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Rated power of earthing transformer

Rated power of earthing transformer

Rated power of earthing transformer

(OP)
In our current project we have 33 kV grid of wind farm with 33 kV earthed via earthing transformer and neutral earthing resistor in step-up (33/110 kV) substation. I am working now on the model of the grid for short circuit currents calcualtion and relay protection coordination.
In the software I have to input some transformer data, as rated zero sequence active and reactive power, rated zero sequence short circuit voltage (%). Can somebody help me with any typical data for similar transformer? Grid voltage is 33 kV, earth fault current have to be limited to 300 A/10s, neutral earthing resistor is 63 Ohm.

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It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant
 

RE: Rated power of earthing transformer

Calculate the zero sequence values based on the current through the earthing resistor. The impedance of the earthing resistor will predominate. Ignoring the transformer impedance will introduce a slight error but only a few percentage, and the actual current will be slightly lower than the calculated current.
If you want a more precise answer and an answer for the reactive power you will have to tell us the PU impedance of the transformer and the X:R ratio.
For short circuit voltage you may use 3^2 (1.73) of the line to line voltage.
I suggest doing the calculations, based on just the value of the earthing resistor as a reality check. When you calculate the values with the transformer impedance included, you should be within a few percent. Any more and you should recheck your method.
Exception; The short circuit reactive current will be much reduced by the introduction of the earthing resistor so the reactive power (I^2.R) will be much much reduced compared to a calculation based on the value of the earthing resistor alone.

Bill
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"Why not the best?"
Jimmy Carter

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