5.3.3
Functionality
The fuse failure supervision function SEQSPVC is used to block the voltage-
measuring functions when failure occurs in the secondary circuits between the
voltage transformer (or combi sensor or voltage sensor) and merging unit to avoid
faulty operation of the voltage protection functions.
SEQSPVC has two algorithms, a negative sequence-based algorithm and a delta
current and delta voltage algorithm.
A criterion based on the delta current and the delta voltage measurements can be
activated to detect three-phase fuse failures which usually are more associated with
the voltage transformer switching during station operations.
5.3.4
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 102: 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.
Supervision functions
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SMU615
Technical Manual
Summary of Contents for Relion SMU615
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