US2561967A - Directional and overcurrent electrical relay - Google Patents

Description

y 1951 R. c. BERGVALL ET AL. 2,561,967

DIRECTIONAL AND OVERCURRENT ELECTRICAL RELAY Filed June 19, 1947 77mes Fu// Load Current I .7 41 4 9, F 81,, es, L EL 9 .93

L 17 WITNESSES: INVENTORS t I yal Bergva/l. and

Edwin L. Harden ATTOR N EY Patented July 24, 1951 DIRECTIONAL AND OVERCURRENT ELECTRICAL RELAY Royal 0. Bergva'll, Wilkinsburg, and Edwin L.

Harder, Pittsburgh, Pa., assignors to divestinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application Julie :19, 1947; Serial Now-55,758

10 claim (01. 175 -294 This invention relates to electrical devices I which are responsive to a function of voltage and current, and .it has particular relation to directional relays which have aresponsedesigned to compensate :for a drop in the voltage applied thereto. The invention further relates to relays having both directional and overload characteristics.

In Patent 2,323,176, F. D. Johnson discloses a directional relay comprising two :electrores-pom,

siveunits each having an output or a response varying in accordance with the square of the :energization thereof. These units are differentially associated to provide a resultant output having a watt .or directional characteristic, The

units .are energized respectively in accordance with the sum and .difierence of voltage and cur- .rent in an electrical system with which the nelay .associated.

, Ifthe voltage applied to the Johnson 'relay drops excessively, the relay theoretically operates properly in response to severe fault currents.

However, if the two units differ slightly in their characteristics, the differential effect resulting from heavy currents flowing therethrough, un-

derfault conditions, may prevent proper operation of the relay. Since the voltage of the system;ma;y drop appreciably under severe faults, thewatt response of the relay may; be. lessthan the response of the relay due to differences in the units.

In :such cases, improper operation maybe avoided .by utilization of a voltage regulator through which the Johnson relay is energized from the system. With such a .regulato1:,,. a a

drop in voltage of the system under severe fault conditions does not result in an appreciable drop in the voltage applied to the relay. I

In accordance with the invention, an electrical device, such as a relay, is provided which.

is based on the relay described in the aforesaid Johnson patent. However, the relayis so designed that .energizations derived from the current :fiowing in an electrical system, with which the relay is associated, provides compensation for the drop in voltage'of the system under severe fault conditions. To this end, the two arms of the relay which contain the electroresponsive units are energized differently vby the-currents of the electrical systemwith which the relay;

is associated. In a preferred embodiment of the invention, the two arms have different impedances; and, consequently, different currents flow therethrough in response to energization ofv the arms in accordance withcurrent from the structural the associated electrical system. A relaydesigned ineaccorda'nce with the invention may respond to smaller large reversals in the direction of power flow, and in "addition thereto, may respond to excessive current flow in the associated system in a forward direction.

It :is, therefore, an object of the invention'to provide.v anqimproved :electroresponsive device which :is responsive to a function ofthe voltage andourrent of an electrical system.

iIt-is-a further object of the invention :toprovide a directional .electroresponsive device :having, an overload response.

It is also an object of the invention toiprovide two. opposed electroresponsive elements. which are energized respectively in accordance with the sum andv difference of voltage wandcurrentof .anflassociated electrical system, .and wherein the eneogizationsof the elements due to the current of the associated electrical system are dissimilar.

,It :is a still-further object of the invention.

to provide a pair of differentially associated thermo-responsive units which have responses proportionalto the square of their-energizations and which are energized respectively in accordance with the sumand difference of voltage and current of an associated electrical system,'the

energizations of the units due to the current of p the associated electrical systembeing dissimilar.

Other objects of the invention will be apparent. from the following description, taken in conjunction with the accompanying drawing, in

which:

:Figure 1 a schematic view; of an electrical system having a relay associated therewith which embodies the invention;

Fig, 2 is :a graphical representation of the char-- .acteristics of the relay illustrated in Fig. 1;

I Fig. .3 is a graphical representation showing further characteristics of the relay illustrated in ;v i

Fig. 4 is a schematic view of an electrical system having a further embodiment of -:a relay associated therewith which embodies the invention and Figs, 5, 6, and 7, are schematic views showing 'variousemloodiments of relay units suitable for association with the systems illustrated in Figs.

,lande.

,Referring to the drawing, Figure 1 shows van electrical system which includes a source of alternating electrical energy. This source may ,he a poly-phase or sin le-phase source of energy;

but, for the purpose of discussion, it will be astoward the load 1.

sumed to be a single-phase source, operating at a frequency of sixty cycles per second. This source is connected through conductors 3 and to a suitable load I. It will be assumed that the load I is capable of returning electrical energy to the source I under certain conditions, and that such return of energy is objectionable. A circuit interrupter 9 is provided for controlling the connection of the load I to the source The circuit interrupter 9 has a tripping solenoid associated therewith.

In order to control the tripping of the circuit interrupter 9, an electroresponsive control device I3 is provided which may take the form of an electrical relay having a fixed contact l5 and a movable contact H which is movable into and out Of engagement with the fixed contact l5. These contacts control the connection of the tripping solenoid across a battery l9, or other suitable source of electrical energy.

The movement of the movable contact I1 is controlled by two electroresponsive elements or units 2| and 23. Each of theseunits has a response proportional to the square of the energization thereof. In Fig. 1, the units 2| and 23 take the form of bimetallic elements each having one end secured to a fixed supporting structure the strut 21 and the contact I! in the direction of the arrow 29, or to the right, as viewed in Fig. 1, into engagement with the fixed contact IS. The

bimetallic element 23 is disposed, in response to heating thereof, to urge the strut 21 and the movable contact II in the direction of the arrow 3|, or to the left, as viewed in Fig. l, for the purpose of interrupting or preventing engagement of the contacts l5 and I1.

Suitable connections are provided for energiz- 'ing the bimetallic elements 2| and 23 from the associated electrical system respectively in accordance with the vectorial difference and sum of voltage E and current I of the electrical system, when power flows from the electrical source energization of the bimetallic elements 2| and 23 respectively in accordance with the sum of the voltage and current (E+I) of the associated electrical system and the difference of the voltage and current (E-I) ofthe associated electrical system, when power flows from the load 1 toward the source To this end, a separate voltage transformer and a separate current transformer may be provided for each of the bimetallic elements. However, it is desirable, for most applications, to employ a single voltage transformer and a single current transformer, asshown in Fig. 1.

It should be understood that the aforesaid sum and difference may have other bases. For example, if k is a constant, one element may be energized in' accordance with the sum quantity (EH-k1) and the other element in accordance with the difference quantity [E(1i+k)I]. The elements may be designed to produce equal and opposite forces at predetermined energizations. For present purposes, it will be assumed that the elements are similar.

By reference to Fig. 1, it will be observed that the conductor 5 has the primary winding 33 of a The connections also assure 4 current transformer 35 included in circuit therewith. The bimetallic elements 2| and 23 are connected in series across the secondary winding 31 of the current transformer. It will be noted that the secondary winding 31 is provided with a tap 39 which is disposed between the terminals of the secondary winding. In addition, a terminal 4| is provided between the directly connected ends of the bimetallic elements 2| and 23. The tap and the terminal are connected by the secondary winding 43 of a voltage transformer 45, the primary winding 41 of the voltage transformer being connected across the conductors 3 and 5.

Instantaneous directions of current flow are indicated in Fig. 1 by arrows. It will be noted that the current transformer 35 directs currents I1 and I2 respectively through the bimetallic elements 2| and 23; whereas, the voltage transformer 41 directs currents i1 and is through the bimetallic elements 2| and 23. It might be said that the bimetallic elements in effect are in series across the terminals of the secondary winding of the current transformer 35 and are connected in parallel paths across the secondary winding of the voltage transformer 45. However, it should be noted that with respect to the voltage transformer the secondary winding of. the current transformer operates as an auto-transformerto enforce substantially equal division of current from the voltage transformer through the aforesaid parallel paths despite. diiference between the resistanecs of the paths. As shown by the arrows, when power flows from the source to the load I, the current components Ila/11d i1 subtract vertorially in the bimetallic element 2|, and the current components I2 andir. add'vectorlally in the bimetallic element 23. Should the direction of power flow in the electrical system of Fig. 1 reverse, the direction of flow of the current components I]. and I2 also-reverses, the components I1 and i1 add vectorially in the bimetallic element 2|, and the current components I: and i2 subtract vectorially in the bimetallic element 23. It will be understood that the current components I1 and I2 vary in accordance with current flowing in the associated electrical system; whereas, the current components i1 and i2 vary in accordance with the voltage" of the associated electrical system.

As thus far specifically described, the electroresponsive control device of Fig. 1 is similar to devices illustrated and described in the aforesaid Johnson patent. From a consideration of the Johnson patent, it will be understood that the electroresponsive control device l3 exhibits a directional or watt response and operates to trip the circuit interrupter 9 when the power flow in the electrical system is from the load 1 toward the source I. i

In accordance with the teachings of the Johnson patent, the currents I1 and I2 would be equal, and the components ii and i: would be equal. If a severe fault occurs on the system, the voltage E may drop to an abnormally low value, and the current components 11 and i2 consequently-would drop to extremely low values. Under these conditions, the current components I1 and Iz'would rise to abnormally high values. Ifthe'bim'etallic elements 2| and 23 and their associatedcomponents are exactly similar, the relay ordinarily, under such conditions, would operate satisfactorily. However, if slight irregularities are presone of the bimetallic elements.-

l alone, in passing through .the bimetallic .ele-

merits, may produce a resultant force actingon may be effected by displacing the tap .39 ,from a mid-position between the terminals of the second:- ary winding 31. Such movement of the tap would result-in an unbalance of the components ii and i2, and may resultin a no-load force acting on the movable contact l1. Although the force could be compensated in any suitable way, as by a spring, the desired inequality of the com- "POHBntS'II and I2 preferably is. obtained by ineluding impedance in the path associated "with Theimpedanee employed may have a power factor selected to maintain the desired phase relationship between the current components 12 and 12. In most cases. the impedance may take the form of the resistor R which is illustrated in Fig. l as included in the electrical path associated with the bimetallic element 23. r

The current transformer 35 tends .to maintain equal voltages across the two halves .of its secondary winding. Consequently, the ,efiect of the resistor R is to reduce the current component I2 to a value below that of the current component I1. Despite the presence of the resistor R, the auto-transformer action of the current transformer secondary winding tends to maintain the current components i1 and is substantially equal.

The effect of the resistor B may be understood froma consideration of the resultant force developed by the bimetallic elements 2] and 23. It

can be shown that the total or resultant force is'represented by the following expression:

In'theforegoing expression, the angle 0 represents the phase displacement between the voltage and current of the associated electrical system. From a consideration of the expression, it will be observed that the relay has a watt response which, for forward power, urges the movable contacts i 1'! toward the left, as viewed in Fig. 1. This watt component or force Fw is represented by the fol-- lowing expression:

Fwa- (Iiii 00S 0+I2i2 COS 0) The force component Fw is directed toward the left, as represented by the arrow 31 in Fig 1, when power flows from the source I toward the load fl and is directed toward the right, as shown by the arrow 29 in Fig. 1, when power flows from-the load 1 toward the source I.

" The relay also has a force component F1 which is indicated by the following expression:

Fm (I12--I22) Since I1 is always larger than I2, the force F1 is always directed toward the right or in the directionof the arrow 29 of Fig. 1.

Finally, the resultant force of the relay includes a component F1 which is represented as follows:

always directed-toward the right as viewed in Fig. 1. As pointed out above,

the components 2'1 and 1'2 are held substantially equal .by the .autotransformer action of the cur-- ment of the movable contact [1.

rent transformer; .A slight difierence may be present because of the exciting current required :for the, .autotransformer action, but the force component ,Fi ordinarily is so small compared to the force component F1, that theforce component Fi'may be neglected. Although the force com- -:ponent F1 has a negligible value, it is mentioned tact ll away from the fixed contact 15 is indicated in Fig. 2 as movement of contact to left.

Response of the relay 13 to power flowing from the source to the load I is illustrated in Fig. '2 by a curve 51. It will be noted that, for low values of current flowing from the source to the'load, the largest force applied to the movable contact I! is that due to the force component Fw, and this urges the movable contact I! away from the fixed contact. At some point A, the curve 51 has zero slope and this indicates that the sum of the force components Frand TF1 has reached equality with the force component 'Fw. As the current flowing to the load continues to increase, the sum of the force components Fi+Fl exceeds the value of the force component Fw, and the movable contact I! conse- I the movable contact 11, when it is in engagement with the fixed contact I5, is represented in Fig. 2 by a dotted line B. It will benoted that, as the current supplied by the source I to the load 1 increases, the curve 5! finally reaches the dot- =ted line B which indicates that the contacts [5 and I1 engage to trip the circuit interrupter 9. Consequently, the relay operates substantially as an overload-current relay. The intersection of the curve 5| with the line B may take place at a desired value of full load current such as 4.3 times full load current. v

' Upon reversal of the flow of power, the load :1 supplies current to the source I. Such reversal changes the sign or direction of the force component Fw and the total .force acting on the contact I! is the sum of the components FI+Fi+FWJ Under these conditions, th movement of the movable contact I! is represented, in Fig. 2, by a curve 53. It will be observed that the utilization of the resistor R. does not appreciably alter the shape of the curve 53. The intersection of the curve 53 with the line B indicates the lowest value of current at which the contacts l5 and I1 engage to trip the circuit interrupter 9.

The force component Fw is dependent to some extent on the power factor at which the electrical system operates; whereas, the force components F1 and Pi are substantially independent of power factor. If the curve 5| of Fig. 2 represents unity power factor operationof the electrical system, changes in power factor may result in a change in shape of the curve, but the general principles are unchanged and the exact curve can be computed for any desired power factors.

Increase in the resistance value of the reto the load 1.

terupter 9 while the source I is supplying power Such an increase in-resistance results in an increase in the difference between the currents I1 and I2 and-consequently inithe value of the force component F1. Although the resistor R may be fixed in value in accordance with any desired operating condition, the relay conveniently may be provided with an adjustable resistor to permit adjustment of the performance of the relay. l

1 Since the relay is designed to handle appre- 'ciable fault currents, it may be desirable to incorporatesome protection for the bimetallic, elements. Such protection may be provided by designing the current transformer 35 .of Fig. 1 to saturate at a desired value of fault current, or by providing an overcurrent relay for shunting the bimetallic elements 2| and 23. Protection for the relay will be discussed further below.

In Fig. 3, the inverse time charactistics of the relay of Fig. 1 are illustrated. Abscissae represent the current 1; whereas, ordinates represent the time in seconds required for the relay to close its contacts l5 and i1.

Curves C and C show the forward tripping characteristics of the relay. The curve C represents the time required for the relay to close its contacts when the relay starts from a deenergized or no-load condition. A curve C illustrates the time required for the relay to close its contacts when the relay starts from a full load energized condition. Both of these curves. C and C, are for a forward fiow of power from the source I to the load 1. If some current intermediate no-load and full-load currents is flowing at the time an excessive current is applied to the load, the resulting curve will be disposed in a shaded area between the two curves C and C. Since such curves correspond quite closely to the heating characteristics of electrical equipment, they are quite satisfactory for relay operation.

Curve D represents the time required for the relay to close its contacts when the direction of power flow is from the load 1 to the source I. Curve D represents the relay performance when the relay starts from a deenergized or no-load condition. A curve D represents the performance of the relay when the relay starts from a normal full-load energization. When the relay starts from intermediate energizations, the correspondin curves fall in a shaded area between the two curves D and D. The differences between the curves D and D and between the curves C and C are due to the thermal lag of the relay. Such differences may be reduced by reducing the thermal lag of the relay.

If desired, the relay may be biased in a desired direction in any suitable manner. For example, load current may be passed through a heater adjacent one of the bimetalic elements for the purpose of biasing this element in accordance with load current. This will be discussed further below.

In order to decrease the spread between the no-load and full-load curves C and C or D and D, the relay may be designed to permit a slow transfer of heat between the bimetals. This tends to maintain the relay adjacent its neutral position and the relay responds properly to sudden faults. This modification may not be satisfactory for systems wherein fault or overload currents may increase slowly.

8 In Fig. 4, an electroresponsive control device [3a is associated with th electrical system which again is represented by the conductors 3 and 5. The circuit interrupter 9 and the tripping solenoid ll, together with the battery I9, also are illustrated in Fig. 4. The control device l3a includes, in effect, two relays 13b and I30. The relay l3b is similar to the corresponding relay of Fig. 1 and'includes the bimetallic elements 2| and 23 together with the associated contacts l5 and II which are employed for controlling the tripping of the circuit interrupter 9. The relay l3c is similar to the relay l3b, but includes bimetallic elements Ho and 23a which are'responsive to values of current larger than those which may be applied safely to the bimetallic elements 2| and 23. The elements 2|, 23, 2m and 23a all are connected in series across the secondary terminals of a current transformer 35a which corresponds to the current transformer 35 of Fig. 1. The resulting series circuit may be traced from one terminal of the secondary winding through a conductor 55, the bimetallic element Ma. a conductor 51, the bimetallic element 2|, a conductor 59, the bimetallic element 23, a conductor 6|, the bimetallic element 23a and a conductor 63 to the remaining terminal of the secondary winding of the current transformer.

In addition, the bimetallic elements are connected in two parallel arms across the secondary winding of a voltage transformer 45a which corresponds to the voltage transformer 45 of Fig. l. The parallel arms are located between a tap 39a on the secondary winding of the current transformer 35a and a terminal Ha which is connected to the conductor 59. It will be observed that the secondary windin of the voltage transformer 45a has one terminal connected to the tap 39a; whereas, the remaining terminal is connected to the terminal Ma through impedances Z and ZA. By studying Fig. 4. it will be observed that each of the relays I31) and I30 is energized in substantially the same manner discussed with reference to Fig. 1. In order to unbalanc the two parallel arms connected between the tap 39a and the terminal Ma, the conductor 63 may hav a resistance higher than that of the conductor 55. but it will be assumed that the tap 39a is displaced from the midpoint of the secondary winding of the current transformer. It will be assumed further that the direction of displacement is such that the current I1 flowin through the bimetallic elements Zia and 2| is greater in magnitude than the current In flowing through the bimetallic elements 23 and 2311. It will be understood that the relay I3b is substantially more sensitive than the relay I30 and may be designed to trip, for example, for a range of load current up to three times full load. For values of load currents above that for which the relay l3b is designed, shunts are established around the bimetallic elements 2| and 23 by operation of an overcurrent relay B1. The relay l3c thereupon operates over a further overcurrent range which may be, for example, of the order of three to ten times full load current.

The overcurrent relay 61 has an operating winding connected for energization from the secondary winding of a current transformer 69 which is associated with. the conductor 5. The relay 61 is designed to pick up and close its contacts 61a and 61b when the current flowing through the conductor 5 is above a desired value, such as three times full load current. Closure of the contacts of the relay 6'! shunts the biaseigcsrz 9 v metallic elements H and 23 and only the relay l'3c' remains energized for further operation. It will be noted that closure of the contacts of re lay 61 in efiect connects the conductors Hand 61' to a terminal H inter-mediate the two impedances Z and ZA. This'removes the impedance ZA from service andresults in an increase in the current supplied to the bimetallic elements 21a and l3'a by the voltage transformer 45a. Consequently, operation or the relay 6*! tends to compensate, tosorne extent, for the fall in voltage across the conductors 3. and which results from theflow o1 excessive current therethrough. Removal of the-impedance ZA from service may affect the values of the current components n and I2 somewhat. The impedances Z and Zn may be of any desired type and may have values selected to'provide the desired compensation;

In Figs. I and 4, bimetallic elements are shownwhichare energized or heated by current flowmg directly therethrouglr. I-f desired,'external heaters may be employed, orother electrore sponsiveunits may be employed which haveoutputs responsive to the squares of their energizations', as discussed in some detail in the aforesaid Johnson patent. For example, in Fig. 5, thermall'y responsive metallic bellows 81 and" 83 eachhave an end connected toa movable contact 85. The metallic bellows are heated respectively by resistors am and Bib. Each of the heatin resistor has 'an end connected to the terminal 4|. Consequently; the terminal 4| of Fig. 5 ma be connected to the tap 39 through the secondary winding 43 of'Eig; 1,, and the remaining ends of the resistors Sta and 81b may be connected to the terminals of the secondary winding 31 of Fig. I with the resistor R disposed in one of the connections in the manner discussed. with reference to Fig; 1. Since the operation of the device shown. in Fig. 5 otherwise is similar to that of the device of Fig. 1, and will be understood by reference to the Johnson patent, further dis cusslon thereof is believed to. be unnecessary. Thermally responsive metallic b'ellowsj'are dis closed" in Fig. 3 crime Johnson patent. In order to bias the control devices of Fig. 5', an auxiliary heating. resistor 81c i provided adjacent the bellows 83.. As previously pointed out, this resistor 8 lo may be energized in accordance with the load current of an associated. electrical system, or in are differentially connected in series to the sole- 1 noid= It. These thermocouples are disposedtobe heated respectively by the resistors Bid and 84 Although 110- battery need be employed with'the thermocouples, it may be desirable" to am plif-ythe output of the thermocoupl'esprior to the application thereof to the-solenoid ll. Since thelmod ification of Fig. 6 otherwise is similar to: that discussed for Fig. 5. and since the operation. of'the thermocouples is described witl i' reference to Fig. 4 of the aforesaid Johnson patent, further discussion of Fig. 6 is believed to be unnecessary.

In Fig. 7, magnetic devices 9! and 93 are provided in place of the bimetallic elements 2| and 23 of Fig. 1. Each of the magnetic devices includes an E-shaped magnetic structure em or 93a which has associated therewith a common magnetic armature 95. This armature carries the movable contact I1 for movement into and out of engagement with the contact l5 in the manner discussed with reference to Fig. 1. Each of the magnetic devices 9 and 93: has 'a coil 91b and 93b associated therewith for the pun-- pose; when energized, or urging the magneticv armature 95- toward the associated magnetic structure. Since the device of Fig. 7' otherwise operates in a manner similar to that discussed for Fig. l, and sincemagnetic devices of this'type: are discussed in the aforesaid Johnsonpatent, it is believed thatthe foregoing description there'- of sufli'ces'. i

Although the invention has been discussed-with reference to certain embodiments thereof, 'numerous modifications are possible. Therefore, the appended claims have been drafted to cover all such additional modifications which fall with in the spirit and scope of the invention We claim as our invention:

1. In an electroresponsive control device, a first electroresponsive unit'having an output propor tiona-l substantially to the square of the input to the unit, a second electroresponsive unit hav'-' ing' an output proportional substantially to the square of the input to the last-named unit. an element differentially connecting" the outputs of the el'ectroresponsive units to produce a resultant outputsubstantially equal to the di-lference betwe enthe outputs of said electroresponsive units, and a circuit electrically connectingsaid units" for first energizations in accordance with a first alternating quantity; said. units and the circuit having impedanc'es selected to provide" a ratio of said: energizations other than unity,'and circuit elements. electrically associated with said circuit forvectori'ally adding, to the first energizatibn or thefirst electroresponsive unit, a second energization proportional to a second alternating quantity and for vectorially subtracting from the second electroresponsive unit a second ener'gi'zae tion proportional to the second alternating quarrtity.

2.. In a. control device which is responsive to a function. of voltage quantity and a current quantity in an. alternating. electrical circuit, a pairv of. velectroresponsi've unit's responsive to electrical current supplied thereto, electrical circuit elements connecting, said] el'ectroresponsive units for. energizations respectively in accordance with thevector. sum and the vector difference oil said quantities, the impedances of. said units and the circuit. elements beihgsel'ected to provide a ratio or: the. portions of said energizations which are dependent. on a first one oi said quantities dif felling. substantially from unity, and translating means differentially. responsiveto the outputs of the; electroresponsive units; M r

In. an electroresponsive control' dei' ice', a pair of electroresponsive units each having alrie sponsedependeutonthe square ofelectricalf current. supplied. thereto... a circuit connecting said .electroresponsive. units in parallel for energizerti'onfrom a first. source of electrical energy and inlseries for encrgi'zat'ion from a secondsource of electrical energy, the parallel, arms of said circuit having diifercnt" impedan'ces', and translating means difterentially responsivegtoit'he outputs" of said electroresponsive units.

4. In an electroresponsive control device, a transformer having a primary winding and having a secondary winding provided with a tap intermediate the terminals of the secondary winding, a pair of electroresponsive units connected in a series circuit across said secondary winding, each of said electroresponsive units having an output dependent on the square of the energization thereof, said series circuit having a terminal intermediate the electroresponsive units, whereby the tap and the terminal constitute terminals of a parallel circuit having two arms each containing a separate one of the electroresponsive units, and translating means responsive differentially to the outputs of the electroresponsive units, said arms having different electrical impedances.

5. A device as defined in claim 1 wherein when said alternating quantities correspond to the voltage and current of an alternating current circuit the resultant output has a directional characteristic, said ratio being selected to provide a resultant output having a first directivity for a flow of power in the alternating current circuit in a first direction and for a flow of power above a predetermined value in the alternating current circuit in a second direction, the resultant output for theselected ratio having a second directivity for a flow of power below said predetermined value in the alternating current circuit in the second direction.

6. In an electroresponsive control device, a first electromotive unit having an output proportional substantially to the square of the input to the unit, a second electromotive unit having an output proportional substantially to the square of the input to the last-named unit, an element differentially connecting the outputs of the electromotive units to produce a resultant movement substantially proportional to the difference between the outputs of said electromotive units, and a circuit electrically connecting said units for first energizations in accordance with a first alternating quantity, the units and the circuit having impedances selected to provide a ratio of said energizations other than unity, and circuit elements electrically associated with said circuit for vectorially adding to the fiist energization of the first electroresponsive unit a second energization proportional to a second alternating quantity and for vectorially subtracting from the second electroresponsive unit a second energization proportional to the second alternating quantity, and an electrical switch operable in response to the resultant movement of said electromotive units in a predetermined direction 7. In an electrical relay system, a pair of operating units each having an output proportional to the square of the energization thereof, a pair of electrical relay contacts differentially responsive to the outputs of said operating units, a pair of conductors for carrying an alternating current when an alternating voltage is established thereacross, and means for energizing a first one of the operating units substantially in accordance with the vector sum of the voltage and the current of said conductors and for energizing a second one of the operating units substantially in accordance with the vector difference between the current and the voltage of said conductors, the operating units and the energizing means being proportioned to provide a ratio of the components of said energizations due to the current flowing in said conductors other than unity.

8. A device as claimed in claim 3 wherein said transformer having a primary winding and having a-secondary winding provided with a, tap intermediate the end turns of the secondary winding, a pair of electroresponsive units connected in a series circuit across said secondary,

winding, each of said electroresponsive units having an output dependent on the square of the energization thereof, said series circuit having a.

terminal intermediate the electroresponsive units, whereby the tap and the terminal constitute terminals of a parallel circuit having two arms each containing a separate one of the electroresponsive units, and translating means responsive differentially to the outputs of the electroresponsive units, said tap being substantially displaced from the electrical center of said secondary winding, andfrom the end turns of the secondarywinding.

10. In a relay system for an alternating electrical circuit, a relay unit having a directional element to be actuated in a first direction inresponse to a first course of alternating power flowing in the circuit and in a second direction in response to a reverse course of alternating power flowing in the circuit, said relay unit having voltage input means and current input means connected for energization in accordance with the alternating voltage and the alternating current respectively of the circuit, and modifying means for modifying said input means to actuate the directional element in a first direction in response to the first course of power flow in the alternating electrical circuit, said modifying means modifying the input means to actuate the directional element in a second direction in response to power flow in the alternating electrical circuit in the reverse course within a predetermined range, and said modifying means modifying the input means to actuate the directional means in the first direction in response to .a power flow in the alternating electrical. circuit in the reverse course outside of said predetermined range.

ROYAL C. BERGVALL.

EDWIN L. HARDER.

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

UNITED STATES PATENTS Number Bohn June 21, 1949

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