suppression coil. An efficient protecting method against earth faults occurring in a
medium-voltage compensated network is the earth-fault compensation. It is carried
out by inserting an inductive coil (arc suppression coil or Petersen coil) between the
transformer's star point and the earth in order to compensate the zero-sequence
capacitive current of the network. It increases the probability of the arc extinction in
case of a temporary earth fault. The arc extinction coil is effective only if its value is
tuned to the zero-sequence capacity of the network so they are in resonance state
and as a consequence the earth-fault current is very low.
9.11.8 Commissioning
During the coil setup process, it is not yet needed to connect the ASC to the
network. The coil setup consists of two parts:
• Calibration of coil
• Evaluation of coil linearity
The coil calibration procedure is started by activating ST_CALIB input which can
be done via local HMI application. Before starting the procedure, it must be
checked that coil end switches (HIGH_LIMIT and LOW_LIMIT) are connected to the
controller. If end switches are not available, end positions are detected during the
calibration process if there was no coil movement for more than 20 s.
First, in the coil calibration procedure the coil is moved automatically from the
lower-end switch to the upper-end switch. In both locations, the corresponding
potentiometer values are recorded for further use. Also, the coil movement speed
is determined during the calibration procedure. Secondly, the coil is moved to
its middle position and the after-running and mechanical play of the coil are
determined. Finally, the potentiometer gaps are determined. All results from coil
calibration (running speed, after running, mechanical play and potentiometer gap
locations) are visible in the Monitored data view.
After the calibration, the coil linearity is evaluated. The automatic coil calibration
determined the potentiometer ohmic end-switch values. These values are displayed
on the HMI and can be entered into the linearization table. The corresponding
coil position values (that is, inductive current of the coil) might be entered, for
example, from the coil routine test report delivered by the coil manufacturer.
The values are entered at coil nominal voltage level which is defined with
Coil V
Nom
setting. Moreover, if the potentiometer/coil position relationship is nonlinear,
additional eight interpolation points, or part of them, might be applied. This is
done by entering the potentiometer and corresponding coil position values into
the linearization table. Values which are left to default value of 0.0 are discarded
from the actual linearization curve. Both end values of the linearization table are
displayed on the HMI view of the resonance curve. An example of the linearization
table is given in
Table 1591
and the corresponding linearization curve is plotted in
Figure 929
.
The values put in ascending order are automatically adjusted so they are in the
neighboring positions of the array, irrespective of the position in the linearization
table.
1MRS759142 F
Control functions
REX640
Technical Manual
1745
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