Basler Electric BE1-CDS240 General Information - Manual (Page 14)

Figure 1-5. Three-Phase Connections, Delta-Wye Configuration, CT Compensation
There are several drawbacks to the traditional solution:
• The delta connection requires a dedicated set of CTs that generally cannot be used for other
purposes.
• The delta connection is more difficult to test.
• The delta-connected CTs experience greater burden than wye-connected CTs because the lead
burden must be multiplied by a factor of three in the CT performance calculation.
The BE1-CDS240 relays support the traditional solution so that they may be used in retrofit/modernization
projects. However, in a numerical relay, it is possible to connect all of the CTs in wye as shown in Figure
1-6 so that the drawbacks mentioned above are not a consideration. The BE1-CDS240 relay can
numerically combine currents internally to accomplish a numerical delta if required for phase angle
compensation.
The setup parameters for each of the current input circuits are described in Section 3, Input and Output
Functions, Power System Inputs. The CT connection and the transformer connection are included to
allow the BE1-CDS240 relay to automatically determine the appropriate combination of currents to
present to the differential protection function.
NOTE
The BE1-CDS240 relay uses transformer internal connection information to
determine the correct phase compensation to use. It is not possible to reliably
determine the phase compensation settings based simply upon phase angle
shift information because the phase shift from high to low side is dependent
upon the phase-sequence of the power system phasors. That is, a power
system with ABC phase-sequence will produce a different phase shift from
high to low than a power system with ACB phase-sequence in the same
transformer connection. By specifying the transformer connections from the
three-line diagram, the correct phase compensation can be determined in all
cases.
H
2
H
1
H
3 C
B
A
X
2
X
1
X
0
X
3 C
B
A
A13
A14
A9
A11
A7
A8
A5
A6
*
BE1-CDS240
*An alternative to grounding one corner of the delta connected CTs is
to connect the ground to a lead connected to terminal A10, 12, or 14.
P0017-03
02-28-03
A4
A3
A12
A10
1-12 BE1-CDS240 General Information 9365200990 Rev M