Current Transformer Supervision; Figure 43: Time To Saturation - External An Fault - GE P642 Technical Manual

Chapter 6 - Transformer Differential Protection
The ratio of delta differential to delta bias is smaller than a fixed threshold when the delta bias start signal is
asserted.
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.
I/KA
2
1
0
-1
IA-1
I/KA
2.5
0.0
-2.5
-5.0
IA-5
PU
1.0
0.5
0.0
IA-DIFF
PU
1.5
1.0
0.5
IA-BIAS
V03124

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:
114
IB-1 IC-1
IB-5
IC-5
Time to saturation = 31.5ms
IB-DIFF
IB-BIAS
IC-DIFF
IC-BIAS
P64x
P64x-TM-EN-1.3