Auxiliary Grounding Transformers for switching station

[KojoSincal]

HELLO EVERYONE Thanks in advance once again.

I propose a ZNyn11 Auxiliary grounding transformer for a 33kV GIS Switching station. However looking through the threads on here; I do not know the rating of the upstream transformer. I was thinking of proposing a 100kVA because the LVAC load is quite small and 1000A for 10s. The double bus bar rating is 2500A,31.5kA for 3s. However; I would like help with calculation method for sizing this Aux/grnd transformer for this scenario?

 

[prc]

What is the secondary load of the grounding transformer?

 

[Kiribanda]

If your 33kV system is unearthed then the YNyn11 earthing transformer has to be sized according to the total capacitive charging current
of the 33kV system. So you have to get that information first to start sizing.