ABB RET670 - Page 120

delta, as shown in the right-hand side in figure 28, it must be ensured that the 24.9 kV
currents are rotated by 30° in anti-clockwise direction. Thus, the DAB CT delta
connection (see figure 28) must be used for 24.9 kV CTs in order to put 115 kV & 24.9
kV currents in phase.
To ensure proper application of the IED for this power transformer it is necessary to do
the following:
1. Check that HV & LV CTs are connected to 5 A CT inputs in the IED.
2. For second solution make sure that LV delta connected CTs are DAB connected.
3. For wye connected CTs make sure how they are 'star'red (that is, grounded) to/from
protected transformer.
4. Enter the following settings for all three CT input channels used for the HV side
CTs, see table
31.
Table 31: CT input channels used for the HV side CTs
Setting parameter Selected value for both solutions
CTprim 400
CTsec 5
CT_WyePoint ToObject
5. Enter the following settings for all three CT input channels used for the LV side
CTs, see table "CT input channels used for the LV side CTs".
CT input channels used for the LV side CTs
Setting parameter
Selected value for both Solution 1
(wye connected CT)
Selected value for both Solution 2
(delta connected CT)
CTprim 1500
1500
866
3
=
EQUATION1889 V1 EN (Equation 31)
CTsec 5 5
CT_WyePoint ToObject ToObject
To compensate for delta connected CTs, see equation 31.
6. Enter the following values for the general settings of the differential protection
function, see table32.
Section 3 1MRK504116-UUS C
IED application
114
Application manual