ABB REG670 Applications Manual page 758

Section 24
Requirements
752
142
³ =
ALF 17.8
( )
+
3 5
EQUATION2540 V2 EN
CTs with the following data will fulfil the requirements for the generator differential
protection in this application:
• Class 5P20 (5P18), 5 VA and R
It shall be noted that even if the rated burden of this CT is specified to 5 VA it is not
possible to have an actual burden more than 2.8 Ω and still fulfil the CT requirements.
It is of course also possible to specify the CT according to other classes. For example
a CT with the following data will also fulfil the requirements:
• Class PX, R < 3 Ω and the knee point e.m.f.
CT
³ × = ×
E 0.8 E 0.8 142 114 V
k al
EQUATION2541 V2 EN
As an alternative it can be suitable to provide the CT manufacturer with the data
according to equation 299
I
³ = × NG ×
E E 30
al alreqRat
I
pr
EQUATION2542 V2 EN
E
³
al
30
( )
+ +
R R R
CT w addbu
E
3250
³ × × =
al
30 1 24.4
+
R 2.8 4000
CT
EQUATION2543 V2 EN
This can give the CT manufacturer a possibility to optimize the relation between the
resistance of the CT winding and the area of the iron core.
If the CT shall be specified as a class PX the following relation between the knee point
e.m.f. E and R shall be fulfilled:
k ct
E
³
k
24.4
( )
× +
0.8 R 2.8
ct
EQUATION2544 V2 EN
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
< 3 Ω.
ct
=
as follows:
( )
+ + =
I R R R 30
sr ct w addbu
I
× ×
NG
I
sr
I
pr
E
³
k
or 19.5
+
R 2.8
ct
1MRK 502 071-UEN -
(Equation 297)
(Equation 298)
3250
( )
× × × +
1 R 2,8
ct
4000
(Equation 299)
(Equation 300)
(Equation 301)
Application manual