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Re: [TCML] The Dreadful Task of Ballasting (longish)
Phil,
I wanted to add that because your transformer is "hefty" at 11kV at
350mA, an LCR meter is not a good avenue to use to measure the
inductances. The meter just can't put enough umph into the core to make
an LCR reading useful. Ioc and Isc measurements are needed and then to
calculate the inductances from that data (and thus the spreadsheet to
help with the calc's).
Take care,
Bart
Hi Phil,
My gut feeling is that resonance is not the problem. It may be an
inductive kick, but possibly it is simply due to cap charge and time.
Are you running a rotary gap?
I'll forward you an Excel spreadsheet I use now and then for looking
at various aspects of a transformer. I typically run a series of
measurements at various voltages logging open and short circuit
currents, voltages, etc., but this can be done at a single voltage of
course. I think you may be better off attempting to attack some of
this data so that your sure about the inductances and about the true
Cres of the transformer. If you give the spreadsheet good data, it
will tell you inductances, reactances, leakage inductances, leakage
reactances, mutual inductance, coupling, and actual Cres, based on
measurements. After a new build like this, these are things I would
want to know for sure about the transformer.
But regarding your problem. The cap appears to already be very STR
even at 43.2nF. I did some back calcs on your given inductances and it
looks like Cres is around 120nF. But this also assumes all the data is
good. Added ballast inductance will be reflected to the secondary side
and will of course alter Cres, but I think you are still very STR, so
if it's a rotary and possibly the time to alignment was slow, the
safety gap may simply be reaching breakdown due to cap charging. The
new transformer certainly gives you 3X the charging current, so it's
reaching potential that much faster and if there nothing to break to,
then it will continue to charge beyond the 11kV guestimate until the
safety gap breakdown voltage is reached.
Take care,
Bart
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