[Heathkit] Re: F/S voltage reducer ----> transformer loss of life

[Gerry Steffens]

I recently had a 345,000/161,000 volt auto transformer fail.  It was 448 =
million volt-amperes rated.  I am a utility engineer.

The very same thing causes old power transformers in electronic =
equipment to fail as does large scale power transformers.  Those things =
are heat and contamination.  Transformers usually die because the =
insulation dies or impurities have leaked in and caused corrosion to eat =
away at things (and this also causes heat).

Assuming that a transformer is well sealed (electronic, by coating means =
and large power, by pulling vacuum and then sealing), transformers are =
all made to a design BIL (basic insulation level).  In the utility =
business we have computer programs that will analyze transformers in =
terms of temperature/load profile/overload, etc.  These programs can =
calculate the loss of life of insulation based on the physical =
parameters the insulation experiences.

In electronic equipment, the same things happen (heat and load exposure =
- sometimes folks would even add tubes to receivers and shorten the =
transformers lives).  Each time a piece of equipment is run the =
transformer insulation looses some miniscule portion of life.  Slowly =
insulation looses its effectiveness.  At some point when the BIL becomes =
inadequate, it fails.  The secret to long surviving transformers - find =
a BA that has not been used extensively.  Chances are that the =
transformer will then outlast you.

The minor differences between 112 to 124 volts on a primary are =
insignificant in design, likewise the effects when carried to an 800 =
volt secondary (remember we are dealing with percentages and percent =
change here).  These units are and were designed with safety tolerances =
in the 50% to 100% range.  In some instances the same physical =
transformer was marketed for electronic purposes with different markings =
and spec sheet (different voltages and currents but the same insulation =
and all,  just different paper descriptions). Remember that a =
transformer is merely an electromagnetic device with a turns ratio.  The =
only thing different is the basic insulation level (BIL).   P.S.  Most =
new ones are far less tolerant because of much tighter design specs. =
(dollars, y'all know!)=20

However, once a transformer is on its last legs, of course small voltage =
variations will hasten the demise.  But chances are that 121 volts only =
accelerated the death by a few months on the outside. =20


Gerry


Collecting & Restoring since 1959
Gerald Steffens P.E.
Rochester, MN


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