Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates generally to circuit
interrupting devices and, more particularly, to a magnetic
; contactor having an arc chute.
The outlying dimensions of magnetic contactors
are primary considerations in their acceptance by industry
and their commercial success. This is particularly true of
contactors for use in industry, such as marine, railroad,
mining, off-shore drilllng, off-road construction, where
space is at a premium. In some of these applications,
machinery has already been designed around a particular size
of contactor. Consequently, new contactors must be directly
interchangeable with the prior contactor. Associated with
the foregoing is a requirement that continuous current car-
rying capacity and interrupting ratings be greater than the
, original contactor.
I It is well known in the art that forcing an arc ~ -
I into intimate contact with arc chute walls and/or grid
plates is a definite aid to arc interruption. In conven-
tional grid plate design, the arc loops are symmetrical so
¦ 20 that the legs thereof are directly opposite each other on
opposite sides of the gride plates, which construction has
the disadvantage of creating a resulting force of zero
acting on the legs so that the arc tends to center itself in
the air space between the gride plates. Another disadvantage
` with the grid plates of conventional arc chute construction
has been ionized gas back flow which results in arc
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restriking with a resulting delay in arc interruption or
' failure to interrupt the arc at all.
t~ Disclosed herein is a circuit interrupter comprising
first and second contacts separable between closed and open
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positions to establish an arc, an arc chute having a
. housing including spaced side walls, a top edge wall, and
opposite end walls of electrically insulating material and
~ providing an arcing compartment extending in a zone sub-
stantially parallel to the plane o~ movement of separation
of the contacts, the housing comprising half portions, each
of which portions includes one side wall and alternate grid
plates 3 first and second arc conductors leading from spaced
locations near the contacts and extending to other spaced
locations within the arcing compartment and remote from the
: contacts, line conductor means connected to the first
contact and to the first arc conductor, load conductor
means connected to the second contact and to the second arc
conductor, means for creating a magnetic field across the
compartment in a direction perpendicular to the length of
. the arc to effect movement of the arc away from the contacts,
a plurality of spaced grid plates stacked between the first
and second arc conductors at said other spaced locations
; thereof, the grid plates being inclined at an angle to the
. 20 length of the arc extending between the first and second arc ~.
. conductors, the grid plates being inclined at an acute angle .
generally to the advancing arc, each grid plate having front ::
' and rear edges, the front edge belng nearer the contacts and¦ being inclined outwardly from the center of the arcing
compartment toward lts corresponding slde wall, the grid
plates being inclined towards the upper end wall so that :~
ionized gas generated between the grid plates is directed ::~
towards the upper end wall and deflected into the compartment - :
to cause gas flow turbulence to effect deionization of the
gas, the front edges of the grid plates being beveled to
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.~, direct the arc downwardly into grid slots and between
adJacent grid plates, the compartment portion in which
the grid plates are disposed being wider than the reduced -
constric~ed zone nearer the contacts to effect reduced
back pressure of ionized gas, the outwardly inclined front - .
edge of each grid plate terminating at a shoulder extending :
toward the opposite slde wall, and the outwardly inclined
. front edges of opposite side grid plates to form a series .
of alternately angled slots to an advancing arc.
With an arc chute such as disclosed herein, an
arc is lengthened and forced against the grid plate surface ~
which cools and extinguishes the arc, the unique angular :
positioning of the grid plates directing ionized alr
toward the top of the arc chute where it is deflected to
: cause air tubulence which helps to deionize the hot gases.
. 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 vertical sectional view through a
contactor with an arc chute attached, and showing the con-
tacts in the open position,
Figure 2 is a front view of the contactor;
Figures 3-7 are sectional views taken on lines
of corresponding numbers in Figure l;
Figure 8 is a sectional view taken on the line
VIII-VIII of Figure 7;
Figure 9 is a sectional view taken on the line
. IX-IX of Figure l;
Figure 10 is a sectional view taken on the line
X-X of Figure 9; and
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Figure 11 is an enlarged fragmentary view showing
the manner in which an are advances along the ~rontal edge
sur~aces of grid plates.
In Figure 1, the contactor generally indieated
at 1 comprises a base plate 3, electromagnetie means or
electromagnet 5, an electrically insulating housing 7,
`~ arc blowout unit 9, and an arc chute 11. The contac~or
1 also comprises a stationary contact 13, movable eontaet
15, which are mounted on conductor struetures 17 and 19,
respectively. The contacts 13, 15 are movable between elosed
and open positions.
The contactor to whieh the invention is shown
applied, by way of example, is o~ the type generally
deseribed in U.S. Patent Specification No. 3g511,950,
an electric circuit through the contactor 1 ineluding
a line terminal 21, a blowout coil 41, the contact support
strueture 17, contacts 13, 15, the eonductor structure 19,
a shunt 25, a shunt connector 27, and a load terminal 29.
~he eleetromagnet 5 ineludes a coil 31, a eore
33, a U-shaped magnetic frame 35, and an armature 37.
The armature is pivotally mounted at 38 on the base
3 and, when the eleetromagnet 5 is energized, the armature
37 eloses against the upper end of the ~rame 35, thereby
pulling the movable eontaet 15 to a elosed position
with the stationary eontaet 13 as indieated by the
broken line position 15a. Conversely, when the operating
eoil 31 is deenergized, the armature 37 moves to the
open position as shown and thereby moves the movable
eontaet 15 to the open position. When the eontaets
13, 15 separate under load, an are 39 develops between them.
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The arc blowout unit 9 and the arc chute 11 are
provided to extinguish the arc 39 and mlnimlze its effect
upon the contacts. The arc blowout unit 9 comprises a
magnetic blowout coil 41 and a ferromagnetic core 43. The
coll 41, being mounted on the insulating base 7~ consists o~
a single turn around the core 43 and is a continuatlon o~
the line terminal 21. Inasmuch as the electric clrcuit
moves from the line terminal 21 and through the blowout coil
.
41, the coil is on continuous duty. Since space ls not :
available for a multiple turn continuous duty coil, an
auxiliary coil 45 is provided which operates intermlttently,
that is, when the arc 39 strikes a line arc horn 59 after
the contacts 13, 15 are separated. The auxiliary coll 45
comprises end portions 45a and 45b, the former of which is
secured by suitable means, such as a screw 479 to the end of
the blowout coil 41. The end portion 45b is connected to a
!1 line arc horn connector 81 through a conductor 51 extending
, through an insulator mounting 53. The auxiliary coil 45 has
a plurality of, such as four, coil turns around the core 43.
20 A pair of pole pieces 55, 57 (Fig. 2) extends from the ends
of the core 43. The pole pleces 55, 57 are ferromagnetic
flux-carrying members, one pole piece extendlng from one end
of the core 43 and the other pole piece extending from the
other end of the core and radially of the coils 41, 45 to
opposite sides of the arc chute 11, whereln a magnetic field
is generated between the pole pieces. ~he arc 39 is more
readily transferred from the contacts 13, 15 to a line arc
horn or conductor 59 and a load arc hor~ or conductor 61, as
shown by the position of the arc at 39a.
Under heavy load conditions, the single turn blow-
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out coil 41 provides sufficient magnetizing forces to
saturate the ferromagnetic core 43 so that a maximlzed
blowout fi.eld strength is available when the contacts 13, 15
separate. When the arc 39 transfers to the llne arc con-
. ductor 59 and the load arc conductor 61, the auxiliary coil
45, which is connected in series with the coil 41, increases
` the blowout magnetizing force within the arc chute 11.
Under heavy load conditions the core 43 is saturated and the
additional magnetizing force developed by the auxiliary coil
. 10 45 is unnecessary. However, where lighter loads exist, the
single turn coil 41 is unable to develop su~ficient mag-
netizing force to provide an adequate blowout field strength .-
to interrupt the arc 39. Under this condition the extra
magnetizing force provlded by the multiple turn auxiliary
; coil 45 i.s necessary.
: When the operating coil 31 of the contactor ls
deenergized, the contacts 13, 15 separate and an arc 39 is
drawn between the contacts if load current, voltage, and
inductance are sufficient to maintain an arc. If not, the
arc 39 will be extinguished without movlng off of the con-
tacts 13, 15. In the event load conditions are such as to .
maintain an arc, the current ~low through the single turn .
continuous duty blowout coil 41 will magnetize the core 43
and pole pieces 55, 57 to establish a magnetic field between :
the pole pieces which react with the arc 39. The relative
polarity of the blowout field and the arc 39 are such that : ;
the arc is propelled in an upward direction to position 39a,
39b, 39c, 39d, 39e~ When the arc 39 transfers3 the left end ..
of the arc moves ~rom the stationary contact 13 to the line
30 arc horn 59, causing current to flow through the auxiliary .
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blowout coil 45 to strengthen the magnetic ~ield acting uponthe arc. This increase in the arc driving ~orce is desirable
to aid in driving the arc through the constricted arc compart-
ment region within the arc chute llo
The arc chute 11 comprises a housing made of an
electrically insulating material, such as melamine-as~estos,
cement-asbestos, zircon or glass polyester, and comprising a
pair of side walls 65, 67 which define therebetween an arc
compartment extending ~rom the arc receiving end of the hous-
ing, at the end wall 73, to the venting end at end wall 75thereof, the arc conductors 59 and 61 being disposed in the
arc compartment and bouding it at its top and bottom. me
arc chute 11 consists of two halves secured together by suit-
able means, such as screws 63, the two halves being formed by
the side walls 65 and 67 with portions thereo~ forming the
opposite end walls 73, 75 and upper and lower walls 69, 71.
Each side wall 65 or 67 has formed therein a pair of elongated
grooves 77, 79 in which the arc conductors 59 and 61, respect-
ively, are seated. As seen from Figo lp the arc conductors 59,
61 have respective first portions which extend in spaced and
i diverging relationship with each other from adjacent the con-
tacts 13, 15, and respective second portions which extend ~rom
the first portions and diverge at an angle which is consider-
ably larger than the angle o~ divergence between the first
arc conductor portions. A conductor 81 extending from the arc
- horn 59 is connected with a screw 83 to the conductor 51, whilst
a conductor 85 connects the load arc horn 61 electrically to
the conductive base 3. Thus, when an arc exists, as at 39a,
; between the arc horns or conductors 59, 61, a circuit extends
from the coil 45 through the conductors 51, 819 the arc
conductor 59, the arc, the arc conductor 61, the conductor 85
1,
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and the base ~ to the load terminal 2g. The side walls 65, 67
include inwardly slanting portions 87, 89, respectively
(see also Fig. 3), which define an arc entrance region o~ the
arc compartment extending immediately from above the contacts
13, 15 toward and to the constricted arc compartment region 91
which, in turn, ex-tends towards and connects with the wider
end region of the arc compartment at its venting end.
In Fig. 4, the arc is shown located at the arc posi-
tion 39b within the constricted region 91~ and the arc voltage
required per inch of arc length to maintain the arc is higher
than at arc position 39a. If the load current is too high to
permit extinction of the arc at this point, the arc will travel
on to position 39c (Figs. 1 and 5) where it requires still a
higher voltage for maintaining it, and whence it will enter a
stack o~ grid plates 93-111 interdigitated in spaced relation-
ship with each other in the above-mentioned end region of the
- arc compartment. It will be understood that the arc is propelled
through the arc chamber and into the stack of grid plates by a
force provided in part by the blowout unit 9, by the electro
dynamic reaction between the arc and the current ~lowing through
the arc conductors 59, 61, and by the stray field ~rom the pole
pieces 55 t 57-
Arc interruption is improved in the arc chute accord-
ing to the invention by ~orcing the arc to follow a unique path
o~ increased length which also provides increased contact o~ -
the arc with the grid plates 93-111. For this purpose, the grid
plates are inclined at an angle other than 90 with respect to
the length of the advancing arc 39c between the arc conductors
59, 61 or, in other words, with respect to a plane which extends
substantially perpendicular to the direction of spacing be-
tween the arc conductors 59, 61 at the end region of the arc
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compartment. The angle of inclination o~ the grid plates pre-
~erably is about 450 but other angles, except goo, may also
be found suitable.
me stack of grid plates 93-111 comprises an arc
lengthening section beginning at the arc-confronting edges
115 (Fig~ 1) of the grid plates, and a de-ionizing section
which adjoins the arc lengthening section and ends at the
venting-end edges 117 of the grid plates. In the arc leng-
thening section, each alternate grid plate, such as plate
107 in Figs. 7 and 8, has an arc-confronting edge portion
119 ~rhich is bevelled and extends obliquely from one side
of the constricted region 91 toward the opposite side wall 6?
and the venting-end edge of the plate or, more speci~ically,
to a position nearer said opposite si~e wall 67 and said vent-
ing-end edge where the bevelled edge portion 119 terminates
at a shoulder or lateral portion 121 of the arc-confronting
edge. Each of the other grid plates, such as plate 105 in
Figs. 9 and 10, has a similarly bevelled arc-con~ronting edge
portion 125, extending however obliquely from the other side
of the constricted region 91 toward the opposite side wall
which, in this instance, is the side wall 65, and terminating
at a shoulder or lateral portion 127 of the arc-confronting
edge of the plateO In other words, the arc-confronting edges
119 and 125 of adjacent grid plates 105 and 107 in the stack
start from adjacent opposite sides of the constricted region
91 and are bevelled in opposite directions.
As seen from Figs. 7~10, the arc-confronting edges
of the grid plates cooperate with respective opposite side
wall portions or fins 114, 116 to define narrow slots 113a
which interconnect the adjacent spaces 113 between the grid
plates and communicate with the constricted arc compartment
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region 91, the slots 113a in the successive planes of the
grid plates and fins alternately angling toward the one and
the other of the side walls 65, 67. Although the grid plates
93-111 could be individual insulating plates either assembled
in a separate stack or supported from the side walls 65, 67
in the preferred embodiment they are shown as integral parts
of the molded insulating side walls, the plates 93, 97, 101,
105 and 109 forming integral parts of the wall 67, and the
plates 95, 99, 103, 107 and 111 forming integral parts of
the wall 65. Thus1 when the two arc chute halves are assembled,
the grid plates 93-111 assume their intersticial positions and
form the spaces 113 therebetween.
Again as seen from Figs. 7 to 10, the arc-confront-
ing bevelled edge portion of each grid plate also has a bevel-
led surface 123 (Fig. 7) or 129 ~Fig. 9) which helps to guide
the arc into the respective narrow slot 113a, the bevel of
the surfaces 123, 129 being approximately ~
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45 to gulde the arc to the shoulders 121, 127. As the arc
passes the location 39c, it encounters the front edges o~
the several grld plates 93-111 (Flg. 11) and is gulded by
the tnclined front edges 119, 125, as well as the beveled
sur~aces 123, 129 to the arc position 39e (Flg. 11) where
;the arc confronts the shoulders 121, 127 and ln so dolng is
~orced to follow an irregular zigzag path wlthln the Blots
and between the grld plates. More particularly, the arc at
the position 39e ls forced to take an irregular path designed
to mlnlmize equal and opposite magnetlc forces actlng withln
the arc loops so as to eliminate the undersirable centering
of the arc in the air spaces between the grid plates as
found in the prior art grid stacks. Eliminatlon of the arc
centerlng forces thus allows the arc to come into intimate
contact with the grid plates to provlde maxlmum arc coollng
and to increase arc interrupting ability. When the arc
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starts to take the zigzag or looping path, the loops them-
~elves set up additional forces which act to enlarge the arc
loops to lengthen the arc and at the same time force the arc
: 20 into intimate contact with the grid plates as shown in Figs.
6 and 11.
As shown in Fig. 11, alternate arc loops are large
; and small loops. Magnetic forces developed wlthln the small
loops attempt to force the tip of the arc loop back out o~
the grld stack towards the arc conductor 59. Since the
slots 113a between the fins 114, 116 and the edges 119,
125 are angled, the tips of the small loops are forced
against the edges of the grid slots (Fig. 6), rather than
out of the grld stack. At the same time, the arc drivlng
force of the arc conductors 59, 61 and the pole fleld are
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driving the tip of the small loop lnto the grid stack. The
sum of the forces acting on the tip of the small arc loop is
approximately zero when the tip o~ the small arc loop ~ust
enters the grid stack space so the position of the tip of
the small loop will be established at thls point. Centering
of the arc between the grld plates is elimlnated slnce
external magnetic forces actlng on the large arc loop and
magnetlc forces developed wlthin the large loop all aot to
force the large arc loop into the stack and against the
shoulders 121, 127 and the large flat surfaces on the
undersides of the grid plates 93-111. The legs of the small
arc loops are on opposlte sides of the grid plates, but
angle downward into the paper in Fig. 11 to afford an
improvement in arc interrupting ability slnce the legs are
not directly opposite each other even though they are on
opposlte sides of the grid plates. Moreover, as shown ln
Flg. 6, the legs of the small loops have an angular dis-
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placement so that the magnetic forces, developed within the
small loops act to lncrease the angular displacement still
more to create additional mlld arc loops to strengthen and
- force the arc into intimate contact with the grid plate
surfaces rather than centerlng the arc ln the air space 113
between the grid plates.
~ he deionizing section of the grld stack is formed
by the solid portion of the grid plates 93-lli. The deioni-
zing section deionizes the ionized gases generated in the
arc lengthening section of the grid stack and discharges
- them into thelr surrounding atmosphere. The delonizin~
section is located in the rear portion o~ the g~id stack and
has a wider dimension as indicated by the arrow 131 (Fig. 6)
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78~398
than the constricted compart~.ent 91. Decreaslng the space
bet~een the grid plates and/or increasing the length of the
: deionizing portion of the grid plates increases the deionlzlng
abllity of the grid stack, but at the same tlme increases
the back pressure which in turn limits the volume of the gas
whlch can be discharged from the arc chute. To reduce the
back pressure, spacing between the arc chute walls is in-
creased in the exhaust section of the grid stack, as indl-
cated by the arrow 131. At load currents which exceed the
- lO interruptlng rating Or the contactor, the arc wlll generate
more ionized gas than the grid stack can deionlze and dis-
charge. Thus, ionized gas backs up into the constricted
compartment 91 ahead of the grid stack. When this occurs
under heavy load conditions, the arc will restrike across
the arc conductors 59, 61 at some critical point such as 39b
(Fig. 1) and hang on indefinitely until the arc chute is
destroyed. At lighter loads a certain amount of ionized gas
may blow back into the arc compartment 91 to cause the arc
to restrike between the arc conductors, such as at arc
position 39b. In this case, the arc may then travel back
- into the grid stack and be interrupted, or hang on and
destroy the arc chute.
In accordance with this invention~the ionized back
flow in the arc chute is avoided by providing the grid
plates 93-lll at an angle which will direct the ionized gas
generated between the upper grid plates toward the top of
the arc chute (Fig. l) as indicated by the broken lines 133
from where the gas is deflected downwardly to collide wlth
streams of gas coming from the adJa~ent grid plates as
indicated by broken lines 133. This results in gas flow
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turbulence which in turn acts to deionize the gas as well as
restricting gas flow into the critical area at arc posltion
39b. This provides an improvement in arc interrupting
ability over that of arc chutes having grid plates at a
horlzontal position. Finally, the inclined grid plates 93-
111 e~ect the ionized gases from the arc chute downwardly at
the same angles, such as 45~. This advantage plus the
increased length of the grid plates due to their incllned
posltion rather than horizontal, increases the interrupting
ratlng without increasing the horizontal arcing clearance or
horizontal pro~ection Or the arc chute.
Accordingly, the arc chute structure of this
invention solves problems Or prior art construction by
forcing an arc into more intimate contact wlth grid plates
than in prlor art. Finally, ionized air is redirected
towards the top of the arc chute where it is deflected to
cause air turbulence which in turn helps to delonize the hot
gases.
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