Basler Electric BE1-11t - Manual (Page 307)

9424200995 Rev H 295
Note
The CT input circuit settings are used by the auto-tap calculation
function to calculate the correct tap adjustment factor for the
differential functions. When entering these settings via the ASCII
command interface, the validation routine and auto-tap calculation is
performed on exit after all parameters have been entered.
When entering these settings using the front panel, the validation
routine and auto-tap calculation is performed on exit of each screen.
This may cause an Out of Range error message from the auto-tap
calculation function. The user is advised to enter valid CT input circuit
settings on the Sensing Transformers screen prior to entering the
auto-tap calculation settings. If the user has previously set the auto-
tap calculation settings and needs to change the CT input circuit
settings, it may be necessary to temporarily change the auto-tap
function setting to Manual on the Transformer Setup screen in order to
enter the new CT settings.
See the
Phase Current Differential (87) Protection chapter for more
information on the auto-tap calculation function.
If there is a ground source within the protected zone, the user can apply a numerical, zero-sequence trap
to remove the zero-sequence components from the current to prevent misoperation on external ground
faults when a ground bank is in the zone of protection. This setting is optional. It is not required to enter a
ground source setting of 1 to describe a grounded wye transformer connection. Even though not all
grounded wye transformer connections are ground sources, the BE1-11t 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 BE1-11t
chooses delta compensation for a wye transformer connection so that the zero-sequence components are
blocked.
Figure 234 shows how the currents will be calculated for each set of current inputs for use by the Current
Differential Protection (87) element. The calculation is dependent upon the phase compensation chosen
as shown in the previous tables and the ground source setting.
Table 99. Internal Compensation Chart
Compensation
Ground
Compensation
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
DDAB 0 = No or 1 = Yes (I
A
- 2I
B
+ I
C
) /3 (I
A
+ I
B
- 2I
C
) /3 (-2I
A
+ I
B
+ I
C
) /3
BE1-11t Configuration