Transformer Phase Capacitive Currents

[Rodmcm]

I am looking for some typical information on the phase capacitve currents of transformers.

I have a specific need for the selection of a neutral earth NET/NER on a small generator. The specification requires the sizing to be the greater of 10A or 3 x Icap where Icap is calculated from the generator, cable connection, LV of transformer
The generator is a 5MVA 0.9pf 11kV
Transformer is 5MVA 33/11kV YNd11 ( The Y on the 33kV not earthed)

I have gone to the transformer/generator manufacturer for this specific requirement but am interested in some general information for a design database

Anyone with some references, data?

 

[7anoter4]

Walling (1992) derived an empirical equation to estimate the line-to-ground transformer capacitance per phase in microF:
C=0.000469*Skva^0.4/VkV^0.25[microF]
R.A.Walling formula [from Electric Power Distribution Handbook by T.A.Short] ch.4.10.2 Ferroresonance.
Walling, R. A., “Ferroresonance Guidelines for Modern Transformer Applications [1992]

 

[magoo2]

I think Walling's work on ferroresonance was on grounded-wye grounded-wye transformers. These were either 15, 25 or 35 kV primary and the secondary was either 208 or 480 V. These were all five-legged core designs.

I suspect your 33 kV/11 kV rating might be a three-legged core design. I'd be real cautious in using Reigh's formula unless you check it out.