Gordon Bennett wrote:
"rex" wrote in message
...
Thanks for your informative reply , I owe you
I am in Greece and waiting for a specialist to come from England,
unfortunatley next week 
so I had to do something myself ...I
understand the danger and I will follow your instructions step by
step.
Trying to work again today since the voltage -not accurate measures
I
took looked "normal" to me, that is instead of 400 V/50 Hz ...
430-460
V due to harmonics I supose.
So after talking to him despit the heating up of the busbars he told
me I can work ... I have a short circuit thyristor more ((
Amperage was not high , according to the instruments steadily at 900
A
- it is designed for 1.300 A, thyristors can take 1800 V - Itav 1400
A
Yes , it is an Inverter ... I take two bus bars from the 6 bridge
rectifier SCR's that is DC ... passing through a secondary
protection
coil goes to an Inverter ... 2 pairs of fast , inverter grade
thyristors and they finaly give to the Load high frequency AC at
600-1000 Hz
All started two weeks ago with the secondary coil overheating - just
one widing , it has two , one for each DC phase I supose
I was told that it is short circuit and it went for rewind ... waste
of time and money ...
After having the same overheating at the secondary - protection
coil ... I was told and it was true that I had one water cooled
cable
to the load cut ... it was so
After that I was able to work for some melts until the source coming
bus bars started to overheating ... I though it was from bad
thyristors they can;t take too much heat for long , though the
system
has everything on it like drops the power from overheating at
various
points etc.
Water that cools the cabinet components are highly deionised but I
noticed that in this particular winding , water pressure was low
....
the same cooling line passes from the thyristors so I am thinking of
giving a new one just for the coil and thyristors with enough
pressure
to cool them down
Tomorrow I will have one new slow rectifier phase thyristor to test
I am also suspecting short circuit at the load coil ... it is
heavily
built up with yokes and supporting woods and isulations between
them ... so I have to exclude any short circuit conditions on the
load
side
I exchange two thyristors ... 1-3 and the voltage ... with the
multimeter I did measured it ... seems normal as I told you before .
THanks for the thyristor and triggering instructions I shall try
them
also tomorrow !
Anybody else out there following this thread with absolute horror? I
have been in electronics for 40 years and I am picturing all sorts in
my minds eye. One thing is for sure, I wouldnt go within 100 metres of
it when its fired up, faulty or not!
Gordon
Ha, don't let that bother you, I've had 2500 Amp Scr's explode from old
reliance drives right in front of me!, ceramic chips everywhere!
Some time's they don't die silently!
--
"I'd rather have a bottle in front of me than a frontal lobotomy"
http://webpages.charter.net/jamie_5