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Functions
Rated Frequency
System Starpoint
6-10
Ratio of earth current transformer
⁄
----------------------------------------------------------------------------------------------------- -
I
I
=
4
ph CT
Ratio of phase current transformers
This is independent on whether the device has a normal measured current input for
I
or a sensitive measured current input for I
4
non-earthed systems)
Example:
Phase current transformers 500 A/5 A
Cable core balance current transformer 60 A/1 A
60 1 ⁄
⁄
---------------- -
I
I
=
500 5 ⁄
4
ph CT
• Connection of the I
4
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
Example:
Current transformers on protected feeder 1200 A
Current transformers on parallel feeder 1500 A
1500
⁄
------------ -
1.250
I
I
=
=
4
ph
1200
• Connection of the I
4
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
input is not required, the following settings are applied:
4
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.
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.
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.
0.600
=
input to the earth current of the parallel line (for parallel line
N paral. line
input to the neutral current of a power transformer; this con-
(for sensitive earth fault detection in
4
/I
.
N prot. line
C53000-G1176-C156-2
7SA6 Manual
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