ABB Relion Technical Manual page 150

Section 6
Differential protection
144
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 55: 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
90 deg
120 deg
IminNegSeq
270 deg
1MRK 502 048-UUS A
NegSeqROA
(Relay Operate Angle)
Internal fault
region
0 deg
Internal /
external fault
boundary.
Default ± 60 deg
en06000433-2.vsd
Technical manual