Siemens siprotec 7SA6, Manual

Page: 200 / 876

Functions
6-10
7SA6 Manual
C53000-G1176-C156-2
This is independent on whether the device has a normal measured current input for
I
4
or a sensitive measured current input for I
4
(for sensitive earth fault detection in
non-earthed systems)
Example:
Phase current transformers 500 A/5 A
Cable core balance current transformer 60 A/1 A
•
Connection of the
I
4
input to the earth current of the parallel line (for parallel line
compensation of the distance protection and/or fault location function, refer to Ap-
pendix A, Figure A-36 or A-37):
Address
220
is then set to:
I4 transformer
=
In paral. line
and
usually address
221
is set to
I4/Iph CT
=
1
.
If the set of current transformers on the parallel line however has a different ratio to
those on the protected line, this must be taken into account in address
221
:
Address
220
is then set so that:
I4 transformer
=
In paral. line
and
Address
221
so that
I4/Iph CT
= I
N paral. line
/ I
N prot. line
.
Example:
Current transformers on protected feeder 1200 A
Current transformers on parallel feeder 1500 A
•
Connection of the I
4
input to the neutral current of a power transformer; this con-
nection can be used for the polarisation of the directional earth fault protection (refer
to Appendix A, Figure A-38 or A-39):
Address
220
is then set to:
I4 transformer
=
IY starpoint
, and
address
221 I4/Iph CT
according to the ratio of the transformation ratios of the
current transformer in the transformer neutral and the set of current transformers on
the protected feeder.
•
If the I
4
input is not required, the following settings are applied:
Address
220 I4 transformer
=
Not connected
,
Address
221 I4/Iph CT
is then irrelevant.
In this case the zero sequence current for the protection functions is computed by
means of the sum of the phase currents.
Rated Frequency Address
230 Rated Frequency
corresponds to the frequency at which the power
system operates. The preset value is dependent on the model number of the relay pur-
chased, and must be in accordance with the nominal frequency of the power system.
System Starpoint The system starpoint must be observed for the correct processing of earth faults and
double earth faults. Therefore address
207 SystemStarpoint Solid Earthed
or
Peterson-Coil
or
Isolated
must be set correspondingly. For low-resistant
earthed systems set
Solid Earthed.
I
4
I
ph CT
⁄
Ratio of earth current transformer
Ratio of phase current transformers
------------------------------------------------------------------------------------------------------
=
I
4
I
ph CT
⁄
60 1
⁄
500 5
⁄
-----------------
0.600 = =
I
4
I
ph
⁄
1500
1200
------------- 1.250
= =