Negative Sequence Internal/External Fault Discriminator Feature - ABB REG670 Applications Manual

Section 7
Differential protection
7.3.3.3
172
IdUnre: IdUnre is the sensitivity of the unrestrained differential protection stage. The
choice of setting value can be based on calculation of the largest short circuit current
from the generator at fault in the external power system (normally three-phase short
circuit just outside of the protection zone on the LV side of the step-up transformer).
IdUnre is set as a multiple of the generator rated current.
OpCrossBlock: If OpCrossBlock is set to Yes, and START signal is active, activation
of the harmonic blocking in that phase will block the other phases as well.

Negative sequence internal/external fault discriminator feature

OpNegSeqDiff: OpNegSeqDiff is set to Yes for activation of the negative sequence
differential features, both the internal or external fault discrimination and the sensitive
negative sequence differential current feature. It is recommended to have this feature
enabled.
IMinNegSeq: IMinNegSeq is the setting of the smallest negative sequence current
when the negative sequence based functions shall be active. This sensitivity can
normally be set down to 0.04 times the generator rated current, to enable very sensitive
protection function. As the sensitive negative sequence differential protection
function is blocked at high currents the high sensitivity does not give risk of unwanted
function.
NegSeqROA: NegSeqROA is the "Relay Operate Angle", as described in figure 70.
The default value 60° is recommended as optimum value for dependability and
security.
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
1MRK 502 071-UEN -
Application manual