Figure 374: Functional module diagram
Impedance calculation
This module calculates the apparent impedance based on the selected voltages
and currents. The
Measurement mode
and
Phase Sel for Z Clc
settings determine
which voltages and currents are to be used. If the
Measurement mode
is set to
"1Phase-earth" or "1Phase-phase", the
Phase Sel for Z Clc
setting is needed for
determining which phase or phase-phase voltages ("A or AB", "B or BC" and "C or
CA") and currents should be used for calculating the impedance.
Table 682: Voltages and currents used in impedance calculation
Measurement mode Phase Sel for Z Clc Voltages and currents
1Phase-earth A or AB U_A, I_A
1Phase-earth B or BC U_B, I_B
1Phase-earth C or CA U_C, I_C
1Phase-phase A or AB U_AB, I_A, I_B
1Phase-phase B or BC U_BC, I_B, I_C
1Phase-phase C or CA U_CA, I_C, I_A
3Phase-earth N/A U_A, U_B, U_C, I_A, I_B, I_C
3Phase-phase N/A U_AB, U_BC, U_CA, I_A, I_B, I_C
Pos seqn N/A { U_A,U_B,U_C } or { U_AB,U_BC,U_CA } and
I_A, I_B, I_C
If all three phase voltages and phase currents are fed to the protection
relay, the positive-sequence alternative is recommended.
1MRS757644 H Protection functions
620 series
Technical Manual
721
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