I'd have a close look at the vector diagrams first ! ! ! !

first of all you cannot connect two transformer in parallel with different vector groups. when +30 lead while other -30 lag. to parallel the phase angle of the transformer shall match in addition to voltage and frequency.

With different transformer vector???? You must be joking... Nobody parallel two transformer with different vector.

Could be fun, just so long as I'm watching it via a video link!

As for "If these two transformers were connected together in parallel, what is the suitable earth fault connection to be used ?."

A bloody big one!

Your Trafo 2 vector group notation is WRONG. It cannot be YDN11 as Delta cannot have a neutral. It should be YNd11. Similarly, the Trafo 1 notation should be Dyn11 (not as you have mentioned; you have to be very careful with CAPS when specifying Trafo Vector Groups).

I am surprised at all the previous answers taht soem of them have mentioned that these two transformers belong to two differeny vector groups. I am sorry! Both these transformers belong to the same vector group (+ 30 degrees group). It is only that the HV & LV connections are different. These tweo transformers can very well be paralleled.

As regards the earthing connections go, definitely the LV Neutral in the Dyn11 shall be earthed (either effcectively or thro an impedance, depends on the LV Voltage); similarly, the HV Neutral in the YNd11 may be earthed (again either effectively or thro an impedance) if it is connected to an earthed source.

Please ensure all other CR4 readers are some hundreds of metres away before doing this, for pity's sake!