ABB Relion 670 Series Application Manual page 43

1MRK 505 382-UEN E
138
Z =
S
A
1700
EQUATION14000034 V1 EN-US
138
=
Z
S
B
1200
EQUATION14000035 V1 EN-US
Calculating the short circuit impedance of the transformer gives:
e
Z =
trf
100
EQUATION14000036 V1 EN-US
Based on the Thevenin equivalent, it is possible to calculate the fault current on the HV side of
the transformer:
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 a fault on the LV side of the
transformer,
If
1 2 .
> ×
I
EQUATION14000038 V1 EN-US
IdMin
=
EQUATION14000040 V1 EN-US
To allow the differential protection to act as a backup protection for internal faults and faults
on the LV side of the transformer,
Imax AddDelay . Differential currents below the set value for Imax AddDelay are time delayed.
Value two times the rated current of the transformer on the HV side is chosen. The setting is
calculated as:
ImaxAddDelay
EQUATION14000041 V1 EN-US
Communication set-up, 670/650 series
Application Guide
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
If
1 2 . 138 11 5 .
× =
I
Base
S
n
2
= ×
3 U I
× ×
n Base
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Analog and binary signal transfer for line differential protection
. Ω
= 198Ω
trf
If
138
AddDelay is set to On , and a suitable setting is calculated for
2 0 .
=
If
gives = 403 A
138
Section 4
(Equation 7)
(Equation 8)
(Equation 9)
(Equation 10)
(Equation 11)
(Equation 12)
(Equation 13)
(Equation 14)
37