US1967110A - Simultaneously tripping relaying system - Google Patents

Description

July 17, 1934. BERGVALL 1,967,110

SIMULTANEOUSLY TRIPPING RELAYING SYSTEM Filed June 19, 1930 2 Sheets-Sheet l INVENTOR RoyaZ Cfierguall.

'z/ ATT'ORNEY July 17, 1934. R c BERGVALL 1,967,110

SIMULTANEOUSLY TRIPPING RELAYING SYSTEM Filed June 19, 1930 2 Sheet-Sheet 2 l I I I I I l I l High 'Frequemy Afpafafl/S Fig. 3

85 INVENTOR l I l I l l I I I I l I I I I I l I I I I l I I I I l I I I Patented July 17, 1934 SIMULTANEOUSLY TRIPPING- RELAYING SYSTEM Royal C. Bergvall, Wilkinsb'ur'g, Pa., assignor to Westinghouse Electric & Manufacturing Company,"a corporation of Pennsylvania Application June 19, 1930, Serial No. 462,534 .27 Claims." (01. 175-294) My invention relates to relaying systems, and it has more particular relation to high-frequency relaying systemsand also to a system for simultaneously tripping the circuit breakers at the two ends of a faulty section of a transmission line.

In order to obtain selectivity, in relaying systems prior tomy invention, it has been necessary to have the circuit breakers at each end of a faulty line section open in succession instead of simultaneously. In such prior relaying systems, it was necessary for the fault-responsive element to operate very much more slowly for the more remote faults'than for the nearby faults, and this time-delay action had to be so great that, for

" faults at'or b'eyondthe far end of the line section,

the time 'delay was greater than the relaying time for nearby faults plus the very much longer time required for the circuit breaker action.

' Studies of the stability of transmission lines have shown the very great importance of clearing afaultyl line section as quickly as possible, particularly when the clearing time is made as small as 12 cycles, more or less if possible, on a cycle's'ystern. t

It is the object of my present invention to provide means for simultaneously tripping the circuit breakers at both ends of a faulty line section. A further object of my invention relates to a high-frequency relaying system and to-a novel coupling means for coupling the high-frequency apparatus to the transmission line.

A still further object of my invention relates to means for preventing the loss of several cycles of relaying time which has been'encountered heretofore by reason of the fluttering or chattering of the fault-responsive relay element for certain types of faults. Because of the high 'reactance of the tripping coil, which retards the instantaneous building up of the tripping current, it has been possible, forthe fault-responsive element to flutter rapidly, so that its contacts do not remain closed for a sufiicient time't'o'enable the tripping current to build up to a value of the order of an ampere, or other value sufiicient to maintain a very tiny arc across the fluttering contacts, as has been shown by oscillographic tests. This disadvantage is overcome by shunting the highly inductive tripping coil with a nonin'ductive impedance which will permit the flow of an instantaneous current large enough to are over the fluttering contacts. i r

With the "foregoing and other objects inview; my invention consists in the methods, system s,

' combinationsfjand apparatus hereinafter described and claimed and illustrated in the accompanying drawings, wherein i Figural is a diagrammatic view of circuits and apparatus embodying somefeatures of my invention in a polarized-current pilot-wire system,

Fig. 2 is a similar view illustrating my invention as applied to a highJrequency relaying system utilizing the transmission line' as the means for carrying the high-frequency relaying currents, and

Fig. 3 is a similar'viewillustrating the application of my invention to a high-frequency pilotwire relaying system. r a

In Figure 1 my invention is shown applied to a two circuit three-phase transmission line, only one end of which is shown, the other end being omitted as being a duplicate ofthe first end. Two three phase transmission lines 4 and 5 are connected to a -bus 6 through circuit breakers 7 and 8, respectively, said circuit breakers having tripping coils 9 and 10. i

r In the system shown in Figure 1, two different types of 'fault-distance responsive tripping, relayelements, namely, a high-speed or instantaneous diiierential ground relay 12 for detecting single phase to ground faultsand twelve impedance relays'l3 to 24 for detecting all other faults on either one of the two lines 4 and 5, are used.

Energy is provided for supplying the several relays, by means of two Y-connected current transformers 26'and 27, connected in the respective lines, and a potential transformer 28. The differential ground relay -12 isessentially a quicka'cting wattmeterdevice having a stationary element provided with two coils30 and 31 which are connected in the neutral or residual-current circuits of the respective current transformers 26 and 27, for jointly providing a field whichoperates "dynamo-electrically on a movable element which is energized from two other current coils 33 and Bl' hich are-connected in the respective residual-current circuits aforesaid: The two field coils 30 and 31 areconnected in opposition and the twocurrent coils- '33 and 34 are connected cumulatively, or the other way around, so that when there is any residual or zei'oephase-sequence ground current ineither one of thetransmission lines, the differential ground relay 12 will respond to a predetermined degree of unbalance of these residual currents. The residual differential ground .relay l2uis provided with a movable contact member 36 which engages one or therother of two pairs of stationary contact members 35 and :37, depending on which lineis faulteda. r .5 M. M

The impedance relays 13 to 24 are shown schematically as each comprising a current-responsive actuating coil and voltage-responsive restraining coil 41, so that the relays pick up at a predetermined apparent impedance, or ratio between voltage and current. I intend, by the term fimpedance element, however, to include any element which responds to either the apparent or real impedance of the transmission line, or which picks up at any predeterminable ratio of any voltage quantity or component to any current quantity or component. The current coils of the relays 13-14, 15-16, and 17-18 are con.- nected across the respective delta phases of the current transformer 27 of transmission line 5, whereas the current coils of the relays 19-20, 21-22, and 23-24 are connected across the delta phases of the other current transformer 26. The voltage coils 41 of the impedance relays 13 to 24 are connected across the corresponding delta phases of the potential transformer 28.

All of the impedance-responsive elements 13 to 24 are quick-acting. or instantaneous in their operation, by which I mean that the time required.

for their operation is quitesmall compared to the time required by the circuit breaker to clear a fault after its tripping circuit has been energized, and by which I also meanthat the relay time is not significantly varied in accordance withthe distance of the fault so as to secureselectivity by suchv variation in the relay time.

It will be noted that theimpedance elements 13 to 24 are connected in pairs, so that each delta phase of each line has two impedance relays, The first, instantaneous impedance-responsive element, which is indicated by the numerals 13, 15, 17, 19, 21 and 23 in the respective phases, never picks up for faultslocated as far away as the circuit breaker (not shown in Fig. 1) at the corresponding station at the other end of the line sections 4 and 5. The second instantaneous impedance-responsive element, whichis indicated by the numerals 14, 16, 18, 20, 22 and 24 in the respective phases, will pick up for faults located as far away as the other circuit breaker at the other end of the corresponding line section. The first impedance elements are provided with normally open tripping contacts 43. The second intantaneous impedance elements are provided with contacts 44 for setting in operation a time-switch element represented as a small synchronous motor 46 for closing tripping contacts 4'7 after a predetermined time interval which gives the first impedance elements at the other end of the line a chance to first clear the fault, through their circuit breakers, if they are going to clear the fault at all. The timing switch 46 is shown as being energized from a small current transformer 48 in circuit 1 with the current coil of the corresponding sec,

being fed from the-line in which the particular relay. .is located, and this function is accomplished, in the case of the residual current differential-ground relay 12,'by means of two highspeed directional residual current-relays50 and i 51 which compare the direction of the respective residual currents with the direction of the residual voltage, the latter quantity being obtained from three serially connected tertiary windings 52 on the potential transformer 28, the primary and secondary windings of this potential transformer being connected in star so as not to shortcircuit out the residual of zero-phase-sequence voltage.

In the case of the impedance elements 13 to 24, the direction-discriminating function is accomplished by two sets of three similar directional elements 54 connected in the respective delta phases of the two lines, so as to compare the delta current with a voltage which is derived from an auxiliary voltage bus 56 which is energized, from an'auxiliary potential transformer 5'7,'through three impedance devices 58. The auxiliary voltage bus 56 is further energized from a small synchronous condenser 59 which'fioats across its terminals and serves to prevent too great a variation in the phase and/ or magnitude of the voltage applied to the voltage coil of the directional element 54, even though the line voltage should be suddenly reduced to zero by a dead short-circuit nearby. Correct operation of the directional elements 54 is thus assured for a suflicient time to enable the fault to be cleared. Each directional element is provided with'normally open contacts 61 and normally closed contacts 62, associated respectively with the first and second induction relay contacts 43 and 44, meaning, by normally, in the present instance, the conditionof the directional element when'tripping is not desired.

The tripping circuit of the circuit breaker 7 in line 4 comprises its tripping coil 9 which is energized from a battery 64 through several sets of contacts which are connected in parallel between a tripping bus 65 and a positive bus 66 connected to the battery 64. In response to single phase ground faults occurring within a predetermined distance which is less than the total distance to the next relaying station, the circuit breaker 7 is tripped by the closing of the contacts 35 of the differential ground relay, in series with the contacts of the directional residual relay 50. In response to any other faults, up to a distance less than the length of the line up to the next relaying station, the circuit breaker '7 is tripped by one of the first impedance elements 19, 21 or 23, the contacts 43 of which are in series,*respectively, with the respective normally open contacts 61 of the associated directional element 54, as shown in Fig. 1. In case the'first impedance element 19, 21 or 23 in any phase should fail to cause the fault to be cleared, the circuit breaker 7 may be tripped by one of the three associated timing switches 46, the contacts 47 of which are connected in parallel across the tripping buses 65 and66.

The tripping circuit for the circuit breaker 8 in line 5 comprises its tripping coil 10, the same battery 64, the same positive battery bus 66, the relay. contacts as shown and as will be understood from the foregoing explanation, and a relaying bus 67 which is connected tothe tripping coil 10.

The fault-distance-responsive tripping-relay elements which operate instantaneously cannot be made to respond to f'aults in a certain small section of the line close to the nextrelaying station, becauseof the impossibility of certainly discriminating between faults located in'the line section between its two circuit'breakers and faults located in some other line section close to the far end'of the line in which the relays'in question are located-'.'- As to nearby faults, however, it is easy to discriminate between the faulty line and the clear line by means of the fault-distance-responsive elements in combination with the respective directional elements.

In accordance with my invention, I secure instantaneous tripping in all cases, whenever a fault is located anywhere on a line section, by sending a tripping impulse to the far end of the line whenever the tripping coil of the near circuit breaker is energized. Thus, both ends of a faulty line section are cleared substantially simultaneously in response to the operation of any instantaneous fault detecting relay element.

In Fig. 1, the means for sending tripping impulses from one relaying station to the next 'comprises a pilot wire 70, a cable or a pair of overhead conductors, which is energized, at each end, by means of two quick- acting relays 71 and 72, the actuating coils 73 and 74 of which are connected in parallel with the respective tripping coils 9 and 10 of the circuit breakers associated with the two parallel lines 4 and 5. Means may be provided for preventing the simultaneous operation of the two relays 71 and 72, as is suggested by the interlocking contacts 75 as shown. The two relays 71 and 72 energize the pilot wire 70, in opposite polarities, from the tripping battery 64, so that the tripping impulse may be regarded as being a positive impulse, for one of the lines, and negative for the other. 7

The tripping impulses carried by the pilot wire 70 are received by means of a polarized relay 77 having contacts 78 and 79 which are energized in accordance with the direction of the impulses in the pilot wire.

It is not feasible, with most pilot wires, to have a circuit breaker or line-interrupting device 01)- erate every time an impulse is received, because of the susceptibility of the pilot wire to inductive disturbances, producing impulses which have not been sent. In accordance with my invention, therefore, one or more fault-detector interlockcontact relay elements are provided, at each relaying station, for indicating the existence of a fault somewhere on the system, without neces sarily discriminating as to the particular line section in which the fault is located. The polarized relay 77 is locked out of action at all times except when the existence of some sort of fault is indicated by the fault-detector interlock-contact relay element or elements.

As shown in Fig. 1, one terminal of the polarized relay 77 is connected to the positive battery bus 66, and its two contacts 78 and 79 are connected to two polarized- relay buses 81 and 82, respectively, which are joined to the two tripping buses 55 and 67, respectively, through a plurality of fault-detector interlock-contact relay elements, which, in the particular system shown in Fig. 1, comprise two over-current relays 84 and 85 connected in the residual-current circuits of the respective current transformers 26 and 27, for detecting the presence of single phase ground faults, and an auxiliary normally open contact 86 on each of the second impedance elements 14, 16, 18, 20, 22 and 24 in the respective phases, for detecting the presence of all other faults. The overcurrent relays 84 and 85 are set to operate slightly below the value of current corresponding to a' ground fault at the far bus, so that it will respond to ground faults located slightly beyond the far bus. The second instantaneously operating impedance element in each phase is selected for cooperation with the polarized relay 77 because this second element will operate for faults in the distant and zone. The contacts of the overcurrent fault-detector relay 84 are connected in parallel with the contacts 86 of the second impedance relays 20, 22 'and r 24, between the polarized-relay bus 82 and the tripping bus 65. In like manner, the contacts of the over-current relay 85 are connected in parallel with the auxiliary contacts 86 of the other three second impedance elements 14, 16 and 18, between the polarized-relay bus 32 and the tripping bus 67. Improper operating of circuit breakers should not occur due to disturbances on the pilot wire since the interlock contacts will not be closed except when a fault exists on the system. The pilot wires can easily be supervised with indicating lamps and bell alarm so that grounds, open wires, or short circuits can quickly be detcted. Thecontacts' on'the interlock relays will prevent improper opening of circuit breakers in case the pilot wire protectors break down due to induced voltages during fault conditions.

The operation of the polarized relay 77, at each relaying: station, may be summarized as follows. This relay is for the purpose of tripping either of the circuit-breakers 7 or 8 (according to the direction of the direct current through the relay 77) in response to faults which are so close to the next relaying station (not shown in Fig. 1) that'the instantaneous relays 50, 19, 21 and 23 (for circuit-breaker 7) or 51, '13, 15 and 17 (for circuit-breaker 8) cannot be set so as to respond thereto. (If said instantaneous relays were set so as to respond to such remote faults near the far ends of the line-sections which they protect, they would also respond to some still more remote faults which are not in the line-section which is being protected, thus tripping out the line-section when there is no fault therein.) However, a fault, in the linesection 4 or 5, which is remote with respect to the relaying station shown in Fig. 1, is close to the next relaying station at the right-hand ends of said line-sections, so that the aforementioned instantaneous relays at said next relaying station readily respond to said faults and energize the pilot wires 70 in the proper polarity.

When the polarized relay 77 of Fig. 1 is thus energized, it connects the positive battery terminal to one of the relay busses 81 or 82, but it does not trip the circuit-breaker 7 or 8 unless the presence 'of a fault somewhere on the system is assured by a fault-detector interlock-contact means, such as the ground-relay 84 and the auxiliary contacts 86 of the more remotely responsive instantaneous impedance relays 20, 22 and 24 (for the circuit-breaker 7), or the ground-relay 85 and the auxiliary contacts 86 of the more remotely responsive instantaneous impedance relays 14, 16 and 18 (for the circuit-breaker 8); In this way, a chance shock-excitation or inductiveinterference excitation of the pilot wires 70, when there is no fault on the system, will not trip out a'sound line.

As shown in Fig. 1', each circuit breaker 7 and 8 has an auxiliary contact 87 in series with its tripping coil for deenergizing the corresponding tripping coil 9 or 10 and theassociated pilotwire relay 71 or 72, as soon as the circuit breaker has been opened or partially opened.

As the current coils 40 of the respective impedance elements are connected in delta, in the system shown in Fig. 1, it is necessary to pro vide a return path for the residual or zero sequence currents, which is done by means of two Y-connected transformer banks '88 and 89;

the neutral points of which are connected to the neutral circuits of the current transformers 26 and 27, so that the residual currents of each current transformer may return to the neutral Y connection of said current transformer through the associated residual- current apparatus 12, 50, 8 1 and 12, 51, 85, respectively. The Y-connected transformer banks 88 and 89 are provided with secondary windings 90 which are so connected as to permit the non-inductive flow of equal, inphase, or zero-sequence, currentsin the three primary phases, while permitting only small magnetizing currents to flow in the case of the positive and negative phase-sequence components. As shown in Fig. 1, the secondary windings "90 may be connected ina single closed delta cir-J cuit for each of said transformer banks.

In my invention is shown in what is perhaps referred form of embodiment, uti lining his "requency impulses superimposed on one of the iase conductors of one of the parallel lines 1 and 5. In Fig. 2, the far end of the lines and 5 is also indicated, the same comprising a bus 91, a circuit breaker 92 in each line, and a duplication or the tripping and relaying apparatus of the first line terminal.

In 2, the re laying apparatus at each ter' minal is disposed in three groups, designated trippin relays'93, interlock relays 94 and high-frequency apparatus 95, as indicated by dotted line rectangles. The tripping and inter lockingrelays may be the same as shown in Fig. 1 or they maybe of any other preferred type, and they are indicated much more sketchlly than in Fig; 1. In Fig. 2, for example, the current coils of the impedance and directional elements 96 and 9'? are connectedin star, only one phase of each tra "mission line being indicated with the understan= g that the apparatus is duplicated for the other phases. The voltage coil 98 of each impedance relay as is connected to the delta voltage which leads the corresponding line current by 30 degrees when the line is operating at unity power factor. The voltage-coil terminals 99 of each directional element are energized from the delta line voltage which lags 30 degrees behind said current when the line is operating at unity power factor.

The high-frequency apparatus at each terminal oi the three-phase transmission system shown inv Fig. 2 is single-phase apparatus con-- nected to any phase of the line 5, such as the C phase, by means or" a novel coupling means which constitutes an important item in the design of a j practically usable superimposed high-frequency system.. In this high-frequency relaying system a different frequency is used for each of the lines 1 and 5, in order'to obtainselective tripping of the two lines, 720 cycles being utilized for trip-,

; ping line 4 and 180 cycles being utilized for tripping the other line 5. In order to provide an overabundance of tripping energy, 5 kilowatts are provided each of the two high frequencies, so that the coupling means must be designed to sat isfactorily handle this power.

The coupling means at each end of the line comprises two air-core chckecoils or reactors 101 and 102 connected in series with the C phase conductor of the line 5. No connection is necessary to line 4 because the lines are bussed together at their two ends. To give a concrete illustration, in a system in which the normal fullload Gil-cycle current is 1000 amperes, at 220 kilo- Volts, each of the reactors 101 and 102 is rated at 1000 amperes and has a Gil-cycle impedance of about. one-half ohm, so that the total Gil-cycle vcltage-drop across the two reactors is about 1000 volts, which may be increased to 10,000 volts upon the occurrence of a fault.

The high-frequency apparatus is insulated from the 220-kilovolt transmissionline by means of an insulating transformer 103 having any suitable ratio, such as 5/1 or 7/1. The highvoltage side of the insulating transformer 103 is connected across the two reactors 101 and 102, whereas the low-voltage side is connected to the high-frequency sending and receiving apparatus. The insulating transformer must be of the ironcore type in order to have reasonable efiiciency, but it must be designed so that it will not become saturated by the maximum 60-cycle voltage, in this case 10,000 volts, which may be impressed across it at times of system faults, sothat the coupling transformer will still be useful for transmitting the highfrequency impulses at these times. The coupling transformer is designed to carry 5 amperes of high-frequency energy at 1000 volts on the high-frequency. side of the transformer.

The high-frequency energy is preferably excluded .from'the reactors 10land 102 by means of twobanlrs of outdoor capacitors 104 and 105, rated respectively at 120 Ell "A at cycles, which are connected in parallel to the two reactors 101 and 102, respectively, so as to provide anti-resonant circuits for the 720-cycle currents and the fiZG-cycle currents, respectively.

The secondary winding of the coupling transformer 10:2 isconnected exclusively to circuits which are tuned for the high-frequency cu rents, so that substantially no 60-cycle current flows except the magnetizing current which is quite small. Two principal tuned circuits are connected across the coupling or insulating transformer 103 on-the low voltage side, the same comprising a small air-core reactor 10? in series with a capacitor 108 tuned to 180 cycles, and a small air-core reactor 109 in series with a capacitor 110 tuned to 720 cycles.

The high-frequency energy is coupled to the respective coils 1.07 and 109 just mentioned, whenever the tripping circuits 6"! or 65, respectively, are energized, this function being accomplished by relays 112 and 113 which are connected across the respective tripping circuits, said relays having nor: ally on n contacts 11 1 and 115, respectively, for connecung the highfrequency sources to the respective reactors 107 and 109, which may be tapped for the purpose.

The high-frequency source comprises two single-phase 5- kiiowatt generators 113 and 119 of 1B0 cycles and '120 cycles, r spectively. These are dynamo-electric machines which are constantly running, being driven at a high speed, through suitable gearing 120, from a motor 121, and being excited from an cxciter bus 122.

High-frequency current of either sec cycles or 720 cycles is thus fed into the transmission system 4, 5, 6, 91, according as the tripping coil 10 of line 5 or the tripping coil 9 of line 1 is energized, this being accomplished by the quick-acting relays 112 and 113, the actuating coils of which are connected in parallel with the respective tripping coils 10 and 9.

The high-frequency currents which are sent out over the C phase conductor of the transmission system areof only 2. cycles duration, withrespect to Gil-cycle energy, because they are interrupted, soon as the circuit-breaker tripping-energy is interrupted by means of the spaced stations, means at each station for sending a line-discriminatory tripping current to the other station whenever a tripping circuit is energized, and line-discriminatory means at each station for'receiving said tripping current and ap: plying it to the tripping of its proper circuit breaker for clearing'the other end of the faulted line.

' 3. The combination with a multi-circuit power system comprising a plurality of lines in parallel between two spaced stations, of circuit breakers and relaying equipment at each station, each circuit breaker having a tripping circuit, and each relaying equipment comprising fault-distance-responsive line-discriminatory tripping-relay elements for energizingthe tripping circuit of the proper adjacent circuit breaker for clearing a faulted line in response to faults up to predetermined distances, said predetermined distances being lessthan the distance between the two spaced stations, means at each station for sending a line-discriminatory tripping current to the other station whenever a tripping circuit is energized, and line-discriminatory means at each station for receiving said tripping current and applying it to the tripping of its proper circuit breaker for clearing the other end of the faulted line, said line-discriminatory receiving means comprising means for segregating, and selectively responding to the different line-discriminatory tripping currents, and also comprising fault-detector interlock-contact relay elements which are not of themselves able fully to discriminate the faulted line'under all conditionsbut which are able to detect and indicate the presence of a fault somewhere.

. 4. The combination with an alternating-current power line having two circuit breakers therein at spaced stations, each circuit breakerhaving a tripping circuit, of relaying equipment at each station, comprising fault distance responsive tripping-relay elements for energizing the tripping circuit of the adjacent circuit breakerin response to faults up to predetermined distances, said predetermined distances being less than the distance between the two, spaced stations, tuned high-frequency means at each station for sending a high-frequency tripping current to the other station whenever a tripping circuit is energized, and tuned high-frequency means at each station for receiving said tripping current and applying it to the tripping of its circuit breaker, characterized by means for coupling said highfrequency sending and receiving means to a lineconductor at each of said stations, each coupling means comprising an inductive reactor shunted by a tuned capacitor directly connected as an anti-resonant circuit tuned to said high-frequency in series with said line-conductor, and an insulating transformer having one winding connected across said inductive reactor and another winding connected to said high-frequency sending and/or receiving means.

' 5. The combination with a multi-circuit polyphase power system comprising a plurality of lines in parallel between two spaced stations, of circuit breakers and relaying equipment at each station, each circuit breaker having a tripping circuit,' and each relaying equipment comprising fault-distance-responsiveline-discriminatory tripping-relay elements for energizing the tripping circuit of the proper adjacent circuit breakerfor clearing a faulted line in response to faults up to predetermined distances, said predetermined distances being less than the distance between the two spaced stations, means at each station for sending aims-discriminatory highfrequency tripping current to the other station whenever a tripping circuit is energized, said sending means sending a currentof a different frequency for each of the parallel power lines, and line-discriminatory means at each station for receiving said tripping current and applying it to the tripping of its proper circuit breaker for clearing the other end of the faulted line.

6. The combination with a multi-circuitpowcr system comprising a plurality of linesin parallel between two spaced stations, of circuit breakers and relaying equipment at each station, each circuit breaker having a tripping circuit, and each relaying equipment comprising fault-distense-responsive line-discriminatory tripping-relay elements for energizing the tripping circuit of the proper adjacent circuit breaker for clearing a faulted line in response to faults'up to predetermined distances, said predetermined distances being less than the distance between the two spaced stations, means at each station for sending a line-discriminatory alternating tripping current to the other station whenever a tripping circuit is energized, said sending means sending a current of a different frequency for each of the parallel power lines, and line-discriminatory means at each station for. re ceiving said trippingcurrent and applying it to the tripping of its proper circuit breaker for clearing, the other end of the faulted line.

7. The combination with a multi-circuit polyphaise vpower system comprising a plurality of lines in parallel between two spaced stations, of circuit breakers and relaying equipment at each station, each circuit breaker having a tripping circuit, and each relaying equipment comprising faul -distance-responsive line-discriminatory tripping-relay elements for energizing the tripping circuit of the proper adjacent circuit breaker for clearing a faulted line in response to faults up to predetermined distances, said predeter mined distances being less than the distance between the two spaced stations, means at each station for sending a line-discriminatory highfrequency tripping current to the other station Whenever a tripping circuit is energized, said sending means sending a current of a different frequency for each of the parallel power lines, and line-discriminatory means at each station for receiving said tripping current and applying it to the tripping of its proper circuit breaker for clearing the other end of the faulted line, said line-discriminatory receiving means comprising means for segregating, and selectively responding to, the different line-discriminatory tripping currents, and also comprising fault-detector interlock-contact relay elements which are not of themselves able fully to discriminate the faulted line under all conditions but which are able to detect and indicate the presence of a fault somewhere. I

8. The combination with a multi-circuit power system comprising a pluralityof lines in parallel between two spaced stations, of circuit breakers and relaying equipment at each station, each circuit breaker having a tripping circuit, and each relaying equipment comprising fault-distanceresponsive line-discriminatory tripping-relay ele-' ments for energizing the tripping circuit of the proper adjacent circuit breaker for clearing a faulted line in response to faults up to predetermined distances, said predetermined distances being less than the distance between the two instantaneous H I and further characterized by the fact that said spaced stations, means at each station for sending a line-discriminatory alternating tripping current to the other station whenever a tripping circuit is energized, said sending means sending a current of a 'diiferent frequency foreach of the parallel power lines, and line-discriminatory means at each station for receiving said tripping current and applying it to the tripping of its proper circuit breaker for clearing the: other end of the faulted line, said line-discriminatory receiving means comprising means for segregating, and selectively responding to, the different linediscriminatory tripping currents, and also com-. prising fault-detector interlock-contact relay elements which are not of themselves able fully to discriminate the faulted line under all conditions butwhich are able to: detect. and indicate the presence of a fault somewhere.

9. The combination with an electric power line having two circuit breakers therein at spaced stations, of relayin equipment at each station, each circuitbreaker having a tripping circuit, and each relaying equipment comprising faultdistance-responsive tripping-relay elements. for

; energizing the tripping circuit of the adjacent ircuit breaker in response to faults up to pre; determined distances, said predetermined distances being less than the distance between. the two spaced stations, means at each station for sending a tripping current to the other station Whenever a tripping circuit :is energized, and means at each station forreceiving said tripping current and applying it to the tripping of its circuit breaker, said receivingmeans comprising fault-detector interlock-contact relay elements which are not of themselves able fully to discriminate the faultedline under all conditions but which are able to detect and indicate the presence of a fault somewhere.

10. The combination with an electric power line having two circuit breakers therein at spaced stations, each circuit breaker having a tripping circuit, of relaying equipment at each station, comprising response to faults up to predetermined distances, said predetermined distances being less. than the distance between the two spaced stations, means at each station for sending a tripping current to the other station whenever a tripping circuit is, energized, and means at each station for TGCGiV,

ing said tripping current and applying it to the tripping of its circuit breaker, said receiving means comprising fault-detector interlock-contact relay elements which are not of themselves able fully to discriminate the faultedline under all conditions but which are able todetect and indicate the presence of a fault somewhere; characterized by the fact that said fault-distance-responsive tripping-relay elements comprise an element which never picks up for faults located as far away as the other circuit breaker, asec- 0nd instantaneous impedanceqesponsive element which will pick up for faults located as far away as the other circuit breaker, and a time-delay relay-element set in operation by said second I impedance responsive element;

fault-detector interlock-contact relay element's comprise contacts on said second instantaneous impedance-responsive element.

11. The combination withan alternating-cur 'rent power line having two circuit breakers fault-distance-responsive 1 tripping-relay elements for-energizing the. trip.-,, ping circuit of the adjacent circuit breaker in.

instantaneous impedance-responsive therein at spaced stations, each circuit breaker having a tripping circuit, of relayin equipment at each station, comprising fault-distanceresponsive,tripping-relay elements for energizing theitripping. circuit of the adjacent circuit breaker iniresponse to faults up to predetermined distances, said: predetermined distances being less than the distancebetween the two spaced stations, tuned high-frequency means at each station for sending a high-frequency tripping current tolthe other station whenever a tripping circuit is energized,.and tuned high-frequency means'at each station for receiving said tripping current and applying it tov the tripping of its circuit breaker, said receiving means comprising fault-detector interlock contact relay elements-which are not of themselves able fully to discriminate the faulted line under all conditions but whichare able to detect and indicate the presence of a fault somewhere.

12. The combination with an electric power l'ne having two circuit breakers therein at spaced stations, each circuit breaker having a tripping circuit, of relaying equipment at each station, comprising fault-distance-responsive tripping relay elements for energizing the tripping circuit of the adjacent circuit breaker in response to faults up to predetermined distances, said predetermined distances being less than the dis tance between the two spaced stations, means tripping current to the other station whenever a tripping circuit is energized, means at each station for receiving said tripping current and applying it to the tripping of its circuit breaker and means responsive to the opening of a circuit breaker for interrupting the high-frequency tripping current.

13. The combination with a multi-circuit polyphase power system comprising a plurality of lines in parallel between two spaced stations, of circuit breakers and relaying equipment at each station, each c rcuit breaker having a tripping circuit, and each relaying equipment comprising faultdistance-responsive linediscrimina'tory. tripping-relay elements for energizing the. trippTng circuit of the proper adjacent circuit breaker for clearing a faulted line in response to faults up to predetermined distances, said predetermined distances being'less than the dis tance between the two spaced stations, means at each station for sending a line discriminatory high-frequency tripping current to the other station whenever a tripping circuit is energized, said sending means sending a current of a different frequency for each of the parallel power lines, line-discriminatory means at each station for receiving said tripping current and applying it to the tripping of its proper circuit breaker for'clearing the other end of the faulted line, and means responsive to the opening of a circuit breaker for interrupting the high-frequency tripping current.

'14,. The combination with a multi-circuit polyphase power system comprising a plurality of lines in parallel between two spaced stations, of circuit breakers and relaying equipment at each stat'on, each circuit breaker having a tripping circuit, and e'achrelaying equipment comprising fault e distance responsive line-discriminatory tripping-relay elements for energizing the trippingcircuit of the proper adjacent circuit breaker for clearing a faulted line in response to faults up to predetermined distances, said predetermined distances being less than the distance between the two spaced stations, means at each station for sending a line-discriminatory highfrequency tripping current to the other station whenever a tripping circuit is energized, said sending means sending a current of a different frequency for each of the parallel power lines, linediscriminatory means at each. station for receiving said tripping current and applying it to the tripping of its proper circuit breaker for clearing the other end of the faulted line, said line-disciminatory receiving means comprising means for segregating, and selectively responding to, the different line-discriminatory tripping cur rents, and also comprising fault-detector interlock-contact relay elements which are not of themselves able fully to discriminate the faulted line under all conditions but which are able to detect and indicatethe presence of a fault somewhere, and means for automatically interrupting the high-frequency tripping circuit after a brief time sufficient for the tripping of the circuit breaker.

15. An electric power line comprising a circuit breaker, a tripping coil therefor, a source of tripping current for said tripping coil, a line-fault res onsive relay having contacts for closing a tripping circuit through said tripping coil from said source, a contactor switch for closing a holding circuit across the relay contacts when the I tripping circuit is energized, and a substantially non-inductive resistance shunted across said tripping coil, said resistor having a resistance such as to carry a current of the order of an ampere for producing an arc across said relay 'I contacts in the event of fluttering of the latter.

16. An electric power line comprising a circuit breaker, atripping coil therefor, a source of tripping current for said tripping coil, a line-fault esponsive relay having contacts for closing a tripping circuit through said tripping coil from said source, a contactor switch having an actuating coil energized by said tripping circuit and having contacts for closing a holding circuit across the relay contacts when the tripping circuit is energized, a substantially non-inductive impedance device shunted across said tripping coil, said device having an impedance such as to carry a current of the order of an ampere for producing an arc across said relay contacts in the event of fluttering of the latter, and means responsive to the opening of the circuit breaker for interrupting the current in the tripping coil.

17. An electric power line comprising a circuit breaker, a tripping coil therefor, a source of tripping current for said tripping coil, a line-fault responsive relay having contacts for closing a tripping circuit through said tripping coil from said source, and a bypass circuit in which current builds up faster than in said tripping coil 1 for instantly drawing a sufficient current through said relay contacts to maintain a short arc and thus prevent interruption of the tripping circuit upon chattering of the relay contacts.

18. The combination with an electric power line having two circuit breakers therein at spaced stations, each circuit breaker having a tripping circuit, of relaying equipment at each station, comprising fault-distance-responsive trippingrelay elements for energizing the tripping circuit of the adjacent circuit breaker in response to faults up to predetermined distances, said predetermined distances being less than the distance between the two spaced stations, means at each station for sending a tripping current to the other station whenever a tripping circuit is energized,

and means at each station for receiving said tripping current and applying it to the tripping of its circuit breaker, characterized by having auxiliary relay-means for normally disconnecting the tripping-current sending means and connecting the tripping-current receiving means, said auxiliary relay means being automatically operable to disconnect the receiving means upon the energization of the tripping circuit of the circuit breaker which is associated with said receiving means, and a contactor switch for closing a holding circuit across the tripping circuit before said auxiliary relay means is actuated.

19. The combination with a multi-circuit alterhating-current power system comprising a plurality of lines in parallel between two spaced stations, of circuit breakers and relaying equipment at each station, each circuit breaker having a tripping circuit, and each relaying equipment comprising fault-distance-responsive line-discriminatory tripping-relay elements for energizing the tripping circuit of the proper adjacent circuit breaker for clearing a faulted line in response to faults up to predetermined distances, said predetermined distances being less than the distance between the two spaced stations, means at each station for sending a line-discriminatory high-frequency tripping current to the other station whenever a tripping circuit is energized, said sending means sending a current of a different frequency for each of the parallel power lines, and line-discriminatory. means at each station for receiving said tripping current and applying it to the tripping of its proper circuit breaker for clearing the other end of the faulted line, characterized by means for coupling said high-frequency'sending and receiving means to a lineconductor at each of said stations, each coupling means comprising as many inductor elements as there are high-frequency tripping currents, each inductor element being shunted by a tuned ca pacitor to provide a plurality of anti-resonant circuits tuned to the respective high-frequency currents, said anti-resonant circuits being in series with eachother and directly connected in series with said line-conductor, and an insulating transformer having one winding connected across said serially connected anti resonant circuits and another windingv connected to said high-fre-' quency sending and/ or receiving means, the latter comprising means for substantially excluding currents of the power-line frequency and for segregating, and selectively responding to, the different line-discriminatory tripping currents.

20. An electric power line comprising a circuit breaker, a tripping coil therefor, a source of tripping current for said tripping coil, a line-fault responsive relay having contacts for closing a tripping circuit through said tripping coil from said source, and a contactor switch for closing a holding circuit across the relay contacts when the tripping circuit is energized, characterized by meansfor insuring such speed of action of the contactor switch that it will respond to substantially the first momentary closure of the tripping relay contacts in spite of chattering of the latter.

21. The combination with an electric power line, of means for isolating both ends of a faulty line section, comprising fault-distance responsive relaying means at both ends of such character as to produce, by their own operation, simultaneous substantially instantaneous relaying response for centrally located faults and sequential response for faults located close to either end. of the line section, characterized by substantially 'instantaneously operating means for sending a tripping impulse from one end to the other so as to produce substantially simultaneous isolation of both ends of the line section for faults located anywhere therein.

22. The combination with an electric powertransmitting system having a plurality of individual line-sections each having a circuit breaker at each end thereof, of an auxiliary source of relaying energy of a frequency different from said power line, selective line-discriminatory tunedcircuit relaying means responsive to said relaying frequency for insuring the substantially simultaneous tripping of both circuit breakers of a faulty line-section, and interlock-contact relaymeans carrying currents derived from the power line rather than the relaying-frequency source for detecting the presence of a fault somewhere on the power system without always discriminating as to which line-section is faulted, said interlock-contact relay-means comprising contacts for locking out said tuned relaying means except when there is a fault somewhere on the system.

23. A multi-circuit polyphase transmission line comprising sectionalizing circuit breakers in the several circuits, and a relaying system for selectively tripping the relays of a faulty circuit, comprising current-transformer coupling means in series with the same phase of the transmission system at each of two sectionalizing points, an auxiliary source of a different tripping-frequency cru'rent distinctive to each of said parallel circuits for discriminating therebetween, and tunedcircuit relaying means for receiving said auxiliary currents, said auxiliary sources and tuned-circuit relaying means being connected to said currenttransformer coupling means.

24. The combination with a sectionalized alternating-current transmission system having a line-section with a circuit-interrupter means at each end, of a relaying station associated with each of said circuit-interrupter means for isolating said line-section in the event of a fault therein, each of said relaying stations comprising a source of relaying current of frequency different from the line-frequency at which power is transmitted over said transmission system, quick-acting fault-detecting means responsive to some function of the line-frequency current and the line-frequency voltage of the transmission system for selectively operating its circuit-interrupter means at the same station in response to faults lying within the line-section being protected and at least within its nearest half of said line-section and for at the same time superimposing upon the line-section a relaying current from its relaying-current source, and auxiliary relaying means selectively responsive to relaying currents superimposed on the line at the other end of the line-section for effecting an operating control on the circuit-interrupter means at its own end of the line-section.

25. The combination with a sectionalized alternating-current transmission system having a line-section with a circuit-interrupter means at each end, of a relaying station associated with each of said circuit-interrupter means for isolating said line-section in the event of a'fault therein, each of said relaying stations comprising quick-acting fault-detecting means responsive to some function of the line-frequency current and the line-frequency voltage of the transmission system for selectively operating its circuit-interrupter means at the same station in response to faults lying within the line-section being protected and at least within its nearest half of said line-section and for at the same time causing a high-frequency relaying-current impulse to be communicated to the relaying station at the other end of said line-section, and auxiliary relaying means selectively responsive to high-frequency relaying-current impulses received from said other station for effecting an operating control on the circuit-interrupter means at its own.

end of the line-section.

26. The combination with an alternating-current power line, of means for isolating both ends of a faulty line section, comprising fault-distance responsive relaying means at both ends responsive to some function of the line-frequency current and the line-frequency voltage of the power line so as to produce, by their own operation, simultaneous substantially instantaneous relaying response for centrally located faults and sequential response for faults located close to either end of the line section, characterized by substantially instantaneously operating means for sending a tripping impulse from one end to the other so as to produce substantially simultaneous isolation of both ends of the line section for faults located anywhere therein.

27. A multi-circuit alternating-current line comprising a plurality of line-sections normally having their corresponding line conductors bussed together at their respective ends, and high-frequency relaying means for said line, characterized by means for supplying high-frequency currents, and coupling means for introducing and taking off the high-frequency currents in series circuit relation in and from a circuit which includes one of said line-conductors extending in one direction throughout the length of one line-section, through the bus at that end, back throughout the length of a parallel line-section, and through the other bus to the starting point.

ROYAL C. BERGVALL.

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