U3P
I3P
OPERATE
START
Under
impedance
detection
BLOCK
Impedance
calculation
t
Timer
Blocking
logic
I_B
I_A
I_C
U_A_AB
U_B_BC
U_C_CA
Figure 570: Functional module diagram
Impedance calculation
This module calculates the impedance based on the selected voltages and currents.
The
Impedance Meas mode and Phase Sel for Z Clc settings determine which
voltages and currents are to be used. If
Impedance Meas mode is set to "1Phase-
phase", the
Phase Sel for Z Clc setting is needed for determining which phase-phase
voltages ("AB", "BC" and "CA") and currents should be used for calculating the
impedance.
Table 960: Voltages and currents used in impedance calculation
Impedance Meas mode
Phase Sel for Z Clc
Voltages and currents used
in impedance calculation
1
1Phase-phase
AB
ZAB
U
AB
I
A
I
B
=
−
_
_
_
1Phase-phase
BC
ZBC
U
BC
I
B
I
C
=
−
_
_
_
1Phase-phase
CA
ZCA
U
CA
I
C
I
A
=
−
_
_
_
3Phase-phase
N/A
ZAB
U
AB
I
A
I
B
=
−
_
_
_
ZBC
U
BC
I
B
I
C
=
−
_
_
_
ZCA
U
CA
I
C
I
A
=
−
_
_
_
If all three phase or phase-phase voltages and phase currents are fed to
the protection relay, the "3Phase-phase" mode is recommended.
1
Voltages and currents in the calculations are given in volts and amps.
Protection functions
1MRS759142 F
1028
REX640
Technical Manual