MINCB_OPEN
DISCON_OPEN
Negative
phase
sequence
criterion
Current and
voltage
delta
criterion
I
2
I3P
I_C
I_B
I_A
BLOCK
Voltage
check
CB_CLOSED
U_A_AB
U3P
U
2
U_C_CA
U_B_BC
Decision
logic
FUSEF_3PH
FUSEF_U
Figure 758: 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
The calculated delta quantities are compared to the respective set values of the
Current change rate
and
Voltage change rate
settings.
The delta current and delta voltage algorithms detect a fuse failure if there is a
sufficient negative change in the voltage amplitude without a sufficient change in
1MRS759142 F
Supervision functions
REX640
Technical Manual
1333
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