ABB Relion SMU615 Technical Manual page 149

1MRS758407 B
SMU615
Technical Manual
GUID-27E5A90A-6DCB-4545-A33A-F37C02F27A28 V1 EN
Figure 100: 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.
Section 5
Supervision functions
143