Nanocrystalline alloys are a new class of soft magnetic materials supp
lementing the existing spectrum with high permeabilities. The reliabil
ity of the production processes by rapidly quenching techniques, low c
ost raw materials and the consequences of zero magnetostriction make V
ITROPERM(TM) (Fe73.5Cu1Nb3Si15.5B7) the most prominent representative
of these new alloys. The combination of a saturation value of 1.2 Tesl
a, permeabilities variable over a wide range between 20,000 and roughl
y 200,000, lowest eddy current losses up to high frequencies, the pron
ounced linearity of the flat hysteresis loop and the high thermal stab
ility make VITROPERM(TM) equal or superior to permalloys, ferrites or
amorphous cobalt based alloys in a wide field of applications. The pap
er summarizes the most important advantages of nanocrystalline magneti
c cores in transformers for pulse-current sensitive earth leakage circ
uit breakers, current transformers with small errors in phase angle an
d amplitude, common mode rfi chokes for EMC and KW power transformers.