Gordon Bennett wrote in message
...

"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



Likewise
I went to a regional power station open day one day.
It was necessary to kick in one generator set while we were there.
I couldn't believe my eyes when someone had to open up a door on the side of
the casing, reach in , and do something, I don't know what, and there was an
almighty roof rattling bang as bus-bars contacted or something.
The public , including me, was 50 yards away.
Anyone ever visited the National Grid pylon and insulator test facility at
Leatherhead, Surrey , sci-fi kit there.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/