ABB Relion REG670, Руководство по применению

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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.
8.3.4 Setting guidelines
8.3.4.1 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 input card is used to automatically convert the measured secondary input
signals to primary values used in ZMFCPDIS.
The following basics must be considered, depending on application, when doing the
setting calculations:
• Errors introduced by current and voltage instrument transformers, particularly
under transient conditions.
• Inaccuracies in the line zero-sequence impedance data, and their effect on the
calculated value of the earth-return compensation factor.
• The effect of infeed between the IED and the fault location, including the
influence of different Z
0
/Z
1
ratios of the various sources.
1MRK 502 071-UEN -
Section 8
Impedance protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 247
Application manual