ABB RELION 670 Series Applications Manual page 149

1MRK 505 337-UUS A
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
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
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.
Application manual
× ×
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
26 it is obvious that the ASCT rated ratio is declared for balanced three phase
24 and equation
× × )
3 I
0
Differential protection
(Equation 24)
(Equation 25)
25 into the equation 21 the
(Equation 26)
Section 6
143