ABB REG650 Technical Manual page 132

Section 6
Differential protection
126
Angle could not be
measured. One or both
currents too small
180 deg
External fault
region
The characteristic is defined by the
settings:
IMinNegSeq and NegSeqROA
IEC06000433 V2 EN
Figure 51: NegSeqROA determines the boundary between the internal and
external fault regions
Unrestrained negative sequence differential protection
If one or more pickup signals have been set by the restrained differential protection
algorithm, because one or more of the fundamental frequency differential currents
entered the "operate" region of the restrained differential protection, then the internal/
external fault discriminator can enhance the final, common, trip command by the
differential protection. If a fault is classified as internal, then any eventual block
signals by the harmonic criterion are ignored, and the differential protection operates
immediately without any further delay. This makes the overall generator differential
protection very fast. Operation of this protection is signaled on the output of GENPDIF
(87G) as TRNSUNRE.
Sensitive negative sequence differential protection
The difference from the unrestrained negative sequence differential protection,
described above, is that the sensitive one does not require any pickup signal to be set. It
is enough that both of the negative sequence currents, contributions to the total
negative sequence differential current, which should be compared, are above the
setting IMinNegSeq. Thus, this protection can be made very sensitive. Further, an
intentional delay of one cycle is added in order not to inadvertently operate for some
eventual transients. Further, the sensitive negative sequence differential protection is
automatically disabled when the bias current exceeds 1.5 times the rated current of the
90 deg
120 deg
IminNegSeq
270 deg
1MRK 502 043-UUS B
NegSeqROA
(Relay Operate Angle)
Internal fault
region
0 deg
Internal /
external fault
boundary.
Default ± 60 deg
en06000433-2.vsd
Technical Manual