US3436597A

US3436597A - Electric circuit breaker with assisted arc interruption

Info

Publication number: US3436597A
Application number: US662968A
Authority: US
Inventors: Ralph L Hurtle
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1967-08-24
Filing date: 1967-08-24
Publication date: 1969-04-01
Anticipated expiration: 1986-04-01

Description

R. L. HURTLE 3,436,597

TRIC CIRCUIT BREAKER WITH ASSISTED ARC INTERRUPTION April 1, 1969 Sheet Filed Aug. 24, 1967 tkansfcr E W WJ U R M; Wu P L W Y 5 5 2 9 2 m m M M m L H 4 Wm April 1, 1969 R. HURTLE 3,

ELECTRIC CIRCUIT BREAKER WITH ASSISTED ARC INTERRUPTION Filed Aug. 24. 1967 Sheet 3 of 2 RALPH L HURTLE I BY/?M%@u A T TORNi Y United States Patent 3,436,597 ELECTRHC CIRCUKT BREAKER WITH ASITED ARC INTERRUPTION Ralph L. Hurtle, West Hartford, (Iona, assignor to genfiral Electric Company, a corporation of New Filed Aug. 24, 1967, Ser. No. 662,968 Int. Cl. HtlZh 7/16 US. Cl. 317-11 11 Ciaims ABSTRACT OF THE DISCLQSURE An alternating current circuit interrupter, including means for drawing an arc between two stationary spaced contacts; a pair of electrodes are positioned in the arc path, each adjacent one of the stationary contacts and each connected through a rectifier (diode) and resistor to the opposite contact or breaker terminal; when the arc strikes the electrodes, it is forced into one of the by-pass paths (which one depending on the direction of the current at the time) by the voltage drop across the arc; the are then is" extinguished except for a short are in the gap between the aforesaid contact and electrode; in the preferred form, the total arc voltage before transfer to the by-pass path is greater than the line voltage, and the by-pass path has sufiicient resistance to make the power factor essentially unity after transfer, with the result that the current is extinguished at the next succeeding voltage zero point of the system. In a second embodiment, the arc voltage developed does not exceed line voltage and interruption takes place at a second or third succeeding voltage-zero point. The resistors used in both embodiments may be standard resistors, but preferably are high positive temperature coefficient of resistance resistors, so that afterthe current is transferred to the by-pass path, the resistors heat and increase their resistance, reducing the current and further assisting interruption. The resistors are of high enough minimum (cold) value to protect the rectifiers from burn-out by excess current.

Background of the invention Field of the invention-This invention relates to electric circuit interrupting devices. More particularly, the invention relates to low cost, alternating current circuit interrupting devices employing by-pass means shunting a pair of terminals or contacts between which an arc is drawn, to assist the interruption of the arc.

Description of the prior art.-Parallel assisted circuit interrupting devices are devices which achieve current interruption by means of transferring the current from a main path to a shunt path in parallel with the main contacts of the interrupter. I11 such devices, upon the occurrence of an overcurrent, interruption is initiated in a first path including the main current carrying contacts. These contacts, which are designed to be separated and to withstand a predetermined amount of arcing, are employed to initiate the interruption. Subsequently, the current in the arc is transferred to a path electrically in parallel with the arc, and the interruption process is assisted in one or more of various ways.

In my copending application Ser. No. 542,806, filed Apr. 15, 1966, and entitled, Electric Circuit Interrupt- 'ice ing Device, assigned to the same assignee as the present invention, several novel parallel assisted circuit interrupting devices are disclosed. The interrupting devices disclosed in the aforesaid application possess many advantages over prior art devices assigned to achieve parallel assisted interruption and are entirely satisfactory for many circuit applications. The invention disclosed in the aforesaid application, however, requires the use of vacuum gap interrupters, ignitrons, gate controlled sen1icon ductor rectifiers, or other similar gate controlled conducting devices in the parallel assisting path. This introduces the need for generating, applying, controlling and disconnecting a triggering or gating signal, leading to the necessity for relatively complicated devices and circuits.

Objects of the invention It is a primary object of the present invention to provide a new and improved low cost, alternating current, parallel assisted circuit interrupting device.

It is a particular object of the invention to provide an electric circuit interrupting device of the parallel assisted interruption type which does not require the use of a gate controlled, grid controlled or triggered conducting device in the parallel assisting path.

It is another object of the invention to provide an electric circuit interrupter of the type described which is capable of utilizing conventional solid state devices, thus obviating the need for evacuated enclosure type devices.

it is a further object of the invention to provide an electric circuit interrupter of the type described which makes effective use of are generating devices of the type described in my aforesaid application caapble of generating an arc having a voltage drop greater than the line voltage of the circuit in which they are used.

It is also an object of the invention in one form to provide a circuit interrupting device of the parallel assisted type which is capable of utilizing a circuit interrupter of the conventional type which does not develop an arc voltage higher than the line voltage of the circuit in which it is used.

It is a further object of the invention to provide an electric circuit interrupting device of the parallel assisted type including means in the by-pass path for increasing circuit impedance in the by-pass path after transfer has occurred and prior to circuit interruption, thereby facilitating final circuit current interruption.

Summary of the invention In practicing the invention, an alternating current electric circuit interrupter is provided which comprises means for generating an arc between a pair of spaced electrodes or contacts. Interruption assisting means is provided in parallel circuit relationship across the contacts for diverting current to a parallel path to facilitate extinction of the arc. The interruption assisting means comprises a pair of electrodes, each positioned adjacent one of the contacts so as to be struck by the are after the arc has been elongated a predetermined amount and has therefore generated a predetermined voltage drop. Each of the second electrodes is connected through a resistor and a unidirectional conducting device such as a diode, to the opposite contact or breaker terminal to form two by-pass paths. When the arc strikes the second electrodes, the current is shunted through one of the by-pass paths (which one depending on the direction of the current at the time), a short are remaining between one of the contacts and its adjacent second electrode. The current continues to flow through this by-pass path until the next voltage zero point in the AC cycle, at which time conduction ceases through the previously conducting by-pass path, current in the reverse direction being blocked by the unidirectional conducting device therein. Current cannot flow in the other by-pass path, since there is a now deionized air-gap therein between the other one of the second electrodes and its adjacent contact. In the preferred form, the total arc voltage before transfer to the by-pass path is greater than the line voltage, and the bypass path has sufficient resistance to make the power factor essentially unity after transfer, with the result that the current is exinguished at the next succeeding voltage zero point of the system. In a second embodiment, the are voltage developed does not exceed line voltage and interruption takes place at a second or third succeeding voltage-zero point. The resistors used in both embodiments ma be standard resistors, but preferably are high positive temperature of coefficient resistors, so that after the current is transferred to the by-pass path, the resistors heat and increase their resistance, reducing the current and further assisting interruption. The resistors are of high enough minimum (cold) value to protect the rectifiers from burnout by excess current.

Brief description of the drawings In the drawings:

FIGURE 1 is a schematic circuit diagram of a current interrupting device constructed in accordance with the present invention;

FIGURE 2 is a voltage and current vs. time diagram showing current and voltage conditions in the circuit interrupter of FIGURE 1 during interruption, the current vs. time scale being greatly compressed in order to facilitate the description;

FIGURE 3 is a schematic circuit diagram of another embodiment of the invention;

FIGURE 4 is a schematic circuit diagram of another embodiment of the invention;

FIGURE 5 is a voltage and current vs. time characteristic curve illustrating operation of the circuit shown in FIGURE 1, and

FIGURE 6 is a current and voltage versus time characteristic curve illustrating operation of another embodiment of the invention.

Description of the embodiment 0] FIGURE 1 In the embodiment of the invention shown in FIGURE 1 of the drawings, a parallel assisted circuit interrupter is disclosed wherein the contact-separating device employed comprises a high arc-voltage generating circuit breaker, having the ability to generate an arc with a voltage greater than the line voltage of the power system in which the circuit interrupter is used. This high arc-voltage ordinarily is generated within three milliseconds of the incidence of an overcurrent condition due to a short circuit or the like. By this means, the rising current is crested or reversed in slope and driven toward zero, the complete interruption taking place within a half cycle of alternating current.

In other embodiments of the invention, the use of conventional, low arc-voltage circuit breakers is contemplated. Whether the circuit employed is a high arc-voltage circuit breaker or a low arc-voltage circuit breaker, however, the degree of improvement of the interruptin ability of any such breaker of a given rating is several fold. In the instant invention, this considerable improvement in interrupting ability is achieved using relatvely low cost components not requring trigger elements or special circuitry for applying turn-on gating potential, etc.

Referring now particularly to FIGURE 1, the invention is shown as incorporated in an electric circuit interrupting device including a bridging contact type, high arcvoltage arc generating means, shown generally at 12. The are generating means 12 shown is generally similar to that included in the circuit breaker disclosed and claimed in prior application Ser. No. 457,557, filed May 21, 1965, by R. L. I-Iurtle and H. G. Willard, and assigned to the same assignee as the present invention. The bridging contact type circuit breaker 12 includes an insulating casing support having a generally cup-shaped portion 13 and has a pair of spaced-apart stationary contact assemblies mounted thereon by suitable means, not shown. The stationary contact assemblies include

contact members

14 and 15 inclined toward each other, and are

runner members

16 and 17 which are electrically connected to and may be an integral part of the

contact members

14 and 15, respectively. A generally wedge-shaped movable bridging contact member 18 is carried at the end of a reciprocally movable contact operating rod 19, and is tapered, having contact faces 21 and 22 mating with the faces of

contact members

14 and 15. The area immediately adjacent the movable contact member 18 is enclosed by the insulating enclosure 13 so as to form a pressure chamber in the space 23. A first arc blow-out coil 24 is connected between the stationary contact face 14 and a connection point 25, and a second blow-out coil 26 is connected between the stationary contact face 15 and a second connection point 27 The flux generated by the

blowout coils

24 and 26, combined with the pressure of gases generated by the are, causes the arc to be moved up along the

arc runner members

16 and 17 and elongated. A pair of insulating side plates, not shown, are provided adjacent the arc area, composed of an acetal resin material such as a polyoxymethylene.

The assembly further comprises a solenoid 28 having an actuating winding 29. The solenoid 28 has a reciprocally movable plunger portion that is connected to and moves the connecting rod 19 to cause the movable contact faces 21 and 22 to move into or out of engagement with the fixed contact faces 14 and 15, respectively. The assembly is completed by a plurality of relatively closed spaced arc intercepting and cooling plates 31 disposed in a row between the ends of the

arc chute members

16 and 17. The

end plates

32 and 33 are slightly longer than the remaining intercepting and cooling plates 31, for a purpose to be described.

In operation, when the breaker is closed, the movable contact member 18 is retained in closed circuit position by suitable means, not shown, which may be manual and/or automatic, so as to form a closed current path. Upon the occurrence of an overcurrent condition caused by a short circuit or the like, however, the movable contact 18 is moved from its closed to its open circuit position shown in FIGURE 1 by the action of the

solenoid

28, 29. This occurs due to the high overcurrent through the solenoid winding 29 irrespective of the condition of the manual and/ or automatic operating mechanism used to close movable contact member 18 on the fixed contact faces 14 and 15. For a more complete description of the construction and operation of the circuit breaker 12, reference is made to the aforementioned copending application Ser. No. 457,557, assigned to the same assignee as the present invention.

Interruption assisting means shown generally at 35 comprises two current by-passing paths or circuits between the

terminals

25 and 27. A first path includes diode 36 connected in series with a high positive temperature coefficient of resistance resistor 38 connected between the terminal 27 and the end arc-interrupting and cooling plate 33. A second path includes an oppositely-di rected diode 3'7 similarly connected in series with a high positive temperature coefficient of resistance resistor 39 between the terminal 27 and the end arc-interrupting and cooling plate 32.

The interrupter is shown as disposed in series circuit relationship between the alternating current source terminals 41a, 41b and a load 42 for controlling current supplied to the load 42.

The operation of the circuit interrupter shown in FIG- URE 1 is as follows, assuming the circuit breaker 12 to be in the closed condition so that the current is supplied from supply input terminals 41a and 41b to the load 42. For so long as the current flow is at rated value, all of the current flowing in the circuit passes through the

contacts

14, 21 and 22, 15 of the circuit breaker. None of the current passes through the parallel paths comprising by the

diodes

36 and 37 and their associated high positive

temperature coefficient resistors

38 and 39 under normal current conditions due to the fact that there is an open circuit or gap in each of these paths, namely at 16, 32 and 17, 33, respectively. Upon the occurrence of an overcurrent condition caused by a short circuit of load 42, etc., the current in the circuit increases extremely rapidly. Upon the current increasing above a predetermined value, the solenoid winding 29 acts to move contact 18 out of engagement with fixed

contacts

14 and 15.

As the contact 18 moves toward its open circuit position, a pair of short arcs are drawn between the contact faces 14, 21 and 15, 22. These short arcs are immediately forced together by the combined action of magnetic forces and the blow-out pressure of gas generated by the arc impinging upon adjacent insulating material. As a consequence of this combined action, the two short arcs combine into a single long are extending between the

contacts

14 and 15. The single long are is rapidly moved out along the diverging

arc runner members

16 and 17 by the action of the blow-out

coils

24 and 26 assisted 'by the upward gas pressure. By this time the arc has assumed a sustained high voltage drop condition due to the unique design and action of the circuit breaker 12.

As the arc moves outwardly along the

arc chute members

16 and 17, it comes in contact with the arc plates 31, including the end are

plates

32, 33. Upon the arc contacting the end are

plates

32 and 33, a circuit is formed through one of the

diodes

36 or 37 depending upon the polarity of the current at the time. For example, if it is assumed that at the time of overcurrent, supply terminal 41a is positive with respect to supply terminal 41b, then the diode 37 will block current due to the polarity of its connection. The diode 36 will accept current, however, thereby establishing a parallel conducting path through the resistor 38, diode 36 and the portion of the arc existing between end plate 31 and are chute runner member 17. At this instant in time, the resistor 38 exhibits its minimum resistance which is so chosen that this parallel circuit offers less resistance to the ilow of current than does the high voltage drop arc. Consequently, the current in the arc is transferred quite rapidly to the parallel path so that the arc, except for that part between end plate 33 and are chute member 17, is completely extinguished.

This rapid transfer of the current from the breaker arc path to the diode 36 and resistor 38 parallel path is made possible primarily by the fact that a high voltage drop exists across the breaker at this time due to the arc and is maintained by the breaker 12 during transfer. Thus, assuming a 600 volt RMS voltage circuit (peak 850 volts) such as is illustrated in FIGURE 2, the circuit breaker 12 generates an are having a voltage-drop such that the total voltage-drop across the breaker is 1,000 volts or more. Since the current at the time oftransfer is about 40,000 amperes and the cold resistance of resistor 38 is about .019 ohm, it follows that with all of the current flowing through the parallel path, the drop through such path would be less than 1,000 volts. Accordingly, the parallel path is therefore the preferred path since there is always a dominating or transferring voltage existing in the circuit breaker path.

FIGURE 2 of the drawings illustrates the voltage and current vs. time operating characteristics of the circuit interrupter shown in FIGURE 1 during its interrupting action as described above. In FIGURE 2, the current scale has been greatly compressed in order to illustrate it along with the voltage for convenience. The supply source voltage is shown at e and the overcurrent condition is considered to have occurred at time t just prior to the crest of the supply voltage. This is the point in time in the voltage wave when it is most diificult to interrupt, since there is substantial source voltage existing across the circuit and available increasing voltage to further increase the short circuit current after incidence. The voltage appearing across the interrupter shown at e starts a short period of time (about .75 millisecond) after the onset of the overcurrent condition and rises to a peak value in excess of the crest value of the source voltage. Thus, it will be appreciated that the circuit breaker arc voltage will exceed or dominate the source voltage and cause a reversal of the current rise as illustrated by the test current curve. Also, it should be noted that the short circuit current, if completely unrestrained (trace marked prospective current) would reach a peak of approximately 166,000 amperes whereas the actual test current allowed to flow by the interrupter (trace marked test current) reaches a peak of only about 44,000 amperes.

As stated above, the current curves shown in FIGURE 2 are represented on a compressed scale for the purpose of facilitating analysis and explanation. In considering FIGURE 2, it should be noted that prior to time t (the onset of the overcurrent condition) the current through the circuit breaker is of only nominal value and therefore is imperceptible on the scale of the curve. At the time t however, the current through the circuit breaker 12 rises rapidly as indicated by the test current trace until at time t (approximately .75 millisecond) the

sole noid

28, 29 acts on movable contact 18 to separate the movable contact faces 21 and 22 from the fixed contact faces 14 and 15. Upon this occurrence, a pair of arcs are drawn between the separating contacts, and these arcs are quickly joined to form a single are as described above. This results in inserting a substantial resistance in the circuit so that an arc voltage (shown at e exceeding the normal line voltage of the circuit is produced. This are resistance or opposition to current flow halts the rise of the current through the circuit breaker 12 at about 44,000 amperes.

It should be noted that whereas the voltage drop across the interrupter prior to time t was so minute that it was imperceptibe on the scale of the current curve shown in FIGURE 2, this voltage drop increases rapidly to nearly 200 volts at the instant that the short circuit occurs. This instantaneous rise of voltage across the interrupter is due to the voltage appearing across the device because of the inductance of the circuit, including the inductance of

blowout coils

24 and 26 and the solenoid 29. It will be observed that during this time the current through the circuit breaker 12 is increasing extremely rapidly, and if no further impedance were introduced in the circuit by the are produced across the breaker contacts as previously described, the current would continue to rise and would reach a peak prospective value of 166,000 amperes as indicated by the trace marked prospective current. The action of the high are voltage wedge contact circuit breaker 12, however, causes the voltage across the interrupter to increase sharply at about .75 millisecond after the onset of the short circuit current thereby cresting the current at this point.

When the high voltage arc producing circuit breaker 12 draws its high voltage are and the arc reaches the

end arclplate

32 and 33, the voltage appearing across the arc is applied across the two parallel paths comprising the diode 36 and its series connected resistor 33 and diode 37 and its series connected resistor 39. When this occurs, current flow is established in one of the parallel paths depending on the polarity of the source voltage at this instant. Assuming that the terminal 41a is positive with respect to the terminal 41b at this time, then current flows from terminal 25 to resistor 38 to diode 36 to are plate 33 to are runner 17. It should be noted that the current through the overall interrupter does not continue to increase despite the introduction of this parallel path, but instead, the net current as indicated by the trace (test current) decreases very sharply towards zero, and reaches zero substantially concurrently with the supply voltage e This is primarily due to the novel action of the high are voltage circuit breaker 12 which exerts on the arc existing therethrough such a high extinguishing action that the current is not only forced through the parallel path including diode 36 as described above, but also is actually diminished in total magnitude sharply.

The

diodes

36 and 37 assist the interruption procress by blocking reignition current after quench. For example, if terminal 410 of FIG. 1 is positive at fault incidence, current will flow clockwise. Upon the currents transferring to the parallel assisting path, diode 3'6 and are 3347 carry current in series circuit relationship until quench. After quench, terminal 41!) becomes positive, attempting to drive current counterclockwise in the circuit. Although arc gap 33-17 tends to be conductive because of the arcing just terminated there, diode 36 blocks counterclockwise current. Two other possible paths exist. One is through gaps 1522 and 21-14 in series. The other is through diode 37 and gap 32-46. All three gaps, however, were recovering their dielectric strength during the time current was clockwise in the parallel assisting path and thus are able to prevent arc reignition. The danger of arc reignition across these gaps is further lessened because the supply voltage at this time is essentially zero, as shown in FIG. 2. Thus the by-pass

paths including diodes

36 and 37, while offering negligible opposition to transfer of current from the main path to the parallel assisting path, become essentially nonconductive and block current fiow at quench.

In addition to the above described action on the part of the high are voltage circuit breaker 12, it is important to note that the resistor 38 included in the by-pass parallel path, has an initial cold resistance of predetermined value and has its resistance rapidly increased by passage of current due to its high positive temperature coefficient of resistance characteristic. The effect of this high positive coefficient of resistance characteristic is to introduce power factor correcting resistance into the by-pass parallel circuit path during the alternation during which the path conducts current bringing the power factor closer to unity. As a consequence, the overall circuit transiently alters its power factor so as to bring the current through the interrupter into phase with the supply voltage and the current is driven to zero simultaneously with the supply voltage. Thus, it can be appreciated that while the by-pass parallel path through the diode 36 and resistor 38 may be thought of as an escape valve relieving the circuit breaker 12 of some of the opposition to its rapid extinction of the arc therethrough, it also represents a valve which following initial action is gradually closed off to decrease the extent of this path as an escape route for the current. The material used for the resistors must of course not only have a high positive temperature coefficient of resistance, but must have substantial current carrying and thermal capacity. Suitable high positive temperature coefiicient of resistance materials include iron, molybdenum and tungsten. Resistors of these materials may increase their resistance by a factor of 10* to times normal resistance in the possible range of operation.

During the latter part of the system voltage half-cycle, the transferred current continues to decrease due to two factors. First, the system voltage 2 is decreasing at this time. The current decreases with the voltage because the action of the interrupter in inserting the high resistance first of the arc of the circuit breaker 12 and then the resistance of resistor 38, has the net effect of improving the power factor of the circuit. That is to say, the circuit is made primarily a resistive circuit in which the current decreases substantially in phase with the applied voltage. Secondly, although the initial resistance of the resistor 38 is substantial, its resistance values continues toincrease following transfer of current due to the heating action of the current passing therethrough. This increased resistance serves to further decrease the total current and to improve the power factor. These two factors cause fairing out of the current so that the current gradually decreases until the system voltage reaches zero, at which time the current also reaches zero and complete extinction occurs.

The feature that the current reaches zero at the same time as the system voltage is extremely important in that it allows the diode 36 to regain its blocking capability prior to being required to withstand a reapplied, reverse polarity potential. If, in contrast to this condition, the current were to reach zero at a time when the supply voltage was at appreciable magnitude in the reverse direction, there would be a danger of break-down conduction in the reverse direction as a consequence of high induced voltage because of too rapid extinction of reverse current by the diode. The present invention avoids this possibility by transiently altering the power factor of the interrupter so as to bring the current to zero simultaneously with the system voltage. Additionally, it should be noted that the current path through the interrupter following transfer to the series connected diode and resistor includes a short are path between the end plate 33 and the arc chute member 17. By causing the current through the interrupter to go to zero concurrently with the system voltage, there will be no substantial voltage existing across this are path at the time of the current zero tending to continue current flow therethrough.

The embodiment described above and illustrated in FIGURE 1 makes optimum use of a high are voltage are generating means of the type shown in my aforesaid prior application, and provides an alternating current circuit interrupter which provides current interruption at the first voltage Zero point of the alternating current cycle following transfer of current to the parallel path in most interruptions.

The embodiment of the invention illustrated in FIG- URE 4 is similar to that of FIGURE 1, excepting that the interrupter 12' illustrated is not of the high arc voltage are generating type, but instead is a conventional circuit interrupter type in which the arc voltage does not attain a value exceeding that of the line voltage of the circuit in which it is used.

In this form of the invention, current interruption may not take place until the second or possibly the third zero point in the alternating current voltage wave, but nevertheless the interrupting capacity of the basic interrupter is substantially increased by means of the invention.

In order for transfer of current to be effected at most parts of the alternating current cycle, the voltage across the arc must be sustained at a voltage at least as great as the line voltage of the system in which the device is used. In the neighborhood of the current-zero point in the AC wave, however, the arc voltage need not be so high, since the current at this point is low and therefore the IR drop through the by-pass path will be low. In addition, in the period immediately following a current zero in the AC cycle, the deionization of the original arc will have had some time to proceed, making a restrike less likely.

In accordance with the invention in this form, therefore, a parallel assisted circuit interrupting device is provided which can use a conventional are generating means, circuit interruption being effected near a current zero point, which may be the second or third current zero following initiation of the fault.

If transfer of current in this for-m occurs just prior to a current zero, reignition, that is, current conduction through the oppositely directed parallel path, will occur because there is substantial voltage (this being out of phase with the current) and ionization is still high in the region of the arc-plate-to-arc-nunner space. As the new alternation begins, however, the original arc path has regained much of its impedance by deionization because of the recent zero current. At the same time, the 1R drop through the parallel path is relatively low because the current has not reached a large magnitude (is still near zero) so that transfer is established at the start of this alternation, allowing 180 of time for the parallel path resistor to become heated and to modify the power factor to near unity. This allows quenching of the current at the next current zero point.

An interruption of this type is illustrated in the current voltage versus time diagram of FIGURE 5. In this figure, the symbols used have the following significance:

t the point of initiation of the short-circuit or extremely high current condition,

r -the point in time when the breaker contacts separate and begin drawing an arc,

h -the point in time in which the current is shifted from its path in an are directly between the

electrodes

16 and 17 to one of the by-pass paths including one of the

diodes

36, 37,

t the time when the slope of the current is sharply reversed, beginning reduction toward zero,

Q -the point in time when the current is completely extinguished,

i -voltage across the breaker terminals,

Test currentthe total current flowing in the line,

Prospective current--the value of current which would flow if the circuit breaker had not opened.

FIGURE 6 illustrates the voltage and current conditions existing in a circuit breaker of the type shown in FIGURE 4 in the condition in which the first natural current zero in the line occurs before the arc has been elongated and moved outwardly on the

arc runners

16 and 17 sufficiently to contact the end are

plates

32, 33. In this case, as illustrated in the diagram, the arc current reverses within the arc chute of the circuit breaker before transfer occurs to the parallel path. Complete extinctionv of the current therefore does not occur until the third current zero point following initiation of the are or short circuit condition.

FIGURE 3 of the drawings illustrates another embodiment of the parallel assisted current interrupter shown in FIGURE 1. In this embodiment, current limiter devices of the vaporizable conductor type are provided in the parallel assisting path. The parallel path comprising the diode 36 and resistor 38 and the series connected current limiter device 45, is connected between the terminal 25 and the arc plate 33 of the high arc-voltage, wedge contact type circuit breaker 12. Likewise, diode 37 and its series connected resistor 39 and current limiter device 46 are connected in series between terminal 27 and are plate 32.

The

current limiter devices

45 and 46 are of the type disclosed and claimed in my prior Patent 3,117,203, issued Jan. 7, 1964, and assigned to the same assignee as the present invention, to which reference should be had for a more complete description thereof. Briefly, however, the

current limiters

45 and 46 each include a rigid highly refractory insulating member having one or more relatively fine holes therethrough interconnecting a pair of metallic terminal members on either side of the insulating body. The holes contain a vaporizable conductive medium, preferably mercury, completely filling the hole and interconnecting the end terminals. Upon the occurrence of predetermined excessive current conditions through the current limiter, the conductive medium is transformed to a vapor state while confined to substantially the identical volume it occupied as a liquid. Since the vapor is not basically a conductor, conduction therethrough is in the nature of an arc, having very high resistance characteristics. The result is that the current is arrested in its rising condition and depressed toward zero. In a first form of the current limiter, called a regulating current limiter, the dimensions of the limiter are so chosen with respect to the parameters of the circuit that the current is depressed toward zero but is not completely extinguished but is maintained or regulated at some predetermined low value until complete interruption is performed by some means electrically in series therewith. In a second form, called a quenching current limiter, the current limiter is designed with respect to the parameters of. the circuit so that the current is actually driven to zero. In the absence of other events, the material in the opening then recondenses, reestablishing circuit continuity and current again flows causing vaporizing of the material, a second time and again causing the current to be driven to zero. In accordance with special design techniques the current-zero time is extended, as shown for example in my copending application Ser. No. 660,982, filed Aug. 16, 1967 and assigned to the same assignee .as the present invention.

Whether the

current limiters

45 and 46 are of the regulating or of the quenching type, the operation of the circiut is generally similar to that described in connection with FIGURE 1. Thus interruption is initiated by movement of the movable contact 18 drawing a pair of short arcs which immediately join together to form a single long are between the

arc runners

16 and 17. When the arc has moved out on the

runner

16 and 17 far enough to encounter the

arc plate

32 and 33, current is established in one of the by-pass paths depending on the instantaneous polarity of the current at the time of transfer. Assuming the direction of current flow to be in the direction of diode 37, the current path will be from the terminal 27 through the limiter 46 through the resistor 39 through the diode 37 to the arc plate 32, and thence through an arc in air to the arc runner 16. Immediately following transfer, the current is depressed close to the zero point by the regulating limiter 46 combined with the action of the resistor 39. The current is maintained at this low level until the next succeeding voltage zero point occurs on the system voltage, at which time conduction through this path ceases. Since there is thereafter an air gap in each of the by-pass paths as well as in the main path through the breaker 12, and no continued arcing, the current remains extinguished.

A distinct advantage is obtained by the use of a quenching current limiter at 45 and 46. In this case, immediately following transfer of current to the by-pass path, the current limiter fires, and immediately drives the current to Zero, without waiting for a natural current zero or voltage zero point of the electrical wave. This significantly reduces the duty required of the

diodes

36, 37, as well as shortening the arcing time within the circuit breaker 12.

This form has the further important advantage of being usable in direct current circuits as well as in alternating current circuits. In the direct current application, only a single unidirectional device or diode is required, arranged to conduct current in the proper direction. Transfer of the arc current occurs as previously described, following Which the quenching current limiter fires reducing the current to zero for a short period of time. This allows the gap between the electrode and adjacent contact to become deionized, thereby inserting an air gap in the by-pass circuit, so that when the current limiter again becomes conductive, the circuit will nevertheless remain open until the main contacts are reclosed. Whether regulating limiters or quenching type current limiters are used, however, the

resistances

38, 39 are optional, and may be conventional type resistors or high positive temperature coeificient of resistance resistors.

From the foregoing description, it will be appreciated that the invention provides a low cost, alternating current, assisted current interrupting device which employs conventional low cost semiconductor diodes and temperature sensitive resistance elements in the assisting path. As a consequence of these arrangements, no additional control electrode triggering circuit connections are required and fast, complete current interruption can be achieved with a minimum of arcing. This latter characteristic allows the separable contacts of the interrupter to be designed for minimum interruption duty further reducing the cost of the overall interrupting device.

Having described several embodiments of new and improved, low cost, alternating current, parallel assisted current interrupting devices in accordance with the invention, it is believed obvious that other modifications and variations of the invention are possible in the light of the above teachings.

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

1. An electric circuit interrupter for use in an alternating current power system comprising:

(a) a support;

(b) at least one pair of contacts supported on said support;

(c) a first electrode supported on said support adjacent a first one of said contacts to provide a first arc gap;

(d) a second electrode supported on said support adjacent the other of said contacts to provide a second arc gap;

(e) first unidirectional conducting means electrically connected between said first contact and said second electrode;

(f) second unidirectional conducting means electrically connected between said other contact and said first electrode;

(g) said first unidirectional conducting means being arranged to conduct current between said contacts in a direction opposite to that of said second unidirectional conducting means;

(h) means for creating an arc between said contacts and for moving said are to a position where a first portion of said arc bridges at least one of said first and second arc gaps, whereby the remaining portion of said arc is by-passed and extinguished and said current between said contacts is conducted through said first portion of said are and one of said unidirectional conducting means until reversal of the voltage of said power system whereupon said first portion of said are is extinguished.

2. An electric circuit interrupter as set forth in claim 1 wherein said circuit interrupter also includes an electrical resistor connected in series with each of said unidirectional conducting means respectively.

3. An electric circuit interrupter as set forth in claim 2 wherein said resistors each comprise a high positive temperature coefficient of resistance material.

4. An electric circuit interrupter as set forth in claim 1 wherein said interrupter also includes a current limiter device in series with each of said unidirectional conducting devices, each of said current limiter devices being of the repetitively operable vaporizing and recondensing conductor type.

5. An electric circuit interrupter for use in an alternating current power system comprising:

(a) a support;

(b) at least one pair of contacts supported on said support;

(h) means for creating an are between said contacts and for moving said arc to a position where a first portion of said arc bridges at least one of said first and second arc gaps, whereby the remaining portion of said arc is by-passed and extinguished and said current between said contacts is conducted through said first portion of said arc and one of said unidirectional conducting means until reversal of the voltage of said power system whereupon said first portion of said arc is extinguished; and

(i) a current limiting device connected electrically in series with each of said unidirectional conducting devices, each of said current limiting devices comprising a current limiting device of the repetitively operable vaporizing and recondensing conductor type capable of driving the current therethrough to zero following vaporizing of the conductor therein, whereby said circuit interrupter is capable of interrupting current prior to current zero of the alternating current wave, whereby said circuit interrupter is also capable of use in direct current systems.

6. An electric circuit interrupter as set forth in claim 1, said circuit interrupter also including an electrical resistor and a current limiting device of the repetitively operable vaporizing and recondensing conductor type connected electrically in series with each of said unidirectional conducting devices.

7. An electric circuit interrupter as set forth in claim 6, wherein said resistors comprise high positive temperature coefircient of resistance resistors.

8. An electric circuit interrupter as set forth in claim 1, wherein said means for creating said arc comprises high are voltage arc generating means capable of generating an arc having a voltage drop equal to or greater than the voltage of said power system.

9. An electric circuit interrupter as set forth in claim 2, wherein said unidirectional conducting means each comprises a solid state diode and wherein said resistors have a minimum resistance value sufficient to protect said diodes from excess current when used in said system.

10. An electric circuit interrupting device as set forth in claim 1, wherein said arc generating means comprises a pair of spaced stationary contacts, a movable bridging contact, means supporting said bridging contact for rectilinear movement between open and closed circuit positions with respect to said stationary contact along a predetermined path, enclosure means housing said movable contact and said spaced stationary contacts, said enclosure means enclosing the space adjacent said movable contact in the direction of its movement away from said stationary contact to provide an essentially closed arc initiating chamber, and insulating side plates positioned closely adjacent said stationary contacts, said insulating side plates comprising an acetal resin material.

11. An electric circuit interrupter for use in a direct current power system comprising:

(a) a support;

(b) at least one pair of contacts supported on said support;

(0) an electrode supported on said support adjacent one of said contacts to provide an arc gap;

(d) unidirectional conducting means electrically connected between said electrode and the other of said contacts;

(e) a current limiting device of the repetitively operable vaporizing and recondensing conductor type capable of driving the current therethrough to zero following vaporizing of the conductor therein con- 13 14 nected electrically in series with said unidirectional References Cited conducting means and said electrode; UNITED STATES PATENTS (f) means for creatmg an are between sald contacts and for moving said arc to a position where a por- 211961820 4/1940 VersF 317-41 tion of said arc bridges said are gap whereby the re- 5 2,208,399 7/1940 Sleplan 317-11 maining portion of said arc is by-passed and extinguished and current between said contacts is con- JOHN COUCH Pr'mary Exammer' ducted through said unidirectional conducting means I, D, TRAMMELL, Assistant Examiner. and said current limiting device and said are gap,

said current being driven to zero by said current 10 U.S.C1.X.R. limiting device whereupon said portion of said arc is 317-78; 307136 extinguished.