2.11 Overcurrent protection
215
7SA522 Manual
C53000-G1176-C155-3
2.11.3 Setting Notes
General During the configuration of the device scope of functions (address ) the available
characteristics were determined. Only those parameters that apply to the available
characteristics, according to the selected configuration and the version of the device,
are accessible in the procedures described below.
Address is set according to the desired mode of operation of the overcurrent
protection: 2SHUDWLQJ0RGH = 21DOZD\VDFWLY means that the overcurrent pro-
tection works independently of other protection functions, i.e. as a backup overcurrent
protection. If it is to work only as an emergency function in case of a transmission fail-
ure, 21ZLWK97ORVV must be set. Finally, it can also be set to 2)).
If some stages are not needed, those not needed can be deactivated by setting the
pickup value to ∞. But if you set only an associated time delay to ∞ this does not sup-
press the pickup signals but prevents the timers from running.
The stub protection remains in service even if the overcurrent mode of operation
setting is 21ZLWK97ORVV.
One or several stages can be set as instantaneous tripping stages when switching
onto a fault. This is chosen during the setting of the individual stages (see below). To
avoid a spurious pickup due to transient overcurrents, the delay 627)7LPH'(/$<
(address ) can be set. Typically, the presetting of 0 is correct. A short delay can
be useful in case of long cables for which high inrush currents can be expected, or for
transformers. The time delay depends on the severity and duration of the transient
overcurrents as well as on which stages were selected for the fast switch onto fault
clearance.
High Set Current
Stages I
ph
>>, 3I
0
>>
The I>> stages ,SK!! (address ) and ,!!3,&.83 (address ) together
with the I> stages or I
p
stages result in a two-stage characteristic. Of course, all three
stages can be combined as well. If one stage is not required, the pickup value has to
be set to ∞. The I>> stages always operate with a defined delay.
If the I>> stages are used for instantaneous tripping before the automatic reclosure,
the current-setting corresponds to the I> or I
p
stages. In this case only the different
delay times are of interest. The times 7,SK!! (address ) and 7,!! (ad-
dress ) can then be set to 0 or a very low value, as the fast clearance of the fault
takes priority over the selectivity before the automatic reclosure is initiated. These
stages have to be blocked before final trip in order to achieve the selectivity.
For very long lines with a small source impedance or on applications with large reac-
tances (e.g. transformers, series reactors), the I>> stages can also be used for current
grading. In this case they must be set in such a way that they do not pick up in case
of a fault at the end of the line. The times can then be set to 0 or to a small value.
When using a personal computer and DIGSI
®
to apply the settings, these can be op-
tionally entered as primary or secondary values. If secondary quantities are used, all
currents must be converted to the secondary side of the current transformers.
Calculation Example
:
110 kV overhead line 150 mm
2
:
s (length) = 60 km
R
1
/s = 0.19 Ω/km
X
1
/s = 0.42 Ω/km
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