Ballast question (fwd)

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---------- Forwarded message ----------
Date: Tue, 16 Nov 2004 16:48:37 -0600
From: Carl Litton <Carl_Litton@xxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Ballast question



Carl Litton

Hello

Thanks to everyone who responded on the transformer stack question.
Tremendous amount of useful knowledge gained that is much appreciated.

We have now gotten the use of a very nice inductance meter, measuring up
to 500 Henries.  Of course, we immediately set about measuring every
possible combination of ballasting devices with a wide variation in the
results from a few microhenries to one that was 300 Henries.  One of the
things we did with large frame transformers was to measure the primary
winding with secondary short and open and the secondary winding with
primary short and open.  

Without exception, the inductance of a transformer winding is several
orders of magnitude higher when the other winding is open.  Shorting the
other side drops inductance usually into the microhenries.

The question is:

Why is it that it is almost uniformly recommended that transformers used
for ballasting (MOT's mostly) have the magnetically coupled winding
shorted?  Is this related to changing the inductance or simply to
prevent arcing?


All comments appreciated,

Carl Litton