ABB RELION 670 SERIES Applications Manual page 763

1MRK 506 369-UUS -
Line distance protection REL670 2.2 ANSI
Application manual
during power system faults, the time during which the protection schemes must perform
their tasks flawlessly.
The logic supports the following communications schemes:
• blocking scheme
• permissive schemes (overreach and underreach)
• direct intertrip
A permissive scheme is inherently faster and has better security against false tripping than
a blocking scheme. On the other hand, permissive scheme depends on a received CR
signal for a fast trip, so its dependability is lower than that of a blocking scheme.
When single-pole tripping is required on parallel lines, an unwanted three-pole trip can
occur for simultaneous faults near the line end (typical last 20%). Simultaneous faults are
one fault on each of the two lines but in different phases, see figure 371. When
simultaneous faults occur, the phase selectors at the remote protection IED - relative to the
faults, see the A side in figure
line and on the parallel line. The phase selector must be set to cover the whole line with a
margin and will also detect a fault on the parallel line. Instantaneous phase-selective
tripping for simultaneous faults close to line end is not possible with the information that
is available locally in the remote protection IEDs relative to the faults. The protection IED
near the faults detects the faults on the protected line as a forward fault, and on the parallel
line in reverse direction. The directional phase selector in the two IEDs near the faults can
discriminate between the faults and issue correct single-pole tripping commands.
Station A
A C
B
ANSI06000309 V2 EN
Figure 371: Simultaneous faults on two parallel lines
By using phase-segregated channels for the communication scheme, the correct phase
information in the protection IED near the faults can be transferred to the other side
371 - cannot discriminate between the fault on the protected
Ground
IED IED
Section 16
Scheme communication
Station B
A C
B
ANSI06000309_2_en.vsd
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