Level detector's main task is to release the coil automatic tuning procedure in
case of network switching operation. After every successful tuning procedure, the
measured zero-sequence voltage is stored as a new reference voltage U
ref
. Also, the
calculated network admittances are stored as new reference admittances Y
symm_ref
and Y
asymm_ref
(for more information, see
Chapter 9.11.6.3 Network parameter
calculation
).
If the change in the measured zero-sequence voltage exceeds the setting
V Res
change level
with respect to U
ref
, then a new coil tuning procedure is released. The
measured zero-sequence voltage must exceed the threshold at least by the time
defined with
Tuning delay
setting, otherwise the start of the tuning procedure is
canceled.
Zero-sequence voltage change can be determined considering the voltage
amplitude only or a phasor value. Setting
V Res Meas mode
is used to select
between these two modes. The available options are "Amplitude" and "Phasor".
The phasor triggering mode is explained in
Figure 924
. Monitored data output
TUNING_TRIGG indicates the relation between present zero-sequence voltage and
the reference voltage. When TUNING_TRIGG value is below 100%, the controller is at
stand-by. When TUNING_TRIGG value is above 100%, that is, Uo vector in
Figure 924
enters the red area, the tuning delay is started.
Re(U)
Im(U)
Red area
= Trigger of tuning procedure
Green area (r= dUo threshold)
= No trigger
U
0
dUo threshold
Figure 924: Phasor triggering mode
Level detector also includes a threshold-based earth-fault detection functionality.
The detection is based on
V Res EF level
voltage threshold setting. If the
measured zero-sequence voltage exceeds the threshold at least by the time
defined in
Transient time EF
setting, the earth fault is indicated by activating the
EARTH_FAULT output and the controller proceeds as described in
Chapter 9.11.6.4.1
Operation during earth faults
.
The delay defined in
Tuning delay
can be bypassed by activating ST_TUNING input,
for example, via HMI application. When the rising edge of the signal is detected,
the controller skips the tuning delay and proceeds immediately with the coil
automatic tuning procedure. The automatic tuning procedure can be started with
ST_TUNING input even without the zero-sequence voltage trigger. The automatic
1MRS759142 F
Control functions
REX640
Technical Manual
1735
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