High coulomb lightning duty on distribution MOV blocks

Distribution arrester ZnO MOV blocks were tested with high coulomb one-half sine wave surge currents. Of the 180 tested, 156 were tested in circuits which delivered greater than 0.6 C. All these blocks were evaluated using the ANSI 20-shot 250/2mS LCLD test. A statistic based upon the ability to survive this test was used to evaluate the MOV block durability. This statistic predicts at about the 99% confidence level that there is only a 1% probability that the block will fail to pass the 20 shot 250/2mS LCLD test after discharging three 0.54 C lightning surges (independent of current level between 1 kA and 60 kA). Only one 0.54 C surge would be expected in 43 years in areas of North America where the discharge frequency is calculated to be 0.5. Well made ZnO MOV blocks have capability well in excess of this in that the statistic was developed for three repeated shots.<
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