ABB REG650 Technical Manual page 126

Section 6
Differential protection
120
IAn
ANSI07000018 V3 EN
Figure 47: Internal fault
IAn
External fault: IAn = - IAt
IAt
ANSI07000019 V2 EN
Figure 48: External fault
Generator differential protection GENPDIF (87G) function uses two mutually
independent characteristics to which magnitudes of the three fundamental frequency
RMS differential currents are compared at each execution of the differential protection
function. These two characteristics divide, each of them independently, the operate
current – restrain current plane into two regions: the operate (trip) region and the
restrain (block) region, as shown in figure 50. Two kinds of protection are obtained:
IAt
IAt
IAn
ANSI0700018_3_en.vsd
IAt
Idiff = 0
en07000019-2_ansi.vsd
1MRK 502 043-UUS B
Idiff
IAn
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