Rraghunath, I concur with you from the theoretical standpoint that is unlikely to distribute the energy of the overvoltage equally in both arresters in parallel. I suspect that only one arrester will switches on during overvoltage event because small difference in impedance and response time causing potential risk for overload the arrester that operates first.
Contrary to the obove, one reputable surge arrester manufacturer claim that two Metal Oxide Surge Arrester (MOSA) in parallel conduct current at the same time. On the other hand I have recently the opportunity to observe in a current application in Puerto Vallarta, Mexico, a few failures in single arrester but none failure in a parallel connection.
I hope others in this forum could join us discussing if there is any merit using two MOSA in parallel at least for MV distribution application.
I aggree it is an interesting question. My knowledge is limited to modeling and some theory. The first MOSA that have a spakover of the gap will cause a drop in the voltage that can cause a reduction in the current of the second MOSA to below the spark-over point(this current is well within the capability of a single surge arrestor). If the current still increase beyond the initial spark-over level, the voltage would increase, providing the opertunaty for the second MOSA to spark over and reduce the current in the first MOSA. This will take place at high currents where a current shearing is needed.
I installed Lightning arrestors in parrallel. The application was pole top arrestors at the end of OH distribution lines. The geographical location was subject to lightning storms however, the utility I worked for generally did not experience as many storms as we had in our little jurisdiction.
After each storm we had to replace many failed arrestors, blown apart by more fault current than what they could handle. We noticed that arrestors installed in the midwest and areas prone to lightning were much larger than the little guys our utility was purchasing.
Unable to talk our company into getting larger more robust arrestors, we starte putting them up in parallel. I beleive they were MOV (MOSA as you call them now). I don't believe we ever blew up a Parallel set, but neither could we quantify what duty they sustained. Very unscientific but we got some emotional satisfaction out of it
