US2445429A

US2445429A - Ground-fault protective relaying system

Info

Publication number: US2445429A
Application number: US586991A
Authority: US
Inventors: Shirley L Goldsborough
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1945-04-06
Filing date: 1945-04-06
Publication date: 1948-07-20
Anticipated expiration: 1965-07-20

Description

July 20, 1948. v s. L. GOLDSBOROUGH 2,445,429

v GROUND-FAULT PROTECTIVE RELAYING' SYSTEM Filed April 6, 1945 I 2 Sheets-Sheet 1 2 1Pelizy responds ATTORNEY July 20, 1948. s. LJGOLDSBOROUGH 2,445,429

GROUND-FAULT PROTECTIVE RELAYING SYSTEM Filed April 6, 1945 2 Shegts-Sheet 2 WlTNESSES; lNVENTOR ATTORNEY filed February -10, 1944,,Patent ,No.

Patented July 2 0, 1948 GROUND-FAULT PROTECTIVE RELAYING SYSTEM Shirley L. Goldsborough, Basking Ridge, N. J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 6, 1945, Serial No. 586,991

25 Claims. (Cl. 175294) My invention relates to a protective relaying system and apparatus, for providing a distanceresponse to ground faults on a polyphase trans- ,mission line.

One of the objects of my invention is to provide a simplified reactance ground relay which utilizes only one reactance element, or two elemerits if a second-zone response is required as well as a first-zone response. The application of distance-type relaying to ground-relaying requires a comparison of the line-to-ground voltage of .the faulted phase with either the line-current of that phase, or the residual current, or both, as set forth in the Lewis Patent 1,897,022, granted February 7, 1933. It

also requires some sort of automatic supervision,

-more, both the distance-responsive ground-relay and, its double-ground supervisory-relay must be quite sensitive to light ground-faults, without responding to load-currents. The cost of such relays, and the imperfection with which they have :met their conflicting requirements, have militated strongly against them in the past.

In my copending application Serial No. 521,801, 2,408,208, granted September 24, 1946, I have shown a simplified and improved distance-measuring groundfault-relaying-system, requiring only one distame-measuring element for a three-phase line, andhaving improved double-ground supervisorymeans; but its limitations were such that I preierrednot to use it on solidly grounded systems which are apt to have ground-faults having little fault-resistance.

Anobject of my present invention is to provide a distance-measuring ground-fault relay or relays, which are so supervised as to be generally applicable, whether the transmission system has resistance in its grounded neutral or in its ground-faults, or not.

fagainst resistanceless double-ground faults, by a special connection of the distance-type phasea relays, which are, in general, required on any system having distance-type ground-fault relaying.

7 With the foregoing and other objects in View, my invention consists in the systems, circuits, combinations, elements and methods hereinafter described and claimed, and illustrated in the accompanying drawings, wherein Figure 1 is a diagrammatic view of circuits and apparatus illustrating my invention in a form of embodiment utilizing the ground directional element to block the action of the ground distance relay on two-phase-to-ground faults involving no substantial neutral-resistance or fault-resistance.

Figs. 2 and 3 are vector diagrams, and

Fig. 4 is a view similar to Fig. 1 showing a form of embodiment in which a distance-responsive phase-fault relay is utilized to prevent the response of the distance ground relay on twophase-to-ground faults.

I have illustrated my invention, in Fig. 1, as being applied to the protection of a three-phase line-section I, having phases A, B and C. This may be a part of a three-phase, 60-cycle transmission or distribution system. The three-phase line I is connected to a three-phase bus 2 through a three-phase circuit-breaker 3, which is illustrated as having an auxiliary make-contact 3a, and a trip-coil TC. The three-phase relaying currents and voltages are derived from the line by means of current-transformers 5 and potential transformers B, respectively.

When the relaying equipment is utilized for the protection of a power-system which is grounded at more than one point, or which otherwise involves errors in ground-fault distance-measurement due to the manner in which the positive, negative, and zero-sequence currents distribute themselves, it is necessary .to utilize some sort of compensating means as set forth in the aforesaid Lewis Patent 1,897,022. By way of illustration, I

' former, such as an interconnected star bank 10.

The various relays which make up my protective-relaying system include various line-responsive relays, the various coils and contacts of which are separated into alternating-current circuits and direct-current circuits, respectively, the various circuits being arranged, so far as practicable, after the matter of a schematic diagram or across-the-line diagram. In each case, the main or operating coil of the relayis givena letter-designation or legend, andthe same letterdesignation or legend is applied to all of the contacts of that relay. The relays and switches are invariably shown in their open or deemedgized positions. When a given relay has, in addition to its main or operating winding, an auxiliary winding, such as a restraining or polarizing coil or winding, the auxiliary winding ls given the same letter-designation, with a subscript. Arrows or dotted lines are used, to symbolically indicate how the various parts of each relay are connected together. When corresponding elements are utilized in different phases, they are distinguished by suifixes, such as A, B and C, for the different phases.

My improved relaying system, which is shown Fig.1, utilizes a single distance-responsive ground-fau t relay X0, which suflices'for all three phases of the protected line section. This distance-responsive ground-fault element X is a differential relay of the reactance type, having a current and voltage-responsive operating coil X0, and having a voltage-responsive restraining-coil XOv, as shown in the Lewis Patent 1,967,093, granted July 17, v1934. This distance-type ground-fault relay X0 is provided with a make-contact which is also'designated X0.

The ground-reactance or distance-responsive relay X0 is responsivetoa selected voltage which is applied to a relaying-bus H, as will be subsequently described. As explained in the Lewis Patent 1,967,093, the operating winding X0 of the ground-reactance relay X0 is energized to be responsive to the vectorial sum' of the residual current or zero sequence current-component of the line-current, and the proper line-to-ground voltage-phase. In order to obtain such a response, I have shown a mixing transformer l3 for energizing the operating coil X0. This mixing transformer [3 has two primary "windings!!! and IS. The first primary winding [4 is a currentresponsive winding which is connected 'in the residual-current circuit of the line-current transformers 5. The other primary winding l5 isa voltage-responsive winding which is energized from the relaying-bus I I through a phase-advancing means such as a capacitor l6. 7 The restraining winding XOv of the ground reactance relay X0 is energized from the same relaying- .bus I I, through a resistor I! which keeps the cur- .rent approximately in phase with the applied .until a mornent after the application of a voltage to the relaying-bus II. I r

The distance-measuring ground-reactance relay X0 properly responds to the distance (or reactance) of a single line-to-ground fault, provided that the rela is properly energized from the suitably compensated line-to-ground voltage of the faulted phase, and from the residual or zerodisadvantage or another. preferred form of phase-selector, a group of'sesequence line-current. In the case of a two-lineto-ground fault, however, the ground-reactance relay X0 will underrespond if its voltage-response is obtained from the leading phase of the two faulted hases, which is quite satisfactory because this type of fault is taken care of by the usual phase-fault relays with which my present invention is not concerned. However, on such a. t'wo-phase-to-ground fault, if the voltage-response of the ground-reactance relay X0 is obtained from the lagging phase of the two faulted phases, it will overrespond; that is, it will respond for faults beyond the distance to which the distance-responsive relay should reach, which would result in a faulty tripping-operation; and if the ground-reactance relay X0 is energized from the sound phase, on a tWo-phase-to-ground fault, the. relay will very much overreach.

In order to select the proper ground reactance response, in the event of a two-phase-to-ground 'fiault, it is necessary to provide some suitable form of ground-fault selector-means, which Since, in either event, a'phas'e-selector supervision is needed, I have preferred to illustrate, in Fig. 1, a relaying system utilizing only a single 'ground-reactance "element X0, utilizing the phase-selector as a means for selecting the proper voltage-energization for the relay.

Several forms of ground-fault phase-selector means are known, all of which are subject to one I have chosen, as the quence-responsive directional elements SA, 'SB and SC,'one for each phase, each being directionally responsive to its own'pha'se of two difierent phase-sequence components of a three-phase quantity derived from the line; that is, phasesequence components of either the line-current or the line-voltage. I have chosen to illustrate directional phase-selector relays SA,'SB' and SC, having current coils SA, SB and SC which are energized inr'esponse to the corresponding'phase of the negative-sequence component of the linecurrent, and having voltage coils which are dis.-

grammatically indicated, as a group,;under the designation Sv in the drawing, said voltage'coils 'Sv being energized in response tothe residual line-current, or the zero-sequence component of the line-current. Such a phase-selector is. described and claimed in my Patent 2,320,361, granted June 1, 1943. It directionally compares the corresponding phase of the negative-sequence current with the zero-sequence current-component.

, In the case of a single lineto-ground fault, the phase-selectorsSA, SB and SC properly select the faulted phase, through the response of the selec-, tor which is energized from thatphase, while the other two selectors do not respond.

In the case of a double line-to-ground fault,

several different kinds of selector-responsescan be obtained, depending upon the transmissionline condition. Thus, if the double ground-fault has no neutral-resistance or fault-resistance, the

negativeand zero-sequence directional selectors SA, SB and SC will erroneously select the sound phase for the ground-reactance or distance-response, which would cause the reactance or distance relay to very much overreach, and this action must be blocked. If the double ground-fault has either neutral or fault resistance, the leading faulted phase may be additionally selected by the phase-selectors, in addition to the sound phase, so that it is necessary to provide circuit-connections for selecting only the lagging one of the two phases selected by the phase-selectors, if two phase-selectors respond, so that the ground-reactance or distance-responsive element will be energized from the leading faulted phase, and will underrespond rather than overrespond.

In the drawing, the negative-sequence currentcomponent, for energizing the current-coils SA, SB and SC, is obtained, for each phase, by adding the voltage-drop produced by passing the line-current of that phase through a resistor 3R, to the voltage-drop which is obtained by passing the difference between the other two line-currents through an impedance a'VBR, as described and claimed in the Lenehan Patent 2,309,649, granted February 2, 1943. Thus, the operating coil SA of the phase-A selectg, is energized so as to be responsive to 3RIa+jV3R(Ic-Ib).

The zero-sequence current-response, for energizing the voltage coils Sv of the three phase-selectors SA, SB and SC, is obtained by means of an auxiliary current-transformer E9 in the residual-current connections of the line-current transformers 5.

I also utilize a ground-directional element D0, which is a wattmetric or product-responsive relay, having a current-coil DO, a voltage-coil DOv, and a make-contact DO.

The tripping-circuit, for energizing the tripcoil TC of the circuit-breaker S, is extremely simple, consisting simply of the contacts DO and X0, of the ground-directional and ground-reactance elements, respectively, these contacts being connected in series with each other, and in series with the auxiliary breaker-switch 3a, to energize the trip-coil TC.

In the form of embodim nt of my invention shown in Fig. 1, I utilize a special voltage-coil energization of the ground-directional element DO, The current-coil D0 is energized from the zero-phase-sequence or residual current, as usual. Ordinarily, the voltage-coil DOv would be energized in response to the zero-sequence voltage, so that the ground-directional element properly responds to the direction of the residual current,

or zero-sequence component of the line-current.

However, in the form of my invention shown in Fig. 1, I make a special use of the ground-directional relay DO, by making it respond just oppositely to the proper directional response, in the event of a two-phase-to-ground fault, having no neutral or fault resistance, so that the grounddirectional relay DO may be used to block the erroneous response of the ground-reactance or distance-responsive element under such circumstances.

I accomplish this special response of the ground-directional element DO by energizing its voltage coil DOV in response to the phase-toground voltage which leads the phase selected by the ground-fault phase-selector. To accomplish this, I utilize three auxiliary contactor-switches CSA, CSB and CSC, the operating coils of which are energized in series with the make-contacts of the corresponding phases of the phase-selectors SA, SB and SC, supervised by the back-contacts of the next lagging phase-selectors SB, SC and SA, respectively, so that, if two of the phaseselectors respond, the one having the lagging phase is selected. Thus, the CSA coil is energized in response to the closure of the SA make-contact, and the non-opening of the SB back-contact, thus energizing this CSA coil if the SA relay responds and the SB relay does not respond. If both the SA and SB relays respond, but not the SC relay, the CSB coil is energized in response to the closure of the SB make-contact. It is to be noted that the selected phase, B, is the lagging one of the two phases A and B which are selected, or responded to, by the phase-selectors SA and SB in the event of a two-phase-toground fault.

As shown in the bottom half of Fig, 1, I make two uses of the relay-contacts CSA, CSB and CS0. One set of make-contacts of the auxiliary relays CSA, CSB and CS0, as indicated at 2|, is utilized to energize the previously mentioned relaying-bus H from the correspondingly lettered phase of the line-to-ground voltage, with the compensator-impedance 8 included in series with the line-to-ground voltage, A second set of make-contacts of the auxiliary relays CSA, CSB and CS0, as shown at 23, is utilized to connect the next leading phase-to-ground voltage-phase to the voltage-coil DOV of the ground-directional relay DO, so that, for example, if the phase-A auxiliary relay CSA picks up, it energizes the ground-directional voltage-coil DOv in response to the phase-C line-to-ground voltage.

The operation of my specially energized ground directional element D0 will more readily be understood. by reference to Figs. 2 and 3. Fig. 2 shows the three line-to-ground phases of the linevoltages EA, EB and Ed. Fig. 2 also shows two difierent fault-current conditions. One current is a single-phase ground-fault current, which is characterized by equal components of positive, negative, and zero-sequence components, all in phase with each other, as indicated at I1, 12 and I0. Such a fault is assumed to be on phase-A. The other fault-current condition, indicated on Fig. 2, is for a double ground-fault, which is assumed to be on phases B and C, for a two-phaseto-ground fault, with the fault-currents In and Io, respectively. It should be understood, of course, that the single-phase and the double-phase faultcurrents do not exist at the same time. They are for different fault-conditions. The symmetricalcomponent resolution of the two-phase fault-currents B and C of Fig. 2, with no phase-A current, is shown in Fig. 3.

The operation of my specially energized ground-directional relay DO can thus be understood by reference to Figs. 2 and 3.

In the event of a single-phase ground-fault, say on phase-A, the phase-A selector SA will energize the CSA auxiliary relay, and this will apply the phase-C line-to-ground voltage to the voltage-coil DOv of the ground-directional element DO. Reference to Fig. 2 will show that the zero-sequence current-component I0, which energizes the current-coil D0 of the ground-directional relay, is in a proper direction to make the relay respond when its voltage-coil DOv is energized with the phase-C voltage E0, the responsearea under such circumstances being when the zero-sequence current-vector extends to the right of the dotted line 24, as indicated in Fig. 2. Under such circumstances, the ground-directional relay DO responds, and closes its make-contact D0 in the tripping-circuit, which results in a tripping operation if the ground-fault is within the limiting distance to which the ground-reactance relay X responds.

In the event of a,- two-line-to-ground fault, involving, say, phase-conductors B and C, two different conditions may prevail. If there is no neutral resistance or fault resistance, the phase-selector SA, for the sound phase, will erroneously respond, and neither of the two faulted-phase selectors S3 or SC will respond. The response of the sound-phase selector SA energizes the CSA auxiliary relay, and applies the sound-phase lineto-ground voltage to the ground-reactance element X0 causing the latter to overreach, which would involve erroneous tripping-operations if tripping were not otherwise blocked. Under such circumstances, however, the CSA auxiliary contactor applies the phase-C line-to-ground voitage E0 to the ground-directional element DO, as shown in Fig. 2, but Fig. 3 shows that the zerosequence components IoA, I03, Inc are almost 189 out of phase with the single-fault zero sequence current Io in Fig. 2, so that the zero-sequence current-component is now in a phase which results in no response of the ground-directional relay DO when it is energized with the phase-C voltage E0. Thus the ground-directional contacts 130 do not close in the tripping-circuit, and no tripping sul'ts.

In case the double groundfault on phases B and C is accompanied by either neutral or fault resistance, the phase-selector SB for the leading fault-ed phase B may pick up (if the resistance is suflicient), in addition to the sound-phase se-- lector SA. Under such circumstances, the opening of the SB back-contact prevents the energi zation of the auxiliary relay CSA, while the phase-B auxiliary relay CSB will pick up in response to the closure of the SB make-contact. One of the CSB make-contacts applies the phase- B line-to-ground voltage to the ground-reactance element X0, which makes it underrespond, which is a safe condition. Another CSB make-contact applies the sound-phase voltage EA of Fig. 2 to the voltage-coil DOV of the ground-directional element. Comparison of Figs. 2 and 3 will show that the phase of the zero-sequence component of the two-phase fault-currents IB and Io is somewhere near the border-line between a response and a non-response of the ground directional relay DO, when energized with the phase-A voltage EA- If the ground-directional relay DO does not respond, there will be no tripping-action in response to the ground-reactance element X0, which is all right because a double ground fault will be properly taken care of by the phase-fault relays, which are always provided, and which constitute no part of my present invention. If the ground-directional relay DO does respond, under the circumstances just described, again no harm is done, because the ground-reactance relay DO underresponds because of its energization with the voltage of the leading faulted phase B.

It will thus be seen that my special energization of the ground-directional" relay DO enables it to properly supervise the ground-reactance or distance-responsive element X0, so that my ground-responsive relaying-apparatus always responds properly, on single-phase ground-faults, and it either does not respond at all, or underresponds, in the event of a two-phase-to-ground fault, which is a safe condition, leaving such faults to be handled by the phase-fault relays (not shown).

In Fig. 4, I have shown another means for supervising the ground-fault relays, so that they will not improperly operate, in the event of twophase-to-ground faults having little or no neutral resistance or fault resistance. As explained in connection with the Fig. 1 embodiment of my invention, such a fault results in an erroneous response of the sound-phase phase-selector, such as the selector SA fora B-to-C ground-fault; and the operation of. the SA selector results in applying the phase-A line-to-ground voltage to the distance-responsive ground-reactance element D0, which causes it to over-reach, enabling it to respond to faults which are too far away. In Fig. 1, an erroneous tripping-response was prevented by a special. line-to-ground voltage-energiza-tion of the ground-directional element DO, causing the latter to also falsely respond, cancelling the false response of the phase-selector SA, and thus preventing the overreaching response of the ground-reactance element X0, in the tripping circuit.

In Fig. 4, instead of providing this special lineto-ground voItage-energization of the grounddirectional element DO, I energize the voltagecoil DOV of the ground-directional relay D0 in response to the zero-sequence line-voltage component, in the conventional manner, as, for example, by utilizing a bank of auxiliary potential transformers 21, which are energized from the potential transformers 6, for providing the response to the zero-sequence voltage-component. This makes the ground-directional element DO respond correctly for all ground-faults, including double ground-faul-ts, whether with or without resistance.

In Fig. 4, instead of utilizing auxiliary relays GSA, CS3 and CSC, to respond to the picking up of the respective selector-relays SA, SB and SC, whenever the next lagging phase of the selectorrelays does not pick up, I utilize the respective front and back contacts of the selector-relays, in the same pairs as before, in the corresponding phases of the line-to-ground voltages which are applied to the relaying bus I I, these selector-relay contacts being in lieu of the auxiliary contacts 2| of the contactor-switches CSA, CSB and CSC in Fig.1.

To prevent faulty response, or overreaching, of the ground-reactance relay X0, in Fig. 4, in the event of a resistanceless double-phase groundfault, which energizes only the sound-phase, phase-selector SA, for example, I provide contactor-switch back-contacts CSB, CSC and CSA, respectively, in the phase-A, phase-B and phase- C voltage-circuits, responsively, and I energize the operating-coils of the auxiliary relay CSA, CSB and CSC in response to the correspondingly lettered; third-zone phase-fault impedance relays 23A, 23B and Z30 of the phase-fault relaying equipment. Any transmission system which warrants the expense of distance-type groundfault relaying, will, in general, also have distance-type phase-fault relays, among which will be included third-zone phase-fault distance-relays 23A, Z313 and Z30, for the three line-phases A, B and C, respectively. These third-zone phaserelays may be, for example, of a differential type, having operating windings Z3A, 23B and 23C, energized from the respective phases of the linecurrents, and having restraining winding ZAv and ZB'v and ZCv, energized from the corresponding phase-voltages of the line.

In the operation of the system shown in Fig. 4, whenever there is a double phase-to-ground resistancel'ess fault, involving, say, phases B and C,

within the reach of the ground-fault relay X0, the phase-B third-zone phase-fault distanceelement Z313 will always respond, thus energizing the phase-B auxiliary relay CSB, which opens its back-contact CSB which is in series with the make-contact of the phase-A selector-relay SA, As previously described, this phase-A selectorrelay SA erroneously responds to such a resistanceless double ground-fault, and no other selector-relay responds under such circumstances. Hence, neither one of .the three alternative vol-tage-circuits which are connected to the auxiliary relay-bus ll is energized, which means that the ground-reactance relay X is not energized, and there is no ground-fault tripping-operation under such circumstance.

In .the case of a double ground-fault having resistance, the phase-C third-zone phase-fault relay Z3Cmay sometimes pick up, in which case it would block the operation of the ground-reactance relay X0, but this will do no harm, as the phasefault relays properly take care of faults involving two phases of the line-conductors, through phasefault tripping-circuits which I have not shown, as they are, or may be, conventional.

In the event of a single-phase ground-fault, say on phase-A, in the Fig. 4 embodiment of my invention, the phase-B third-zone phase-fault relay Z3B cannot respond to a fault involving only phase-A; and'any possible response of the phase- A phase-fault relay 23A would not block my phase-A ground-fault tripping.

While I have shown my invention in two illustrative forms of embodiment, I desire it to be understood that my invention is not limited to these precise forms, and that the appended claims are to be accorded the broadest construction consistent with their language.

I claim as my invention:

1. Relaying apparatus for ascertaining groundfaults on a three-phase line, comprising a singlephase distance-measuring ground-fault reactance-responsive relaying-means for responding to the line-'reactance of a predetermined phase of the line-conductors, said distance-measuring response being ac-curate only if a single groundfault occurs on said predetermined phase, in combination with ground-fault phase-selector means for making a selection of an apparently groundfaulted phase, said phase-selector means being operative to properly select the faulted phase in the event of a single ground-fault, and being operative to select only the leading one of the two faulted phases in the event of a double groundfault having adequate resistance, and being operative to erroneously select the sound phase in the event of a resistanceless double ground-fault, said phase-selection of the phase-selector means being made without an accurate determination of the distance of the fault by said phase-selector means, means for obtaining an indication of a joint response of said distance-measuring relaying-means in said predetermined phase, and a selection of that same phase by said phase-selector means, and means for blocking said indication in responseto a double ground-fault of predeterminably low resistance.

2. Relaying apparatus for ascertaining groundfaults on a three-phase line, comprising a singlephase distance-measuring ground-fault relaying-means energized from line-derived quantities including a phase-to-ground line-voltage and the zero-sequence line-current, in combination with ground-fault phase-selector means for making a selection of an apparently ground-faulted phase, said phase-selector means being operative to properly select the faulted phase in the event of a single ground-fault, and being operative to select only the leading one of the two faulted phases in the event of a double ground-fault having adequate resistance, and being operative to erroneously select the sound phase in the event of a resistanceless double ground-fault, said phase-selection of the phase-selector means being made without an accurate determination of the distance of the fault by said phase-selector means, means for obtaining a joint indication of a phase-selection and a distance-response to the phase-to-ground voltage of the selected phase, and means for blocking said indication in response to a double ground-fault of predeterminably low resistance.

3. Relaying apparatus for ascertaining groundfaults on a three-phase line, comprising a singlephase distance-measuring ground-fault relaying-means, means for supplying said groundfault distance-measuring relaying-means with a relaying-current dependent upon the zero-phasesequence line-current, means for supplying said ground-fault distance-measuring relaying-means with any one of a plurality of relaying-voltages dependent upon the different phase-to-ground line-voltages respectively, ground-fault phaseselector means for selecting and applying one of said relaying-voltages to said distance-measuring relaying-means, means for performing a lineprotective operation in response to said distancemeasuring relaying-means, and means for blocking said line-protective operation in response to a double ground-fault of predeterminably low resistance.

4. Relaying apparatus for ascertaining groundfaults on a three-phase line, comprising a singlephase distance-measuring ground-fault reactance-responsive relaying-means for responding to the line-reactance of a predetermined phase of the line-conductors, said distance-measuring response being accurate only if a single groundfault occurs on said predetermined phase, in combination with a plurality of ground-fault phase-selector relays, one for each phase, each being directionally responsive to its own phase of the negative and zero phase-sequence components of a three-phase quantity derived from the line, means for obtaining an indication of a joint response of said distance-measuring relaying-means in said predetermined phase, a response of the phase-selector relay for that phase, and a non-response of the phase-selector relay for the next lagging phase, and means for blocking said indication in response to a double ground-fault of predeterminably low resistance.

5. Relaying apparatus for ascertaining groundfaults on a three-phase line, comprising a singlephase distance-measuring ground-fault relaying-means, means for supplying said groundfault distance-measuring relaying-means with a relaying-current dependent upon the zero-phasesequence line-current, means for supplying said ground-fault distance-measuring relayingmeans with any one of a plurality of relayingvoltages dependent upon the different phase-toground line-voltages respectively, a plurality of ground-fault phase-selector relays, one for each phase, each being directionally responsive to its own phase of the negative and zero phase-sequence components of a three-phase quantity derived from the line, means for selecting and applying one of said relaying-voltages to said distance-measuring relaying-means in accordance with the phase selected by the response of any phase-selector relay, means for blocking said voltage-application in response to a simultaneous response of the phase-selector relay for the next lagging phase, means for performing a line-protectlve operation in response to said distancemeasuring relaying-means, and means for blocking said line-protective operation in response to a double ground-fault of predeterminably low resistance.

6. Relaying apparatus for ascertaining groundfaults on a three-phase line, comprising a singlephase distance-measuring ground-fault reactance-responsive relaying-means for responding to the line-reactance of a predetermined phase of the line-conductors, said distance-measuring response being accurate only if a single groundfault occurs on said predetermined phase, in combination with ground-fault phase-selector means for making a selection of an apparently ground-faulted phase, said phase-selector means being operative to properly select the faulted phase in the event of a single ground-fault, and being operative to select only the leading one of the two faulted phases in the event of a double ground-fault having adequate resistance, and being operative to erroneously select the sound phase in the event of a resistanceless double ground-fault, said phase-selection of the phaseselector means being made without an accurate determination of the distance of the fault by said phase-selector means, a ground-directional relaying-means energized from line-derived quantities including a phase-to-ground linevoltage and the zero-phase-sequence line-current, and means for obtaining an indication of a joint response of said distance-measuring relaying-means in said predetermined phase, and a selection of that same phase by said phase-selector means, and a ground-directional response to the phase-to-ground voltage which leads the phase selected by the phase-selector means.

'7. Relaying apparatus for ascertaining groundfaults on a three-phase line, comprising a singlephase distance-measuring ground-fault relayingmeans energized from line-derived quantities including a phase-to-ground line-voltage and the zero-sequence line current, in combination with ground-fault phase-selector means for making a selection of an apparently ground-faulted phase, said phase-selector means being operative to properly select the faulted phase in the event of a single ground-fault, and being operative to select only the leading one of the two faulted phases in the event of a double ground-fault having adequate resistance, and being operative to erroneously select the sound phase in the event of a resistanceless double ground-fault, said phase-selection of the phase-selector means being made Without an accurate determination of the distance of the fault by said phase-selector means, a ground-directional relaying-means energized from line-derived quantities including a phase-to-ground line-voltage and the zerophase-sequence line-current, and means for obtaining an indication of a joint response of said distance-measuring relaying-means in said predetermined phase, and a selection of that same phase by said phase-selector means, and a ground-directional response to the phase-toground voltage which leads the phase selected .by the phase-selector means.

8. Relaying apparatus for ascertaining groundfaults on a three-phase line, comprising a singlephase distance-measuring ground-fault relayingmeans, means for supplying said ground-fault distance-measuring relaying-means with a relaying-current dependent upon the zero-phase-sequence line-current, means for supplying said ground-fault distance-measuring relaying-means with any one of a plurality of relaying-voltages dependent upon the different phase-to-ground line-voltages respectively, a ground-directional relaying-means, means for supplying said ground-directional relaying-means with a relaying current dependent upon the zero-phase-sequence line-current, means for supplying said round-directional relaying means with any one of a plurality of relaying-voltages dependent upon the different phase-to-ground line-voltages respectively, ground-fault phase-selector means for selecting and applying one of said relayingvoltages to said distance-measuring relayingmeans, and for applying the phase-to-ground voltage of the next leading phase to said grounddirectional relayingmeans, and means for performing a line-protective operation jointly in response to said distance-measuring relayingmeans and said ground-directional relayingmeans.

9. Relaying apparatus for ascertaining groundfaults on a three-phase line, comprising a singlephase distance-measuring ground-fault reactance-responsive relaying-means for responding to the line-reactance of a predetermined phase of the line-conductors, said distance-measuring response being accurate only if a single groundfault occurs on said predetermined phase, in combination with a plurality of ground-fault phaseselector relays, one for each phase, each being directionally responsive toits own phase of the negative and zero phase-sequence components of a three-phase quantity derived from the line, a ground-directional relaying-means energized from line-derived quantities including a phaseto-ground line-voltage and the zero-phase-sequenoe line-current, and means for obtaining an indication of ,a joint response of said distancemeasu-ring relaying-means in said predetermined phase, a response of the phase-selector relay for that phase, a non-response oi the phase-selector relay for the next lagging phase, and a response of said ground-directional relaying-means in the phase leading said predetermined phase.

1.0. Relaying apparatus for ascertaining ground-faults on a three-phase line, comprising a single-phase distance-measuring groundfault relaying-means, means for supplying said ground-fault distance-measuring relaying-means with a relaying-current dependent upon the zero-phase-sequence line-current, means for supplying sa-id ground-fault distance-measuring relaying-means with any one of a plurality of relaying-voltages dependent upon the different phase-to-ground line-voltages respectively, a ground-directional relaying-means, means for supplying said ground-directional relayingmeans with a relaying-current dependent upon the zero-:phase-sequence line-current, means for supplying said ground-directional relaying means with any one of a plurality of relaying-voltages dependent upon the difi'erent phase-to-ground line-voltages respectively, a plurality of groundfault phase-selector relays, one for each phase, each being directionally responsive to its own phase of the negative and zero phase-sequence components of a three-phase quantity derived from the line, :means for selecting and applying one of said relaying-voltages to said distancemeasuring relaying-means, and for applying the phase-to-ground voltage of the next leading phase to said ground-directional relaying-means, in accordance with the phase selected by the response of any phase-selector relay, means for blocking said voltage-applications in response to a simultaneous response of the phase-selector relay for the next lagging phase, and means for performing a llne-pr0tective operation jointly in response to said distance-measuring relayingmeans and said ground-directional relayingmeans.

11. Relaying apparatus for ascertaining ground-faults on a three-phase line, comprising a single-phase distance-measuring ground-fault reactance-responsive relaying-means for re sponding to the line-reactance of a predetermined phase of the line-conductors, said distancemeasuring response being accurate only if a single ground-fault occurs on said predetermined phase, in combination with ground-fault phase-selector means for making a selection of an apparently ground-faulted phase, said phase-selector means being operative to properly select the faulted phase in the event of a single ground-fault, and being operative to select only the leading one of the two faulted phases in the event of a double ground-fault having adequate resistance, and being operative to erroneously select the sound phase in the event of a resist'anceless double ground-fault, said phase-selection of the phase selector means being made without an accurate determination of the distance of the fault by said phase-selector means, a phase-fault relayingmeans which is responsive to predeterminably severe faults on the two phases of the line-conductors other than said predetermined phase, and means for obtaining an indication of a joint response of said distance-measuring relayingmeans in said predetermined phase, and a selection of that same phase by said phase-selector means, and a non-response of said phase-fault relaying-means.

12. Relaying apparatus for ascertaining ground-faults on a three phase line, comprising a single-phase distance-measuring ground-fault relaying-means energized from line-derived quan-: tities including a phase-to-ground line-voltage and the zero-sequence line-current, in combination with ground-fault phase-selector means for making a selection of an apparently groundfaulted phase, said phase-selector means being operative to properly select the faulted phase in the event of a single ground-fault, and being operative to select only the leading one of the two faulted phases in the event of a double groundfault having adequate resistance, and being operative to erroneously select the sound phase in the event of a resistanceless double ground-fault, said phase-selection of the phase-selector means being made Without an accurate determination of the resistance of the fault by said phase-selector means, a phase-fault relaying-means which is responsive to predeterminably severe faults on the two phases of the line-conductors other than said predetermined phase, and means for obtaining an indication of a joint response to said distancemeasuring relaying-means in said predetermined phase, and a selection of that same phase by said phase-selector means, and a non-response of said phase-fault relaying-means.

13. Relaying apparatus for ascertaining ground-faults on a three-phase line, comprising a single-phase distance-measuring ground-fault relaying-means, means for supplying said ground fault distance-measuring relaying-means with a 14 relaying-current dependent upon the zero-phasesequence line-current, means for supplying said ground-fault distance-measuring relaying-means with any one of a plurality of relaying-voltages dependent upon the different phase-to-ground line-voltages respectively, ground-fault phaseselector means for selecting and applying one of said relaying-voltages to said distance measuring relaying-means, means for performing a lineprotective operation in response to said distancemeasuring relaying-means, and means for blocking said line-protective operation in response to a predeterminably severe double-phase fault on the two phases of the line-conductors other than the phase selected by said phase-selector means.

14. Relaying apparatus for ascertaining ground-faults on a threephase line, comprising a single-phase distance-measuring ground-fault reactance-responsive relaying-means for responding to the line-reactance of a predetermined phase of the line-conductors, said distance-measuring response being accurate only if a single ground-fault occurs on said predetermined phase, in combination with a plurality of ground-fault phase-selector relays, one for each phase, each being directionally responsive to its own phase of the negative and zero phase-sequence components of a three-phase quantity derived from the line, means for obtaining an indication of a joint response of said distance-measuring relayingmeans in said predetermined phase, a response of the phase-selector relay for that phase, and a non-response of the phase-selector relay for the next lagging phase, and means for blocking said indication in response to a predeterminably severe double-phase fault on the tWo phases of the line-conductors other than said predetermined phase.

15. Relaying apparatus for ascertaining ground-fau1ts on a three-phas line, comprising a single-phase distance-measuring ground-fault relaying-means, means for supplying said ground-fault distance-measuring relaying-means with a relaying-current dependent upon the zerophase-sequence line-current, means for supplying said ground-fault distance-measuring relayingmeans with any one of a plurality of relayingvoltages dependent upon the different phase-toground line-voltages respectively, a plurality of phase-fault fault-detector means, one for each pair of phases, a plurality of ground-fault phaseselector relays, one for each phase, each being directionally responsive to its own phase of the negative and zero phase-sequence components of a three-phase quantity derived from the line, means for selecting and applying one of said re laying-voltages to said distance-measuring relaying-means in accordance with the phase selected by the response of any phase-selector relay, means for performin a line-protective operation in response to said distance-measuring relayingmeans, and means for blocking said line-protective operation in response to an operation of either the phase-selector relay for the next lagging phase or the phase-fault fault-detector means for a fault on the two phases other than the phase selected by said response of a phase selector relay.

l6. Relaying apparatus for ascertaining ground-faults on a three-phase line, comprising a single-phase distance-measuring ground-fault reactance-responsive relaying-means for respending to the line-reactance of a predetermined phase of the line-conductors, said distance-measuring response being accurate only if a single-phase relaying-means, means for enemas a single ground-fault occurs on said predetermined phase, :being under-responsiveif a double ground-fault occurs on said predetermined phase and the next lagging phase of the line, and being over-responsive if a double ground-fault occurs on any other combination of two line-phases, in combination with selective-phase-sequenceresponsive ground-fault selector-means for so responding to double ground-faults as to render said distance-measuring ground-fault reactanceresponsive relaying-means ineffectual upon the occurrence of any double ground-fault other than one which involves said predetermined phase and the next lagging phase of the line.

17. Relaying apparatus for ground-faults on a three-phase line, comprising a single-phase distance-measuring ground-fault reactanceeresponsive relaying-means for responding to the line reactance of a predetermined phase of the line-conductors, selectivephase-sequence-res.ponsive ground-fault selector-means for responding to ground-faults so as to permit effectual operation of said distancemeasuring relaying-means only when said predetermined phase is responded to by said selector-means and when the next lagging phase is not responded to by said selector-means, and means for rendering said distance-measuring relaying-means ineifectual in response to a double ground-iault of predetenninably low r resistance.

18. Relaying apparatus for ascertaining round-faults on a three-phase line, comprising distance-measuring groundfault relaying means energized from line-derived quantities including a phaseetc-ground linevoltage and the zero-sequence line-current, in combination with selective-phase-sequence-responsiye ground-fault selector-means for so responding to double ground-faults as to render said distance-measuring ground-fault reactanceresponsive relaying-means ineffectual upon the occurrence .of any double ground-fault other than one which involves said phase-to-ground line-voltage and the next lagging phase 01' the line.

l9. Relaying apparatus for ascertaining ground-faults on a three-phase line, comprising a single-phase distance-measuring ground-fault relaying-means, means .for supplying said groundefault distance-measuring relaying-means with any one of a plurality of relaying-voltages dependent upon the different phase-to-ground line-voltages respectively, in combination with selective-phase-sequence-responsive fault selector-means for responding to groundfaults so as to select and apply, to said distancemeasuring relaying-means, the relaying-voltage dependent upon the faulted line-phase in the event of a single ground-fault, and so as to .either select and apply, to said distance-measuring relaying-means, the relaying-voltage dependent upon the leading faulted line-phase or to render said distance-measuring relaying-means inefiectual in the event of a double ground-fault, depending upon the neutral resistance and the fault-resistance.

20. Relaying apparatus for ascertaining groundefaults on a three-phase line, comprising a single-phase distance-measuring ground-fault supplying said ground-fault distance-measuring relaying-means with any one of ,a plurality of relaying-voltages dependent upon the different phase-.to-ground line-voltages respectively, in combination with ascertaining groundselective-phase-sequence-responsive g r o u n dfault selector-means for responding to groundfaults so as to select and apply, to said distancemeasuring relaying-means, the relaying-voltage dependent upon the line-phase responded to by the selector-means, provided that the next lagging line-phase is not also responded to by the selector-means, and means for rendering said distance-measuring relaying-means ineffectual in response to a double ground-fault of predetermin-ably low resistance.

21. Relaying apparatus for ascertaining ground-faults on a three-phase line, comprising a single-phase distance-measuring ground-fault reactance-responsive relaying-means for responding to the line-reactanoe of a predetermined phase of the line-conductors, a groundclirectional reiaying-means for responding to a predetermined direction of a ground-fault linequantity in the phase next leading said predetermined phase, and means for performing a line-protective operation jointly in response to said distance-measuring relaying-means and said ground-directional relaying-means.

22. Relaying apparatus for ascertaining ground-faults on a three-phase line, comprising a single-phase distance-measuring ground-fault relaying-means energized from line-derived quantitles including a phase-to-ground line-voltage and the zero-sequence line-current, a ground-directional relaying-means energized from line-derived quantities including the zero-sequence linecurrent and the phase-to-ground line-voltage next leading the phase which is applied to said distance-measuring relaying-means, and means for performing a line-protective operation jointly in response to said distance-measuring relaying-means and said ground-directional relayingmeans.

23. Relaying apparatus for ascertaining ground-faults on a three-phase line, comprising a single-phase distance-measuring ground-fault relaying-means, a ground-directional relaymeans, means for supplying said ground-fault distance-measuring relaying-means with any one of a plurality of relaying-voltages dependent upon the different phase-to-ground line-voltages respectively, means for supplying said ground-directional relaying means with any one of a plurality of relaying-voltages dependent upon the different phase-to-ground line-voltages respectively, selective phase sequence responsive ground-fault selector-means for responding to ground-faults so as to select and apply, to said distance-measuring relaying-means, the relaying-voltage dependent upon the line-phase responded to by the selector-means, provided that the next lagging line-phase is not also responded to by the selector-means, and so as to apply, to said ground-directional relaying-means, the relaying voltage dependent upon the line-phase which next leads the phase which is applied to the distance-measuring relaying-means, and means for performing a line-protective operation jointly in response to said distance-measuring relaying-means and said ground-directional relaying-means.

24. Relaying apparatus for ascertaining ground-faults on a three-phase line, comprising a, single-phase distance-measuring ground-fault reactance-responsive relaying-means for responding to the line-reactance of a predetermined phase of the line-conductors, selective-phase-sequence-responsive ground-fault selector-means for responding to ground-faults so as to permit effectual operation of said distance-measuring relaying-means only when said predetermined phase is responded to by said selector-means and when the next lagging phase is not responded to by said selector-means, and phase-fault relaying-means, sensitively responsive to phase-faults involving the line-phase next lagging said predetermined phase, for rendering said distancemeasuring ground-fault relaying-means ineffectual.

25. Relaying apparatus for ascertaining ground-faults on a three-phase line, comprising a single-phase distance-measuring ground-fault relaying-means, means for supplying said groundfault distance-measuring relaying-means with any one of a plurality of relaying-voltages dependent upon the different phase-to-ground linevoltages respectively, in combination with selective-phase-sequence-responsive ground-fault selector-means for responding to ground-faults so as to select and apply, to said distance-measur- 18 ing relaying-means, the relaying-voltage dependent upon the line-phase responded to by the selector-means, provided that the next lagging linephase is not also responded to by the selectormeans, and phase-fault relaying-means, sensitively responsive to phase-faults involving the line-phase next lagging said line-phase responded to by the selector-means, for rendering said distance-measuring ground-fault relaying-means ineffectual.

SHIRLEY L. GOLDSBOROUG-H.

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

UNITED STATES PATENTS Number Name Date 1,897,022 Lewis Feb. 7, 1933 20 2,408,208 Goldsborough Sept. 24, 1946