ABB RELION REX640 - Page 1028

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