Basler Electric BE1-CDS240 General Information - Manual (Page 16)

contained in the CT circuit setup parameters. In the example shown in Figure 1-7, the compensation logic
would require that the delta compensation be applied to the grounded wye winding. The grounding bank
on the delta side will cause the differential protection to operate for external ground faults. Figure 1-7
shows how this would be done with traditional differential relays.
Figure 1-7. Traditional Zero-Sequence Trap for Application with Ground Banks
This application is greatly simplified with the BE1-CDS240. The user can connect all CTs in wye and
specify that the delta transformer winding has a ground source. The BE1-CDS240 will apply delta
compensation to the wye winding to obtain phase shift and zero-sequence compensation for that current
input. For the delta winding with ground source, it will numerically remove the zero-sequence components
from that current input just as would traditionally be done with a zero-sequence trap. The setup
parameters for each of the current input circuits are described in Section 3, Input and Output Functions,
Power System Inputs. The parameters specifying CT connection, transformer connection and ground
source for each current circuit determines the angle and zero-sequence compensation used on each
current input.
NOTE
The BE1-CDS240 relay does not automatically remove the zero-sequence
components from all currents presented to the differential protection functions
as that can unnecessarily reduce the relay's sensitivity to internal ground faults
by 33%. Also, since the zero-sequence components are removed from all
phases, it can result in confusion during single-phase testing by introducing
differential current in phases not under test.
C
B
A
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b
a
D2837-16
12-14-98
I
B
I
C
Delta CT Connection
Wye/Delta (DAB)
Transformer with Ground
Bank on Delta Side
Wye CT Connection
GROUNDING
BANK
I O
I O
I O
I O I O I O
3I O
3I O
1 2
C
1 2
C
1 2
C
87T
87T
87T
I A -I B
I B -I C
I C -I A
Ia-Io
Ib-Io
Ic-Io
I O I O I O
I O I O I O
I
c
I
b
I
C
I
a
1-14 BE1-CDS240 General Information 9365200990 Rev M