US3446928A - Interrupting device having u-shaped parallel current paths - Google Patents

Description

May 27, 1969 w. E. HARPER ETAL 3,446,923

INTERRUPTING DEVICE HAVING USHAPED PARALLEL CURRENT PATHS Filed Oct.

Sheet 8. 94301 @11 2 23;? JQI 1" Q L gig-8 -SHAPED PARALLEL CURRENT was lfl -Z- w. E. HARPER ETA!- Jon 2: 7

INTERRUPTYING DEVICE HAVING u Filed'Oct.

May 27, 1969 May 27, 1969 w, HARPER ETAL 3,446,928

INTERRUPTING DEVICE HAVING U-SHAPED PARALLEL CURRENT PATHS Fild Oct. 20, 1965 Sheet 3 era J02 L; 145 L 104 gi /l9- 4 1. I: M1 m if! I I 14/ L, 9 14.9 14/ United States Patent US. Cl. 200-146 3 Claims ABSTRACT OF THE DISCLOSURE There is disclosed an oil circuit breaker having a pair of spaced apart line terminals extending into the top of a tank containing oil. When the circuit breaker is in closed condition, two U-shaped parallel current paths are established between the line terminals. The exterior U-shaped current path comprises one or more pairs of separable main contacts. The interior (and exterior U-shaped current path comprises one or more pairs of separable auxiliary contacts. The circuit breaker is arranged so that the contacts in the interior circuit open first and close last as regards the contacts in the exterior circuit. The disposition, length and inductance of the two U-shaped current paths is such that more current tends to flow in the interior circuit because of magnetic eflects caused by current flow through each U- shaped path. The separable contacts in both U-shaped current paths are housed in suitable arc interrupting devices which are supported by upper, intermediate and lower heat dissipating platforms. Impedance devices, such as resistors, associated with the contacts are also supported by the platforms.

This invention relates generally to electric circuit breakers and particularly to oil circuit breakers of the fluid blast type, although not necessarily limited thereto.

Some oil circuit breakers comprise one pair or a plurality of series connected pairs of separable contacts for each phase or line of a circuit being protected. In practice each pair of contacts is adapted to operate inside the housing of an arc interrupting device 'which confines the arc formed between the contacts. Usually, fluid blast means are provided in the housing to aid in extinguishing the arc.

In one well known type of oil circuit breaker a pair of spaced apart line terminals extend into the top of a tank containing a body of fluid such as oil and a pair of main arc extinguishing devices are submerged in the fluid. Each main arc extinguishing device comprises an arc confining housing in which a stationary contact is mounted and the latter is connected to one of the line terminals. A reciprocably movable electrically conductive cross arm is located inside the tank and is provided with a pair of spaced apart bayonet type movable main contacts. Each movable contact is adapted to cooperate with the stationary contact Within the housing of one of the main arc extinguishing devices. Thus, when the circuit breaker is closed a U-shaped current path or circuit is established between the line terminals.

In some circuit breakers of this type, four or more main arc extinguishing devices are used instead of the two described but the U-shaped current path retains its identity.

It is an object of the present invention to increase the continuous and short circuit current carrying capacity of such circuit breakers by means which economically exploit the design and inherent operating characteristics thereof.

Another object is to increase both the normal and short circuit carrying capacity of such circuit breakers 3,446,928 Patented May 27, 1969 ice by providing an additional or second current carrying circuit in parallel with the aforementioned or first U- shaped circuit.

Another object is to locate the second circuit with respect to the first circuit so that electromagnetic forces interacting between the two circuits cause a large proportion of continuous current to flow through the second circuit.

Another object is to provide a second circuit which comprises one or more pairs of auxiliary contacts connected in shunt with the main contacts in the main arc interrupters and located generally on the inside of the first U-shaped circuit.

Another object is to have the auxiliary contacts open before and close after the main contacts so that the main burden of arc interruption is handled by the main contacts.

Other objects and advantages of the invention will hereinafter appear.

The accompanying drawings illustrate several preferred embodiments of the invention but it is to be understood that the embodiments illustrated are susceptible of modifications with respect to details thereof without departing from the scope of the appended claims.

In the drawings:

FIG. 1 is an elevational view, partly in section, of one embodiment of an oil circuit breaker employing the present invention.

FIG. 2 is a top plan view of a portion of the circuit breaker taken along line IIII of FIG. 1;

FIG. 3 is a cross sectional view of an auxiliary contact structure or are extinguishing device shown in FIG. 1, showing it in open position;

FIG. 4 is a view similar to FIG. 3 but shows the auxiliary contact structure in closed position;

FIGS. 5, 6 and 7 are diagrammatic showings of a portion of the electric circuitry of the circuit breaker shown in FIGS. 1 and 2, and show it in closed, partially open, and fully open positions, respectively; and

FIG. 8 is a diagrammatic showing of another embodiment of an oil circuit breaker employing the present invention.

Referring to FIG. 1, there is shown an oil circuit breaker incorporating the present invention and having a tank 10 which is filled to a level 12 with an arc extinguishing fluid such as oil. A pair of line terminal bushings 14 and 16 comprising electrical conductors 18 and 20, respectively, for connection to a power line being protected extend into tank 10. Arc extinguishing assemblies 22 and 24 are suspended from the inner ends of the terminal bushings 14 and 16, respectively. The as semblies 22 and 24 are understood to be similar to each other, therefore, only the former will be described in detail.

Referring to FIGS. 1 and 2, assembly 22 comprises upper, intermediate and lower electrically conductive platform castings 26, 28 and 30, respectively. Upper casting 26 is electrically and mechanically connected to conductor 18 of terminal bushing 14. Intermediate cast ing 28 is spaced from and mechanically supported on upper casting 26 by means of insulating supports such as support 32. Lower casting 30 is spaced from and mechanically supported on intermediate casting 28 by means of insulating supports which are understood to be similar to support 32.

Upper and lower main arc interrupters 36 and 38 depend from the upper and intermediate castings 26 and 28, respectively, and, as FIGS. 5, 6 and 7 show, comprise stationary contacts 40 and 42, respectively, which are electrically connected to the upper and intermediate castings, respectively. Reference may be had to Patent Number 3,067,307 for Fluid Blast Interrupting Device for Oil Circuit Breakers issued Dec. 4, 1962 to J. M.

Ramrath and assigned to the same assignee as the present application for a detailed description of an interrupter of a type suitable for application as the main arc interrupters herein referred to.

Upper and lower auxiliary contact structures 44 and 46 are mounted adjacent the main interrupters 36 and 38, respectively, and, as FIGS. 5, 6 and 7 show, comprise stationary contacts 48 and 50, respectively, which are electrically connected to the upper and intermediate castings 26 and 28, respectively.

Upper auxiliary contact structure 44 is similar to lower auxiliary contact structure 46, therefore, only the former will be described in detail. As FIG. 3 shows, contact structure 44 comprises a metallic top section 100 adapted for electrical and mechanical connection to upper platform casting 26. Top section 100 is provided with oil refill ports 102 in the side walls thereof. Adome shaped piston 104 is located within top section 100 and is provided with openings 106 for equalizing oil pressure on each side thereof and with a vent 108 through the top thereof. Piston 104 is provided with a piston ring 105. A nonmetallic piston push rod 110 has one end bearing against piston 104 and its other end abutting against a movable auxiliary contact 78, hereinafter described. Push rod 110 is adapted to maintain vent 108 closed when it bears against piston 104. A push rod driving spring 112 is disposed between a portion of top section 100 and push rod 110. A piston driving spring 114 is disposed between a portion of top section 100 and piston 104. Stationary contact 48 which is located in contact structure 44 comprises a contact housing 116 in which a cluster of spring biased contact fingers 118 are located. Contact housing 116 comprises a spider section 120 which adapts it for electrical and mechanical connection to top section 100. The lower end of top section 100 is closed by an insulating bafile plate 122 having a hole 124 for accommodating movable auxiliary contact 78.

High ohmic value resistors 52 and 54 are electrically connected, respectively, between the upper and intermediate castings 26 and 28 and between the intermediate and lower castings 28 and 30.

An electrically conductive cross bar 56 which is reciprocably movable vertically (with respect to FIG. 1) by an insulating rod 57 is provided at its extreme ends with upwardly projecting or bayone type electrically conductive movable contacts and movable contact operators, hereinafter described. Preferrably, cross bar 56 comprises two separate members 5611 and 56b to enhance thermal conductivity therefrom. The end of cross bar 56 which is associated with are extinguishing assembly 22 comprises a movable lower main contact 58 and a movable lower auxiliary contact 60 and a pair of contact operators 62 and 64.

Lower casting 30 of assembly 22 is provided with a pair of sliding contacts 66 for accommodating the movable contacts 58 and 60. Lower casting 30 is also provided with a pair of openings 68 in alignment with the contact operators 62 and 64. The contact operators 62 and 64 cooperate with electrically nonconductive contact push rods 72 and 74, respectively. The push rods 72 and.74 are connected to and operate a reciprocably movable upper main contact 76 and a reciprocably movable auxiliary upper auxiliary contact 78, respectively, which extend through a pair of sliding contacts 80 and 81, respectively, mounted on intermediate casting 28. Contacts 76 and 78 extend into main arc interrupter 36 and auxiliary contact structure 44, respectively, when the circuit breaker is closed.

Push rod 72 and its attached movable upper main contact 76 are enclosed in an insulated housing 79 shown in FIG. 1 and suitable biasing means, such as a spring 83, in housing 79 tend to bias the push rod and upper main contact downwardly with respect to FIG. 1. It is to be understood that similar provisions are made for housing 4. and biasing the other push rods and their attached movable upper contacts.

When the circuit breaker is fully closed, as shown in FIGS. 1 and 5, there are two parallel U-shaped current paths between the conductros 18 and 20 of the terminal bushings 14 and 16, respectively, with one path being located substantially within the other.

The outer and longer path extends from conductor 18, through upper casting 26, stationary contact 40 of upper main interrupter 36, movable contact 76, intermediate casting 28, stationary contact 42 of lower main interrupter 38, movable contact 58, cross arm 56, movable contact 58a, stationary contact 42a of lower main interrupter 38a, intermediate casting 28a, movable contact 76a, stationary contact 40a of upper main interrupter 36a, upper casting 26a, to conductor 20.

The inner and shorter path extends from conductor 18, through upper casting 26, stationary contact 48 of upper auxiliary contact structure 44, movable contact 78, intermediate casting 28, stationary contact 50 of lower auxiliary contact structure 46, movable contact 60', cross arm 56, movable contact 60a, stationary contact 50a of lower auxiliary contact structure 46a, intermediate casting 28a, movable contact 78a, stationary contact 48a of upper auxiliary contact structure 44a, upper casting 26a, to conductor 20.

No substantial current flows through the impedances 52, 54, 52a or 54a when the circuit breaker is closed.

Current flow through both paths is accompanied by generation of a magnetic field around each path and these magnetic fields interact to cause a large portion of the current flow through the circuit breaker to travel through the inner path hereinbefore described. More specifically, the outer path is longer than the inner path and therefore has greater inductance and the larger portion of current will flow through the shorter inner path. Since the inner path includes the auxiliary contact structures which are adapted to be more readily cooled by the oil in the circuit breaker than the main interrupters, larger currents can be carried by the inner path than would otherwise be the case if the same current were channeled through the outer path.

FIG. 8 shows another embodiment of the invention wherein only one pair of main ar-c interrupters 36b and 36c and one pair of auxiliary contact structures 44b and 440 are employed in a circuit breaker. The main interrupter and auxiliary contact structures shown in FIG. 8 are understood to be similar to the corresponding structures hereinbefore described in connection with FIGS. 1-7. Main arc interrupters 36b and 36c comprise stationary main contacts 40b and 400, respectively, and the auxiliary contact structures 44b and 440 comprise stationary auxiliary contacts 48b and 480, respectively. A reciprocably movable bridge 56a is provided having movable main contacts 76b and 76c and having movable auxiliary contacts 78b and 780. Two platform castings 26b and 260 are provided from which the main and auxiliary interrupters depend.

When the circuit breaker is in the closed position shown in FIG. 8, an outermost and longer first U-shaped circuit is established from platform casting 26b, through contacts 401) and 76b, through bridge 56a, and through contacts 76c and 40c, to platform casting 26c.

Furthermore, an innermost and shorter second U- shaped circuit is established from plat-form casting 26b, through contacts 48b and 78b, through bridge 56a and through contacts 78c and 48c, to platform casting 260.

It is to be understood that the auxiliary contacts in the auxiliary contact structures 78b and 78c are adapted to open before and close after the main contacts in the main arc interrupters 36b and 360.

If preferred, suitable shunt resistors could be employed with the embodiment disclosed in FIG. 8.

Assuming that the circuit breaker is closed as shown in FIGS. 1 and .5 and that a fault occurs which causes it to open, the following sequence of operations occurs.

Rod 57 moves cross bar 56 downwardly thereby causing all the movable contacts and contact operators on the cross bar to start their withdrawal. As FIG. 6 shows, the contacts in the inner path, i.e., those contacts in the auxiliary contact structures 44, 46, 44a and 46a, open shortly before the contacts in the main interrupters 36, 38, 36a and 38a. All current flow is now carried by the outer path. As cross bar 56 continues to move downwardly, the contacts in the main interrupters 36, 38, 36a and 38a open simultaneously and the impedances 52, 54, 52a and 54a, respectively, are then connected in parallel with the arcs produced in the main interrupters to equalize circuit recovery voltage across the main interrupters upon opening. By the time cross bar 56 moves to the fully open position shown in FIG. 7, the arcs are extinguished and the current flow through the impedances ceases since the movable contacts 58 and 60 are disengaged from the sliding contacts in the lower castings 30 and 30a.

More specifically, as regards operation of auxiliary interrupter 44, during the initial portion of the opening stroke of auxiliary bayonet contact 78 is also accelerated by the forces exerted downward against the tip thereof by both piston push rod spring 112 and the piston spring 114. However, after a fraction of an inch of piston stroke, the lower edge of piston ring 105 seals off the bottom of the refill ports 102. After this occurs, any further downward motion of piston 104 and piston ring 105 can be accomplished only by displacement of the oil in top section 100 of structure 44. At this point, the velocity of the piston is very greatly reduced since the limited area of orifice 124 between baffie plate 122 .and moving auxiliary bayonet contact 78 allows very little oil to fiow out of structure 44 as long as auxiliary bayonet contact 78 penetrates the baffie plate.

However, during the opening stroke the travel of piston push rod 110 is not hindered by the travel of piston 104 nor is the spring force acting on the piston push rod in any way reduced by piston travel as is the case in US. Patent No. 3,076,080 to J. M. Ramrath Fluid Blast Interrupting Device for Oil Circuit Breakers Employing Auxiliary Contact. Thus, when the velocity of piston 104 is reduced by the impedance of the oil beneath it, piston push rod 110 continues to be driven downward by piston push rod spring 112. Piston push rod 110 continues to accelerate auxiliary bayonet contact 78 even after the electrical separation of the auxiliary contacts. This follow through action terminates only when the flange at the upper end of piston push rod 110 comes into contact with the top of the stationary contact housing .116 to prevent any further push rod travel. At this point, the lower end of piston push rod 110 approaches the upper surface of baffle plate 122, forming a relatively small annular orifice between the bottom end of the piston push rod and the upper surface of the bafile plate through which oil from auxiliary interrupter 44 may flow, and through which any are between the stationary auxiliary contacts and the moving auxiliary contact must pass. The piston push rod stroke is terminated only after the auxiliary contacts have developed an appreciable separation, approximately 4" in an actual embodiment. In this manner auxiliary bayonet contact 78 receives an accelerating force from piston push rod spring 112, suificient to assure that the velocity of .auxiliary bayonet contact 78 does not fall below that of bayonet 76 in interrupter 36. It also assures electrical separation of the auxiliary contacts 48 and 78 at a precisely controlled period of time before the associated main contacts 40 and 76 of main interrupter 36. This assures that the gap etween the auxiliary contacts will at all times be greater than the corresponding gap between the main contacts which are electrically in parallel. As the piston continues to be driven downward by the force generated by the piston spring, it pressurizes the oil beneath it. The oil pressure drives the oil inward toward the lower tips of the stationary contact fingers 118 and thence through annular orifice 124 and out into the tank. As the oil is forced through orifice 124, it impinges on any are which may tend to persist between the auxiliary contacts 118 and 78 after their separation. This action subjects the arc to an oil blast which causes a turbulent mixture of the arc plasma with the cold oil driven in from the cylinder. The resulting deionization of the arc products causes a rapid extinction of the arc. After the arc is extinguished, the continuation of a flow of fresh oil through orifice 124 flushes any gas from the gap between the auxiliary contacts 48 and 78 assuring the maintenance of a high dielectric strength of the gap.

On reclosing of the circuit breaker under load from the position shown in FIG. 7, the contacts in the auxiliary con tact structures 44, 46, 44a and 46a must close within one quarter of a cycle of the contacts in the main interrupters 36, 38, 36a and 38a in order to distribute the load and to prevent high magnetic blowotf of the main contacts as the main contacts continue to close. The main contacts continue to move to final closed position after the auxiliary contacts are closed.

As auxiliary bayonet contact 78 penetrates hole 124 in baffle plate 122, it is guided into axial alignment with the cluster of stationary contacts to minimize bouncing of the fingers when contact is made. The upper tip of auxiliary bayonet contact 78 comes into physical contact with the lower end of piston push rod 110. As it continues its upward movement, it drives piston push rod 110 upward thereby compressing piston push rod spring 112. Piston push rod 110 also bears against piston 104 forcing it and piston ring 105 upward, compressing piston spring 114. Immediately before electrical contact is established between the auxiliary contacts 78 and 48, the parallel contacts 76 and 40 in interrupter 36 are closed to establish the outer circuit thus minimizing arcing between the auxiliary contacts. Further protection against auxiliary contact deterioration can be provided by the application of a silver-tungsten alloy on the tips of the contact fingers 118. At the end of the closing stroke, piston 104 is driven upward beyond the refill ports 102 in the side of top section 100. This allows any gas from previous interruptions to escape and also allows the oil to establish convection currents for effective cooling of the auxiliary contact structure while carrying heavy continuous currents.

It is to be understood that the embodiment of the invention shown in FIG. 8 operates in substantially the same manner as that described in connection with FIGS. 17, except that only one pair of main interrupters and one pair of auxiliary contact structures are involved.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In an electric circuit breaker,

a pair of spaced apart line terminals,

a pair of electrically conductive upper platforms,

each upper platform being mechanically supported on and electrically connected to one of said line terminals,

a pair of upper main arc interrupters,

each upper main arc interrupter having a stationary main contact therein,

each upper main arc interrupter being mechanically supported on one of said upper platforms and having its stationary main contact electrically connected to its respective upper platform,

a pair of upper auxiliary arc interrupters,

each upper auxiliary arc interrupter having a stationary auxiliary contact therein,

each upper auxiliary arc interrupter being mechanically supported on one of said upper platforms and having its stationary auxiliary contact electrically connected to its respective upper platform,

a pair of electrically conductive intermediate platforms,

each intermediate platform being mechanically supported by and electrically insulated from one of said upper platforms,

a pair of lower main arc interrupters,

each lower main arc interrupter having a stationary main contact therein,

each lower main arc interrupter being mechanically supported on one of said intermediate and having its stationary main contact electrically connected to its respective intermediate platform,

a pair of lower auxiliary arc interrupters,

each lower auxiliary arc interrupter having a stationary auxiliary contact therein,

each lower auxiliary arc interrupter being mechanically supported on one of said intermediate platforms and having its stationary auxiliary contact electrically connected to its respective intermediate platform,

a pair of upper movable main contacts for cooperation with said stationary main contacts in said pair of upper main arc interrupters,

each upper movable main contact being slidably mounted on and electrically connected to one of said intermediate platforms and normally biased to open position,

a pair of uper movable auxiliary contacts for cooperation with said stationary auxiliary contacts in said pair of upper auxiliary arc interrupters,

each upper movable auxiliary contact being slidably mounted on and electrically connected to one of said intermediate platforms and normally biased to open position,

an electrically conductive bridge movable to open and closed positions and having a pair of movable main contacts for cooperation with said lower stationary contacts and a pair of movable auxiliary contacts for cooperation with said lower auxiliary stationary contacts,

said bridge also having a pair of upper main contact operators and a pair of upper auxiliary contact operators,

and means for operating said bridge so that when said bridge is moved to closed position, the movable main contacts engage their respective stationary main contacts before said movable auxiliary contacts engage their respective stationary contacts,

and being further adapted so that when said bridge is moved to open position, said movable auxiliary contacts disengage from their respective stationary auxiliary contacts before said movable main contacts disengage from their respective stationary main contacts.

2. A circuit breaker according to claim 1 wherein when said bridge is in closed position a first U-shaped circuit is established through said main arc interrupters and said bridge which is longer than a second U-shaped circuit through said auxiliary arc interrupters and said bridge.

3. In an electric circuit breaker,

a line terminal,

an electrically conductive upper platform mechanically supported on and electrically connected to said line terminal,

an electrically conductive intermediate platform mechanically supported by and electrically insulated from said upper platform,

an electrically conductive lower platform mechanically supported by and electrically insulated from said intermediate platform,

an upper main arc interrupter and an upper auxiliary arc interrupter mechanically supported on said upper platform,

each of said upper interrupters having a stationary contact therein which is electrically connected to said upper platform,

a lower main arc interrupter and a lower auxiliary arc interrupter mechanically supported on said intermediate platform,

each of said lower interrupters having a stationary contact which is electrically connected to said intermediate platform,

an upper movable main contact and an upper movable auxiliary contact for cooperation with said stationary contact in said upper main arc interrupter and said upper auxiliary arc interrupter, respectively,

each of said upper movable contacts being slidably mounted on and electrically connected to said intermediate platform and movably biased out of engagement from their associated stationary contacts,

a first resistor electrically connected between said upper and intermediate platforms,

a second resistor electrically connected between said intermediate and lower platforms,

an electrically conductive bridge movable to open and closed positions and having a lower movable main contact and a lower movable auxiliary contact thereon for cooperation with the stationary contacts in said lower main arc interrupter and said lower auxiliary arc interrupters, respectively,

said bridge also having an upper main contact operator and an upper auxiliary contact operator,

and means for operating said bridge so that when said bridge is moved to closed position said lower movable main contact first establishes contact with said lower platform to insert said first and second resistors in circuit, then said upper and lower movable main contacts simultaneously engage said upper and lower stationary main contacts, respectively, and then said upper and lower movable auxiliary contacts simultaneously engage said upper and lower stationary auxiliary contacts, respectively,

and so that when said bridge is moved to open position said upper and lower movable auxiliary contacts simultaneously disengage from said upper and lower stationary auxiliary contacts, respectively, then said upper and lower movable main contacts simultaneously disengage from said upper and lower stationary main contacts, respectively, and then said lower movable main contact disengages from contact with said lower platform.

References Cited UNITED STATES PATENTS 3,017,480 1/ 1962 Klaassen 200--146 3,259,725 7/1966 Harper 200-150 592,497 10/ 1897 Scott 200-146 977,577 12/ 1910 Wikander 200--146 2,792,476 5/ 1957 Cushing 200-146 2,977,446 3/1961 Baker 200148.2 X

FOREIGN PATENTS 489,082 7/1928 Germany.

72,321 5/ 1916 Switzerland.

ROBERT S. MACON, Primary Examiner.

US. Cl. X.R. 200144

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