Page 6-1
FPU-32 Feeder Protection Unit
Rev.
2-A-103014
Theory of Operation
6. T
HEORY
OF
O
PERATION
6.1 S
IGNAL
-P
ROCESSING
A
LGORITHMS
The FPU-32 obtains thirty-two samples per cycle of
each current signal
the sampling frequency is 1.6 kHz
in 50-Hz applications and 1.92 kHz in 60-Hz applications.
A
Discrete-Fourier-Transform
(DFT) algorithm is used to
obtain the magnitudes and phase angles of the fundamental-
frequency components of the current waveforms. These
values provide true positive-, negative-, and zero-sequence
components. True RMS values of phase currents include up
to the 16
th
harmonic. Fundamental-frequency values are
displayed.
Peak-to-peak currents are measured and compared to
DFT values to compensate for CT saturation.
