small to maintain the grounding are or to prevent its prompt extinction.

The majority of the faults, on a reasonably well-constructed polyphase transmission-line, are arcing ground-faults on a single phase-conductor. For these faults, it is sufficient to disconnect only the one phase-conductor of the protected line-section, in order to remove the fault 'from the system, provided that the inter-phase ing less than all of the phase-conductors of the protected line-section.

A more specific object of my invention is to make the positive-sequence and zero-sequence shunt-reactances of the protected line-section so nearly alike that the current flowing in the arc, during the period of de-energization of the faulted line-conductor, is reduced to an amount whereby the arc is promptly extinguished. lhe positive-sequence shunt-reactance is the reactance which defines the amount of positivephase-sequence reactive current which is withdrawn from the line, between the ends of the linesection, as a result of the capacitance of the line, while the zero-sequence shunting-reactance is the equivalent reactance which defines the impedance to the flow of the shunt zero-phase-sequence reactive current, or the flow of line-toground current as a result of the capacitance between the three line conductors and ground. It is obvious that the ground-current, or zerosequence current, cannot flow through the interphase reactance, or the reactance from one phase-conductor to another, but the positivesequence shunt-reactance current can flow, from phase to phase, by way of the grounding capacitances, as well as through the interphase capacitances, so that the positive-sequence capacitance of the line is always larger than the zero-capacttance, by an amount equal to the interphase capacitance of th line. Except in the case of lines utilizing single-conductor cables, with the cablesheathings well grounded, there is always an interphase capacitance between the several phaseconductors of a polyphase aerial transmission line, and thus it may be said that an object of my invention is to make an ordinary suspendedconductor, open-air, polyphase transmissionline, or a three-conductor cable, similar, in effect, to a polyphase line utilizing single-conductor cables for the several phase-conductors, insofar as the effect of capacity-currents are concerned.

A more specific object of my invention is to provide either temporary or permanent means for connecting a reactive impedance to all, or to a plurality, of the phases of the protected linesection, so that the said impedance is in operative connection to the protected line-section, between the two switching-points which are at the respective ends of the line-section, at least sometime during the time when the faulted line-conductor is de-energized, said reactive impedance being either an ungrcunded interphase inductive reactance, which reduces the positive-sequence capacitance sufiiciently closely to the zero-sequence capacitance to permit ground-fault extinction, or said reactive impedance may be a grounded capacitive reactance which is so connectcd to the protected line-section as to increase the zero-sequence capacitance without increasing the positive-sequence capacitance, as by means of a grounding-transiormer which excludes the positive-sequence current, thus bringing up the zero-sequence capacitance to near enough equality with the positive-sequence capacitance so that the capacitance-current flowing through the ground-fault will not prevent the prompt clearing of said fault during time when the faulted line-conductor is de-energized.

A further object of my invention relates to means for altering a shunt-reactance of the line during the existence of [aulhconditions resulting in a fault-clearing line-sectionalizing operation of less than all the single-pole breakers at each end of the protected line-section.

With the foregoing and other objects in view, my invention consists in the apparatus, combinations, systems, and methods hereinafter described and claimed, and illustrated in the accompanying drawing, wherein Figure l is a diagrammatic view of circuits and apparatus illustrating my invention in a preferred form of embodiment,

Figs. 2 and 3 are schematic diagrams illustrating the protected line-section in accordance with equivalent phase-sequence impedances, and

Fig. 4 is a simplified diagram, of the kind involved in Fig. 1, illustrating a difierent form of embodiment of my invention.

In Figure 1, I have shown my invention applied to the protection of a line-section of a three-phase transmission-line which is connected between the two polyphase buses BI and B2 at different line-sectionalizing switching and relaying stations. The phase-conductors of the protected line-section are designated by the letters A, B and C. It is assumed that the illustrated line-section is of the type which has been hereinabove discussed, and provided, at each end, with single-pole breakers BA, BB and BC, respectively, and relaying-equipment, which is indicated in general, by the rectangle R. As the three breakers at each end of the line-section are similar, a description of one will sufiice for all, and as the two relaying-equipments R at the two ends of the line are similar, a description of one will suffice for both.

The breaker BC, at the sending-end bus Bi, is illustrated as comprising main contacts 5 in series with the phase-C line-conductor, a plurality of auxiliary breaker-switches 6, 1, B and 9, which are utilized for various relaying and controlling purposes, a closing-coil CCC, and breaker-opening mechanism including a latching-device ii and a trip-coil 'ICC.

The relaying-equipment R, at the station represented by the bus Bi. is represented as comprising a relaying panel RP having three groups of relaying contacts, which are schematically indicated, in each case, as comprising a single contact per phase, although it is to be understood that each contact may represent a plurality of contacts in series with each other, for jointly effecting a partial completion of a relaying circuit. The first set of contacts are marked TPA, 'I'PB and TPC, to represent the directional and phase-fault-responsive tripping-contacts for the respective line-phases A, B and C. The second group of contacts are designated Z2A, Z2B and Z2C, to represent the make-contacts of second-- zone impedance-relays in the respective phases A, B and C, for sensitively detecting the presence of fault-current flow of predetermined magnitude in the respective phase-conductors of the line. The third and last group of relay-contacts of the relay-panel RP are designated TOA, TOB and TOC, to represent the directional and ground-fault responsive, or zero-phase-sequence, tripping-contacts in the respective phases, it being assumed that these contacts are responsive, not only to the direction of the ground-current flow, and to the existence of zero-phase-sequence currents of a predetermined small magnitude, but also to some sort of selector-means for determining in what phase the ground-fault current is flowing.

The relaying panel RP is illustrated as being energized from a bank of line-current transformers l3, and from a bank of potential transformers l4, and as being interconnected, also, with a carrier-current equipment which is represented by a transmitter I5, a receiver 16 and a coupling-circuit H for coupling the carrierequipment to the phase-C conductor of the protected line-section.

The relaying panel RP is also illustrated as comprising four auxiliary relays, namely, an MK relay or contactor, the operating coil of which is connected between the positive relaying bus and one terminal of each of the phasefault tripping-contacts 'I'PA, 'I'PB and TPC, so that the MK relay will be energized whenever any one or more of the phase-fault relays indicates the presence of an interphase, or phase-t0- phase, fault within the limits of the protected line-section. The MK relay has three backcontacts [3, which are respectively in series with the three second-zone impedance-contacts ZZA, Z213 and 22C. The other three auxiliary relays which are illustrated on the relaying panel RP, are the relays or contactors KA, KB and KC, respectively, the operating coils of which are serially connected to the respective ground-fault tripping-contacts 'IOA, TOB and TOC. Each of the auxiliary relays KA, KB and KC has a make-contact, which will be sufliciently designated by reference to the relay type-designation, KA, KB or KC, as the case may be.

While I have referred to one particular type of relaying panel RP, I wish it to be understood that any equivalent device might be utilized. The particular panel which is illustrated embodies features which are described and claimed in a Goldsborough application, Serial No. 424,957, filed December 30, 1941, on Single-pole switching, and a Goldsborough and Smith application, Serial No. 424,958, filed December 30, 1941, on Arcing-fault discrimination, both assigned to the Westinghouse Electric & Manufacturing Company.

The trip-coil of each of the three single-pole breakers BA, BB and BC, such as the phase-C trip-coil TCC, is adapted to be energized from a tripping-bus which is indicated at 20. This tripping-bus may be energized, from the positive terminal through either one of two paths, namely, through the MK operating-coil and the phase-C phase-fault tripping-contact TPC, or through the phase-C ground-fault tripping-contact TOC and the KC operating-coil. In either event, the tripping-current flows through the tripping-bus 20, and thence through the tripcoil TCC and the auxiliary breaker-switch 8, and thence to the negative bus the breakerswitch 8 being open when the breaker is open.

The closing-coil, such as CCC, is energized through a circuit which may be traced from the positive bus the KC make-contact, the Z20 relay-contact, and one of the back-contacts 18 of the MK relay, and thence to the closing-coil CCC, the circuit being completed through the auxiliary breaker-switch 9 and the negative bus the breaker-switch 9 being closed when the breaker is open.

It will be noted, from Fig. 1, that I have also illustrated the closing-coil circuit as including both the appropriate second-zone impedancecontact, such as Z20, and one of the back-contacts l8 of the phase-fault responsive-relay MK. While these two additional contacts, in the closing-coil circuit, are not necessary in every case, they are frequently advantageous.

Thus, the impedance-responsive contact ZZC distinguishes between arcing-grounds, which draw sufficient current to energize the sensitive line-current-responsive relay-element Z20, and non-arcing grounds, or non-self-healing groundconditions, which would not be removed by the momentary removal of voltage from the faulted conductor, as would be the case if one of the lineconductors broke and fell onto the dry ground. In such an event, because of the dryness of the ground and the smallness of the ground-current which would be drawn, the ground-fault relays might not be able to promptly respond again if a reclosing breaker-operation were permitted, thus leaving the :broken conductor lying on the ground, as a distinct hazard to life, until such time as the ground-current should happen to become momentarily large enough to pick up the sensitive ground-relays.

The back-contact [8 of the phase-fault-responsive relay MK is advantageous in preventing an automatic reclosing-operation of the breaker in the event that the fault involves more than one phase-conductor, which may be a desirable safeguard in some cases, while, in other cases, it might be desirable to omit this MK relay.

Since the KC make-contact is closed as soon as the phase-C ground-fault tripping-contact TOC is closed, it will be noted that the closingcoil C is energized at the same time that the tripping-coil TCC is energized, in the event of a ground-fault on the phase-C line-conductor.

The energization of the trip-coil TCC, in the particular type of breaker which is illustrated, results in a very quick tripping-operation, so that the main breaker-contacts become separated far enough to extinguish the arc therebetween within a short time, which may be of the order of three or four cycles. Meanwhile, the more ponderously operating closing-mechanism is being brought into play by the powerful closing-coil CCC, so that, after the main contacts have opened far enough to extinguish the arc, the moving elements of said main contacts come into contact with the closing parts of the closingmechanism, resulting in a quick and prompt reclosure of the main contacts 5, so that said contacts may have remained open, after the interruption of the arc at said main contacts, fora matter of some two to four cycles, more or less, depending upon the particular conditions of the em. f f t will be understood that, if a fault persists on the system, or if the fault restrikes after the reclosure of the main breaker-contacts 5, the trip-coil TCC will again instantly be energized, repeating the operation. It is to be understood that any suitable cycle-counting means, or means for blocking automatic reclosure after a predetermined number of openings (not shown), may be utilized, as is common in all automatic-reclosure systems, and that suitable means (not shown) may be utilized for automatically efiect ing an'opening-operation of the remaining single-pole breakers, in the event that any one of the three breakers may open under conditions when it will not automatically reclose again, thus avoiding the continued operation of the system in an unbalanced condition, as is well known, in other inventions prior to my present invention, as described, for example, in the previously mentioned Goldsborough application. My present invention is not limited to any particular relaying or controlling scheme except that preferably some sort of single-pole switching and control is desirable.

In accordance with my invention, I utilize a plurality of reactive impedances, which are illustrated as comprising three delta-connected shunt-reactors, or ungrounded interphase inductive reactances, L, which are, or may be, connected across the respective line-phases A, B' and C on the line-side of the breakers BA, BB and BC. As will be subsequently described, these inductive-reactor banks L may be either permanently or temporarily connected to the protected linesection, and they may be either bunched in a single locality, or distributed at two or more points along the protected line-section, between the switching-points at the respective ends of the line-section. In the particular system shown in Fig. 1, I have illustrated the general case in which half of the total kva. 0f the interphase shuntconnected inductors L is connected in each end of the protected line-section, in each case on the line-side of the respective breakers BA, BB and BC.

As shown, in more detail, for the equipment at the sending-end where the bus BI is located, each inductor-bank L, L, L may be either permanently connected in phase-to-phase relation across the line-conductors A, B and C, as by the closure of a three-pole switching-means LM, which may be either a breaker or a hand-operated switch, or it may be only temporarily connected into service at a time so that it will be in operative connection at least sometime during the time when the faulted line-conductor is de-energized, in the event of a single-phase arcing-type ground-fault, under the control of suitable electro-responsive switchingdevices LA, LB or LC.

If the inductors L are permanently connected, 7

they will have-the advantage of reducing the charging-current of the line, which is frequently a very desirable thing to do, but they will have the disadvantage of causing the inductors to be much more expensively built, for constant-service rating at the required kva. rating, which will usually involve a fairly large bank of inductors, besides introducing certain necessary losses which would be constantly imposed upon. the protected line-section.

As some sort of switching-means will be necessary, in any event, for the shunt-connected inductors L, I believe that the inductor-switching equipment might best be utilized to very considerably reduce the size and cost of the shunt-connected inductor-equipment by causing said equipment to be connected into service for only the matter of a few cycles at a time, while the single-pole breaker-contacts are opening and reclosing, so as to reduce the otherwise significant cost of the shunt-connected inductors to a rather insignificant amount. I have not undertaken to show the practical details of the control-equipment for the switching-apparatus for connecting the shunt-inductors L into service at the beginning of a ground-fault condition, and for removing said shunt-inductors at the termination of the ground-fault disturbance, as the details of suitable control for that purpose will be understood, by relaying-engineers from the present description.

In Fig. l, I have indicated, very diagrammatically, the use of three fault-responsive relays, LA, LB and LC, the contacts of which may be utilized,

either directly, or through suitable circuit-breaker control, to connect the three inductors L in delta-circuit relation across the transmissionline conductors A, B and C. The three operating-coils of these relays LA, LB and LC are energized, respectively, from some suitable point in the relaying-circuits which are responsive selectively to ground-faults as distinguished from faults involving a plurality of phase-conductors, such circuits being the circuits of the respective closing-coils, such as the phase-C closing-coil circuit of the BC breaker. For simplicity of illustration, I have illustrated the operating-coils LA, LB and LC as being energized, respectively, from the make-contacts of the respective auxiliary relays KA, KB and KC, so that one of the inductorconnecting relays, such as LC, is energized whenever the corresponding ground-fault-responsive auxiliary-relay, KC, is energized.

Before describing, in detail, the operation of the system which I have illustrated in Fig. l, I shall make reference to the equivalent phase-sequence circuit represented by Fig. 2, representing the conditions for the three line-conductors A, B and C, extending between the two buses BI and B2, assuming an arcing-ground fault F on the phase-C conductor near the bus Bl, with the phase-C breakers open, at both ends of this faulted-conductor, as indicated at 23 and 24. I have indicated the positive-sequence series-impedance of the protected line-section as Z1, and the zerosequence series-impedance as Z0, the positivesequence line-capacitance as C1, and the zerosequence line-capacitance as Co.

In Fig. 2, I have made the closely approximating, simplifying, assumption that, instead of the line-capacitances C1 and C0 being uniformly distributed throughout the length of the protected line-section, they are concentrated with half of the total value at one end and half at the other end, and I have indicated these half-value capacitances, in each case, as star-connected impedances. The zero-sequence shunt-capacitances at each end are represented, therefore, as three capacitors, each having an impedance -:i/2wCo,

each connected between one of the line-conduc- V tors A, B or C, and the zero-sequence returnconductor 1'35. Since the positive-sequence current can flow through the grounding impedances j/2wC0 as well as through the ungrounded interphase capacitance of the line, I have indicated, in Fig. 2, at each end of the line-section, a bank of ungrounded star-connected interphase capacitors, each having a value -j/2w(C1-Co), each representing the equivalent of half of the interphase capacitance (CIC0) of the line.

In cases where the line-section is extremely long, or where, for any other reason, the series line-impedance Z1 is unusually high, the equivalent circuit of Fig. 2 may be adhered to, and each of the interphase capacitances, 7/2w(C1-Co),

ill

may be separately neutralized, as indicated by the neutralizing reactors L of Fig. 1; or even closer approximations of the distributed-capacitor effect may be made by subdividing the total interphase capacitance (CiCo) into three or more parts. In the vast majority of cases, however, the shunt reactance of the protected linesection, as indicated by the capacitive impedance -j/w(C1-Co), is large in comparison to the series impedances of the line and of the source. so that these series impedances can be neglected without introducing any important error in calculating the fault-current which flows after the faulted conductor has been disconnected.

The equivalent diagram of Fig. 2 may thus be simplified by omitting the line-impedances Z1 and Z0, thus producing the equivalent diagram which is shown in Fig. 3, in which case the grounding and interphase capacitances are shown as being bunched at a single point, which may be any point in the line, inasmuch as the line is assumed to have a negligible impedance. In Fig. 3, I have also indicated my neutralizing reactance 1X, in the form of an ungrounded bank of star-connected inductances, each having an impedance which is equal and opposite to the interphase capacitive line-impedance -j/w(CiCo). With this value of X connected to the line, it will be obvious that no reactive leading or lagging positive-sequence current can flow into the ungrounded star-connected impendances 1X and j/w(C1Cu) because the lagging current drawn by the one, is exactly compensated for by the leading current drawn by the other, so that the efiective positive-sequence line-reactance is reduced from the impedance :i/wCi to the impedance a'/wCn, making the positive-sequence line-capacitance equal to the zero-sequence line-capacitance. Thus the faultcurrent which flows through the fault F is reduced to zero.

While I have utilized ungrounded star-connected shunting-impedances X, in Fig. 3, in conformity with the use of star-values for the linecapacitances Cl and Co, it will be readily understood that equivalent delta-connected impedances might be utilized, so long as the same kva. of impedance is provided in each case. A bank of ungrounded delta-connected impedances having the same kva. rating as a bank of ungrounded star-connected impedances, would have individual impedance-branches of one-third the amount of impedance, and Vii times the voltage-rating, of each impedance-branch of the equivalent star-connected bank. As shown in Fig. 1, it may be preferable to utilize delta-connected banks of ungrounded shunting inductances L, as the delta connection simplifies the excess-voltage protection (not shown).

As previously intimated, it is by no means necessary to very exactly neutralize the interphase line-capacitance with the interphase shunt-connected inductances, as a certain amount of current may easily flow through an arcing groundfault without interfering with the prompt extinction of the are. It is only when the ground-fault current is quite large that the arc fails to extinguish itself readily. It is not necessary that the neutralization be carried out with any high degree of accuracy. Usually, calculated values of line-reactances are quite accurate enough to work with, although, obviously, fieldtested and accurately adjusted values of shuntmg-impedances L may be utilized, if desired or heeded.

Referring, now, more particularly to the opera-- tion of the system shown in Fig. 1, it will be noted that, when a fault involving ground occurs, within the protected line-section, one or more of the phase-selecting ground-fault tripping-contacts TOA, 'IOB or TOC will be closed, simultaneously energizing both the trip-coil and the c1osing-coil of the appropriate breaker or breakers BA, BB or BC, as the case may be. At the same time, the corresponding one or more of the inductor-controlling relays LA, LB or LC, as the case may be, will be actuated, thus bringing the inductors L into operative delta-circuit connection (or other ungrounded phase-interconnection) to the-protected line-section A, B, C, at a point on the lineside of the breakers BA, BB and BC. As previously pointed out, these shunt-inductances L may be all lumped at a single point, anywhere within the protected line-section, between the breakercontact points at the respective ends of the linesection, as shown in the equivalent diagram of Fig. 3, or half of the total kva. of inductive impedance may be inserted at each end of the protected line-section as shown in Fig. 1. If the shunting-inductances are lumped all at one point,

it may be advantageous, in many cases, to place the inductances at the sending-end, represented by the bus BI, as the load withdrawn from the receiving end, represented by the bus B2, is usually an inductively lagging load, anyway.

It is assumed that the effective response and operation of the inductor-connecting relays LA, LB or LC, as the case may be, is sufficiently rapid to get the shunt-inductors L into circuit before the extinction of the arc across the main breakercontacts 5, although it may suflice, in some cases, for the inductors L to be connected at any time whichis significantly in advance of theinstant of reclosure of the main breaker-contacts 5.

While I have illustrated my invention as inserting all of the shunting reactance at once, and as compensating only for the conditions involving single ground-faults on the protected line-section, I wish it to be understood that my inductor-controlling relays LA, LB and LC may be regarded, generically, as any means for effecting an alteration of an effective shunt-reactance of the protected line-section, so as to control the conditions existing during, or at sometime during, the time when the faulted line-conductor is deenergized at both ends thereof.

My invention, in its broadest aspects, also contemplates any control of the effective phasesequence shunt-reactanees of the protected linesection, so as to make the effective positivesequence and zero-sequence reactanees nearly enough alike so that charging-currents of the effective line. reactance, flowing through the fault, will not be of sufficient magnitude to prevent the prompt extinction of the fault when the faulty line-conductor is de-energized, or disconnected from voltage-sources at both ends of the protected line-section. This may obviously be done, as well, by increasing the zero-sequence line-capacitance so as to make it equal, or approximately equal, to the positive-sequence linecapacitance, as by decreasing the effective positive-sequence line-capacitance so as to make it equal or approximate the zero-sequence linecapacitance.

In Fig. 4, I have thus illustrated a means for adding additional shunt-capacitance to the effective zero-sequence capacitance of the protected five-sequencing capacitance thereof, this being done by connecting the capacitive impedance -7'/3w(C1-Co) to ground through a groundingtransformer such as the zigzag-connected transformer 3!], or other transformer which effectively introduces the added capacitance in the zerosequence shunting-circuit of the protected linesection, without effectively, or as effectively, adding it in the positive-sequence shunt-circuit of the protected line-section. If the grounding-transformer 30 has a material zero-sequence inductance dXt, the grounded capacitive impedance -7'/3w(C1-Co) would have to be increased by an additional capacitive impedance ;iXt/3 to compensate for this inductance, making a total capacitive impedance of connected in the grounded neutral circuit of the grounding-transformer 30.

In Fig. 4, by way of illustration, this connection is permanently made at the center of the protected line-section, although it is to be understood that it could be made at one or both ends, either permanently or temporarily, in accordance with the previous descriptions. The single-pole breakers BA, BB and BC and the relaying equipments R may otherwise be similar to those shown in Fig. 1.

While I have described my invention more particularly in respect to single line-to-ground faults, calculations have shown that both single and doube line-to-ground faults can be taken care of with the same interphase inductances L, or with the same effective value of capacitance 7'/3w(C1-Co) inserted in the neutral of a grounding transformer such as 30. This means that making the effective positive and zero phase sequence shunt reactanees equal will neutralize the groundcurrent for an arcing ground-fault involving less than all of the phase-conductors, during the time that the faulted conductor or conductors are conductively isolated from the rest of the system.

While I have illustrated my invention in several different forms of embodiment, and exline-section, without increasing the effective posiplained its mode of operation in accordance with my best understanding, at the present time, I do not desire to be limited altogether to these particular illustrations or explanations, as many changes and modifications may be made and adopted by those skilled in the art without departing from the essential spirit of my invention, particularly in its broader aspects. I desire, therefore, that the appended. claims shall be accorded the broadest construction consistent with the prior art.

I claim as my invention:

1. Protective equipment for a line-section of a polyphase transmission-line of such high interphase. capacitance and such high voltage that, in the event of an arcing ground-fault involving less than all of the phase-conductors of the protected line-section, and in the eventof switching-operations opening both ends of only the faulted phase-conductor or conductors, leaving the sound phase-conductor or conductors energized, the charging-current of the interphase capacitance, flowing in the arc, might tend to be so large as to prevent the prompt extinction of the ground-fault arc, comprising the combination, with such a line-section, of switching and relaying means operative, in response to such an arcing ground-fault, to automatically bring about switch-ing-operations opening both ends of only the faulted phase-conductor or conductors, leaving the sound phase-conductor or conductors energized, and to automatically effect prompt reclosure-operations re-energizing both ends of the aforesaid faulted phaseconductor or conductors, in combination with means for connecting a reactive impedance to a plurality of phases of the protected linesection so that said impedance is in operative connection to the protected line-section, between the switching-pomts, at lewt sometime during the time when the faulted line-conductor or conductors are die-energized, the manner of connection and the amount and kind of impedance being such that the positive-sequence and zerosequence shunt-reactances of the protected line-section are made so nearly alike that the current flowing in the arc, during the period of de-energization of the faulted line-conductor or conductors, is reduced to an amount whereby the arc is promptly extinguished.

2. Protective equipment for a line-section of a polyphase transmission-line of such high interphase capacitance and such high voltage that, in the event of an arcing ground-fault on a single phase-conductor of the protected line-section, and in the event of switching-operations opening both ends of only the faulted phaseconductor, leaving the sound phase-conductors energized, the charging current of the interphase capacitance, flowing in the arc, would tend to be so large as to prevent the prompt extinction or" the ground-fault arc, comprising the combination, with such a line-section, of switching and relaying means operative, in response to an arcing ground-fault on a single phase-conductor of the protected line-section, to automatically bring about switching-operations opening both ends of only the faulted phase-conductor, leaving the sound phase-conductors energized, and to automatically effect prompt re-closureoperations re-energizing both ends of the aforesaid phase-conductor, in combination with means for connecting a reactive impedance to all of the phases of the protected line-section so that said impedance is in operative connection to the protected 1inesection, between the switching-points, at least sometime during the time when the faulted line-conductor is de-energized, the manner of connection and the amount and kind of impedance being such that the positive-sequence and zero-sequence shuntreactances of the protected line-section are made so nearly alike that the current flowing in the arc, during the period of de-energization o! the faulted line-conductor, is reduced to an amount whereby the arc is promptly extinguished,

3. The invention as defined in claim 1, characterized by the fact that said reactive impedance is an llllglOlll'lded interphase inductive reactance,

The invention as defined in claim 2, characterized by the fact that said reactive impedance is an ungrounded interphase inductive reactance.

5. The invention as defined in claim 1, characterized by the fact that said reactive impedance is a grounded capacitive reactance so connected to the protected line-section as to increase the zero-sequence capacitance of the line-section more than it increases the positivesequence capacitance of the line-section.

6. The invention as defined in claim 2, characterized by the facts that said reactive impedonce is a capacitive reactance, and said means for connecting it to the protected line-section includes a transformer 01 a type which includes the capacitive reactance in the zero-sequence shunting-circuit, but not the positive-sequence shunting-circuit, of the protected line-section.

7. The invention as defined in claim 1, characterized by said reactive impedance being normally permanently connected to the protected line-section between the switching points at the ends of the line-section.

8. The invention as defined in claim 1, characterized by said reactive impedance being a temporary-duty impedance, and said means for connecting it to the protected line-section including switching and relaying means, responsive to the fault-condition, for switching the impedance into service only at times of fault.

9. The invention as defined in claim 2, characterized by said reactive impedance being normally permanently connected to the protected line-section between the switching-points at the ends of the line-section.

10. The invention as defined in claim 2, characterized by said reactive impedance being a temporary-duty impedance, and said means for connecting it to the protected line-section including switching and relaying means, responsive to the fault-condition, for switching the impedance into service only at times of fault.

11. The invention as defined in claim 1, characterized by said reactive impedance being an ungrounded interphase inductive reactance, and being normally permanently connected to the protected line-section between the switchingpoints at the ends of the line-section.

12. The invention as defined in claim 1, characterized by said reactive impedance being an ungrounded interphase inductive reactance, and being a temporary-duty impedance, and said means for connecting it to the protected linesection including switching and relaying means. responsive to the fault-condition, for switching the impedance into service only at times of fault.

13. The invention as defined in claim 2, characterized by said reactive impedance being an ungrounded interphase inductive reactance, and being normally permanently connected to the protected line-section between the switchingpoints at the ends of the line-section.

14. The invention as defined in claim 2, characterized by said reactive impedance being an ungrounded interphase inductive reactance, and

being a temporary-duty impedance, and said means for connecting it to the protected linesection including switching and relaying means, responsive to the fault-condition, for switching the impedance into service only at times of fault.

15. The invention as defined in claim 1, charterized by said reactive impedance being a grounded capacitive reactance so connected to the protected line-section as to increase the zero-sequence capacitance of the line-section more than it increases the positive-sequence capacitance of the line-section, and being normally permanently connected to the protected line-section between the switching-points at the ends of the line-section.

16. The invention as defined in claim 2, characterized by said reactive impedance being a capacitive reactance, and said means for connecting it to the protected line-section including a normally permanently connected transformer of a. type which includes the capacitive reactanoc in the zero-sequence shunting-circuit, but not.

the positive-sequence shunting-circuit, of the protected line-section between the switchingpoints at the ends of the line-section.

17. Protective equipment for a line-section of a polyphase transmission-line of such high interphase capacitance and such high voltage that, in the event of an arcing ground-fault on a single phase-conductor of the protected linesection, and in the event of switching-operations opening both ends of only the faulted phaseconductor, leaving the sound phase-conductors energized, the charging-current of the interphase capacitance, flowing in the arc, would tend to be so large as to prevent the prompt extinction of the ground-fault arc, comprising the combination, with such a line-section, of switching and relaying means operative, in response to an arcing ground-fault on a single phase-conductor of the protected line-section, to automatically bring about switching-operations opening both ends of only the faulted phase-conductor, leaving the sound phase-conductors energized, to automatically effect prompt reclosure-operations re-energizing both ends of the aforesaid phase-conductor, and to alter a phasesequence shunt-reactance of the portion of the protected line-section between the switchin points at its ends.

18. In combination, two line-conductors electro-statically coupled to one another, an ener gized alternating-current power-bus, means for at times operating one of said line-conductors in an energized, power-conducting condition in oooperation with said power-bus, means for at times operating the other of said line-conductors in a substantially de-energized, non-power-conducting condition in substantial power-isolated relation to said power-bus, and inductive reactance-means connected between said line-conductors in such amount as to approximately neutralize the effective capacitance between the two line-conductors whereby any fault-current flowing between said de-energized line-conductor and ground is approximately neutralized allowing arc-extinction.

19. In combination, a plurality of line-conductors electrostatically coupled to one another, an energized, multi-conductor, alternating-current power-bus, means for at times operating,

one or more of said line-conductors in an energized, power-conducting condition in cooperation with said power-bus, means for at times operating another one or more of said line-conductors in a substantially de-energized, nonpower-conducting condition in substantial power-isolated relation to said power-bus, and inductive reactance-means connected between said energized and tie-energized line-conductors in such amount as to approximately neutralize the effective capacitance between them whereby any ground-fault current flowing between said deenergized line-conductor or conductors and ground is approximately neutralized allowing arc-extinction.

RAYMOND L. WITZKE.

Images