ABB RELION REX640 Technical Manual page 1588

Section 9
Control functions
1582
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 switches the connection status of the parallel resistor
for three seconds and then switches the resistor back to its original connection status.
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
1MRS759142 C
REX640
Technical Manual