US2323776A - Electrical protective system - Google Patents

Description

July 6, 1943. JOHNSON 2,323,776

ELECTRICAL PROTECTIVE SYSTEM Filed April 11, 1941 s Sheets-Sheet 1 AQAAAAAAA II' 'IIY Ill-Ill.

VIII IYVV III .llllllll IIIIIII WITNESSES: INVENTOR 655%. [7090 2 Johnson.

Patented July 6, 1943 ELECTRICAL PROTECTIVE SYSTEM Floyd D. Johnson, Forest Hills, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 11, 1941, Serial No. 388,080

9 Claims.

This invention relates to electrical control systems, and it has particular relation to directional relays for protecting electrical circuits and apparatus.

Conventional prior art directional relays generally employ rotatively mounted armatures for operating control contacts. For example, induction type directional relays are extensively employed. Although such relays have excellent characteristics, the art has numerous applications wherein a simple, sturdy and inexpensive directional relay is desired.

In accordance with the invention a directional control device or relay is provided which employs a pair of simple translating or operating means. This means may take the form of a thermally responsive device such as a bimetallic thermostat, metallic bellows, or thermocouple. As a further example, the means may take the form of a magnetic device operating by magnetic attraction or repulsion.

lwo translating or operating means are disposed with their outputs in opposition to each other. Circuit controlling means such as electrical contacts are associated with the translating or operating means to be actuated differentially thereby.

One of the operating means is designed for ener ization normally in accordance with the sum of two quantities. For example, if the relay is designed to respond to the direction of energy flow in an electrical circuit, the translating or operating means is energized in accordance with the sum of the voltage and current present in the circuit. When the energy flow in the circuit reverses, the translating or operating means then is energized in accordance with the difierence between the voltage and current present in the circuit. Consequently, the translating or operating means may be designed to discriminate between the two directions of energy flow.

When one of the translating or operating means is normally energized in accordance with the sum of two quantities, the remaining means preferably is energized in accordance with the differ ence between the same quantities. With such normal energizations of the two means, when energy flow reverses in the associated electrical circuit in the case of a directional relay, the sum and difference energizations for the two means are interchanged. This greatly increases the sensitivity and effectiveness of the relay.

It is, therefore, an object of the invention to provide an electrical directional device having a simple and sturdy design.

It is a further object of the invention to provide a directional element which normally is energized in accordance with the sum of two quantities and which under abnormal conditions is energized in accordance with the difference between the same quantities.

It is a further object of the invention to provide a control device differentially responsive to the output of opposed operating means, which means are normally energized, respectively, in accordance with the sum and difference of two quantities.

It is a still further object of the invention to provide a directional relay system having two opposed thermally responsive elements normally energized, respectively, in accordance with the sum and the difierence of two quantities.

It is a still further object of the invention to provide a directional relay system having two opposed magnetic responsive elements normally energized, respectively, in accordance with the sum and the diiierence of two quantities.

Other objects of the invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which:

Figure 1 is a schematic view of an electrical system embodying the invention; and

Figs. 2 to 9 are schematic views showing modifications of the system disclosed in Fig. 1.

Referring to the drawings, Figure 1 shows an alternating current electrical system including a circuit l for supplying electrical energy from a suitable source such as a transformer 2 to a load. Although the system may vary appreciably and may be a polyphase system, for the purpose of illustration, the circuit l is a single phase circuit having the midpoint of the secondary Winding of the transformer 2 grounded. For the purpose of controlling the connection of the load to the transformer 2 a circuit breaker 3 is provided. This circuit breaker includes a tripping latch 3a and a conventional tripping solenoid 4 having an energizing battery 5 associated therewith.

In order to control the tripping of the circuit breaker 3 in accordance with the direction of energy flow in the circuit l, a directional relay 6 is provided. This directional relay includes circuit controlling means such as a movable contact l and a fixed contact 8. Movement of the movable contact I is effected by a pair of translating or operating means 9 and I8, which in Fig. 1 are represented as bimetallic thermostats. Each of these bimetallic thermostats has one end fixed to a stationary common support II. A

bridge 52 connects the free ends of the thermostats and carries the movable contact I.

The bimetallic thermostats 9 and ID are de signed to move in opposition to each other as they are heated. This movement may be either away from or towards each other, but in the specific example of Fig. l the movements of the thermofacilitating flexure of the bimetallic thermostats.

The bimetallic thermostats 9-and Hi may be heated in various ways. If desired, separate heaters l3 and it may be provided for the respective bimetallic thermostats.

As previously explained, it is desired that the heaters be energized respectively in accordance with the sum of, and difference between, the same quantities under normal operating conditions of the circuit l. Such energization may be provided by several constructions. In the embodiment of Fig. l the heaters l3 and M are connected with the secondary winding of a current transformer iii in a series circuit. If the current transformer I5 is associated with one of the conductors of the circuit l, a current component I1 traverses both of the heaters 33 and Hi, which is substantially proportional to the current I flowing in the circuit 1. For the purpose of illustration, the current component If at a predetermined point in the wave of voltage applied to the circuit l is assumed to flow upwardly-in the-heater l3 and downwardly in the heater Since the system of Fig. l is an alternati. g current system the various current and voltage quantities may be treated as vector quantities.

Each of the heaters 53 and id also is energized by an additional. current component Ie which is proportional to thevoltage E of circuit I. In the specific embodiment of Fig. 1 such additional energization is provided by connecting a conductor of the circuit l to a tap llia centrally disposed on the secondary winding of the current transformer l5. By inspection of Fig. 1, it will be noted that with respect to the voltage to ground E of the circuit I the two heaters l3 and i6 are connected in parallel to a common resistor it. This current component Ie at the selected point of the voltage wave is assumed to flow downward in eachof the heaters l3 and it.

Since the current 21s flows through the centrally disposed tap on the secondary winding of the current transformer E5, the current divides equally and flows in opposite directions through the two halves of the secondary winding. For this reason the current transformer offers substantially no inductive reactance to the current Is. In view of the fact that the heaters I3 and i and the resistor l6 offer substantially pure resistance to the flow of the current Ie, it follows that the current Is is substantially in phase with the voltage E.

From the foregoing discussion it will be appreciated that for normal unity power factor conditions in the circuit I, the component currents brief mathematical analysis thereof.

Ia and Ii add in the heater l4 and subtract in the heater l3, Consequently, the resultant force exerted by the two bimetallic thermostats 9 and it operates to move the movable contact 7 away from the contact 8.

If the direction of energy flow in the circuit l reverses and the power factor remains at unity, the component currents It and I1 dd in the heater l3 and subtract in the heater it. There- .fore, the resultant force operates to move the movable contact I into engagement with the fixed contact 8 to trip the circuit breaker 3.

The performance of the system illustrated in Fig. 1 may be understood more clearly from a In the following analysis the line-to-ground voltage E is employed as a reference for phase angle relationships. Since an alternating current system is involved, the following relationships hold.

Values for the component currents Ie and Ii may be indicated as follows:

11 (cos 6+ sin 0)=0E 5 wherein the quantities in parenthesis represent real and reactive current components, respectively:

Ie+Ii= cE+lsI cos a) +5001 sin 0) 3) The difference of the component currents in the remaining heater is: V

As previously pointed out, the thermostats oppose each other. Consequently, the resultant force operating on the thermostat assembly may be represented by the dilference between Equations 5 and 6,-or the resultant force From Equation 8 it is clear that the resultant force operating'on the contacts is proportional to the power flowing in theelectrical circuit as representedby the wellkncwn expression EI cos 0.

For angles between 270 and. 90, cos 0 is positive. Values of cos 6 for angles between 90 and 270 are negative. Consequently the resultant force F varies in sign in-accordance with the direction of energy flow in the electrical circuit, and the direction of movement of the contact also is dependent on the direction of energy flow.

Although only one directional relay '6 is disclosed in Fig. 1, as many additional relays may be employed as are required. For example, a pair of movable contacts Ia and 8a are shown connected in parallel with the contacts I and 8. Closure of the additional contacts Ia and 811 also operates to complete a tripping circuit for the tripping solenoid 4. These contacts Ia and 8a may be the movable and fixed contacts, respectively, of a directional relay similar to the relay 6 and associated with the remaining conductor of the circuit I.

If desired, an auxiliary contact Il may be associated with the relay 6 for completing a control circuit when energy flowing in the normal direction in the circuit I exceeds a predetermined value. sive energy flowing in a normal direction actuates the movable contact "I into engagement with the fixed contact II to complete a tripping circuit for the tripping solenoid 4.

In Fig. 2 a directional device 6a is disclosed which corresponds to the directional relay 6 of Fig. 1. One of the bimetallic thermostats 9 of the device 6a is positioned to engage directly the tripping latch 3a of the circuit breaker 3. From an inspection of Fig. 2 it will be noted that no 3 contacts are required.

Fig. 2 also discloses a modified method of heating the bimetallic elements 9 and IU of the directional device to. These bimetallic elements are connected directly in a series circuit with the secondary of the transformer I5. The free ends of the bimetallic thermostats are bridged by a conductor I8 through which the bimetallic thermostats are connected to the resistor I'B. Since the bimetallic thermostats inherently have electrical resistance, current flowing therethrough, operates to heat the thermostats directly, thereby dispensing with the heaters I3 and I4 provided in Fig. 1. Since the system disclosed in Fig. 2 otherwise conforms to that shown in Fig. 1, it is believed that the operation thereof i clear.

The embodiment 61) illustrated in Fig. 3 is similar to that of Fig. 1 except for the replacement of the bimetallic thermostats 9 and I0 by flexible metallic bellows 9a and Illa. One end of each of the bellows is attached to a fixed support Ho. The remaining ends of the bellows are connected to a common movable contact Ia which operates to bridge fixed contacts 8a. or I Ia. Bridging of the contacts 8a results in the completion of a tripping circuit for the tripping solenoid 4.

Thermally responsive metallic bellows are well known in the art. Such bellows may contain a fluid having a temperature coefficient of expansion or a vapor pressure which varies appreciably with temperature. Consequently, when the bellows lilo, is heated, the movable contact la is urged into engagement with the fixed contacts Ila. Similarly, when the bellows 9a is heated the movable contact la is urged into engagement with the fixed contacts 8a. Since the system of Fig. 3 otherwise corresponds to that of Fig. 1, it is believed that the operation thereof will be understood from the foregoing description.

As previously pointed out in discussing Fig. 2, it is possible to eliminate all contacts from the directional device. A further modification wherein contacts maybe eliminated is depicted in Fig.

In the specific example of Fig. 1, exces- 4. In Fig. 4 a directional device 60 is disclosed wherein the component parts are similar to those of Fig. 1 except for a substitution of thermocouples 9b and Iiib for the bimetallic thermostats 9 and II As well understood in the art, a thermocouple has a direct current output which varies in accordance with the temperature to which the thermocouple is heated. In Fig. 4 the thermocouples 9b and Illb are heated, respectively, by the heaters I3 and I4. The outputs of the thermocouples ab and lIlb are connected in opposition for the purpose of controlling a tripping solenoid 4a which is polarized to respond to a predetermined polarity of the resultant thermocouple output. Consequently, the tripping solenoid 4a. is energized in accordance with the difierence between the outputs of the thermocou ples 9b and IE1). If desired, an amplifier I9 may be inserted between the thermocouples and the tripping solenoid M for the purpose of amplifying the resultant output of the thermocouples.

In certain applications it may be undesirable to provide a centrally disposed tap for the secondary winding of the current transformer I5. In such applications the modifications illustrated in Fig. 5 may be employed. The only difference between the relay 6d disclosed in Fig. 5 and that shown in Fig. 1 resides in the path offered for the current component Ie. It will be noted that one terminal of the secondary winding of the current transformer I5 is connected through a conduotor 26 to one conductor of the circuit I. In addition, an auxiliary heater 2| is inserted between the resistor I6 and the heaters I3 and I4.

3 This auxiliary heater is positioned to heat the bimetallic thermostat 9. Tracing the flow of the current components Ia and Ii, it will be noted that the component Ii flows through the heaters I3 and I4 in the same manner as in Fig. 1. However, the current component Ie now flows from the conductor 20 through the heater I4, the auxiliary heater 2! and the resistor It to ground. Since separate heaters I3 and 2 I, associated with the bimetallic thermostat 9, are provided for the current components, it follows that the resultant heating efiect of the current components on the bimetallic thermostat 9 must be the same regardless of the direction of energy flow in the circuit I. Therefore, the only discrimination between the directions of energy flow in the circuit I is that provided by the heater I4 wherein the current components Ie and Ii either add or subtract, depending upon the direction of energy flow. Although this energy responsive discrimination may be employed for controlling the circuit breaker 3, the relay 6d of Fig. 5 is not as sensitive as the relay 6 of Fig. 1.

In the previous discussion, it is pointed out that the methods for energizing the directional relay or device may vary appreciably. A further variation is disclosed in Fig. 6. In this figure the relay 6 of Fig. 1 is employed for controlling the circuit breaker 3. By inspection of the circuit connections, it will be noted that the heaters I3 and I4 of Fig. 6 are connected in series with the secondary winding of a voltage transformer 22. The primary of the voltage transformer 22 is connected across the circuit I. One conductor of the circuit I is connected to a centrally disposed tap 22a on the secondary winding of the voltage transformer 22. Current flowing in this conductor divides between the two halves of the secondary winding and flows through the heaters I3 and I4 before reentering the circuit I through a conductor 23. In certain cases it may be de- 'sirable to supply this current to the heaters through. a current transformer (not shown) associated with the circuit vlas well known in the art.

The direction of flow of the current components Ie and Ii is shown in Fig. 6 for a predetermined point on thevoltage wave. It will be noted that the current component Ie flows. downwardly in one of the heaters .Hi and upwardly in the remaining heater 53, whereas the..current component Ii flows downwardly in each of the heaters. Consequently, the current components add in one of the heaters It and subtract in the remaining heater it. If the direction of energy flow in the circuit l reverses, the current components Ie and Ii add in the heater l3 and subtract in the heater it. The analysis presented for Fig. 1 also applies fcr Fig. 6.

In the modifications thus far described the translating or operating means have taken the form of thermally responsive devices, such as bimetallic thermostats, metallic bellows, or thermocouples. It is also possible to employ magnetic devices for this purpose. Such a device is illustrated in Fig. 7.

Referring to Fig. '7, a directional relay tie is disclosed which corresponds to the relay 6 of Fig. 1 except for the replacement of the bimetallic thermostats 9 and It by magnetic devices 90 and I and the replacement of heaters i3 and i4 by energizing windings iila and lea. From an inspection of Fig. 7 it will be observed that each of the magnetic devices 90 and I00 includes a projecting pole element'i' surrounded by one of the energizing windings and includes magnetic return paths 2.5. A common armature structure 28 is associated with the magnetic devices 9c and 40c and has a first armature portion 21 extending to a point adjacent the pole element 2 of the magnetic device 9c and a second armature portion 28 extending to .a point adjacent the pole element 24 of the magnetic device 500. The armature structure 25 is reciprocable relative to the magnetic devices 90 and 100. The movable contact I is carried by the armature structure 28 on a pin 29 for movement into and out of engagement withthe fixed contact 8.

Normally the armature structure 26 is biased by means of a spring 30 against a fixed stop 3|. The purpose of the stop 3! is to position the armature structure symmetrically relative to the magnetic devices to and ltc, with the same gap present between each of the pole elements 24 and the armature structure 26. The provision of equal gaps assists in maintaining equal impedances for the energizing windings i3a and lea during normal conditions of operation of the circuit I. A predetermined relationship between the impedances of the windings l3a and I ia is desirable in order to assure a predetermined division of the current component Ie therebetween.

Each of the magnetic devices when energized urges the armature structure 26 in the direction indicated by an associated arrow 0 or d. If the contacts 1 and 8 are to be disengaged under normal operating conditions of the circuit l, the current components Ie and I1 should add in the energizing winding i311, and should subtract in the energizing winding I la. This addition and subtraction is indicated by arrows in Fig. 7 which represent an instantaneous direction of flow for the current components Ie and Ii.

Since the operation of the relay 6c of Fig. 7 is similar otherwise to that of the relay 6 of Fig.

nated soft iron.

In certain cases it may be desirable to insulate the path of the current component Ie from that of the current component Ii. Fig. 8 discloses a relay 5] wherein such insulation is provided. This relay corresponds closely to that of Fig. 7 but includes an auxiliary energizing winding I31) and Mb on each of the magnetic devices and I00. The current component Iris supplied to the energizing windings l3a and Main the same manner as that disclosed for Fig. 7. In order to insulate the path for the current component Ii from that of the current component Ie, the current component Ie is supplied only to the auxiliary energizing windings ltb and Mb. To this end a path is established for the current component Ie from a conductor of the circuit I through a conductor 34, the auxiliary windings Mb and 5317, a conductor 35, and the resistor I 6 to ground. From an inspection of Fig. 8 it will be noted that the auxiliary windings i319 and MD are energized in opposite directions by the current component Ie. These directions are so selected that under normal operating conditions the magnetic fluxes produced by the current components Ie and Ii add in the magnetic device Sc and subtract in the 'magnetic device 00. Consequently, the operation of the relay 6 is substantially similar to that of the relay fie despite the fact that the paths for the current components I9 and Ii are electrically insulated from ach other. Instead of the vector addition and subtraction of current components provided by the relay of Fig. the relay 6 provides vector addition and subtraction of magnetic fluxes.

It will be noted that the construction shown in Fig. 8 eliminates the centrally disposed tap from the current transformer l5. A further modification wherein this tap is eliminated is disclosed in Fig. 9.

The system shown in Fig. 9 is substantially similar to that illustrated in Fig. 7 except for the provision of a winding extension I30 for the wind- ,ing [3a. The path for the current component Ii remains substantially unchanged, this current flowing from the current transformer [5 through the energizing windings i311 and I ia in series. The path for the current component Is is some- .what modified. Th s path may be traced from one conductor of the circuit; I through a conductor 32, the energizing winding Me, a con- .ductor 33, the winding extension H30, and the re 'sistor I6 to ground. Under normal conditions or operation the magnetic fluxes produced by the current components Ii and Ie add in the magnetic device 90 and subtract in the magnetic devic lflc. If the d rection of energy flow in the circuit I reverses from the normal direction, the magnetic fiuXes then add in the magnetic device I Go and subtract in the magnetic device 90, thereby urging the movable contact I into engagement with the fixed contact 8. Therefore, the operation of the relay v(5g disclosed in Fig. 9 is substantially similar to that of the relay 6e and 6 of Figs. '7 and 8.

Although circuit connections for the contacts I and 8 of Figs. '7, 8, and 9 and cooperating controlled elements for the relays have been omitted for simplicity, it is to be understood that these contac s or cooperating controlled elements for the relays may be employed for any control operation such as that illustrated in Fig. 1 or 2.

In the translating or operating means herein referred to, it is desirable that the output or force developed by the means be proportional to the square of the resultant current employed for energization of the means. Both the thermoresponsive and magnetic types herein disclosed provide such a relationship of output to current.

Although the invention has been described with reference to certain specific embodiments thereof, numerous modifications thereof are possible.

Therefore, the invention is to be restricted only i by the appended claims.

I claim as my invention:

1. In an electrical protective system for an electrical circuit, means responsive to the relationship of a first quantity in said electrical circuit to a second quantity therein, comprising circuit control means, a pair of thermoresponsive operating means, means differentially responsive to said operating means for actuating said circuit control means, and select ve energizing means dependent on the relationship of said quantities for selectively energizing either of said operating means in accordance with the sum of said quantities, said energizing means being effective for energizing the remaining operating means in accordauce with the difference or said quantities.

2. In an electrical protective system for an electrical circuit, directional means controlled by the sum quantity and difference quantity of voltage and current present in said system, comprising circuit control means, a plurality of therrnoresponsive operating means, means differentially relating said operating means for actuating said circuit control means, and energizing means selectively controlled by the direction of energy flow in said circuit for selectively energizing a first one of said operating means in accordance with either of said quantities, said energizing means including means for energizing a second on of said operating means selectively in accordance with the remaining one of said quantities.

3. In an alternating current system, a feeder circuit, a load circuit for receiving energy from said feeder circuit, and coupling means for coupling said load circuit to said feeder circuit, said coupling means including a circuit breaker for connecting and disconnecting said circuits, a Winding, means for inducing in said Winding a voltage controlled by the current flowing in said feeder circuit, a pair of translating means having an output proportional to the square of their energization, means connecting said translating means in series with said winding, first means for energizing sa d translating means in parallel in accordance with voltage present on the feeder circuit side of said circuit breaker, each of said translating mean being energized in accordance with the vector resultant of currents supplied by said winding and said first means, and control means differentially responsive to the outputs of said translating means for tripping said circuit breaker.

4. In an electrical protective system for an electrical circuit, directional means controlled by the resultant sum quantity and difference quantity of voltage and current present in said system, comprising circuit control means, a pair of thermally responsive operating means, means diiferentially relating said operating means for actuating said circuit control means, and energizing means selectively controlled by the direction of energy flow in said circuit for selectively heating a first one of said operating means in accordance with the square of either of said quantities, said energizing means including means for heating a second one of said operating means in accordance with the square of the remaining one of said quantities.

5. In an electrical protective system for an electrical. circuit having a voltage quantity and a current quantity therein, an electrical path having a pair of arms, means for passing through said arms in series a current dependent on a first one of said quantities, -ns for passing through said arms in parallel, a current dependent on a second one of said quantities, and thermoresponsive means 1y to the squares of the resultant cur, ...versing said arms for controlling an electrical circuit.

6. In an electrical protective syst m. for an electrical circuit having a voltage quantity and a current quantity therein, an electrical path having a pair of arms, means for through said arms in series a current dependent on a first one of said quantities, means for passing" through said arms in parallel a on cut on a second one of said quan thermally responsive device connected for ergization in accordance with th resultan our traversing a first one of said a second the:- mally responsive device connected for one" tion in accordance with the resuitant current traversing a second one of said arms, and means difierentially responsive to the outputs of said devices for controlling an electrical circuit.

'7. In a directional relay system for electrical circuit having a voltage quantity and current quantity therein, a transformer having its primary winding connected. for energizer-tion in accordance with a first one of said qua-ht.- s, an electrical path having two ar .5 connected in series with the secondary Wl'fldlof said transformer. means for en gizing arms par allel in accordance v. a second one of quantities, translating means for developing an output controlled by the resultant current flowin through a first one of said arms, translating means for developing output controlled by the resultant current flowing through a second one of said arms, and circuit control means elfferentially responsive to said outputs.

8. a directional relay system for electrical circuit having a voltage quanti current quantity therein, a transformer having a primary winding connector. for energiz 1' accordance with a first one of said uantiand having a secondary Winding provid d a centrally disposed tap, a pair of thermaliy r sponsive motive devices, a pair of contacts disposed for actuation by said motive devices, a first one of said devices being effective when heated for moving said contacts together, and a second one of said devices being effective when heated for opposing said motion of said contacts, means connecting said thermally responsive de vices with said secondary in a series circuit for energization therefrom, and means for energizing said thermally responsive devices in parallel in accordance with a second one of said quantities, said last named means including a connection to said centrally disposed tap.

9. In an electrical protective system for an electrical circuit, directional means controlled by the sum quantity and difference quantity of voltage-and current present in said system, comprising icircuit control means, a plurality of operating means, means differentially relating said operating means for actuating said circuit control means, and energizing means selectively controlled by the direction of energy flow in said circuit for selectively energizing a first one of said operating means in accordance with either of said quantities, said energizing means including'means for energizing a second one of said operating means in accordance with said sum quantity.

FLOYD D. JOHNSON.

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