Electric power switch with slotted commutation end plate

In an electric power switch in which an arc generated between movable and stationary contacts 6, 14 migrates to an arc runner 15 and a commutation end plate and is extinguished by a grid 2 arranged therebetween, a cut is formed at least in the lower half of the end plate which confronts the grid, whereby the end of the arc is driven towards the center of the end plate and away from a surrounding arc box 1.

BACKGROUND OF THE INVENTION 
This invention relates to electric power switches, and more particularly to 
an improved commutation plate adapted to constrain the migration of the 
end of an arc formed on the movable contact of such a switch. 
In a conventional power switch as schematically shown in FIG. 1 the end 
portion of the commutation plate 3 is bent in the form of an upwardly open 
U-shaped groove. An opening 3b extends across the bottom of the groove and 
up the side thereof opposite a grid confronting end plate 3a, and a 
contact 6 on a movable contact arm 5 is disposed in the opening 3b thus 
formed. 
When an arc is generated at off-center position P on the end plate 3a, the 
values of the current components i.sub.1 and i.sub.2 flowing into the arc 
from the commutation plate 3 are substantially equal to each other, and 
the sum (i) of the components i.sub.1 and i.sub.2 is the arc current. As 
is apparent from FIG. 1, 1.sub.1 &gt; 1.sub.2 at position P. Accordingly, the 
force F.sub.1 of the current i.sub.1 affecting the arc is larger than the 
force F.sub.2 of the current i.sub.2, as a result of which the arc is 
driven in the direction of the force F.sub.1. The arc is thus shifted 
directly toward an arc box surrounding the grid, which is likely to damage 
the arc box. 
Similar constructions are also disclosed in U.S. Pat. Ser. No. 4,237,355, 
and in commonly assigned copending application Ser. No. 380,314, filed May 
20, 1982. 
SUMMARY OF THE INVENTION 
Accordingly, an object of this invention is to provide an electric power 
switch in which a central cut or slit is formed in the commutation plate 
to prevent any damage to the arc box. The effect of such a cut is to drive 
an arc formed on the grid confronting surface of the commutation plate 
toward the grid, whereby an electric power switch can be provided in which 
the arc box is protected from damage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A first embodiment of an actual electric power switch according to this 
invention is constructed as shown in FIGS. 2 through 5. 
In FIGS. 2 and 3 an arc-extinguishing arc box 1 made of heat-resisting 
material fixedly mounts commutation plates 3 and grids 2 made of magnetic 
material in correspondence to the number of electrical phases to be 
switched on and off. Other components include a cross-bar 4, a movable 
contact arm 5, contacts 6 on both ends of the arm, a movable contact 
retainer 7, a retaining spring support 8, a contactor spring 9, and a stop 
10. 
The contactor spring 9 is fixed under tension between the lower portion of 
the stop 10 and the lower portion of the retaining spring support 8. The 
upper portion of the retaining spring support 8 abuts against the upper 
surface of the movable contact retainer 7, while the upper surface of the 
movable arm 5 abuts against the lower surface of the retainer 7, when 
assembled. The stop 10 is inserted into a hole in the cross-bar 4. 
Further in FIGS. 2 and 3, reference numeral 11 designates a base having an 
open bottom and a side opening 11a (FIG. 4) for withdrawing an 
electromagnetic drive device (described later), 12 designates terminals 
secured to the upper portion of the base 11 with screws, 13 is a U-shaped 
stationary contactor which is secured to the upper surface of the terminal 
12 with screws, a stationary contact 14 being secured to the upper surface 
of the stationary contactor 13, 15 is an arc runner secured to the 
stationary contactor 13, and 16 is an insulating barrier for electrically 
insulating the terminals 12 from one another. The insulating barrier is 
fixedly secured by being partially inserted in grooves formed in the arc 
box 1 and the base 11. Reference numeral 17 designates a movable rubber 
cushion, 18 is a movable iron core which is fixedly coupled to the lower 
portion of the cross-bar 4 by pins 22, 19 is a stationary iron core which 
is spaced a predetermined distance from the movable core 18, and 20 is an 
electromagnetic drive control device through which the legs of the 
stationary core 19 extend. 
The drive control device 20 (FIG. 5) includes an electromagnetic coil 21, 
and rail engaging pieces 20b for forming U-shaped recesses 20a. Reference 
character 20c designates a through-hole into which a leg of the core 19 is 
inserted. Reference character 22' designates a stationary cushion spring 
mounted on the lower portion of the core 19, the spring 22' serving to 
relieve any shock which may be imparted to a mounting board (not shown) 
when the electromagnetic contactor is operated. Reference numeral 24 
designates pins which penetrate through the lower portion of the core 19 
as shown in FIGS. 2 and 3, with both ends protruding from the core into 
rubber cushions 25 inserted into guides 26 made of low friction material. 
Each guide 26 has recesses 26a at both ends, the diameter of which is 
substantially equal to the outside diameter of the cushions 25. Reference 
numeral 27 designates a rail plate which has two parallel, U-shaped rails 
27a at its midportion. The rails 27a have rail stoppers 27b at their 
deepest ends. The rail plate is secured to the base 11 with screws 28. The 
drive control device 20 has a ratchet 29, as shown in FIGS. 4 and 5, 
having vertically movable recesses 29a engaged with a vertical protrusion 
20d of the drive control device, biased downwardly by a return spring 30. 
The ratchet 29 has a protrusion 29b at its lower end which engages a slot 
27c in the rail plate 27. A trip spring 31 is disposed between the lower 
end of the cross-bar 4 and the upper surface of the rail plate 27 to urge 
the cross-bar upwardly. An apertured mounting plate 32 for securing the 
electromagnetic contactor to a panel (not shown) is secured to the bottom 
surface of the rail plate. Auxiliary contacts 33 are secured to the side 
of the base 11. The arc box 1 is screwed to the base 11, and the cross-bar 
4 is vertically guided by the inner wall of the base 11. As shown in FIG. 
2, the arc runner 15 is divided into two parts: a first part substantially 
parallel with the stationary contactor 13, and a second part substantially 
perpendicular thereto. 
In operation, and referring to FIGS. 2 and 3, upon the application of a 
drive voltage to the control device 20, the latter forms magnetic flux 
which produces an attractive force between the movable iron core 18 and 
the stationary iron core 19. As a result, the cross-bar coupled to the 
movable core 18 is pulled downwardly against the force of the spring 31, 
so that the movable contacts 6 are brought into engagement with the 
stationary contacts 14. The open gap between them is smaller than the gap 
between the movable core 18 and the stationary core 19. Therefore, the 
cross-bar 4 continues to move downwardly until the cores are brought into 
contact with each other, which compresses the spring 9. The elastic force 
of the spring, in this operation, is transmitted through the support 8 and 
the retainer 7 to the contact arm 5, so that the terminals 12, which form 
an electrical path, are electrically connected under a predetermined 
contact pressure. 
When the voltage to the drive control device 20 is interrupted, the 
electromagnetic attraction between the cores 18 and 19 is broken, whereby 
the cross-bar 4 is moved upwardly by the compressed spring 31 and the 
contacts are disengaged. This generates an arc between the movable contact 
6 and the stationary contact 14. The feet or ends of the arc migrate from 
the movable contact 6 to the commutation plate 3 and from the stationary 
contact 14 to the arc runner 15, respectively, and the arc is further 
driven into the grid 2 by the electromagnetic repulsion force between the 
arc current and the contactor current. As a result, the arc is cooled, 
divided, and finally extinguished. The electrical path between the 
terminals 12 can thus be switched on and off by controlling the voltage 
applied to the drive control device 20. 
In the first embodiment schematically shown in FIG. 6, the grid confronting 
end plate 3a of the commutation plate 3 has a vertical slit S which 
divides it into two parts. 
Accordingly, as shown in FIG. 6 in association with FIG. 7, the force 
F.sub.1 due to the current i.sub.1 is eliminated, and the arc is driven 
only by a force F.sub.2 due to the current i.sub.2. In other words, the 
arc which migrates from the movable contact 6 to the end plate 3a is 
always driven towards the center of the end plate. Accordingly, the arc 
never jumps to or contacts the arc box directly to damage it, which 
greatly improves the durability of the switch. 
In the second embodiment schematically shown in FIG. 7, reference numeral 
105 designates a movable contact arm, 106 is a movable contact, and 103 is 
a commutation plate having a pair of legs 117, a grid confronting end 
plate 118, and a slit 116 cut in the lower half of the end plate. 
When the switch contacts are opened an arc is produced, which shifts to the 
legs 117 of the commutation plate and to the arc runner (not shown). 
Eventually the arc spans the gap between the end plate 118 and the 
confronting arc runner surface as indicated by reference character C. One 
foot of the arc is at point P on the end plate, while the other foot is at 
a predetermined position (not shown) on the arc runner surface. The arc 
current i flows in the direction of the arrow, and i=i.sub.1 +i.sub.2. 
An arc driving force F.sub.1 due to the current i.sub.1 is produced 
transversely along the end plate, while a force F.sub.2 due to the current 
i.sub.2 is produced downwardly as shown in FIG. 7. The resultant force F 
is directed towards the wall of the arc box (being perpendicular to the 
commutation plate and adjacent to the side surface thereof) in a plane 
including the end plate, and the foot of the arc at point P is thus moved 
towards point Q. 
Similarly, when the foot of the arc is established at point R on the end 
plate, it is forcibly driven towards point S. 
Accordingly, the arc foot can never jump away from the end plate; i.e., it 
is positioned near the slit 116 at all times. Thus, the problem of the arc 
contacting and damaging the wall of the arc box is eliminated. The slit 
116 is shown as being rectangular, but this configuration is not limiting. 
A third embodiment is schematically shown in FIG. 8, wherein a V-shaped cut 
216 is formed in the end plate 203 which confronts the grid. With this 
construction the arc driving force F.sub.2 due to the current i.sub.2, 
being perpendicular to the force F.sub.1 due to the current i.sub.1, will 
not drive the arc towards the side wall of the arc box, so that the arc C 
is driven towards the center of the end plate 203. At the same time, the 
arc current forms magnetic flux .phi. as indicated in FIG . 8, which 
creates a force F.sub..phi. to drive the arc towards the deepest point S 
of the V-shaped cut. Reference character F.sub.0 designates the resultant 
of the forces F.sub.1, F.sub.2 and F.sub..phi.. 
As is apparent from the above description, the deformation of the 
commutation electrode due to arc thermal stress can be Positively 
prevented, and the arc is always driven towards the center of the end 
plate according to the invention. Therefore, even when the power switch is 
operated a great number of times, damage to the arc box is prevented. 
In the third embodiment the V-shaped cut is employed; however, it may be 
replaced by a U-shaped cut. That is, all that is necessary is that the 
configuration of the cut allow the magnetic flux to form an 
electromagnetic driving force F.sub..phi.. 
While the invention has been described with reference to an electric power 
switch, the technical concept of the invention is equally applicable to 
other electric power switching means such as circuit breakers.