![background image](http://html.mh-extra.com/html/abb/relion-615-series/relion-615-series_technical-manual_2395525.webp)
Next, the settings for the CT ratio correction can be calculated.
CT ratio correction
=
I
I
n
nT
1
GUID-F5F45645-C809-4F99-B783-751C8CC822BF V1 EN
(Equation 90)
I
1n
nominal primary current of the CT
After the CT ratio correction, the measured currents and corresponding setting values of
87T are expressed in multiples of the rated power transformer current I
r
(xI
r
) or percentage
value of I
r
(%I
r
).
The rated input current (1A or 5A) of the relay does not have to be same for the HV and
the LV side. For example, the rated secondary current of 5 A can be used on the HV side,
while 1A is used on the LV side or vice versa.
Example
The rated power of the transformer is 25 MVA, the ratio of the CTs on the 110 kV side is
300/1 and that on the 21 kV side is 1000/1
GUID-DC9083B2-CB07-4F6B-8C06-52979E5F484A-ANSI V1 EN
Figure 260:
Example of two-winding power transformer differential protection
The rated load of the transformer is calculated:
HV side: I
nT_Wnd1
= 25 MVA / (1.732 x 110 kV) = 131.2 A
LV side: I
nT_Wnd2
= 25 MVA / (1.732 x 21 kV) = 687.3 A
Settings:
CT ratio Cor Wnd 1
= 300 A / 131.2 A = “2.29”
CT ratio Cor Wnd 2
= 1000 A / 687.3 A = “1.45”
1MAC059074-MB A
Section 4
Protection functions
615 series ANSI
519
Technical Manual
Содержание Relion 615 series
Страница 1: ... RELION PROTECTION AND CONTROL 615 series ANSI Technical Manual ...
Страница 2: ......
Страница 39: ...Section 17 Glossary 1181 Table of contents 615 series ANSI 33 Technical Manual ...
Страница 40: ...34 ...
Страница 64: ...58 ...
Страница 210: ...3 19 4 Settings Section 3 1MAC059074 MB A Basic functions 204 615 series ANSI Technical Manual ...
Страница 216: ...210 ...
Страница 884: ...878 ...
Страница 1038: ...1032 ...
Страница 1136: ...1130 ...
Страница 1172: ...1166 ...
Страница 1180: ...1174 ...
Страница 1186: ...1180 ...
Страница 1192: ...1186 ...
Страница 1193: ...1187 ...
Страница 1194: ......
Страница 1195: ......