ABB Relion 670 Series Applications Manual page 150

Section 6
Differential protection
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
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 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
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 25:
é ù
IA
ê ú
=
IB
ê ú
ê ú
IC
ë û
EQUATION1788-ANSI V1 EN-US
where:
a
By including Equation 22, Equation 23, Equation
for the series-connected, ASCT secondary current (that is, summated current) can be derived according
to equation 26:
I =
SUMM
EQUATION1114 V1 EN-US
144
= × - × -
N 1 IA N 2 IC
= N;
×
× ×
3 N
is 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).
é 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 + 2
1 2
k
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+ +
N IA IB IC 3( )
24 and Equation
× × )
3 I
0
1MRK 505 370-UUS Rev. K
25 into the Equation 21 the equation
Busbar protection REB670
Application manual
M12143-3 v4
(Equation 21)
(Equation 22)
(Equation 23)
(Equation 24)
(Equation 25)
(Equation 26)