It is also very common that during power system faults,
when the protection devices have to quickly disconnect the
protected equipment or grid segment, the CT cores saturate
and the CTs produce distorted output waveform [3]. This may
cause the microprocessor IEDs to misbehave, i.e. delay
tripping or even fail to trip. The microprocessor IEDs typically
run Fourier or cosine filter algorithms for detecting
overcurrent condition, and these algorithms are based on
estimation of the fundamental component ideally from a nondistorted
sinusoidal signal inputs. The delayed tripping can
lead to system stability problems.