ABB Relion 670 Series Applications Manual page 149

1MRK 505 370-UUS Rev. K
6.1.6.6 SLCE 8/ASCT characteristics for end-connection
Typical ASCT end-connection is shown in Figure 85. For this ASCT connection type, the ampere-turn
balance equation has the form according to Equation 15:
×
N 4 I
SUMM
EQUATION1785-ANSI V1 EN-US
The relationships between number of turns for this SLCE 8, ASCT for REB670, is shown in Equation 16,
Equation
N1 N2
=
EQUATION1108 V1 EN-US
×
N3 = 2 N
EQUATION1109 V1 EN-US
N4 = k
EQUATION1110 V1 EN-US
where:
k
The well-known relationship, between positive, negative and zero sequence current components and
individual phase current quantities is shown in Equation 19:
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
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
system, when only positive sequence current component exist. For any unbalanced condition (that is,
Busbar protection REB670
Application manual
= × + × +
N 1 IA N 2 ( IA IB
17 and Equation 18:
N;
=
× ×
3 N
a constant, which depends on the type of ASCT
(that is, k=1, for 1/1A ASCT or k=5 for 5/1A ASCT or k=2 for 2/1A ASCT)
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
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 current
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+ × + +
) N 3 ( IA IB IC )
18 and Equation
× × )
3 I
0
Differential protection
19 into the Equation 15 the equation
Section 6
M12141-3 v4
(Equation 15)
(Equation 16)
(Equation 17)
(Equation 18)
(Equation 19)
(Equation 20)
143