ABB Relion REG670, Applications Manual

Page: 758 / 780

( )
³ =
+
142
ALF 17.8
3 5
EQUATION2540 V2 EN
(Equation 297)
CTs with the following data will fulfil the requirements for the generator differential
protection in this application:
• Class 5P20 (5P18), 5 VA and R
ct
< 3 Ω.
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
CT
< 3 Ω and the knee point e.m.f.
³ × = × =
k al
E 0.8 E 0.8 142 114 V
EQUATION2541 V2 EN
(Equation 298)
As an alternative it can be suitable to provide the CT manufacturer with the data
according to equation
299 as follows:
( ) ( )
³ = × × + + = × × × + NG
al alreqRat sr ct w addbu ct
pr
I
3250
E E 30 I R R R 30 1 R 2,8
I 4000
EQUATION2542 V2 EN
(Equation 299)
( )
³ × ×
+ +
³ × × =
+
al NG
sr
CT w addbu pr
al
CT
E I
30 I
R R R I
E 3250
30 1 24.4
R 2.8 4000
EQUATION2543 V2 EN
(Equation 300)
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
k
and R
ct
shall be fulfilled:
( )
³ ³
× + +
k k
ct ct
E E
24.4 or 19.5
0.8 R 2.8 R 2.8
EQUATION2544 V2 EN
(Equation 301)
Section 24
1MRK 502 071-UEN -
Requirements
752 Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual