Strange power transformer behaviour

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Christoph Bohr" <cb-at-luebke-lands.de> 

Hello coilers.

I made some strange observations on my
6MOT-Supply yesterday I can't quite eyplain
and hoped some of the more experienced
folks on the list could give me some hints.
When I turn the voltage to the transformer
up with my variac, I find a steady increase in
input current up to 14amps until I reach 100Volts,
which is about 45% on my 230V line. When I
go further to 230V the current drops again until
almost zero at 230V....?! What is going on there?
This only happens with the TC connected. Without
a load I get a very small current and with shorted
secondary current rises smoothly to the preset
value from the ballast. Under this condition I get no
output from the coil. When I switch the transformer
off and back on several times this effect disappears
and the coil starts working normally. I wonder if
something in the MOT-stack failed, but I can only
do low voltage measurements which turn out to be OK,
but maybe something is failing at higher voltage.
This really left me confused, so any help is appreciated.

regards

Christoph Bohr