US3836819A

US3836819A - Current limiting circuit interrupter device

Info

Publication number: US3836819A
Application number: US00390064A
Authority: US
Inventors: C Clausing
Original assignee: ITE Imperial Corp
Current assignee: ABB Inc USA
Priority date: 1973-08-20
Filing date: 1973-08-20
Publication date: 1974-09-17
Anticipated expiration: 1991-09-17
Also published as: CA1032598A

Abstract

A helically wound coil is connected in series with a circuit interrupter and electrical contacts on diametrically opposite sides of each turn of the coil form direct current paths in parallel for each coil so that substantially no inductance is in the power circuit when the contacts are closed. The contacts are opened sequentially in response to a fault current to gradually introduce one or more turns of the coil in the series circuit in order to limit the rise of fault current before the series interrupter device is operated.

Description

United States Patent [1 1 Clausing Sept. 17, 1974 CURRENT LIMITING CIRCUIT INTERRUPTER DEVICE [75] Inventor: Challiss I. Clausing, Marlton, NJ.

[73] Assignee: I-T-E Imperial Corporation, Spring House, Pa.

[22] Filed: Aug. 20, 1973 [21] Appl. No.: 390,064

[52] US. Cl 317/11 C, 200/144 AP, 307/136 [51] Int. Cl. H02h 7/22 [58] Field of Search 200/144 AP; 317/11 C, 11 A;

Primary Examiner-James D. Trammell Attorney, Agent, or Firm Ostrolenk, Faber, Gerb & Soffen 7] ABSTRACT A helically wound coil is connected in series with a circuit interrupter and electrical contacts on diametrically opposite sides of each turn of the coil form direct current paths in parallel for each coil so that substantially no inductance is in the power circuit when the contacts are closed. The contacts are opened sequentially in response to a fault current to gradually introduce one or more turns of the coil in the series circuit in order to limit the rise of fault current before the series interrupter device is operated.

17 Claims, 8 Drawing F igures' 02am 701/5 /6 ia/4N0 BACKGROUND OF THE INVENTION This invention relates to a current limiting device, and more specifically relates to a novel device for introducing impedence into a circuit in response to some predetermined condition, such as a fault or overload condition, in order to limit the magnitude of the fault current.

Current limiting devices are well known to those skilled in the art and frequently take the form of current limiting fuses or the like which tend to substantially increase circuit impedance over the range of their operation. Such current limiting fuses are frequently used in combination with circuit breakers so that the fuse will tend to substantially limit the magnitude of fault current if the short circuit would exceed breaker rating. The circuit breaker interrupts relatively low currents up to its rating and the fuse clears fault currents which could have been supplied from the circuit being protected above the breaker rating. Other arrangements are well known for limiting the fault current in a circuit in-which impedance, and particularly resistance, is sequentially introduced into the circuit as a circuit interrupter is operated.

BRIEF DESCRIPTION OF THE PRESENT INVENTION The present invention provides a novelcurrent limiting device which can be formed as a subassembly, and used'by itself or in combination with series connected power fuses or circuit breakers, or the like. The novel device can then be sized to limit current to a value within the rating of the main interrupter device and is resettable and reusable.

The current limiting device of the invention consists of an electrical winding having a plurality of turns. The winding is connected in series with a circuit to be protected. The individual turns of the winding are normally short-circuited by individual contact element bearing on opposite sides of the individual turns or groups of turns of the winding. These individual contacts are then spring-biased into engagement with their respective turn, and are arranged to blow off due to the magnetic field of a fault current which may be produced in this circuit. When these contacts blow off, the individual turn which they cooperate with is inserted into the power circuit, thereby to insert an inductive impedance in the circuit.

The various contacts may be further arranged so that they are sequentially forced out of engagement with their respective coils, so that the full impedance of the entire winding is relatively gradually inserted into the circuit.

The current through the circuit may then be limited either until it returns to some normal value, or the limited current can be interrupted by aconventional interrupter in series with the circuit. As pointed out previously, the current will be limited to a value within the rating of this main interrupter device. Once the current has returned to its normal value or has been interrupted by the main interrupter device, the individual contacts bearing on the turns of the helical coil can be reclosed by releasing latches which latch the contacts open when they reach an opened position.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates the present invention where the current limiting impedance is a helical winding.

FIG. 2 is a side view, partially in cross-section, of a circuit breaker equipped with the novel current limiting device of the invention, wherein the impedance takes the form of a helical winding.

FIG. 3 is a cross-sectional view of FIG. 2 taken across the section line 3-3 in FIG. 2.

FIG. 4 is a plan view of the top of the circuit breaker of FIG. 2.

FIG. 5 shows a modified arrangement for the mounting of a contact finger.

FIG. 6 is a side view of a further embodiment of the invention wherein the coil is spirally wound as contrasted to the helically wound coil of FIGS. 2, 3 and 4.

FIG. 7 is an end view of the coil of FIG. 6.

FIG. 8 is a cross-sectional view through section line 8-8 of FIG. 7 which illustrates the inter-connection between the contact elements of the spiral coil.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates the circuit of the present invention, and shows one phase of a power circuit having input and output terminals 10 and 11, respectively, wherein a circuit breaker 12, which may be of any conventional type, is connected in series with terminals 10 and 11 and is provided with a conventional operating mechanism.

The current limiting device of the invention is shown as device 14 and consists of a multi-turn winding 15 connected in series with the main power circuit. The input side of the circuit has a conductive support 16 which supports a plurality of moving contacts 17 to 21 which, as will be later seen, are spring-loaded into engagement with individual turns at locations which are physically on the same side of the coil 15. The output of the device 14 contains similar contact fingers 22 to 26, supported from conductive support 16a, which are in engagement with individual coil turns on the opposite side of coil 15 from the side which receives contacts 17 to 21.

The normal current flow in the circuit of FIG. I will then be from terminal 10 through interrupter 12, through all of input fingers 17 to 21 and then through all of the output fingers 22 to 26 of the terminal 11. The current flow from contacts 17 to 21 to contacts 22 to 26 for a given coil turn will be in one direction over the top of the turn and the opposite direction through the bottom of the turn. Thus, the entire winding 15 is, in effect, split up into parallel conductors with no current flowing around the coil as in an inductive device. Thus, the coil 15 has no intentional impedance. The various contact fingers 17 to 26 are then arranged, as will be later seen, to be blown off by the current flow through the sections of the coil. Note, however, that any other desired operating mechanism can be provided to operate the individual contact fingers 17 to 26. If the blowoff mode is used when a short-circuit occurs, the contact fingers 17 to 26 will blow off at some level determined by respective contact pressure springs. Once open, each finger may be held open by an individual latch. Note that the blow open action will be cumulative in that, as soon as one finger blows off, more current must flow in the remaining parallel paths to force the sequential operation of each of the contact fingers 17 to 26. The springs may further be adjusted to ensure a particular sequence of operation such that contacts 17 through 21 blow off in sequence, contacts 22 through 26 blow off next in sequence. By properly controlling the number of turns and the geometry of coil 15, arcing at the individual contact fingers can be eliminated, or minimized to a point where the arc can be easily extinguished.

After the circuit has been operated and the circuit breaker 12 is opened, the contact fingers can be reset by spring pressure of their biasing springs when the individual latches of contacts 17 to 26 are removed.

FIGS. 2, 3 and 4 schematically illustrate a conventional type of circuit interrupter which has been modified to receive a current limiting device of the general type shown in FIG. 1. Referring first to FIG. 2, there is schematically illustrated a circuit breaker of a generally conventional type and which has a molded support housing 40 which carries tubular

conductive terminals

41 and 42 which have tulip type disconnect contact assemblies 43 and 44 connected thereto by webs 45 and 46, respectively. The tulip type disconnect contacts 43 and 44 are then engageable with appropriate stationary conductors such as the

stationary conductors

47 and 48, respectively, which may be the stationary disconnect contacts contained in the interior of a conventional switchgear housing. Note that the breaker shown in FIG. 2 is of the type that is conventionally racked in and out of its switchgear cubicle. Conventional auxiliary equipment is provided for the circuit breaker such as the

current transformers

50 and 51 which encircle the lower terminal of the device.

The lower elongated terminal 41 is then connected to a movable contact arm 60 which is pivotally mounted on stationary pivot 61 and which is operated by rotation about pivot 61 by a conventional operating mecha nism 62. Operating mechanism 62 is equivalent to mechanism 13 in FIG. 1. The movable contact 60 then cooperates with stationary contact elements, such as contact fingers disposed beneath contact springs 63 to In accordance with the invention, the current con ducting member 68 of FIG. 2 is connected as by brazing or bolting, or the like, to the terminal 70 of the multi-helical winding 71.

The helical winding 71 of FIG. 2 is also shown in FIGS. 3 and 4 along with its input conductor 70. It will be seen from FIGS. 3 and 4 that the winding 71 is a tenturn winding and has an output conductor 72 which is appropriately connected as by bolting or brazing, or the like, to the conductive support 42 of the circuit breaker. I

The conductive member 68 of the circuit breaker of FIG. 2 has an elongated conductive plate member 80, shown in FIGS. 2, 3 and 4, which serves as a support for a plurality of contact fingers 90 to 99 which, as can be best seen from FIG. 2, are pivotally mounted on a pivotal shaft 100 connected with contact finger 90.

Note that the pivot 100 can be a common pivot for each of contact fingers 90 to 99 or, alternatively, each contact finger can have its own pivotal support cooperating with an extending support finger of conductive body 80. Note further that the pivotal connection between the member and the fingers to 99 is a current carrying connection which can be conventionally achieved in any desired manner as by conductive washers and the like. Thus, in FIG. 4 and for the case of contact finger 91 there is shown a silver washer 91a which makes good electrical connection between the finger 91 and the extending comb-like recess of elongated conductive plate 80. A belleville type washer 91b presses finger 91 against the washer 91a.

It will be noted that each of the fingers 90 through 99 is arranged to engage the lateral side of each respective turn of the coil 71. Moreover, each of the contact fingers is provided with a biasing spring, such as the biasing spring 110, shown for finger 90, where the spring is carried on bracket 111. A similar compression spring is provided for each of the contact fingers 91 through 99 as schematically illustrated in FIG. 3, where these springs are supported from the block 68.

The bottom of contact fingers 90 through 99 are then provided with latch rollers, such as the latch roller 120, shown in FIG. 2 for finger 90, where the latch roller cooperates with pivotally mounted latch 121 which is pivoted on a fixed support shaft 122. Latch 121 is further provided with a tension spring 123 which tends to normally rotate the latch clockwise and into engagement with a reset bar and stop member 124. Thus, the bar 124, which is movable from the position shown and to the left and in the direction of arrow 125 of FIG. 2, may be a single bar which operates all of the latches similar to latch 121, which cooperate with the fingers 91 to 99.

It can now be understood that when the latch 121 and the other similar latches are in the position shown, that the spring 110 and finger 90 along with the other contact fingers will be pressed into engagement with the respective turns of windings 71. Note, however, that if the contact fingers 90 to 99 are operated to an open position by rotation in a clockwise direction about pivot 100, that the latches such as latch 121 will rotate clockwise to the stop position defined by bar 124 in order to latch the individual latch rollers, such as roller120 of FIG. 2.

A substantially identical contact finger configuration is provided on the opposite side of winding 71 and is shown in FIG. 3 by the contact fingers to 139. These contact fingers are mounted and biased and latched in a manner substantially identical to that described above in connection with fingers 90 to 99. Thus, the fingers are pivotally mounted on pivots such as pivot which are current carrying pivots, and are spring biased into engagement with each of the turns of the coil by biasing springs, such as the biasing spring 141 carried from bracket 142 carried on member 42.

Latches such as latch 143 are similarly provided to latch the latch rollers, such as latch roller 144 of the contact fingers 130 to 139, where the latch 143 and similar latches are biased counterclockwise about their support pivots, such as pivot 145 by tension springs 146. A reset stop bar 147 is also provided which is movable in the direction of arrow 148 in order to allow reset of the individual contact fingers 130 to 139 under the influence of their biasing springs, such as spring 141.

The current limiting device shown in FIGS. 2 and 3 is operated in response to the current flow through the individual contact fingers 90 through 99 and 130 through 139, where these fingers are opened due to the magnetic blow-off effect of the current. Thus, the normal current path through the entire assemblage of FIGS. 2 and 3 will be from terminal 47 through conductor 41, movable contact 60,

stationary contact elements

63, 64, 65, 66 and 67, into the

conductive members

68 and 80 and then into the parallel conductive the right-hand side of the turn of coil 71 which is engaged by contact 90. This change in current direction then forms a blow off path which creates a force which would tend to rotate the contact finger 90 (as well as 7 fingers 91 to 99) in a clockwise direction and in opposition to the biasing force spring 110. Under normal current conditions, the biasing force ofspring 110 is sufficiently high to maintain good pressure contact but, when the current increases, as due to a short circuit in the circuit being protected by the device, the magnetic forces created are sufficiently strong to rotate fingers 90 to 99 to an open position, where they are latched by their respective latches, such as latch 121. A similar blow-off path is formedfor each of contacts 130 to 139, so that they too will be blown off when the current carried through these contact fingers becomes sufficiently high. 7

Preferably, the biasing springs, such as biasing springs 110 and 141, are so arranged that the fingers blow off in a sequential manner. Thus, the biasing forces can be so arranged that contact finger 90 will be the first to open when a predetermined current magnitude appears. Then fingers 91 through 99 will blow off in sequence. This will then insert the first turn of the inductive winding 71 into the circuit to cause a relatively small inductive impedance to appear in the circuit which will tend to limit current. At the same time, an increased current will flow into the remaining closed fingers so that the next fingers will open, such as contact fingers 130 through 139 in sequence, thereby to insert successive turns into the circuit which is being protected. Ultimately, each of the contact fingers will be opened so that the full coil 71 is inserted in series with the circuit being protected in order to limit the current flow in the circuit.

FIG. 5 shows an alternate arrangement for mounting and latching the contact fingers and is shown in connection with contact finger 90. Thus, in FIG. 5 an angle member 160 is secured to plate 80 or may be otherwise secured. for example, to the support molding 40 and carries the shaft 122 which pivotally mounts the various latches, such as latch 121.

The biasing spring 123 for latch 121 is shown in FIG. 5 as a compression spring which is seated at one end on the bracket 161 and at its other end on the interior surface of latch 121, thereby to bias latch 121 in a clockwise direction and against stop bar 124. Clearly, other support arrangements could be provided for supporting and biasing the latches such as latch 121.

The novel invention has been described above in connection with a helically wound inductance coil where current flow through the coil from the contact fingers is along the winding length. FIGS. 6 to 8 schematically illustrate a further embodiment of the invention in connection with a spirally wound coil where current flow between the contact elements is perpendicular to the length of the winding, with the contacts engaging the winding at its end surfaces rather than its lateral surfaces as in FIGS. 2, 3 and 4.

Thus, in FIGS. 6, 7 and 8 there is shown a two-turn spiral winding which has terminal ends 171 and 172 (FIG. 7).

As best shown in FIGS. 6 and 8, contact means including contact pairs 173-174, 175-176, 177-178 and 179-180 are electrically connected to and supported by

conductive members

181 and 182. Terminal 172 is electrically and mechanically connected to conductive member 182 while terminal 171 is electrically and mechanically connected to conductive member 181. Thus, the terminals of coil 170 are connected so that the coil is in series between

conductive members

181 and 182 which are, in turn, appropriately connected to a circuit interrupting device as in the case of FIGS. 2, 3 and 4. The individual contact members 173 to 180 are then arranged in a manner similar to that described, for example, in connection with FIGS. 3, 4 and 5 where, for example, the contacts are associated with appropriate biasing springs and latches, and the like.

During operation, the individual contact slements engage the ends of respective coil portions so that the electrical winding is simply a conductive shunt between the

conductive members

181 and 182. However, when the electrical contacts 173 to 180 open, the inductance of the coil 170 is inserted in series with

conductive members

181 and 182 to introduce impedance into a circuit which could, in turn, limit current rise in the circuit.

Although this invention has been described with respect to preferred embodiments, it should be understood that many variations and modifications will now be obvious to those skilled in the art, and it is preferred, therefore, that the scope of this invention be limited, not by the specific disclosure herein, but only the the appended claims.

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

1. A current limiting device comprising a helically wound winding having first and second terminals at its ductance of at least said one turn into a circuit connected to said first and second terminals.

2. The device of claim 1 wherein said operating means includes circuit connection means defining a blow-off path for magnetically moving each of said first and second contact means to their said out of engagement positions with said lateral surfaces of said at least one turn.

3. The device of claim 1 which further includes biasing means for normally biasing said first and second contact means to their said engagement positions with said lateral surfaces of said at least one turn.

4. The device of claim 1 which further includes circuit interrupter means connected in series with said first and second terminals.

5. The device of claim 1 which further includes latch means for latching each of said first and second contact means in their said out of engagement positions after they are moved to said out of engagement positions by said operating means.

6. The device of claim 3 which further includes latch means for latching each of said first and second contact means in their said out of engagement positions after they are moved to said out of engagement positions by said operating means.

7. The device of claim 3 wherein said operating means includes circuit connection means defining a blow-off path for magnetically moving each of said first and second contact means to their said out of engagement positions with said lateral surfaces of said at least one turn.

8. The device of claim 6 wherein said operating means includes circuit connection means defining a blow-off path for magnetically moving each of said first and second contact means to their said out of engagement positions with said lateral surfaces of said at least one turn.

9. The device of claim 8 which further includes circuit interrupter means connected in series with said first and second terminals.

10. A current limiting device comprising a helically wound winding having first and second terminals at its opposite ends for connecting said winding in series with a circuit to be protected, first and second pluralities of contact means disposed on laterally opposite sides of said winding and movable into and out of engagement with respective lateral surfaces of respective turns of said winding, means connecting said first and second pluralities of contact means to said first and second terminals respectively, and operating means disposed relative to each of said first and second pluralities of contact means to move said contact means to their said out of engagement positions in response to a given electrical condition, thereby to introduce the inductance of said respective turns into a circuit connected to said first and second terminals.

11. The device of claim 10 which further includes biasing means for normally biasing each of said first and second pluralities of contact means to their said engagement positions.

12. The device of claim 11 which further includes circuit interrupter means connected in series with said first and second terminals.

13. The device of claim 12 which further includes latch means for latching each of said first and second contact means in their said out of engagement positions after they are moved to said out of engagement positions by said operating means.

14. The device of claim 13 wherein said operating means includes circuit connection means defining a blow-off path for magnetically moving each of said first and second contact means to their said out of engagement positions with said lateral surfaces of said at least one turn.

15. The device of claim 10 wherein said first and sec ond pluralities of contact means are sequentially operated by said operating means.

16. The device of claim 1 wherein said winding is helically wound and wherein said contact means are disposed adjacent lateral surfaces of said winding and move in a direction perpendicular to the axis of said winding.

17. The device of claim 1 wherein said winding is spirally wound and wherein said contact means are disposed adjacent end surfaces of said winding and move in a direction parallel to the axis of said winding.

Claims

1. A current limiting device comprising a helically wound winding having first and second terminals at its opposite ends for connecting said winding in series with a circuit to be protected, first and second contact means disposed on opposite sides of said winding and movable into and out of engagement with respective opposite surfaces of at least one turn of said winding, means connecting said first and second contact means to said first and second terminals respectively, and operating means disposed relative to each of said first and second contact means to move said contact means to their said out of engagement positions in response to a given electrical condition, thereby to introduce the inductance of at least said one turn into a circuit connected to said first and second terminals.

15. The device of claim 10 wherein said first and second pluralities of contact means are sequentially operated by said operating means.