US1785718A - Protective system - Google Patents

Description

Dec. 16, 1930. s. L. BAUM 1,7

PROTECTIVE SYSTEM Filed July 16, 1928 Fig. 5.

Inventor: Se mouh L. Baum.

His Attor nqgf Patented Dec. 16, 1930 UNITED STATES PATENT OFFICE snvmoun LEOIPOLD BAUM, or NEW ROCHELLE, NEW YORK, nssrenon 'ro GENERAL ELECTRIC COMPANY, A conronarron or NEW YORK PROTECTIVE sYs'rnm Application filed July 16,

My invention relates to protective systems and particularly to systems for controlling the connections between two alternating current circuits so that they are disconnected from each other in response to predetermined abnormal conditions of power flow between said circuits and are connected togetherin response to a predetermined phase relation between the Voltages of the two circuits.

In certain types of electric circuits directional relay protection is desirable. By 011- rectional protection is meant such operation that the relay will operate upon reversal of the direction of power flow. Such protection, for example, would be desirable at the end of a feeder, connecting a generating station with a substation. In this case, as long as power flows toward the substation conditions are normal, but should power flow back from the substation the conditions would be abnormal and the relay should begin to function. Another place where such a relay is desirable is on a network switch which connects a bank of transformers to a secondary distribution grid in the streets. In this case the relay should operate and open the network switch, were power to flow from the low voltage mains in the street back into the transformers. In the case of such a relay, however, an additional function is concerned, namely, that of reclosing the network switch when conditions again become normal.

In all the above described cases it has been assumed that the relay is to operate upon mere reversal of power regardless of the amount of power involved. Usually, however, it is desirable to have the relay operate only when the reverse power exceeds a certain amount, so called reverse-power-overload protection.

This protectioncan not be given by an ordinary wattmeter type of reverse power relay for the following reason: When trounamed, the relay might fail to function prop- 1928. Serial No. 293,189.

ble develops on an electric system, it is often accompanied by an extreme drop in voltage or potential. But as'before stated, in relays of the wattmeter type, the torque on the disc is proportional to the product of voltage and current, whence it follows that a reduction in the voltage will materially decrease the operating torque on the disc of the relay, even though the current be very large due to a short circuit or other abnormal condition. In other words, when the relay isintended to operate there is grave danger that the actuating torque will be very small and therefore any opposing or restraining torque on the disc, such for instance as a spring, must be very light. Were. a heavy spring or other large mechanical torque to be used to restrain the disc, to secure the overload-response feature aboveerly under a short circuit with the usual accompanying drop in voltage. In practice, therefore, reverse power protection has hitherto been obtained with a wattmeter type relay, but the overload protection with an entirel difierent type of apparatus, the operating contacts of each of the two relays being then connected in series.

Furthermore a network relay, in addition to efiecting the opening of a network switch, also has to efiect the reclosing of the switch in response to the phase relation between the network voltage and the secondary voltage of the network transformer.

On object of my invention is to provide an improved arrangement of connections for such a control rela whereby it effects the opening of the switc i in response to minimum values of reverse power which vary directly with the voltage and efi'e'cts the closing of the switch when a desired phase relation exists between the voltages of the two circuits and whereby the trippin characteristic'of the relay does not inter are with the reclosing' characteristic of the relay.

My invention will be better understood from the following description, when taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Referring to the accompanying drawing Fig. 1 illustrates diagrammatically an arrangement of connections for a control relay embodying my invention, Fig. 2 is another arrangement of connections embodying my invention, and Figs. 3, land 5 illustrate other modifications of my invention.

Referring to Fig. 1, 1 and 2 represent two electric circuits which are arranged to be connected together by suitable switching means 3. The switching means 3 may be provided with any suitable closing and tripping means, examples of which are so well known in the art that it is deemed unnecessary to illustrate them in the drawing. For controlling the tripping means of switching means 3 so that it is opened inresponse to a flow of power between the circuits 1 and 2 in a predetermined direction, I provide a reverse power relay 4 of the induction wattmeter type which includes a voltage winding 5 connected across the circuit 1 and two current windings 6 and 7 which are respectivel energized in response to the currents owing through the two main contacts of the switchin g means 3 when closed. As shown the windings 6 and 7 are energized by the current transformers 8 and 9 respectively. The windings 5, 6 and 7 are so arranged on the magnetic structure of the relay that they exert a torque proportional to El cos 9, where E is the voltage, I the current and 6 the angle between E and I.

In order that the relay 4 may control the reclosin of the switching means 3 in response to the phase relation between the voltages of the circuits 1 and 2 when the switching means 3 is open, the relay is also provided with the phasing windings 10 and 11 which are respectively connected across the main terminals of the switching means 3 so that the windings are energized in response to the instantaneous voltage difierence between the two circuits 1 and 2. A suitable resistor such as a tungsten lamp 12 is connected in series with the phasing winding 10 and a similar resistor or lam 13 is connected in series with the phasing winding 11. The coils 5, 10 and 11 are so arranged on the magnetic structure of the relay 4 that the rela o erates in response to a predetermined p ase relation between the two voltages to effect the reelosing of the switching means 3.

Relays connected and arranged in the manner heretofore described have been used to control the operation of a network switch where it is desired to effect the opening of the switch in response to a relatively small power reversal; Such relay arrangements, however, cannot be used satisfactorily in places where it is desired to arrange the relay so that it has a relatively high reverse power setting because the operation of the relay is materially affected by changes in the voltage of the circuit. For example, under low voltage conditions, which are apt to occur under short-circuit conditions, the abnormal reverse current which is produced by the shortcircuit may not develop suflicient torque in the relay, due to the-low voltage, to cause the relay 'to operate in opposition to its normal biasing means to eiiect .the opening of the switching means 3.

In accordance with my invention I provide an arrangement whereby the relay 4 at normal voltage has a relatively high reverse power setting and whereby the amount of reverse power required to operate the relay decreases as the voltage of the interconnected circuits decreases. I accomplish this result by providing in opposition to the torque produced by the reverse power, a restraining torque which is proportional to the voltage of the interconnected circuits. Therefore, the lower the voltage, the smaller the torque produced by the reverse power has to be in order to operate the relay 4.

In the arrangement disclosed in Fig. 1, I obtain this restraining torque, which is proportional to the voltage of the circuits, by connecting the phasing coils 10 and 11, an adjustable impedance I l and the auxiliary contacts 15 on the switching means 3 in series across the circuit 2 when the switching means 3 is closed. Therefore, when the switching means 3 is closed and power is in the reverse direction the torque T on the movable element of therelay is T=KEI cos 6KaE where E is the voltage of the interconnected circuits, I is the current flowing between the circuits, 9 is the phase angle between E and I, K is a constant, and K is a constant dependent upon the phase angle between the currents in windings 5 and 10, 11.

By providing the adjustable impedance 1% in the circuit of the windings 10 and 11, it is possible to vary the phase angle between the current in the windings 10 and 11 and the current in the winding 5 so as to vary the value of K and, therefore, the reverse power setting of the relay. 1

The auxiliary contacts 15 on the switching means 3 are provided in the circuit of the windings 10 and 11 across the circuit 2 so that this circuit is opened when the switching means 8 is opened. Therefore. the voltage restraint produced by the windings 10 and 11 during the tripping operation of the relay has -no eiiect upon the reclosing characteristic of the relay.

In the modification shown in Fig. 2 I have shown my invention applied to another well known type of network relay in which the two lCU current windings 6 and 7 are not* only respectively connected across the secondary windings of the transformers 8 and 9 but are also respectively connected in series with the resistance lamps 12 and 13 across the main contacts of the switching means 3. In this modification the voltage restraint is produced by the windings 10 and 11 which, in series with the variable impedence 14 and the auxiliary contacts 15 on the switching means 3, are connected across the circuit 1.

With the particular relay connections shown in Fig. 2 the windings 6 and 7 function as the phasing windings and the windings 10 and 11 are deenergized when the switching means 3 is open.

In Figs. 3 and 4 I have shown other modifications of my invention in which a voltage restraint is obtained by energizing the current winding of the relay in response to the voltage of the circuit in addition to the current of the circuit. In order to simplify the disclosure the phasing connections of the relays have been omitted in these two figures.

In Fig. 3 the current winding 6, in addition.

to being connected across the secondary of the current transformer 8 is also connected in a series circuit with the variable impedance 14 and the auxiliary contacts 15 across the circuit 1 when the switching means 3 is closed.

In the modification shown in Fig. 4 both the voltage winding 5 and the current winding 6 are energized from the secondary of a potential transformer 20, the primary of which is connected across the circuit 1. In series with the winding 6 is connected the variable impedance 14:. The winding 6 is also connected across the secondary of the current transformer 8.

It will be observed that the same reverse power characteristics are obtained with the combined current-restraint winding shown in Figs. 3 and 4 as are obtained when the current windings and restraining windings are separate windings as shown in Figs. 1 and 2.

All of the preceding description applies specifically to a single phase type of relay. Similar constructions may, however, be used for polyphase relays, each phase being considered and. treated independently and having its own potential winding and restraining winding. Another and perhaps better method of utilizing the windings which are in the polyphase relay is to arrange the windings so that the potential winding of each phase will act with a restraining winding which is energized from another phase. Such an arrangement is shown in Fig. 5 which diagrammatically illustrates a polyphase relay 4 which has the voltage and current windings of each element associated with one phase in the manner shown in Fig. 2, and the restraining winding connected across a difierent phase. For example, the voltage winding 5 and current winding 6 of the upper element are energized respectively in response to the voltage and current of the phase X of the circuit 1 whereas the restraining coil 10 of the upper element, in series with auxiliary contacts 15 and a variable impedance 14, is connected across phase Z when the switch 3 is closed. In a similar manner the voltage winding 5 and current winding 6 of the middle element are energizedrespectively in response to the voltage and current of phase Y of the circuit and the restraining winding 10 of the middle element is connected across phase X whenthe switch 3 is closed, and the voltage winding5 and current winding 6 of the lower element are energized respectively in response to the voltage and current of phase Z of the circuit and the restraining winding 10 of the lower element is connected across phase Y when the switch 3 is closed. The advantage of this method over the first is the following: In the first method if the voltage on any one phase, such for example as on phase X only, drops to zero due to a short circuit, then the restraining torque is reduced to two-thirds of its normal value. In the second method, however, the two restraining coils are aflt'ected and the torque is reduced to one-third of its normal value, thereby making the relay correspondingly more sensitive.

Referringonce more to the above equation T KEI cos 9 KaE it will be observed that, with a constant current, the operating torque on the disc will increase with a decrease in voltage within certain limits. In other words, in the case of a short circuit, with a severe voltage drop, the nearer the fault, the faster the relay will operate. This gives the relay impedance characteristics and if these relays are placed at different points along the feeder, the one nearest the trouble will always be the first to respond.

My device thus has the following advantages and points of novelty:

1. The relay combines overload current and directional current response in a single disc type. which operates as rapidly or even more rapidly at reduced potential than at full voltage.

2. The fact that the restraining coilis energized only while the main'switch is closed allows the characteristics mentioned above to be combined with normal characteristics of a network relay for closing conditions.

3. I have provided arelay wherein the speed of action is proportional directly to the current and inversely to the voltage, and having a single disc and a single set of contacts,

that is, a relay operating in response to the impedance drop or ahmic drop without requiring any additional apparatus, such as coils, plungers and the like.

4. The possibilityof giving an ordinary wattmeter type induction relay any of the above described characteristics by connecting the current coil so that it is energized in accordance with both the current and the volta e of the circuit, as shown for example in Figs. 3 and 4.

5. Any of the above characteristics may be embodied in a polyphase relay as well as in a single phase type.

While I have, in accordance with the patent statutes, shown and described several em-.

bodiments of my invention, other changes and modifications will be obvious tothose skilled in the art, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

I claim:

1. In combination, two electric circuits, a switch connecting said circuits, and a control relay responsive to a minimum reverse power value which varies with the volta e of the interconnected circuits when said switch is closed and responsive to the phase relation between the voltages of said circuits when said switch is open including means controlled by said switch for producing a restraining torque in said relay which circuits when said switch-is open including said circuits when said switch 18 open includtwo windings arranged to produce a restraining torque which varies with the voltage of said circuits, and contacts in the circuit of one of said windings controlled by said switch so that said windings produce said restraining torque only when said switch is closed.

3. In combination, two electric circuits, a switch connecting said circuits, and a combined power directional and phasing relayresponsive to power flow between said circuits in a predetermined direction when said 1 switch is closed and responsive to a predetermined phase relation between the voltages of ing a voltage winding, a current winding, a restraining winding, a circuit for said restraining winding across one of said electric circuits, and contacts in the circuit of said restraining winding controlled by said switch.

4. In combination, two electric circuits, a switch connecting said circuits, and a combined power directional and phasing relay responsive to power flow between said circuits in a predetermined direction when said switch is closed and responsive to a predetermined phase relation between the voltages of said circuits when said switch is open including a voltage winding responsive to the voltage of one of said circuits, a current winding responsive to the current flowing through said switch, a phase winding responsive to the voltage diii'erence between said circuits when said switch is open, and means responsive to the closing of said switch for connecting said phasing winding across one of said circuits whereby said phasing winding coperates with said voltage winding to produce a restraining torque which carries directly with the voltage of said one of said circuita,

5. In combination, two polyphase circuits, :1 switch connecting said circuits, and a polyphase relay responsive to a minimum reverse power value which varies with the voltage of one of said circuits when said switch is closed and responsive to the phase relation between the voltages of the corresponding phases of said circuits when said switch is open including an operating element associated with each phase and having a voltage winding responsive to the voltage of the associated phase, a current winding responsive to the current in the associated phase, and a restraining winding responsive to the voltage of another phase.

6. In combination, a polyphase circuit, and a polyphase relay responsive to a minimum reverse 'power value which varies with the voltage of the said circuit including coopcrating voltage windings respectively energized from different phases of said circuit for producing a restraining torque in opposition to the torque produced by a reversal of power.

7. In combination, a polyphase circuit, and a polyphase relay responsive to a minimum reverse power value which varies with the voltage of said circuit including a plurality of reverse power elementsrespectively associated with difi'erent phases of said circuit, each element including a voltage winding responsive to the voltage of the associated phase, a current winding responsive to the current in the associated phase and a re stfi-aining winding energized from another p ase.

8. In combination, a polyphase circuit and a poly phase reverse power relay connected in said'circuit and including avplura'lity' of torque producing means respectively energized in response to the power in different phases of said circuit, each of said torque producing means including two voltage windings respectively responsive to the voltages of difierent phases of said circuit whereby difi'erent values of reverse power are required 'to effect the operation of said rela'y when the voltage of said circuit varies.

9. In combination, two polyphase circuits, a switch connecting said circuits and a polyphase relay responsive to the power flow between said circuits when said switch is closed and to a predetermined phase relation between'corresponding phase voltages of said Patent No. 1,785,718.

hereto. I

SEYMOUR L. BAUM.

CERTIFICATE OF CORRECTION.

Granted December 16, 1930, to

SEYMOUR LEOPOLD BAUM.

It is hereby certified that error appears in-the printed specification of the above numbered patent requiring correction as follows: Page 1, line 80, for the word "On" read'One; page 3, line [25, claim 3, for "ahmic" read ohmic; page 4, line 68, claim 4, for the word "phase" read phasing, and line 75, same claim, for the word"'carries" read varies; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office. v

Signed and sealed this 13th day of January, A. D. 1931.

M. J. Moore,

(Seal) Acting Commissioner of Patents.

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