EP0128403A2

EP0128403A2 - Current limiting circuit breaker with insulating barriers and baffles

Info

Publication number: EP0128403A2
Application number: EP84105775A
Authority: EP
Inventors: Jere Lee Mckee; William Ellsworth Beatty, Jr.; Glenn Robert Thomas; Donald Wayne Lovett
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1983-06-08
Filing date: 1984-05-21
Publication date: 1984-12-19
Also published as: ES8600563A1; BR8402761A; AU2835584A; ES533205A0; JPS609027A; KR850000760A; CA1257636A; ZA843753B; EP0128403A3

Abstract

The invention relates to a circuit interrupter including an insulating housing and, disposed therein, several pole units each comprising a pair of cooperable contacts and a pair of terminals electrically interconnected through the contacts.

At least the line terminals of the interrupter have disposed therebetween insulating barriers (49) which extend from the circuit interrupter housing a distance sufficient to prevent ionized gases at the terminals from intermixing before they have become sufficiently deionized to prevent conduction. This enables the circuit interrupter to operate at higher voltage levels.

Description

The invention relates generally to circuit interrupters and, more particularly, to circuit interrupters operating under short circuit conditions to limit the flow of current through the interrupter to a value lower than the available fault current which the circuit is capable of supplying.
Circuit breakers are widely used in industrial, residential, and commercial installations to provide protection against damage due to overcurrent conditions. As the usage of electrical energy has increased, so has the capacity of sources supplying the electrical energy so that, upon the occurrence of a short circuit condition, extremely large currents may be flowing through distribution circuits, too large for conventional circuit interrupters to prevent damage to apparatus connected downstream of the interrupters.
Current limiting circuit interrupters were developed to provide the degree of protection necessary on circuits connected to power sources capable of supplying very large fault currents. One type of circuit interrupter provides such current limiting action during short circuit conditions through extremely rapid separation of its contacts,causing the arc voltage across the separating contacts to quickly approach the system voltage, and thus limiting the current flow between the contacts. Although circuit interrupters of this current limiting type have proven very satisfactory in many applications, it is the principal object of this invention to extend their use to higher voltage levels in the order of, say, 1000 volts or more.
The invention secondarily resides in a multi-pole circuit interrupter comprising an insulating housing with insulating walls which define pole unit compartments within the housing, a separate pole unit disposed in each pole unit compartment and including a pair of cooperable contacts, and means common to all pole units for closing and opening the contacts therein, each pole unit including further a line terminal and a load terminal electrically connected to each other through the contacts of the associated pole unit, characterized in that at least the line terminals of the pole units have disposed therebetween insulating barriers which extend from said insulating housing a distance sufficient to prevent ionized gases generated in the pole units during contact opening operations from intermixing until the gases have become sufficiently deionized to prevent conduction.
It has been found that a circuit interrupter provided with insulating barriers such as defined above can be used in conjunction with higher,voltage levels without objectionable arcing occurring between and from its line terminals. This renders the circuit interrupter particularly suitable for use in fields, such as the mining industry, where arcing is most undesirable.
The insulating barriers can be formed integral with the insulating housing of the circuit interrupter, especially with the cover forming part of the housing, or as part of an insulating barrier structure, such as a terminal cover, formed, e.g. molded, separate from and secured to the insulating housing of the interrupter. Furthermore, the insulating barriers include baffles positioned to direct said gases away from the insulating housing.
A preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 is a sectional side-elevational view of a multi-pole current-limiting circuit interrupter embodying the invention;
Fig. 2 is a top view of one outside pole of the circuit interrupter shown in Fig. 1;
Fig. 3 is a view similar to Fig. 1, with the circuit interrupter shown in a tripped condition;
Fig. 4 is a view similar to Figs. 1 and 3, with the circuit interrupter shown during a current limiting operation;
Fig. 5 is a perspective view of the circuit interrupter, with the cover shown in place;
Fig. 6 is a detail cross-sectional view looking at the front of the insulating barrier structure;
Fig. 7 is a top view of the barriers and baffles;
Fig. 8 is a rear view of the barriers and baffles; and
Fig. 9 is a cross-sectional view taken along line IX-IX of Fig. 6.

Referring now to the drawings, Fig. 1 shows a three pole circuit breaker 3 comprising an insulating housing 5 and a high-speed circuit breaker mechanism 7 supported in the housing 5. The housing 5 comprises an insulating base 9 having a generally planar back, and an insulating front cover 11 secured to the base 9 which together form the housing 5. The housing 5 includes insulating walls 4 separating the base 9 into three adjacent side-by-side pole unit compartments.
The circuit breaker mechanism 7 comprises a single operating mechanism 13 and a single latch mechanism 15 mounted on the center pole unit. The circuit breaker mechanism 7 also comprises, in each of the three pole units, a separate thermal trip device 16 and a high-speed electromagnetic trip device 17. The high-speed electromagnetic trip device is more completely described in U.S. Patents 4,255,732 and 4,220,935.
A pair of separable contacts 19 and 21 attached to upper and lower pivoting contact arms 20 and 22, respectively, are provided in each pole unit of the breaker. An arc extinguishing unit 23 is also provided in each pole unit. The upper contact 19 is electrically connected, through the upper contact arm 20, constructed of conducting material to a shunt 24 which is in turn connected through a conducting strip 25 and the thermal and magnetic trip devices 16 and 17 to a terminal connector 26. The lower contact 21 is connected through the lower contact arm 22, also constructed of conducting material, through a shunt 27 and conducting strip 28 to a similar terminal connector 29. With the circuit breaker 3 in the closed position as is shown in Fig. 1, an electrical circuit thus exists from the terminal 26 through the conducting strip 25, the shunt 24, the upper contact arm 20, the upper contact 19, the lower contact 21, the lower arm 22, the shunt 27, and the conducting strip 28 to the terminal connector 29.
The upper contact arm 20 is pivotally connected to the point 30 to a rotating carriage 32, which is fixedly secured to an insulating rotatable tie bar 35 by a staple 34. A tension spring 36 connected between the left end of the upper contact arm 20 and a bracket 37 attached to the carriage 32 serves to maintain the upper contact arm 20 in the position shown in Fig. 1, with respect to the carriage 32. The upper contact arm 20 and carriage 32 thus rotate as a unit with the crossbar 35 during normal current conditions through the circuit breaker 3.
The single operating mechanism 13 is positioned in the center pole unit of the three pole circuit breaker and is supported on a pair of spaced metallic rigid supporting plates 41 that are fixedly secured to the base 9 in the center pole unit of the breaker. An inverted U-shaped operating lever 43 is pivotally supported on the spaced plates 41 with the ends of the legs of the lever 43 positioned in U-shaped notches 56 of the plates 41.
The U-shaped operating lever 43 includes a member 44 extending through a hole in a slide plate 46. The slide plate 46 is slidingly attached to the cover 11 by a support plate 47, and includes a member 48 seated in a molded handle 149.
The upper contact arm 20 for the center pole unit is operatively connected by means of a toggle, comprised of an upper toggle link 53 and a lower toggle link 55, to a releasable cradle member 57 that is pivotally supported on the plates 41 by means of a pin 59. The toggle links 53 and 55 are pivotally connected to each other by means of a knee pivot pin 61. The lower toggle link 55 is pivotally connected to the carriage 32 of the center pole unit by means of a pin 65 and the upper toggle link 53 is pivotally connected to the releasable cradle member 57 by means of a pin 63. Overcenter operating springs 67 are connected under tension between the knee pivot pin 61 and the bight portion of the operating lever 43. The lower contact arm 22 is pivotally mounted at the point 18 to the base 9.
A leaf spring 31 urges the lower contact arm 22 in a counterclockwise direction about the pivot point 18, the counterclockwise travel of the lower contact arm 22 being limited by a pin 40. Since the clockwise force upon the upper arm 20 in the closed position is greater than the counterclockwise force on the lower arm 22, a degree of overtravel is provided from the first point of contact between the arms until the fully closed position. This allows for the effect of contact wear.
The contacts 19 and 21 are manually opened by movement of the handle. 149 in a leftward direction as seen in Fig. 1 from the ON position to the OFF position. This movement causes the slide plate 46 to rotate the operating lever 43 in a counterclockwise direction. The rotating movement of the operating lever 43 carries the line of action of the overcenter operating springs 67 to the left causing a collapse, to the left, of the toggle linkage 53, 55. The collapse of the toggle linkage 53, 55 causes the crossbar 35 to rotate in a counterclockwise direction to simultaneously move the upper contact arms 20 of the three pole units to the open position, opening the contacts of the three pole units. The operating mechanism 13 is then in the position shown in dashed lines in Fig. 1.
The contacts are manually closed by reverse movement of the handle 149 from the OFF to the ON position, which movement moves the line of action of the overcenter springs 67 to the right to move the toggle linkage 53, 55 to the position shown in Fig. 1. This movement rotates the crossbar 35 in a clockwise direction to move the upper contact arms 20 of the three pole units to the closed position.
The releasable cradle 57 is latched in the position shown in Fig. 1 by means of the latch mechanism 15. The latch mechanism 15 comprises a primary latch member 71 and an insulating trip bar 73 pivoted at the point 70. The primary latch member 71 comprises a generally U-shaped latch lever 75 and a roller member 77 movably supported for limited travel in a pair of slots 78 in opposite legs of the lever 75. A torsion spring 81 biases the roller member 77 to one end of the slots. The primary latch member 71 is pivotally supported on the supporting plates 41 by means of a pin 83. The free end of the cradle 57 moves within a slot in the bight portion of the lever 75.
The trip bar 73 is a molded insulating member pivotally supported in the support plates 41, and is provided with a secondary latch member 89 for engaging the bight portion of the latch lever 75 of the primary latch member 71 to latch the primary latch member 71 in the position seen in Fig. 1. The releasable cradle 57 is provided with a hook portion 58 serving as a primary latching surface for engaging the roller 77 to latch the cradle 57 in the position seen in Fig. 1.
The primary latch member 71 includes a bias spring 72 secured at the upper end thereof, with the other end of the bias spring 72 being seated against the trip bar 73. The bias spring 72, in compression, urges the primary latch member 71 in a clockwise direction about its pivot point 83. Thus, as soon as the trip bar 73 is rotated in the counterclockwise direction raising the secondary latch 89 away from the top of the latch lever 75, the bias spring 72 will rotate the primary latch member 71 in a clockwise direction allowing the cradle 57 to be released from the roller 77. The action of the bias spring 72 is overcome during a resetting operation as will be described hereinafter.
Included in each pole unit is a separate high-speed electromagnetic trip device 17. Each of the electromagnetic trip devices 17 comprises a generally U-shaped pole piece 95, the legs of which extend around the conducting strip 25. An armature structure 97 is pivotally supported in the housing 5 and includes a laminated magnetic clapper 101 and an actuating member 103.
A separate thermal trip device 16 is also included in each pole unit. The thermal device 16 includes a bimetal element 105 welded to the conducting strip 25. The upper end of the bimetal element 105 includes an adjusting screw 107 threaded therein. The magnetic 17 and thermal 16 trip devices may also be of the electronic type illustrated in Figure 5, instead of the mechanical types described herein.
When the circuit breaker is in the latched position as seen in Fig. 1, the springs 67 operate through the toggle link 53 and pivot 63 to pivot the cradle 57 in a clockwise direction about the pivot point 59. Clockwise movement of the cradle member 57 is restrained by engagement of the latching surface of the hook portion 58 under the roller 77 of the primary latch member 71, with the cradle member 57 pulling the primary latch member 71 in a clockwise direction about the pivot 83. Clockwise movement of the primary latch member 71 about the pivot 83 is restrained by engagement of the primary latch member with the secondary latch part 89 on the trip bar 73. The force of the primary latch member 71 against the secondary latch 89 of the trip bar 73 operates through the axis of the pivot 70 of the trip bar 73 so that clockwise movement of the primary latch member 71 is restrained by the trip bar 73 without tending to move the trip bar 73 about its axis. Thus, the trip bar 73 is in a neutral or latching position latching the primary latch member 71 and cradle member 57 in the latched position as seen in Fig. 1.
The circuit breaker is shown in the closed and reset position in Fig. 1. Upon occurrence of a high overload current above a predetermined value in any of the pole units, the clapper 101 is attracted toward the associated pole piece 95 whereupon the armature structure 97 pivots in a clockwise direction closing the air gap between the pole piece 95 and clapper 101 and pivoting the armature actuating member 103 in a clockwise direction against the extension 79 of the trip bar 73. This causes rotation of the trip bar 73 in a counterclockwise direction moving the secondary latch 89 of the trip bar 73 out of engagement with the latch lever 75. The upward force of the cradle member 57 upon the roller 77 now rotates the primary latch 71 in a clockwise direction, releasing the hook portion 58 of the cradle member 57. The force of the operating springs 67 upon the knee pin 61 is transmitted through the upper toggle link 53 to cause the cradle member 57 to rotate in a clockwise direction about the point 59. Continued rotation of the cradle member moves the upper toggle pin 65 to the right of the line of action of the operating springs 67, causing collapse of the toggle linkage 53, 55 which in turn rotates the carriage 32 and the attached crossbar 35 in a counterclockwise direction and move all three upper contact arms 20 in a counterclockwise direction to simultaneously open the contacts of the three pole uits. During this movement, the handle 149 is moved to a TRIP position between the OFF and ON positions to provide a visual indication that the circuit breaker has been tripped.
Before the circuit breaker can be manually operated after an automatic tripping operation, as shown in Fig. 3, the circuit breaker mechanism must be reset and latched. This resetting operation is effected by movement of the handle 149 from the intermediate TRIP position to the left to the full OFF position. During this movement, the slide plate 46 acts upon the member 44 of the operating lever 43 to rotate the operating lever 43 in a counterclockwise direction about the pivot point at the notch 56 in the support plates 41. A lower extending member 45 of the operating lever 43 engages a corresponding surface 54 of the cradle member 57 to move the cradle member 57 from the position shown in Fig. 3 in a counterclockwise direction about the point 59.
During this movement, the hook portion 58 of the cradle member 57 moves down in the slot in the bight portion of the latch lever 75 of the primary latch member 71 and the hook portion 58 of the cradle member 57 comes in contact with the roller 77 to move the roller 77 to the right in the slot 78 with the hook portion wiping past the roller 77. Once the hook portion 58 of the cradle member 57 passes the roller 77, the spring 81 snaps the roller 77 back to the position seen in Fig. 1. As the primary latch member 71 reaches the position seen in Fig. 1, the member 71 clears the latch part 89 of the trip bar 73, whereupon the spring 72 biases the latch part 89 into latching engagement with the primary latch member 71 to latch the primary latch member 71 in the position seen in Fig. 1. Thereafter, upon release of the handle 149 by the operator, the springs 67 again act upon the toggle link 55 to bias the cradle member 57 in a clockwise direction to move the hook portion 58 up to engage the roller 77 in a latched position seen in Fig. 1. The handle 149 can then be manually moved back and forth between the ON and OFF positions to close and open the contacts.
With the circuit breaker in the closed and latched position as seen in Fig. 1, a low current overload condition will generate heat in the conductor strip 25 and cause the upper end of the bimetal member 105 to flex to the right as seen in Fig. 1. The adjusting screw 107 impinges on the armature actuating member 103 of the armature structure 97. This causes counterclockwise rotation of the trip bar 73 to initiate a tripping action and'achieve automatic separation of the contacts in all three pole units as hereinbefore described with regard to a magnetic trip.
As can be seen in Figs. 1, 2 and 3, the circuit breaker also includes a slotted magnetic drive device 110. The magnetic drive device 110 includes a housing 112 having a slot 118 within which are disposed the upper and lower contact arms 20 and 22. The magnetic drive device 110 is described more completely in U.S. Patent 4,220,934.
A bumper member 120 is provided to limit the travel of the upper contact arm 20 during current limiting operations as will be described hereinafter. The bumper member 120 is composed of shock absorbing material such as polyurethane or butyl plastic. This type of material has a very large mechanical hysteresis loop, thus absorbing a maximum amount of energy and minimizing rebound. A similar member 121 mounted to the base 9 is provided for the lower arm 22.
Under short circuit conditions, extremely high levels of overload current flow through the circuit breaker 3. The current flow through the conductor member 28 and lower contact arm 22 generates a large amount of magnetic flux in the slotted magnetic drive device 110. This flux and the current flow through the lower contact arm 22 produces a high electrodynamic force upon the lower contact arm 22, tending to drive the arm 22 from the closed position shown in dashed lines in Fig. 4 toward the bottom of the slot 118. In addition, the current flow through the contact arms 20 and 22 in opposite directions generates a high electrodynamic repulsion force between the arms 20 and 22. This force builds up extremely rapidly upon occurrence of a short circuit condition, causing the upper contact arm 20 to pivot in a counterclockwise direction about the pin 30, acting against the tension force of the spring 36, from the closed position shown in dashed lines in Fig. 4 to the current limiting position shown in solid lines. The upper contact arm 20 is thus driven with great force into the bumper member 120, which is designed so as to minimize the amount of rebound of the upper contact arm 20. This rebound is undesirable since the established arc which has been extinguished by the arc extinguishing device 23 may restrike if the contacts 19 and 21 return to close proximity. The high-speed magnetic trip device 17 is therefore designed to operate the latch mechanism 15 to release the operating mechanism 13 before the arms 20 and 22 can reclose. As the operating mechanism 13 moves from the closed position shown in Fig. 4 to the tripped position shown in Fig. 3, the carriage 32 rotates in a counterclockwise direction to raise the pivot point 30 of the upper contact arm 20 before the tension spring 36 returns the upper contact arm 20 to the first position with respect to the carriage 32 as shown in Fig. 1.
The initial high opening acceleration of the contact arms produces a high arc voltage resulting in extremely effective current limiting action. The combination of the high speed electromagnetic trip device and high speed operating mechanism assures that the contacts will remain separated to prevent re-establishment of the arc after it is extinguished.
The current limiting circuit interrupter 3 thus far described has been a highly reliable and extremely efficient interrupting device at its existing voltage classifications. However, in extending the voltage interrupting capability of this breaker to higher levels, say on the order of 1000 volts or higher to, say, 1500 volts, problems have arisen due to arcing between the line terminals 29 and between the line terminals 29 and the enclosure 5. To prevent this and to enable the circuit interrupter to function properly at 1000 volts or higher (at 25 kA or higher), the breaker 3 was modified by redesigning the primary channels which direct the gases generated by the arc interruption. The modifications made were the inclusion of an increased length insulating barrier and the provision of insulating baffles.
Referring now more particularly to Figs. 5-9, there are illustrated therein in greater detail the barriers 49 and baffles 51 utilized to increase the voltage rating of the current limiting circuit interrupter. As illustrated, the insulating barriers 49 are made of a molded insulating material separate from the insulating cover 11, but attached thereto through the screws 10._" Alternatively, although not illustrated, the barriers 49 and baffles 51 can be molded integrally with the insulating cover 5.
As can be seen more particularly in Figs. 5 and 1, the insulating barriers 49 extend heightwise in the direction from the cover 11 to the base 9, and are disposed between adjacent pole unit terminals 29 at the line end of the circuit interrupter 3. This is the end of the circuit interrupter closest to the separable contacts 19, 21. The insulating barriers 49 are extended in the lengthwise direction (vertically as illustrated in Fig. 5) a distance sufficient to prevent the gases, which are generated during a contact opening operation end present at the terminal 29 of each pole unit, from mixing with the gases at adjacent pole unit terminals 29 until such time as said gases have become deionized sufficiently to prevent conduction. For a circuit interrupter 3 in the voltage range of 1000 volts or higher, this length should be at least 3.8 cm, and preferably may extend a distance of approximately 4.30 cm beyond the terminal 29 in the lengthwise direction.
As can be readily appreciated from Fig. 8, the insulating barriers 49 have a plurality of grooves 50 disposed therein in the heightwise direction, that is, in the direction from the base 9 towards the cover 11. The presence of these grooves 50, which are disposed on both sides of the insulating barriers 49, funnels the gases away from the insulating housing 5. The barriers 49, as illustrated, extend lengthwise outwardly farther than the base 9 itself, aiding in the dispersion of the arcing gases.
As can be seen from Figs. 5-9, between the insulating barriers 49 there are disposed molded insulating baffles 51 which also function to direct the arcing gases away from the housing 5 and the adjacent terminals 29 to thereby further increase the interrupting capability of the circuit interrupter 3. In particular, these baffles 51 direct the arcing gases away from the insulating housing 5 to prevent arcing to ground. The baffles 51, as shown, extend in a direction perpendicular to the insulating base walls 4, or in other words, extend in the widthwise direction across each pole unit in the vicinity of the terminals. The baffles 51, with their angular alignment 52 more particularly noticeable in Fig. 9, function to direct the arcing gases outwardly away from the housing 5 and upwardly as shown in the drawings away from the insulating housing 5.
With the inclusion of the insulating barriers and the insulating baffles, herein is provided a current limiting circuit interrupter which is capable of functioning satisfactorily at extended voltage ranges of 1000 volts or higher at 25 kA or higher.

Claims

1. A circuit interrupter comprising an insulating housing with insulating walls which define pole unit compartments within the housing, a separate pole unit disposed in each pole unit compartment and including a pair of cooperable contacts, and means common to all pole units for closing and opening the contacts therein, each pole unit including further a line terminal and a load terminal electrically connected to each other through the contacts of the associated pole unit, characterized in that at least the line terminals of the pole units have disposed therebetween insulating barriers which extend from said insulating housing a distance sufficient to prevent ionized gases generated in the pole units during contact opening operations from intermixing until the gases have become sufficiently deionized to prevent conduction.

2. A circuit interrupter according to claim 1, characterized in that said insulating barriers are formed integral with the insulating housing.

3. A circuit interrupter according to claim 2 wherein said insulating housing comprises a base having the pole unit compartments formed therein, and a cover removably secured to the base, characterized in that at least major portions of said insulating barriers are formed integral with said cover.

4. A circuit interrupter according to claim 1, characterized in that at least major portions of said insulating barriers are formed as integral parts of a separate insulating barrier structure secured to said insulating housing.

5. A circuit interrupter according to claim 1, 2, 3 or 4,characterized in that said insulating barriers include baffles positioned to direct said gases away from the housing.

6. A circuit interrupter according to claim 4, characterized in that said baffles extend in a direction perpendicular to said insulating walls.

7. A circuit interrupter according to any of the preceding claims, characterized in that said insulating barriers have a plurality of grooves formed therein.

8. A circuit interrupter according to claim 7, characterized in that said barrier grooves extend in a direction parallel to a rear-to-front direction with regard to said housing.

9. A circuit interrupter according to any of the preceding claims,characterized in that said insulating barriers extend at least 3.80 cm from said housing.

10. A circuit interrupter according to any of the preceding claims, characterized in that said insulating barriers extend substantially for the full height of said housing having regard to the rear-to-front direction thereof.