Switch for high voltages
The invention relates to a switch for high voltages comprising at least one spherical, stationary contact and a spherical, movable contact co-operating therewith said stationary contact having a segment-shaped recess on the side facing the movable contact when the latter is in its on-position, said recess being covered in the off-condition of the switch by an electrically conductive potential screen complementing the spherical shape and occupying a position inside the sphere in the on-condition of the switch. Such a switch is known from Dutch Pat. No. 136,432 to which U.S. Pat. No. 3,657,504 corresponds. 
     In this known switch a contact member is mounted in the stationary contact next to the potential screen. The contact member may be annular and is engaged by a contact pin provided on the movable contact. In order to obtain between contact pin and contact member a sufficiently large contact surface to satisfy the requirements accurate positioning of the movable contact with respect to the fixed contact is required. Therefore, in the case of a rotatable contact the angle of rotation from the off-position to the on-position should be very accurately defined. Moreover, the permitted tolerances of the connection of the movable contact with the guiding arm and of that of the fixed contact with the voltage bar are very limited. 
     The object of the invention is to obviate the aforesaid disadvantages. According to the invention this is achieved in that the contact surface of the stationary contact intended to conduct the main current is formed by the potential screen. The measure according to the invention makes it possible to obtain a sufficiently large contact surface between the movable contact and the stationary contact at considerably less accurate positioning. This is particularly so when in a preferred embodiment the contact surface is formed by one or more contact fingers movable parallel to themselves and to one another. The contact fingers are relatively independently movable and the extent of the movement of the contact fingers towards the inside of the sphere is, therefore, completely determined by the position of the stationary contact with respect to the movable contact. The contact fingers may be arranged so that the or each contact finger is movable only in a direction at right angles to the base plane of the spherical segment. The potential screen may also consist of one or more pivotable contact fingers. The pivot of the or each contact finger may then be located near the spherical surface of the stationary contact. This construction of the potential screen is particularly advantageous when employed in a switch, in which the movable contact is adapted to move parallel to the base plane of the ball-segment-shaped recess of the stationary contact. 
     The invention will be elucidated more fully with reference to embodiments shown in the accompanying drawing. 
    
    
     In the drawing: 
     FIG. 1 is a sectional elevational view of a switch in accordance with the invention, 
     FIG. 2a is an elevational view of the stationary contact in accordance with the invention, 
     FIG. 2b is a sectional elevational view of the contact shown in FIG. 2a, 
     FIG. 2c is an elevational, sectional view taken on the line II--II in FIG. 2b, 
     FIG. 3 is a sectional elevational view of a further embodiment of the stationary contact, 
     FIG. 4 is a sectional elevational view of a third embodiment of the invention, and 
     FIG. 5 is a diagrammatic view illustrating certain principles of the invention. 
    
    
     The voltage bars 1,2 and 3 (FIG. 1) associated with the three phases of a multiphase busbar system are provided with the respective stationary contacts 4,5, and 6 of the isolator switch 7. The isolator switch is adapted to move from the closed position, as shown, to the opened position by turning in the direction indicated by arrows A. As noted above, each contact is adapted to move parallel to the base plane of the ball-segment-shaped recess of its associated stationary contact. Such a base plane is illustrated at P in FIG. 5 and, for each stationary contact 4, 5, 6, such base plane is of consequence parallel to the plane within which the direction line L in FIG. 1 lies. In the closed position a connection is established between the movable spherical contact and the associated stationary contact, for example, contacts 8 and 5; 9 and 6. The stationary contact comprises a potential screen serving also to conduct the main current. The stationary contact of FIG. 2 comprises a plurality of contact fingers 10 approaching together the spherical shape, said fingers being movable parallel to themselves and to one another in a direction at right angles to the base plane P of the spherical segment. Each contact finger, for example 10, has a reset spring 11. The fingers are guided by pins, for example 12. Arranged centrally between the contact fingers is an intermediate piece 13 of synthetic resin. The current path extends through the fingers 10 to the housing 21, whilst the spring 20 bearing on the intermediate piece 13 provides the required contact pressure. 
     In the embodiment shown in FIG. 3 the contact fingers are pivoted about an axis. The contact finger 14 is pivoted about the axis 15 and is biassed by a reset spring 16. 
     In the embodiment shown in FIG. 4 the contact fingers are also pivoted about an axis. The contact finger 17 is adapted to swing about the axis 18 and is loaded by the reset spring 19. 
     FIG. 5 illustrates how the potential screen of a stationary contact cooperates with a movable contact. The fingers 14 are as shown in FIG. 3, being movable about their axes 15. The movable contact 9, being movable back and forth as indicated by the double arrow direction line parallel to the plane P and that of line L in FIG. 1, engages the tips T of the fingers to swing them inwardly within the envelope E. The envelope E is the spherical extension of the body 6. The tips T normally lie in a plane parallel to plane P and on or substantially on such envelope as will be evident from FIG. 3. However, when the movable contact engages them as shown in FIG. 5, the tips T are depressed inwardly of the envelope E and lie in a plane, again parallel to the plane P, and on the contact 9.