Introduction to Detecting and Testing for Shorted Turns
Inductors are made up of a length of wire, usually
wound around a core.
The core is usually some type of magnetic material such
as iron or ferrite, however air cores are also sometimes used.
The wire, is referred to as
the “winding”, and this winding is made up of a number of turns.
Generally, inductors are a
single winding, and transformers mostly have multiple windings, (there
are special cases, such as “Auto transformers” where only a single
winding exists) and in many transformers different wire diameters can be
used in the various windings.
Inductors and/or transformers
that are wound using a large number of turns and/or using very fine
wire, require a method of detecting the existence of shorted turns, and
also the ability to stress the winding in order to detect imperfections
or potential weaknesses in the winding insulation that could be a weak
point over time.
Winding imperfections can
normally be attributed to damaged enamel caused by physical damage
during manufacture of the transformer, or imperfections during the
manufacture of the raw wire itself.
These imperfections can
result in shorted turns during normal operation if undetected at point
of manufacture.
The high temperatures
resulting from the increased current at the short will fairly quickly
cause copper melting and create a low resistance spot weld.
This low resistance short
will then completely short out one turn, affecting the performance of
the winding and hence the whole transformer