ABB RELION 650 Series Applications Manual page 102

Section 6
Differential protection
ZsA
IEC14000046 V1 EN-US
Figure 49: Thevenin equivalent for tap transformer
Converting of the sources into impedances gives:
138
Z =
S
A
1700
EQUATION14000034 V1 EN-US
138
=
Z
S
B
1200
EQUATION14000035 V1 EN-US
Calculating of the short circuit impedance of the transformer gives:
e
Z =
trf
100
EQUATION14000036 V1 EN-US
Based on the Thevenin equivalent below we calculate the fault current at HV side of the
transformer as:
If =
138
EQUATION14000037 V1 EN-US
where:
(
Zs
Z =
res
EQUATION14000039 V1 EN-US
The numerical value for
To avoid unwanted operation of the differential protection for fault on LV side of the
transformer, the setting of
If
> 1 2 . ×
I
EQUATION14000038 V1 EN-US
96
ZlA
E
2
= 11 2 . Ω
2
= 15 9 . Ω
2 2
U 138
k n
× = 0 1 . × = 190 4
S 10
n
138
3 × Z
res
) ( )
+ Zl × Zs + Zl
a
A B B
+ Z
Zs + Zl + Zs + Zl
A a B B
Z
input in the formula for
res
IdMin must be set to:
138
Base
ZlB ZsB
IEC14000046-1-en.vsd
. Ω
= 198Ω
trf
If
138
If
gives = 403 A
138
Application manual
1MRK 505 363-UEN A
(Equation 23)
(Equation 24)
(Equation 25)
(Equation 26)
(Equation 27)
(Equation 28)