Alstom MiCOM P846, Technical Manual

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Operation P846/EN OP/D
MiCOM P846
(OP) 5-7
P4088ENa
OP
Figure 4: Frequency response of the Kalman-filter used in the DLO
The fundamental positive and negative sequence voltage and current phasors and the DC
components are the signals that are transferred from the Kalman filter to the next stage of
the algorithm, the preprocessor.
1.3.3 Preprocessing stage
A significant amount of the algorithm engineering is contained in this stage. The main
variables computed by the pre-processor MW, MVar, KA and KV are simply the classical
positive sequence active power, reactive power, line current and bus voltage, acquired using
a single cycle response Kalman Filter. The other variables, derived from the main ones, are
computed with various FIR (finite impulse response) filters, peak detectors, averaging
functions, slope detection and delta detection algorithms. The output of the
preprocessor is a
set of ten variables to be processed by the fuzzy-logic engine.
For convenience, all variables are converted to per unit quantities using the two following
base parameters specified in the relay settings:
Vbase: Base voltage equal to the rated line to line voltage
Pbase: Base power equal to the line surge impedance loading (SIL)
a nditions, the positive sequence quantities used
in the pre-processor are not consistent, due to hard signal distortion as in faulty conditions or
severe switching transients (open-line energization). These two special conditions can be
recognized and the corresponding signals modified to ensure their physical continuity and
consistency.
The fault detector provides the fault signal which is a pulse of duration equal to that of the
actual fault. It is used to improve the reliability and security of the relay. Indeed, the
prolonged fault signal allows the blocking to zero of some decisional variables during the
fault. The overall behaviour of the detector is to provide a pulse of duration equal to that of
the actual fault or magnitude discontinuity superimposed on the positive sequence voltage.
For the time period that this indicator is active, three pre-processor variables are inhibited
and blocked to their default values.
Besides these ten variables, the pre-processor generates two additional signals to handle
f ult and start-up conditions. Under these co