US2813953A - Circuit interruptions with non-linear resistance - Google Patents

Description

Nov. 19, 1957 T. o. EATON 2,813,953

CIRCUIT INTERRUPTIONS WITH NON-LINEAR RESISTANCE Filed Aug. 16, 1954 5 Sheets-Sheet l INVENTOR. EE- 1 7mm Mm mv wb Nov. 19, 1957 T. o. EATON 2,813,953

CIRCUIT INTERRUPTIONS WITH NON-LINEAR RESISTANCE Filed Aug. 16, 1954 3 Sheets-Sheet 2 E5. 5. E. 5a-

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CIRCUIT INTERRUPTIONS WITH NON-LINEAR RESISTANCE Filed Aug. 16, 1954 3 Sheets-Sheet 3 IN V EN TOR. E. 5- 7211; 0- 'flranl ited States Patent CIRCUIT INTERRUPTIONS WITH NON-LINEAR RESISTANCE Temple 0. Eaton, Narberth, Pa., assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa., a company of Pennsylvania Application August 16, 1954, Serial No. 449,989 1 Claim. (Cl. 200-147) My invention relates to circuit interrupters and is more particularly directed to a novel arrangement wherein a non-linear resistance is used to decrease the rate of increase and decrease of the fault current as it passes through zero in order to facilitate the extinguishing of the arc. The magnitude of the resistance is such at low voltage that the current and voltage will be in phase making the best conditions for are interruptions.

Circuit breakers of the prior art have been provided with linear resistance which is inserted in the circuit after an arc is drawn. That is, when rated current is flowing through the cooperating contacts of the circuit interrupter, the auxiliary resistor is not in the circuit. However, on the occurrence of a fault current, when the cooperating contacts separate and an arc is drawn between, the auxiliary resistance is automatically inserted in the circuit. This resistance serves to limit the maximum value which will be reached by the fault current. That is, the magnitude of the let through current does not reach the available short circuit current value due to the large magnitude of resistance which is inserted at the instant of circuit interruption.

Although this prior art arrangement serves to limit the maximum magnitude which the fault current will reach, it does not substantially alter the rate of increase or decrease of the current as it passes through zero and hence, does not substantially aid in interrupting the arc. That is, it merely limits the maximum magnitude of current so as not to subject the network being protected by the circuit interrupter from the extreme magnitude of the available short circuit current but does not substantially aid in the interruption of the arc.

In my novel arrangement I have provided a non-linear resistance which is inserted in the circuit when an arc is drawn. The non-linear resistance has the characteristics of a maximum magnitude of resistance when the voltage is zero or minimum and has a minimum magnitude of resistance when the voltage is large.

Thus, assuming that the voltage and current are in phase (i. e. 100% power factor), the magnitude of resistance will be at its minimum value when the voltage is at its maximum value. Hence, the fault current may reach the available short circuit current value since the magnitude of resistance is relatively small at that instant.

However, when the voltage is passing through zero, due to the non-linear characteristics of the resistor, the magnitude of the resistance will be maximum and hence will cause the current to hesitate or step as it goes through zero. That is, it will be substantially decreased in the rate of increase or decrease of the current as it passes through zero. Hence, the current will remain about the zero value for a longer period of time. Also there is a substantial reduction in the ionization of the gases so that the arc chute will have a longer period of time and better conditions to extinguish the are when it is at its minimum magnitude.

In the event that the current and voltage are not in 'ice phase, i. e. either an inductive or capacitive network, then the insertion of a large magnitude of resistance as the voltage passes through zero will tend to improve the power factor that is decrease the degree of current lead or lag and thus facilitate the extinguishing of the arc as above noted.

Accordingly a primary object of my invention is to provide a novel arrangement wherein a non-linear resistance is inserted in the network immediately following the initial contact separation.

Another object of my invention is the provision of a resistance, inserted in the circuit when an arc is drawn, which will have a maximum magnitude of resistivity when the voltage is at a minimum value to thereby decrease the rate of current increase or decrease as it passes through zero and thereby provide a longer period of time for the arc to be extinguished by the arc chute when the current is at its minimum value.

These and other objects of my invention will be apparent when taken in connection with the drawings in which:

Figure 1 is a side view of a circuit interrupter and illustrates the manner in which a non-linear resistor is inserted in series with the blow-out coil. In the first embodiment of Figure l the non-linear resistor is connected between the stud of the stationary contacts and the blowout coil.

Figure 2 is a plot of voltage vs. current and illustrates the non-linear characteristics of the resistor used in my novel system.

Figure 2A is a characteristic curve of the non-linear resistor used in my invention and is a plot of resistance vs. voltage.

Figure 3 is a schematic circuit diagram of a resistive network.

Figure 3A is an oscillogram of voltage and current vs. time and the circuitry of Figure 3 and illustrates the hesitation or step of the fault current as it passes through zero.

Figure 4 is a schematic circuit diagram of an inductive network.

Figure 4A is an oscillogram of voltage and current vs. time and the circuitry of Figure 4 and illustrates the hesitation or step of the fault current as it passes through zero.

Figure 5 is a side view of the circuit interrupter similar to that of Figure 1 and illustrates a modification of the embodiment therein wherein the non-linear resistor is connected in series between the stud of the movable contact and the arc runner and the front are horn of the arc chute.

Referring now to the figures in Figure l I have shown a side view of a typical circuit breaker to which my invention may be applied. The circuit breaker shown in Figure 1 may be of the type shown in co-pending application Serial No. 307,843 filed September 4, 1952, now Patent No. 2,761,934, issued Sept. 4, 1956, and has the following components: a stud 10 to which the stationary main contact 11 is connected and a lower stud 12 on which the movable contact arm 13 is pivoted at 17. The movable contact arm 13 is biased to an open position (not shown) and is moved to the closed position by means of linkage l4 and 15. The links 14 and 15 are pivotally secured to each other at 16 and the link 14 is pivotally connected to the movable contact arm 13. The movable contact arm contains the main movable contact 18, first moving arcing contact 19 and the second moving arcing contact 20. These contacts make respectively with the main stationary contact 11, the first stationary arcing contact 21 and the second stationary arcing contact 22 when a circuit breaker is moved to the closing position by means of the linkage 1415.

An arc chute 23 is mounted above the cooperating contacts and is provided with a back arcing horn 26 and a front arcing horn 24. The back arcing horn 26 is received by the disconnect contacts when the arc chute 23 is pushed in place. The disconnect contacts 25 are connected by means of a lead 27 to the blow-out coil 28 and is mounted on the magnetic core 29 which has a U-shaped configuration and slits the arc chute 23.

The opposite end of the blow-out coil 28 is connected by means of conductor 31 to the non-linear resistor 33 which in turn is connected by means of the conductor 32 to the upper stud 10. When the main contacts 1118 of the circuit breaker are in engagement, the current will flow from the upper stud 10 through the main stationary contact 11 to the main movable contact arm 13 to the lower stud 12. Hence, when normal current is flowing through the line with the circuit breaker contacts in engagement, the non-linear resistor is out of the circuit.

The non-linear resistor 30 has the characteristics illustrated in Figures 2 and 2A wherein the magnitude of resistance is at a maximum value when the voltage is at a minimum value and the magnitude of resistance is at a minimum value when the voltage is at a maximum value, as clearly seen in Figure 2A. Thus, as seen in Figure 2, in the plot of current versus voltage, the non-linear characteristics of the resistor 30 will cause the current to hesitate or step as it passes through zero although there is no time lag between applied voltage and resulting current.

That is, since the magnitude of the non-linear resistor 30 is extremely high at the time that the voltage is at a zero or minimum value, it will influence the magnitude and rate of current at that time. The non-linear resistor 30 may be made of a material known in the trade as Thyrite, which is described in Calculation of Circuits Containing Thyrite, by Theodore Brownlee, G. E. Review, volume 37, No. 4, pages 175-179 and pages 218 223 of volume 37, No. 5; Thyrite: A New Material for Lightning Arrestors, by K. B. McEachron, General Electric Review, vol. 33, No. 2, pages 9299, and Performance of Thyrite Arrester for Any Assumed Form of Traveling Wave and Circuit Arrangement, by K. B. McEachron and H. G. Brinton, General Electric Review, June 1930, page 350.

On the occurence of a fault current a trip coil will be sufiiciently energized to initiate the separation of the cooperating contacts as is well known in the circuit interrupter art. At the first instant when the main cooperating contacts 11-18 separate the current will be diverted through the first set of arcing contacts 2119. That is, since the member 33 which carries the movable arcing contact 19 is pivotally mounted at 34 on the movable contact arm 13 the initial separation will drive the first movable arcing contact 19 into engagement with the first stationary arcing contact 21.

Hence, the circuit will be energized through upper stud 10, through the first set of arcing contacts 21-19, through the member 33, through movable contact arm 13 and to the lower stud 12. As the contact arm 13 continues to rotate in a clockwise direction about its pivot 17 the arc will be transferred from the first set of arcing contacts 2119 to the second set of arcing contacts 222). The insulator 35 is positioned between the first arcing contact 21 and the second arcing contact 22 introduces an air gap between these two members so that the arc will not exist between the arcing contact 21 and the arcing contact 22 until there is a sufficient air gap between the arcing con tacts 21-19.

Thus, in this position the current will flow from the upper stud 10 to the first arcing contact 21. An arc will exist from the first arcing contact 21 to the second stationary arcing contact 22 and from this contact to the second movable arcing contact 20 through the conducting member 33 to the movable contact arm 13 and then to the lower stud 12.

Upon continued movement of the movable contact arm 13 toward the open position the arcing horn 33 of the movable member will engage the front arcing horn 24. At this time the current will be diverted through an alternate path which consists of the conductor 32, the non-linear resistor 30, through the conductor 31, the blow-cut coil 28 through the conductor 27 through the disconnect contacts 25, the back arcing horn 26 through the arc chute 23 to the front arcing horn 24 to the movable arcing horn 33 and then through the movable contact arm 13 to the lower stud 12.

Hence, it is only after an arc is drawn and the current diverted through the blow-out coil 28 that the non-linear resistor 39 is introduced into the circuit.

if the circuit being protected by the circuit breaker of Figure l is resistive, then Figure 3 represents a schematic diagram of same wherein the source 36 having a voltage 2 supplies the short circuit line through the non-linear resistor 30.

In Figure 3A I have illustrated the oscillograrn of the voltage and current vs. time when the non-linear resistor 30 is inserted in the circuit.

As heretofore noted when the voltage is at a minimum or zero value the resistance of the non-linear resistor 39 will be at a maximum value as illustrated in Figure 2A. As seen in Figure 2 the current will be caused to step or hesitate at the time that the voltage is at its zero or minimum value. Thus, the oscillogram of Figure 3A clearly illustrates this condition existing in the circuitry of Figure 3.

Since the rate of current increase and decrease is decreased as it passes through zero magnitude there will be a longer period of time that the current is at its minimum value and also a substantial reduction in the ionization of the gases within the arc chute 23. Hence, the arc interrupting device 23 will have both a longer period of time and more desirable conditions over which to extinguish the arc which has been moved therein by means of the blow-out coil 28.

In Figure 4 I have illustrated the schematic network diagram for an inductive circuit which may be protected by the circuit breaker such as in Figure 1. The circuit diagram of Figure 4 is that which exists after the nonlinear resistor 30 has been inserted in the circuit. The inductance of the line is represented by the lumped inductor 37.

In Figure 4A I have illustrated the voltage and current conditions which would exist in a network such as illustrated in Figure 4. Since a very high magnitude of resistance is inserted in the circuit at the time an arc is drawn and the current is flowing through the blow-out coil the resistance will have the efiect of bringing the current in closer phase relationship with the voltage. That is, there will be a substantial increase in the power factor.

Hence, as clearly seen in Figure 4A there will be a substantial hesitation or step of the current as it passes through zero even though there is not a power factor.

It will be noted that the above desirable conditions which are achieved by means of Thyrite in inductive circuit can also be achieved by means of a non-linear resistor in a capacitive circuit.

That is, assuming that the non-linear resistor has a magnitude of resistance to substantially ofiset the impedance of either the capacitive or inductive circuit to improve the power factor of these circuits then there will be a substantial hesitation of the current as it passes through zero.

Thus, the decrease in the rate of current increase or decrease as it passes through zero, due to the large magnitude of resistance whenever the voltage is at a minimum or zero value, can be achieved with either an inductive. capacitive or resistive network.

In Figure 5 I have illustrated a modification of my invention wherein the non-linear resistor 30 may be inserted between the lower stud 12 and the front arcing horn 24. It will be noted that in the arrangement of Figure the non-linear resistor 30 is not inserted in the circuit until the blow-out coil 28 is inserted in the circuit in substantially the same manner as heretofore described in connection with Figure 1.

In the foregoing, I have described my invention in connection only with preferred embodiments thereof. Many variations and modifications of the principles of my invention within the scope of the description herein are obvious. Accordingly, I prefer to be bound not by the specific disclosure herein, but only by the appending claim.

I claim:

An air magnetic automatic circuit interrupter being comprised of a pair of terminals, a pair of cooperating contacts and a series circuit; said pair of cooperating contacts having an engaged and disengaged position with respect to each other and being electrically connected across said terminals; said series circuit being comprised of a non-linear resistor, a blow-out coil and an arc chute; means to electrically connect said series circuit across said terminals when said cooperating contacts are being moved from said engaged to said disengaged position as a result of the occurrence of a fault current; said nonlinear resistance being effective to improve the power factor of fault current flow through said interrupter when said contacts are being disengaged, said non-linear resistance having the characteristics of a larger magnitude of resistance when the voltage thereacross is at a small magnitude than when the voltage is at a large magnitude to thereby be effective to decrease the rate of current increase and rate of current decrease as the current passes through zero magnitude, to thereby aid in circuit interruption of fault currents.

References Cited in the file of this patent UNITED STATES PATENTS 1,841,091 Crago Jan. 12, 1932 2,052,318 Siegmund Aug. 25, 1936 2,292,252 Thommen Aug. 4, 1942 2,295,305 Summers Sept. 8, 1942 2,546,818 Curtis Mar. 27, 1951 2,586,290 Baker et al. Feb. 19, 1952 2,611,058 Rawlins Sept. 16, 1952 FOREIGN PATENTS 632,718 Great Britain Dec. 5, 1949

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