Electrical switch contact arrangement having quick break arcing contacts

An electrical switch contact arrangement having a spring which snaps the movable arcing contact away from the stationary arcing contact at a high rate of speed to open the arcing contacts, but only after the movable main contact has moved through a considerable portion, for example, at least about 50%, of its opening movement away from the stationary main contact. The spring is tensioned as the main contacts open. At an intermediate point during the opening movement of the movable main contact, the moveable main contact positively initiates opening movement of the arcing contacts whereupon the spring snaps the arcing contacts open at a high rate of speed independent of the opening speed of the main contacts.

BACKGROUND OF THE INVENTION 
Industrial type switches, such as transfer switches, contacters, circuit 
breakers, and interrupters, are required to handle heavy electrical loads, 
typically comprising hundreds and even thousands of amperes at voltages 
ranging up to 15,000 volts AC and 1,500 volts DC. 
Every switching operation produces arcing between the cooperating switch 
contacts, and when the electrical load being handled is heavy, the arcing 
created has the potential to cause considerable damage to the contacts. To 
mitigate this problem, it is customary to protect the main contacts, which 
carry the load, with arcing contacts which open after the main contacts 
open and close before the main contacts close. Thus, in theory, the arc is 
drawn only between the arcing contacts and not between the main contacts. 
The latter are formed of relatively soft, good conducting metals, such as 
silver or copper, which have low melting points and hence are very 
susceptible to damage by uncontrolled arcing. The arcing contacts are made 
of materials, such as refractory metals, e.g., tungsten, capable of 
withstanding extremely high temperatures while experiencing only moderate 
erosion. Nevertheless, the sacrificial activity of arcing contacts does 
eventually lead to damage, but they are easily field replaceable. 
A problem develops due to the fact that the impedance of the arcing 
contacts is much higher than that of the main contacts. As a result, 
during opening of a switch, when all current flowing through the main 
contacts is transferred to the arcing contacts, a voltage drop is created 
across the main contacts while the air gap between them is still quite 
small. Consequently, on occasion, an arc is engendered between the 
separating main contacts potentially damaging to those contacts. If the 
current level is sufficiently high, unacceptable damage can occur 
rendering the main contacts unusable, thereby requiring major repair or 
replacement of the switch. The problem becomes more acute if, at the 
critical moment of main contact separation, the arcing contacts bounce or 
are otherwise disturbed in a manner which increases their impedance. 
Environments in which the damage of arcing between the main contacts is 
particularly severe are those in which the switch is called upon to handle 
excessive motor loads or transformer inrush currents which are by their 
nature highly inductive. Thus, when switching highly inductive loads on a 
DC circuit, such as traction motors in a typical transit system, it is 
important to ensure as much as possible that all arcing takes place across 
the arcing contacts and none across the main contacts. 
Even when an arc is confined to the arcing contacts, it is important that 
the arc be extinguished as quickly as possible. Rapid quenching of the arc 
not only minimizes erosion of the arcing contacts, but reduces the 
opportunity for the arc to jump into the gap between the opening main 
contacts. 
From the discussion above, it will be appreciated that arcing across, and 
consequent damage to, the main contacts can be eliminated or at least 
greatly reduced, by insuring as large an air gap as possible between the 
opening main contacts before the arcing contacts begin to separate, and by 
thereafter insuring very rapid opening of the arcing contacts. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide an electrical 
switch contact arrangement having arcing contacts spring-biased to open at 
very high speed after the main contacts have opened and have initiated 
opening of the arcing contacts. 
It is another object of the invention to provide such an electrical switch 
contact arrangement wherein the movable main contact moves through at 
least one half of its opening movement away from the stationary main 
contact before opening of the arcing contacts is initiated. 
It is a further object of the invention to provide such an arrangement 
wherein the speed of opening of the arcing contacts is independent of the 
rate at which the main contacts open. 
It is an additional object of the invention to provide such a switch 
contact arrangement wherein the spring for driving the movable arcing 
contact to its open position is tensioned during the first part of the 
opening movement of the movable main contact. 
It is yet another object of the invention to provide such an arrangement 
wherein the movable main and arcing contacts move together during their 
closing movement, the arcing contacts closing before the main contacts 
close. 
It is still a further object of the invention to provide such an 
arrangement wherein the movable arcing contact is gripped against movement 
during the tensioning of its opening spring so that the spring is 
ineffective until opening of the arcing contacts is positively initiated.

The switch chosen to illustrate the present invention is used to connect or 
disconnect a power source bus 10 and a load bus 11 (FIG. 1). A mounting 
block 12 is fixed to source bus 10, and another mounting block 13 is fixed 
to load bus 11. Block 12 carries the stationary contacts of the switch, 
and block 13 carries the movable contacts. 
Mounted within block 12 is a stationary main contact arm 14, (FIGS. 1 and 
5) carrying at its lower end stationary main contact 15. Contact arm 14 is 
actually capable of a small degree of arcuate movement about pivot axis 
16, and is constantly urged toward the left, or clockwise, in FIG. 1 by a 
spring 17. This spring-backed mounting insures good contact between the 
stationary and movable main contacts. 
Secured to the top of block 12 are a pair of parallel plates 20 (FIGS. 1, 
5, and 6) constituting the stationary arcing contact. The plates 20 are 
held by, and swingable about, a bolt 21 threaded into block 12. Block 12 
also carries a stationary post 22 from which headed pins 23 project 
through the holes in plates 20. Compression springs 24 surround pins 23 
and seat against the heads of the pins and the plates 20 so as to 
constantly urge the plates toward each other. At its end opposite bolt 21, 
each plate is formed with a ridge-like protuberance 25, the two 
protuberances opposing each other. That end of each plate 20 is also 
formed with an arc-guiding tail 26 having an angled edge 27 which diverges 
from an angled edge 28 of the movable arcing contact. As an arc moves 
upwardly along these diverging edges it is lengthened and hence more 
easily extinguished. 
Mounted within block 13 is a movable main contact arm 31 (FIGS. 1 and 5) 
carrying at its upper end movable main contact 32. The latter is 
engageable with contact 15, as shown in FIG. 1, to close the main contacts 
of the switch. Contact arm 31 is pivotable with respect to block 13 about 
pivot axis 33 Movable main contact arm 31 carries two lateral projections 
in the form of pins 34. A bracket 35 is fixed to contact arm 31, the 
bracket including two fingers 36 at its lower end, bent at right angles to 
the body of the bracket, and a tongue 37 at its upper end bent out of the 
plane of the bracket body. Tongue 37 carries a detent in the form of a set 
screw 38. 
A movable arcing contact assembly includes two brackets 41 (FIGS. 1 and 5) 
pivoted at their lower ends in block 13 about the same axis 33 around 
which contact arm 31 is pivoted. Around its midpoint, each bracket 41 is 
bent toward the other, at which point a tab 42 extends from each bracket, 
and closer to their upper ends the brackets are bent again to define two 
parallel heads 43. Sandwiched between heads 43 is the lower end of a 
movable arcing contact 44 having a blade-like configuration. Depending 
from arcing contact 44 is a stop 45 engageable by detent 38. 
Near its upper end, the arcing contact blade 44 is formed in its opposite 
faces with depressions 46 (FIG. 6) which accommodate the protuberances 25 
of plates 20. Due to the force exerted by springs 24, protuberances 25 are 
pressed tightly into depressions 46 so that the stationary arcing contact 
plates 20 securely grip the movable arcing contact blade 44 when the 
switch is fully closed (FIGS. 1 and 6). 
The edge of each bracket 41, near pivot axis 33, constitutes an abutment 47 
located in the path of movement of one of the projections 34 carried by 
contact arm 31. During opening movement of contact arm 31 away from 
contact arm 14, projections 34 engage abutments 47 to initiate opening 
movement of the arcing contacts. A tension spring 48 extends between each 
finger 36 of bracket 35 and a tab 42 of one of the brackets 41. Springs 48 
serve to quickly snap the arcing contacts open after opening is initiated 
by the cooperative engagement of projections 34 and abutments 47. 
A conventional operator means for the switch involves a toggle arrangement 
including two schematically-indicated links 51 and 52 pivoted together at 
53. Link 52 passes through a hole 54 (FIG. 5) in bracket 35 and is 
pivotally connected at 55 to movable main contact arm 31. When the switch 
is closed, links 51 and 52 are aligned, as shown in FIG. 1. 
When the switch is to be opened, link 51 is rotated about axis 56 in the 
direction of arrow 57 (FIG. 2), thereby causing movable main contact arm 
31 to pivot and separate movable main contact 32 from stationary main 
contact 15 to open the main contacts, without at first disturbing the 
fully closed condition of the arcing contacts 20 and 44. Since bracket 35 
moves with contact arm 31, but arcing contact assembly 41,44 has not yet 
moved, springs 48 are tensioned, and detent 38 moves away from stop 45. 
When contact arm 31 moves through at least one-half, and preferably 60%, of 
its total travel away from contact arm 14, projections 34 carried by arm 
31 engage abutments 47 of brackets 41, as shown in FIG. 2. Upon such 
engagement, continued opening movement of contact arm 31, by links 51 and 
52, causes contact arm 31 to positively move the movable arcing contact 
assembly 41,44 in a counterclockwise direction in FIG. 2 resulting in the 
initiation of the opening movement of the arcing contacts. Specifically, 
this means that arcing contact blade 44 begins moving out from between 
stationary arcing contact plates 20, so that protuberances 25 disengage 
from depression 46, while the blade and plates remain in contact. However, 
once the grip of plates 20 on blade 44 is relieved in this way, tensioned 
springs 48 snap movable contact blade 44 away from stationary contact 
plates at a high rate of speed to very rapidly open the arcing contacts. 
The fully open switch is shown in FIG. 3, wherein springs 48 have returned 
to the degree of tension they had when the switch was fully closed, and 
stop 45 has reengaged detent 38. 
To close the switch, link 51 is rotated in the direction of arrow 58 in 
FIG. 4. Links 51 and 52 move contact arm 31 toward contact arm 14, and 
this movement is transmitted to arcing contact assembly 41,44 through 
bracket 35, detent 38, and stop 45. In this way, both the movable main and 
arcing contacts move in unison toward the switch-closed condition. As 
shown in FIG. 4, movable arcing contact 44 engages stationary arcing 
contact 20 before movable main contact 32 engages stationary main contact 
15, i.e., the arcing contacts close prior to closing of the main contacts. 
Upon further movement of contact arm 31 from its position in FIG. 4 to the 
position of FIG. 1, main contacts 32 and 15 engage and contact arm 14 
moves slightly against the force of spring 17. At the same time, movable 
arcing contact blade 44 is positively driven between the stationary arcing 
contact blades 20 until protuberances 25 snap into depressions 46. 
It will be appreciated that the movable arcing contact 44 is positively 
driven into its closed position, by means of detent 38 and stop 45, and 
that opening of the arcing contacts is positively initiated, by means of 
projections 34 and abutments 47, with a lost motion provided between these 
two drives. The lost motion provided by the spacing between projection 34 
and abutments 47, as well as the one-way drive action of detent 38 and 
stop 45, present the opportunity for springs 48 to rapidly open the arcing 
contacts independent of the speed of opening of the main contacts. 
The invention has been shown and described in preferred form only, and by 
way of example, and many variations may be made in the invention which 
will still be comprised within its spirit. It is understood, therefore, 
that the invention is not limited to any specific form or embodiment 
except insofar as such limitations are included in the appended claims.