Electromagnetically operated electric switch

A contactor has a movable contact assembly which is connected to the magnet armature in such a way that the contact assembly moves translatorily in the same direction as the armature between a closed and an open position. The contact assembly comprises a movable main contact with relatively small contact elements of silver alloy and a movable arcing contact with contact elements of silver-free material. The arcing contact makes and breaks the main current, whereas the main contact carries almost the entire current in closed position. The contacts have separate contact pressure springs. The contactor has at least one opening spring which is obliquely directed in relation to the direction of motion of the armature and is clamped between two bearing points, of which one is fixed whereas the other, upon operation of the electric switch, is displaced together with the armature in the same direction of motion. Thereby, the component of the spring force which counteracts the attractive force of the magnet will be reduced upon closing, which means that, despite double contact and spring systems, it is possible to use an operating magnet with relatively small dimensions.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an electromagnetically operated electric 
switch, for example a contactor, comprising an operating magnet, the 
armature of which, upon operation of the switch, performs a translatory 
movement. The armature is connected to the movable contact assembly of the 
electric switch in such a way that the contact assembly moves in the same 
direction as the armature between a closed and an open position. 
2. Prior Art 
Normally, the contact assemblies of large contactors are designed with a 
movable main contact and one or more fixed main contacts in each phase. To 
reduce the risk of contact welding and increase the life of the contacts, 
the contacts are normally provided with contact elements of some silver 
alloy, for example silver cadmium oxide. Silver alloys are expensive 
materials, and the cost of said contact elements constitutes a not 
insignificant part of the price of a contactor. It is therefore desirable 
to reduce the required amount of silver. 
In prior art contactors, it has been proposed to use separate movable main 
contacts and arcing contacts with separate spring systems (see e.g. German 
Auslegeschrift No. 1 237 667 and French patent specification No. 1 431 
326). In such a design, the arcing contacts make and break the main 
current, whereas the main contact for the most part carries the current in 
closed position. A drawback in connection with the proposed contactors 
with double contacts is, however, that they require a relatively great 
operating power for the closing operation, since prior art contactors of 
this kind are provided with helical type opening springs, which are 
disposed in the direction of movement of the magnet armature. These 
springs are arranged to influence directly a contact carrier, fixed to the 
magnet armature, with a returning force acting against the attractive 
force of the magnet. Upon closing of such a contactor, the opening springs 
are compressed, the counter force from the springs thus increasing with 
reduced magnet air gap. Since the operating magnet at the final stage of 
the closing must also overcome the counter force from the contact pressure 
springs, it is necessary to use, in such a design, a relatively strong 
operating magnet. This has an adverse effect on the dimensions, price and 
power consumption of the contactor. 
It is also known (for example, from German Auslegeschrift No. 1 140 263 and 
U.S. patent specification No. 3,873,952), in a contactor with a 
conventional contact system, to arrange its opening springs in such a way 
that the returning force emanating from the springs is reduced upon 
closing. 
SUMMARY OF THE INVENTION 
The object of the present invention is to be able to reduce, in an 
electromagnetically operated electric switch, the required amount of 
silver in the contact system without simultaneously having to increase the 
dimensions of the electric switch. According to the invention, this is 
achieved by a combination of 
(a) a contact system with one movable main contact and one movable arcing 
contact, which are influenced by different contact pressure springs, and 
(b) a magnet system with a so-called degressive opening spring. 
By using separate movable main contacts and arcing contacts with separate 
spring systems, where the arcing contact makes and breaks the main current 
whereas the main contact for the predominant part, for example to about 
95%, carries the current in closed position, the contact elements of the 
arcing contacts may consist of a silver-free material, for example copper 
cadmium oxide or copper-tungsten, and only the main contacts need be 
provided with contact elements of silver-containing material. Since the 
main contacts make and open in an approximately arc-free manner, the 
contact wear on these contacts is small and therefore the contact elements 
may be relatively small. The total silver content in such a contactor can 
therefore be reduced considerably. In addition, by using an opening spring 
with a negative force characteristic, the advantage is obtained 
that--despite double contact and spring systems--it is sufficient with an 
operating magnet with relatively small dimensions without reducing the 
demand for reliable closing in one stage. This results in lower costs and 
lower power consumption.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The contactor shown in the drawing has three poles and has a rated voltage 
of, for example, 660 V. The rated current of the contactor may, for 
example, be in the range of from 40 to 800 A. The contactor is built up on 
a stand 1 of pressure-cast light metal. The stand supports a plastic 
holder 2 with connection bars 3, 4 for connecting the contactor into an 
external main circuit. 
The contact assembly of the contactor, shown in the open position on the 
drawing, is surrounded by an arc chute 5 of plastics material (FIG. 2) 
provided with arc extinction plates 6. The contact assembly comprises in 
each pole two electrically series-connected breaks which are arranged in 
respective breaking chambers 7, 8 formed in the arc chute. Each break has 
a fixed contact 9 and 10, respectively, which is attached to the 
connection bar 3 and 4, respectively. In closed contact position, the 
fixed contacts are connected to each other by a bridge contact assembly, 
which comprises a movable main contact 11 and a movable arcing contact 12. 
The bridge contact assembly is mounted in an opening 13 of a contact 
carrier 14 which is connected to the armature 15 of the operating magnet 
of the contactor, the magnetic core and coil of which are designated 16 
and 17, respectively. The armature 15 is influenced by four opening 
springs 18 (FIGS. 2-4). When the coil 17 is nonenergized, these springs 
press the armature 15 to the position shown on FIG. 2. The bridge contact 
assembly 11, 12 passes between the legs 19 of a U-formed yoke 20, which is 
axially movable in the contact carrier 14. The free ends of the yoke legs 
19 are interconnected through a pin 21. Between this pin and the movable 
arcing contact 12 there is a leaf spring 22. 
In the yoke 20, two contact pressure springs 23, 24 in the form of helical 
springs having different diameters are coaxially arranged. The spring 23, 
which has the smaller diameter, is connected to the movable main contact 
11 via a centrally arranged pin 25, whereas the larger spring 24 
influences the movable arcing contact 12 via the yoke 20, the pin 21 and 
the leak spring 22. 
The movable contact 11 may suitable be made of, for example, copper and 
provided with a contact element 26 of silver alloy, for example 
silver-cadmium oxide, at either end to carry out the electrical contact 
function. 
The movable arcing contact 12 may suitably be made of, for example, steel 
and provided with a contact element 27 of silver-free contact material, 
for example copper-cadmium oxide or copper-tungsten, at either end. 
The fixed contacts 9, 10 may suitably be made of copper and be provided 
each with two contact elements 28, 29 arranged in different planes. The 
contact elements 28 are arranged to cooperate with the contact element 26 
of the movable main contact 11 and are made of the same silver alloy as 
these. The other contact elements 29 of the fixed contacts cooperate with 
the contact elements 27 of the arcing contact 12 and are made of the same 
silver-free material as these. The fixed contacts 9, 10 are further 
provided with arc horns 30. 
The opening springs 18 (FIGS. 2-4) are helical springs mounted on 
individual supporting pins 31, which are obliquely directed in relation to 
the direction of movement of the contact carrier 14. At one end the pin 31 
is guided in a hole 32 in a bearing housing 33 and at its other end 
rotatably journalled at a bearing point 35 on a returning pin 34. The 
supporting pin 31 is pressed against the bearing point 35 by the spring 
18, which rests against the bearing housing 33 and, via the pins 31 and 
34, influences the contact carrier 14 in a contact-opening direction. The 
contactor has two returning pins 34 arranged on one side each of the 
operating magnet 16, 17. Each such returning pin is influenced by two 
opening springs 18 (FIG. 4), arranged in V-form, which are arranged on 
opposite sides of the pin 34. 
Upon closing of the contactor, the attractive force of the magnet increases 
as the magnet air gap decreases. During the first part of the closing 
operation, the magnetic force is counteracted only by the opening springs 
18, the angular position of which is changed as the returning pins 34 are 
being displaced, whereby the component of the spring force which 
counteracts the magnetic force is reduced. The movable contact assembly 
will thereby be rapidly accelerated. At the final stage of the closing 
operation, the total counter force is increased intermittently in two 
stages when first the contact making of the arcing contacts 12 and 
thereafter the contact making of the main contacts 11 occurs. Thus, in 
addition to the counter force from the opening springs 18, the magnet also 
has to overcome the counter forces from the contact pressure springs 24 
and 23. However, since in this position the counter force of the opening 
springs is smaller than in the open position of the contactor, it is 
sufficient to have a lower magnetic attractive force and thus a smaller 
contactor magnet than with a conventional spring arrangement. 
Upon closing, the arcing contact breaks 27, 29 make before the main contact 
breaks 26, 28, whereas upon opening the arcing contact breaks open after 
the main contact breaks. In this way, the advantage is obtained that the 
main contacts make and open in an approximately arc-free manner, whereby 
the wear on these contacts is low. Therefore, the contact elements 26, 28 
can be small, for example smaller than one-third of the volume of the 
contact elements 27, 29 of the arcing contacts. Thus, the necessary amount 
of silver is relatively small, which means that the cost of the contact 
can be considerably reduced.