Contact arrangement

Abstract: The invention relates to a contact arrangement designed as a catch connector and primarily intended for use in withdrawable apparatus for locking the plug-in contacts of the apparatus in the operating position when a short-circuit current flows through the apparatus. The arrangement comprises two contact members (40, 50) which are displaceabe in relation to each other, as well as a plug-in contact device (16) which is supported by the first contact member (40) and is insertable into the second contact member (50). The two contact members (40, 50) each have two contact surfaces (43, 44 and 54, 55, respectively) facing each other. The contact device (16) comprises two cooperating elongated contact members (20, 30) with transversally projecting end portions. The two contact members form two electrically parallel-connected current paths between the two contact members. At the two end portions of the contact device, the current paths intersect each other, whereas in a relatively long middle portion of the contact device the current paths are parallel to each other thus generating an electrodynamic contact pressure reinforcement. The above-mentioned second contact member (50) has two parallel and each other opposing legs, each of which exhibits a tongue (51) which is arranged inside a locking strip (53) formed by the free end portion of the leg. Each tongue forms a contact surface for cooperation with the plug-in contact device (16). Upon a short circuit, current forces are generated which attract the two contact members (20, 30) of the contact device towards each other and force the end portions of the contact members in behind the locking strips (53), thus preventing contact separation.

Description: The invention relates to a contact arrangement according to the precharacterising part of claim 1. The arrangement is primarily intended for use in withdrawable apparatus which, in case of a short circuit, are traversed by high current, for example truck-mounted high-voltage circuit breakers. Upon a short-circuit, a truck-mounted high-voltage circuit breaker is subjected to large ejection forces. The forces result in deflection of the poles, and attempt to move the truck in the direction of travel. If the movement becomes larger than the contact engagement, the circuit breaker will break down. US-A-4 596 438 describes a plug-in contact device for connection of two bars which are displaceable in relation to each other and each of which exhibits a contact slot with two confronting parallel contact surfaces. The contact device comprises two cooperating elongated contact members which are influenced by a contact pressure spring and form two electrically parallel-connected current paths between the two bars. At the two end portions of the contact device the current paths intersect each other, whereas in a relatively long middle portion of the contact device the current paths extend parallel and relatively close to each other, whereby the contact pressure is automatically increased upon an inrush current due to the electrodynamic forces arising. The invention aims at developing a contact arrangement of the above-mentioned kind with a catch connector by means of which the above-mentioned problems in, for example, truck-mounted high-voltage circuit breakers can be eliminated. To achieve this aim the invention suggests a contact arrangement according to the introductory part of claim 1, which is characterized by the features of the characterizing part of claim 1. Further developments of the invention are characterized by the features of the additional claims. In the device according to the invention, the current forces are utilized to keep the contacts of the circuit breaker in position in case of an inrush current. In this way, the breaker poles can be dimensioned according to the other stresses and the locking of the truck can be made simpler. The device is to a certain extent based on the contact device described in the above-mentioned US-A-4 596 438 but has been improved according to the invention to be used for other purposes. By way of example, the invention will now be described in greater detail with reference to the accompanying drawings showing in Figure 1a truck-mounted circuit breaker connected to a high-voltage switchgear and provided with a contact arrangement according to the invention, Figures 2 and 3 the contact arrangement in a side view and a plane view, respectively, during normal operation, Figure 4 the contact arrangement in a side view when a short-circuit current flows therethrough. The high-voltage circuit breaker 1 shown in Figure 1 is designed for a rated voltage of 72.5 kV and comprises three poles, only one of which is shown in the Figure 1. The breaker is mounted together with its operating device 2 on a carriage 3, which can be displaced between an operating position and a disconnected position by means of a hand crank or a motor. By devices for interlocking of the carriage in the positions mentioned, faulty operation is prevented. Each breaker pole has a breaking unit 5 which is supported by a hollow support insulator 4 and accommodates the current-interrupting contacts of the breaker pole. Closing and opening of the circuit breaker are achieved by the operating device 2 via an insulating operating rod arranged in the support insulator 4. The breaking unit 5 is provided with an upper and a lower connecting member 6 and 7, respectively, to which fork-shaped plug-in contacts 8 and 9, respectively, are fixed. In the operating position of the circuit breaker, the plug-in contacts 8 and 9 are conductively engaged with fixed contact bars 12 and 13, respectively, supported by support insulators 10 and 11. The upper contact bar 12 may, for example, be connected to a busbar, and the lower contact bar 13 may be connected to an outgoing line. If a short-circuit current flows through the circuit breaker, the breaker poles are subjected to great mechanical forces which in the absence of suitable preventive measures can cause a deflection of the poles to the position indicated by the dash-dotted lines 1'. This may cause contact separation at the contact point 8, 12 before the current has been broken in the breaking unit 5. Such contact separation would result in the creation of an arc between the contact points 8, 12 which may lead to a breakdown of the circuit breaker and other damage to the switchgear. To prevent the deflection of the breaker poles described above, a catch connector, influenced by the current, is arranged according to the invention parallel to the contact points 8, 12. This connector, which is shown separately in Figures 2-4, comprises a plug-in contact device 16 which is supported by a first contact member 40 which is fixed to the upper connecting member 6 of the circuit breaker and which, in the operating position of the circuit breaker, is inserted into a second contact member 50 fixed to the fixed contact bar 12. The plug-in contact device 16 is, in principle, designed as described in the above-mentioned US-A-4 596 438. It comprises two elongated contact members 20 and 30 and a surrounding spring 17. The contact members 20, 30 are each made with a plane rectangular middle portion 21 and 31, respectively, and two end portions extending from the plane of the middle portion in the same direction transversely to the longitudinal extension of said middle portion. One of the end portions consists of a middle contact tongue 22 and 32, respectively, located in the symmetry plane of the respective contact member, whereas the other end portion consists of two side contact tongues 23, 24 and 33, 34, respectively, located on either side of the symmetry plan. The gap between the side contact tongues is larger than the thickness of the middle contact tongue. The two contact members 20, 30 in the contact device are positioned so as to face each other such that the middle contact member 22 of the contact member 20 enters between the side contact tongues 33, 34 of the contact member 30, whereas the middle contact tongue 32 of the contact member 30 enters between the side contact tongues 23, 24 of the contact member 20. The spring 17 consists of a leaf spring, bent substantially into U-shape, which surrounds the contact members 20, 30, the legs of the spring being formed with spring arms 18, 19 extending in opposite directions in the longitudinal direction of the contact members. The plug-in contact device 16 is fixed in a slot 41 in the contact member 40 which is supported by the upper connecting member 6 of the circuit breaker. The contact member 40 is provided with locking edges 42 which are arranged such that the end portion 22, 33, 34 of the plug-in contact device 16 can be pressed into the slot 41, whereupon the locking edges 42 retain the contact device 16 in the contact member 40. The slot 41 is formed with confronting contact surfaces 43, 44 with which the end portions of the contact members 20, 30 of the plug-in contact device make contact. The second contact member 50 fixed to the upper stationary contact bar 12 consists of a substantially U-shaped yoke made of resilient sheet of, for example, beryllium copper. The yoke may be composed of two L-shaped parts, as shown in Figure 2, or be made in one piece. A tongue 51 is punched in each leg of the yoke for forming a locking hole 52 located inside a locking strip (53) formed by the free end portion of the leg (Fig. 3). The confronting flat sides of the two tongues form contact surfaces 54, 55 facing the end portions 23, 24 and 32, respectively, of the contact members 20 and 30, respectively, of the plug-in contact device. Between the upper ordinary plug-in contact device 8, 12 of the circuit breaker and the parallel-connected catch connector 16, 40, 50, a division of current takes place, whereby only a small part of the total current passes through the catch connector. At normal operating current the force generated by the current through the two contact members 20, 30 and acting as an attractive force between the middle portions of the parallel contact members 20, 30 is relatively low; thus the resilient tongues 51 of the contact member 50 are not significantly influenced but retain their position in the plane of the yoke legs according to Figure 2. On the other hand, if a short circuit arises in the circuit into which the circuit breaker is connected, a heavy increase of the current takes place instantaneously, whereby the attractive force between the contact members 20, 30 will considerably exceed the spring force of the tongues 51. This results in the end portions 23, 24 and 32, respectively, of the contact members being pressed against the force of the tongues 51 into the locking holes 52 (Fig. 4), thus preventing deflection of the breaker pole and the ensuing risk of arcing between the contacts 8 and 12. The invention is not limited to the embodiment shown but can be used also with other types of withdrawable apparatus to keep the contacts in position with the aid of the current forces when a short-circuit current flows through the apparatus.

Claims: Contact arrangement for electrical connection between two connecting members (6, 12) which are displaceable in relation to each other, said arrangement comprising a plug-in contact device (16) which is supported by a first contact member (40) fixed to one of the connecting members (6) and is insertable into a second contact member (50) fixed to the other connecting member (12), each of said two contact members (40, 50) having two confronting contact surfaces (43, 44 and 54, 55, respectively), the plug-in contact device (16) comprising two cooperating, elongated contact members (20, 30) which are arranged adjacent to each other and form two electrically parallel-connected current paths (I 1 , I 2 ) between the two contact members (40, 50) and are influenced by a contact-pressure-generating spring (17), the contact members (20, 30) being designed such that said current paths (I 1 , I 2 ) at the two end portions of the contact device intersect each other and, in a relatively long middle portion of the contact device, are substantially parallel to achieve an electrodynamic contact pressure reinforcement, characterized in that said second contact member (50) comprises two substantially parallel legs, each of which exhibits a resilient tongue (51) arranged inside a locking strip (53) formed by the free end portion of the leg, the confronting flat sides of the tongues (51) constituting the contact surfaces (54, 55) of said second contact member (50). Contact arrangement according to claim 1, characterized in that the contact members (20, 30) of the contact device (16) each comprise a substantially straight middle portion (21, 31) and two end portions extending from the middle portion in the same direction side-wise to the longitudinal direction of said middle portion (21, 31). Contact arrangement according to claim 1 or 2, characterized in that said second contact member (50) is made by punching and bending of sheet of resilient material, for example beryllium copper. Use of a contact arrangement according to any of the preceding claims as a catch connector in parallel with an ordinary plug-in contact (8, 12) on a withdrawable high-voltage apparatus (1) in order to secure the plug-in contact in the contact position when a short-circuit current flows through the apparatus.

Inventors: KARLSSON JAN, KARLSSON, JAN
Applicants: ASEA BROWN BOVERI, ASEA BROWN BOVERI AB
Application year: 1993
Main classification: H01H1
IPC codes: H01H1, H01R13