Surge arrester arrangement

Abstract: The invention relates to a surge arrester arrangement comprising a surge arrester (4) and a cut-out device (6) arranged in series with the arrester for automatic disconnection of the arrester in the event of arrester failure. The arrester arrangement is intended to be connected in parallel with an insulator (2) arranged for suspension of a power line (1) from a power line tower (3). The surge arrester (4) is connected to the power line conductor (1) via a connecting link (5) in the form of a flexible electric conductor (10) enclosed in a tube of, for example, aluminium, which is divided into several parts. A helical spring (8) which, for example, may be arranged inside the tube, keeps the connecting link at insulation distance from the power line conductor (1) when the arrester has become disconnected by means of the cut-out device (6).

Description: The invention relates to a surge arrester arrangement according to the precharacterising part of claim 1. Surge arresters with cut-out devices are previously known, for example from the US-A-2 305 436 and EP-B-0 013 401. They are used, inter alia, in transmission lines to protect against back flashover caused by thunder, or against switching surges. The arresters are placed on the towers of the transmission line and are connected between the conductor of the respective phase of the line and the grounded tower construction. For a surge arrester connected between phase and ground, a failure in all probability results in a permanent ground fault. However, if the arrester is provided with a cut-out device which automatically disconnects the arrester in the event of a failure, the operation of the line can continue and the faulted arrester be located and replaced at some suitable time. It is, however, important that the disconnected connection between the line conductor and the arrester does not get near the line conductor in case of hard wind, to prevent a ground fault on the line. Hitherto, there has been no good solution to this problem, and it is therefore common to arrange in line surge arresters, instead of cut-out devices, an open spark gap in series with the arrester. However, this normally provides inferior protective effect, since it is difficult, from the point of view of voltage, to coordinate an arrester and a series-connected, separate spark gap. Another drawback with this solution is that there is no indication if the arrester has failed. Document EP-A-0 328 771 discloses a surge arrester disconnecting device comprising a link for connecting the arrester to the line conduction, said link comprising a movable, rotable arm and spring means for pushing the movable arm out from connection when a failure occurs. The invention aims at developing a surge arrester arrangement of the above-mentioned kind in which the surge arrester is connected to the power line via a connecting link with the following properties: Good flexibility such that the insulator chain is able to swing in case of wind load without stressing the arrester, heavy dimensions with respect to corona discharges, that is, a large cross section diameter, a low weight, spring back property such that the disconnection becomes efficient upon a failure, the property to remain suspended straight under the arrester even in case of hard wind after a failure of the arrester. To achieve this aim the invention suggests a surge arrester 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. According to an especially suitable embodiment of the invention, the connecting link comprises a tube, divided into several parts, preferably of aluminium and provided with an inner helical spring extending between the ends of the tube, and with a continuous cable inside the helical spring to bring about the electrical contact between the line conductor and the arrester. By imparting to the helical spring a considerable prestress, the link will remain straight at the bending stresses which may arise because of wind stresses after a failure of the arrester. By way of example, the invention will now be described in greater detail with reference to the accompanying drawings showing in Figure 1, in side view, a first embodiment of a surge arrester arrangement designed according to the invention, during normal operation, Figure 2 the same surge arrester arrangement after the arrester has failed, Figure 3, in axial section, a part of a connecting link of the surge arrester arrangement according to Figure 1, Figure 4, in side view, a part of an alternative embodiment of a connecting link of an surge arrester arrangement according to the invention. Figure 1 shows a power line conductor 1 which, by means of a suspension insulator chain 2, is suspended from a power line tower, of which only an end portion of the horizontal cross beam 3 is shown. At the outer end of the cross beam, at insulation distance from the conductor 1, a surge arrester 4 is arranged. The lower end of the surge arrester is connected to the conductor 1 via a connecting link 5 and a cut-out device 6. The surge arrester 4 may be of the frequently used design having an elongated insulating casing, in which a number of preferably cylindrical ZnO blocks are arranged between two end electrodes. The cut-out device 6 may, for example, be of the design described in SE-A-9 200 525-5. The connecting link 5 is made in the form of an aluminium tube 7 (Fig. 3) consisting of a plurality of tube parts 7a, 7b, arranged one after the other, and provided with an inner helically wound tension spring 8 which extends between the inner ends of the tube. The tube parts 7a, 7b are provided with end inserts 9, preferably of metal. A continuous cable 10 inside the helical spring 8 provides the electrical contact between the conductor 1 and the arrester 4. By imparting to the helical spring 8 a considerable prestress, the connecting link 5 develops a force that tries to straighten the connecting link. In the event of overload and failure of the arrester 4, the arrester is automatically disconnected with the aid of the cut-out device 6, whereupon the connecting link 5 assumes the vertical position shown in Figure 2. In this way, the operation of the power line can continue undisturbed in spite of the arrester failure. At the same time, a clear indication of failure of the arrester is obtained. Faulty arresters can therefore be easily located by inspection from the ground or from a helicopter and be replaced at some suitable time. Thanks to straightening force developed by the prestressed spring and by making the end surfaces of the inserts 9 plane, the connecting link 5 will remain straight despite of bending forces which may arise as a result of wind forces after a failure. When the link 5 is connected to the conductor 1, it will exert a sufficient tensile force on the cut-out device 6 to ensure a fast disconnection upon an arrester failure. Figure 4 shows an alternative embodiment of the resilient member required for straightening of the connecting link 5. Instead of the long, through-going spring 8 shown in Figure 3, there is used in the embodiment according to Figure 4 an outer, relatively short close-wound helical spring 11 at each joint between two adjacent tube parts 7a and 7b. The spring is fixed in the axial direction by inserting the ends of the spring wire into fixing holes in the respective tube part.

Claims: Surge arrester arrangement comprising a surge arrester (4) and a cut-out device (6) arranged in series with the arrester for automatic disconnection of the arrester in the event of an arrester failure, which arrester arrangement is adapted to be connected parallel to an insulator (2) arranged for suspension of a power line conductor (1) from a power line tower (3), characterized in that the surge arrester (4) is connected to the power line conductor (1) via a connecting link (5) in the form of a flexible electric conductor (10) enclosed in a tube (7) divided into several parts arranged one after the other, resilient members (8, 11) being arranged adjacent the tube (7) to straighten the connecting link (5) so as to keep it at insulation distance from the power line conductor (1) when the arrester (4) has become disconnected by means of the cut-out device (6). Arrangement according to claim 1, characterized in that said resilient members consist of a helical spring (8) arranged inside the tube (7) and extending between the ends of the tube. Arrangement according to claim 1, characterized in that said resilient members consist of a number of helical springs (11) which surround the tube (7) at each joint between two tube parts (7a, 7b). Arrangement according to any of the preceding claims, characterized in that the tube (7) is made of metal, preferably aluminium.

Inventors: LUNDQUIST JAN, LUNDQUIST, JAN
Applicants: ASEA BROWN BOVERI, ASEA BROWN BOVERI AB
Application year: 1993
Main classification: H01C7
IPC codes: H01H85, H01C7, H01B17, H01T1