ABB RELION REX640 Technical Manual page 950

Section 4
Protection functions
944
Table 879: Voltages and currents used in impedance calculation
Impedance Meas mode
1Phase-to-phase
1Phase-to-phase
1Phase-to-phase
3Phase-to-phase
1) Voltages and currents in the calculations are given in volts and amps.
If all three phase or phase-phase voltages and phase currents are fed to
the protection relay, the "3Phase-to-phase" mode is recommended.
The current measurement of the function is based on two alternative measurement
modes, "DFT" and "Peak-to-Peak". The measurement mode is selected using the
Measurement mode setting.
If the current magnitude is below 0.02 · I
impedance value is not evaluated and the maximum impedance value (99.999 pu) is
shown in the Monitored data view.
The calculated impedances are converted to a pu impedance as the
operating characteristics are defined using the Polar reach setting in
%Zb.
The calculated phase-phase impedance amplitudes Z_AMPL_AB, Z_AMPL_BC and
Z_AMPL_CA are available as pu values in the Monitored data view.
Underimpedance detection
The operating characteristic is an origin-centric circle on the impedance plane. The
origin-centric circular characteristic is defined using the Polar reach setting. If the
calculated impedance value enters the circle in the impedance plane, the module sends
an enabling signal to start the Timer.
Phase Sel for Z Clc
AB
BC
CA
N/A
, where I is the nominal phase current, the
N N
1MRS759142 C
Voltages and currents used in
1)
impedance calculation
U AB
_
ZAB
=
I A I B
_ _
−
U BC _
ZBC
=
I B I C
_ _
−
U CA _
ZCA
=
I C I A
_ _
−
U AB
_
ZAB
=
I A I B _ _
−
U BC
_
ZBC
=
I B I C _ _
−
U CA _
ZCA
=
I C I A
_ _
−
REX640
Technical Manual