( ) ( )
³ = × × + + = × × × + + =
tf
al alreqExt sr ct w addbu
pr
I
13000
E E 2 I R R R 2 1 3 2.5 0.3 38V
I 4000
EQUATION2538 V2 EN-US (Equation 288)
The conclusion is that we need a CT with E
al
> 142 V. For example a CT class 5P with
the rated burden 5 V
A and R
CT
< 3 Ω shall fulfil the following:
( ) ( )
³ = × × + = × × +
al sr ct b
E 142 ALF I R R ALF 1 3 5
EQUATION2539 V2 EN-US (Equation 289)
EQUATION2540 V2 EN-US (Equation 290)
CTs with the following data will fulfil the requirements for the generator differential
protection in this application:
•
Class 5P20 (5P18), 5 V
A 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-US (Equation 291)
As an alternative it can be suitable to provide the CT manufacturer with the data
according to equation 292 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-US (Equation 292)
( )
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-US (Equation 293)
1MRK 502 071-UUS A Section 24
Requirements
Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062 803
Application manual
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