The ratio of delta differential to delta bias is smaller than a fixed threshold when the delta bias start signal is
asser
ted.
The External Fault Detection algorithm is on a per phase basis. If an external fault is detected on phase A, B or C,
signals External fault A, External fault B or External fault C are asserted. The external fault detector resets after 6
seconds from the start or after 25 cycles from the start if the current is less than 0.9Is1.
The following figure shows the time to saturation for an external fault.
V03124
IA-1 IB-1 IC-1
I/KA
2
1
0
-1
I/KA
2.5
0.0
-2.5
-5.0
IA-5 IB-5
IC-5
PU
1.0
0.5
1.5
0.0
PU
IA-DIFF IB-DIFF IC-DIFF
Time to saturation = 31.5ms
1.0
0.5
IA-BIAS IB-BIAS IC-BIAS
Figure 43: Time to saturation - external AN fault
3.8.7 CURRENT TRANSFORMER SUPERVISION
If the CTS Status setting in the SUPERVISION Column is set to restrain, then upon detection of a CTS condition, and
following the CTS Time Delay, the minimum operating current is raised to the Is-CTS value.
This has the effect of lifting the minimum operate current threshold on the bias characteristic as follows:
Chapter 6 - Transformer Differential Protection P64x
114 P64x-TM-EN-1.3
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