Alstom MiCOM P846, Техническое руководство

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Operation P846/EN OP/D
MiCOM P846
(OP) 5-11
OP
The fuzzy rules operate according to physical principles. For example, we may define with
fuzzy variables "Active power" and "DeltaP" presented in figure 6 the following rules:
A steady state rule for security: If (Active Power is not SMALL) than Line is CLOSED
A transient rule for reliability: If (DeltaP is LARGE) than line is being OPENED
All the rules for detecting (quickly or slowly) the close to open switching action of the line
breaker relies on a
∆ -filter principle just described. In addition, when the line is opened at the
remote end, the ∆ -filter is combined with a so-called ’Line Charging’ threshold to assert the
situation. Steady-state ’off’ rules heavily rely on two concepts: steady-state indicators (with
redundancy) and the short-term memory of the line the past status.
The consistency of the voltage signals are reflected in the excess negative sequence voltage
and the excess sub-synchronous voltage, which are expressed in fraction of the positive
sequence voltage magnitude. These variables are used in two complementary rules and in
order to rapidly detect the open line condition while the line is still discharging into shunt
elements at both ends, with or without sub-synchronous resonance in the bus voltage.
The decision system is built in such a way that closing the line suddenly will be signalled up
to 4 cycles after the 3-cycle active power crosses the 1.5% threshold, while an open-line
condition is detected with a variable time lag, ranging from 25 to 40 ms for power transfer
higher than 1.5%. For lower power transfer (i.e. < 1.5%), the time response is degraded but
remains in the 50ms-range. Additionally, when it is locked in a closed state and the line is
actually closed, the relay remains in that state with a 100%-level of security i.e. whatever the
specified faults on parallel lines, switching transients, power ramps, power transfer direction,
etc.
1.3.4.3 Crisp decision sent to the output
The last step in figure 6 called defuzzyfication consists in converting the evaluation results of
the 16 criteria into a single decision. Each criteria states that the line is open or closed with a
given probability and defuzzyfication really aims at reconciling all partial decisions using an
aggregation procedure.
1.4 Two out of three detection
In normal operation, the DLO is made to detect an open line when all three phases of the
line breaker are opened. The detection is essentially based on the complete loss of active
power on the line. However, it may happen that a circuit breaker fails to open its three
phases leaving one of them still closed. In the context of SPS (Special Protection Systems)
using topology detection to trigger remedial actions, the loss of two out of three phases of a
transmission line is a significant event that may require similar action as a complete loss of a
line. For this reason, a mechanism has been incorporated in the DLO to detect this kind of
circuit breaker failure.
The 2 out of 3 detection is a separate block that does not require the DLO fuzzy variables
and rules. It is based on the detection of asymmetrical currents that prevail during such
conditions. Its response time is typically 40ms. As for the DLO main output, the 2 out of 3 is
an internal signal available for the PSL. (Programmable Scheme Logic).