US2439165A - Selective tripping of circuit breakers in a system - Google Patents

Description

April 6, 1948. H. c. GRAVES, JR 2,439,165

SELECTIVE TRIPPING OF CIRCUIT BREAKERS IN A SYSTEM Filed Feb. 17, 1944 10 Sheets-Sheet l TYPICAL AIR.

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SELECTIVE TRIPPING OF CIRCUIT BREAKERS IN A SYSTEM Filed Feb. 17, 1944 10 Sheets-Sheet 3 Fig: 6

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April 6, 1948. H. c. GRAVES, JR 2,439,165

SELECTIVE TRIPPING 0F CIRCUIT BREAKERS IN A SYSTEM Filed Feb. 17, 9 l0 Sheets-SheetA IN V EN TOR. HERBERT (GEM 3 JP.

SELECTIVE TRIPPING OF CIRCUIT BREAKERS IN A SYSTEM Filed Feb. 17, 1944 10 Sheets-Sheet 5 IN VEN TOR.

BY: W My April 6, 1948. H. c. GRAVES, JR 2,439,165

SELECTIVE TRIPPING OF C I RCUIT BREAKERS IN A SYSTEM Filed Feb. 17, 1944 10 Sheets-Sheet 6 INVEN TOR. 3 HEPBEPT c GPAl/A) JP. N

Apnl 6, 1948. H. c. GRAVES, JR 2,439,165

SELECTIVE TRIPPING OF CIRCUIT BREAKERS IN A SYSTEM Filed Feb. 17, 1:944 10 Sheets-Sheet 8 "llllllllllllllulllllluljllllllllu l i' ,-v I

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p E94. H. as. GRAVES, m ,439gm5 SELECTIVE TRIPPING OF CIRCUIT BREAKERS IN A SYSTEM Filed Feb. 17', 184-4 19 -$heeis$heet 9 --eso I N VEN TOR.

HEPBEPT C. GPWEJ JP.

P 9 9 3- H. GRAVES, m 2,43%165 SELECTIVE TRIPPING OF CIRCUIT BREAKERS IN A SYSTEM Filed Feb. 17, 194- 5 10 Sheets-Sheet l0 ZNVENTOR.

HZPBEPT C, GPAYEJ JP.

' Patented Apr. 6, 1948 I I Ni? @Hiiiliti SELECTIVE TRIPPING F CHEW/WT BREAKERS IN A. SYSTEM Herhett C. Groves, in, West @hester, essignos to i. ii. E. Circuit Breaker Company, Finiiedei phis, 2 's., it corporation of Pcnnsyivsnie Appiicetion llebruoi'y 17, 1944, Sexist his, 522,?

to cities (oi. its-sot ii My invention relates to e novel system of cit cuitbreokers arranged for sequential tripping over the entire protective tripping range of the circuit breakers including the short Oliililit cur= rent senses, and more particularly solutes to novel circuit breelser apparatus provided with direct acting overload devices which they be adjusted to secure sequential tripping with respect to other breakers in the system,

In distribution systems within, for instance, a. large industrial plant, the power enters plant through c. main circuit breaker to the main dis-= tributlon switchboard and is there fed out on a number oi feeder circuits each protected by circuit breaker, These i'eeders may escii go to large loads. Eiome, or all, however, may go to additional distribution switchbosrds where they are egsin divided into smaller distribution citcuits. Each of these circuits may in turn so to load centers or power panels for distribution of the energy to s multiplicity oi loads.

Distribution systems of this type (or which a simplified diagrammatic illustration is hereinafter shown in the figures) are utilized not only in most industrial plants, but also wherever a large quantity or apparatus in a. relatively compact unit must be operated from a. central power source.

In such distribution systems, the fault current due to fault or short circuit conditions in one of the feeder circuits, or even in one oi. the load circuits, passes through several breakers in series and may result not merely in a tripping of the circuit breaker protecting that particular load, but in a tripping 01 each of the circuit breakers back of and in series with that par-- ticular circuit breaker back to the source, so that one of the main feeder breakers, or even the main breaker itseli, may be tripped and thus disconnect the entire distribution system.

Accordingly, the primary problem to which this invention is directed is the construction and arrangement 01' such circuit breakers in a distribution system in such a novel manner that high speed selective trlpping will occur, and so that the circuit breaker nearest the fault will be operatlve to clear an overcurrent, fault, or short circuit condition on the particular circuit it is protecting before the circuit breakers between it and the source can complete a tripping operation, and so that each circuit breaker in the system will be protected by the circuit breaker immediately behind it toward the source.

More specifically, I have invented a. novel system in which the overload mechanisms oi the it circuit breakers in the system are so adjusted that the suioiiect ciscuit creditors for protecting the individual lends have a higher speed trip characteristic other bieuisers in series with them, up to their maximum interrupting capscity. At or below innidniuiu interrupting cepecity oi iced bseuiseis, the adjustment of the overload mechanism oi stliscent circuit breaker in series with the iced unit breaker (toward the combo) becomes quick acting to trip its associated circuit bteukeis quickly and, ther :fore, protects the smaller iced breaker. The overload mechsnism of this adjacent circuit breaker is in turn sdjustecl to trip its associated brenker foster then next circuit breaker (toward the source) in the series circuit thereby preventing; tripping oi this next ciicuit breaker, ot short circuit values approximately up to or below the maximum interrupting copecity of the preceding circuit breaker. This last circuit breaker is, in turn, tripped substantially instanstsneously at short circuit currents of values substantially equal to or below the maximum interrupting capacity or the circuit breaker ad iscent it toward the load.

In sequential tripping systems heretofore employed, the time separation between the various circuit breakers in the system has been effected by the provision of relays which have been set to various time delays and which, on operation, energize the shunt trip coils. Such systems are either very expensive and involved or can only provide sequential operation by timed intervals in the range oi seconds since it is necessary in such a system that the relay first be energized sumclently long to pull up its armature to close its contacts. When the armature has been moved to the energized position, and then only, does it energize the shunt trip coil which in turn must operate a second armature to operate the trip mechanism. Where instantaneous features were added, as was often the case, all circuit breakers in the sequence would open, thus losing continuity of service.

I have discovered that I can secure sequential tripping of circuit breakers in a. power system not only in the overload current ranges such as may occur in motor starting circuits, but also in the range of short circuit currents where the tripping must be substantially instantaneous.

This I efl'ect by providing overload devices having an inverse time ratio which may substantially simulate the heating conditions 01a. load such as a motor to provide a time delay trip for the protection of such a load. .This is followed by a quick trip protection at greater overload conditions such as at two to ten times th overload value of the particular breakers with a short inverse time or definite minimum time characteristic. In addition, a more definite ratio can be obtained by saturation of the magnetic circuit in the overload device.

Finally there is provided an instantaneous trip mechanism individual to each of said breakers. This latter is so arranged with respect to each of the other circuit breaker trip curves that each of the larger breakers (in a cascaded system) has substantially the same instantaneous tripping time as the next smaller breaker at the interrupting capacity of that smaller breaker.

At less than this interrupting capacity each of the quick trip mechanism, however, has a slightly lower tripping operation measurable in terms of a few cycles than the next smaller circuit breaker so that sequential tripping is still effected in such a short circuit current range close to maximum interrupting capacity of the breakers of the system. I

Accordingly an object of my invention is to provide a novel system in which sequential'tripping is secured in the short circuit current ranges and without substantial tlme'delay in the tripping which would otherwise tend to damage the circuit breaker and the equipment being protected thereby, and also reduce interrupting capacity of the breakers.

A-further object of my invention is to provide a novel power system in which the circuit breakers are all arranged to have characteristic curves for protecting normal overloads such as currents in motor circuits, in which sequential operation is secured and which also provides sequential operation at short circuit currents where very fast operations of the circuit breakers are necessary.

A further object of my invention is to provide a novel sequential tripping system in both the long time delay periods and quick trip operating periods.

In order to secure the sequential tripping at short circuit current values where extremely fast operations are necessary, I have discovered that I may, by the use of time delay mechanism such as inertia members in the overload devices, effect close timing between the overload devices of successive circuit breakers at short circuit values of current. This is due to the fact that the operation of the tripping mechanism of the circuit breaker is effected by a direct acting overload coil and that the inertia or other time delay devices are accurate for very short timing periods.

In one form of my invention there is interposed between the armature and the tripping mechanism of the circuit breaker an inertia mass which provides the inverse time delay in the movement of the armature towards the tripping mechanism. When however one of the circuit breakers having a slightly faster operation engages the tripping mechanism and the circuit breaker thereupon eflects an opening of the system, the remaining armatures of the other circuit breakers in the system (each having been delayed by the mass in the manner herein described, for slightly longer periods) will not yet have reached the tripping position; and since the clearance of the fault by one circuit breaker will reduce the magnetic attraction exerted by one overcurrent magnet on the armature to the full load level or less, and since the armature is normally restrained by a spring having a somewhat greater force than that exerted by the magnet at full load even at the reduced air gap, the armature will return without reaching the trip position.

Although the masses in the overload devices of each of these other circuit breakers will, through their inertia, continue to move forward. the energy stores in these masses is ineffective to perform any further action on the tripping mechanism since actual tripping is, as stated above, efiected by direct .action of the armature on the tripping mechanism and the armatures being of exceedingly lightweight and being held back by comparatively powerful springs have been restored. as stated above, immediately upon the opening of the circuit by the next lowest breaker.

In other words, by a reliance on the use of a very light armature restrained by a comparatively powerful spring, there is at no time any substantial kinetic energy stored in the armature in its movement in response to the overload magnet.

Accordingly. a further object of my invention is to provide novel direct operating overload apparatus in circuit breakers to secure a novel sequential tripping system.

Still a further object of my invention is to provide restraining or tim delay mechanism on the quick trip armature of the overcurrent trip magnet.

Still another object of my invention is to provide a sequential tripping system in which the circuit breakers directly operated from the ormature have inertia members interposed between the armature and the tripping mechanism for providing inverse time action in the quick trip period and enable sequential tripping action in this period as well as in the overload period.

In selecting and constructing circuit breakers for installation on such a system in accordance with this invention, some or all of the following conditions are necessary:

1. Each main, feeder, sub-feeder, and load center breaker should preferably have a current carrying capacity equal to the carrying capacity of the cable or the load that it feeds.

2'. The overload tripping device should have a time delay feature greater in current value and time than the normal operating surges that are imposed upon it, such as motor starting current. This is to prevent unnecessary tripping on harmless overloads. The time delay should have inverse characteristics, and be selective with the other breakers in series with it.

3. At current values greater than normal surges, each breaker should trip as quickly as ossible to minimize any damage to the breaker itself or the cable or load which the breaker feeds.

4. But, at current values greater than normal surge values, there should be sufflcient time delay in the short circuit device of the breakers in series, so that the breaker nearest the fault will open first. Only this breaker should open (if the fault current is within the interrupting capacity of this breaker) leaving the remainder of the system intact and feeding the load. Here selectivity is obtained by the higher speed selective'device.

5. If the fault current is greater than the interrupting capacity of the breaker nearest the fault (as may happen in installations where breakers are installed in cascade") then, not only must the breaker nearest the fault open in the shortest time, but also the next breaker in series, which has a higher interrupting capacity. This breaker must open to aid and protect the first breaker, and must open quickly. It the'sec ond breaker in the series has insuficieht lnter= rupting capacity the process must continue back towards the main breaker until a breaker opens that can clear the fault. n these high values of current, the breakers must open quickly to limit any damage and only the necessary breakers should open. Here the high speed instantaneous element is efiective to trip faster than. either of the two timing elements.

6. On each of the trip features, calibrated odjustment should preferably be provided so that a breaker may be coordinated with the other break= ers in the system in which it may be used.

In the foregoing conditions or requirements. the first three items have been known cud ere in substantial use. The lectures described in items 4, and s set forth objects which my present invention is designed to provide and carry out.

These objects will become apparent iron: the following description and drawings in which:

Figure l. is a schematic diagram of e. group oi circuit breakers in a typical. distribution system together with a graph showing the tripping charecteristics oi each of the circuit breakers in the group.

Figure 2 is c. schematic diagram oi another typical distribution system where, in addition to the problem or the selective tripping of feeder breakers, there are goresented the problems which arise from the utilization of two sources of power together with bus tie breakers; this figure also includes a graph showing the tripping characteristics of the breakers in the system.

Figure 3 is a side view showing the construction and operation of a time delay device for a typical circuit breaker in the distribution systems of Figures 1 and 2; the view of Figure 3 shows the relationship of all of the parts in the lie-energized position of the circuit breaker tripping armature.

Figure 4 is a view corresponding to that of Figure 3 showing the position of the parts of the momentum absorbing device of Figure 3 after an overload has persisted long enough to break the film between the discs of the dashpot and the said discs have separated, allowing the armature to go to the closed gap position to trip the circuit breaker.

Figure 5 shows the position of the parts of the device of Figure 3 when the current is of sufficient value to bring the quick trip elements into play.

Figure 6 is a view corresponding to that of Figure 3 showing the position of the elements thereof, however, when there is an extremely heavy short circuit and no delay at all is desired.

Figure 7 is a view showing a modified form of momentum absorbing device for a circuit breaker showing the armature and associated parts in the unenergized or unattracted position.

Figure 8 is a view corresponding to that of- Figure 7 showing the position of the elements for tripping after the dashpot discs forming a time delay have separated.

ill

Figure 11 is a view of a further modified form of momentum absorbing device for utilization in connection with the present invention showing the parts thereoi in the unenergized position.

Figures l2, l3 and 1? illustrate the successive steps or the operation of the device of Figure 11 for tripping an overload es the dashpot discs separate giving the time delay.

Figure 14 illustrates the quick trip position under heavy overcurreht conditions.

Figure 16 is a view of another modified form of momentum absorbing device for use in connection with the present invention.

Figure 17 is 2. view oi another modified form of momentum absorbing device for use in com nection with the present invention.

Figure 18 is a view showing a somewhat n1odifled iorm oi the construction of Figure 17.

Figures 19 and 2t) cross-sectional views partly in elevation showing the manner in which one of my tripping devices (that oi Figures l to it) may be incorporated in a circuit brook-er structure.

Referring now to Figure l, I have here shown a typical distribution system having a plurality of circuit breakers together with o. graph showing the tripping characteristics thereof. In this dis tribution system, the electrical energy is distrib uted at a utilization voltage oi. dill volts, the various interrupting capacities for each oi the breakers are shown in the curves.

The power enters the main plant by the circuit breaker l, and then passes to e. main distribution switchboard. whence it is out on a. number of feeder breakers 3. These feeders may each go to large loads. some, or all, however, may go to additional distribution switchboerds where they are again divided into e. plurality of small distribution circuits to which energy is fed out over the circuit breakers 2. Each oi? these circuits may in turn so to load centers or power panels for distribution of the energy over the circuit breakers i to a multiplicit of loads.

As above pointed out:

1. Each circuit breaker should have a, continuous capacity approximately equal to the capacity of the cable or the load (whichever is smaller) that it feeds.

2. Unnecessary tripping on harmless overloads, occurring because of normal operating surges, should be avoided by an appropriate time delay feature having proper inverse time charactervalues greater than the normal surge values,

' er should be eifectlve to clear that fault without Figure 9 is a view corresponding to that of I Figure 10 is a view corresponding to that of Figure 7 showing the final tripping position of the device of Figure "l.

causing a tripping of circuit breakers 2, 3 and 4. Consequently, breakers 2, 3 and 4 should have sufllcient time delay so that breaker I will have an opportunity to clear the fault.

5. However, if the fault current is greater than the interrupting capacity of the breaker nearest the fault, then not only should the nearest breaker open, but also the next breaker in series which has a higher interrupting capacity. Thus, should the fault in a load circuit protected by circuit breaker I be greater than the capacity of breaker i, but less than the capacity or breaker 2, then not only should breaker I open immediately, but also breaker 2 should open as quickly as possible to protect not only the apparatus originally protected by breaker l, but to protect breaker I. If breaker 2 should have insufllcient interrupting capacity for this purpose, then breaker 3 should'open; and ii breaker 3 should, in turn, have insuflicient interrupting capacity, then breaker 4 should also open. I

Thus, on extremely high values of current, the breakers must open quickly without any time delay to limit any damage; and yet, however, only the necessary breakers should open. 1

6. Calibrated adjustments should be provided on the trip features of each circuit breaker so that a circuit breaker may be coordinated with the other breakers in the system in which it may be used. I

The graph of Figure 1 illustrates these operations in connection with the distribution system of Figure 1. Each of the circuit breakers in the distribution system has similar characteristics of operation, and a specific description of one of the curves for one of the circuit breakers should sumce to illustrate the operation of the reset at a high value to take care of starting motors directly across the line and other large surges frequently encountered in present day installations.

At ten times normal current or 6000 amperes at point I), the quick trip feature comes into play. This quick trip also has an inverse time feature. but the time delay value is very small, being of the order of one to six cycles of a 60 cycle wave. As shown, however, at portions and d of curve 2, even this small time delay is defeated, and breaker 2 will open immediately at the value of the interrupting capacity (15,000 amperes) of the next smaller breaker (circuit breaker i) to protect this next smaller breaker. (For safety. this instantaneous trip may be 80% of 15,000 or 12,000 amperes.)

This illustration of the operation of circuit breaker 2 in connection with curve 2 illustrates a main principle underlying the present invention-that is, that each circuit breaker is ordinarily arranged to open the circuit which it protects before the circuit breakers of greater capacity back of it in series come into operation. Where however the capacity of the circuit breaker nearest the fault is exceeded, the next circuit breaker of greater capacity back of it in series will come into operation, and so on, until a cir-' cuit breaker is reached which can clear the load.

Each circuit breaker is given time delay characteristics which enable it to come into operation at the appropriate times, in order to protect the circuits as well as the circuit breakers which follow it in series.

In each circuit breaker a quick trip operation may be provided in addition to the overload time delay, which has a short inverse or minimum time characteristic. This short inverse time delay functions to assure that any smaller breakers nearer the fault trip first and any larger breakers further from the fault trip later than any given breaker in the series.

Under very heavy currents. however. which completely exceed the interrupting capacity of the next smaller circuit breaker in series following a given circuit breaker, even the quick trip time delay is by-passed, and the given circuit breaker opens instantaneously without any delay whatever. This provides for immediate protection not merely of the original load and circuit, but also of the circuit breakers which follow in series after the given circuit breaker. Also, the instantaneous feature may increasethe ruptur= ing capacity of the breaker to which it is attached.

Thus in the system shown in Figure l, the circuit breaker i, as will be obvious, requires no instantaneous trip, but the quick trip is useful in order to quickly clear a fault before damage occurs and to make it selective with breaker 2 beyond 6000 amperes. Thus following curve 1 for circuit breaker i, the section a, as above described, shows the operation of the circuit breaker under overcurrents which permit the time delay to operate.

Circuit breaker i is normally a 100 ampere circuit breaker with time delay up to ten times normal current; after which a quick trip is provided having a very short inverse time delay. Circuit breaker i has maximum interrupting capacity of 15,000 amperes.

Thus, following curve 1, it will be seen that at an overcurrent value of a little more than 200 amperes, it will take more than 100 seconds for the circuit breaker to trip. At an overcurrent, however, of 700 amperes, the circuit breaker will trip, should this overcurrent continue for only 10 seconds.- At an overcurrent value of 900 amperes, the circuit breaker will trip, should this overcurrent continue for about 8 seconds. However, should the overcurrent value be 1000 amperes, or 10 times the'normal rating, then the quick trip comes into play, as shown at curve b or c, and the circuit breaker will trip within .05 second or substantiall three cycles.

At greater overcurrent values, the tripping operation will even be faster, as for example at 4,000 amperes in which case tripping occurs in .016 second or substantially one cycle.

- cuit breaker No. 2 would take 10 seconds to open tion d of curve 2.

The other elements of curve 2 correspond in operation to the previously mentioned elements of curve 1. However, it will be seen that even a quick trip operation 17 of curve 2 occurs with some small time delay over portion c, roughly, of the order of .15 second between c and c".

The instantaneous trip at 15,000 amperes is arranged, however, sothat even the quick trip time delay is overcome, and the circuit breaker opens in .016 second, and thus in icss than a single cycle to protect circuit breaker it,

Again, circuit breaker 2 has, as shown on drawing, a maximum interrupting capacity or 25,000 amperes. Consequently, it is necessary that circuit breaker become instantaneous at this point.

Circuit breaker 8, as shown by curve 3, has an ordinary time delay for ordinary overcurrent surges, a quick trip, and a time delay on the quick trip, as above pointed out in connection with curves 1 and 2. Circuit breaker i also has an in stantaneous trip d which comes into operation at 25,000 amperes to by-pass even the quick trip time delay and to make the operation or circuit breaker 0 instantaneous at 25,000 amperes, so that it too trips in about .016 second at this current value.

Similarly, since circuit breaker 0 has a maximum interrupting capacity of 50,000 amperes, circuit breaker 0 is arranged to be instantaneous at this value, as will be obvious from the graph of Figure 1; and thus circuit breaker t is instan= taneous at any value from 50,000 to 75,000 am= peres. The 75,000 amperes maximum interrupting capacity of circuit breaker 0 is designed to be greater than any possible current intensity which may occur in the entire distribution system.

The following specific examples are thus taken from the graph of Figure 1:

a. A fault condition in one of the circuits protected by a circuit breaker I of approximately 2,000 amperes.

Circuit breaker I will open within less than .02 second. The overload time delay of circuit breakers 2, 3 and 4 will not yet have permitted these circuit breakers to go into operations, and only circuit breaker i will benecessary to clear the fault.

b. A fault current of 10,000 protected by a circuit breaker Circuit breaker I will clear the fault within .02 second. The quick trip of circuit breaker 2 will have commenced operation, but the quick trip time delay. will have been brought into action thus delaying the opening of circuit breaker 2 to about .05 second. Before .05 second has elapsed, circuit breaker I, operating within less than .02 second, will have tripped open and cleared the fault, so that the quick trip time delay of circuit breaker 2 will thus have delayed the opening of circuit breaker 2 until the fault has been cleared, and the armature of circuit breaker 2 will then drop back without tripping circuit breaker 2. The quick trip time delay, as hereinafter pointed out, is essentially a momentum or energy absorbing device.

0. Assuming now a fault in the circuit protected by a circuit breaker I of 20,000 amperes- Circuit breaker I will trip open within less than .02 second, but since its maximum capacity is 15,000 amperes, it will not serve to clear the fault. Simultaneously, circuit breaker 2, which becomes instantaneous at only 15,000 amperes, will be brought into immediate operation and will open within the same time of less than .02 .second thus protecting circuit breaker I. The quick trip of circuit breaker 3 will have been brought into operation, but the quick trip time delay will have slowed down the operation of the quick trip of circuit breaker 3, so that at 20,000 amperes it would take .05 second to open; but by the time .05 second has elapsed, circuit breakers I and 2 will have opened, thus clearing the fault by means of a. circuit breaker having sufllcient capacity to amperes in a circuit do so, and the momentum absorbing device on circult breaker 3 will then have been suillcient to prevent the completion or the trip of circuit breaker 2.

a. Assuming a fourth current mun of some e. Assuming 00,000 ampere fault in one oi the individual circuits protected by circuit breaker No. 8 that is fed by circuit breaker No. 0-

In that event, the circuit breaker No. 4 individual to that circuit will open instantaneously. Similarly a 40,000 ampere fault in an individual circuit of one oi the circuit breakers No. 3 would only cause that particular No. 0 circuit breaker to trip leaving the remainder of the system unaifected.

It is believed that these eration of my system.

Thus, even though an overcurrent or short circuit condition occurs, at a value at which the quick trip of a principal circuit breaker is brought into operation-nevertheless, the provision of an energy absorbing device in the quick trip provides a very short time delay of the order of l to 12 cycles for the circuit breaker next in series to clear the fault-so that only those circuit breakers absolutely'necessary to clear the fault will be brought into operation, and so that the others will remain closed.

Even this energy absorbing device which creates an extremely short time delay, as above pointed out, may be by-passed where the overcurrent or fault condition is of such value as to exceed the interrupting capacity of this or any other circuit breaker in series, in whichcase an instantaneous trip occurs.

The adaptability and flexibility of the sequention tripping arrangement described in Figure 1 makes it possible to apply this system in more complicated circuits. Since each of the characteristics of the tripping devices may be varied over wide ranges, many variations of the system and the settings may be made while nevertheless remaining within the principles of my invention.

In many systems, the normal surges may be small and the time delay may therefore be set for the commonbus oi the examples explain the opa much shorter period; or the quick-trip may be. set at three times normal instead of ten times normal for closer protection.

In the above, I have given a more or less general application of my invention. In order to illustrate the kind of protective problems that may be solved in accordance with the principles of this invention, I have included Figure 2 which illustrates a special case. In Figure 2 the system includes, in addition to tive tripping of feeder breakers, also the problem of two sources of power and bus-tie breakers.

Tripping of the feeder breakers is in the same manner as for the radial distribution system described in connection with Figure 1. Consequently, the curves with respect to breakers I and 2 need not be again reviewed.

In the case of Figure 2, however, the generators brought into operation to clear the problem of the selecl1 feeding the system are relatively small and can supply only a limited amount of short circuit current. For that reason the quick trip and instantaneous trip of all the breakers in this system may be set for a lower current value than the distribution system shown in Figure 1.

For instance, in Figure 2 while the quick trip of breaker No. l isthirteen times normal, the quick trip of breakers Nos. 2 and 3 and 4 is less than twice normal as compared with ten times normal in the typical distribution system shown in Figure 1.

Likewise the instantaneous trip on breakers Nos. 2, 3 and s is set at approximately 15,000 to 20,000 amperes so as to be well within the short circuit current given by three generators fees into a fault in the fourth generator.

Since normally the load is fed at each generator station and the bus tie is provided for emergency operation, the bus tie breaker has been selected to have a current capacity equal to one generator only and its overload calibration is set to 80% of one generator capacity.

Referring to the curves in Figure 2, the advantages of this system will become apparent if we assume various fault conditions and note the operation of the system:

1. A fault in the feeder protected by breaker No. I of less than its interrupting capacity of 15.000 amperes. will be opened by breaker No. i without disturbing any of the rest of the system.

2. A fault in the feeder protected by breaker No. l greater than 15,000 amperes and not exceeding 25,000 amperes will cause the opening of breaker No. I and breaker No. 2 leaving the remainder oi the system unaflected.

s. A fault in the feeder protected by breaker No. l exceeding 25,000 ,amperes will be fed from three sources, from each of the two generator breakers No. 4 and the bus tie breaker No. 3. Even if th current should divide equally, all thre of these breakers would open to clear the fault in approximately 6 cycles (60 cycle wave) leaving one generator station in operation.

4. Assuming a fault on bus ll of any current value. then the two generator breakers No. 4 and the bus tie breaker No. 3 must open to clear the fault,

5. Assuming a fault on the bus rent value, then the breaker No. 3 receives twice as much current as any generator breaker which w ll result in the bus tie breaker No. 3 opening before the generator breakers No. 4. This will isolate the bus tie circuit without affecting either of t e generator stations which will continue to feed their respective loads.

6. Assuming a fault in the generator 52 which will be fed by the other generator connected to the bus and also by the two generators over the bus t e, breaker No. 4 for generator i2 due to this high current, will open in advance of the other generator breakers or the bus tie breaker 3, and this generator will be isolated without interfering with the operation of the remainder of the system.

With these settings, it will be seen that all faults that may be expected on the system are cleared by the breaker nearest the fault and only the necessary breakers will be opened.

Thus, circuit breakers 2 protect the circuit breakers i, as will be seen from the chart of Figure 2 in the manner previously described in connection with Figure 1. It will also be seen that tie 9 of any curthe full short circuit current of all the generators in the system.

The element that makes this type of operation possible is the construction of the very short time delay used on the quick trip devices. Thus, in

addition to the ordinary time delay which pre vents the tripping of the circuit breakers as a resuit of normal current surges, there is an additional relatively minute time delay in the quick trip with an inverse characteristic and instantaneous trip device. Accordingly, where the over= current or short circuit condition is of suficient intensity to overcome the time delay device and thus result in a quick trip without the interposition of the normal time delay, my invention contemplates that even the quick trip device be fitted with atime delay device resulting in a relatively minute delay in order to enable the selective operation above described to occur.

Where it becomes necessary, however, that absolute instantaneous operation be achieved, then my invention contemplates that even the relatively minute time delay of the quick trip device be overcome so that on greatly excessive overcurrent conditions or on full short circuits, all of the devices will be fully protected. Also this instantaneous trip increases the rupturing capacity of the breaker to which it is attached.

One form of such combination time delayquicktrip-instantaneous device is shown in Figures 3 and 6. I

In these figures only the tripping armature and its associated elements are shown. It will be understood, of course, that the tripping armature structure here shown is part of a complete circuit breaker and that the various devices secured to said armature may, with only obvious adaptations, be secured to cooperate with any type of tripping mechanism of a circuit breaker.

It must be understood that the minute time delay achieved in connection with the quick trip device must be a time delay which is of the very shortest duration possible which will serve to momentarily halt the armature, such as momentarily delaying .the motion to clear the overcurrent or short-circuit condition.

If this relatively minute time delay is of too great a duration, then the circuit breaker does not fully protect the line and the load between which it is connected. If the time delay is too short, then the circuit breaker may b unnecessarily brought into operation. The time delay period selected therefore must be just that time period which is necessary to afiord the next succeeding subsidiary circuit breaker time to clear the fault. This time delay should not be of any greater duration.

Obviously of course, as above pointed out, should the fault condition be such that the next succeeding subsidiary circuit breaker could not possibly clear the fault, then even this minute time delay should be removed. For this purpose the time delay on the quick trip device contemplated by this invention requires reliable operatlon at short periods of time, such as 1 to 12 circuit breakers 3 and 4 are respectively arranged 76 cycles.

of the armature, to

In Figure 8 the various parts of the time delay device are shown in the at-rest or de-energized position where no fault of any kind has occurred and where only normal current is flowing with no surges of any kind. The tripping device is enclosed in any suitable housing H which may be secured in any appropriate manner to a circuit breaker panel or housing. The tripping mamnet as (which is ordinarily energized by a series coil) is secured in appropriate position with re spect to the housing in any suitable manner, as for instance by the angle brackets 23 and 26 which in turn are secured tothe housing it by the bolts and 28.

The tripping armature l0 isurotatably mounted on the pin it which in turn is secured between side plates of the housing. Armature it is pro vided at one end thereoi with a plate 82 oi a suitable magnetizable materialwhich may read ily be attracted by the magnet 22 on the occur rence of pro-determined fault conditions. The armature it is provided with an adjustable abutment 3b which bears asainstthe undersuriacc '38 of the latch tripping member :1. Latch tripping member 31 is likewise rotatably mounted on the pin it and at its opposite end is provided with a roller 38 held in position in any suitable mannor, as for instance by the cotter pin 39, which roller '(as is shown in Figure 6) may be brought into engagement with the latch mechanism 40 of the circuit breaker itself in order to rotate this latch mechanism for the purpose of tripping the circuit breaker open.

Any suitable means (not shown) may be provided to retain the trippin member 31 in the normal position shown in Figure 3. Such means are commonly known and used in the art and may, for instance, comprise a coil spring (not shown) surrounding the pin 3i and bearing against the right hand surface of the tripping member II. The abutment I! is adjustable, as above pointed out, by reason of the fact that it constitutes the head of a bolt 42 which is threaded through the suitable tapped openings 43 in the armature so and which may be adjusted by means of the slot 44. It is held in the proper adjusted position by the lock nut 48.

The armature 30 has secured thereto (in the manner hereinafter described or in any suitable manner) a quick trip lever III which (in all cases except for the instantaneous trip) rotates with the armature 30 as it rises and falls. The quick trip lever 50 is itself rotatably mounted on the pin 3| and is secured to the armature 30 in such manner that for all purposes it is substantially a part thereof; except that when the instantaneous trip point is reached, as hereinafter described, the armature 30 may be freed from the quick trip lever 50. This manner of securement will be more specifically described in connection with the description of the operation of the tripping device at and above the instantaneous trip point.

Thequick trip lever to cooperates with the elements hereinafter described to aflord the minute time delay previously pointed out. Since this quick trip lever is itself intended to engage the momentum absorbing device or weight without affecting the armature setting itself, the quick trip lever is not intended to have any specific weight of its own. In other words, the quick trip lever Ill serves as a'means for transmitting the driving force of the armature to a momentum absorbing weight and in an ideal situation trip lever Ill would itself be substantially weightless tween the armature 30 itself and the magnet '22.

An additional weight on the armature itself may well make this calibration diiiicult.

In order. therefore, to attain this substantially weightless condition of the quick trip lever It, a coil spring I: is provided which surrounds the bushing 68 on the pin'il. one end 55 or the coil spring bears against the inside wall of the housing it and the other end it of the coil spring it bears against the right hand surface of the quick trip lever It.

The coil spring I2 is thus arranged so that it will substantially counterbalance the weight of the quick trip lever 50 so that the quick trip lever Eli will not itself act as a drag upon the armature 30 while the quick trip lever will nevertheless be able to transmit the momentum of the armature to the momentum absorbing device.

The momentum absorbing device comprises a mass as which is rotatably mounted on the shaft it. A spur gear 02 is also rotatably mounted on a shaft 8| alongside the mass 60. The gear teeth 83 in the quick trip lever 50 always mesh with the teeth of the spur gear 62. Consequently any movement of the quick trip lever 80 will result in corresponding rotation of the spur gear 62.

A pawl 88 is rotatably mounted on a stud B8 on the mass 80. The end of the pawl is biased inwardly toward the center 8| in any suitable manner as for instance by the coil spring 68. A ratchet 89 is provided on the spur gear 82 alongside the gear teeth of the spur gear 62. It will be clear that this ratchet is so arranged that any upward movement of the quick tri lever so of Figure 3 which thus results in a counterclockwise rotation of the spur gear 82 will, through the ratchet I! and the pawl 85, result in a similar counterclockwise rotation of the mass 80.

Immediately upon the removal of the overcurrent condition which resulted in a rise of the armature 30 and the quick trip lever 50, the quick trip lever and armature may fall back under the influence of the springs hereinafter described, without any interference from the mass 60. This is so because, on the clockwise rotation of the light spur gear 82, there is then no driving con nection between the spur gear 82 and the mass Bil owing to the pawl and ratchet arrangement above described.

By means of the pawl and ratchet arrangement, a quick rc-set of the armature is thus provided in the event that the quick trip time delay has been sumcient to enable another circuit breaker to clear the fault. The mass 60 which has thus absorbed the momentum of the armature 30 during the rise of the armature will therefore, because of the pawl and ratchet arrangement, not be effective to prevent the quick re-set. The

. time delay is thus achieved by reason of the fact .the mass 80 and trips the circuit interrupter.

The time delay which is thus obtained in bringing the mass 60 into movement is of the order of 1 to 12 cycles. In that period of time any This quick trip time delay device is, of course,v

intended to operate only when the circuit conditions are such that the original time delay device has been nullified. In other words, referring back once more to Figure 2, and taking for instance circuit breaker 2 in that chart, the original time delay which has not thus far been described, is effective from 900 amperes to just short of 1600 amperes to eflect the necessary time delay to avoid false tripping on normal surges. The quick trip setting is eflective at 1600 amperes that is, at 1600 amperes the original time delay is nullified, the circuit breaker tripping device operates as if there were no original time delay, and the quick trip relatively minute time delay which has just been described comes into operation. Subsequently, at 20,000 amperes the instantaneous setting is reached where even the quick trip relatively minute time delay is nullified.

The ordinary time delay which prevents false tripping on normal surges will be described first. This ordinary time delay comprises the dashpot 15, in which the sucker disc 16 connected to the armature in a manner hereinfater described engages the disc 11 at the base of the dashpot. The overload device does not permit movement of the armature so that the setting of the armature is not afiected by overloads until the sucker disc releases. Thus after overload conditions the current may drop to 100% and the armature will not continue its travel to trip. The short time device is restrained at the first part of the stroke and releases from restraint at the last part of the stroke. It will also reset it the current drops to 100%.

The operation oi. the dashpot 15 which aflords a time delay by reason of the fact that discs 16 and 11 cannot be separated until the oil film between them is broken, is well understood and requires no further description. The upper disc 16 is connected by means of an extension 80 and a pin 8i to the vertical sleeve 82. Rod 83 is slidably mounted in the sleeve 82 and extends through an opening in the top cover plate 84 of the sleeve 82 and is connected in any suitable manner to the pin 85 on the armature 30. A compression spring 86 is mounted between an adjusting washer 81 on the rod 83 and the underside of the top plate 84. The washer 81 may be vertically adjusted along the rod 83 to vary the compressionof the compression spring 86 and once it is moved to the proper position may be maintained in a set position with respect to rod 83, by means of the set screw 88 which projects through a vertical slot 89 in the side of the sleeve 82.

A similarly adjustable washer 9| held in position by the set screw 92 may be provided on the rod 83 above the top plate 84 of the sleeve 82 to limit the downward movement of the rod 83 so as not to impose any additional counterclockwise rotative strain on the armature 30 and the quick trip lever 50. I

The compression spring 86 is adjusted so that on normal surges it is substantially uncompressible. Thus for instance, referring again to circuit breaker 2 of Figure 2 the time delay setting begins to be effective at 900 amperes. At this point the discs 18 and I1 begin to separate and a time delay is aflorded by the time taken to break the oil film between discs 16 and'li. The force exerted on the armature 80 by the magnet at 900 amperes is not suiilcient however to compress the spring 50. The spring. 86 is adjusted however so that anyiorce exerted by the magnet on the armature will not be sumcient to compress the spring 88 until the current value reaches or exceeds 1600 amperes. Accordingly, up to 1800 amperes the time delay device operates as if there were a single, solid bar connecting the armature with the'sucker discs. Accordingly up to 1600 amperes the e delay is achieved only by the time taken to separate the sucker discs in the dashpot.

The compression spring 88, however, is so adjusted that at 1600 amperes the magnet 22 exerts sufiicient force on the armature 80 to compress the spring 0%. When such force is exerted which is thus suificient to compress the spring 60, then the armature 3d rises even though the discs is and it stay together. The rod 03 is pulled up so that the washer 8T! presses the spring d6 against the top plate $6 and the armature on such overcurrent conditions (in the example takenl600 amperes or over) may thus rise toward the magnet as if the time delay dashpot 15 were not secured thereto, as illustrated in Figure 5.

However, the spring tends to restore the armature to its original position if the current drops to 100% before the tripping motion is completed.

According y, it is now seen how both the ordinary time delay and the quick trip time delay may be incorporated in a single unit. In the example taken (circuit breaker 2 of Figure 2) the armature 30 now moving up quickly and pulling up the quick trip lever 50 with it rotates the spur gear 62 and consequently rotates the mass 60. This operation results in the very short time delay, above described, and for the purposes above described.

It is obvious of course that the quick trip timev delay element which includes the lever 50 and the mass 60 has no appreciable effect on the movement of the armature between 900 amperes and 1600 amperes (in the example' takencircuit breaker 2 of Figure 2). Here the rising of the armature under the time delay afforded by the separating of the discs 18 and TI is relatively very slow and the mass has no appreciable efiect in slowing up this initially slow operation.

The quick trip as above pointed out comes into eflect when the time delay i5 is mechanically shunted out by the compression of spring 86' and when the armature moves very quickly. The quick trip time delay acts in eifect as a momentum absorber and .timer to absorb the initial shock of movement of the armature 38 and thus efiect a time delay of from 1 to 12 cycles. The quick trip time delay acts throughout the time delay period to delay the motion. If the magnet 22 continues to be energized sufliciently to attract the armature 30, the armature will nevertheless proceed with this delayed action through its course to eilect a tripping operation.

Under certain conditions, as above described in ,connection with the discussion of Figures 1 and is not directly and rigidly secured to the armature 30, but rather is so secured thereto that for all purposes up to the instantaneous trip point it operates with the armature while above the instan-.

taneous trip point the armature is freed therefrom. For this purpose the means of connection between the quick trip lever 50 and the armature 30 comprises a threaded rod Hi which is pivotally secured in any suitable manner at one end to the pin 85. The opposite end of the rod idli passes through an appropriate opening tilt in the cross-piece 102 on the quick trip lever 50 (the cross piece W2 may be simply secured to the upper surface of the quick trip lever I50 and extend normally thereto in order to provide for the open ing lti; or in order to obtain a better balanced structure, two quick trip levers 50 may be used on either side of the armature 30 and connected together by the cross-piece M2) The rod 500 is provided at its lower end with an adjustable nut m6 which carries a spring center ing sleeve [10?]. Adjacent the other end of the rod not another adjustable nut W4 is provided which also carries a spring centering sleeve {405.

The nut 904 is greater in diameter than. the open "ing Hill in the bridging plate 402, while the sleeve 105 is smaller in diameter so that the said sleeve may readily pass therethrough. A compression spring idisvcapture'd between the upper surface of the adjusting nut 60S and the undersuriace of the bridging plate 502, and is adjusted to the proper compression by appropriate rotation of the nuts tilt and tilt.

When the proper compression of the spring H0 is obtained, then the nuts I04 and lilo are locked in position by the lock nuts iii and M2. Compression spring M0 is so adjusted that for all current values up to the predetermined instan= taneous trip point it is substantially incompressible; and thus for all current values up to that point the armature 30 and the quick trip lever 50 areessentially a single unit. Spring i is, however, so adjusted that at the instantaneous point, and above, the magnet 22 exerts sufilcientforce on the armature 30 to compress the spring H0.

Accordingly, above this instantaneous value the spring H0 may be compressed by the rise of the armature 30 so that the armature may operate free of the quick trip lever 50. Thus again referring to circuit breaker 2 of Figure 2, it is again pointed out that the time delay effected by the dashpot 575 is effective between 900 amperes and 1600 amperes. At 1600 amperes the spring 80 becomes compressible so that the dashpot id is mechanically shunted out. At 1600 amperes, however, the quick trip time delay becomes efiective so that on rapid movement of the armature 30 the quick trip lever 5t brings the mass 60 into movement so that a relatively short time delay of 1 to 12 cycles is effected.

At 20,000 amperes which is the instantaneous trip point of breaker 2, Figure 2, the quick trip time delay is itself mechanically shunted out reason or the fact that the spring till becomes compressible at that point. Accordingly the ar mature 30 may rise and if the quick trip lever 50 is even momentarily held back when the cur ver is thus detained; and the armature 30 is thus freed from the quick trip lever by reason of the fact that the spring H0 is compressible as above pointed out.

As above pointed out, the spring 86 is adjustable so that different pick up settings for normal surges may be obtained. Likewise the spring H0 is adjustable so that different instantaneous trip points may be obtained. The armature itself is calibrated by means of the spring l which is attached at its upper end to an extension of the end plate 84 of sleeve t2 and at its lower end to the adjusting lever Mil. That is, it will be obvious that the spring are need not necessarily be connected directly to the armature since the end plate M is connected to the armature through the sleeve til, the rod and the compression spring 86, and since the compression spring 06 is substantially incompressible at current values below the quiclr trip point.

Accordingly, initial calibration of the armature is achieved by [means of the spring i20 so that for all current values up to the quiolr trip point the spring lid may be relied on to main- "tain the predetermined calibration of the circuit breaker tripping device. The fact that the spring 820 is connected, however, to the end plate 8d of the sleeve 02 makes it possible also to mechanically shunt out the spring 120 when quick operation is desired. Thus, when the time delay afiorded by the dashpot lid is mechanically shunted out by the compression of spring 36, the calibrating spring i253 is at the same time mechanically shunted out and the operation of the armature thereafter depends upon the quick trip lever 50 and the mass G0 or in certain cases on the compressibility of the spring H0. Thus, for quick trip or instantaneous operation the possibly complicating factor ofsthe calibrating spring M20 is removed from the necessary calculations. But as above pointed out, up to the point where the quick trip is intended to become efiective by compression of spring 86, the spring 02d serves as a calibrating spring which is a may nevertheless rise although the quick trip is factor in controlling the rise of the armature 30. Also, change in calibration of one spring does not affect the other calibration.

The adjusting lever tZt is an angular member as may be obvious from Figure 3, which at one end is mounted on the pin I23 carried by the lug [24 in the housing 2i, and at the other end carries an extension iZB which bears against the undersurface of the adjusting nut E27. Adjusting nut IE7 is in threaded engagement with the adjusting rod M20. The adjusting nut lt'l has an indicator l2ll which extends therefrom outwardly through the slot M0 in the housing M. The adjusting rod i243 isprovided at its lower end with a thumb screw 1132 so that the adjusting rod 620 may be rotated. Rotation of rod E28 by means of the thumb screw i352 will result in a movement upward or downward of the ad-- lusting nut i This is so because the adjusting nut cannot rotate by reason of the fact that its indicating extension l20 is engaged in the slot l30.- The movement upward or downwardly of the adjusting nut it? will result in a corresponding rise or fall of the end ill? of the adlusting lever Hi and in a consequent adjust ment of the calibrating spring iilil. J-l suitable scale may be placed on the outside of the housing adjacent the slot 13d and parallel to the path oi travel of the indicating extension 3'29 to in dicate the extent of adjustment.

As above pointed out, Figure 3 shows the relation of the parts in the tie-energized position,

19 that is, when the circuit breaker is either open or when it is carrying only normal load, so that the calibrating spring I20 is sufiicient by itself to .prevent a rise of the armature 30.

Figure 4 shows the relationship of all the parts ."fter an overload has persisted long enough to break the film between the discs in the dashpot l5 and they have separated, allowing the arma= ture to-go to the closed gap posltionto ,trip the circuit breaker. As above pointed out, calibration of the time is secured by turning the dashpot in the usual manner. Calibration of the overload value is secured by changing the tension of the spring E20 as the indicating arm l29 is moved over the scale. The position of Figure 4 therefore, referring back once more to circuit breaker 2 of Figure 2, shows the condition where an overload between 900 amperes and 1600 amperes has persisted for a sufflciently long time to result in separation of the dashpot discs l6 and 71.

Figure 5 shows the position of all of the parts when the current is of sufiicient value to mechanically shunt'out the time delay dashpot l5 by compression of the spring 00 and thus to bring the quick trip into play. In this case the quick trip lever 50 has moved up with the armature. A time delay of short duration as above pointed out has been obtained by reason of the engagement of the gear teeth in the quick trip lever 50 with the spur gear 02 which in turn drives the mass 60. The pawl and ratchet arrangement above pointed out between the spur gear and the mass 60 provides for quick re-set if the overload is removed before the tripping position is reached.

Changing the momentum of the mass 60 changes the time setting.

The position shown in Figure 5 when related back to circuit breaker 2 of Figure 2 shows the condition of the circuit breaker when an overload occurs at current values between 1600 amperes and 20,000 amperes.

Figure 6 shows the position of the parts when there is a severe shortcircuit and substantially instantaneous trip is desired. In this case both the dashpot l5 and the quick trip momentary time delay are mechanically shunted out by the compression of spring H0. Again as above pointed out, only a very heavy short circuit current can cause the magnet 22 to exert sufficient force on the armature 30 to compress the spring I H0. The position shown in Figure 6 when related to circuit breaker 2 of Figure 2 corresponds to a short circuit condition of over 20,000 amperes.

In the foregoing Figures 3 to 6, I.have shown one physical embodiment of a combination time delay-quick trip-instantaneous trip circuit breaker tripping device which will be effective to carry out all of the principles set forth in connection with Figures 1 and 2.

.As has been above emphasized, in order to obtain proper sequential cascading operation, each of the circuit breakers in the system should be provided with a time delay device to obviate false tripping on normal current surges of short duration with a means for obtaining a quick trip above such normal surges (for instance, at 10 times normal load) with means nevertheless for obtaining 'a very short time delay with the quick trip to prevent unnecessary tripping of circuit breakers; and with additional means to mechanically shunt out even the quick trip momentary time delay to obtain a truly instantaneous trip on very heavy short circuit currents.

The construction of the unit shown in Figures 3 to 6 accomplishes all of these functions and thus this unit may be used in the circuit breakers which have been discussed in connection with Figures 1 and 2. Many other arrangements for obtaining these results should of course now .be obvious in view of theforegoing descriptions. In the following I have illustrated and described several preferred constructions which differ in' some respects from the methods and means illustrated in connection with Figures 3 to 6.

In Figures 7 to 10 inclusive, I have shown 7 another design of circuit breaker'tripping device which may be utilized to accomplish substantially the same purpose except that the final instantaneous trip is not shown. The construction shown in Figures '7 to 10 therefore would be used when the circuit breakers are not connected in cascade but where selectivity is required. The design and operation of the quick trip time delay of Figures 7 to 10 has already been described in connection with the description of the shock absorbing devices in my application Serial No. 488,841 filed May 28, 1943, of which this is a continuation application.

Figure 7 shows the arrangement of the parts of the tripping device in the unenergized condition or in a position where the circuit protected by the circuit breaker is carrying the normal load for which it is designed. The tripping device 220 is contained in a housing 222i to the upper portion of which is secured in any suitable manner the pole piece 222 of the series overload magnet. The armature 230 is rotatably mounted on the pin 23! and is provided at its opposite end with a plate of magnetizable material 232 which may be attracted by the magnet.

The armature 230 is provided with an abutment member 235 which engages against the undersurface 236 of the striking member 231. The end 238 of the striking member 237, when the striking member is rotated clockwise by the armature 230, bears against the latch trip 200 of the circuit breaker. The abutment 235 constitutes the end of a threaded bolt 2&2 which may be rotated in a suitably tapp d opening of the armature 230. The adjusted position of the abutment 235 is maintained by the lock nut M3.

A quick trip lever or striking member 250 is also rotatably mounted on the pin 23!. Quick trip lever 250 is provided with an extension 25! through which the pin 285 passes to integrate the quick trip lever 250 with the armature 230. In order to provide for better balance of the structure there may be two quick trip levers 250,

one on either side of-the armature 230, with a similar duplication of the shock absorbing or weight members hereinafter described. This is in accordance with my disclosure in the aboveidentified application.

An abutment 262 is rotatably mounted on the pin 26! and is secured by means of a plurality of bolts 265, 265 to the mass 260. The quick trip lever or striking member 250 has a striking surface 263 which, when the armature is raised thus resultingin a clockwise rotation of the quick trip lever 250, bears against the surface 266 on the abutment 262. As shown in Figure 9, when the armature is attracted by the magnet, the surface 263 on the quicktrip lever 250 strikes against the surface 266 on the abutment 262. These surfaces are so arranged that should the attraction of the magnet continue after they have met, the surface 263 may slide with respect to the surface 266 to rotate the abutment 262 in

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