ABB REB670 Series Applications Manual page 147

1MRK 505 370-UEN D
6.1.6.6 SLCE 8/ASCT characteristics for end-connection
Typical ASCT end-connection is shown in Figure 84. For this ASCT connection type, the
ampere-turn balance equation has the form according to Equation 12:
×
N4 I
SUMM
EQUATION1107 V1 EN-US
The relationships between number of turns for this SLCE 8, ASCT for REB670, is shown in
Equation 13, 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 16:
IL1
=
IL2
IL3
EQUATION1111 V1 EN-US
where:
a
By including Equation 13, Equation 14, Equation
equation for the end-connected, ASCT secondary current (that is, summated current) can be
derived according to equation 17:
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.
Busbar protection REB670
Application manual
× × (
= N1 IL1 + N2 IL1 +
14 and Equation 15:
= 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)
1 1 1 I
1
2
× I
a a 1
2
2
I
a a 1
0
complex constant (that is, a=-0.5+j0.866).
1
-j30° j30°
-- - × ( × ×
I e I e
+ +
1 2
k
17 it is obvious that the ASCT rated ratio is declared for balanced three phase
) × (
IL2 + N3 IL1 + IL2 + IL3
15 and Equation
× × )
3 3 I
0
Differential protection
)
16 into the Equation
Section 6
M12141-3 v4
(Equation 12)
(Equation 13)
(Equation 14)
(Equation 15)
(Equation 16)
12 the
(Equation 17)
141