ABB Relion 670 series, Technical Reference Manual

Page: 186 / 1232

6.1.3.4 Measuring principles
Fault loop equations use the complex values of voltage, current, and changes in the
current. Apparent impedances are calculated and compared with the set limits. The
apparent impedances at phase-to-phase faults follow equation
4 (example for a phase A
to phase B fault).
=
V
A
- V
B
Z
app
I
A
- I
B
EQUATION1545 V1 EN
(Equation 4)
Here V and I represent the corresponding voltage and current phasors in the respective
phase Ln (n = 1, 2, 3)
The ground return compensation applies in a conventional manner to phase-to-ground
faults (example for a phase A to ground fault) according to equation
5 .
=
+ ×
app
N
V _ A
Z
I _ A I KN
EQUATION1546 V1 EN
(Equation 5)
Where:
V_A, I_A and IN are the phase voltage, phase current and residual current present to the IED
KN is defined as:
Z0 Z1
KN
3 Z1
-
=
×
EQUATION-2105 V1 EN
0 0 0 Z R jX
= +
EQUATION2106 V1 EN
1 1 1 Z R jX
= +
EQUATION2107 V1 EN
Where
R0
is setting of the resistive zero sequence reach
X0 is setting of the reactive zero sequence reach
R1 is setting of the resistive positive sequence reach
X1 is setting of the reactive positive sequence reach
Section 6
1MRK505222-UUS C
Impedance protection
180
Technical reference manual