Siemens SIPROTEC, Manual

Page: 48 / 776

Functions
2.1 General
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
48
Example:
Phase current transformers 500 A / 5 A
Earth 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 dis-
tance protection and/or fault location):
Address
220
is then set to:
I4 transformer
=
In paral. line
and usually address
221 I4/Iph CT
= 1.
If the set of current transformers on the parallel line however has a different transformation ratio to those on
the protected line, this must be taken into account in address
221 :
Address
220
is then set to:
I4 transformer
=
In paral. line
and address
221 I4/Iph CT
= I
N paral.
line
/ I
N prot. line
Example:
Current transformers on protected line 1200 A
Current transformers on parallel line 1500 A
• Connection of the
I
4
input to the starpoint current of a transformer; this connection is always used for the
restricted earth fault protection and occasionally for the polarisation of the directional earth fault protection:
Address
220
is then set to:
I4 transformer
=
IY starpoint
, and address
221 I4/Iph CT
is accord-
ing to transformation ratio of the starpoint transformer to the transformer set of the protected line.
• If the input I
4
is not required, set:
Address
220 I4 transformer
=
Not connected
,
Address
221 I4/Iph CT
is then irrelevant.
In this case, the neutral current is calculated from the sum of the phase currents.
Rated frequency
The rated frequency of the power system is set under address
230 Rated Frequency
. The factory presetting
according to the ordering code (MLFB) only needs to be changed if the device is applied in a region different
from the one indicated when ordering. You can set
50 Hz
or
60 Hz
.
System starpoint
If the distance protection has been configured as the main protection function or in combination with differential
protection, the manner in which the system starpoint is earthed must be considered for the correct processing
of earth faults and double earth faults. Accordingly, set for address
207 SystemStarpoint
=
Solid
Earthed
,
Peterson-Coil
or
Isolated
. For „low-resistant“ earthed systems set
Solid Earthed
.