Slce 8/Asct Characteristics For Series-Connection - ABB REB670 Applications Manual

1MRK 505 337-UUS -
6.1.5.7
Application manual
é ù é ù é ù
IA 1 1 1
ê ú ê ú ê ú
=
2
IB a a 1
ê ú ê ú ê ú
ê ú ê ú ê ú
2
IC a a 1
ë û ë û ë û
EQUATION1786-ANSI V1 EN
where:
a is complex constant (that is, a=-0.5+j0.866).
By including equation 16, equation 17, equation
the equation for the end-connected, ASCT secondary current (that is, summated current)
can be derived according to equation 20:
1
-j30°
× ( ×
-- -
I = I e + I
SUMM 1 2
k
EQUATION1112 V1 EN
From equation 20 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.

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 1 IA N
×
N 4 I
SUMM
EQUATION1787-ANSI V1 EN
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 = N;
EQUATION1108 V1 EN
×
N3 = 2 N
EQUATION1109 V1 EN
I
1
×
I
2
I
0
18
j30°
× × × )
e + 3 3 I
0
× - + +
2 IC N IA IB IC 3(
Differential protection
and equation 19 into the equation
)
Section 6
(Equation 19)
15
(Equation 20)
(Equation 21)
(Equation 22)
(Equation 23)
159