US1994921A - Automatic circuit breaker - Google Patents

Description

March 19, 1935. H. A. ROSE 1,994,921

AUTOMATIC CIRCUIT BREAKER Filed May 20, 1932 0. 6T Saul-0e.

WITNESS s INVENTOR Herbert A. Rose.

ATTORNEY Patented Mar. 19, 1935 UNITED STATES AUTOMATIC CIRCUIT BREAKER Herbert A. Rose, Forest Hills, Pa., laalgnor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application May 20, 1932, Serial No. 612,463

12 Claims. (Cl. 175-294) My invention relates to circuit interrupters and particularly to circuit breakers of the high-speed direct current type, in which the contacts are held closed against a bias by a holding coil, and are immediately released upon the occurrence of predetermined abnormal circuit conditions to give high-speed interruption thereof.

One object of my invention is to provide a highspeed interrupter for use particularly with rectifier circuits.

Another object of my invention is to provide 'means for opening a circuit interrupter at high speed upon the reversal of the direction of current fiow in the circuit to be interrupted, and at the same time permitting the opening of said interrupter, at a slower speed, upon overload or other predetermined circuit conditions.

A further object of my invention is to obviate the present necessity of using two circuit breakers per unit in rectifier circuits by providing a single circuit interrupter capable of performing the functions of both.

A further object of my invention is to provide means whereby a direct current circuit breaker designed for high-speed operation on reversed current fiow may be opened at normal load or greater than normal load conditions.

A still further object of my invention is to provide means whereby any unit in a system of paralleled rectifiers-each protected by a single high speed breaker designed to open at high speed in the event of backfire within the associated rectifier unit-may be removed from the circuit without the use of a second circuit breaker.

The principal field for immediate application of my invention is in connection with high-speed direct-current circuit breakers for use with mercury arc rectifiers, and I shall hereinafter describe an embodiment of my invention as applied thereto, without, however, in any way intending to restrict the scope of my invention except as indicated in the appended claims.

The adaptation and present widespread application of mercury arc rectifiers to direct-current power circuits; has resulted in certain difiiculties; some of these are inherent in the rectifier itself, and others are a result of a combination of inherent faults and external circuit conditions. Specifically, one inherent fault for which no adequate means of prevention has been found is the backfire. As long as rectifiers were used singly and on direct current circuits incapable of supplying power to the rectifier, the backfire condition was confined to an anode to anode short circuit and could be adequately protected against by circuit interrupters in the line side of the transformer. The present practice, however, of using rectifiers in parallel and in regenerative network circuits has greatly intensified the momties arising from backfire. In these circuits the 5 former anode to anode short circuit now becomes,

in addition, a cathode to anode short circuit and thereby permits a destructive fiow of current through the rectifier. In view of this, the protective system for the paralleled rectifiers must in- 10 clude a circuit breaker in the direct current side for backfire protection.

In fact, prior to my invention, it was common practice to provide each rectifier unit with two di rect current breakersone a high-speed breaker 15 of the bucking bar type polarized to open on reverse current, and the other a conventional mod erate speed breaker connected through suitable switching means. In some installations two high speed breakers have been used. The necessity 20 for these two breakers becomes at once apparent from a study of the conventional high-speed bucking-bar breaker. In such a circuit breaker, the switch member is biased to the open position by a spring and is held closed by the attraction 25 between an electromagnet and an armature affixed to the switch member. A bucking bar responsive to predetermined conditions within the circuit to be interrupted, and polarized to oppose the attraction of the electromagnet upon reverse 30 current fiow, is placed within a suitable gap in the electromagnet core. The operation of this type of breaker is substantially as follows: reversal of the current fiow, the holding fiux is shunted or destroyed by the opposing M. M. F. of the bucking bar and the biasing spring opens the breaker at high speed. This is the desired and necessary result because the reversed current accompanying the backfire must be interrupted within a very short period of time-usually about one quarter of a cycle-to prevent damage to the rectifier. On overload, however, the situation is entirely different, now the bucking bar supplies an M. M. F. which aids that of the holding magnet, and as soon as the load reaches some given value, dependcut upon the particular interrupter involved, the M. M. F. supplied by the bucking bar alone is sufficient to hold the breaker closed. Ordinarily, this action occurs at a load value which is less than the rated output of the rectifier and for all current i values in excess of that adequate to hold the breaker closed by bucking bar action above a new problem arises. How may the direct-current circuit be interrupted when the rectifier is supplying this load or when an overload comes on? A de- 5 energizing of the holding coil will be ineffective, especially since this holding action of the bucking bar flux ls intensified by an increasing overload or by the use of inductive shunts. The usual solution, prior to my invention, was to use two directcurrent breakers.

It is important to note in this connection that very high speed interruption is necessary only on reversed current; little damage is done to a rectifier by an overload as compared with the damage resulting from the reversed current accompanying a backfire. Therefore, the breaker made possible by my invention, which opens within a fraction of a cycle on reversed current and within several cycles on overload or upon the operation of suitable switching means, satisfactorily meets the present day requirements, and obviates the difiiculties encountered with previous structures.

One method of opening the rectifier circuit on overload includes a suitably excited trip coil on the alternating current breaker which protects the rectifier transformer. This method has been tried commercially, and has not been found entirely satisfactory. For example, if, due to leaks or other causes, the vacuum pressure within the rectifier begins to increase, it is necessary to remove the rectifier from service. The alternating current breaker will disconnect the rectifier from the alternating 'current source, but will not prevent an insulation breakdown already beginning within the tank due to lack of vacuum, this breakdown will be of the nature of a backfire and will require a second interruption of the circuit, this time by the high speed breaker. Also, the time delay of the usual alternating current breaker used in this service is much larger than that of the corresponding direct-current breaker, especially when relay action is necessary. This delay alone may be suificiently objectionable to necessitate a second direct current breaker.

The features of my invention which I believe to be new are particularly pointed out in the appended claims. For a full understanding of the principles of the invention and one mode of applying the same, reference may be had to the accompanying drawing in which the single figure illustrates diagrammatically the general system and apparatus of my invention.

Referring to the drawing, the leads 1 connect the primary 3 of the transformer 2 to a suitable alternating-current source. Leads 5 connect the tapped secondary 4 of the transformer 2 to the anodes 7 of the rectifier proper 6. Leads 11 and 12 connect the cathode 10 and the tapped secondary 4, respectively, with the contact member 16 and terminal 60 of the circuit interrupter 13. A bridging contact 17 connects the contact members 16 and 18, and the circuit is completed to a direct-current bus by the lead 19. Terminal 60 connects with the bucking bar 14 and the switch 63 which is used for paralleling the bucking bar and the inductive shunt 62-both of which terminate at the contact point 61. The lead 15 connects the contact point 61 with the positive direct-current bus.

The circuit interrupter 13 comprises, in general a contact structure biased to the open position, suitable linkages for actuating the contact structure, a movable armature, and a holding electromagnet. Specifically, the bridging contact 17, which is pivoted on the link 22, is biased to the open position by spring 23. Link 24, which is pivoted on link 22, connects with one end of links 25 and 26. The moving armature 27 is pivotally connected to the other end of link 26; the other end of link 25 is fixed. The holding electromagnet 30 includes a core 31 which terminates in two pole pieces 33 and has an air gap 34 therebetwecn. The holding electromagnet is normally excited by a holding coil 41, and the magnetic circuit is completed through the armature 27. A separate source of power for the holding coil may be used, as shown, or the direct-current load bus itself may be employed. The air gap 34 is of reduced section at the inner and outer portions of the core proper, and there are two projections 32 extending from the pole pieces 33 into the air gap 34. These projections provide a low reluctance flux path and this assists in the shifting of the flux by the bucking bar 14 which passes through the enlarged portion of the air gap 34. The polarity of the bucking bar is such that the breaker is opened by a reverse current fiowing therethrough.

In addition to the bucking bar 14, I provide a further breaker opening means such as coil 40. I have shown this coil as being energized from the same source as the holding coil 41, but this construction is, of course, optional. The M. M. F. of this coil is opposed to that of the holding coil 41 and also to that set up by the bucking bar 14 when current is flowing therethrough in the normal direction.

Coils 40 and 41 are energized from the directcurrent source through the leads 35 and 36 and the switching means 3'7. The switching means 37 comprises an overload trip relay 42 and a manually operated switch 43. The overload trip has a coil 44, connected in current responsive relationship with the output lead 19, an armature 45, and a switch member 46. The manually operated switch 43 comprises an operating member 53 connected to a contact member 54.

When the interrupter is in the closed position, coil 41 is energized through the lead 35 to contact point 47, through contact element 46 of the overload trip relay 42 to contact point 48, thence to contact point 55, through the contact element 54 of the manually operated switch 43 to contact point 56, and thence through the coil 41 and lead 36 to the other terminal of the directcurrent source. In the event of a predetermined overload, the magnetic attraction of the coil 44 moves the armature 45 and its associated contact element 46 upwardly and thereby opens the circuit to coil 41 through the points 47 and 48. As the upward movement of the armature 45 continues, the circuit through the'contact points 49 and 50 is completed and the coil 40 is energized. In like manner, the manually operated switch de-energizes coil 41 by opening the circuit between contact points and 56, and substantially simultaneously energizes coil 40 by completing the circuit through contact points 5'! and 58.

As previously stated, the bucking bar 14 may be paralleled by the inductive shunt 62. The

purpose of this shunt is to make the curren which flows through the bucking bar 14 responsive both to the rate of change of current and to the magnitude of the current in the leads 11 and 15, rather than responsive only to the magnitude of the current in those leads. This is particularly desirable in rectifier currents because the backfire condition is always accompanied by a very rapid change in magnitude of the current.

The operation of the apparatus of my invention is as follows. On backfire within the rectifier 6which causes a reverse current flow in the bucking bar 14very high speed opening of the bieaker is secured; an alternating-current ,interrupter (not shown) in the line side of the transformer opens in response to suitable means to clear the anode to anode short within the rectifler. 0n overload, or in response to a predetermined electrical condition in the circuit to be interrupted, the switching means 37 deenergizes the holding coil 41 and energizes the neutralizing coil 40, which coil then demagnetizes the core and thus .permits the breaker to open; the opening operation is slower when caused by the neutralizing coil due to the time which must elapse while the direction 01' the flux within the core is being reversed-the bucking bar alone eil'ects more or action, the flux passing through the projections 32 rather than through the armaturez'l.

For removal of a fully or partially loaded rectifier from the line, the manually operated switch 43 is employed. It is not necessary that the holding coil 41 be de-energized when tripping the breaker by the use of the neutralizing coil 40, although I prefer this method because it reduces the size of the neutralizing coil.

In the particular embodiment 01' my invention disclosed above, I have restricted myself to one particular structure and one particular application thereof. Other structures and other applications will suggest themselves to those skilled in the art, and it is my intention that the broad idea disclosed in the specification shall apply thereto except as restricted in the appended caims. Especially is it my wish and intention that the claims should read on structures having a plurality of electromagnetic means for neutralizing the electromagnetic holding means.

I claim as my invention:

1. In a circuit interrupter, i'neans tending to open said interrupter, electromagnetic means for holding said interrupter closed, and electromagnetic means for neutralizing said holding means, including an electro-magneti'c means responsive to a predetermined current condition in the circuit to be interrupted, and a second electromagnetic means, normally de-energized, which is energized by means responsive to a different current condition in said circuit.

2; In a circuit interrupter, a switch member, means for biasing said switch member to one position, electromagnetic means including a core member for restraining said switch member against said biasing means, and a plurality of windings for bucking the flux normally traversing the core of said restraining electromagnet, one of said windings being responsive to a predetermined electrical condition in the circuit to be interrupted, and another of said windings being energized through the actuation of mechanically movable switching means to supply a substantially constant deenergizing M. M. F. of predeterminedmagnitude to said core.

3. In combination, an electrical circuit, an interrupter therein, said interrupter being biased to the open position and being held closed by a normally energized electromagnet, and means for neutralizing and thereby rendering ineifective said holding electromagnet; said neutralizing means comprising electromagnetic means responsive to the current flowing in the circuit to be interrupted and so connected that neutralization is secured therefrom upon a reversal of the normal direction of current flow, other electromagnetic means, normally de-energized, which when energized neutralizes the then existing holding force, and means responsive to the cura shunting than a neutralizing electromagnetic rent flowing in said circuit for energizing said other electromagnetic means.

4. An electrical circuit interrupter for use on network systems, said interrupter being biased to the open position and being held closed by electromagnetic means including a core member, said interrupter having selective electromagnetic opening means whereby it opens at very high speed upon a reversal of the current flow in the circuit to be interrupted and at a slower speed upon the occurrence of a predetermined electrical condition in said circuit, said selective electromagnetic opening means including a plurality of windings associated with said core member.

5. An electrical circuit interrupter for use on network'systems, said interrupter being biased to the open position and being held closed by means including a core member, having selective electromagnetic opening means comprising a plurality 01 Windings associated with said core member whereby it opens at very high speed upon a reversal of the current flow in the circuit to be interrupted and at a slower speed upon the operation of suitable switching means.

6. A protective system for use with electrical circuits wherein a circuit interrupter biased to the open position and held closed by electromagnetic means is provided with further electromagnetic means for opening said interrupter, said further electromagnetic means including means responsive to predetermined current conditions in the circuit to be interrupted, means, normally deenergized, for supplying asubstantially constant M. M. F. when energized, and means responsive to different predetermined current conditions in the circuit to be interrupted for e1- fecting the energization of said normally deenergized electromagnetic means.

7. A protective system for use with electrical circuits wherein a circuit interrupter biased to the open position and held closed by electromagnetic means is provided with further electromagnetic means for opening said interrupter, said further electromagnetic means including a plurality of windings, means whereby one oi said windings is energized in response to the current flowing in the circuit controlled by said interrupter, that said winding causing high speed opening of said interrupter upon a reversal of the normal direction of current flow in said circuit, and mechanically movable switching means for energizing another of said windings, said other winding being normally deenergized and being so arranged that, when energized, it causes the circuit opening operation 01' said interrupter to take place at a slower speed than said firstmentioned winding.

8. In combination in an electrical circuit, a rectifier, and a circuit interrupter for said rectifler, said circuit interrupter being biased to the open position, held closed by electromagnetic means and provided with further electromagnetic means for opening said interrupter, said further electromagnetic means including twowindings, one of said windings being energized by a current responsive to that flowing in the circuit to be interrupted and being so wound that high speed opening 01' the interrupter is secured upon a reversal of the normal direction of current flow in said circuit, the other of said windings being normally de-energized and being provided with switching means which substantially simultaneously energize said other winding and de-energize said holding electromagnet thereby securing said interrupter 4- a moderately 'high speed opening of said interrupter.

9. A circuit interrupter for direct current networks, said interrupter-being biased to the open position, being held closed by electromagnetic means, and having further electromagnetic means for opening said interrupter at selective speeds; said further electromagnetic means comprising two windings, the winding for high speed operation having energizing means whereby a current propoitional to the value of, and to the rate of change of, the current traversing said circuit is made to pass therethrough and being wound in such a direction that the interrupter is opened by a reversal of the direction of current flow, the winding for slow speed operation being normally de-energized and being energized through switching means.

10. A circuit interrupter for direct current networks, said interrupter being biased to the open position, being held closed by electromagnetic means, and having further electromagnetic means for opening said interrupter at selective speeds; said further electromagnetic means comprising two windings, the winding for high speed operation having energizing means whereby a current proportional to the value of, and to the rate of change of, the current traversing said circuit is made to pass therethrough and being wound in such a direction that the interrupter is opened by a reversal of the direction of current flow, the winding for slow speed operation being normally de-energized and being energized through switching means, which switching means substantially simultaneously de-energizes said electromagnetic holding means.

11. In a circuit interrupter, a switch member, means biasing said switch member to the open position, an electromagnet having a core member, means for producing magnetic iiux in said core member, and an air gap located in the path of the flux set up by said flux producing means, an armature for bridging said air gap, which said armature holds said switch member closed against said biasing means, and a plurality of means for neutralizing the holding action of said electromagnet, said plurality of means including flux shifting means, located in the air gap of said electromagnet, responsive to a set of predetermined current conditions in the circuit to be interrupted, and other means associated with the core of said electromagnet and energized by means responsive to a diiierent set of predetermined current conditions than said means located in said air gap for substantially deenergizing said core.

12. In a circuit interrupter; a switch member; means biasing said switch member to the open position; an armature connected to said switch member; an electromagnet for attracting said armature to hold said switch member in the closed position against said biasing means, said electromagnet having a core member and a normally energized winding for producing flux in said core member, said core member having pole pieces providing parallel flux paths one.of which is completed by said armature; a winding positioned between said parallel flux paths for shifting the flux from said armature to the other flux path upon the occurrence of a predetermined current condition; and a second winding associated with said core member for substantially deenergizing said core member to efi'ect the release of said armature upon the actuation of mechanically movable switching means.

HERBERT A. ROSE.

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