ABB RELION REB670, Applications Manual

Page: 179 / 554

1
2
2
2
0
1 1 1
1
1 IA I
IB a a I
IC a a I
= ×
é ù é ù é ù
ê ú ê ú ê ú
ê ú ê ú ê ú
ê ú ê ú ê ú
ë û ë û ë û
EQUATION1786-ANSI V1 EN-US
(Equation 16)
where:
a
complex constant (that is, a=-0.5+j0.866).
By including Equation 13 , Equation 14 , Equation 15 and Equation 16 into the
Equation 12 the equation for the end-connected, ASCT secondary current (that is,
summated current) can be derived according to equation 17 :
I
SUMM
1
k
---
I
1
e
-j30°
×
I
2
e
j30°
×
3 3 I
0
× ×
+ +
( ) ×
=
EQUATION1112 V1 EN-US
(Equation 17)
From Equation 17 it is obvious that the ASCT rated ratio is declared for balanced three
phase current system, when only positive sequence current component exist. For any
unbalanced condition (that is, external or internal fault), both negative and zero
sequence current components will give their own contribution to the summated current.
6.1.6.7 SLCE 8/ASCT characteristics for series-connection
M12143-3 v4
Typical ASCT series-connection is shown in Figure 86 . For this ASCT connection
type, the ampere-turn balance equation has the form according to equation 18 :
4
1 2 3( )
SUMM
N I
N IA N IC N IA IB IC
×
= × - × - + +
EQUATION1787-ANSI V1 EN-US
(Equation 18)
The relationships between the number of turns for this SLCE 8 ASCT for REB670, is
shown in Equation
19 , Equation 20 , Equation 21 :
N1 N2 N; = =
EQUATION1108 V1 EN-US
(Equation 19)
N3 2 N
×
=
EQUATION1109 V1 EN-US
(Equation 20)
1MRK 505 370-UUS A
Section 6
Differential protection
Busbar protection REB670 2.2 ANSI 173
Application manual