ABB RELION 670 SERIES REG670 Applications Manual page 809

1MRK 502 071-UUS A
Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
Application manual
I
(
³ = × ×
tf
E E 2 I
al alreqExt sr
I
pr
EQUATION2538 V2 EN-US
The conclusion is that we need a CT with E
the rated burden 5 VA and R
(
³ = × ×
E 142 ALF I R
al sr ct
EQUATION2539 V2 EN-US
142
³ =
ALF 17.8
( )
+
3 5
EQUATION2540 V2 EN-US
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-US
As an alternative it can be suitable to provide the CT manufacturer with the data
according to equation 292
I
³ = × NG ×
E E 30 I
al alreqRat
I
pr
EQUATION2542 V2 EN-US
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-US
13000
)
+ + = ×
R R R 2
ct w addbu
4000
> 142 V. For example a CT class 5P with
al
< 3 Ω shall fulfil the following:
CT
) ( )
+ = × × +
R ALF 1 3 5
b
< 3 Ω.
ct
=
as follows:
( )
+ + =
R R R 30
sr ct w addbu
I
× ×
NG
I
sr
I
pr
Section 24
Requirements
( )
× × + + =
1 3 2.5 0.3 38V
3250
( )
× × × +
1 R 2,8
ct
4000
(Equation 288)
(Equation 289)
(Equation 290)
(Equation 291)
(Equation 292)
(Equation 293)
803