Setting Guidelines; General - ABB RELION 670 SERIES Applications Manual

Section 8
Impedance protection
8.13.4
8.13.4.1
420
RAA I
FC1
X
F
RAB I
FC2
CSAB
ANSI06000629 V1 EN
Figure 219: Current reversal phenomenon on parallel operating circuits
It is possible to expect faster IED operation and breaker opening at the bus closer to fault,
which will reverse the current direction on the healthy circuit. Distance IED RBB will
suddenly detect fault in forward direction and, if CRBB signal is still present due to long
reset time of IED RAB and especially telecommunication equipment, trip its related
circuit breaker, since all conditions for POTT have been fulfilled. Zero sequence mutual
impedance will additionally influence this process, since it increases the magnitude of
fault current in healthy circuit after the opening of first circuit breaker. The so called
current reversal phenomenon may cause unwanted operation of protection on healthy
circuit and this way endangers even more the complete system stability.
To avoid the unwanted tripping, some manufacturers provide a feature in their distance
protection which detects that the fault current has changed in direction and temporarily
blocks distance protection. Another method employed is to temporarily block the signals
received at the healthy line as soon as the parallel faulty line protection initiates tripping.
The second mentioned method has an advantage in that not the whole protection is
blocked for the short period. The disadvantage is that a local communication is needed
between two protection devices in the neighboring bays of the same substation.
Distance protection used on series compensated lines must have a high overreach to cover
the whole transmission line also when the capacitors are bypassed or out of service. When
the capacitors are in service, the overreach will increase tremendously and the whole
system will be very sensitive for false teleprotection signals. Current reversal difficulties
will be accentuated because the ratio of mutual impedance against self-impedance will be
much higher than for a non-compensated line.
If non-unit protection is to be used in a directional comparison mode, schemes based on
negative sequence quantities offer the advantage that they are insensitive to mutual
coupling. However, they can only be used for phase-to-ground and phase-to-phase faults.
For three-phase faults an additional protection must be provided.

Setting guidelines

General

The settings for Distance measuring zones, quadrilateral characteristic (ZMFCPDIS) are
done in primary values. The instrument transformer ratio that has been set for the analog
I RBA RAA I
FC1 FC1
RBB RAB I
FC2
CRBB CSAB
1MRK 506 369-UUS -
RBA
X
F
RBB
CRBB
en06000629_ansi.vsd
Line distance protection REL670 2.2 ANSI
Application manual