zero-sequence voltage that the controller does not exceed when obtaining the
required Uo variation. If the zero-sequence voltage reaches the value defined in
V Res maximum
setting, the controller seeks the required Uo variation from the
direction of decreasing zero-sequence voltage.
The measured zero-sequence voltage level must exceed setting
V Res minimum
during the whole tuning process. If the measured zero-sequence voltage is initially
below the
V Res minimum
setting, the controller extends the search range in order
to achieve this minimum level. If the minimum required level of zero-sequence
voltage cannot be reached, the controller cancels the tuning. If the required zero-
sequence voltage variation cannot be reached, the controller moves the coil to
Error
position
.
The most accurate tuning is possible when
Pass resonance
setting is enabled: the
controller moves the coil over the network resonance point and collects additional
measurement points resulting in the most accurate estimate of the network
parameters. Particularly passing the resonance point improves the estimate of
network losses. Setting
V Res maximum
can deny the resonance point passing
functionality.
V Res EF level
setting should be set to a higher value than
V Res
maximum
.
If the coil is equipped with a parallel resistor, the resistor switching mode offers
a fast alternative to obtain the change in measured zero-sequence voltage. In
the resistor switching mode, the controller changes the connection status of the
parallel resistor for three seconds and then switches the resistor back to its
original position. If the change in the measured zero-sequence voltage exceeds
the
V Res variation
setting, the controller can proceed immediately to network
parameters calculation. If the change defined in
V Res variation
setting cannot
be obtained using resistor switching, the controller automatically uses the coil
movement method.
In the case of resistor switching, the setting
V Res maximum
is
ineffective.
After sufficient change in the measured zero-sequence voltage is obtained
using coil movement or resistor switching, the controller calculates new network
parameters and compares them to the reference values. If the network’s capacitive
earth-fault current has changed, the controller moves the coil to maintain the set
compensation level. The active compensation mode is selected with
Compensation
mode
setting. The available options are "Absolute" (tuning level selected with
Detuning level
setting) and "Relative" (tuning level selected with
Detuning level
Rl
setting). The controller monitors the actual coil current while moving it to the
desired tuning position. Taking into account the after-running of the coil motor, it is
stopped just before reaching the desired tuning point. If the zero-sequence voltage
reaches the voltage level set with
V Res maximum
setting, the controller stops the
coil movement.
If the parallel resistor is installed in the system (setting
Parallel resistor
= "True"),
PASANCR includes a feature to temporarily connect the parallel resistor into the
system while moving the coil to the desired tuning position if the resistor is initially
disconnected. The temporary connection of the parallel resistor should lower the
zero-sequence voltage and therefore the movement of the coil to the desired tuning
position could be possible. The feature can be enabled with
Temporary damping
setting. The available options are "True" and "False".
1MRS759142 F
Control functions
REX640
Technical Manual
1739
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