EP0688464A1

EP0688464A1 - Blade transfer runner and arc shunt for a double break circuit breaker

Info

Publication number: EP0688464A1
Application number: EP95907446A
Authority: EP
Inventors: Dale W. Bennett; Jerry L. Scheel; Randall L. Siebels; Matthew D. Sortland; John M. Winter
Original assignee: Square D Co
Current assignee: Schneider Electric USA Inc
Priority date: 1994-01-13
Filing date: 1995-01-13
Publication date: 1995-12-27
Also published as: JPH08507651A; WO1995019631A1; MX9503935A; CA2156629A1

Abstract

A double break circuit breaker includes a pair of contact assemblies, an arc stack and an arc extractor. At least one of the contact assemblies interrupts the current by moving from a normally closed position to at least one open position, and the arc stack is disposed sufficiently adjacent the pair of contact assemblies to absorb arc energy resulting from one of the primary contact assemblies moving from the normally closed position. The arc extractor has a conductive portion located adjacent the arc stack and sufficiently adjacent the pair of contact assemblies to prevent the arc energy within the arc stack from collapsing into a region between the pair of contact assemblies.

Description

BLADETRANSFERRUNNERANDARCSHUNT FORADOUBLEBREAKCIRCUITBREAKER

Field Of The Invention

The present invention relates generally to circuit breakers and, more particularly, the manner in which a circuit breaker accommodates arc energy developed between two circuit breaker contacts as they separate from one another when the circuit breaker interrupts the current path.

Background Of The Invention

Use of circuit breakers is widespread in modern-day residential, commercial and industrial electric systems, and they constitute an indispensable component of such systems toward providing protection against over-current conditions. Various circuit breaker mechanisms have evolved and have been perfected over time on the basis of application-specific factors such as current capacity, response time, and the type of reset (manual or remote) function desired of the breaker.

One type of circuit breaker mechanism employs a thermo-magnetic tripping device to "trip" a latch in response to a specific range of over-current conditions.

The tripping action is caused by a significant deflection in a thin bi-metal or thermostat-metal element which responds to changes in temperature due to resistance heating caused by flow of the circuit's electric current through the element. The thermostat metal element is typically in the form of a blade and operates in conjunction with a latch so that blade deflection releases the latch after a time delay corresponding to a predetermined over-current threshold in order to "break" the current circuit associated therewith. Circuit breaker mechanisms of this type often include an electro-magnet operating upon a lever to release the breaker latch in the presence of a short circuit or very high current condition. Typically, the thermostat metal element is arranged as part of the same current path that the circuit breaker contacts interrupt in response to the predetermined over-current threshold. This type of circuit breaker tripping arrangement is used in both single-break circuit breakers, which have only one set of contacts in the current path, and double- break circuit breakers, which have two sets of contacts in the current path. See, for example, U.S. Patent Nos. 3,944,953, 3,96,346, 3,943,316, 3,943,472, 5,003,139, 5,075,657, and 5,097,589, each of which is assigned to the instant assignee and incorporated herein by reference.

When the circuit breaker contacts separate in response to the short circuit or very high current condition, undesired arc energy develops between the separating contacts because of their voltage differential. To complete the interruption of the current path promptly, the residual arc energy path must be eliminated. This has typically been accomplished using an arc-attracting element (a.k.a. "arc stack") adjacent the gap separating the contacts. In addition, some implementations have a used metal plate next to the arc stack to divert high level current faults around the bimetal element so not to overly stress its fragile structure due to the short circuit or high level current condition.

While the arc is sufficiently removed by such implementations in line voltage applications of 277 volts or less, they are insufficient in higher line voltage applications, for example, around 346 volts or more. In accordance with the present invention and in connection with such higher line voltage applications, it has been discovered that low to medium level fault currents cause the arc energy to collapse back into the gap separating the contacts. In the presence of low to medium level fault currents, the metal plate next to the arc stack does not aid in interrupting the arc and the arc stack cannot maintain the arc energy. Consequently, the arc energy collapses back between the contacts, lowers the arc voltage across the contacts, and causes interruption problems at these higher line voltage applications.

Accordingly, to accommodate such line voltage applications and without unduly adding complexity or significant cost to the circuit breaker arrangement, there is a need for an improved circuit breaker structure which enhances the interruption performance for current faults at both low and high level current faults.

foimmarv Of The Invention Generally, the present invention provides a circuit breaker arrangement which overcomes the above-mentioned deficiencies of the prior art.

More specifically, the present invention provides a combination blade transfer runner and arc shunt, useful for either a double break or single break circuit breaker, which improves the interruption performance of the circuit breaker at low and high level current faults.

The present invention also provides a solution to a problem discovered by the inventors of the present invention: in higher line voltage applications, low to medium level fault currents cause the arc energy to collapse back into the gap separating the contacts. In the presence of low to medium level fault currents, it has been discovered that known implementations using a metal plate next to the arc stack do not aid in interrupting the arc, and the typical arc stack arrangement cannot maintain the arc energy. Consequently, the arc energy collapses back between the contacts, lowers the arc voltage across the contacts, and causes interruption problems at these higher line voltage applications. The arrangement of the present invention prevents the arc energy from collapsing from within the arc stack into the adjacent gap which separates the contacts.

In one embodiment, the present invention is realized by providing a circuit breaker a pair of contact assemblies, an arc stack and an arc extractor. At least one of the contact assemblies interrupts the current by moving from a normally closed position to at least one open position, and the arc stack is disposed sufficiently adjacent the pair of contact assemblies to absorb arc energy resulting from one of the primary contact assemblies moving from the normally closed position. The arc extractor has a conductive portion located adjacent the arc stack and sufficiently adjacent the pair of contact assemblies to prevent the arc energy within the arc stack from collapsing into a region between the pair of contact assemblies.

In another embodiment of the present invention, a circuit breaker passes current between two circuit breaker terminals during a normal condition and, in response to at least one abnormal condition, interrupts the current at least momentarily. The circuit breaker includes a pair of primary contact assemblies, at least one of which interrupts the current by moving away from a normally closed position; a pair of secondary contact assemblies, at least one of which interrupts the current by moving away from a normally closed position in response to a blow-off force; an arc absorbing element disposed sufficiently adjacent the pair of primary contact assemblies to absorb arc energy resulting from one of the primary contact assemblies moving away from the normally closed position; and an arc extractor having a conductive portion located adjacent the arc stack and within a certain distance with respect to the pair of primary contact assemblies to prevent the arc energy within the arc stack from collapsing into a region between the pair of primary contact assemblies.

In yet another embodiment, the circuit breaker described in the preceding paragraph is constructed such that the greatest distance between the conductive portion of the arc extractor and the pair of contact assemblies is about 0.25 inch, and the closest distance between the pair of contact assemblies when the contact assemblies are in the open position is between about 0.42 inch and 0.39 inch.

The above summary of the present invention is not intended to represent each embodiment, or every aspect, of the present invention. This is the purpose of the figures and the detailed description which follow. Brief Description Of The Drawings

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which: FIG. 1 is a side view of a double break circuit breaker including an arc extractor embodying principles of the present invention; and

FIG. 2 is an enlarged side view of the arc extractor of FIG. 1.

While the invention is susceptible to various modifications and alternative forms, a specific embodiment thereof has been shown by way of example in the drawings and will be described in detail. It should be understood, however, that it is not intended to limit the invention to the particular form described. On the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

Description Of The Preferred Embodiments

Turning now to the drawings, FIG. 1 illustrates the basic configuration of a combination blade transfer runner and arc shunt (hereinafter "arc extractor") 10 embodying the present invention in the context of a double-break circuit breaker. The present invention is discussed in the context of such an exemplary double-break circuit breaker for illustrative purposes only, because it was in this environment that the inventors discovered the problem and its solution. The particular circuit breaker illustrated and described (FIG. 1) should not be construed to limit the possible applications for the present invention, as these applications encompass a wide variety of circuit breaker types including those serving low level voltage lines and having reduced contact gap separations.

The circuit breaker of FIG. 1 includes a circuit breaker base 14 which carries all of the internal components of the circuit breaker. The current path through the circuit breaker begins at a line terminal 16, and from the line terminal 16 the current path goes through a flexible pigtail 18. The flexible pigtail 18 is attached to a secondary blade 20 with a moveable contact 22 mating with a stationary contact 24. Current flows through the moveable and stationary contacts 22, 24 to the mid terminal 26, which is configured in an S form. The other side of the mid terminal 26 includes another stationary contact 28 connected thereto. Positioned opposite the stationary contact 28 is a mating moveable contact 30 attached to a primary blade 32. Current flows through the stationary and moveable contacts 28, 30, through the primary blade 32, and into one end of a primary flexible connector or pigtail 34. The other end of the primary flexible connector 34 is attached to a bimetal 36, which provides the thermal tripping characteristics for the circuit breaker. Finally, the current flows from the bimetal 36 through a load terminal 38 and out of the load end of the circuit breaker via a lug 40.

The primary section of the circuit breaker includes the primary blade 32, a trip lever 42, a handle 44, a magnetic armature 46, a pigtail 34, and a primary arc stack 13. The secondary section includes the secondary blade 20, the pigtail 18, an extension spring 48, and the secondary arc stack 12. In the illustrated circuit breaker, using conventional magnetic and thermal trip protection features, the primary section provides the breaking capacity for all levels of current from one ampere to approximately 3000 amperes without operational assistance from the secondary section. The magnetic armature 46 is drawn to a yoke 50 during high current flow.

This allows the trip lever 42 to disengage from the magnetic armature 46 and rotate to the trip position, which, in turn, allows the primary blade contact 30 to separate from the stationary contact 28 to break the current flow. As the contacts 28, 30 are separated, an arc voltage is generated in the primary arc stack 13. A thermal trip via the bimetal 36 results in the same sequence of events and, additionally, results in the trip lever 42 disengaging from the magnetic armature 46.

The normal ON and OFF operation of the primary blade 32 occurs in response to rotation of the handle 44 in a clockwise or counterclockwise motion. In response to rotation of the handle 44 in either direction, the primary blade 32 either opens or closes the circuit via the primary moveable contact 30 and the primary stationary contact 28. Rotation of the primary blade 32 is tied directly to the handle 44 for the normal ON and OFF operation of the primary blade 32. Furthermore, the secondary section is not affected by the normal ON and OFF operation of the primary blade 32.

The secondary blade contact 22 and the secondary stationary contact 24 remain closed.

As previously explained, the secondary section of the circuit breaker has limited operation below 3000 amperes of fault current. However, at current levels above 3000 amperes, the secondary section begins to contribute to interruption performance. In particular, the secondary blade 20 derives contact force from the extension spring 48. The secondary blade 20 pivots about the blade pivot 52 with the extension spring 48 extended as the secondary blade 20 opens up in response to a current fault above 3000 amperes. In response to the occurrence of a current fault above 3000 amperes, the constriction resistance of the secondary blade contact 22 and the secondary stationary contact 24 provides a magnetic force that tries to separate the contacts. Simultaneously, the current path configuration of the mid terminal 26 and the secondary blade 20 forms a magnetic blowoff loop which also tries to separate the contacts 22, 24. The addition of both of these opening forces to the secondary blade

20 causes the secondary blade 20 to separate at the contacts 22, 24. As the secondary blade 20 opens, the extension spring 48 begins to stretch. The extension spring 48 permits the secondary blade 20 to continue to open as long as the force to open the blade is greater than the extension force of the spring 48. As the contacts 22, 24 are separated, an arc voltage is generated in the secondary arc stack 12. The combination of the arc voltage generated by the secondary arc stack 12 and the arc voltage generated by the primary arc stack 13 make these voltages add together. This allows a very fast rise of arc voltage and also allows high levels of arc voltage consistent with double break circuit breakers.

As the current fault level rises significantly above 3000 amperes, the faster and higher the secondary blade 20 will be moved. As the interruption takes place and the electric arc is extinguished in the primary and secondary sections, the secondary blade 20 is biased to return to the closed position because of the spring bias from the extension spring 48, and the primary blade is latched in the open position (versus being in the open "OFF" position via the manual handle operation). At this point, the interruption of the current fault is complete with no opportunity to re-establish itself.

For further information regarding the overall construction and operation of the circuit breaker shown in FIG. 1, reference may be made to U.S. Patent Application

Nos. (CRC-11/SQUC112), entitled "Circuit Breaker Having Double

Break Mechanism" , and (CRC-13/SQUC118), entitled "Double Break Circuit Breaker Having Improved Secondary Section". The construction of the arc stacks is further discussed in U.S. Patent Application No. (CRC-

14/SQUC113), entitled "Arc Stack For A Circuit Brewer". Each of the above has been filed concurrently herewith, assigned to the instant assignee and incorporated herein by reference. The normal current path for the double break circuit breaker in FIG. 1 enters the line terminal 16, and passes through the flexible connector 18, the secondary blade 20, the mid terminal 26, the primary contacts 28 and 30, into the primary blade 32. The primary blade 32 passes current to the flexible connector 34, the bimetal 36, the terminal 38, and the current then exits into the lug 40. This current path, which requires all current flowing through the bimetal 36, is considered normal operation when the current is at a relatively low level and no fault current is applied to the circuit breaker. FIG. 2 is an enlarged view of the circuit breaker components highlighting the arc extractor 10 of the present invention. At high level fault currents, the shunt 10 serves both to divert arc energy from the bimetal member 36 and to shunt arc energy from between the contacts. At low to medium level fault currents, the arc extractor 10 serves to shunt arc energy from between the contacts and prevent the energy from collapsing into the gap separating the contacts. With respect to high level fault currents, during the interruption process high levels of current flow through the stationary contact 28 and the moveable contact 30. In response to these high level current faults, the primary blade 32 blows open counterclockwise about its blade pivot 23. The blade 32 rotates counterclockwise until the back 93 of the blade 32 impacts blade stop 89. As the blade 32 is blown open, the generated arc is drawn back between the contacts 28 and 30. Up to this point in time, all the current is passing through the primary current path passing from the flexible connector 34, through the bimetal 36 and the terminal 38, and then out to the lug connection 83. In response to the blade 32 impacting the back of the blade stop 89, the arc transfers some of the current to arc shunt surface 87 so as to generate a secondary shunting current path parallel to the primary current path. The current in this secondary path now travels through the body of arc extractor 10 to interface point 88, then travels to load terminal interface point 85. From this point current travels the rest of the way through the final section of the load terminal to lug connection point 83. The shunting path of current reduces the total amount of current that goes through the bimetal, thereby reducing the energy stress on the bimetal 36. This type of arc shunting practice expands the short circuit capacity of the circuit breaker, which is otherwise limited by the current capacity of the bimetal 36. An arc shunt transfer function occurs in response to the application of lower level fault currents to the circuit breaker. This becomes important at the lower level fault currents because at these low levels, the secondary blade 20 does not aid in the current interruption. Instead, the primary blade 32 alone interrupts the current flow. The arc transfer system works by first initiating a fault between the contacts 28 and 30. In response to such a fault, the primary blade 32 blows open and pivots about the pivot point 23. The primary blade 32 continues to pivot until it impacts against the blade stop 89. At this point the moveable contact 30 is in close proximity to the transfer tip 90 so that the generated arc can easily jump to the transfer surface 87.

When the arc engages the transfer surface 87, the arc has a linear travel path from arc runner 54, through the first arc plate 91, up through all the plates to top plate 92, and finally to the transfer surface 87. Once the arc has engaged these components, the arc will not come out of the arc stack and reignite between the stationary contact 28 and the moveable contact 30. By transferring the arc to the transfer surface 87, the interruption quality of the circuit breaker at low level fault currents is improved.

In an exemplary embodiment, certain separation distances defined from the tip of the blade 32 in its respective open positions and the end of the conductive arc extractor 10, and defined from the contact 28 to its mating contact 30 in its respective open positions, were found to be acceptable. When the blade 32 is in its open "OFF" position resulting from the manual action via the handle, the separation distance should be about 0.25 inch defined from the tip of the blade 32 to the end of the arc extractor 10, and about 0.39 inch and from the contact 28 to its mating contact 30. When the blade 32 is in its open latched position resulting from a trip or blow-off force, the separation distance should be about 0.08 inch defined from the tip of the blade 32 to the end of the arc extractor 10, and about 0.42 inch and from the contact 28 to its mating contact 30. Thus, a range of about 0.08 inch to about 0.25 inch is acceptable for the distance between the tip of the blade 32 to the end of the arc extractor 10, and a range of about 0.39 inch to about 0.42 inch is acceptable for the distance between the contact 28 to its mating contact 30.

It can be seen from the foregoing description that the combination of arc transfer for low level current interruption and arc shunting at high level current interruption improves the interruption performance of the circuit breaker. Those skilled in the art will readily recognize that various modifications and changes may be made to the present invention without departing from the true spirit and scope thereof, which is set forth in the following claims.

Claims

What is claimed is:

1. A circuit breaker for passing current between two circuit breaker terminals during a normal condition and, in response to at least one abnormal condition, for interrupting the current, comprising: a pair of contact assemblies, at least one of the contact assemblies being constructed and arranged to interrupt the current by moving from a normally closed position to at least one open position; an arc stack disposed sufficiently adjacent the pair of contact assemblies to absorb arc energy resulting from said at least one of the primary contact assemblies moving from the normally closed position to said at least one open position; and an arc extractor having a conductive portion located adjacent the arc stack and sufficiently adjacent the pair of contact assemblies to prevent the arc energy within the arc stack from collapsing into a region between the pair of contact assemblies.

2. A circuit breaker, according to claim 1, wherein the closest distance between the conductive portion of the arc extractor and the pair of contact assemblies is between about 0.08 inch and 0.25 inch.

3. A circuit breaker, according to claim 1, wherein the closest distance between the pair of contact assemblies when said at least one of the contact assemblies is in said at least one open position is between about 0.42 inch and 0.39 inch.

4. A circuit breaker, according to claim 1, wherein the arc extractor is electrically connected to one of the circuit breaker terminals.

5. A circuit breaker, according to claim 1 , wherein the conductive portion located adjacent the arc stack is at an end of the arc extractor.

6. A circuit breaker, according to claim 1 , wherein the conductive portion located adjacent the arc stack is at an end of the arc extractor and wherein the arc extractor is electrically connected to one of the circuit breaker terminals.

7. A circuit breaker, according to claim 1, wherein the closest distance between the conductive portion of the arc extractor and the pair of contact assemblies is between about 0.08 inch and 0.25 inch, and the closest distance between the pair of contact assemblies when said at least one of the contact assemblies is in said at least one open position is between about 0.42 inch and 0.39 inch.