20 kV Delta System

Why would one want to do that?

The zingzag Trafo + NGR is for the bus earthing, by creating an artificial neutral on the 20kV Delta side, to avail the benefits of an earthed system.

The 380V LV generator neutral is solidly grounded for human safety reasons. For, only when solidly grounded, the single-line-to-earth fault current would be equal to the three phase symmetrical short circuit current and even any short circuit protective device would isolate the faulty portion without the ned for any special earth leakage protective device.

No.

It is very important that you maintain low impedance, common neutral bussing connected to ground on all the transformer "Y" star-points.

If you interrupt/disconnect the ground continuity the "B" phase voltage will become unstable and significantly higher than the other two phases. (A, C)

This will severely disrupt the system protection and will cause circuit differential voltage tripping.

Thanks electricalexpert65 and SHOCKHISCAN for your comments.

To summarize all, the neutral of the Y generator should be solidly grounded for personel protection, and the phase of the Y generator can be connected to the LV Delta transformer, while the neutral of the MV Y transformer should be bussing connected to ground?

But what should I do with the ZZ transformer then?

And bussing to ground the MV side of the transformers would create higher fault rate?