6.5.4 Operation principle
The function can be enabled and disabled with the
Operation
setting. The
corresponding parameter values are "On" and "Off".
The operation of SEQSPVC can be described with a module diagram. All the
modules in the diagram are explained in the next sections.
Figure 480: Functional module diagram
Negative phase-sequence criterion
A fuse failure based on the negative-sequence criterion is detected if the measured
negative-sequence voltage exceeds the set
Neg Seq voltage Lev
value and the
measured negative-sequence current is below the set
Neg Seq current Lev
value.
The detected fuse failure is reported to the decision logic module.
Voltage check
The phase voltage magnitude is checked when deciding whether the fuse failure is a
three, two or a single-phase fault.
The module makes a phase-specific comparison between each voltage input and
the
Seal in voltage
setting. If the input voltage is lower than the setting, the
corresponding phase is reported to the decision logic module.
Current and voltage delta criterion
The delta function can be activated by setting the
Change rate enable
parameter
to "True". Once the function is activated, it operates in parallel with the negative
sequence-based algorithm. The current and voltage are continuously measured in
all three phases to calculate:
• Change of voltage dU/dt
• Change of current dI/dt
1MRS757644 H
Supervision functions
620 series
Technical Manual
899
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