Sl. Yu et Jc. Gu, Removal of decaying DC in current and voltage signals using a modified Fourier filter algorithm, IEEE POW D, 16(3), 2001, pp. 372-379
Protecting transmission lines frequently involves applying distance relays.
Protective relays must filter their inputs to reject unwanted quantities a
nd retain signal quantities of relevant interest. Accuracy and convergent s
peed of filter algorithm are essential for protective relays. A widely appl
ied filter algorithm, the Discrete Fourier Transform (DFT) can easily remov
e integer harmonics using simple calculation. However, the voltage and curr
ent signals contain serious harmonics and decaying de during the fault inte
rval. In addition, the decaying de and higher order harmonics seriously dec
rease the precision and convergence speed of fundamental frequency signal f
rom DFT. In this investigation, we derive a novel algorithm which combines
the appropriate analog low pass filter and modified Full Cycle DFT (FCDFT)
or Half Cycle DFT (HCDFT) algorithm to remove the decaying de in a voltage
or current signal, Using the Electromagnetic Transients Program (EMTP) simu
lates the transient responses of transmission lines during the fault period
. Applying the proposed algorithm in distance relays effectively suppresses
the decaying de and quickly decomposes the accurate fundamental frequency
components.