US3617970A

US3617970A - Device for protecting thermally responsive element of circuit interrupter

Info

Publication number: US3617970A
Application number: US37369A
Authority: US
Inventors: Tutomu Hanafusa; Yoshio Kobayashi
Original assignee: Terasaki Electric Co Ltd
Current assignee: Terasaki Electric Co Ltd
Priority date: 1966-12-26
Filing date: 1970-05-06
Publication date: 1971-11-02
Anticipated expiration: 1988-11-02
Also published as: NL6717416A; GB1206970A; NL141020B; FR1575555A; DE1588891B1

Abstract

A protective device for protecting a thermally responsive element disposed in a circuit breaker comprising a movable contact carried by one end of a resilient conductor disposed in slightly spaced, parallel relation to a rigid conductor. The resilient conductor is connected at a point intermediate both ends to the bimetallic element through a flexible lead. A short circuit current flows in opposite directions through both parallel conductors to immediately generate an electromagnetic repulsion between them. This causes the movable contact to engage the associated stationary contact to complete a branch circuit around the bimetallic element to protect it from the short circuit current.

Description

United States Patent Inventors Appl. No. Filed Patented Assignee Priority DEVICE FOR PROTECTING THERMALLY RESPONSIVE ELEMENT OF CIRCUIT INTERRUPTER 2 Claims, 4 Drawing Figs.

U.S. Cl. 337/3, 337/70, 337/83, 337/103, 335/16 Int. Cl H0lh7l/l6,

I-IOlh 73/54, I-IOlh 75/12 50 Field ofSearch 337/3, 15, 16, 20,24, 26,45,46, 47, 4s, 54, 37, 70, 71, 76, 83, 103; 335/16, 195

[5 6] References Cited UNITED STATES PATENTS 2,989,606 6/1961 Walker et al. 335/37 3,104,297 9/1963 Powell et al. 337/83 Primary Examiner-Bernard A. Gilheany Assistant Exam inerDewitt M. Morgan Attorney-Wenderoth, Lind & Ponack ABSTRACT: A protective device for protecting a thermally responsive element disposed in a circuit breaker comprising a movable contact carried by one end of a resilient conductor disposed in slightly spaced, parallel relation to a rigid conductor. The resilient conductor is connected at a point intermediate both ends to the bimetallic element through a flexible lead. A short circuit current flows in opposite directions through both parallel conductors to immediately generate an electromagnetic repulsion between them. This causes the movable contact to engage the associated stationary contact to complete a branch circuit around the bimetallic element to protect it from the short circuit current.

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DEVICE FOR PROTECTING TI-IERMALLY RESPONSIVE ELEMENT F CIRCUIT INTERRUPTER This application is a continuation of application, Ser. No. 690,234 filed Dec. 13, 1967 and now abandoned.

This invention relates in general to a circuit interrupter, and more particularly to a protective device for protecting'a thermally responsive element disposed in a circuit interrupter.

In the conventional type of circuit interrupters including a trip device responsive to heat due to any flow of excessive current therethrough and especially a thermally responsive element such as a bimetallic element having a low current rating, a flow of excessive current due to a short circuit fault or the like may cause the thermally responsive element to be rapidly raised to a high temperature resulting in fusing of the bimetallic element or its heater or in permanent deformation of "the bimetallic element. For the purpose of eliminating that disadvantage, there has been heretofore provided in a circuit interrupter a separate electromagnetic trip device responsive to an extraordinarily excessive current such as a short circuit current flowing therethrough to close the-associated shunt contacts thereby to form a shunt circuit around the bimetallic element. Such an electromagnetic trip device, however, has a response time of from 1.5 to milliseconds before it begins to operate to close the associated shunt contacts through attraction of a movable armature of the associated electromagnet. Because of this time delay,all the short circuit current of from to ka. or more flows through a main current path including a low-current rating bimetallic element and within this time delay the bimetallic element is instantaneously overheated leading to a serious disadvantage that the overheated bimetallic element can not be again used.

Accordingly it is the primary object of the invention to provide a new and improved device for completely protecting a thermally responsive element of a circuit interrupter from any damage due to a flow of excessive current therethrough which device has an extremely short response time such that closure of the associated shunt contacts is accomplished within an interval of time as short as from 0.15 to 0.45 millisecondafter the occurrence of a short circuit fault.

According to one aspect of the invention, there is provided a protective device for protecting a thermally responsiveelement of a circuit interrupter, connected in parallel circuit relationship to the thermally responsive element connected in the main current path in the interrupter, characterized by an elongated conductor member of resilient material and an elongated rigid conductor member disposed in slightly spaced, parallel relationship and connected together at one end, one portion of the resilient conductor member and the rigid conductor member being disposed in the main current path, the resilient conductor member having a movable shunt contact carried at the other end disposed out of the main current path, the arrangement being such that, a flow of excessive current through the circuit interrupter generates an electromagnetic repulsion between the parallel conductor members and the movable contact engages the associated stationary contact only by means of the action of the electromagnetic repulsion to complete a protective circuit through the contacts around the thermally responsive element.

Also there are known the type of protective devices for protecting a thermally responsive element of a circuit interrupter wherein an electromagnetic trip device when operated closes shunt contacts to complete a protective circuit around the associated thermally responsive element. This type of protective device uses an electromagnet and in a range of fault currents relatively low in magnitude, can effectively prevent reopening of the closed shunt contacts for the reason that the attractive force exhibited by the electromagnet is greater than the repulsion between the contacts tending to separate them from each other. However, as the shunt current increases, that repulsion increases in proportion to the square of the magnitude of the shunt current whereas the attractive force provided by the electromagnet reaches a certain limit due to the saturation of the electromagnets core. Eventually the repulsion becomes greater than the attractive force and causes separation of the closed shunt contacts. Then the contacts thus separated'ag'ain engage each other by means of the actionof the attractive force of the electromagnet. Therefore the contacts are repeatedly closed and opened resulting in the disadvantage that repeated arcing across the shunt contacts greatly wears, damages and deforms them.

Further there has been previously proposed atype of protective device for protecting a thermally responsive element of a circuit interrupter wherein the shunt contacts involved are adapted to be closed by the action of an electromagnetic repulsion generated between a pair of parallel conductors connected in the main current path of the circuit interrupter by a flow of short circuit current through the latter. In this type of protective device the electromagnetic repulsion generated between the'paralle] conductors by a fault current within a range of from one to 2.5 times the threshold current for the device serves to effect closure of the shunt contacts against'a restoration force ofa resilient conductor member carrying themovable shunt contact. However, a repulsion is exerted on the shunt contacts simultaneously with the closure of the contacts to tend to separate them from each other. Then the separated contacts again engage each other. The process just described is repeated lea ding to the same disadvantage as in the protective devices of the type described in the preceding paragraph.

According to another aspect of the invention there is provided a protective device for protecting a thermally responsive element of a circuit interrupter in which the above-mentioned disadvantage is eliminated. The device is characterized in that after the shuntc'ontacts have engaged each other through a flow of short circuit through the interrupter to complete a shunt circuit around the element, an electromagnetic repulsion is additionally generated between that portion of the contact carrying'conductor having only a shunted current flowing therethrough and the other portion of the conductor having the full short circuit current flowing therethrough, the repulsion being sufficient to maintain the shunt contacts in their closed'position against the repulsion between the closed contacts tending to separate them from each other.

The invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawing in which:

FIG. I is a side elevational view, partly in section of a circuit interrupter embodying the principles of the invention;

FIG. 2 is a side elevational view of a protective device constructed in accordance with the principles of the invention and illustrated in its closed position;

FIG. 3 is a perspective view of the device shown in FIG. 2 and illustrated in its closed position; and

FIG. 4 is a schematic diagram illustrating the passage of current flowing through the protective device in its closed position.

Referring now to the drawing and FIG. 1 in particular, there is illustrated a circuit interrupter embodying the principles of the invention. The arrangement illustrated comprises a housing 10 open at one end or the upper end as viewed in FIG. 1, a cover member 12 detachably covering the open end of the housing 10, and a pair of movable contact rods 14 and 16 disposed in opposed relationship within the housing 10. The housing and cover members 10 and 12 respectively are molded of any suitable electrically insulating material and both contacts rods 14 and I6 are of any suitable electrically conductive material and are provided at one end with a 'pair of contacts 18 and 20 respectively. When in their closed position as shown in FIG. I, the upper and lower contact rods 14 and 16 are partially in parallel with each other. v

The lower movable contact rod 16 is pivotably mountedby a pivot pin 22 to a support member 24 secured to the housing 10. A tension spring 26 extends between an anchor pin 28 disposed on the support member 24 and a pin 30 extending through the lower contact rod 16 on that side of the pivot pin 22 opposite to the anchor pin 28 to tend to rotate the contact rod 16 in the clockwise direction as viewed in FIG. I about the axis of the pivot pin 22 when the rod 16 is in its position as illustrated in the same figure thereby to establish a predetermined contact pressure between the lower contact 20 and the mating contact 18. In order to limit rotational movement of the lower movable contact rod 16 in the clockwise direction a stop 32 is suitably disposed on the support member 24. The lower contact rod 16 has the other end connected to a flexible conductor 34 which is, in turn, connected to a conductor 36 leading to a source terminal (not shown).

The upper movable contact rod 14 is pivotably mounted by a pivot pin 30' to a contact holder 36 rigidly secured to a contact shaft 38 of any suitable electrically insulating material. The upper contact rod 14 is connected through a flexible conductor 40 to a connector block 42. If the circuit interrupter is of a polyphase type, the contact holder 36 has the remaining upper movable contact rods pivotably mounted thereto.

In order to drive both contact rods 14 and 16 from their closed position as viewed in FIG. 1 to their open position and vice versa the interrupter includes an operating mechanism generally designated by the reference numeral 45. The operating mechanism 45 comprises an operating handle 46, operating springs 48 and trip lever 50 connected to the contact holder 36 through a pair of toggle levers 52 and 54. Since the operating mechanism 45 is of a conventional construction and forms no part of the invention it need not be described in detail.

The circuit interrupter further includes a thermally responsive mechanism generally designated by the reference numeral 55. This mechanism 55 comprises a bimetallic element 56 provided at the upper free end as viewed in FIG. 1 with a pusher in the form of an adjusting screw 58 and a flexible conductor 60 for a purpose which will be apparent from the following description. An electromagnetically responsive mechanism generally designated by the reference numeral 62 comprises a stationary magnetic core 64, an exciting winding 66 inductively disposed on the magnetic core 64 and a movable magnetic piece or an armature 68. The winding 66 forms an electromagnet along with the stationary magnetic core 64 and also serves to connect the connector block 42 to the other or lower end of the bimetallic element 56 secured to a connecting piece 69 which is, in turn, suitably fixed to the housing 10.

If an excessive current flows through the bimetallic element 56, the latter is arranged to be deflected toward the left as viewed in FIG. 1 about its lower end to cause the pusher 58 to actuate a trip mechanism of the conventional construction generally designated by the reference numeral 70. More specifically the pusher 58 pushes against a trip element 72 opposed to the same to rotate a trip shaft 74 integral with the trip element 72 in the counterclockwise direction as viewed in FIG. 1. Therefore a trip hook 76 disengages from a catch 78 secured to the trip shaft 74 to perform a tripping operation in the known manner.

If an extraordinarily excessive current exceeding from eight to ID times the rating current for the interrupter occurs, the electromagnetically responsive mechanism 62 is operated such that the current flows through an exciting winding 66 to magnetize the stationary magnetic core 64 or the electromagnet which, in turn, attracts an armature 68 to rotate the trip shaft 74 in the counterclockwise direction to perform a tripping operation in the same manner as above described.

In order to protect the bimetallic element 56 against an excessive current flowing therethrough a protective device generally designated by the reference numeral 80 is shunted across the bimetallic element 56. The protective device 80 comprises a stationary shunt contact 82 carried by an electrically conductive holder 84 connected to the connector block 42 through a flexible conductor 86 and a shunt conductor 88. A movable shunt contact 90 opposed to the stationary shunt contact 82 is carried at one end or a lower end as viewed in FIG. 1 ofa contact support conductor 92 in the form of a rod or a strip of any suitable resilient, electrically conductive material disposed in substantially parallel relationship with respect to a conductor 94 in the form ofa rod or a strip of any suitable rigid, electrically conductive material, to define a narrow space therebetween. The resilient conductor 92 is connected at a point intermediate its two ends to the flexible conductor 60 and also at the other or upper end to the adjacent end of the rigid conductor 94 which is, in turn, connected at the other end to a conductor 96 leading to a source terminal (not shown).

In the normal operation, the circuit interrupter thus far described has a current flowing through the following main current path traced from the source conductor 36, through the flexible lead 34, the lower movable contact rod 16, the lower contact 20, the upper contact 18, the upper movable contact rod 14, the flexible conductor 40, the connector block 42, the electromagnet winding 66, the bimetallic element 56, the lead 60, the resilient conductor 92, the rigid conductor 94 and thence to the load conductor 96.

If a short circuit fault or the like occurs to cause an excessive current exceeding several thousand percent of the rating current for the interrupter to flow through the above-mentioned main current path, it excites the winding 66 of the stationary magnetic core 64 to cause the core to attract the movable armature 68 (see FIG. 2) to perform a tripping operation as previously described.

Simultaneously with the initiation of this tripping operation, a current flows through the

parallel conductors

92 and 94 in the opposite directions as indicated the arrows in FIG. 1, to generate an electromagnetic repulsion. This repulsion permits the resilient conductor 92 to be instantaneously rotated in the clockwise direction as viewed in FIG. 1 about its upper end to engage the movable contact with the stationary contact 82 (see FIGS. 2 and 3) to complete the following shunting branch around the bimetallic element 56. This branch is traced from the connector block 42 through the shunt conductor 88, the lead 86, the support member 84, the stationary contact 82, the movable contact 90 to the resilient conductor 92. This causes the current flowing through the bimetallic element 56 to greatly decrease thereby to prevent the latter from being subject to any damage such as a permanent deformation due to its extraordinary heated state.

Then the electromagnetic responsive mechanism 62 or the thermal responsive mechanism 55 operates to interrupt the fault current in the manner as previously described.

After the interruption or attenuation of the fault current, the resilient conductor 92 returns to its normal position as shown in FIG. 1 by means of its own resilience where the movable contact 90 is separated from the stationary contact 82 to open the shunt circuit around the bimetallic element.

As previously described, it is already known to close shunt contacts such as the

contacts

82 and 90 through the attraction of a magnetized stationary electromagnet exerted upon the associated armature. This measure inevitably leads to a time delay required to magnetize the electromagnet and also to actuate the armature due to its inertia and the closure of the shunt contacts has normally accomplished with a time delay corresponding to from 0.1 to 0.3 cycles of alternating current measured from the occurrence of a fault current. Depending upon the magnitude of the fault current and the configuration and dimension of the thermally responsive element such as the bimetallic element, it was difficult to protect the element from damage because it might be raised to an elevated temperature at which the element may be permanently deformed, within an interval of time required to engage the contacts with each other. For this reason, the conventional type of protective device had generally an upper limit of the order of l5,000 amperes below which they could protect the associated bimetallic element having a rating current of 15 amperes from damage due to its overheating.

For the conventional type of circuit interrupters having a full interruption time ranging from 8 to 13 milliseconds, a protective device having a response time of from 0.15 to 5 milliseconds could protect the associated bimetallic element from a flow of excessive current although such protection was not completely satisfactory. On the other hand, it will be apparent to those skilled in the art from the arrangement shown in FIG. I that, upon the occurrence of a flow of extraordinarily excessive current such as a short circuit current, the current flows in the opposite directions through the upper and lower movable contact rods disposed in generally parallel relationship and causes an electromagnetic repulsion therebetween to separate the rods and hence the contacts from each other without an appreciable time delay and regardless of the tripping mechanism involved. Since in this case the interruption time is on the order of 0.3 cycle of alternating current, with any conventional protective device having a response time of from 1.5 to 5 milliseconds it is difficult to achieve the result that the as sociated bimetallic element is completely protected from permanent deformation because the response time is comparative with the interruption time.

This invention eliminates the above-mentioned disadvantages. More specifically it has been found that the provision of the resilient conductor 92 and the rigid conductor 94 disposed in spaced parallel relationship permits the

shunt contacts

82 and 90 to be engaged each other rapidly with a time delay corresponding to from 0.15 to 0.45 milliseconds. In other words, the present device can complete a shunt circuit around the associated bimetallic element within an extremely short time as compared with the prior art devices with the result that the bimetallic element is protected from a large magnitude of fault current flowing therethrough. For example it has been found that a bimetallic element having a rating current of IS amperes is sufficiently protected from a short circuit current in excess of 50,000 amperes, without any permanent deformation and the like.

Also it will be appreciated that the invention is applicable to a circuit interrupter of the limiting current type having an interruption time of 5 milliseconds with a satisfactory result.

Upon the occurrence of a flow of fault current an electromagnetic repulsion is generated between the resilient conductor 92 and the rigid conductor 94 parallel thereto to effect closure of the

contacts

82 and 90 as previously described. At that time the

closed contacts

82 and 90 will have exerted thereon an electromagnetic repulsion tending to separate them from each other. This repulsion increases as the fault current increases. However, the electromagnetic repulsion generated between the two conductors tend to engage the contacts with each other also increases thereby preventing the contacts from being separated from each other.

It is recalled that within a range of relatively low currents of from one to 2.5 times the threshold magnitude of current for the shunt contacts device the movable contact 90 may be repeatedly contacted by and separated from the stationary contact 82. The invention effectively prevents such repeated opening and closing of the contacts. As shown in FIGS. 3 and 4, the flexible lead 60 to the bimetallic element 56 is connected to the resilient conductor 92 at a point 92A positioned intermediate the upper fixed end 92B and the lower free end at which the movable contact 90 is secured. Therefore a fault current flows from the lead 60 through the junction 92A of the conductor 92 and the lead 60, that portion 92C of the conductor 92 extending from the junction 92A to the upper end and thence through the adjacent portion of parallel conductor 94 to generate an electromagnetic repulsion therebetween which, in turn, actuates the resilient conductor 92 to engage the contact 90 with the contact 82 completing the shunt circuit around the bimetallic element 56. This causes the fault current I to be divided into a current portion I flowing through the bimetallic element 56 and a shunted current portion I flowing through the

contacts

82 and 90. The shunted current portion I, generates an electromagnetic repulsion between the

contacts

82 and 90 tending to separate them from each other. However an electromagnetic repulsion is now generated between that portion 92D of the conductor 92 disposed between the contact 82 and the junction 92A and having only the shunted current I, flowing therethrough and the adjacent portion of the conductor 94 to tend to engage the contact with the contact 82 thereby to render me ectlve the effect of the repulsion tending to separate the contacts from each other. This ensures that for the duration of the fault current, the movable contact 90 is maintained contacting the contact 82 to prevent any loss and fusion of the contacts. Thus it will be appreciated that the invention effectively protects the bimetallic element from any excessive current larger in magnitude than currents from which the prior art devices could protect the associated bimetallic elements.

We claim:

1. In combination, a thermally responsive element of a circuit interrupter, and a protective device for protecting the thermally responsive element, said device comprising an elongated resilient conductor member and an elongated rigid conductor member disposed in substantially parallel relationship to define a narrow space therebetween, and connected together at one end, said resilient conductor member having a movable shunt contact carried at the other end thereof, a flex ible conductor connected to said resilient conductor between said shunt contact and said one end, said device being connected in the main current path of the interrupter in series with said thermally responsive element by said flexible conductor and the other end of said rigid conductor member, and a fixed shunt contact opposed to said movable shunt contact and coupled to the main current path of the circuit interrupter in parallel with said thermally responsive element, whereby a flow of excessive current through the circuit interrupter generates an electromagnetic repulsion between said parallel conductor members which acts as the one and only force for engaging the movable shunt contact with the associated stationary shunt contact to complete a circuit through the contacts around the thermally responsive element, and an additional electromagnetic repulsion is generated between that portion of said resilient conductor member having only a shunted current flowing therethrough and the rigid conductor member having the full excessive current flowing therethrough, said repulsion being sufficient to maintain the shunt contacts in their closed position against a repulsion exerted upon said contacts tending to separate them from each other.

2. In combination, a thermally responsive element of a circuit interrupter, and a protective device for protecting the thermally responsive element, said device comprising an elongated movable conductor member and an elongated stationary conductor member disposed in substantially parallel relationship to define a narrow space therebetween, and connected together at one end, said movable conductor member having a movable shunt contact carried at the other end thereof, a flexible conductor connected to said movable conductor at the other end thereof, said device being connected in the main current path of the interrupter in series with said thermally responsive element by said flexible conductor and the other end of said rigid conductor member, and a fixed shunt contact opposed to said movable shunt contact spaced from said movable shunt contact by a small gap in the normal condition of said device and coupled to the main current path of the circuit interrupter in parallel with said thermally responsive element, whereby a flow of excessive current through the circuit interrupter generates an electromagnetic repulsion between said parallel conductor members which acts as the one and only force for engaging the movable shunt contact with the associated fixed shunt contact to cqmplete an electrically parallel circuit through the contacts around the thermally responsive element.

Claims

1. In combination, a thermally responsive element of a circuit interrupter, and a protective device for protecting the thermally responsive element, said device comprising an elongated resilient conductor member and an elongated rigid conductor member disposed in substantially parallel relationship to define a narrow space therebetween, and connected together at one end, said resilient conductor member having a movable shunt contact carried at the other end thereof, a flexible conductor connected to said resilient conductor between said shunt contact and said one end, said device being connected in the main current path of the interrupter in series with said thermally responsive element by said flexible conductor and the other end of said rigid conductor member, and a fixed shunt contact opposed to said movable shunt contact and coupled to the main current path of the circuit interrupter in parallel with said thermally responsive element, whereby a flow of excessive current through the circuit interrupter generates an electromagnetic repulsion between said parallel conductor members which acts as the one and only force for engaging the movable shunt contact with the associated stationary shunt contact to complete a circuit through the contacts around the thermally responsive element, and an additional electromagnetic repulsion is generated between that portion of said resilient conductor member having only a shunted current flowing therethrough and the rigid conductor member having the full excessive current flowing therethrough, said repulsion being sufficient to maintain the shunt contacts in their closed position against a repulsion exerted upon said contacts tending to separate them from each other.

2. In combination, a thermally responsive element of a circuit interrupter, and a protective device for protecting the thermally responsive element, said device comprising an elongated movable conductor member and an elongated stationary conductor member disposed in substantially parallel relationship to define a narrow space therebetween, and connected together at one end, said movable conductor member having a movable shunt contact carried at the other end thereof, a flexible conductor connected to said movable conductor at the other end thereof, said device being connected in the main current path of the interrupter in series with said thermally responsive element by said flexible conductor and the other end of said rigid conductor member, and a fixed shunt contact opposed to said movable shunt contact spaced from said movable shunt contact by a small gap in the normal condition of said device and coupled to the main current path of the circuit interrupter in parallel with said thermally responsive element, whereby a flow of excessive current through the circuit interrupter generates an electromagnetic repulsion between said parallel conductor members which acts as the one and only force for engaging the movable shunt contact with the associated fixed shunt contact to complete an electrically parallel circuit through the contacts around the thermally responsive element.