Alstom MiCOM P846, Technical Manual

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Operation P846/EN OP/D
MiCOM P846
(OP) 5-9
Figure 6: Fuzzification of two decision features
1.3.4.2 Fuzzy logic inference on the decision features, using sixteen rules or criteria
The inference engine contains 16 rules unevenly divided into 11 rules for detecting the open-
line status under various circumstances (’Open’ rules), and 5 rules for detecting the closed-
line status (’Closed’ rules). In each category, the rules can be further classified in terms of
steady-state and transient rules.
Steady state behaviour:
The physical process behind opening a disconnected line is not so different from a closed
line at a zero active power transfer. Therefore, it is important to access, by theoretical
OP
computations, to what happens to critical measured variables such as the voltage and
reactive power when the active power, transmitted by a connected line, vanishes. In
analysing the classical ABCD line model in terms of the sending and receiving end variables
such as active power, reactive power and voltage, it can be shown that by varying the
so
voltages and power angle at either end, the power quantities can be eliminated at both ends
of the line. Figure 7 shows that, for a given line length, an operating point can be found
that, as seen from the sending end, both active and reactive powers vanishes.
Figure 7: Operating conditions resulting in zero MW and Mvar at the sending end