Current Input Exclusion Function; Current Input Exclusion Logic; Application Notes; Current Input Exclusion Example - GE P642 Technical Manual

Chapter 13 - Monitoring and Control
5

CURRENT INPUT EXCLUSION FUNCTION

In the P643 and P645, it is possible to exclude current inputs from the protection functions. This may be useful for
example in a phase shifting transformer, or during the commissioning or maintenance process.
When a current input is excluded, the device sets the current from that input to zero for calculation purposes, even
if the current measured is not zero. The device compares the actual current flowing with the under current element
threshold to ensure that the CT input is excluded if the current is below the undercurrent threshold when the
master CT exclusion DDB signal is not asserted. The under current threshold is fixed to 0.05 In.
5.1

CURRENT INPUT EXCLUSION LOGIC

CT Exclu Ena
CT1 Exclu Ena
CT1 PhA UnderCur
CT1 PhB UnderCur
CT1 PhC UnderCur
V01231
CT1 Excluded
CT2 Excluded
CT3 Excluded
CT1 Excluded
CT2 Excluded
CT3 Excluded
CT4 Excluded
CT5 Excluded
V01232

Figure 125: CT Exclusion logic

Only one current input can be excluded from the P643 and a maximum of three current inputs can be excluded
from the P645. An alarm DDB (Insuff No. of CT) is issued when more than the maximum number of current inputs
are excluded. The status of the exclusion DDB signals (CTx Excluded) is stored in the device's internal non-volatile
memory. An alarm (CTexcl disa prot) is raised if the stored statuses do not match the statuses after the power
supply is re-established. When the CTexcl disa prot DDB signal is asserted, all protection functions using the
relevant CT inputs are blocked.
Note:
For the differential element to operate correctly, the number of CTs used cannot be less than 2. Also CTs should be excluded
one at a time.
5.2

APPLICATION NOTES

5.2.1

CURRENT INPUT EXCLUSION EXAMPLE

In the following figure, the adjacent isolators to CB1 are open and locked because of maintenance work on CB1.
276
&
&
&
&
1
P643
≥2
P645
≥4
1 S
Q
R
Note: This diagram does not show all stages . Other stages follow similar principles.
P64x
CT1 Excluded
insuff No. of CT
insuff No. of CT
P64x-TM-EN-1.3