Z
S
A
=
=
138
1700
11 2
2
.
Ω
EQUATION14000034 V1 EN-US
(Equation 7)
Z
S
B
=
=
138
1200
15 9
2
.
Ω
EQUATION14000035 V1 EN-US
(Equation 8)
Calculating the short circuit impedance of the transformer gives:
Z
e
U
S
trf
k
n
n
=
×
=
×
=
100
0 1
138
10
190 4
2
2
.
.
Ω
EQUATION14000036 V1 EN-US
(Equation 9)
Based on the Thevenin equivalent, it is possible to calculate the fault current on the HV side of
the transformer:
If
Z
res
138
138
3
=
×
EQUATION14000037 V1 EN-US
(Equation 10)
where:
Z
Zs
Zl
Zs
Zl
Zs
Zl
Zs
Zl
Z
res
A
B
B
A
a
B
B
trf
a
=
+
(
)
×
+
(
)
+
+
+
+
=
198
Ω
EQUATION14000039 V1 EN-US
(Equation 11)
The numerical value for
Z
res
input in the formula for
If
138
gives
If
138
= 403 A
To avoid unwanted operation of the differential protection for a fault on the LV side of the
transformer,
IdMin must be set to:
>
×
1 2
138
.
If
I
Base
EQUATION14000038 V1 EN-US
(Equation 12)
IdMin
If
I
Base
=
×
=
1 2
11 5
138
.
.
EQUATION14000040 V1 EN-US
(Equation 13)
To allow the differential protection to act as a backup protection for internal faults and faults
on the LV side of the transformer,
AddDelay is set to On, and a suitable setting is calculated for
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
S
U
I
n
n
Base
=
×
×
×
=
2
3
2 0
.
EQUATION14000041 V1 EN-US
(Equation 14)
1MRK 505 382-UEN E
Section 4
Analog and binary signal transfer for line differential protection
Communication set-up, 670/650 series
37
Application Guide
© Copyright 2017 ABB. All rights reserved
Summary of Contents for Relion 670 series
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