ABB REG650 Technical Manual page 116

Section 5
Differential protection
110
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 52: NegSeqROA determines the boundary between the internal and
external fault regions
Unrestrained negative sequence differential protection
If one or more start 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 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 start 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 protected generator. Operation of this protection is signaled on
the output of the function as TRNSENS.
90 deg
120 deg
270 deg
1MRK 502 034-UEN -
NegSeqROA
(Relay Operate Angle)
Internal fault
region
0 deg
IminNegSeq
Internal /
external fault
boundary.
Default ± 60 deg
en06000433-2.vsd
Technical Manual