Setting Guidelines - ABB REL670 2.2 IEC Applications Manual

1MRK 506 369-UEN B
8.1.3
8.1.3.1
Line distance protection REL670 2.2 IEC
Application manual
RAA I
FC1
F
RAB I
FC2
CSAB
IEC06000629 V1 EN-US
Figure 99: 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 in 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-earth and phase-
to-phase faults. For three-phase faults an additional protection must be provided.

Setting guidelines

General
The settings for the distance protection function are done in primary values. The
instrument transformer ratio that has been set for the analog input card is used to
automatically convert the measured secondary input signals to primary values used
in the distance protection function.
I RBA RAA I
FC1 FC1
RBB RAB I
FC2
CRBB CSAB
Section 8
Impedance protection
RBA
F
RBB
CRBB
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SEMOD168247-4 v2
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