Parameter Value Description
RMS value
Select this method of measurement if you want the stage to take harmonics
into account (for example, at capacitor banks). Do not set the threshold
value of the tripping stage under 10 V for this method of measurement.
fund. comp. long filter
To implement particularly strong damping of harmonics and transient
disturbances, select this method of measurement. At 2 periods, the length
of the filter is longer than that of the standard filter.
Please note that in this case the pickup time of the stage increases slightly
(see Technical Data).
Parameter: Pickup delay
•
Recommended setting value (_:331:107) Pickup delay = 0.00 ms
The Pickup delay parameter allows you to delay the analysis of the measurand (to generate the pickup)
depending on the occurrence of the residual voltage. A pickup delay can be necessary if high transients are
anticipated after fault inception due to high line and ground capacitances.
Siemens recommends using the default setting Pickup delay = 0.00 ms.
Parameter: Threshold
•
Default setting (_:331:3) Threshold = 30.000 V
27
The threshold value of the function is set as the zero-sequence voltage V
0
. The device calculates the zero-
sequence voltage V
0
either from the residual voltage measured via the broken-delta winding or from the
3 phase-to-ground voltages.
The setting value depends on the system grounding:
•
Since virtually the full residual voltage occurs during ground faults in isolated or arc-suppression-coil-
grounded systems, the setting value is uncritical there. It should range between 20 V and 40 V. A higher
sensitivity (= lower threshold value) can be necessary for high fault resistances.
•
You should select a more sensitive (smaller) value in a grounded system. This value must be higher than
the maximum residual voltage anticipated during operation caused by system unbalances.
EXAMPLE
For an isolated system
The residual voltage is measured via the broken-delta winding:
•
If the ground fault is fully unbalanced, a residual voltage of 100 V is present at the device terminals.
•
The threshold value should be set so that the stage picks up on 50 % of the full residual voltage.
•
At full residual voltage, the zero-sequence voltage is 100 V/√3 = 57.7 V
Setting value: 0.5 ⋅ 57.7 V = 28.9 V ≈ 30 V
Parameter: Dropout ratio
•
Recommended setting value (_:331:4) Dropout ratio = 0.95
The recommended set value of 0.95 is appropriate for most applications. The dropout ratio can be reduced
for example, to 0.98 to achieve a high measurement precision.
Parameter: Operate delay
•
Default setting (_:331:6) Operate delay = 3.00 s
The Operate delay allows you to prevent transient residual voltages from initiating a trip. The setting
depends on the specific application.
27
The specific setting limits depend on the transformer data and transformer connections set.
Protection and Automation Functions
6.24 Overvoltage Protection with Zero-Sequence Voltage/Residual Voltage
SIPROTEC 5, Overcurrent Protection, Manual 707
C53000-G5040-C017-8, Edition 07.2017
To Next Page
Loading...
