Electric Automatic Switch

Subject of the Invention

[001] The subject of the present invention is a low-loss electric automatic switch intended for the protection of electrical installations. The invention more specifically concerns a contact assembly. The switch with a contact assembly of the invention is preferably intended as a switch corresponding to size 1 according to DIN 43880 and has a module width 18 mm and more and it has low own power loss and assures selectivity.

Technical Problem

[002] The technical problem solved by the invention is how to conceive such contact assembly in an automatic switch of this type that will provide for circuit interruption within prescribed time upon prescribed over-current or rather upon prescribed short-circuit current and that at prescribed number of repeats of such interruptions, whereby the structure of the contact assembly should also be adequate for large-series production or even mass production in compliance with all standards, on the basis of which such product may appear on the market and that for a market acceptable price.

Prior Art

[003] The Slovene patent application P-2005 0 0358 (Eti Elektroelement d.d.) discloses an electric automatic switch comprising a contact assembly. This contact assembly is actuated by a striker pin comprised within a coil. When over-current occurs within the coil, the striker pin hits toward the switch assembly and opens the main contact by preserving the contact of the secondary circuit closed. Should the over-current be maintained within the protected circuit above the prescribed value and exceeding the prescribed time, a bimetal linked in series in the secondary circuit in the switch switches off the switch of the secondary circuit. The velocity of contact switch-off in the switch assembly is very high in short-circuit current. Further, said

switch reacts also when a short-cuircuit current occurs as a continuation of an over- current or independently due to defects in a protected circuit. All switch-off times of the protected circuit with said switch are standardised as to values of nominal current, over-current and short-circuit current, whereas the minimum number of perfect switches-off at prescribed various values is required.

[004] When conceiving a contact assembly of such electric automatic switch there is a problem of proper successive interrupting of the first and second contact in case of over-current and short-circuit current. A movable contact element is arranged between fixed contact elements with at least one spring. Due to potent butts of forces appearing during the operation of the electro-magnetic assembly, especially in case of short-circuit current, irregular interrupting of contacts appears, since a spring or springs cannot provide for the positioning of the movable contact element in this situation as foreseen or expected. Tests could not prove a sufficient number of repeats of switch-offs in case of over-current of the first contact only without the second contact opening simultaneously at least for a short moment. If also the second contact opens in case of over-current, the principle of operation of the electric switch breaks down and unacceptable disturbances appear, namely an electric arc between the contact elements of the second contact, which is not adapted to extinguish the electric arc due to spacial limitations of the switch then the fact that due to irregular opening of the second contact the regular/planned operation of the entire electric switch breaks down. The second contact makes it sure that upon the switch-off of the first contact a resistance and a bimetal are included in the circuit functioning as selectors. The switch-off of the second contact must occur exclusively due to the bending of the bimetal after over-current with a prescribed value and period has occured and/or manual switch-off of the on/off button.

[005] Since all these commutations happen in a few milliseconds due to the move of a striker pin, which is axially moved by a quickly appearing electro-magnetic field within the coil, said field caused by high over-current within the coil due to a

damage of an optional element in a protected circuit, the construction should be subjected to these forces in the switch in order to provide for proper functioning of the switch under the consideration of standards.

Solution to the Technical Problem

[006] The described technical problem is solved by a contact assembly of an electric automatic switch of the invention by preserved principal operation of the solution disclosed in the prior art in the patent application P-2005 0 0358 in a way that the movable contact element is arranged flexibly over a pressure spring on the rotatable electrically unconductive element set to operating mode by means of a manual knob and a switch arc. When increased current is present in a protected circuit, the bimetal deflects and by shifting a rotatable notch releases the switch lever, so that the spring instantly turns the rotatable electrically unconductive element together with the movable contact for such distance to avoid a harmful electric arc between the contact elements. The second contact may thus be devoid of means for arc extinguishing. The first contact, in which the appearance of an electric arc is to be expected upon opening is equipped with an extinguishing chamber. The movable contact element is attached to the electrically unconductive element by a spring pressing it against the fixed contact elements of the second contact. As the first contact opens due to the over-current in the coil caused by a shock of the striker pin comprised within said coil, the second contact always remains closed due to a brisk butt of the striker pin on the movable contact element due to the action of the spring pushing the movable contact against the fixed contact elements of the second contact in direction of the butt of the striker pin. In other words: the butt of the Strieker pin follows the direction of the force of the spring pushing the movable contact element against two fixed contact elements of the second contact, wherein the force of push of the movable contact element is direct proportional to the force of the butt of the striker pin thereon and thus to the over-current value size. In this way the opening of the second contact is prevented regardless of any opening of the first contact.

[007] A further characteristic of the invention lies in the fact that upon appearance of short-circuit current when the striker pin opens the first and closely afterwards the second contact within a veiy short time period, both contact spots of the second contact get successively opened in order to prevent the appearance of the arc on the second contact, which justifies the structure of the second contact without an extinguishing chamber.

[008] If the invention is to provide for large series production for a price acceptable on the market, it was necessary to conceive such new and simple structure of the second contact that will always ensure an efficient successive switching-off of both contact spots of the second contact. This is achieved by slantingly leaning one extremity of the movable contact that dictates the described successive switching-off of both contact spots of the second contact during the operation of the striker pin.

[009] The characteristics of the invention will now be described in the continuation by way of an embodiment and with reference to the enclosed drawings, in which:

Fig. 1 shows a wiring diagramme of the switch of the invention,

Fig. 2 shows a perspective and exploded view of a schematically shown switching assembly with a coil, Fig. 3 shows a schematic view of the switch of the invention in normal mode of a protected circuit, Fig. 4 shows a view of the switch of the invention in the mode of switch-off of the primary circuit in the switch upon appearance of over-current in the protected circuit Fig. 5 shows a schematic view of the switch of the invention in the mode of complete switch-off of the protected circuit when over-current appears in the protected circuit for a longer time than allowed, or upon the appearance of short-circuit current in the protected circuit.

[0010] The electric automatic switch consists of a housing I ₅ preferably any housing, meeting the standard and intended to be arranged on a busbar that is not shown on figures.

[0011] At one end of the housing there is a connection terminal 2 for a supply connection of the protected circuit not shown in figures together with electric devices included within this circuit. At the opposite end of the housing 1 there is a connection terminal 3 preferably identical to the terminal 2 intended for discharge connection of the same protected circuit.

[0012] Within the housing 1 there are two contacts 4 and 5 having a mutual movable contact element 6, wherein said element 6 is flexibly arranged on a pivotable and electrically unconductive element 7 that will be described in more detail at a later stage.

[0013] The connection terminal 2 is linked via current conductor 8 with a fixed contact element 9 of the contact 5. The second fixed contact element 10 of same contact 5 is connected via bus 11 to a resistance 12 and successively to a bimetal 13, which upon increased current flowing through therethrough triggers the electrically unconductive element 7 to pivot, wherein the movable contact element 6 is removable from both fixed contact elements 9 and 10 of the contact 5, which will be described in more detail in the continuation. The bimetal 13 is further connected to the fixed contact element 16 of the contact 4.

[0014] The movable contact element 6 comprises a contact element 15 engaging with the fixed contact element 16, which is electrically connected with the coil 17 and the latter with the terminal 3. The contact element 15, which is part of the movable contact element 6, and the fixed contact element 16 mutually form the contact 4. So there are two current branches between the terminals 2 and 3, i.e. a first

branch via the contact 4 and the coil 17 and another branch via the contact 5, the resistance 12 and the bimetal 13 in parallel to each other.

[0015] The coil 17 houses a striker pin 18 that acts when over-current in the protected circuit appears, i.e. in the branch between the terminals 2 and 3 via the contact 4, by briskly pivoting the movable contact element 6 in a way to interrupt the contact 4 and yet to keep the contact 5 closed. The entire electric current of the secured circuit is re-directed to the parallel branch from the terminal 2 via the contact 5, the resistor 12 and the bimetal 13 to the terminal 3. Once the over-current within the coil 17 has decreased to the normal value foreseen for the circuit protected by the device of the invention, a spring 17a preferably situated within the coil 17, returns the striker pin 18 to initial position. The core 17b of said coil 17 further houses an element 17c, preferably a short-circuit ring of a non-magnetic material that assures permanent magnetic field at alternate current.

[0016] A circuit conductor 8 originating in the terminal 2 is formed at the opposite end as a convex fixed contact element 9 leaning against a support 19 that is preferably a constituent part of the housing 1. The second fixed contact element 10 of the same terminal 5 is formed identically with the contact element 9 and leans against the same or reasonably similar support 19 co-axially with the contact element 9.

[0017] The electrically unconductive element 7 is rotatingly pivoted within the housing 1 by a bearing 20. The element 7 is further linked to the housing 1 via a spring 21 holding the element 7 upon normal operation of the protected circuit together with the bimetal and a knob 29 in such position that the movable contact element arranged thereon is in simultaneous electric contact with the fixed contacts 9, 10 and 16.

[0018] In each mode of the switch as a whole the proper position of the electrically unconductive element 7 is determined by a pivotable three-member

element 32. One member 32a is intended to engage with the support 33 on the housing 1, a second member 32b engages with the bimetal 13 and a third member 32c comprises a notch 32d, with which engages the Iever31 of the knob 29. As the three- member element 32 rotates due to the action of the bimetal 13 on the member 32b or due to the member 32a leaning against the support 33, the member 32c rotates in a way to discharge the engagement of the lever 31 and the spring 21 can thus rotate the electrically unconductive element 7 in a way to cause both terminals 4 and 5 to open.

[0019] Said rotation of the element 7 and consequently the switch-off of the protected circuit is achieved by one of the described reactions of the switch upon the appearance of over-current or short-circuit current.

[0020] The notch 32d is formed in a self-locking way. If the three-member element 32 is not rotated in any way as described above, the engagement of the lever 31 with the notch 32b is not openable. A person may thus use the knob 29 to manually open both contacts 4 and 5 any time, thus completely separating the protected circuit from the mains network.

[0021] The movable contact element 6 is formed in the shape of a cross. The upper extremity 26, as described above, serves to properly position the element 6 in each of its positions.

[0022] Cross members 30 of the element 6 are intended as complementary contact elements to fixed contact elements 9 and 10, wherein said contact elements form the contact 5.

[0023] The lower longest member 15 of the movable contact element 6 is intended as a complementary contact element to the fixed contact 16, which together form the contact 6.

[0024] Between the terminal 2 and the contact element 16 there is an extinghishing chamber 31 intended for the neutralisation of electric arc upon the opening of the contact 4.

[0025] On the electrically unconductive element 7 in the vicinity of the holder

22 there is a support 25 with a slanting contact surface 25a. The slantingness of the contact surface 25a is provided with respect to the imaginary common surface of contact elements 9 and 10. The slanted surface 25a is foreseen for the extremity 26 of the element 6 during the rotation of the element 7 (regardless of the cause of rotation: manual by the knob 29 or due to over-current causing bending of the bimetal 13) and during the rotation of the contact element 6 around fixed contact elements 9 and 10 to lean against the slanted surface 25a, wherein the spring 23 co-operates in a way that due to the slantingness of the surface 25a, successive opening appears, namely first of the fixed contact element 10 and the belonging member 30 of the element 6 and then of the fixed contact element 9 and of the second or belonging member 30 of the element 6. As already mentioned above, the successiveness of opening ensures the absence of arc upon opening of these contact elements and thus the redundancy of an extinguishing chamber.

[0026] After a defect due to which the switch of the invention interrupted the protected circuit, a manual turning of the knob 29 first closes the second switch 5 and that in series in reverse order, first the contact 10, follows the contact 9 and at the end the first switch 4 is also closed. In this way a regular most rapid response of the switch is ensured, if the defect would not be completely done away with and the switch would interrupt the circuit again.

[0027] The switch of the invention functions as follows: the current of the protected circuit flows from the terminal 2 via closed contact 5 through the contact element 6, via closed contact 4 to the coil 17 and to the terminal 3. From the contact element 10 of the contact 5 the current also flows through the resistance 12 and the

bimetal 13 to the terminal 3. Since the resistance 12 determines a considerably higher resistance of the branch of the contact 10 via bimetal 13 to the terminal 3 than that of the branch determined by the contact 4 and the coil 17, a relatively considerably higher current flows through said second branch.

[0028] When current appears in the coil 17 that exceeds the normative prescribed highest permitted current, which occurs in case of a breakdown on a user or circuit behind a switch, wherein it is foreseen that the circuits or users behind a switch are individually protected by quicker fuses, the induced magnetic field within the coil pushes the striker pin 18 towards the movable contact element 6 and switches the contact 4 off. The current only flows through the branch through the resistance 12 and the bimetal 13. Should in the protected circuit behind the switch reappear the current value lying below the normative prescribed nominal current within a standardised foreseen time interval, current intensity of the magnetic field within the coil 17 drops by the value to allow for the spring 21 to return the movable contact element 6 into the original position and thus also the striker pin 18. The contact 4 is closed again and the current flows along the primary circuit within the switch to the protected circuit. However, if the over-current is maintained in the protected circuit or a longer period of time, i.e. when a defect has not been removed, the bimetal 13 acts on the member 32b after a prescribed time interval is over, wherein the element 32 is rotated and the link of the notch 32d with the lever 31 is interrupted. The spring 21 can now freely turn the element 7 in order to open both contacts 4 and 5. The protected circuit is totally interrupted. The circuit can be closed anew only by the manual knob 29, with which an authorised person after a defect in the protected circuit was done away with, returns the element 7 to normal position, i.e. the element closes the contacts 4 and 5.

[0029] A repeated engagement of the lever 31 and the notch 32d upon manual rotation of the knob 29 is known and is not described herein in more detail.

[0030] The switch of the invention is manufactured by known technological procedures. Since the switch of this type is subject to standards, adequate materials need to be used for individual elements in order to resist the prescribed mechanical and electric loads. A special attention is to be paid to the electrically unconductive element and to the contact element arranged thereon. The time interval after which the switch totally switches the protected circuit off is determined by the construction of the bimetal 13.