Quadrilateral Characteristics - ABB REL650 Applications Manual

Section 6
Impedance protection
6.1.3.3
136

Quadrilateral characteristics

Load impedance limitation, without load encroachment function
The following instructions are valid when Phase selection with load encroachment,
quadrilateral characteristic function FDPSPDIS (21) is not activated. To deactivate the
function, the setting of the load resistance RLdFwd and RldRev in FDPSPDIS (21) must
be set to max value (3000). Check the maximum permissible resistive reach for any zone
to ensure that there is a sufficient setting margin between the boundary and the minimum
load impedance. The minimum load impedance (Ω/phase) is calculated as:
2
V
=
Z
loa d min
S
EQUATION1718 V1 EN
Where:
V is the minimum phase-to-phase voltage in kV
S is the maximum apparent power in MVA.
The load impedance [Ω/phase] is a function of the minimum operation voltage and the
maximum load current:
V
=
min
Z
loa d
×
3 I
ma x
EQUATION1719 V1 EN
Minimum voltage V and maximum current I
min
conditions. Minimum load impedance occurs normally under emergency conditions.
As a safety margin is required to avoid load encroachment under three-
phase conditions and to guarantee correct healthy phase IED operation
under combined heavy three-phase load and ground faults, consider both:
phase-to-phase and phase-to-ground fault operating characteristics.
To avoid load encroachment for the phase-to-ground measuring elements, the set resistive
reach of any distance protection zone must be less than 80% of the minimum load
impedance.
£ ×
RFPG 0.8 Z
load
GUID-AD2F1BE2-8442-4ED1-A558-21D092CEE170 V1 EN
1MRK 506 334-UUS A
are related to the same operating
max
(Equation 51)
(Equation 52)
(Equation 53)
Application manual