ABB RELION RET670, Applications Manual

Page: 286 / 1016

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-US
(Equation 146)
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:
6 1 RFPPZx X Zx
 
IECEQUATION2306 V3 EN-US
(Equation 147)
8.3.3.7 Load impedance limitation, without load encroachment function
SEMOD55087-97 v9
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
loa d min
Z
V
S
=
EQUATION1718 V1 EN-US
(Equation 148)
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:
min
loa d
ma x
Z
V
3 I
=
×
EQUATION1719 V1 EN-US
(Equation 149)
Section 8
1MRK 504 163-UUS A
Impedance protection
280 Transformer protection RET670 2.2 ANSI
Application manual