STRAY-FIELD TRANSFORMER
A leakage transformer, also called a stray-field transformer,
has a significantly higher leakage inductance than other transformers,
sometimes increased by a magnetic bypass or shunt in its core between primary
and secondary, which is sometimes adjustable with a set screw. This provides a
transformer with an inherent current limitation due to the loose coupling
between its primary and the secondary winding. In this case, it is short-circuit inductance which
is actually acting as a current limiting parameter. The output and input
currents are low enough to prevent thermal overload under all load
conditions—even if the secondary is shorted.
Uses
Leakage transformers are used for arc
welding and high voltage discharge lamps (neon
lights and cold cathode fluorescent lamps, which
are series connected up to 7.5 kV AC). It acts then both as a voltage
transformer and as a magnetic ballast.
Other applications are short-circuit-proof extra-low voltage transformers
for toys or doorbell installations.