This part of IEC 62271 is applicable to AC switching devices designed for indoor or outdoor
installation, for operation at frequencies of 50 Hz and 60 Hz on systems having voltages
above 1 000 V and applied for inductive current switching. It is applicable to switching devices
(including circuit-breakers in accordance with IEC 62271-100) that are used to switch
high-voltage motor currents and shunt reactor currents and also to high-voltage contactors
used to switch high-voltage motor currents as covered by IEC 62271-106.
Switching unloaded transformers, i.e. breaking transformer magnetizing current, is not
considered in this document. The reasons for this are as follows:
a) Owing to the non-linearity of the transformer core, it is not possible to correctly model the
switching of transformer magnetizing current using linear components in a test laboratory.
Tests conducted using an available transformer, such as a test transformer, will only be
valid for the transformer tested and cannot be representative for other transformers.
b) As detailed in IEC TR 62271-306, the characteristics of this duty are usually less severe
than any other inductive current switching duty. Such a duty may produce severe
overvoltages within the transformer winding(s) depending on the re-ignition behaviour of
the switching device and transformer winding resonance frequencies.