US2406617A - Relay system - Google Patents

Description

Aug. 27, 1946. y H. w LENSNER 2,406,617

RELAY SYSTEM Filed Sept. 14, 1944 Disam Carrier External Fault My @i WU-'Infernal Fa ult k lNvENToR /Dase-ang/e beween currents ai opp osize ends of [ineseci or; ATTORNEY Patented Aug. 27, '1946 UNITED STATES PATENT OFFICE RELAY SYSTEM Herbert W. Lensner, East range,'N. J., assigner to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 14, 1944, Serial No. 554,037

(Cl. V75-294) 21 Claims. 1

My present invention relates to a carrier-current or other pilot-channel phase-angle-detecting relaying system, adapted to protect a section of a three-phase transmission-line against faults. My present system is an improvement over the system shown in an application of Mehring, Goldsborough and myself, Serial No. 534,846, led May 10, 1944.

The Mehring et al. system has a theoretically possible defect, which might conceivably result in an incorrect blocking-operation on an internal B-C-to-ground fault, under system-conditions in which substantially all of the positive-sequence current comes from one end of the protected linesection, and substantially all of the zero-sequence current comes from the other end. This comes about by reason of the fact that the Mehring et al. system utilizes a derived current-responsive single-phase quantity, which is vectorially compounded of the properly weighted positiveand zero-sequence components of the line-current, to alternately produce a succession of local operating impulses during positive half-cycles of the locally derived line-current quantity, and to transmit, to the other line-terminal, a succession of restraining impulses during negative halfcycles of the locally derived line-current quantity.

An object of my present invention is to avoid the possibility of such a diiiiculty by utilizing only the positive-sequence component of the local linecurrent as the means for developing the alternating successions of operating and restraining impulses, in combination with an overvoltage relaymeans which serves as a means for detecting the relative phase-angles between the two terminal line-currents of the protected section, by responding to the operating impulses when they are not 4effectively opposed by restraining impulses received from a distant line-terminal.

As the positive-sequence line-current component is not a reliable fault-detector, and as it is sometimes desirable to avoid the transmission of restraining impulses under normal fault-free line-operating conditions, a further object of my invention is to also provide a suitable multiresponsive fault-detector means, capable of detecting the existence of any one of a plurality of different kinds and phases of groundand phasefaults, and to utilize said fault-detector means for supervising the operation of the phase-angledetecting relay-means, as by causing the positivesequence means to be effective only when there is a fault-indication by said fault-detector means.

A still further object of my present invention is to utilize a zero-sequence currentor voltagecomponent, or other ground-fault detectormeans, for increasing the effectiveness of the single-phase voltage which is derived in response to the positive-sequence component of the linecurrent. This provision makes it possible to obtain a ground-fault sensitivity of response, which approximates that of a twoor three-phase fault, notwithstanding the fact that the ground-fault may have a much smaller positive-sequence current-component.

This ground-fault-responsive sensitivity-increase of a positive-sequence line-current response is of general application, not limited to apparatus for comparing the current-directions or relative phase-angles at the two ends or terminals of the protected line-section. It is also particularly applicable to the control of a relaytube.

A more generally expressed object of my invention is to provide a single relaying circuit which produces a uni-directional voltage of limited magnitude, in response to a detection of a predetermined ground-fault condition on the line, and adds such a voltage in series with another voltagecomponent which is in some manner responsive to the positive-sequence component of the line-current.

A still further object of my invention is to control a relay-tube or other polarity-responsive device, by causing it to be responsive to a pulsating voltage having a phase which is responsive substantially solely to the positive-sequence component of the line-current, and providing a unidirectional voltage of substantially non-pulsatory form, in the event of a predetermined groundfault condition, for increasing the sensitivity of response to the pulsating voltage. Such groundfault response is preferably so arranged that it will not by itself cause operation of the device.

A still further object of my invention is to utilize a single-phase control-voltage to cause two tubes to be alternately conductive on positive and negative half-cycles, respectively, and to provide a unidirectional voltage of substantially nonpulsatory form in a circuit of said tubes in a polarity facilitating the operative conductivity of said tubes.

With the foregoing and other objects in view, my invention consists in the circuits, systems, apparatus, combinations, parts, and methods, hereinafter described and claimed, and illustrated in the accompanying drawing, wherein:

Figure 1 is a diagrammatic view of circuits and apparatus illustrating an embodiment of my invention, and

Figs. 2 to 13 are curve-diagrams which will be referred to in the explanation of the invention.

In Fig. l, I show the terminal equipment for only one terminal of a three-phase transmission line I4, which is connected to a bus t5 through a three-phase circuit-breaker I6. Only one terminal equipment is illustrated, because the equipments at the other line-terminal or terminals are, or may be, identical to the illustrated equipment. The circuit-breaker i6 is illustrated as having a trip-coil TC, and an auxiliary make-contact breaker-switch lEa.

The three-phase line-current is derived by means of a bank of line-current transformers ll, which respond to current-flow into the protected line-section, at the terminal in question. This three-phase line-current is fed into any suitable phase-sequence network or filter EG, which is provided with a zero-sequence or neutral-current terminal Io, a pair of positive-sequence termi- 1 nals I1 in which a single-phase voltage is produced, which is responsive substantially solely to the positive-sequence component of the line-current7 and a pair of positive-plus-zero phase-sequence terminals 110, in which a voltage is produced in response to the vecto-rial sum of the positive-sequence line-current, plus a constant times the` zero-sequence line-current, as in the type HCB network which is shown in the Harder patent 2,183,646, granted December i9, 1939, and .assigned to the Westinghouse Electric & Manufacturing Company.

The zero-sequence network-terminal Io is utilized to energize a saturating zero-sequence-responsive transformer To, the primary winding of which is connected in the neutral circuit of the line-current transformers il. The pairs of network-terminals I1 and Iio are respectively utilized to energize a saturating positive-sequence transformer T1, and a saturating positive-pluszero sequence-responsive transformer T10.

Usually and preferably, but not necessarily, in accordance with my present invention, some, or preferably all, of the derived network-voltages are of limited magnitude, which may be accomplished by making some or all of the transformers T1, To and T10 saturating. The secondary terminals of some or all of the transformers T1 To and T10, particularly the positive-sequence transformer T1, are also shunted by a voltage-limiting glow-tube I9, as described in the Harder patent.

The zero-sequence transformer To is utilized to energize a load-resistor RI through a doublewave rectifier, such as the rectier-bridge 20, so as to furnish a unidirectional current, having substantially no ripples, to said load-resistor RI. The ripples may be still further removed by a parallel-connected filter-capacitor FC l. The saturating nature oi' the zero-sequence transformer To results in producing a unidirectional current of substantially limited magnitude, which is applied to the resistor Rl, so as to produce a unidirectional voltage-drop of a roughly constant magnitude in the resistor Rl, whenever there is a ground-fault on a transmission system. The negative terminal of the resistor Ri is indicated at 2 l, and the positive terminal at 22.

The positive-plus-zero sequence-responsive transformer T10 is utilized to energize the operating coil of a fault-detector FD, which is intended to be representative of any multi-responsive fault-detector means, or any equivalent combination of fault-detector means, adapted to be responsive to a plurality of different kinds and phases of groundand phase-faults on the threephase transmission-system. This fault-detector FD is utilized to detect the presence of any one of a number of different kinds of faults, preferably all different kinds and phases of faults, whether such faults occur within the confines of the protected line-sectic-n, or outside of said protected line-section.

According lto my present invention, vthe positive-sequence-responsive transformer T1 is utilized to produce a succession of substantially flattopped operating voltage-impulses of substantially constant magnitude during the positive half-cycles of the positive-sequence line-current, and to produce a succession of substantially nattopped restraining voltage-impulses of substantially constant magnitude in response to the negative half-cycles of the positive-sequence currentcomponent. To this end, I p eferably utilize the same means which is shown in +he aforesaid Mehring et al. application, except that the means is responsive to a single-phase voltage, the phase of which is determined substantially solely by the positive-sequence component of the local linecurrent, instead of using the positive-plus-zero sequence-responsive network, as in said Mehring et al. application.

As shown in Fig. l, l provide two gas triodes or other grid-controlled gas tubes GI and G2 of a sustained-discharge type; that is, of a type in which the grid res the tubes, or starts the discharge, but is unable to extinguish the tube or interrupt the discharge. The grids of these tubes GI and G2 are connected `to the respective secondary terminals 23 and 24 of the tube-controlling transformer, in this case the positivesequence transformer T1. An intermediate Voltage of the secondary transformer-circuit is derived from two serially connected resistors R2 and R3, which are connected across the secondary . terminals 23 and 24. 7lhe connecting-point 25 between these resistors is connected to a negative battery-terminal or bus through a C- battery Ec, and the zero-sequence resistor RI, according to my invention. The C-battery Ec is so connected as to make the point 25 more negative than the negative battery-terminal or, in general, so as to make the point 25 have a potential too negative, by a predetermined amount, to cause the tubes GI and G2 to rire, under the impressed anode-cathode voltageconditions. The polarity of the zero-sequence resisto-r Rl is in opposition to that of the C- battery Ec.

The cathode-circuits 2S and 21 of the gas tubes Gl and G2 are connected to the negative battery-terminal (e) through cathode-resistors R4 and R5, respectively. rIhe anode-circuits 29 and 3B of the respective gas tubes Gl and G2 are respectively connected to plate-resistors R5 and R7, the other terminals of which are connected to a common conductor 3| which is connected, through a make-contact 32 of the fault-detector FD, to the positive battery-terminal (+L The two anode-circuits 29 and 30 of the gas tubes GI and G2 are joined by an interconnecting circuit containing a capacitor Cl. Y

The two gas tubes Gl and G2 are thus connected in a so-called trigger circuit, which operates as follows: During positive-sequence linecurrent half-cycles of one polarity, which I shall call the negative half-cycles, or more specifically during the negative half-cycles of the derived current-responsive voltage of .the positivesequence saturating Ytran'sformer T1, the secondi ary transformer-terminal 23 is positive. This transformer-terminal 23 is also the grid-terminal of the gas tube GI. At an early stage in these negative half-cycles, the positive voltage of the secondary terminal 23 with respect to the intermediate secondary point 25, becomes more positive than the blocking bias of the C-battery Eo, or at least suiiiciently positive to cause the first gas tube Gl to fire. It will be understood that the gas tubes have such characteristics that, when they are once fired, or when current is once started in their plate-cathode circuits, such plate-cathode current will continue to ow until the voltage applied `across the plate and cathode terminals of the tube is reduced to zero or reversed, even for a moment.

VAt .the beginning of the next half-cycle of the output-voltage of the positive-sequence transformer T1, which I shall call a positive halfcycle, the other secondary terminal 24 becomes positive with respect to the secondary intermediate point 25, and ires the second gas tube G2.

Before the firing of the second tube G2, the potential of its plate-circuit was substantially the potential of the. positive battery-terminal assuming that the fault-detector contact 32 is closed, while the potential of the platecircuit 29 of the rst tube Gl was at a somewhat more negative value, due to the voltage-drop in the plate-resistor RS of the first tube. When the second tube G2 lires, however, its plate-cir- A cuit 30 tends to drop -to the same potential as the plate-circuit 29 of the rst tube, but the voltagecharge on the interconnecting capacitor C! causes the potential of the anode-circuit 29 of the rst tube GI to momentarily drop to a value which is more negative than the potential of the cathode circuit 25 of said first tube Gl, thus extinguishing the rst tube Gl in the moment required for the discharge of the interconnecting capacitor Cl. In the next half-cycle, the iirst tube GI rires again, and in turn extinguishes .the second tube G2 by momentarily causing a negative voltage to exist across its plate-cathode terminals.

The function of the interconnecting capacitor CI, which shuts off the previously iiring gas tube when the second tube begins to rire, is preferably supplemented by two capacitors C4 and C5, which are connected in shunt across the respective cathode-resistors R4 and R5 of the two gas tubes GI and G2. The eiect of thesershuntingcapacitors C4 and C5 is to short-circuit the associated cathode-resistor, R4 or R5, at the first instant of firing of the associated gas-tube, GI or G2, as the case may be, thus momentarily bringing the anode-potential of the newly iired tube to a value which is more negative than the steady-state anode-potential of the tube which was previously firing.

The interconnecting capacitor Cl, previous to the firing of the newly red tube, was charged in such polarity as to momentarily tend to hold the anode-potential of the previously iiring tube more negative than the anode-potential of the newly ired tube.

The combined effect of the three capacitors Cl, C4 and C5 is to strongly depress the anode-potential of the tube which was ring, at the lirst instant of ring of the second tube, making the anode-potential of the iirst tube momentarily more negative than its cathode-potential, thus extinguishing the tube. At the same time, the shunting-capacitoi` C4 or C5, as Ithe case may be, of the tube that is being extinguished, momentarily holdsvup its cathode-potential to a 6 value close to the value which it had when the tube Was firing, thus assisting in maintaining the reversed tube-voltage for the instant necessary to extinguish the tube.

As explained in the aforesaid Mehring et al. application, the voltage-drops across th'e two cathode-resistors R4 and R5 are utilized to produce -two different efiects. The voltage-drop across the cathode-resistor Ril of the rst gas tube Gl is utilized to produce half-cycle impulses of square-topped positive voltages for supplying a plate-voltage which is sufficient for initiating and maintaining the operation of an oscillatortube OSC of a carrier-current transmitter, by connecting the plate-circuit 34 of the oscillatortube OSC, through a radiofrequency choke RFC,

to the cathode-circuit 2S of the lirst gas tube Gl,

the cathode of the oscillator being connected, at 35, to the negative battery-terminal The voltage-drop across the cathode-resistor R5 of the second gas tube G2 is utilized to apply an operating voltage-component from the cathodecircuit 2l of the second tube G2 to the grid-circuit 36 of a relay-tube RT, which is shown near the bottom oi Fig. l, and which will be subsequently described. A voltage-drop resistor' R-l 5 is included in the connection between the cathode-circuit 2l of the second trigger-tube G2 and the grid-circuit 36 of the relay-tube RT.

The transmitter-oscillator OSC has a grid-circuit 3 which is connected to the cathode-circuit 35 of said oscillator through a grid-leak resistor GL.

The anode-circuit 3d of the transmitter-oscillator OSC is coupled, by means of a blocking capacitor BCE, to a conductor iig, which constitutes one junction-point of a tuned circuit which in'- cludes the conductor G9, a capacitor C6, the cathode-terminal. 35, a capacitor Cl, the gridterminal 43, and a variometer Vl, and thence back to the conducto-r 9. The conductor 49 and the grid-terminal i3 are respectively connected to the grid-terminals M and i5 of two ampliiiertubes A! and A2 by means of blocking capacitors BCS and B04, respectively.

The amplier tubes Ai and A2 have a common cathode-circuit 56, which is co-nnected to the conductor 35, and h'ence the negative battery-terminal through a cathode-resistor R8. The grid-terminals ifi and 45 of the amplifier-tubes Ai and A2 are respectively connected to the negative battery-terminal through resistors R-il and R-IZ. The amplifier-tubes Al and A2 have plate-circuits 5l and 52, respectively, which are connecte-d to the primary-Winding terminals of a coupling-transformer 53, The primary-Winding mid-point 5ft of this couplingtransformer is connected to the positive batteryterminal and it is also connected, through a blocking capacitor B05, to the cathode-terminal 50 of the amplifier-tubes.

One secondary-Winding terminal of the coupling-transformer 53 is grounded, at 5i'. Another tap-point 53 thereof is connected to a variometer V2, and thence, through a coupling capacitor C id, to one of the line-conductors of the protected line-section, in a manner which is Well-known and needs no further description.

The secondary winding of the coupling-transformer 53 is also provided with another tap-point 6U, which is connected to one terminal of the primary winding of a receiver-coupling transformer 62, the other primary-winding terminal of which is connected, through a variable capacitor C I l, to the grounded point 5l'. The primary Winding of the receiver-coupling transformer 62 is also usually shunted by a voltage-limiting gas tube 64.

The receiver-coupling transformer 62 has, a secondary winding, one terminal of which is connected to the grid-circuit E6 of a detectortube or receiver-tube REC, while th'e other secondary-winding terminal is connected to the negative battery-terminal The secondari winding of the receiver-coupling transformer 62 is also shunted by a variable capacitor C -l2, in a manner which is usual in the art.

The receiver-tube REC is provided with a cathode-circuit 69 which is illustrated as being connected to a tap-point near the negative end of a potentiometer lil which is energized from the positive and negative buses and This tube also has an anode-circuit "il, which is connected to the positive battery-terminal through a radio-frequency choke RFC.

The plate or anode-circuit 1l of the receivertube REC is also coupled, by means of a capacitor C -|3, to a point 14 which is connected to the cathode-circuit 21 of the second tube G2 through a large, capacitor-charging resistor R- I4. The point 14 is also connected, through a capacitor C M, to a conductor 15 which is connected to the cathode-terminal 16 oi the lower diode of a double-wave rectiiier-valve RV. The plate-circuit of this lower diode is connected to the gridterminal 36 of the relay-tube RT and to the voltage-drop or load-resistor R--l5. The other terminal of the load-resistor R-It is connected to the cathode-circuit conductor 21 oi the second gas triode G2, as previously described. The upper diode-circuit 11 of the double-wave rectifiervalve RV is connected, in the reverse polarity, between the circuits 21 and 15. The load-resistor R-l5 is shunted by a radio-frequency by-pass capacitor BPC.

The relay-tube RT is provided with a cathodecircuit 8D which is connected to an intermediate point of a potentiometer 6| which is energized across the battery-terminals and (-1-). The relay-tube RT is also provided with a plate-circuit 82, which is connected to the positive battery-terminal through the primary winding of a relay-coupling transformer 84, the secondary of which is connected, through a rectifier-bridge B, to the operating coil R of a tripping-relay R. The relay R is provided with a make-contact B1, which is shown near the top of Fig. 1, in series with the trip-coil TC of the circuit-breaker I6. The output of the rectierbridge 86 may be smoothed, if desired, by means of a filter-capacitor FCZ.

The fault-detector FD is provided with a lmaliecontact 88, which is connected in the tripping circuit of the circuit-breaker I6, said tripping circuit being traceable from the negative batteryterminal through the fault-detector makecontact 8&1, and the tripping-relay make-contact R, to the trip-coil TC, and thence through the breaker-switch ia to the positive battery terminal (-l-).

The operation of the apparatus shown in Fig. 1 may best be explained with reference to the curve-diagrams oi Figs. 2 to 13. The positive-sequence output-terminals I1 of the filter I8 in Fig. 1, with their associated saturating transformer T1 and voltage-limiting gas tube I9, produce a single-phase, positive-sequence-responsive output-voltage, one part of which appears across the conductors 24 and 25. This positive-sequenceresponsive output-voltage is preferably, as indicated in Fig. 2, a substantially sinusoidal singlephase wave which has an approximately constant limiting magnitude, for all except the smallest of fault-currents, and which has a phase-angle which is determined by the positive phase-sequence component of the polyphase line-current at the relaying station.

It is usually desirable to transmit carrier-current energy, for protective relaying purposes, only during times of a fault somewhere on the transmission system, and hence it is desirable to utilize some sort of fault-detector. My previously described fault-detector FD is intended to be representative of a detector of this sort. When this fault-detector FD responds, it picks up its makecontacts 32 and 88. The make-contact 32 applies the direct-current battery-Voltage to the plate-cathode circuits of the two gas triodes Gl and G2, thus supervising the response to the positive-sequence transformer T1. The make-contact 88 supervises the tripping circuit.

At a very early stage in each positive halfcycle, the positive-sequence-responsive filter-output oi Fig. 2 overcomes the negative bias of the C-battery EC, or at least it makes the grid-circuit 24 sufiiciently positive so that the gas triode G2 fires, and produces a positive voltage-impulse, which is obtained across the cathode-resistor R5, and comprises the voltage from the negative battery-terminal to the conductor 21 in Fig. 1, as shown in Fig. 3. This is called the operating voltage, because it is a voltage which tends to make the grid-terminal 35 of the relay-tube R'I positive with respect to the cathode-circuit of this tube, thus tending to cause current to flow in the plate-circuit 82 of the tube. Since the gas triode G2 is energized from battery-terminals and (-l-) having a xed Voltage between them, and since the plate-cathode circuits 30- 21 of this triode are in series with fixed resistors R1 and R5, the positive voltage-impulses which make up the operating voltage are square-topped, and of a substantially constant magnitude, quite irrespective oi the magnitude or the wave-form of the positive-sequence-responsive lter-output I1.

A disadvantage which has heretofore lstood in the way of utilizing a positive-sequence currentresponse in the protection against line-faults has been the very extreme variations which are obtained in the magnitude of the positive-sequence current-component under diierent fault-conditions, ranging from a very large positive-sequence current, in case of a three-phase fault, to a positive-sequence current which may be many times lower than the maximum power-load current in the case of a single line-to-ground iauit of high impedance. This condition is aggravated at a line-terminal which has no source of positivesequence energy, so that only positive-sequence component ci' the fault-current is that which is contributed by the rotating electric machines which are connected to that terminal of the line. It is for this reason that I prefer to provide the previously described zero-sequence resistor RI, o-r some equivalent means for in any manner increasing the sensitivity of the response of the gas triodes Gl and G2 to the positive-sequence linecurrent component. In its generic aspects, my invention relates to any means for accomplishing this sensitivity-increasing purpose in the event of a ground-fault. A preferred form of embodiment of such a means is shown in Fig. 1, which is to be taken as illustrative, also, cf the generic idea.

In the illustrated form of my invention, as

shown in Fig. 1, the zero-sequence resistor RI is connected in series with the C-battery Eo, in a polarity opposite to that of the C-battery. The negative bias or voltage of the C-battery Eo is preferably made abnormally large, or larger than is just barely necessary to prevent excitation of the gas tubes GI and G2 when no single-phase control-voltage is applied across the transformerterminals 23 and 2d, which also constitute the grid-terminals of the respective gas tubes GI and G2. In the event of a phase-fault, involving two or more of the line-conductors E4, the positivesequence current-component will be large enough to saturate the positive-sequence transformer T1, and large enough to exceed the setting of the voltage-limiting gas tube i9, so as to produce a iixed constant magnitude of single-phase voltage which is sufficient to cause the respective gas triodes Gl and G2 to become conducting at an early part of alternate half-cycles of the Voltage-supply, as previously explained.

In the event, however, of a single line-toground fault through a very high impedance, such as would be obtained by a broken line-conductor lying upo-n dry or frozen ground, the positive-sequence Voltage component or output of the transformer T1 might not be large enough to satisfactorily control the gas triodes Gl and G2. In such a case, however, a Zero-sequence currentcomponent will be present, which energizes the zero-sequence transformer To to saturation, and the output of this transformer is rectified and applied to the load-resistor Rl in such polarity as to produce a voltage-drop or potential opposite to the potential of the grid-biasing battery Eo, but preferably having a limited magnitude such that the zero-sequence-responsive unidirectional voltage will not of itself suffice to cause the gas triodes Gl and G2 to begin to transmit platecathode current in the absence of any positivesequence-responsive single-phase control-voltage across the terminals 23 and 24.

The zero-sequence resistor RI nevertheless neutralizes some or all of the C-battery voltage Ec, as indicated at 22 in Fig. 1. the grids of both of the gas triodes GI and G2 to be ready to make the tubes conductive when their respective grids are made just a little bit more positive with respect to their tube-cathodes, as by the application of a relatively small alternating voltage, applied across the grid- terminals 23 and 24, from the positive-sequence transformer T1.

At a very early period in each negative halfcycle of the filter-output which is shown in Fig. 2, the other gas triode Gl of Fig. 1 res, immediately extinguishing the previously ring triode G2, in a manner which has previously been described. The operation of this other gas triode Gl produces a succession of impulses which alternate with the positive impulses which constitute the operating voltage of Fig. 3. The positive voltage-impulses of this other triode Gl are obtained across the cathode-resistor R4, in the form of a positive voltage which appears between the negative battery-terminal and the conductor 2t, which is connected to lthe plate-circuit S4 of the transmitter-oscillator OSC, through the radio-frequency choke RFC of Fig. l. This causes the oscillator OSC to immediately begin oscillating, thus initiating the transmission cf carrier. The transmission of carrier continues, at approximately its full, constant strength, as long as the gas triode Gi is ring, which is to say, during the negative haii-cycles Thus it predisposes i positive voltages. of)

10 of the filter-output of Fig. 2, as shown diagrammatically in Fig. 4.

In Fig. 4, the frequency of the carrier-current waves cannot be shown to scale, because the carrier-current frequency is actually so high that it would not begin to be shown in the space which we have allotted to Fig. 4.

After the rst impulse of carrier-current transmission, during the rst negative half-cycle of the positive-sequence lter-output after the response of the fault-detector FD, the iirst-mentioned gas triode G2 again becomes conducting, extinguishing the triode GI, and thus interrupting the carrier-current transmission for a halfcycle period, corresponding to the next positive half-cycle of the positive-sequence filter-output.

It will be noted that the action just described occurs at both terminals of the protected line-section i d, or at all of the terminals, in case the Drotected line-section has more than two terminals. It will be noted that the equipment at each terminal responds to the positive-sequence component of the line-current input into the protected linesection at its own terminal, that is, from the bus i 5 at that terminal. In the event of an internal fault, that is, a fault within the confines of the protected line-section, the positive-sequence component of the fault-current will be owing into the line-section at each terminal thereof, and these fault-currents will be more or less in phase with each other, because the positive-sequence terminal-voltages of the line are not greatly out of phase with each other, while the line-impedance which limits the fault-current from each terminal to the fault-location has approximately the same impedance-angle in each case. For an internal fault, therefore, it may be assumed, as a first approximation, that the positive-sequence fault-current components are in phase with each other at both or each of the line-terminals, This is depicted in Fig. 5, which shows that the distant carrier, which is transmitted at another lineterminal other than the illustrated line-terminal, is transmitted at the same time as the local carrier which is shown in Fig. 4, for an internal fault, that is, out of phase with the operating impulses of Fig. 3.

In the event or an external fault, however, positive-sequence current will be flowing out of the line-terminal which is closest to the external fault, and it will be Flowing into the protected line-section at at least one other terminal. Since each terminal equipment responds to a positivesequence current-direction looking into the protected line-section at that terminal, the line-current at the terminal closest to the external fault Will be reversed, approximately 180 in the ideal case, with respect to the current in some other terminal. Hence, at each terminal, local carrier will be transmitted at certain half-cycles of the line-frequency, as shown in Fig. 4, and distant carrier will be transmitted at some distant terminal during line-frequency half-cycles which are displaced approximately 180 (inthe ideal case) with respect to the line-frequency half-cycles of the local carrier. Fig. 6 depicts the distant carrier-current transmission for an external fault.

In the operation of the particular system shown in Fig. it will be noted that carrier-current energy, from both the local and distant transmitters. is received by the receiver-tube REC, so as to produce a plate-cathode current through this tube during periods when the carrier-current energy is being received.

When no carrier-current energy is being received, the anode-terminal 'H of the receivertube REC is practically at the potential of the positive battery-terminal. (-1-) and hence the capacitor C-l3 is charged in accordance with the potential-diierence between said anode-terminal ll of the receiver and the cathode-terminal conduct-or 21 of the second gas triode G2, the receiver-connected terminal f the Capacitor C-l3 being positive. The conductor 2l has a potential such as is depicted in Fig. 3, varying between Zero, which is taken as the potential or the negative battery-terminal and a fraction of the total battery-voltage, which is utilized as the operating-voltage for the grid-circuit 3S of the relay-tube RT, this operating-voltage being the voltage-drop or the cathode-resistor R of the second gas triode G2, whenever the latter is firing.

When the carrier-current energy is received, the receiver-tube REC becomes conducting, pulling down the potential of its anode-terminal 'Il to a point which is more or less close to the potential of the negative battery-terminal thus more or less short-circuiting the capacitor C--|3, and causing it to discharge, drawing current through the load-resistor R--lli and the lower diode of the rectifier-valve RV, said diode being connected in such polarity as to permit current-now in the direction from the conductor 2l to the conductor 35, and thence through the lower diode to the conductor 16 and the capacitors C-l4 and C--l3. At the same time, a much smaller current ows through the inucn larger capacitor-charging resistance R--i4, which is utilized to charge the capacitor C-I 3.

During the periods when no carrier-current energy is being received, in the illustrated form of embodiment of my invention, the receiver plate-circuit 'Il again becomes quite positive, so that the upper diode-circuit 'H of the rectifiervalve RV becomes conducting and charges the capacitor C--l4, making the terminal 74 positive and the terminal 'l5 negative, thus causing the capacitor C-M to act as a voltage-doubler for doubling the effective voltage of the capacitor C-l3.

When, therefore, carrier-current energy is again received, on the next half-cycle of the linefrequency current, the two capacitors C--M and C-I3 discharge through the load-resistor R-I5, thus producing a negative or voltage-drop in said load resistor lic-E5, malring the conductor i, and hence the grid of the relay tube RT, negative with respect to the potential of the cathode-circuit conductor 21 of the second tube G2.

C-l3 to discharge, producing a voltage-drop in the load-resistor R--l5, making the grid of the relay-tube RT more negative, and thus effectually preventing this tube from operating in response to the operating-voltage which is produced by the current-flow in the cathode-resistor R5 or the second gas tube G2.

The radio-frequency or carrier frequency coinponent of the plate-voltage of the receiver-tube REC is by-passed from the load-resistor R-EB by the by-passing capacitor BPC.

Fig. 7 shows the negative or restraining voltage, across the resistor R-Iu for an internal fault in which the positive-sequence components of the fault-currents are in phase with each other at both or all of the line-terminals, while Fig. 8 shows the corresponding restraining voltage for an external fault in which the outwardly owing positive-sequence current at one linerestraining The reception of carrier- I current thus causes the capacitors C-lli and terminal is exactly out of phase with the inwardly flowing positive-sequence current or currents at the other terminal or terminals of the protected line section.

The receiver-tube REC preferably has a constant-current characteristic, so that whenever its grid permits plate-current to flow, the plate-current will have an approximately constant value. Thus, as shown in Fig. 8, the half-cycles of receiver plate-current, during which carrier-current energy is being received by the receiver-tube REC Afrom the distant carrier, transmitted from some other line-terminal, are of approximately xed magnitude, regardless of carrier-current attenuation. Hence the restraining voltage-iinpulses in the resistor R--E are oi"- approximately xed magnitude. The receiver platecurrent impulses which are received from the distant carrier are of approximately the same magnitude as the half-cycle impulses or plate-current which are produced when carrier-current energy is being received from the local transmitter, even though the local signals may he the stronger.

It is preferable, also, that the relay-tube RT shall have a constant-current characteristic, so that its plate-current will be constant, as shown in Fig. l1, without sensitive dependence upon the precise magnitude of its grid-voltage. Thus, the exact amount of the restraining voltage, produced by the receipt of carrier-current energy, as shown in Fig. 8, is not important, so long as said restraining voltage is greater than the operating voltage of Fig. 3, or the voltage-drop in the resistor R5, by a safe margin.

It is further to be noted that the only carriercurrent response of any moment is the response to the distant carrier, that is, the carrier-current impulses which are transmitted from some other line-terminal or terminals. The carriercurrent energy received from the local carriercurrent transmitter is immaterial, because, by the very nature of the control, it is always transmitted (and received) during the half-cycles alternating between the half-cycles when the operating impulses of Fig. 3 are present.

The grid-voltage of the relay-tube RT is thus made up of three components: First, there is a negative grid-bias consisting of the voltage between the potentiometer-tap 8B and the negative battery-terminal, which is sufficient to bias the grid of the relay-tube RT so that no platecurrent flows in said tube when there is no restraining or operating voltage present. A second component of the grid-voltage of the relaytube RT is the operating voltage, in the form of positive voltage-impulses produced whenever the cathode-circuit current of the second gas tube G2 flows through the cathode-resistor R5, as shown in Fig. 3. The third grid-voltage component of the relay-tube RT is the restraining voltage, in the form 0f negative voltage-impulses as shown in Figs. '7 and 8, for an internal fault and an external fault, respectively. This restraining voltage is produced by the discharge of the capacitors C-l and C-l3 through the resistor R-l5 whenever carrier-current energy is being received, although the restraining impulses which are received from a distant lineterminal are the only ones of importance. The resultant grid-voltage of the relay-tube RT is shown in Figs. 9 and 10, for an internal fault and an external fault, respectively.

Since the relay-tube RT will be operated, or carry a plate-current, only when its grid is sufciently positive with respect to its cathode, a

plate-current will ow in the relay-tube RT only during the positive-half-cycles of the grid-voltages shown in Figs. 9 and l0, that is, only when the local operating impulses of the second-valve cathode-circuit conductor 21 and its cathode-resistor R5 are not opposed by the restraining impulses received from a distant line-terminal.

When there is an internal fault, accompanied by fault-currents which are in phase with each other at the several line-terminals, the platecurrent of the relay-tube RT takes the form of a succession of square-topped half-cycles corresponding in timing to the line-frequency halfcycles when the second gas tube G2 is ring, as depicted in Fig. 11, thus energizing the local tripping-relay R and causing a local tripping-operation. In the case of an external fault, with linecurrents exactly 180 out of phase with each other, the grid-biasing voltage of the relay-tube RT is entirely negative, as shown in Fig. 10, and the plate-current of the relay-tube RT is zero, as shown in Fig. 12, meaning no response of the relay R, and hence no tripping-operation.

While I have discussed the ideal cases of an internal fault in which there is a 0 phase-angle between the terminal positive-sequence linecurrent components, and an external fault in which there is a 189 phase-displacement, counting inwardly owing currents as positive, or in phase With each other, at each terminal, it is to be noted that, in actual cases, the terminal positive-sequence line-current components for internal faults will not, in general, be exactly in phase with each other, but will vary in phase, by a certain amount, so that the impulses of the plate-current of the relay-tube will be shorter than the half-cycle impulses shown in Fig. l1, depending upon the phase-angle, because the operating impulses of Fig. 3 will be partially overlapped or blocked by received impulses from the distant transmitter, according to the phase-angle between the positive-sequence fault-current components at the different stations.

Fig. 13 shows a plot of the integrated, or rootmeanssquare, or averaged, current in the relaycoil R, in milliamperes, plotted against the phaseangle of the terminal line-currents. It shows that, as the phase-angle departs from zero, in either the leading direction or the lagging direction, the relay-current falls off, or becomes smaller and smaller, until the phase-angle becomes 180. The tripping-relay R is really an overcurrent relay, and it is adjusted to have a pick-up value 9S (Fig. 13) which permits the internalfault currents at the several terminals to be out of phase with each other as much as 120, While still permitting the fault-responsive tripping-relay ER to pick This leaves the phase-angles between 120 and 180 to represent external-fault conditions, during which the relay R does not pick up. It will be understood, of course, that the pick-up value of the relay-current can be set for any desired magnitude, correspondingr to any desired phase-angle between the terminal line-currents, in accordance with the necessities of special conditions existing on any particular line.

The relay-tube RT preferably has a. constantcurrent characteristic, so that whenever its grid permits plate-current to flow, the plate-current will have an approximately constant value, as shown in Fig. l1, without sensitive dependence upon the precise magnitude of the grid-voltage. Hence, the integrated, or root-mean-square, or average, value of the plate-current will depend 14 only upon the relative lengths of the time-periods during which the plate-current is iiowing, as shown in Fig. 13.

Since the relay-current is measured in milliamperes, it is usually more convenient to utilize a sensitive polarized relay R, or other sensitive direct-current relay R, to respond to this platecurrent, rather than utilizing an alternating-current relay for this purpose. For this reason, I have provided the plate-circuit transformer 84, and the rectiiier-bridge 86, so that I may utilize a sensitive direct-current milliampere-relay R, as shown in Fig. l.

The relay R, as previously described, has a make-contact 8l in the tripping-circuit of the breaker l, so that, whenever the relay R picks up, the circuit-breaker l5 is tripped. Because of the sensitive nature of the relay R, and the possibility of shock-excitation of the carrier-current receiver-circuits due to static conditions, or the like, it is usually desirable to safeguard the tripping-circuit by providing some additional faultresponsive contact, in addition to the contact 8l of the relay R, and I have provided for this, in Fig. 1, by means of the contact 88 of the faultdetector FD, which is intended to be representative of any fault-detector contact which is controlled independently of the carrier-current channel, and which is intended merely to make sure that there is a fault somewhere on the transmission system, before a tripping operation is permitted in response to the receiver-relay contact R.

Since my illustrated system utilizes only one fault-detector, which is shown at FD, it is necessary to guard against erroneous relay-operation in the event of a distant fault which might cause a picking up of the fault-detector at only one end or" the protected line-section. Io eliminate the possibility of incorrect relaying under these conditions, I prefer to arrange the circuit-constants so that the gas triode Gl, which controls carrier, res at a lower voltage of the lter output- circuit 23, 24 than the gas triode G2 which provides operating voltage to the grid-circuit 3B of the relay-tube RT.

The gas triode Gi which controls carrier res preferably immediately upon the closure of the contact 32 of the detector FD. The second gas triode G2 fires at a grid-voltage which is sufficiently above the pick-up voltage of the detector FD to insure that the faultdetectors FD at both ends of the line-section will pick up before the second gas triode G2 applies an operating voltage to the relay-tube RT at either end of the line. Consequently, if only one fault-detector picks up, at only one end of the line, there will not be enough control-voltage across 23 and 24 to cause the diode GZ to nre at either end of the line, and hence the relayf-tube RT cannot carry current to operate the tripping-relay R at either end of the line.

In Fig. l, the resistor R2 is illustrated as being larger than R3, so that, with identical tubes GI and G2, the tube Gl will receive the larger portion or" the voltage across and 243. The tube G2 may nre at a voltage which is 20% to 50% above the control-voltage (across 23 and 24) which results in the ring'oi the tube Gi.

It will be observed that I obtain phase-angle comparison of the line-currents at different terminals of a protected lineeseetion by utilizing the positive-sequence components oi the line-cur rents at the respective llne-terminals as phaseangle control-means, for providing, at each terminal, a succession of flat-topped constant-magnitude positive operating-impulses which are effective locally, and, alternating therewith, a succession of flat-topped constant-magnitude negative restraining-impulses which are received from the other line-terminal or terminals. I also supervise this positive-sequence response with a multi-responsive fault-detector means, preferably in the form of a single voltage E10 Which is a composite ci various phase-sequence components or phases of the line-current. I further increase the sensitivity of my response to the positive-sequence components oi ground-fault currents, by means of a ground-fault detector, preferably a ground-fault detector which responds to ground faults by producing a constant-magnitude unidirectional voltage of substantially nonpulsatory form.

I have also provided a novel control-circuit in which a constant-magnitude unidirectional voltage is added to a single-phase positive-sequenceresponsive voltage Whenever there is a groundfault on the system. I have also made use of such a combination of a direct-current voltage added to an alternating-current voltage, in a gas tube GI or G2, each oi which is representative of any polarity-responsive device which is respon.- sive to the voltage half-Waves ci only one polarity.

While I have illustrated my invention in but a single form of embodiment, which I at present prefer, I desire it to be understood that such illustration is only illustrative, and that various changes of omission and addition and substitution may be made without departing from many of the esesntial features of my invention, as will be well understood by those skilled in the art. I desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their language.

I claim as my invention:

l. Terminal equipuent ior one terminal cfa pilot--channel phase-angle-detecting relayingsystem adapted to protect a section of a threephase transmission-line against faults, comprising means operative to develop a single-phase voltage having a phase which is responsive substantially solely to the positive-sequence component of the line-current at said terminal, local control-means operative to develop a succession of operating impulses in response to positive halfcycles oi voltage, pilot-channel means operative to transmit a succession of restraining impulses and to make them effective at another line-terminal or terminals in response to negative half-cycles of said voltage, and phase-angledetecting relay-means operative to respond to said operating impulses when they are not effectively opposed by restraining impulses received from a distant line-terminal.

2. The invention as defined in claim l, in combination with multi-responsive fault-detector responsive to line-conditions at said terminal, for detecting the existence of any one of a plurality of different kinds and phases of groundand phase-faults with uncertainty as to whether the fault is inside oi or outside of the protected line-section, and means for supervising the operation oi said phase-angle-detecting relay-means in response to a fault-indication by said. fault-detector means.

3. The invention as defined in claim 1, in combination with multi-responsive fault-detector means, responsive to line-conditions at said terminal, for detecting the existence of any one 16 of a plurality of diiieient kinds and phases of groundand phase-faults with uncertainty as to whether the fault is inside of or outside of the protected line-section, and means for causing said local control-means and said pilot-channel means to be eiectively operative only when there is a fault-indication by said fault-detector means.

e. The invention as defined in claim 1, in combination with ground-fault detector-means, responsive to line-conditions at said terminal, for increasing the effectiveness of said single-phase voltage in the event of a predetermined groundfault condition.

d. Multi-responsive fault-detector m e a n s adapted to be responsive to a plurality of different kinds and phases oi groundand phase-faults on a three-phase line, comprising positive-sequence means operative to develop a voltage which is substantially solely responsive to the positive-sequence component of the line-current, means responsive to said. voltage, and groundfault detector-means, responsive to line-conditions, ior increasing the effectiveness of said voltage in the event of a predetermined groundfault condition.

5. Multi-responsive fault-detector m e an s adapted to be responsive to a plurality of different kinds and phases of groundand phase-faults on a three-phase line, comprising positive-sequence means operative to develop a voltage which is substantially solely responsive to the positive-sequence component of the line-current, a tube, means for causing said tube to operate response to said voltage, and means for increasing t e sensitivity of tube-response to said voltage in response to a predetermined groundfault condition on the line.

'7. lvIulti-responsive fault-detector m e ans adapted to be responsive to a plurality of different kinds and phases of groundand phase-faults on a three-phase line, comprising means operative to develop a pulsating voltage having a phase which is responsive substantially solely to the positive-sequence compbnent of the linecurrent, ground-fault detector-means operative to develop a ground-fault-responsive voltagecomponent of a limited magnitude and a unidirectional form in the event of a predetermined ground-fault condition on the line, and circuitmeans for combining said voltage-components in series.

8. Multi-responsive fault-detector m e a n s adapted to be responsive to a plurality of different kinds and phases of groundand phase-faults on a three-phase line, comprising means operative to develop a pulsating voltage having a phase which is responsive substantially solely to the positive-sequence component of the line-current, ground-fault detector-means, responsive to line-conditions, for developing a uni-directional voltage of substantially non-pulsatory form in the event of a predetermined ground-fault condition, a polarity-responsive device, means for causing said device to be operatively conducting on alternate half-cycles of the line-current frequency in response to said pulsating voltage, and means, responsive to said substantially non-pulsatory voltage, for increasing the sensitivity of the aforesaid response to the pulsating voltage.

9. Multi-responsive fault-detector means, adapted to be responsive to a plurality of different kinds and phases of groundand phasefaults on a three-phase line, comprising a tube, means for normally providing a tube-circuit voltage which prevents the tube from becoming effectively conductive, ground-fault detectormeans, responsive to line-conditions, for at times providing a unidirectional voltage of substantially non-pulsatory form in a circuit, of said tube and in the polarity tending to make the tube become effectively conductive, means operative to develop a pulsating voltage having a phase which is responsive substantially solely to the positive-sequence'component of the line-current, and means for making said pulsating voltage effective in a circuit of said tube in such manner as to tend to cause the tube to be operatively conductive on alternate half-cycles of the line-current frequency in response to the pulsations of said pulsating voltage.

10. The invention as deiined in claim 9, characterized by said non-pulsatory voltage having a limited magnitude which is insuiicient to cause any material operative conduction of the tube in the absence of a positive-sequence-responsive pulsating voltage.

11. Multi-responsive fault-detector means, adapted to be responsive to a plurality of different kinds and phases of groundand phasefaults on a three-phase line, comprising a tube having control-circuit means, a direct-current plate-voltage supply-circuit for said tube, means for normally providing a control-circuit voltage which prevents the tube from becoming eiectively conductive, ground-fault detector-means, responsive to line-conditions, for at times providing a unidirectional voltage of substantially non-pulsatory form in a control-circuit means of said tube and in the polarity tending to make the tube become effectively conducting, means operative to develop a pulsating voltage having a phase which is responsive substantially solely to the positive-sequence component of the line-current, and means for making said pulsating voltage effective in aicontrol-circuit means of said tube in such manner as to tend to cause the tube to be operatively conductive on alternate halfcycles of the line-current frequency in response to the pulsations of said pulsating voltage.

12. The invention as denned in claim 11, characterized by said non-pulsatory voltage having a limited magnitude which is insufficient to cause any material operative conduction of the tube in the absence of a positive sequence-responsive pulsating voltage.,

13. The invention as dened in claim 9, characterized by said non-pulsatory voltage having a limited magnitude which is insuflicient to cause any material operative conduction of the tube in the absence of a single-phase voltage.

i4. Terminal equipment for one terminal of a pilot-channel phase-angle-detecting relayingsystem adapted to protect a section of a threephase transmission-line against faults, comprising current-responsive voltage-developing means operative to develop a pulsating voltage having a phase which is responsive to a function of the three-phase line-current at said terminal, groundfault detector-means for selectively responding to ground-fault line-conditions more sensitively than said current-responsive voltage-developing means, means controlled by said ground-fault detector-means for making said current-responsive voltage-developing means respond more sensitive- 1y to said function of the three-phase line-current, local control-means operative to develop a succession of operating impulses in response to positive half-cycles of said pulsating voltage, pilot-channel means operative to transmit a succession of restraining impulses and to make them effective at another line-terminal or terminals in response to negative half-cycles of said pulsating voltage, and phase-angle-detecting relay-means operative to respond to said operating impulses When they are not effectively opposed by restraining impulses received from a distant line-terminal.

l5. Multi-responsive fault detector means, adapted to be responsive to a plurality of different kinds and phases of groundand phase-faults on a three-phase line, comprising current-responsive voltage-developing means operative to develop a voltage-component which is responsive to a function of the three-phase line-current, ground-fault detector-means for selectively responding to ground-fault line-conditions more sensitively than said current-responsive voltagedeveloping means, said ground-fault-detectormeans being operative to develop a ground-faultresponsive voltage-component of a limited magnitude and a unidirectional form, circuit-means for combining said voltage-components in series, and means responsive to said combined voltagecomponents.

16. Multi-responsive fault-detector means, adapted to be responsive to a plurality of dierent kinds and phases of groundand phase-faults on a three-phase line, comprising current-responsive Voltage-developing,means operative to develop a pulsating voltage-component having a phase which is responsive to a function of the threephase line-current, ground-fault detector-means for selectively responding to ground-fault lineconditions more sensitively than said current-responsive voltage-developing means, said groundfault detector-means being operative to develop a unidirectional voltage of substantially nonpulsatory form, a polarity-responsive device, means for causing said device to be operatively conducting on alternate half-cycles of the linecurrent frequency in response to said pulsating voltage, and means, responsive to said substantially non-pulsatory voltage, for increasing the sensitivity of the aforesaid response to the pulsating voltage.

17. Terminal equipment for one terminal of a pilot-channel phase-angle-detecting relaying-system adapted to protect a section of a three-phase transmission-line against faults, comprising current-responsive voltage-developing means operative to develop a pulsating voltage having a phase which is responsive to a function of the threephase line-current at said terminal, ground-fault detector-means for selectively responding to ground-fault line-conditions more sensitively than said current-responsive voltage-developing means, said ground-fault detector-means being operative to provide a unidirectional voltage of substantially non-pulsatory form, a tube, means for normally providing a tube-circuit voltage which prevents the tube from becoming effectively conductive, means for making said unidirectional voltage effective in a circuit or" said tube in the polarity tending to make the tube become effectively conductive, means for making said pulsating voltage effective in a circuit of said tube in such manner as to tend to cause the tube to be operatively conductive on alternate halfcycles of the line-current frequency in response to the pulsations of said pulsating voltage, local control-means responsive to said tube for developing a succession of operating impulses during alternate half-cycles of said pulsating voltage, pilot-channel means responsive to said tube for transmitting a succession of restraining impulses and making them effective at another lineterminal or terminals during the other halfcycles of said pulsating voltage, and phase-angledetecting relay-means operative to respond to said operating impulses when they are not effectively opposed by restraining impulses received from a distant line-terminal.

18. Terminal equipment for one terminal of a pilot-channel phase-angle-detecting relayingsystem adapted to protect a section of a threephase transmission-line against faults, comprising current-responsive voltage-developing means operative to develop a single-phase voltage having a phase which is responsive to a function of the three-phase line-current at said terminal, ground-fault detector-means for selectively responding to ground-fault line-conditions more sensitively than said current-responsive voltagedevelopingr means, said ground-fault detectormeans being operative to provide a unidirectional voltage of substantially non-pulsatory form, electronic apparatus comprisingl two tubes, means for making said single-phase voltage effective in circuits of the two tubes in such manner as to tend to cause one tube to be operatively conductive on positive half-cycles of said single-phase voltage and to. tend to cause the other tube to be operatively conductive on negative half-cycles of said single-phase voltage, means for making said unidirectional voltage eiective in circuits of said tubes in a polarity facilitating the operative conductivity of said tubes, local control-means responsive to the operation of one tube for developing a succession of operating impulses, pilotchannel means responsive to the operation of the other tube for transmitting a succession of restraining impulses and making them effective at another line-terminal or terminals, and phaseangle-detecting relay-means operative to respond to said operating impulses when they are not effectively opposed by restraining impulses received from a distant line-terminal.

19. Terminal equipment for one terminal of a pilot-channel phase-angle-detecting relayingsystem adapted to protect a section of a threephase transmission-line against faults, comprising current-responsive voltage-developing means operative to develop a single-phase voltage having a phase which is responsive to a function of the three-phase line-current at said terminal, "t"

ground-fault detector-means for selectively responding to ground-fault line-conditions more sensitively than said current-responsive voltagedeveloping means, said ground-fault detectormeans being operative to provide a unidirectional voltage of substantially non-pulsatory form, electronic apparatus comprising two tubes, each having control-circuit means, supply-leads adapted to provide a direct-current plate-voltage supplycircuit for each tube, means for normally providing each tube with a control-circuit voltage which prevents the tube from becoming effectively conductive, means for making said unidirectional voltage effective in circuits of said tubes in the polarity tending to make the tube become effectively conducting, means for making said single-phase voltage oppositely effective in circuits of the two tubes in such manner as to tend to cause one tube of be operatively conductive on positive half-cycles of said single-phase voltage and to tend to cause the other tube to be operatively conductive on negative half-cycles of said single-phase voltage, local control-means responsive to the operation of one tube for developing a succession of operating impulses, pilot-channel means responsive to the operation of the other tube for transmitting a succession of restraining impulses and making them effective at another line-terminal or terminals, and phase-angle-detecting relay-means operative to respond to said operating impulses when they are not effectively opposed by restraining impulses received from a distant line-terminal.

20. Terminal equipment for one terminal of a pilot-channel phase-angle-detecting relaying system adapted to protect a section of a three-phase transmission-line against faults, comprising phase-sequence means for developing two different single-phase control-voltages in response to two different phase-sequence functions of the line-current at the relaying terminal, local control-means responsive to a rst one of said control-voltages for producing a succession of restraining impulses in response to negative halfcycles of said rst control-voltage when said control-voltage exceeds a predetermined magnitude, and for producing a succession of operating impulses in response to positive half-cycles of said rst control-voltage when said control-voltage exceeds a predetermined magnitude, means responsive to the second control-voltage for increasing the sensitiveness of the response of said local control-means to said first control-voltage, fault-detector means for responding to locally detectable fault-conditions on the transmissionline, means for utilizing said fault-detector means in controlling said local control-means, pilotchannel means operative to transmit said succession of restraining impulses and to make them effective at another line-terminal or terminals, and phase-angle-detecting relay-means operative to respond to said operating impulses when they are not effectively opposed by restraining impulses received from a distant line-terminal.

21. Terminal equipment for one terminal of a pilot-channel phase-angle-detecting relaying system adapted to protect a section of a threephase transmission-line against faults, comprising phase-sequence means for developing a singlephase control-voltage in response to a phase-sequence function of the line-current at the relaying terminal, local control-means responsive to said control-voltage for producing a succession of restraining impulses in response to negative halfcycles of said control-Voltage when said controlvoltage exceeds a predetermined magnitude, and for producing a succession of operating impulses in response to positive half-cycles of said controlvoltage when said control-voltage exceeds a predetermined magnitude, fault-detector means for selectively responding to a locally detectable fault-condition other than a balanced three-phase fault Orr the transmission-line, means for utilizing said fault-detector means to increase the sensitivity of response of said local controlmeans, pilot-channel means operative to transmit said succession of restraining impulses and to make them 4effective at another line-terminal or terminals, and phase-angle-detecting relaymeans operative to respond to said operating impulses when they are not eifectively opposed by restraining impulses received from a distant lineterminal.

HERBERT W. LENSNER.

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