ABB RELION 670 Series Applications Manual page 148

Section 6
Differential protection
é ù é
IA
ê ú
=
IB
ê ú
ê ú
IC
ë û
EQUATION1786-ANSI V1 EN-US
where:
a
By including equation 16, equation 17, equation
equation for the end-connected, ASCT secondary current (that is, summated current) can be
derived according to equation 20:
I =
SUMM
EQUATION1112 V1 EN-US
From equation
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.
6.1.5.7 SLCE 8/ASCT characteristics for series-connection
Typical ASCT series-connection is shown in figure 76. For this ASCT connection type, the ampere-
turn balance equation has the form according to equation 21:
×
N 4 I
SUMM
EQUATION1787-ANSI V1 EN-US
The relationships between the number of turns for this SLCE 8 ASCT for REB670, is shown in
equation 22, equation 23, equation 24:
N1 = N2
EQUATION1108 V1 EN-US
N3 2 N
=
EQUATION1109 V1 EN-US
142
ù é ù
1 1 1 I
1
ê ú ê ú
×
2
a a 1 I
ê ú ê ú
2
ê ú ê ú
2
a a 1 I
ë û ë û
0
is complex constant (that is, a=-0.5+j0.866).
1
-j30° j30°
-- - × ( × ×
I e + I e + 3
1 2
k
20 it is obvious that the ASCT rated ratio is declared for balanced three phase
= × - × -
N 1 IA N 2 IC
= N;
×
18 and equation
× × )
3 I
0
+ +
N IA IB IC 3( )
1MRK 505 337-UUS A
(Equation 19)
19 into the equation 15 the
(Equation 20)
(Equation 21)
(Equation 22)
(Equation 23)
Application manual
M12143-3 v3