[RFI] Lightning / Surge Arrester PLN/RFI

[Chris L. Parker]

Group,
 
Investigating a 16kV distribution pole with 3 lightning arresters, one on each phase. All new poly hardware, composite crossarms, new cutouts, and full complement of wildlife guards. Excellent construction.
 
The pole is producing PLN/RFI from 18MHz to 430MHz (verified, actual frequency. range could be greater, but was not verified)  RE251 registers no discernable acoustic energy at multiple angles. 
 
RE243 shows approximately 4-6ms wide pulse groups (narrow spaced pulses) with gradually rising heights then fairly steep drop off, spaced every 16.6ms (approximately)
 
Question: Does anyone have any experience with damaged/compromised MOV surge arresters exhibiting this half-cycle behavior? 
 
Background information: There was a significant lightning event in the area about 1 month ago.
 
Any input greatly appreciated. Thank you.
 
Chris L. Parker
ARRL Technical Specialist PLN/RFI
Los Angeles Section