Load Impedance Limitation, Without Load Encroachment Function246 - ABB RELION 670 SERIES Applications Manual

Section 8
Impedance protection
8.3.3.7
246
Setting of the resistive reach for the underreaching zone 1 should follow the condition to
minimize the risk for overreaching:
 
RFPEZx 4.5 X1Zx
IECEQUATION2305 V2 EN
The fault resistance for phase-to-phase faults is normally quite low, compared to the fault
resistance for phase-to-ground faults. To minimize the risk for overreaching, limit the
setting of the zone 1 reach in resistive direction for phase-to-phase loop measurement in
the phase domain to:
 
R FPPZx 6 X Zx 1
IECEQUATION2306 V3 EN
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 used. The setting of the load
resistance RLdFwd and RldRev in FDPSPDIS (21) must in this case be set to max value
(3000). If FDPSPDIS (21) is to be used for all or some of the measuring zones, the load
limitation for those zones according to this chapter can be omitted. 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
1MRK 506 369-UUS -
(Equation 141)
(Equation 142)
(Equation 143)
(Equation 144)
Line distance protection REL670 2.2 ANSI
Application manual