ABB RELION REX640 Technical Manual page 1587

1MRS759142 C
REX640
Technical Manual
G Real part of symmetrical part of the total network admittance. The sign is positive and it
symm
represents the shunt losses of the network (excluding the losses of the central coil and the
parallel resistor). If there are distributed compensation coils in the network, their shunt losses
are included in this value.
B Imaginary part of symmetrical part of the total network admittance. The sign is positive
symm
(capacitive) and it represents the capacitive uncompensated earth-fault current of the network.
If there are distributed compensation coils in the network, their effect is included in this value.
G Real part of asymmetry admittance. The sign may be positive or negative depending on the
asymm
actual level of asymmetry.
B Imaginary part of asymmetry admittance. The sign may be positive or negative depending on
asymm
the actual level of asymmetry.
G Real part of the coil admittance. The sign is positive and it represents the resistive losses of the
coil
central coil including the parallel resistor.
B Imaginary part of the coil admittance. The sign is negative and it represents the inductive
coil
current of the central coil, which defines the compensation degree of the network.
All previous admittance terms can be easily converted into equivalent current values
by multiplying them by the system nominal phase-to-earth voltage U
I = (B + B ) ⋅ U
ef_network symm asymm
I = (G + G
loss_network symm asymm
I = B ⋅ U
coil coil n
I = G ⋅ U
loss_coil coil n
Network parameter calculation is based on the forced change in network zero-
sequence voltage. This is achieved by changing the coil position or by changing the
connection state of the parallel resistor of the coil.
Coil automatic tuning
Coil automatic tuning mode is enabled with setting Controller mode = "Automatic".
In this mode, the TUNING_ACT binary output is activated. The coil automatic tuning
procedure consists of two parts. First, sufficient zero-sequence voltage variation is
obtained using coil movement or resistor switching. Secondly, network parameters
are calculated.
The automatic tuning procedure requires a sufficient change to be detected in the
measured zero-sequence voltage. This can be achieved by coil movement or switching
the parallel resistor of the coil. The mode is selected with Tuning mode setting. The
available options are "Coil movement" and "Resistor switching".
In the coil movement mode, the controller first moves the coil a little towards the coil's
default position and determines the direction of raising Uo voltage. Then the
controller moves the coil preferably to the direction of raising zero-sequence voltage
until the measured zero-sequence voltage is changed by the amount defined with V
Res variation setting. V Res maximum setting defines the maximum 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
Uncompensated earth-fault current
n
) ⋅ U Network shunt losses
n
Coil inductive current
Coil loss current
Section 9
Control functions
.
n
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