Direct current switching apparatus

Direct current switching apparatus having two arc extinguishing chambers each comprising a pair of spaced conductors providing cooperable arc runners divergent toward a row of non-ferromagnetic splitter plates and a stationary contact conductively mounted on one conductor, the stationary contacts of respective chambers being mounted on respectively opposite conductors, corresponding conductors in respective chambers being conductively connected to each other and to power terminals of the apparatus, permanent magnets applying a magnetic field across the respective chamber for moving an arc within the chamber, ferromagnetic plates providing flux return paths to optimize and maximize the magnetic field, a movable contact extending into each chamber bridging the stationary contacts and movable to separate from the stationary contacts, drawing an arc therebetween in each chamber, the arc in one chamber bridging the pair of conductors within that chamber establishing a circuit comprising the arc between the conductors and the power terminals in shunt of the movable contact, thereby eliminating the arc in the other chamber, the bridging arc being extinguished in the splitter plates, interrupting the circuit. The magnetic fields are applied in opposite directions in the respective chambers for non-polarized operability of the apparatus and are distorted within the splitter plate area to drive and maintain an arc at a stable arc position against a thickened sidewall portion to withstand erosion.

BACKGROUND OF THE INVENTION 
This invention relates to apparatus for switching direct current (DC) 
electric power. More particularly it relates to apparatus of the 
aforementioned type which is non-polarized or bidirectional, i.e. its 
performance is independent of polarity of the current at the power 
terminals, and can switch high voltage DC power. Still more particularly, 
the invention is related to apparatus of the aforementioned type which is 
compact, lightweight, may be hermetically sealed and can switch high 
voltage DC power at high altitude. 
High voltage DC power is one of the most efficient, reliable and 
lightweight methods to generate and distribute energy. Development of high 
torque samarium cobalt brushless DC motors has resulted in low weight 
alternatives to hydraulic actuators used in weight and 
reliability-sensitive applications, e.g. aircraft. However, difficulties 
in switching high voltage DC power, particularly at high altitude, and the 
weight and volume of conventional DC switching apparatus capable of 
quenching high voltage circuits at altitudes, preclude the use of such 
switching apparatus in aircraft. As a result, the inability to 
satisfactorily switch high voltage DC power at altitude has delayed use of 
this power in aircraft. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide improved DC switching 
apparatus. 
It is a further object of this invention to provide DC switching apparatus 
capable of switching high voltage DC power. 
It is a further object of this invention to provide DC switching apparatus 
which is non-polarized. 
It is a further object of this invention to provide DC switching apparatus 
capable of switching high voltage DC power at high altitude. 
It is still a further object of this invention to provide DC switching 
apparatus capable of switching high voltage DC power at high altitude, 
which apparatus is compact and lightweight. 
It is still a further object of this invention to provide DC switching 
apparatus of the aforementioned type which is economically and efficiently 
manufactured. 
This invention provides DC switching apparatus comprising a pair of arc 
extinguishing chambers each having a spaced pair of conductors, the 
respective conductors of one chamber conductively connected to the 
respective corresponding conductors of the other chamber and to respective 
power terminals of the apparatus, a pair of stationary contacts, one of 
which is conductively mounted on one of the conductors in one chamber and 
the other of which is conductively mounted on an opposite one of the 
conductors in the other chamber, and a movable contact extending into each 
chamber and driven into and out of bridging engagement with the pair of 
stationary contacts, movement of the bridging contact out of engagement 
with the stationary contacts establishing respective arcs therebetween, a 
first arc transferring from the movable contact to the other conductor 
within a chamber establishing a current path comprising the arc directly 
between the first and second conductors, eliminating a second arc in the 
other chamber. 
This invention further provides permanent magnets providing magnetic fields 
across the arc chambers normal to the arc for assisting the mobility of 
the arc, the magnetic fields being oppositely directed across the 
respective chambers providing non-polarized apparatus; return flux paths 
for maximizing and/or optimizing the magnetic fields applied by permanent 
magnets; arc runners as a part of the pair of conductors within each 
chamber to direct the arc into a plurality of arc splitter plates also 
contained within each chamber; a predetermined distortion of the magnetic 
field in the splitter plate area of each arc extinguishing chamber which 
drives and holds the arc at a final stable position against a wall of the 
chamber within the splitter plates. 
The foregoing and other features and advantages of this invention will 
become more readily apparent and understood when reading the following 
description and appended claims in conjunction with the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to FIG. 1 of the drawings, a hermetically sealed 
electromagnetic contactor 2 incorporating the DC switching apparatus of 
this invention is shown in isometric. The contactor 2 comprises an outer 
metal envelope comprising a can 4 having a mounting plate 6 affixed to the 
back thereof by welding or the like and a header 8 hermetically welded 
over an open front side of can 4. As a reference for the term "compact " 
as used herein, the envelope comprising can 4 and header 8 may be on the 
order of 3.42 inches wide by 5.00 inches long by 3.23 inches high. Header 
8 has outwardly projecting flanges 8a extending from opposite lateral 
edges. A pair of stabilizing tubes 10 are secured between mounting plate 6 
and flanges 8a, only one pair of tubes 10 being visible in FIG. 1. Tubes 
10 are closed at the forward end and riveted to flanges 8a and are secured 
to the mounting plate 6 at their opposite ends over holes in the plate 6. 
A multipin connector 12 is hermetically attached within an opening in a 
bottom wall of can 4 to provide connection to control electronics for the 
DC switching apparatus within the envelope as will be described 
hereinafter. DC power terminals 14, 16 are attached and hermetically 
sealed to header 8, electrical insulated therefrom, to extend through the 
header. The externally projecting portions of terminals 14, 16 have tapped 
holes for receiving screws (not shown) which attach power conductors (not 
shown) to the terminals. A generally T-shaped insulating barrier 18 is 
attached to header 8 by a pair of screws 20 (FIG. 3) which threadably 
engage tapped sleeves welded to the exterior of header 8. Barrier 18 
isolates the power terminals 14, 16 and conductors from each other and 
provides a protective cover thereover to reduce electrical shock hazard. 
Header 8 is also provided with a tubular fitting 22 through which the seal 
of the contactor assembly may be checked and may be evacuated and filled 
with a controlled atmosphere medium such as an inert gas or the like, 
after which the fitting 22 is crimped shut and sealed. 
Referring to FIGS. 2 and 3, the DC switching apparatus represented 
generally by the reference numeral 24, is built up upon and attached to 
the interior of header 8 prior to assembly of the external envelope 
members 4 and 8. Four internally tapped posts 26 (two visible in FIG. 3) 
are welded to header 8. Four mounting screws 28 pass through the switching 
apparatus assembly 24 from the rear to threadably engage posts 26, 
securing apparatus 24 to header 8. Screws 28 also have threaded post 
extensions 28a extending rearwardly from hexagonal heads thereof to which 
a control electronics module 30 and an electromagnetic interference (EMI) 
shield 32 are mounted. EMI shield 32 is spaced from module 30 and the 
hexagonal heads of screws 28 by rubber spacers 34. Cylindrical nuts 36, 
having a tapped hole therethrough and a screw driver slot at the rear end, 
are inserted within holes in control module 30 and are turned onto the 
threaded post extensions 28a. Wires 31, partially shown in FIG. 3, extend 
from control module 30 and are connected, as by soldering or the like, to 
internal portions of the pin connectors of multipin connector 12. A wire 
31a (FIG. 3) may be attached to an interior part of can 4 to electrically 
ground the envelope to the system in which the apparatus is used. 
After assembly of header 8 with switching apparatus 24, EMI shield 32 and 
control electronics module 30 attached thereto, to can 4, screws 38 (FIG. 
3) are turned into nuts 36 from the exterior of the envelope through 
aligned holes in mounting plate 6 and can 4 to firmly secure the 
electronics module and shield within the rear of the envelope. Screws 38 
are subsequently sealed to mounting plate 6 by welding or the like. It may 
be seen in FIG. 3 that shield 32 is provided with resilient spring clips 
32a at its top and bottom edges which engage the interior surface of metal 
can 4 to incorporate the metal envelope in the magnetic shielding of the 
electronics. 
Switching apparatus 24 chiefly comprises two identical molded insulating 
housing assemblies disposed back-to-back, within which and to which other 
components of the apparatus are mounted to provide a pair of arc 
extinguishing chambers. Referring additionally to FIGS. 4-8, and 
particularly to FIG. 6, the molded insulating housing assemblies each 
comprise a three-sided molding 40 and a substantially flat cover molding 
42 disposed over the open side of molding 40. The members 40 and 42 are 
symmetrical about a vertically disposed front-to-rear center plane, except 
for a minor deviation regarding mounting grooves for arc splitter plates. 
The interior wall surfaces of molding 40 and cover 42 have a plurality of 
grooves 40g and 42g, respectively, formed therein in closely spaced, 
parallel relation oriented vertically and extending in a row transverse to 
the front-to-rear center plane with regard to the directional orientation 
convention assigned in the description of FIG. 1 above. The grooves 40g 
and 42g are open at their upper ends and extend downwardly varying amounts 
as best seen in FIG. 8 to receive splitter plates 44 of correspondingly 
varying lengths 44a, 44b and 44c. Longer splitter plates 44c are located 
near the center of the housing assembly, spaced by interposed short plates 
44a, thereby providing a wider initial entry space for an arc between the 
lower ends of plates 44c. Intermediate length plates 44b serve the same 
purpose as long plates 44c, but space provisions with the assembly 
prohibit another long plate 44c from being used at the locations of plates 
44b. A vertical center line x--x is shown in FIG. 8 to illustrate that the 
location of plates 44a, 44b and 44c are not symmetrical about the line, 
inconsistent with most other details of the housing assembly. However, 
rotation of one housing assembly 180.degree. about line x--x to place it 
back-to-back against the other housing assembly effects front-to-rear 
alignment or coincidence of the grooves 40g and 42g and plates 44 between 
the two housing assemblies, except that a long plate 44c in one housing 
will be aligned with a short plate 44a in the other housing, and similarly 
for intermediate length plates 44b. This nonsymmetry establishes a gap 45 
between a splitter plate 44c and an adjacent conductor 46 which is greater 
than a corresponding gap 47 between conductor 48 and an adjacent splitter 
plate 44c as shown in FIG. 8 illustrating the rear chamber. The larger gap 
45 is oppositely located in the forward chamber because that housing 
assembly is rotated 180.degree. as aforedescribed. Reasons for the offset 
larger gaps will be described more fully hereinafter. 
Covers 42 have circular slots 42a formed therein open to opposite lateral 
edges to receive a reduced diameter cylindrical center portion 46a, 48a 
machined into extruded teardrop shaped conductors 46, 48. The larger 
teardrop shaped portion of conductors 46, 48 are disposed between 
respective moldings 40 and covers 42 when the two housing assemblies are 
positioned back-to-back as described above. Moldings 40 have ledges 40a on 
their interior surfaces on which conductors 46, 48 rest for positioning 
the conductors therein. Moldings 40 also have holes 40b in the 
transversely extending wall thereof, holes 40b being axially aligned with 
the axes of slots 42a and of power terminals 14, 16. Conductors 46, 48 
each have a hole extending longitudinally therethrough also on the axes of 
power terminals 14, 16, respectively. The power terminals have reduced 
diameter shafts 14a, 16a at the rear end thereof, the distal portions of 
which are threaded. Reduced diameter shafts 14a, 16a form annular 
shoulders on terminals 14, 16 against which a respective conductor 46, 48 
abuts, being held tightly thereagainst in good electrical connection with 
the power terminals by nuts 50 engaging the threaded distal ends of shafts 
14a, 16a and washers 52 interposed nuts 50 and conductors 46, 48 (see FIG. 
5). Within the arc extinguishing chambers formed by moldings 40 and covers 
42, the arcuate surfaces of the teardrop shaped conductors 46, 48 form 
diverging arc runners leading to the splitter plates 44. Completing the 
conductor assembly, stationary contact tips 54, 56 are affixed to the 
underside of the teardrop shaped conductors in good electrical conduction 
therewith, such as by brazing or the like. Stationary contact tip 54 is 
affixed to the underside of the rearmost teardrop shaped portion of 
conductor 46 which is disposed within the rear arc chamber and stationary 
contact tip 56 is affixed to the foremost teardrop shaped portion of 
conductor 48 which is disposed within the forward arc chamber for reasons 
that will be discussed more fully hereinafter. 
A molded insulating cover 58 is attached over the upper ends of the arc 
chamber housing assemblies when the latter are assembled back-to-back. 
Cover 58 has depending projections 58a at its lateral ends which have 
arcuate slots open laterally to be trapped by the uppermost pair of 
mounting screws 28 when the same are inserted through the switching 
apparatus. Cover 58 is also provided with an elongated central slot 58b 
(FIG. 5) extending therethrough and a pair of resilient strips 58c (FIG. 
5) embedded in the underside thereof parallel to slot 58b and protruding 
downward from place, resilient strips 58c bear upon upper edges of 
splitter plates 44 to hold them firmly in place against lower edges of the 
respective grooves 40g and 42g. As seen best in FIG. 5, the opening 58b in 
cover 58 is disposed over the assembled upper edges of covers 42 and a 
center steel plate 62 to be described hereinafter. The interior edges 
defining slot 58b abut flush against the respective interior wall surfaces 
of covers 42 in which grooves 42g are formed. The grooves 42g are open to 
the upper edge of covers 42, and thereby define a plurality of vent 
openings for arc gas created within the respective chambers. With further 
reference to FIG. 5, it is to be noted that the upper edges of arc 
splitter plates 44 adjacent covers 42 are chamfered at 44d to create a 
reservoir area adjacent the vents for the arc gasses. 
A plurality of permanent magnets 60 are positioned within appropriately 
shaped pockets in the external surface of the transversely extending wall 
of moldings 40 to provide a magnetic field across the respective chambers. 
In view of the magnetic field applied to the chambers, arc splitter plates 
are preferably made of non-ferromagnetic material such as copper or the 
like. The permanent magnets 60 are preferably rare earth magnets such as 
samarium cobalt to provide a strong magnetic field which will not vary 
with current magnitude. A plurality of magnets are used instead of one 
larger one to optimize the magnetic field, applying a minimum, or 
necessary, magnetic field intensity in specific areas without applying 
excessive and undesirable magnetic field intensity generally across the 
chamber. This multiple magnet feature also provides advantageous size and 
weight considerations. As seen best in FIG. 6, two magnets 60a and 60b are 
arranged with contiguous top and bottom edges respectively to circumscribe 
the holes 40b in moldings 40. A third magnet 60c is formed in a mirror 
image to magnet 60b. These three magnets 60a, 60b and 60c are first 
positioned within a deeper portion of a respective pocket molding 40, with 
magnets 60b and 60c being laterally spaced apart (see also FIG. 2). Magnet 
60a is disposed in proximity to the respective stationary contact 54, 56 
within the respective chamber. Magnets 60b and 60c are disposed in 
proximity of the ends of the arc runner surface of conductors 46, 48 
adjacent arc splitter plates 44. Inasmuch as only one stationary contact 
is provided in each chamber, that being affixed to the respective 
right-hand conductor as viewed from the exterior of molding 40, a 
left-hand magnet corresponding to magnet 60a is not required. A fourth, 
larger magnet 60d is placed over all three smaller magnets and is 
positioned within a shallower portion of the pocket. The outline or 
profile of magnet 60d generally coincides with the outline of the 
assembled three magnets 60a, 60b and 60c except that it includes a 
lower-left portion substantially a mirror image of magnet 60a. All magnets 
60 are polarized in the direction of their thickness and are arranged with 
north poles outwardly disposed, south poles facing the respective molding 
40 in a magnetic series relationship. 
A ferromagnetic flux return path effectively completes the arc chamber 
assembly portion of the switching apparatus 24. A center steel plate 62 is 
disposed between adjacently disposed covers 42, projecting above the upper 
edges of the covers 42. A forward steel plate 64 having a profile similar 
to magnet 60d, but including a pair of laterally extending tabs 64a having 
holes therein and a pair of slots 64b along an upper edge, is positioned 
against the magnet 60d and exterior surface of forward molding 40, secured 
thereagainst by a screw 66 passing through a hole in a third laterally 
extending tab 64c and threading into an aligned hole in molding 40. A 
third member of the ferromagnetic flux return path is an inverted L-shaped 
steel plate 68, the vertical leg of which is shaped similarly to plate 64, 
having laterally extending tabs 68a and 68c, each with holes formed 
therethrough. A horizontal upper leg 68b of plate 68 has a pair of 
projecting tabs 68d along its distal edge. Plate 68 is positioned against 
the exterior surface of rearmost molding 40 and against the corresponding 
permanent magnet 60d and held thereagainst by a second screw 66 which 
extends through the hole in tab 68c and threadably engages an aligned hole 
in molding 40. Upper leg 68b projects forwardly over the housings and top 
cover 58, bearing against the upper edge of center steel plate 62, and 
interlocking with forward steel plate 64 by engagement of tabs 68d in 
slots 64b. Referring also to FIGS. 5 and 10, the permanent magnets 60 and 
ferromagnetic flux return path comprising steel plates 62, 64 and 68, 
direct a magnetic field across the respective arc chambers formed by 
moldings 40 and covers 42, the magnetic field in one chamber being 
reversed in direction with respect to the magnetic field in the other 
chamber. Center steel plate 62 is common to the flux return path around 
each chamber. Upper pair of screws 28 extend through holes in tabs 68a and 
64a of steel plates 68 and 64, respectively, through aligned holes in 
moldings 40 and laterally open slots in covers 58a, respectively, to 
secure the entire upper area of the arc extinguishing chamber portion of 
switching apparatus 24 together as well as to hold apparatus 24 to header 
8 as aforedescribed. Lower pair of screws 28 similarly hold the lower area 
of the arc chamber portion together, but extend only through aligned holes 
in moldings 40. 
A movable bridging contact 70 (FIG. 7) is attached to the plunger of a 
latching permanent magnet actuator 72, shown best in FIG. 4. Actuator 72 
is of the type shown and described in U.S. Pat. No. 3,040,217 issued June 
19, 1962 to R. A. Conrad, the disclosure of which is incorporated herein 
by reference. Actuator 72 comprises a pair of cylindrical permanent 
magnets 74 polarized axially and disposed at opposite ends of a magnet 
steel cylindrical pole piece 76. Permanent magnets 74 are arranged with 
their north poles inward adjacent pole piece 76. A non-magnetic 
cylindrical plunger guide 78 lines the interior surface of holes through 
pole piece 76 and magnets 74, providing a guide for steel plunger 80 which 
is reciprocally movable axially within guide 78. A coil 82 wound on a 
bobbin 84 is disposed over the pole piece 76 and magnets 74. 
Alternatively, coil 82 may be two coils having opposite polarity 
concentrically disposed on bobbin 84. The assembly is secured together by 
a lower steel frame member 86 having four upstanding legs 86a extending 
along the exterior surface of coil 82, and an upper steel frame member 88 
which has appropriately spaced slots to receive and secure the upper ends 
of legs 86a therein, such as by staking, swaging over, or the like. 
Actuator 72 is latched in its up or down position by a flux pattern from 
the respective permanent magnet, and is operated to the opposite position 
by energizing the single coil 82 with a selected polarity that will cancel 
the permanent magnet flux that was tending to maintain the plunger in its 
existing position and add to the magnetic flux of the opposite permanent 
magnet to attract the plunger to the opposite position. The direction can 
be reversed and the plunger returned to the original position by 
subsequent energization of the single coil 82 with a polarity opposite to 
the initial energization. In the contemplated alternative version desired 
operation is achieved by selective energization of a proper one of the two 
coils. 
A non-magnetic hex head screw 90 extends through a clearance hole in upper 
frame member 88 and threads into a tapped hole in the upper end of plunger 
80. An adjustable spring seat 92 is threaded onto the shank of screw 90. 
Spring seat 92 has an upstanding annular collar which positions and 
maintains separated two concentrically disposed helical compression 
springs 94 and 96. A platform insulator 98 is slidably disposed over the 
shank of screw 90, resting on springs 94 and 96. Insulator 98 has an 
upstanding integral sleeve 98a surrounding the opening therethrough for 
screw 90. Sleeve 98a projects into a central opening 70a in movable 
contact 70 to electrically insulate screw 90 from movable contact 70. An 
upper insulator washer 100 having a depending annular collar 100a is 
disposed around the shank of screw 90 at the upper surface of contact 70, 
the collar 100a telescopically extending along screw 90 into sleeve 98a. A 
washer 102 and the hexagonal head of screw 90 retain the entire movable 
contact assembly together. The axial position of screw 90 provides wear 
allowance adjustment for the contacts, while contact pressure adjustment 
is provided by the axial position of spring seat 92 on screw 90. 
Concentric springs 94 and 96 provide suppression of any resonant 
frequencies during vibration of the apparatus with the consequent 
elimination of undesirable motion of movable contact 70. 
As seen in FIG. 7, movable contact 70 comprises a flat base plate 70b of 
heavy gauge copper or the like in which central opening 70a is formed. 
Extending from opposite lateral ends of plate 70b are legs 70c which are 
offset one from the other front-to-rear and are curled upwardly in 
re-entrant bends wherein the distal ends of the legs are disposed 
centrally over plate 70b. A pair of contact elements 70d are affixed to 
the upper surface of each leg 70c by brazing or the like. The portion of 
each leg 70c extending beyond the contact elements 70d is beveled to 
approximate a converging point 70e. Base plate 70b is also provided with a 
pair of holes 70f located laterally on either side of opening 70a. Holes 
70f cooperatively receive projections 98b (FIG. 8) on the upper surface of 
insulator 98 to maintain proper rotational alignment of movable contact 70 
with respect to insulator 98, and the latter is provided with slots 98c 
along an edge thereof which receive upward projections 88a of upper frame 
member 88 to maintain insulator 98 properly rotationally oriented with 
respect to actuator 72 and the arc chambers. Actuator 72 is attached to 
the assembled arc extinguishing chamber assembly by screws 103 which pass 
through clearance holes in molding 40 and take into tapped holes in 
upstanding tabs 88b formed in upper steel frame member 88 (FIGS. 4 and 5). 
Plunger 80 of actuator 72 also functions to operate an auxiliary 
snap-action switch 104 which is attached to a pair of the legs 86a by a 
bracket 106 (FIG. 8) and screws 108. A non-magnetic button 110 is 
threadably attached to the lower end of plunger 80 and projects through a 
hole in lower frame member 86. A spring steel leaf 112 is mounted between 
a bracket 114 attached to the interior surface of header 8 (FIG. 3) and a 
tab 86b projecting from lower steel frame member 86 by a screw 116. Leaf 
spring 112 extends below frame member 86 across the end of button 110. The 
free end of spring leaf 112 is in alignment with an operator button of 
switch 104. When plunger 80 is in the lower position as shown in the 
drawings, button 110 holds leaf spring 112 depressed wherein the free end 
thereof is out of engagement with the operator button of switch 104. 
However, when plunger 80 is in its upper position, button 110 releases 
leaf spring 112 and the spring bias of that member operates switch 104. 
In operation of the DC switching apparatus of this invention, the single 
coil 82 (or the appropriate coil of a two-coil embodiment) of permanent 
magnet actuator 72 is appropriately energized by connections (not shown) 
from control electronics module 30 to transfer the plunger 80 to its 
uppermost position, thereby closing bridging contact 70 the stationary 
contacts 54 and 56. It will be appreciated that the offset arms 70c of 
movable contact 70 extend within the respective arc extinguishing chambers 
as seen in FIGS. 4 and 5. The apparatus herein disclosed through use of 
appropriate electronics in the module 30 may be used as a remote power 
controller or as an overload sensing and responsive circuit breaker or the 
like. Whatever manner in which the apparatus is used, an appropriate 
signal from the electronics module 30 to energize coil 82 in the opposite 
polarity will cause the actuator to move plunger 80 to its lowermost 
position, separating movable bridging contact 70 from stationary contacts 
54 and 56. 
With reference to FIG. 9, let it be assumed that power terminal 14 is 
connected to the positive side of a high voltage DC power supply such as 
250 amps, 270 volts, while power terminal 16 is connected to the negative 
side of that supply. The magnetic field across the arc chamber containing 
stationary contact 54 is directed out of the paper toward the viewer. Upon 
separation, an arc is drawn between stationary contact element 54 and 
movable contact element 70d and between the other movable contact element 
70d and stationary contact 56. The positive potential arc at stationary 
contact 54 is represented by arrow 120 directed from the stationary 
contact to the movable contact. The arc at stationary contact 56 and 
movable contact 70d is represented by arrow 122 directed upwardly. The two 
arcs 120 and 122 tend to expand and the force applied by the magnetic 
field in the respective chambers moves the arc 120 leftward along the 
pointed extension 70e of movable contact 70 toward the conductor 48. The 
anode end of arc 120 at the stationary contact 54 and conductor 46 moves 
around a short radius corner of the conductor 46 toward the arc runner 
surface thereof. Because an anode end of an arc moves more readily than 
does a cathode end of the arc, it is preferable that the anode end be that 
which traverses the more irregular surface comprising the contact 54 and 
the conductor 46 and the cathode end move along the flat surface of the 
movable contact 70. 
While arc 120 is lengthening and increasing the voltage thereof, arc 122 is 
also moving leftward under the bias of the magnetic field in the forward 
chamber but within a more confined area. The two arcs 120 and 122 
establish additive arc voltages V.sub.120 and V.sub.122 seen in FIG. 11. 
The cumulative voltage of these two arcs is represented by V.sub.120+122 
in FIG. 11 which increases primarily as arc 120 (FIG. 9) lengthens by 
movement of the cathode end along movable contact 70 toward end 70e. 
During this time, the corresponding current I.sub.120,122 decreases 
somewhat as shown in FIG. 12. Within a small interval of time, arc 120 
attaches to the opposite teardrop shaped conductor 48 within the arc 
chamber common to stationary contact 54, establishing a current path 
through arc 120 from conductor 46 to conductor 48, and therefore from 
power terminal 14 to power terminal 16. Inasmuch as conductor 48 in the 
rear chamber is common and conductively connected to the conductor 48 in 
the forward chamber to which stationary contact element 56 is attached, 
the current path previously extending to the movable contact 70 from 
conductor 46 and from the movable contact 70 to conductor 48 is now 
eliminated and arc 122 is eliminated as well. Thereafter, a single arc 124 
progresses along the arc runner surfaces of conductors 46 and 48 within 
the rearmost chamber upward into the splitter plates 44. As mentioned 
above, an arc generally moves more readily along its anode end than along 
its cathode end, and for this reason the anode end of arc 124 moves more 
quickly along the arc runner surface of conductor 46 and leads the cathode 
end thereof along the arc runner surface of conductor 48. As arc 124 moves 
along the arc runner surfaces and becomes lengthened, its voltage 
V.sub.124 increases, thereby decreasing the current I.sub.124 as shown in 
FIGS. 11 and 12. The larger gap 45 (FIG. 8) between the arc runner surface 
and splitter plates is located at the anode side of the chamber because of 
the aforementioned general characteristic of the anode end to be more 
readily movable than the cathode end. The arc 124 is first separated into 
intermediate length segments between the adjacent depending ends of 
splitter plates 44c and between 44c and 44b and thereafter is split into 
smaller lengths as these segments move into the smaller gaps between 
splitter plates 44a and the adjacent plates 44a, 44b or 44c. Once the arc 
is within the splitter plates, the voltage levels at V.sub.EXT in FIG. 11, 
driving the current I.sub.124 to zero to interrupt the circuit. 
The apparatus of this invention operates to establish an arc in each 
chamber between the respective stationary contact and the common movable 
bridging contact, then moves that arc in both chambers by magnetic fields 
applied by permanent magnets in reverse directions in the respective 
chambers. One of the arcs attaches to a spaced conductor which is 
conductively common with the stationary contact in the opposite chamber so 
as to establish a current path directly between the power terminals 
through the conductors and removing the current path from the movable 
contact, thereby eliminating the arc in one of the chambers. Thereafter 
the arc is moved upward into splitter plates to lengthen it and raise the 
voltage thereof, driving the current to zero and interrupting the circuit. 
In the event polarity at the power terminals is reversed, the two-chamber 
structure with reversely directed permanent magnet magnetic fields 
provided herein functions in the same manner, only the arc is eliminated 
in the rearmost chamber and extinguished in the forward chamber. 
Referring next to FIG. 10, the particular structure and arrangement of the 
permanent magnets and the ferromagnetic flux return path are provided to 
drive the arc to a final stable position against an electromagnetically 
non-conductive side wall of the insulating arc chamber while it is still 
within the area of the splitter plates, retaining the arc in that area. 
This eliminates the need for providing a labyrinth of grooves for the 
upper ends of the splitter plates, simplifying construction, since the arc 
cannot extend beyond the end of the splitter plates and reestablish 
itself. As seen in FIG. 10, the upper edge of magnet 60d is disposed 
intermediate the upper and lower ends of splitter plates 44. However, the 
ferromagnetic flux return path comprising center plate 62, upper plate 68b 
and forward plate 64 provide a complete magnetic loop around the upper end 
of the arc chamber. Throughout the central area of the chamber, the 
magnetic field is directed straight across the chamber from magnet 60d 
through plate 64, upper plate 68b and center plate 62 across the chamber 
to magnet 60d. However, at the upper end of magnet 60d, the customary 
fringing of magnetic flux lines occurs. Such fringing is specifically 
directed in reverse loops by the presence of the ferromagnetic return path 
such that the upper flux lines turn back on themselves and return to the 
forward plate 64. This curvature of the flux pattern near the upper end of 
magnet 60d causes a curvature in the trajectory of the arc 124 as it moves 
from between the contacts 56 and 70d upward along the arc runner surface 
of conductors 46 and 48 and into the area of splitter plates 44. As the 
arc moves upward in the splitter plate area of the arc chamber, its 
trajectory, or path, curves more sharply to the right as seen in FIG. 10 
until it impinges against the right-hand interior surface of the wall of 
molding 40, the wall surface and magnetic field preventing the arc from 
this final stable position from moving. To compensate for this repetitive 
occurrence of the arc at the final stable position, the wall of molding 40 
is increased in thickness at 40e (FIG. 10) to absorb the heat of the arc 
and better withstand the erosion thereof. 
The foregoing has described DC switching apparatus for high voltage DC 
power contained within a compact, light weight structure rendering it 
suitable for use in weight and volume sensitive applications, such as in 
aircraft use. The device has been made symmetrical for cost efficiency in 
manufacture and to enable it to be used as a non-polarized switching 
device to accommodate reversed polarity of the DC power. Although the 
device has been disclosed in a preferred embodiment, it is to be 
understood that it is susceptible of various modifications without 
departing from the scope of the appended claims.