Parameter: Dir. measuring method, φ correction, Min.polar.3I0> for dir.det., 3I0> threshold
value
•
Default setting (_:12601:109) Dir. measuring method = cos φ
•
Default setting (_:12601:107) φ correction = 0.0°
•
Default setting (_:12601:102) Min.polar.3I0> for dir.det. = 0.030 A
•
Default setting (_:12601:101) 3I0> threshold value = 0.050 A
These parameters are used to define the direction characteristic of the stage. The direction characteristic to
use is dependent on the neutral-point treatment of the system.
Note that, for the direction determination, basically only a portion of the current vertical to the set direction-
characteristic curve (3I0dir.) is decisive, refer to 6.15.4.1 Description. This portion of the current is compared
to the threshold value Min.polar.3I0> for dir.det.. In contrast, the absolute value of the current 3I0
is compared with the 3I0> threshold value parameter.
System Type/
Neutral-Point Treat-
ment
Description
Grounded In the arc-suppression-coil-ground system, the watt-metric residual current 3I0 · cos φ
of the arc-suppression coil is decisive for the direction determination.
To evaluate the watt-metric residual current, set the parameters as follows:
•
Dir. measuring method = cos φ
•
φ correction = 0.0°
The direction determination for a ground fault is made more difficult in that a much
larger capacitive or inductive reactive current is superimposed on the small watt-metric
residual current. Therefore, depending on the system configuration and the fault eval-
uation, the total ground current supplied to the device can vary considerably in its
values regarding the magnitude and the phase angle. However, the device should only
evaluate the active component of the ground-fault current.
This requires extremely high accuracy, particularly regarding the phase-angle measure-
ment of all the instrument transformers. Furthermore, the device must not be set to
operate too sensitively. A reliable direction measurement can only be expected with
connection to a core balance current transformer. For the setting of the Min.polar.
3I0> for dir.det. parameter, the rule of thumb is: Set the pickup value only to
half of the expected measuring current as only the watt-metric residual current can be
put into use.
The 3I0> threshold value parameter can also be set to half of the expected
measuring current, whereby here the entire zero-sequence current can be put to use.
Isolated In the isolated system, the capacitive ground reactive current 3I0 · sin φ is decisive for
the direction determination.
To evaluate the capacitive ground reactive current, set the parameters as follows:
•
Dir. measuring method = sin φ
•
φ correction = 0.0°
In an isolated system, the capacitive ground-fault currents of the entire electrically
connected system flow through the measuring point in case of a ground fault. The
ground current of the faulty feeder is compensated in the measuring point. As the
pickup value of the Min.polar.3I0> for dir.det. and 3I0> threshold
value parameters, select about half of this capacitive ground-fault current flowing via
the measuring point.
Protection and Automation Functions
6.15 Sensitive Ground-Fault Detection
SIPROTEC 5, Overcurrent Protection, Manual 575
C53000-G5040-C017-8, Edition 07.2017
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