ABB RET670 - Page 251

The final reach in resistive direction for phase-to-ground fault loop measurement
automatically follows the values of the line-positive and zero-sequence resistance, and
at the end of the protected zone is equal to equation 160.
1
R (2 R1PG R0PG) RFPG
3
= × + +
EQUATION1716 V1 EN (Equation 160)
2 X1PE+X0
arctan
2 R1PE+R0
loop j
é ù
×
ê ú
=
×
ê ú
ë û
EQUATION1457 V1 EN (Equation 161)
Setting of the resistive reach for the underreaching zone1 must follow the following
condition:
RFP G 4.5 X1P G£ ×
EQUATION1717 V1 EN (Equation 162)
The fault resistance for phase-to-phase faults is normally quite low, compared to the
fault resistance for phase-to-ground faults. Limit the setting of the zone1 reach in
resistive direction for phase-to-phase loop measurement to:
3 1
RFPP X£ ×
EQUATION570 V2 EN (Equation 163)
Load impedance limitation, without load encroachment function
The following instructions is valid when the load encroachment function is not
activated, which is done by setting the parameter Rld for the Phase Selector to its upper
limit. If the load encroachment function 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 IED 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 (Equation 164)
Where:
V is the minimum phase-to-phase voltage in kV
S is the maximum apparent power in MVA.
1MRK504116-UUS C Section 3
IED application
245
Application manual