electric spike damaging dynamo....

[thoongfoned]

hi wife has a farm that runs 6 big industrial fans (for cooling). each fan has its own dynamo, single 25amp switch (to turn on) said dynamo (hascon 1hp single phase 4 pole 0.75kw 5.4amp running) which are powered by a separate trip (2 x 50amp safe t cut) each trip for 3 fans.

have been using these dynamos for 3 plus years now, good units that work well ect.... have recently started to replace some.

new dynamo installed the other day, worked well for 2 hours, had a power drop (every thing in the farm almost stopped) then came back to pull power, new dynamo would not reach full power after this. other dynamos ( older ones) all good. took new one back, got a replacement. installed new one, worked for 1 day no problem, then electric stop for 10 seconds (happens here from time to time) now the new dynamo will not reach full power again. again old ones all good. had other "sensitive" electrics plugged in as well (computer ect.) no problems with any thing only the second new motor........... any ideas....

over the past year have replaced other dynamos with no problems, I know the shop is going to be a bit funny when I turn up moaning again.