The technical problem successfully solved by the invention in question involves the design and the construction of such switching element that will allow for successful replacement of a combination of several contactor elements, in particular in those applications where one element may replace a combination of two or three contactors, such as required in the existing solutions and constituting an assembly where the power and the control sections between the contactors must be correctly wire-connected, unless the assembly may be damaged or even destroyed.

The existing solutions solving the imposed technical problem, e. g. that of the start up and operation of electromotors with the power exceeding 4 kW, contain three standard contactors and a time switch relay for star-to- triangle switching. Correct operation of such assembly requires correct wire-connection of power contacts of all three contactors, which is

physically more difficult in assemblies of greater powers that involve wires of bigger cross-sections.

The constructional concept of the switching element referred to in this invention provides for three independent positions, which is via the transmission elements transmitted into the contact section where the mobile support of flexible contacts with its movement closes the corresponding contacts, which first provides for electromotor power supply -star (Y)-with reverse connection to the star point, and upon the lapse of certain time, for power supply-triangle (D)-which corresponds to the rated voltage of the electromotor winding, double-step start-up Y-D. The contact system provides smooth operation and significantly simplifies the traditional contactor combinations through the use of three contactors and a time-switch relay. The switching time is adjustable and depends on the load driven by the electromotor, while the starter position is signalized.

The star-to-triangle switching element, such as referred to in this invention, will be explained in detail on the basis of the concrete example and the corresponding figures, showing the following: Figure 1 Star-to-triangle switching element, such as referred to in this invention, cross-section and front view; Figure 2 Star-to-triangle switching element, such as referred to in this invention, cross-section and longitudinal view;

Figure 3 Star-to-triangle switching element, such as referred to in this invention, cross-section and top view; Figure 4 Star-to-triangle switching element, such as referred to in this invention, cross-section and lateral view.

The driving element consists of two fixed armatures 1 and one mobile armature 2. The fixed armatures 1 bear, attached with special loops 3, the coils 4,5, each of them in the make state representing one make state of the switching element referred to in this invention. Suspended between them is the armature 2 in the form of letter E; it moves along lateral metal guides 6 that at the same time provide for adequate spacing of the fixed armatures 1. The mobile armature 2 in the break state of the coils 4,5 is idle, which represents the third, off position of the element. The mobile armature 2 transmits the force over a steel support 7 and over a transmission lever 8 to the mobile support 9 of the flexible contacts 10, 11,12 in the contact section of the switching element.

The input fixed contacts L1, L2, L3 are located on one side of the switching element, and the output fixed contacts U1, V1, W1 and U2, V2, W2 on the other side, which corresponds to the marking of the electromotor connection plate. The contacts are covered by two insulation covers 31 with openings for connection wires.

In case of the coil 4 in the make state the mobile support 9 bearing the contacts 10,11 12 moves to position a. The load current flows from the input fixed contacts L1, L2, L3 via the mobile contacts 11 to the output fixed contacts U1, V1, W1 and through the wires to the electromotor winding. The ends of the winding are connected to the fixed contacts U2, V2, W2, where the star-point 13 is closed via the mobile contacts 10. The electromotor winding is supplie with the voltage 230 V (Y) and the motor rotor achieves 2/3 rated rotations. Upon the lapse of the start-up time, the coil 4 becomes inactive, while the coil (5) becomes active and causes the mobile support 9 with contacts 10,11,12 to move to the position b.

Thereby the star-point 13 opens and the current flows via the flexible contacts 11,12 and permanent contacts U1, V1, W1 and U2, V2, W2 into the electromotor winding. At this moment the electromotor winding is supplied with 400 V (D) voltage, which is the electromotor winding rated voltage, the rotor achieves rated rotations and accordingly provides permanent operation.

The star-to-triangle switching element is controlled as every traditional contactor, either only with the switch 01 or via the ON/OFF key of the existing remote switch; it can be mounted on a standard carrier strip or fixed with screws.