US2191334A - Protective arrangement - Google Patents

Description

Feb. 20, 1940.

A. ARNOLD 2,191,334

PROTECTIVE ARRANGEMENT Filed Feb. 24, 1958 Fig. I.

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0 2 4 6 6 l0 /2 Z J 4 TIME OHMS Inventor:

August, Arnf ld Hi s Attorney,

' relays.

Patented Feb. 20, 1940 PATENT OFFICE PROTECTIVE ARRANGEMENT August Arnold, Brussels, Belgium, assignor to General Electric Company, a corporation of New York Application February 24, 1938, Serial No. 192,369 In Germany March 3, 1937 6 Claims.

My invention relates to improvements in protective arrangements for electric systems and more particularly protective arrangements which embody so-called distance or ohmic responsive One object of my invention is to provide an arrangement for establishing a time-distance operating characteristic which is dependent on the initial value of the fault voltage whereby to obtain a response more nearly independent of lo subsequent changes in circuit conditions during the fault. This and other objects of my invention will appear in more detail hereinafter.

In ohmic responsive or distance relays there is sometimes used a diiferential system which if; consists of a balance-beam at the ends of which forces dependent on a current and a voltage of the circuit are effective. At certain values of the ratio of voltage to current, the beam is tilted in a direction to close the relay contact. In order 20 to obtain a time dependent control, the voltage effective on the relay may be decreased by a time element device which connects an increasing amount of resistance into the circuit of the voltage winding. A relay so built has the dis- 25 advantages of complicated construction, high cost, and trouble likely to arise in the time element which may be, for example, a clockwork driven by a motor. In consequence of this, the desired operation of the relay may be upset.

30 In accordance with my invention, I eliminate these disadvantages by avoiding the use of a clockwork and the inherent complications in switching devices associated therewith and in place of such arrangements use an electrostatic time lag feature. In one embodiment of my invention, I obtain the desired time dependency on the voltage and current ratio by connecting, on the occurrence of a fault, in circuit with the voltage coil of the differential system a capaci- 40 tance and also disconnecting the voltage coil from the circuit being protected.

My invention will be better understood from the following description when considered in connection with the accompanying drawing, and its 45 scope will be pointed out in the appended claims.

In the accompanying drawing Fig. 1 illustrates diagrammatically an embodiment of my invention and Figs. 2 and 3 are characteristic curves explanatory of my invention.

50 In the embodiment of my invention shown in Fig. l, I have chosen for illustration an ohmic responsive relay comprising a balance beam I one end of which carries an armature 2. This is arranged to be excited by a current coil 3 which 55 is connected in series relation with the line or circuit 4 to be protected. On the other end of the beam I is an armature 5 which is arranged to be excited by a voltage coil 6. This coil is connected to be energized in accordance with a voltage of the circuit 4. For this purpose, it may 5 be connected across the bus I to which the circuit E is connected through suitable means such as a latch-closed circuit breaker 8. As shown, the circuit breaker 8 is provided with a trip coil 9 and an auxiliary switch Ill in circuit therewith, the 10 switch it being closed when the circuit breaker is closed and opened when the circuit breaker is opened- In order to make certain that the ohmic responsive relay operates in dependence upon the ratio of initial fault voltage to fault current so as to insure the desired time action response,

I arrange to have a capacitance ll connected in circuit with the voltage winding 6 upon the occurrence of a fault and to disconnect the voltage Winding from the bus 'I. For this purpose any suitable fault detector or fault responsive means such for example as an overcurrent relay l2 having its winding l3 connected in series relation with the circuit 4 may be employed. For the best operation the fault responsive means I2 is a quickly acting relay. As shown, the relay 12 controls normally closed contacts M in the circuit of the voltage coil 6 and normally open contacts [5 in series relation with the voltage coil 6 and the condenser H. Contact controlling members It and H on the fault responsive relay i2 are preferably so arranged as to insure a definite closing of the contacts l5 before the opening of the contacts M. A preferably adjustable resistance l8 may be connected in parallel with the condenser H to control the time constant of the voltage coil and condenser circuit.

In case of a fault on the line 4, the voltage on the coil 6 quickly drops to its initial fault value. Shortly thereafter, the fault responsive relay [2 comes into operation in consequence of the existence of the abnormal conditions to which it responds, excess current in the case illustrated, and operates to close the contacts IS. The voltage coil 5 is thereby connected in circuit with the capacitance H and the resistance I8. Very quickly thereafter, the contacts I4 are opened to disconnect the voltage coil 6 from the bus 1. Consequently, the voltage on the voltage coil 6 decreases in accordance with the time constant of the circuit including the coil 6, the condenser H and the resistance l8. This discharge curve is illustrated graphically in Fig. 2. The characteristic curve or curve of response of the ohmic relay is illustrated in Fig. 3. When the current coil 3 overcomes the effect of the voltage coil 6, the relay operates to close its contacts IS in the circuit of the trip coil 9 whereby to effect the opening of the circuit breaker 8.

If it be assumed first that the ohmic response of the distance relay is set for example for 2 ohms, then the tripping time is substantially instantaneous for all ratios of voltage to current between zero and 2 ohms. If, however, the short-circuit voltage-current ratio is greater than 2 ohms, then the relay is caused to respond only when the voltage on the coil 6 decreases to that value which corresponds to the adjusted ohmic response of 2 ohms. Consequently, the time lag of the response varies in dependence on the magnitude of the short-circuit, as measured by the relay upon the occurrence of a fault. If it be assumed that the short-circuit voltage-current ratio is 4 ohms and the short-circuit cur rent amounts to if) ainperes, then the short-circuit voltage is 40 volts. This value is in Fig. 2 arbitrarily made equal. to 100%. Inasmuch as the ohmic response is at 2 ohms, it corresponds to a voltage of 20 volts in the case of a current of 10 amps. The voltage on the voltage coil 6 must, accordingly, be reduced by for the response voltage of 20 volts to be reached. This, however, as can be seen from Fig. 2, happens after approximately three seconds. The timedistance characteristic of the relay can, of course, be controlled as required by the use of any of the Well-known circuit time modifiers or combina-- tions thereof.

While I have shown and described my invention in considerable detail, I do not desire to be limited to the exact arrangement shown, but seekto cover in the appended claims all those modifications that fall within the true spirit and scope of my invention.

What I claim as new and desire to obtain by Letters Patent of the United States is:

1. In combination an electric circuit, means for controlling said circuit including an ohmic responsive relay having current and voltage windings respectively connected to be energized in accordance with a current and a voltage of responsive relay having current and voltage windings respectively connected to be energized in, accordance with a current and a voltage of the circuit, and means for establishing the time of operation of said ohmic responsive relay in accordance with the initial value of the fault voltage including a capacitance and fault responsive means connected to be energized from the circuit for interconnecting said capacitance with said voltage Winding and disconnecting said voltage winding from the circuit on the occurrence of a fault.

3. In combination an electric circuit, means for controlling said circuit including an ohmic responsive relay having current and voltage I windings respectively connected to be energized in accordance with a current and a voltage of the circuit, and means for establishing the time of operation of said ohmic responsive relay in accordance with the initial value of the fault voltage including a capacitance and fault responsive means connected to be energized from the circuit for first interconnecting said capacitance with said voltage winding and then. disconnecting said voltage winding from the circuit on the occurrence of a fault.

4. In combination an electric circuit, means for controlling said circuit including an ohmic responsive relay having current and voltage windings respectively connected to be energized in accordance with a current and a voltage of g the circuit, and means for establishing the time of operation of said ohmic responsive relay in accordance with the initial value of the fault voltage including a capacitance and a resistance connected in parallel and fault responsive means connected to be energized from the circuit for first interconnecting said capacitance and resistance to said voltage winding and then disconnecting said voltage winding from the circuit on the occurrence of a fault.

5. In combination an electric circuit, a relay having a movable element, and a plurality of electro-responsive means respectively energized from said circuit and exerting opposing eifects on said movable element, one of said means including a winding normally energized in accordance with the voltage of said circuit, and means responsive to a predetermined fault condition of said circuit for causing the voltage across said windingto vary from the initial fault value in a predetermined manner and independently of subsequent variation of the circuit voltage.

6. In combination an electric circuit, a distance relay having a movable element, and electro-responsive torque-producing elements comprising windings'respectively energized by a current and a voltage of the circuit for exerting opposing torques on said movable element, and means responsive to a predetermined fault con dition of said circuit for causing the voltage across the voltage energized winding to decrease from the initial fault value in a predetermined manner and independently of subsequent variation of the circuit voltage.

AUGUST ARNOLD.

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