ABB RELION REB500 Technical Manual page 45

1MRK 505 406-UEN B
IEC19000407 V1 EN-US
Figure 6:
Because of the method used to represent impedances by the processor program, the
impedance settings should not be set higher than necessary, otherwise the resolution for low
impedances will be reduced.
Minimum permissible reach of the underimpedance starters
The starting units must reliably pick-up for a fault towards the end of the next section of line
(backup zone). If the backup protection of the adjacent section of line is not necessary, the
starters must be set to at least 1.3 times the impedance of the protected line. In the case of
short lines, fault resistance becomes a factor to be taken into account.
Maximum permissible reach of the underimpedance starters
• The setting must take account of the considerable increase in the load current of the
healthy circuit of a double-circuit line, when a fault on one circuit is tripped.
• To ensure that the phase selection is correct for single-phase autoreclosure, the starters
in the healthy phases must not pick up for a ground fault on one of the phases (in spite of
any balancing currents which may occur).
The resulting limits are as follows:
• Solidly grounded systems
Z
• Ungrounded systems or system with Petersen coils
Bay protection functions REB500
Technical manual
-RLoad
RB
Underimpedance starting characteristic
U

2 (   )
set
I I
max
B A
© Copyright 2019 ABB. All rights reserved
X
XA
RA
RLoad
XB
Ω/ph
Bay protection functions
AngleLoad
R
18000005--1-en.vsdx
Section 5
39