GB1328312A - Lightning arrester - Google Patents

Abstract

1328312 Spark gaps MITSUBISHI DENKI KK 19 April 1971 [6 March 1970] 23408/71 Heading H1D A lightning arrester device comprises main electrodes 1 and 3, Fig. 4, and a trigger electrode 4 in an electronegative gas such as SF 6 , the location of the trigger electrode being such that the ratio of the spark-over voltages of the two gaps G1 and G2 is between 0À5 and 2. Preferably the electrodes are connected by impedances Z 1 and Z 2 such that the entire voltage is applied across the gap G1 for a steep wavefront having a duration of 1 microsecond whilst only about 40% of the voltage is applied to G1 for a slow wavefront lasting about 100 microseconds. By matching the voltage/time curves of the impedance network (L2, Fig. 6, not shown) and the spark gaps (L1) the sparkover voltage may be made almost independent of the time between the application of the pulse and the initiation of the discharge (curve L3, Fig. 6). In one example the capacitors 5 and 6 are 160 and 100 pf respectively and resistors 7 and 8 are 100 kilohms and 40 megohms respectively. The main electrodes 1 and 3 may be hemispherical (Fig. 3, not shown), and means may be provided for magnetically blowing the arc.