Xfmr death and RSG

From:  Gary Lau  21-Jan-1998 1130 [SMTP:lau-at-hdecad.ENET.dec-dot-com]
Sent:  Wednesday, January 21, 1998 10:41 AM
To:  tesla-at-pupman-dot-com
Cc:  duncand-at-ccsalpha2.nrl.navy.mil
Subject:  Xfmr death and RSG

>From: dwight duncan <duncand-at-ccsalpha2.nrl.navy.mil>
>    Two days ago I fired up my 3 KW Tcoil and got some impressive results
>for being conservative.  I had spent a few days re-building my supply and
>wanted to take it easy for a while using 1000 rpm on the rotary gap.  Last
>night I took photo's of the unit and between frames increased the speed of
>the motor.  After about 30 seconds at 2400 rpm one of my transformers
>again, died.
>    The motor is non-synconus and I believe that is what lead to the
>transformers doom.  Its is a 1/4 HP variable speed AC brush type motor that
>I acquired for free from someone that was throwing it out.  It was the only
>motor I had available so I used it.


No answers, just some further questions.

We've all heard that for less-than-bombproof transformers, sync rotary gaps
appear to offer higher survival rates than non-sync RSG's.  I believe the
explanation offered was that unless the cap is discharged every half-cycle,
the cap resonating with the xfmr secondary will ring up to destructive voltage
levels.  Agreed.  But most non-sync RSG's appear to be operated at far greater
break rates than one would experience with a sync unit, guaranteeing that the
cap is discharged more often than every half-cycle.  So I don't understand how
this explanation holds true.

UNLESS:  If one turned on the transformer before the RSG came up to speed, that
could easily toast your xfmr.  Could this be what happened?  It would appear
that one would either have to have some interlock system, or be very diligent
in applying xfmr power only after the RSG is up to speed.

Gary Lau (working on his sync RSG)
Waltham, MA USA