Magnetics Business & Technology - July/August 2019 - 17

RESEARCH & DEVELOPMENT

Capacitive Discharge
This is one of the toughest failures to detect. This is typified by
failed components in the system with no apparent cause. What
makes this hard to determine is the transformer, once taken out
of the circuit, appears to be fully functional. In affect it is - as
a transformer under static testing it is in fact "good". It is the
dynamic load that produces the "failure" of the transformer. This
can be caused by using the wrong material, improper spacing
between winding, and having the wrong Volts/Turn ratio. This
also includes creep and strike distances that are not appropriate
for the voltages of the system.

of experience in the design and development of transformers,
power supplies and controllers with a specialty in high voltage switching. He has a BSEET from University of Hartford, an
MSEE from Western New England University and DSEE from
Atlantic International University. His career has included positions with Hamilton Standard (now UTAS), Pitney Bowes and
Bicron Technologies. He can be reached at www.McGivernTechnologies.com.

Partial Discharge
Partial Discharge is just that: a failure of a portion of the insulation system. This is caused
when material is ionized inside of the transformer. This ionization causes intermittent failures
within the transformer and shortens the life of
the transformer.
Thermal Considerations
Heat is generated in two major portions of a
transformer. If the size of the wire is not selected
properly there will a large I2R loss in the windings. This loss effects the resistance of the windings and adds heat to the core. An improperly
selected core will run hotter than desired. This is
dictated by the shape of the core, the size of the
core, and the material used in the core.
Repeatability
If a transformer cannot be manufactured consistently within the required criterion, it is probable
that there will be many parts that are shipped at
the outer fringes of the specifications. As in any
process it is highly recommended that key factors are monitored to ensure that they not only
meet the criteria, but they are well within the
ranges specified in the criterion. This is where
knowledge of SPC pays off.
Cost Summary
I maintain that the cost of a transformer is more
than the dollar cost of the unit. If any of the
above failures occur the overall functionality
of the system is compromised. In the case of
each of these failures one should determine
the cost of the system failing and being out of
commission. One also should look at the cost of
operating the system. This cost can be broken
into the cost of the energy to run the system and
the cost of monitoring the system to ensure that
it is operating correctly.
About the Author
Dr. Kevin G. McGivern
is president of McGivern
Technologies, a consulting firm based in Lakeville,
CT. He has over 30 years
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