Basler BE1-CDS220, Instruction Manual

Page: 56 / 476

3-8 Input And Output Functions BE1-CDS220
setting of 1 to describe a grounded wye transformer connection. Even though not all grounded wye
transformer connections are ground sources, the relay always assumes that a wye transformer
connection is a ground source so that it is secure. Zero sequence current unbalance can occur in three
legged core transformers due to the phantom tertiary effect. In all cases, the relay chooses delta
compensation for a wye transformer connection so that the zero sequence components are blocked.
Figure 3-4 shows how the currents will be calculated for each set of current inputs for use by the phase
differential protection function. The calculation is dependent upon the phase compensation chosen as
shown in Table 3-2 and the ground source setting.
Table 3-3. Internal Compensation Chart
Compensation Ground Source A Phase B Phase C Phase
Wye (None) 0 = No I
A
I
B
I
C
Wye (None) 1 = Yes I
A
- I
0
I
B
- I
0
I
C
- I
0
DAB 0 = No or 1 = Yes (I
A
- I
B
) /
√
3 (I
B
- I
C
) /
√
3 (I
C
- I
A
) /
√
3
DAC 0 = No or 1 = Yes
(I
A
- I
C
) /
√
3 (I
B
- I
A
) /
√
3 (I
C
- I
B
) /
√
3
Figure 3-4. Internal Phase and Zero Sequence Compensation
CT connection settings can be entered through BESTCOMS, the optional HMI using screen 6.3.1.1,
SETUP\PWR_S\CON\CTP, and from the ASCII command interface using the SG-CT (setting general-CT
input circuit) command.
If the BE1-CDS220 relay is equipped with the optional independent ground current input, the CT ratio
must be entered for that input. This setting can be entered from the optional HMI using screen 6.3.1.2,
SETUP\PWR_S\CON\CTG, from the ASCII command interface using the SG-CTG (setting general-CT
input circuit ground) command, and through BESTCOMS.
SG-CTn and SG-CTG affect the primary current metering values, the contact duty log (RB-DUTY)
calculations, the transformer duty log (RT-DUTY), and the COMTRADE fault record current levels. The
CT ratios and connections also affect the automatic phase compensation used by the 87 differential
function as well as the auto-tap calculation.
I
A
I
B
I
C
-I
B
-I
C
-I
A
(I
A
-I
B
)/
√
3
(I
B
-I
C
)/
√
3
(I
C
-I
A
)/
√
3
I
A
-I
C
I
B
-I
A
-I
B
I
C
(I
A
-I
C
)/
√
3
(I
C
-I
B
)/
√
3
(I
B
-I
A
)/
√
3
DAB Internal Compensation DAC Internal Compensation
Measured Current Measured Current *(-1) Compensated Current