US3480899A - Circuit interrupters - Google Patents

Description

Nov. 25, 1969 w. LAAKSO 3,480,399

7 CIRCUIT INTERRUPTERS Filed March 18, 1968 I 2 Sheets-Sheet INVENTOR.

WILLIAM L'AAKSO W11 raw;

ATTORNEY Nov. 25, 1969 w. LAAK-SO I I 3,430,399

CIRCUIT-INTERRUPTERS Filed March 18 1968 2 Sheets-Sheet l l 54 I 40 i 807 INVENTOR.

' v "WILLIAM LAAKSO 7O 1' ATTORNEY United States Patent 3,480,899 CIRCUIT INTERRUPTERS William Laakso, Burnaby, British Columbia, Canada, as-

siguor to Federal Pacific Electric Company, a corporation of Delaware Filed Mar. 18, 1968, Ser. No. 713,659 Int. Cl. Htilh 85/30 US. Cl. 3376 Claims ABSTRACT OF THE DISCLOSURE A circuit breaker with a fuse mounted in series with each of the separable contacts. A responder is provided which is responsive to the operative condition of the fuses and which functions to trip and lock the circuit breaker open upon the operation of one of the fuses. The responder gives protection against single phasing and also provides a visual indication at the front of the breaker of the operation of the remotely mounted fuses.

This invention relates to circuit interrupters and more particularly to circuit interrupters of the type comprising a circuit breaker having an overcurrent trip mechanism for interrupting sustained overloads and fusible members electrically connected in series with the circuit breaker for interrupting fault currents which exceed the interrupting capacity of the circuit breaker.

Increased use of electrical power has required larger and larger current handling capacity and has produced an increase in the short-circuit current available. Secondary feeder circuit breakers at a distribution point are normally called upon to carry relatively low currents as compared to the available short-circuit current. Unless certain precautions are taken the short-circuit current may considerably exceed the interrupting capacity of an otherwise suitable circuit breaker. A usual precaution is the provision of a circuit breaker having its overcurrent trips set for the normal current expected on the secondary feeder and having an interrupting rating suflicient to withstand the available short-circuit current. This is an uneconomic arrangement since, in a typical installation, the breaker may have a normal rating of perhaps 400 to 600 a. and the available short circuit current may be in the neighborhood of or in excess of 100,000 a. Breakers of the type normally employed for 600 a. 600 v. service with a 50,000 a. interrupting capacity are considerably less expensive and take up considerably less room than a like unit capable of interrupting 100,000 a. While over loads within the interruption rating of the low rated breaker could be safely handled there are those circumstances where the circuit breaker might be called upon to interrupt a short circuit current in excess of its rated capacity. It is quite possible that the low-rated breaker would fail to clear the fault and would also be destroyed in the process.

Current limiting fuses have been widely used because of their high interrupting ratings. The fuses have been bolted directly to the busses, being used as power takeoff points and they have been used in conjunction with molded case circuit breakers having integral fuse compartments. The current limiting fuse, when used with such a breaker is normally provided with a striker pin. The pin is caused to trip the circuit breaker upon the operation of the fuse, i.e., when the fuse interrupts a short circuit. However, there are many installations where such circuit breakers are not suitable.

lit has, therefore, been necessary particularly in metal clad switchgear, to utilize circuit breakers having high fault current interrupting capacity. The space, size and complexity of the circuit breakers have increased in acp CC cordance with the increased interrupting capacity required. As may be expected, the circuit breakers are very infrequently called upon to interrupt a major fault current and therefore the excess expenditures were burdensome. The use of current-limiting fuses alone had been suggested for such installations to interrupt the major fault currents. However, in order to provide proper protection for the secondary feeders it was necessary to use fuses having a fairly low overload current rating. This low rating resulted in nuisance tripping when minor overloads occurred and required the replacement of such fuses each time such a fault occurred. The circuit breaker elements on the other hand did not need to be replaced when the breaker tripped due to an overload as compared to fuses. However, fuses are particularly advantageous in their ability to interrupt high fault current. It is an object of this invention to provide a circuit interrupter which combines the advantages of circuit breaker protection for moderate overloads with the advanatgeous application of fuses for high fault current interruption. It is another object of this invention to provide a novel circuit breaker particularly suitable for high current interruption with particularly economic apparatus.

Problems have been encountered where fuses have been employed together with circuit breakers. It is particularly desirable that the fuses open only on major fault current and that the circuit breaker contacts interrupt only moderate overloads. This is achieved in practice by closely coordinating the fuse normal current rating and the overcurrent trip setting of the circuit breaker overcurrent sensing means. The normal fuse current rating is usually considerably in excess of the circuit breaker trip point to insure that the fuse will not blow on minor overloads. Most major faults on secondary feeders are phase-to-ground rather than phase-to-phase. Under such circumstances it is possible that only one fuse in a multiphase interrupter will open or blow while the other fuses are not affected. Where only one phase is opened equipment connected between the other two phases will single phase and continue to operate in most circumstances. However, this results in severe increases in the heating and the like of the connected apparatus. Single phasing of three phase motors can be extremely harmful to the motor if it should continue for any appreciable time. It is therefore an object of this invention to provide singlephase prevention in a multi-phase circuit interrupter equipped with current-limiting fuses.

In multi-phase circuit interrupters it is particularly important that the circuit interrupter prevent single-phasing. If an attempt is made to re-energize the circuit interrupter after one phase fuse has blown with either the blown fuse still present or with the fuse removed, the interrupter must immediately trip open the circuit. Most advantageously the circuit interrupter will remain open, i.e., with the circuit breaker in the tripped position upon blowing of any one of the associated fuses. It is therefore an object of this invention to provide an improved circuit breaker which is prevented from reclosing with a fuse blown or absent.

Briefly, in the illustrative embodiment of the invention described in detail below there is shown a circuit breaker that has multiple pairs of separable contacts, common operating mechanism and plural overcurrent relays; one of the relays being connected in series with each of the pairs of separable contacts. Additionally a fuse is mounted on the breaker in series with each of the pairs of separable contacts. A responder is provided which is responsive to the operative condition of the fuses and which functions to trip and lock the circuit breaker open upon the operation of one of the fuses. The responder gives protection against single phasing and also provides a visual indication at the front of the breaker of the operation of the remotely mounted fuses.

The above and other objects and advantages of the invcntion will be best understood from the following decription taken in conjunction with the accompanying drawings in which:

FIG. 1 is a side elevation in partial cross-section of the circuit breaker with some parts in section and other parts omitted in the interest of clarity;

FIG. 2 is a view taken along the line 22 of FIG. 1;

FIG. 3 is an end view taken in the direction of the arrows 3 in FIG. 2;

FIG. 4 is a vertical view corresponding to FIG. 1 showing the position assumed by the indicator and latch upon operation of the fuse;

FIG. 5 is an end view taken in direction of the arrows 5 in FIG. 4; and

FIG. 6 is a schematic wiring diagram of the illustrative embodiment.

Referring to the drawings, the circuit breaker is of the type shown and described in detail in US. Patent No. 2,833,886. It will be understood by those skilled in the art that such circuit breakers may include one, two or three poles depending on the manner in which they are employed. The drawing of FIG. 1 is a synthesis insofar as it shows a portion of the operating mechanism found at the center pole in a multi-pole circuit breaker together with other equipments normally found in the outboard poles. The circuit breaker 10 includes a rear insulating wall 12 and a housing or cover 14 shown in partial section. Circuit breaker 10 includes a pair of movable support members 16 pivoted on fixed shaft 18. Support members 16 carry a spring loaded bridging contact block 20 on which are mounted the main moving contacts 22, 24 and the moving arcing and secondary contact assembly 26. Arcing contact assembly 26 is connected by flexible braid 28 to a bus bar like member 30 that extends along and is secured to the wall '12. One of the main stationary contact members 32 is afiixed to one end of bar 30 and an overcurrent relay 34 is series connected to the other. At the opposite side of the wall 12, adjacent the relay 34, a fuse connector 36 is provided for engagement with one terminal 38 of fuse 40. Fuses 40 herein contemplated are of the well-known current-limting type having interrupting capacities in excess of 100,000 a. The second terminal 42 of fuse 40 is connected to fuse connector 44 which forms part of rearwardly extending contact member 46 for engagement by suitable load-connected contact members, not shown, within the cubicle, not shown.

The circuit breaker is closed by an operating mechanism 47 whose details are unnecessary for an understanding of the present invention. Reference may be made to US. Patent No. 2,833,886 for such details. When the circuit breaker 10 is in its closed circuit condition as shown in FIG. 1 the bridging contact 20 engages stationary contact 32 on bus 30 and a second stationary contact 48 on conductor structure 50 that also mounts the stationary arcing and secondary contacts 52. An arc chute, not shown, is normally positioned about the arcing contact structure. A member 54, connected to conductor structure 50, rearwardly extends through wall 12 for engagement by suitable contact members, not shown, in the cubicle, not shown.

The moving contact structures are held in the closed circuit position of FIG. 1 against the force of the contact springs located within the support members 16 and auxiliary pushoff springs, not shown, by a toggle mechanism indicated generally at 56. Details of the mechanism may be found in the aforementioned Patent 2,833,886. Toggle 56 is maintained in its Slightly over-centered position by a stop 58 formed as a part of the circuit breaker frame. A latch prop 60 is carried by a multi-pole trip bar 62 pivotally supported by the circuit breaker frame. The trip bar extends to each of the poles of the circuit breaker where it may be engaged by the plunger 64 of the overcurrent relay 34 to provide tripping of the breaker upon prolonged overloads or overloads within the interrupting capability of the circuit breaker. For severe overloads the fuses 40, which have a coordinated faster response time, are called upon to limit the current and to interrupt the circuit thereby preventing damage to the circuit breaker 10.

Phase-to-ground faults are the most often encountered types wherein one phase is short circuited to ground. While opening the fuse on the effected phase will interrupt the short circuit current it presents yet another serious problem i.e., single phasing. Serious damage can occur to three phase motors if one phase is disconnected while the others remain energized. While several schemes have been proposed for preventing single phasing they have failed to achieve widespread acceptance due to either excessive cost or complexity. Examples of this are the utilization of striker pin equipped fuses and associated complex interlocks.

The illustrative embodiment of the invention provides an improved means for avoiding single phasing and also allows remote mounting of the current limiting fuses.

Referring to the drawings, the fuse condition responsive means or responder 70 is shown mounted on a wall 72 that extends toward the cover 14 from the rear wall 12 of the circuit breaker. Responder 70 includes solenoid devices 74, 76 and 78 each connected in parallel with a respective one of the fuses as shown in FIG. 6. As an example solenoid 78 is connected tothe ends of fuse 40 by conductors 80, 82. Each of the solenoids 74, 76 and 78 is identical and operates in a like manner when energized. Each solenoid has an armature 80, 82, 84 for driving one of three indicator-actuator bars 8-6, 88, 90, carried by bracket 92, to a trip indicating position. The bars are slidably supported adjacent one end on a roll pin 94 and at the other end by an edge 96 of an aperture 98 formed in the cover 14. It will be noted that the bars are notched at near the coversupported end for purposes to be presently described. Bell cranks 100, 102 and 104 are interposed between their respective armatures and indicator-actuator bars. Movement of an armature is translated into longitudinal movement of the corresponding bar by virtue of projections as for example 105 as seen in FIG. 3. The bell cranks, which are pivoted on brackets 106 by pins 108, engage the projections that are formed at intervals along the bars 86, 88, 90. These projections also serve as spacers to maintain separation of the bars. Pins 108 are normally below the bottom edge of the indicator-actuator bars when the ends 86a, 88a, 90a of the bars etc., are in position on the edge 96 of the aperture 98 in the front cover 14. The indicator-actuator bars are resiliently retained in position by a multi-finger leaf spring 110 mounted on bracket 92 in position for engagement with notches 86b, 88b, 90b, etc., in the respective indicatoractuator bars. Each of the bars has a portion 860, 88c, 900 for engagement with an extension 62b of the multipole trip bar 62.

In order to best understand the invention a cycle of operation will now be described starting with the circuit breaker closed and energized. In the event of a short circuit of sutficient magnitude as to cause the operation of respective one of the fuses, the responder 70 functions as follows: A solenoid device, for example 74, connected parallel with the blown fuse is energized when the fuse opens. This causes the armature 80 to move upward to strike bell crank 100 causing the bell crank to shift the indicator-actuator bar 86 laterally so that portion 86c engages the trip bar extension 62b causing rotation of the trip bar. The rotation of the trip bar causes unlatchirig of the circuit breaker by removing the latch prop 60 allowing the toggle 56 to collapse and thereby prevents single phasing. The longitudinal movement of the bar 86 causes the end 86a of the bar to drop off the edge 96 of the aperture 98 and the edge 96 of the panel enters notch 95 in the bar and locks the bar against return movement even when urged thereto by the trip bar return spring (not shown). The trip bar is maintained in its rotated-unlatching position so that subsequent attempts to reclose the circuit breaker will be ineffective. It will be seen in FIG. 5 that the locking of the indicatoractuator bar 86 by the edge 96 of the aperture provides a positive indication as to which of the fuses has been actuated as well as looking the circuit breaker against reclosing.

In order to render the circuit breaker operative once again, after a fuse has blown, the circuit breaker is withdrawn from the cubicle (not shown) and the blown fuse, which is clearly indicated by the indicator-actuator bars, is replaced. The responder 70 is reset by merely lifting the appropriate bar and sliding it inwardly until the notch 86b is engaged by one of the spring 110 fingers with the bar in position on the edge of the aperture of the front cover 14. The circuit breaker is then returned to the cubicle and may, by appropriate manipulation of the operating mechanism 47, be restored to its closed circuit condition.

While only one embodiment of the invention has been shown and described, it will be understood by those skilled in the art that various changes and modifications may be made herein without departing from the spirit or scope of the invention.

What is claimed is:

1. A multi-pole circuit breaker, a plurality of currentlimiting fuses responsive to a given magnitude of fault current, one of said fuses being electrically connected in series with each pole of said circuit breaker, said multipole circuit breaker including a plurality of pairs of separable contacts each in one pole thereof and each being arranged in series with one of said current-limiting fuses, said circuit breaker including a latching mechanism common to all the poles thereof, and means responsive to the condition of said current limiting fuses, said responsive means causing said latching mechanism to open said pairs of contacts in response to the operation of one of said fuses, said responsive means including means locking said latching mechanism to prevent reclosing of said circuit breaker.

2. A circuit breaker according to claim 1 further ineluding overcurrent responsive means in each pole, said overcurrent responsive means being operatively related to said latching mechanism for causing separation of said plurality of pairs of separable contacts upon occurrence of a fault current of overload proportions of a magnitude less than said given magnitude.

3. A circuit breaker according to claim 1 wherein said responsive means includes a solenoid electrically connected in parallel with each of said fuses, respectively, each of said solenoids having an armature therewith, a plurality of aligned locking members, each locking member being associated with a respective one of said armatures and being displaceable thereby upon operation of the associated fuse, said locking members when displaced engaging said latching mechanism and locking same in a contact opening position.

4. A circuit breaker according to claim 3 wherein said circuit breaker is further provided with a front panel, each of said aligned locking members having an end portion extending through an aperture in said front panel to the exterior thereof, said end portions being normally displayed therethrough in a given position and being displaced to a second, trip indicating, position upon operation of said respective fuse whereby visual indication of operation of the fuse is given at said front panel.

5. A circuit breaker according to claim 4 wherein said end portions of said locking members give visual indication of which fuse has operated.

References Cited UNITED STATES PATENTS 2,833,886 5/1958 Goodwin 335-46 3,009,037 1l/196l Jones et a1. 3377 3,309,478 3/1967 Kiesel et a1 337--7 BERNARD A. GILHEANY, Primary Examiner R. L. COHRS, Assistant Examiner U.S. Cl. X.R. 3377, 8, 79

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