ABB 615 series Technical Manual page 474

Section 4
Protection functions
468
GUID-74289FF5-E90D-4633-9FEE-04DB8E86A3AE V1 EN
Figure 227: Example of CT ratio correction setting calculation with in-zone
transformer
The rated load of the transformer is:
HV side (A): I = 5 MVA / (1.732 × 20 kV) = 144.3 A
nT_A
LV side (A): I = 5 MVA / (1.732 × 10.5 kV) = 274.9 A
nT_B
So the settings for CT ratio Corrections at HV (A) and LV (B) side are:
CT ratio Correction (A) = 200 A / 144.3 A = 1.386
CT ratio Correction (B) = 300 A / 274.9 A = 1.091
CT connections
The connections of the primary current transformers are designated as "Type 1" and
"Type 2".
• If the positive directions of the winding 1 and winding 2 protection relay currents are
opposite, the CT connection type setting parameter is "Type 1". The connection
examples of "Type 1" are as shown in the
• If the positive directions of the winding 1 and winding 2 protection relay currents
equate, the CT connection type setting parameter is "Type 2". The connection
examples of "Type 2" are as shown in the
• The default value of the CT connection type setting is "Type 1".
Figure 228 and Figure 229.
Figure 230 and Figure 231.
1MAC059074-MB A
615 series ANSI
Technical Manual