Measuring Principles - ABB Relion 670 Series Technical Reference Manual

Section 6
Impedance protection
6.5.2.4
266
Both current limits IMinPUPG and IMinOpIR are automatically
reduced to 75% of regular set values if the zone is set to operate in
reverse direction, that is, =.

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.
Here V and I represent the corresponding voltage and current phasors in the respective
phase A, B or C.
The calculation of the apparant impedances at phase-to-ground fault follow equation
The ground return compensation applies in a conventional manner.
VA
=
Z
app
+ ×
IA I KN
N
EQUATION1811-ANSI V1 EN
Where:
VA, IA 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
= +
Z 0 R 0 jX 0
EQUATION2106 V1 EN
= +
Z 1 R 1 jX 1
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
1MRK505222-UUS C
42
(Equation 42)
Technical reference manual