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The zigzag coil is the general model for a grounding transformer. It is usually used to improve the voltage of the neutral or to introduce a ground in a non-grounded network.
PARAMETERS
General
Parameter |
Default |
Unit |
Description |
Name |
|
|
Name of the zigzag coil |
Zigzag coil
Parameter |
Default |
Unit |
Description |
Name |
|
|
Name of the zigzag coil |
R0 |
0 |
Ohm |
Zero sequence resistance |
X0 |
0 |
Ohm |
Zero sequence reactance |
External node
Possibility to connect the neutral point of the zigzag coil to the earthing electrode at another node.
Reliability
Parameter |
Default |
Unit |
Description |
Failure frequency |
0 |
per year |
Mean number of occurrences that the zigzag coil fails (short circuit) |
Repair duration |
0 |
minutes |
Mean duration of repair or replacement |
Maintenance frequency |
0 |
per year |
Mean number of occurrences that the zigzag coil is in maintenance |
Maintenance duration |
0 |
minutes |
Mean duration of maintenance |
maint. cut-off duration |
0 |
minutes |
Mean duration of cancellation of maintenance in case of emergency |
MODELLING
The impedance of the zigzag transformer is measured by applying a voltage to the three parallel connected phases of the transformer. The measured current is then three times as large as the current per phase. The zero sequence impedance per phase is then determined from:
Z0 = (U0 / I0) = 3 (U0 / Imeasured)
IEC (60) 909 and fault sequential
For an IEC (60) 909 calculation and fault analysis, a zigzag transformer is represented as a zero sequence impedance to ground. Including the impedance of the star point earthing, the zero sequence impedance is equal to:
Z0 = ( R0 + 3Ra ) + j ( X0 + 3Xa )