SE423288B - Surge diverter - Google Patents

Abstract

In a surge diverter with ZnO-block comprising several series-connected diverter parts 1, 2, it has been found that an unevenly distributed temperature rise occurs after a long period of outer fouling. A more uniform temperature distribution can be achieved by biasing the diverter with control impedances 13 so that the greatest voltage stress occurs in the central or lower parts 2 of the diverter. <IMAGE>

Description

_> isoo61os-9 10 _15 20- 25 50 35 The active. the parts of a. valve diverters for outdoor use are usually built-in "in a porcelain housing with metallic end flaps. For manufacturing reasons can one such. porcelain housing not made too far .. Diversion for voltages higher than about 150 kV are therefore usually built up of two or more edge mounted diverter parts. By building a diverter with several in shorter porcelain housings, moreover, greater short-circuit safety can be achieved, since tryokavlastnizzg can be arranged at each joint between in the parts.

It has been found that in the case of prolonged external contamination, e.g. salt coating, gets a ZnO diverter, which consists of several series-connected diverter parts, one unevenly distributed temperature rise. This is because a significant leakage current flows along the insulator surface of the dirt coating, which in moist stand electrically conductive, with large fluctuations in the potential of the metal flanges of the splice points appear.

Since the internal active parts of the diverter are in galvanic connection with the the outer surface of the lator housing, the voltage will come on. varistor blocks that - is affected and can locally rise above the maximum minimum value for which the diverter is dimensioned. Due to the strong nonlinearity of the ZnO blocks (small difference in voltage gives a big difference in current) comes the resistive läok current through the blocks in parts of the diverter to thereby temporarily increase and cause an abnormal temperature rise on the blocks. Since the resistive leakage current but in ZnO blocks is strongly temperature dependent, the abnormal temperature will the increase in speed to lead to a further leakage current increase. This can so small- cause the varistor blocks to be destroyed.

Various solutions have been proposed to deal with the above problem. A proposal is based on. that in the joints between the diverter parts uses insulating joint brackets; so. that galvanizing is avoided in these places technical connection between the active parts of the diverter and the outer part of the insulator housing yuo; An oåaon solution is aook difficult to apply in a practical construction.

Another proposal is to connect all diverter blocks in parallel with a separate chain control capacitors to on. same as * in diverter with spark gaps and silicon carbide blocks achieve a more even snow distribution.

By such a purely symmetrical control with equal capacitance over the blocks one admittedly reduce the temperature rise, but to getting down to acceptable values requires high capacitance, which means high costs . 10 15 20 25 50 8006103-9 According to the present invention, the above-mentioned problems are solved by visibly skew the arrester, so that the highest voltage surge occurs in the middle or lower parts of the diverter. This can be achieved by putting control impedances, preferably capacitors, only in the top part of the diverter or top parts. Thereby a more even temperature distribution is obtained between the varistor blocks in the event of external contamination of the diverter. Also needed smaller amount of capacitors than in the previously proposed embodiment with symmetrical capacitive control. An additional advantage is that the requirements for ring can be reduced. It is also conceivable that with this solution in some case could completely abolish the twilight or cope with a relative small shield ring to avoid corona at the top connection of the diverter.

A possible explanation for the more even temperature distribution being achieved by a asymmetric control according to the invention is that at a diverter as below for a certain time is placed in salt mist, saline solution will settle on the insulation surface and drip down from the upper parts of the diverter and give a thicker laying with higher conductivity on the lower part of the isolatory yew.

The invention will be explained in more detail with reference to the accompanying drawing, in which Fig. 1 shows sohematically in cross-section one constructed with zinc oxide varistors valve diverter of previously known design, Fig. 2 shows. correspondingly an embodiment of the invention and Fig. 5 shows the longitudinal spreading distribution for different diverter structures. tioner.

The valve diverter shown in Fig. 1 consists of two electrically connected in series diverter parts 1 and 2. Each diverter part comprises a plurality of cylindrical ones zincozide varistor block 5 arranged in a stack. Varistor stack is arranged centrally in an elongated porcelain housing 4 with metallic ends. flanges 5 and 6. The two diverter parts are assembled coaxially and oriented with the longitudinal axis in the vertical direction. The diverter is equipped with a top connection 7 for connection to a live line and a bottom connection 8 for connection to earth. At the upper end of the breeder is a screen ring 9 suspended. The metal flakes at the joint 10 between the diverter parts 1 and 2 form a galvanic bond between the varistor stacks and porous the outer surfaces of the lens housings. 10 15 _20 25 30 35 sun61os-9 An IZnO block 'has an equivalent circuit consisting of a capacitance 11 in parallel. coupled with .a strong voltage-dependent resistance 12._With normal operating voltage consider the capacitive part of the leakage current, and the equivalent capacitance the citans 11 would, if they could, seem alone. give a purely linear voltage distribution along the diverter 'according to line A in Fig. 5, in which U denotes voltage fi percent of the total voltage across the diverter, and h denotes the distance from the bottom flange in 'percent of the diverter length. Between the diverter and ground However, there are distributed leakage capacitances which give a distortion of the voltage the distribution, so that higher voltage will prevail over the upper part of the diverter shaft.

By the cutting ring 9 a certain improvement of this condition is achieved. The re- The voltage distribution for the arrester according to Fig. 1 is shown in the curve IB in Fig. 3. ~ By the above-mentioned proposed embodiment with a symmetrical capacitive control and a shielding ring, a slightly more even spasm distribution is achieved according to curve G in Fig. 3. Still. however, a higher voltage is across the diverter upper »part than over the lower.

Fig. 2 shows an example of. how a valve conductor according to the present invention can be performed. In parallel with the varistor blocks 5 in the upper the diverter part 1 'is here arranged a chain of control capacitors 15. Condensed the sensors connected to the varistor stack by metal washers 14, wherein between two adjacent such washers an appropriate number of varistor blocks can be arranged. In the lower diverter part 2 there is in this embodiment no control impedances, and the diverter lacks twilight (possibly it can be necessary to arrange a small shield ring for corona protection in directly connection to the diverter's top flalrxs). The control capacitor chain can, for example, have a capacitance of the same order of magnitude as the property of the varistor blocks capacitance. With a diverter according to Fig. 2, an opening distribution is obtained according to curve I) in Fig. 5, where, for example, 54% of the total voltage is over the bottom part 2 and 46 of the diverter i »over the top part 1 (without external dirt erika). nen lampligeeve faeaeiningen kan aeek vary from fen un fail ..

From a production and warehousing point of view, it is »of course an advantage if one in the same arrester can use control capacitors of one and the same size. The may, however, be appropriate. to use in some cases capacitors of different sizes play in different diverter parts. For example, you can use a third-party arrester in control capacitors on. eg 1000 pF in the top part, 500 pF in the middle part * and none capacitor-is all in-bottom part. In principle, it is also conceivable that turn. different capacitors in the same arrester part.

Claims (5)

8006103-9 Instead of control capacitors, it is also possible to use linear control resistors. PATEWIKRAV Valve diverter comprising at least two diverter parts (1, 2) electrically connected in series between a top and a bottom connection (7 and 8, respectively), each of which comprises a mecall bracket (5, 6) provided: solar-arne helga (4) imanen a plurality of electrically connected metal oxide varistor blocks (5) arranged in a vertical stack, the metal flanges in the joint between the diverter dividers (1, 2) forming a galvanic connection between the varistor stacks and the outer surface of the housing (4), characterized in that at least parallel to of the varistor blocks in the diverter part (1) located closest to the top connection, impedance elements (15) are switched on irregularly to control the voltage along the diverter on such that the highest. voltage-prediction.- the sensation occurs in a diverter part located closer to the bottom connection Valve arrester according to claim 1, characterized in that the control impedance elements (15) are arranged to provide an asymmetric voltage distribution axis along the arrester in such a way that the voltage across it (2) of two. series-connected diverter parts (1, 2) which are closer to the bottom connection (8) are higher than the bias over the part (1) lying closer to the top connection (7). Valve diverter according to Claim 1 or 2, characterized in that the control element elements (15) form a gray sphere, in which the impedance of: The impedance elements increases stepwise with increasing distance from the slope of the peak (7). Valve diverter according to one of the preceding claims, characterized in that only the top (s) of the diverter parts (1, 2) are provided (a) with control impedance elements (13). Valve diverter according to one of the preceding claims, characterized in that the control impedance elements (15) are constituted by capacitors.