US1870518A - Electric protective system - Google Patents

Description

Aug. 9, 1932- l H. LEBEN ET AL 1,870,518

ELECTRIC PROTECTIVE SYSTEM Filed July 11. 1929 2 Sheets-Sheet 1 hhhlllklllhllll 1932- H. LEB.EN ET AL 1,870,518

ELECTRIC PROTECTIVE SYSTEM Filed July 11, 1929 2 Sheets-Sheet 2 Patented Aug. 9, 1932 UNITED STATES PATENT @FFEQIEZ HENRY LEBEN, OF NEWCASTLE-UPON-TYNE, AND NORMAN COOKE, 0F SUNDERLAND, ENGLAND, ASSIGNORS TO A. REYROLLE 8c COMPANY LIMITED, 015 HEBBURNON TYNE, ENGLAND, A COMPANY OF GREAT BRITAIN ELECTRIC PROTECTIVE SYSTEIVI Application filed July 11, 1929, Serial No. 377,563, and in Great Britain July 31, 1928.

This invention relates to electric protective systems of the kind generally known as impedance or like protective systems, which depend for their operation on the fact that the impedance or reactance or resistance of the portion of the protected line between the fault and the protective relay is proportional to the distance of the fault from the relay. In such systems a number of time-discriminating relays are disposed at the ends ofsections of the protected line, such relays being employed to give discriminative protection for the sec tions of the line by so arranging them that the time of operation of each relay is proportional to the impedance or other ratio of the line. In such systems it has been proposed that the time-discriminating relays should normally be disconnected and should be brought into circuit on the occurrence of a fault by means of initiating relays operative when the voltage of the line falls to an abnormally low value or when the current there-.

in rises to an excessive value or when the impedance or like characteristic of the line falls below a predetermined value.

The primary object of the present invention is to provide an improved arrangement for controlling the energizing circuits of the time-discriminating relay coils.

In systems of this kind it is necessary to introduce a directional feature, whereby each of the time-discriminating relays, which are provided at both ends of the protected section, is prevented from operating unless the current is entering the section at the adjacent end. lVith some types of'time-discriminating relay a directional feature is present in the relay itself, but in such a case (unless the relay has unduly high power consumption) it is diflicult to ensure operation of the relay at low voltages unless compensating means are provided which would interfere with the accuracy of the time discrimination. On the other hand the employment of separate directicnal relays is undesirable since it increases the already large number of relays necessary to give adequate protection for earth and interphase faults and thus complicates the systern.

A further object of the invention is therefore to provide a system wherein a directional.

feature satisfactorily operative at low voltages can be incorporated into the system without interfering with the accuracy of the time-discriminating relays and without increasing the number of relays employed.

It is usually necessary in such systems to employ separate initiating relays for earth faults and for interphase faults, but with the minimum number of initiating relays in three-phase systems (namely one for earth faults and three for interphase faults) there is risk of inadvertent relay operation owing to the connection of the time-discriminating relay coils to healthy phases instead of to the faulty phase or phases. 7

1 Yet another object of the invention is therefore to provide simple and eiiicient means for ensuring correct energization of the timediscriminating relay coils when a fault occurs.

Still further objects of the invention will be apparent from the appended claims and from the following description of the accompanying drawings, which illustrate by way of example some convenient arrangements according to the invention. In these drawings Figures 1 and somewhat diagrammatically two convenient practical constructions of initiating relay,

Figure 8 is a circuit diagram of the whole protective system, and

Figures l and 5 show modifications'of the system of Figure 3.

In the arrangement of Figure 1, the initiating relay has a single wattinetrical movement, which is illustrated as of the induction type although it will be clear that anal-' ogous arrangements can be employed with other types of wattmetrlcal movement. Thus the relay comprises two field cores A Boooperating with a disc or like contact member 2 respectively illustrate:

and with the current, the two voltage coils A B being connected in parallel with one another. The two coils B B on the second field core B respectively constitute a res rain- 5 ing coil and an operating coil and are arranged to produce opposing fluxes in the core B, the resultant of which interacts with the flux in the core A to exert a torque on the'contact disc C. This torque is proportional to V (1 cos X1 ]cV), where V and I are respectively the voltage and the current in the protected line, is is a constant and X is an angle dependent upon the power factor of the line. In actual practice it is preferable to arrange the angle X to be such that 00s I is never much less than unity, however severe the fault may be. This may be effected by giving a phase lag 9 to the current flowing in the Voltage coils A B A with respect to that flowing in the current coil B (or alternately giving a lead 6 to the current flowing in the current coil 13 with respect to that in the voltage coils A B), the angle Qbeing chosen so that for all types of fault cos D (which is equal to cos (6) where cos D is the power factor of the line) has a value greater than, say, 0.75. In the example illustrated a non-inductive resistance D of suitable magnitude is connected in'series with the voltage coil circuit to give the desired phase lag, a further resistance D being inserted in the circuit of the coil A in order to preventcurrent from the current transformer D being fed to the coil A by gansformer action between the coils B and With this arrangement it will be clear that the relay will operate as soon as the flux operating component I cos E exceeds the restraining component 70V, i. e. when the ratio V/I cos 45 falls below a predetermined value. This arrangement is also directional in operation since a current reversal Will reverse the operating flux component but not the restraining component;

It will beappreciated also that, quite apart from its function in producing the desired ratio characteristic of the relay, the pro vision ofanadditional voltage coil B on the .swattmetrical movement ensures the satisfactory operation of the relay even when the voltage falls toavery low value.

In the arrangement of Figure 2 operating and restraining torques are produced in itwo separateelements mechanically coupled together. The operating element consists of a simple wattmet-rical movement having a voltage coil E and a current coil E so arranged as to produce a torque proportional to VI cos b on the contact disc E, the currents. flowing in the two coils being displaced relatively in phase in the manner above referred to (for instance by means of the resistances D and E in order to ensure a relatively large operating torque for all types of fault. The contact disc E is mechanical ly coupled to the contact member F of the restraining element, which can be arranged in various ways to produce a torque proportional to V opposing the operating torque. Thus for instance the restraining element may consist of a simple electromagnet energized in accordance with the voltage, the square law being obtained by not saturating the iron circuit. Alternatively (as shown), a second watt'metrical movement may be employed, the two coils F F of which are both energized in accordance with the voltage. The desired directional effect is obtained owing to the fact that the operating torque reverses and assists the restraining torque in the event of a current reversal.

Figure 8 illustrates a complete protective arrangement at one end of a section of a hree-phase protected circuit employing initiating relays of either of the above kinds. In this arrangement the protected circuit G I G is provided wih a. potential transformer having s cted primary and secondary wind connected to has ii?) and with a group of current nsforinors having star-connected secondaries J 5 J Three time-discriminating relays K K L L M l 1 are employed, one of the relays K K being operative for earth faults and the otl er two L L and M M for interphase faults. These relays are preferably of t is kind described in the present ap plicants copending U. S. patent application Serial l lo. $1 1,48 dated 17th June 1929 having}; voltage and current coils (of which one voltage coil K or L or M and one current CfOil K or L or M only are shown in the drawings for simplicity) and a variable resistance K or L or M operated by independent timing mechanism (not shown) in the circuit of, or M. The contacts K L M of the timediscriminating relays control a tripping circuit for a circui -breaker G the protected circuit G G in the usual manner. These relays are normally discon iected, but their coils are brought into circuit by the operation of initiating relays of the kind above described. Four initiating relays N N, 0 P P Q Q are provided (each being shown for simplicity having a single-voltage coil N or Q or P or Q and a single current coil. N or O or P or (3}), of which the first N N is associated with earth faults, whilst the other three are associated with interphase faults. The normally open contacts N of the relay N N control. the energizing circuit of the voltage coil K of the relay K K whilst contacts I on the relay N N normally short-circuit the current coil K In a similar manner the contacts Q Q} of the relay Q (3} control the relay M M, and the contacts O O and P P 'of the relays P P and the voltage coil K or L Q Q} together control the relay L L The current coils of the initiating and time-discriminating relays derive their current from the current transformer secondaries J J J Thus the star-point of the current transformer secondaries J J J is connected through contacts N to the current coil N the otl er side of which is connected either through contacts Q and the current coil Q to the secondary J or through the current coil P to the secondary J orthrough contact-s P O and the current coil 0 to the secondary J Whilst the current coils of the time-discriminating relays are connected to the same circuits, the coil K being normally short-circuited by contacts N the coilM by contacts Q4 and the coil L by contacts 0 P*. The voltage coils of the interphase fault initiating relays are energized from the potential transformer second ary busbars H H H the coil O from H E the coil P from H H and the coil Q from H H The voltage coil N of the earth-fault initiating relay derives its current from a small auxiliary potential transformer N although other means may be employed for this purpose such for example as the energization of the voltage coil from the current in an earthing connection to the neutral point of a power transformer in the protected circuit, if available; The contacts N O P Q of the initiating relays control a starting circuit (not shown) for the timing mechanism which drives the contact arms of the resistances K L M The voltage coils of the time-discriminating relays also derive their current from the busbars H H H energizing circuits.

In order to ensure that the time-discriminating relays are correctly energized from the, faulty phases, two phase-selecting relays R R S S are provided, these relays being respectively operative for earth faults and for interphase faults and acting to control the energizing circuits of the voltage coils of the time-discriminating relays.

The earth-fault phase-selecting relay R R comprises a contact-making system (which may be in the form of a pivoted beam R as shown or of arotatable spindle) operated differentially by two coils R R which are connected respectively between the busbars H H and H H i. e. are energized respectively in accordance with the earth voltages of two of the phases G G In the event of an earth fault on the phase G the earth voltage on that phase will drop, as will. also those on the other phases. The earth volt age on the phase G will however be considerably lower than those on the phases G G which will be equal to one another. Thus for such a fault the contact beam R will remain in its normal balanced position, and will allow, the voltage coil K to be energized from. the phase G the initiating relay N N having operated. The energizing circuit for the coil K may be traced from potential transformer busbar H through contact beam R in its central position, contacts N variable resistance K and coil K to neutral busbar H For an earth fault onphase G the coil R will exert a greater force than the coil S and will consequently move the beam R in one direction to energize the coil K from the faulty phase G i. e. from busbar H instead of busbar H in the above traced circuit. A. fault on phase G will similarly move the beam R in the other direction to energize the coil K from the phase G i. e. from busbar H The interphase fault phase-selecting relay is arranged in a similar manner with a contact beam S or spindle operated differentially from two coils S S which however in this case are energized respectively from the interphase voltages G G and G G i. e. from busbars H H and H H. Thus for an interphase fault between the phases G G the beam S will remain in its central position, and owing to the operation of the initiating relay 0 0 the time-discriminating relay L L will be operative with its voltage coil L energized from the phases G G he energizing circuit for the coil L may be traced from busbar H through coil L, variable resistance L contacts 0 and contact beam S in its centralfposition to busbar H For a fault between the phases G G the initiating relay P P will operate and the beam S will move over in a direction to energize the voltage coil L from the phases G G the force of the coil S exceeding that of coil S and pulling down the lefthand end of the beam so that the energizing circuit for the coil L in this case runs from busbar H through coil L, resistance L contacts P and contact beam S to busbar H Similarly for a fault between the phases G G the initiating relay Q Q will operate and the beam S will move to a position in which the'voltage coil M of the re lay M M is energized from the phases G G The circuit for coil M runs from busbar H through'coil M, resistance l contacts Q and contact beam S in its other operated position to busbar H Instead of providing each phase-selectingrelay with contacts in all its three operating positions, it may have two sets of contacts only, these contacts being completed respec-- tlvely in the two unba-lancedpositions of the relay. Such, an arrangement is shown in Figure l for the earth fault phase-selecting relay R- R a similar arrangement being equally applicable also to the interphase fault relay S S In this case two auxiliary contactors T U are provided, whose ener-:

gizing circuits (preferably from a D. C.

sourceindicated at V) are controlled respec-- D. C. contactors X Y. The c the time-discriminating :t-ivelyby the two sets of contacts on the phase-selecting relay R R and by normally open contacts N on the earth fault initiating relay N N One of these contactors T has normally open contacts T controlling the energizing circuit from the phase G to the voltage coil K of the time-discriminating relay, and the other has normally open contacts U controlling the corresponding circuit from the phase G The circuit from the phase G is taken through normally closed contacts T U on the two auxiliary contactors and through normally open contacts N on the initiating relay N N Figure 5 shows a modification in which a single phase-selecting relay is employed both for earth faults and for interphase faults, the energizing circuits for ti :wo coils N W of this relay being con ed by two ctor X is initiating energized whenever the eartl relay N N operates its coi N which replace the contacts N of Figure 3, and acts to supply the correct earth voltages to the coils W W 1 and to the voltage coil K of the earth faulttime-discriminwing relay, the latter circuit also being controlled. by the phase-selecting relay contacts. The contactor Y is likewise operated whenever one or other of the interphase fault relays O P P, Q Q operate their contacts P Q and acts to supply the correct phase voltages to the coils N and to the voltage coils of the interphase fault time-discriminating re lays (this figure showing a symmetrical arrangement in which three time-discriminating relays are used instead of the two in Figure The above arrangements have been described by way of example only and may be modified in various ways within the scope of the invention. Thus for instance the phase-selecting relays may if desired control the energizing circuits to the current coils of relays as well as the voltage circuits, and again maybe employed for the control of time-discriminating relays of other kinds.

hat we claim as our invention and desire to secure by Letters Patent is 1. In an electric protective system having a timediscriminating action dependent on the fault distance, the combination of a circuit-breaker in the protected line, a normally inoperative time-discrin inating relay, means whereby the time-discrimiating reby when rendered operative acts to open the circuit-breaker after a time interval which depends on a ratio dependent on the voltage and current characteristics of the line and representative of the fault distance, an instantaneously acting initiating relay having a contact-making system and coils acting wattmetrically thereon, means whereby the initiating relay acts when operated to and current characteristics of the line wherebythe relay is caused to operate only when I the flow of power in the line is in a predetermined direction and a ratio dependent on the voltage and current characteristics of the line and representative of the fault distance is less than a predetermined value.

2. In an electric protective systemhaving a time-discriminating actiondependent on the fault distance, the combination of a circuit-breaker in the protected line,-a normally inoperative time-discriminating relay, means whereby the time-discriminating relay when rendered operative acts to open the circuit-breaker after a time interval which depends on a ratio dependent on the voltage and current characteristics of the line and representative of the fault distance, and an instantaneously acting initiating relay comprising a contact member, a wattmetrical operating element including coils and a movable member, a restraining element including at least one coil and a movable member, means for mechanically coupling the contact member and the two movable members together, and means for energizing the coils of the relay elements in accordance with the voltage and current characteristics of the line wherebythe relay is operative only when the flow of power in the protected line is in a predetermined direction and when a ratio dependent on the voltage and current characteristics and representative of the fault distance is less than a predetermined value. A

3. In an electric protective system having a time-discriminating action dependent on the fault distance, the combination of, a circuit-breaker in the protected line, a normally inoperative time-discriminating relay, means whereby the time-discriminating relay when rendered operative acts to open the circuit-breaker after a time interval which depends on a. ratio dependent on the voltage and current characteristics of the line and representative ofthe fault distance, and an instantaneously acting initiating relay cornprising a. contact member, a single wattme-trical element having operating. and restraining coils and a movable member, means whereby in such element a single torque due to the interaction of two magnetic fluxes produced by the coils is exerted on the movable member, means whereby such movable member operates the contact member, and means for energizing the coils of the wattmetrical element in accordance with the voltage and current characteristics of the protected line whereby the torque is rendered dependenton the direction of power flow in theline and on a ratio dependent on the voltage and current characteristicsand representative of the fault distance. 7

4c. In an electric protective system having a time-discriminating action dependent on 5 the fault distance, the combination of a circuit-breaker in the protected line, a normal- 1y inoperative time-discriminating relay, means whereby the time-discriminating relay when rendered operative acts to open the cir- -1 cuit-breaker after a time interval which depends on a ratio dependent on the voltage and current characteristics of the line and representative of the fault distance, and an instantaneously acting initiating relay com- 1 prising a contact member, a wattmetrical opera-ting element having Voltage and current coils and a movable member, means for so energizing such coils that they will exert on the movable member an operating torque proportional to VI cos X (where V and I are respectively the voltage and the current in the protected line and I is an angle de pendent on the power factor of the line), a restraining elementhaving at least one coil 2 and a movable member, means for so energizing such coil that a restraining torque proportional to V is exerted on the movable member, and means for mechanically coupling the two movable members to the contact member, the arrangement of the operating element being such that in the event of a reversal of power flow in the protected line the operating torque will reverse and as s'ist the restraining torque.

25 5.In an electric protective system having a time-discriminating action dependent on the fault distance, the combination of a circuit-breaker in the protected line, a normally inoperative time-discriminating relay, means 40 whereby the time-discriminating relay when rendered operative acts to open the circuitbreaker after a time interval which depends on a ratio dependent on the voltage and current characteristics of the line and representative of the faultdistance, and an instantaneouslyacting initiating relay comprising a contact member, 'awattmetrical operating element having voltage and current coils and a movable member, means for so energizing such coils that they will exert on the movable member an operating torque proportional to VI cos X (where V and I are respectively the voltage and the current in the protected line and X is an angle dependent on the power factor of the line),means whereby the'currents flowing in the current coil and the voltage coil of the operating element are dis.- placed in phase relative to one another by such an angle as to ensure a relatively large operating torque for all types of fault,a restraining element having at least one coil and a movable member, means for so ener-' gizing such coil that a restraining torque,

I proportional to V is exerted on the movable member, and means for mechanically coupling the movable members to the contact member, the arrangement of the operating element being such that in the event of a reversal of power flow in the protected line the operating torque will reverse and assist the 7 restraining torque.

6. In an electric protective system having a time-discriminating action dependent on the fault distance, the combination of a circuit-breaker in the protected line, a normally inoperative time-discriminating relay, means whereby the time-discriminating relay when rendered operative acts to open the circuitbreaker after a time interval which depends on a ratio dependent on the voltage and cur- 8 rent characteristics of the line and representative of the fault distance, and an instantaneously actin initiating relay comprising a contact mem er, a movable member mechanically coupled to the contact member, two magnetic circuits the fluxes in which interact to exert a single torque on the movable member, 'a single coil on one magnetic circuit, means whereby such coil is energized in accordance with the voltage in the protected line, an operating coil on the second magnetic circuit, means whereby such coil is energized in accordance with the current in the protected line, a restraining coil on the second magnetic circuit, and means whereby such coil is energized in accordance with the voltage in the protected line, the arrangement of the coils on the second magnetic circuit being such that in the event of a reversal of power flow in the protected line the action of the operating coil will reverse and assist that of the restraining coil.

7 In an electric protective system having a time-discriminating action dependent on the fault distance, the combination of a circuit-breaker in the protected line, a normally inoperative time-discriminating relay, means whereby the time-discriminating relay when rendered operative acts to open the circuitbreaker after a time interval which depends on a ratiodependent on the voltage and current characteristics of the line and representative of the fault distance, and an instantaneously acting initiating relay comprising a contact member, a movable member me chanically coupled to the contact member,

two magnetic circuits the fluxes in which interact to exert a single torqueon the movable member, a single coil on one magnetic circuit, 7 means whereby such coil is energized in accordance with the voltage in the protected line, an operating coil on the second magnetic circuit, means whereby such coil is energized in accordance with the current in the protected line, a restraining coil on the sec- 0nd magnetic circuit, means whereby such coil is energized in accordance with the voltage in the protected line, and means whereby the currents flowing in the operating current coil and in the voltage coil on the first mag- 139 netic circuit are displaced in phase relativeto one another by such an angle as to ensure satisfactory operation of'the contact member for all types of fault, the arrangement of the coils on the second magnetic circuit being such that in the event of a reversal of power flow in the line the action of the operating coil will reverse and assist that of the restraining coil.

8. In a three-phase protective system hav ing a time-discriminating action dependent on the fault distance, the combination of a circuit-breaker in the protected line, a group of normally inoperative time-discriminating relays, means whereby each time-discriminating relay when rendered operative acts to open thecircuit-brealzer after a time interval dependent on a ratio which depends on the voltage and current characteristics of the protected line and is representative of the fault distance, a group ofinitiating relays, means whereby at least one initiating relay is caused to operate on the occurrence of a faulton the line,'means whereby each initiating relay on operating causes a selected timediscriminating relay to be rendered opera tive,'at least one phase-selecting relay, means for-energizing such phase-selecting relay in accordance with the voltage characteristics of. the line whereby it will operate in accordance with the voltage unbalance between the phases of the line set up by the fault, and means whereby the phase-selecting relay acts to ensure that the selected time-discriminating relay is energized from the faulty phase or phases. 1 I

9. In a three-phase protective system having a time-discriminating action dependent on the fault distance, the combination of a circuit-breaker in the protected line,-a group of normally inoperative time-discriminating relays, means whereby each time-discriminating relay when rendered operative acts to open the circuit-breaker after a time interval 1 dependent on a ratio which depends onthe voltage and current characteristics of the protected line and is representative of the fault distance, a group of initiating relays, means whereby at least one initiating relay is j caused to operate on the occurrence of a fault on the line, means whereby each initiating relay on operating causes a selected time-dis criminating relay to be rendered operative, two phase-selecting relays, means for energiz ing such phase-selecting relays in accordance respectively with the earth voltages and with the interphase voltages in the'protected line whereby each phase-selecting relay will opcrate in'accordance with the voltage unbalance between the phases of the line set up by the fault, means whereby one phase-selecting relay acts in the event of an earth fault'to ensure that the selected time-discriminating relay is energized from the faulty phase, and means whereby the other phase-selecting relay acts in the event of aninterphase fault to ensure that the selected time-discriminatingrelayis energized from theifaulty phases.

10. In .a three-phase protective system having a time-discriminating action-dependent on the fault distance, the combination of a circuit-breaker in the protected line, 2. normally inoperative time-discriminating relay means whereby such relay when rendere operative acts to open the circuit-breaker after a time interval dependent on a ratio which depends on the voltage and current characteristics of the protected line and is representative of the fault distance, an initiating relay, means whereby the initiating relay iscaused to operate on the occurrence of an earth fault on the protected line,.means whereby the initiating relay on operating acts torender operative the time-discriminating relay, a phase-selecting relay, means for energizing the phase-selecting relay differentially in accordance withthe earth voltageson two of the three phases of the line whereby the contact member of the phaseselecting relay takes up one or other of three operative positions in accordance with which of the phases is faulty, and means whereby the position of such contact member determinesthe phase of the .line from which the time-discriminating relay is-energiz ed.

11. In a three-phase protective system having. a time-discriminating action dependent on the fault distance, the combination of a circuit-breaker in the protected line, a group of normally inoperative.time-discriminating-relays, meanswhereby each time-discriminating relay when rendered operative acts to open the circuit-breakerzafter-a time interval dependent ona ratio which'depends' on the voltage and current characteristics of the protected. line. and is representativeof thefault distance, a group of initiating relays,

means wherebyatleast one initiating relay is caused to operateon-the occurrence of an interphase fault on the line, means whereby each "initiating relay on operating causes a selected time-discriminatingrelay to be rendered operative, a phase-selecting relay, means for energizing the phase-selecting relay differentially inac'cordance with two of the three interphase voltages whereby the contact member ofthe phase-selecting relay takesup-oneor other of three operative positions in accordance with which of-thepairsofphasesisfaulty, and means whereby the position of such contact member determines the-phases of thelinefrom which the selectedtime-discriminating relay is energized.

1 2. 'In a three-phase protective system having a time-discriminating .action dependent on the fault distance, the combination of acircuit-breaker in the protected line, a group of normally inoperative timeediscriminatingielays, means whereby'each timediscriminating" relay when. rendered operaselected time-discriminating relay to be rendered operative, two phase-selecting relays respectively associated with earth faults and with interphase faults, means for energizing the earth fault phase-selecting relay differ-' entially in accordance with the earth voltages on two of the phases of the line whereby its contact member takes up one or other of three operative positions in accordance with which of the phases is faulty, means for energizing the interphase fault phase-selecting relay differentially in accordance with two of the three interphase voltages whereby its contact member takes up one or other of three operative positions in accordance with which of the pairs of phases is faulty, and means whereby the positions of the contact members of the phase-selecting relays determine the phase or phases of the line from which the selected time-discriminating relay is energized.

13. In a three-phase protective system having a time-discriminating action dependent on the fault distance, the combination of a circuit-breaker in the protected line, a group of normally inoperative time-discriminating relays, means whereby each time-dis criminating relay when rendered operative acts to open the circuit-breaker after a time interval dependent on a ratio which depends on the voltage and current characteristics of the protected line and is representative of the fault distance, a group of initiating re-- lays associated with the individual phases or pairs of phases of the line and each having a contact-making system and coils acting wattmetrically thereon, means whereby each initiating relay on operating causes a selected time-discriminating relay to be rendered operative, means for energizing the coils of each initiating relay in accordance with the voltage and current characteristics of the associated phase or phases of the line whereby such relay is caused to operate only when a characteristic of the associated phase or phases representative of the fault distance is less than a predetermined value and when the flow of power in the line is in a predetermined direction, at least one phase-selecting relay, means for energizing such phase-selecting relay in accordance with the voltage characteristics of the line whereby it will operate in accordance with the voltage unbalance between the phases of the line set up by the fault, and means whereby the phase-selecting relay acts to ensure that the selected time-discriminating relay is energized w from the faulty phase or phases.

'14. In a three-phase protective system having a time-discriminating action dependent on the fault distance, the combination of a circuit-breaker in the protected line, a group of normally inoperative time-discriminating relays, means whereby each time discriminating relay when rendered operative acts to open the circuit-breaker after a time interval dependent on a ratio which depends on the voltage and current characteristics of the protected line and is representative of the fault distance, a group of initiating relays associated with the individual phases or pairs of phases of the line and each .having a contact-making system and coils acting wattmetrically thereon, means whereby each initiating relay on operating causes a selected time-discriminating relay to be rendered operative, means for energizing the coils of each initiating relay in accordance with the voltage and current characteristics of the associated phase or phases of the line whereby such relay is caused to operate only when a characteristic of the associated phase or phases representative of the fault distance is less than a predetermined value and when the flow of power in the line is in a predetermined direction, two' phase-selecting relays respectively associated with earth faults and with interphase faults, means for energizing the earth fault phase-selecting relay differentially in accordance with the earth voltages on two of the phases of the line whereby its contact member takes up one or other of three operative positions in accordance with which of the phases is faulty, means for energizing the interphase fault phase-selecting relay differentially in accordance with two of the three interphase voltages whereby its contact member takes up one or other of three operative positions in accordance with which of the pairs of phases is faulty, and means whereby the positions of the contact members of the phase-selecting relays determine the phase or phases of the line from which the selected time-discriminating relay is energized.

15. In a three-phase protective system having a. time-discrimmating action dependent on the fault dist-ance, the combination of a circuit-breaker in the protected line, a normally inoperative time-discrlmlnating relay associated with earth faults, a group of nor- 1.; :such initiating relayis caused to operate on the occurrence of an earth fault, means whereby theeart-hfifault: initiating relay on .operatingi renders the earth fault time-dis- 'i .rcriminating. relayoperative, three interphase :rfault initiating relays associated respectively -fi' lwith the threepairs of phasesgneans where- "by the appropriate initiatingrelay is operu; rated on the occurrence of an interphase fault,

2510211183118 whereby each interphase fault initiatin'glrelayr onoperating. renders a selected in- ;terphase fault timediscriniinating relay op ';y::erative, two phase-selecting relays respec- 1 tively associatedwith' earth faults and with interphase faults, means for energizing such 1';:nphase-selecting relays in accordance respecikctively with the earthvoltages and with the interphaser voltages in the protected line whereby; each phase-selecting relay will 0peratein accordance with the voltage unbal- 1:: ance-between the phases of the line setup by the;:fault, means whereby one. phase-select- 1 ring: relay. acts in thezeventof an earth .fault to ensure that the earth fault time-discrimizlinating'relayris energized from the faulty paraphase, and means whereby the other phaseselecting'relay acts. in the event of an inter- :ss' vrphase fault toaensur'e that the selected inter- 3": phase afault: time-discriminating relay is en- :13? 2GL'glZBdSfI'Om the faulty phases.

,2 :Irrtestimony'whereof wehave signed our "inn-mes to this specification. l: HENRY. LEBEN.

: NORMAN GOOKE.

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