11kV Generator Plant Protections

Dear all, I request your kind advice for the below,

We are using 11kV generators for the back up supply of 415V system. There is a group of 6nos. 2.75MVA 11kV gensets synchronized then it is distributed by 12nos. outgoing VCBs of the synchronization panel to each building's 11kv/415V transformers. There is total 12nos. of 1600kVA transformers are connected to the panel. (The 11kV switchgear consists of 6nos. incomer VCBs + 12nos. outgoing VCBs, total separate 3groups for the project ie 18gensets)

Its a hospital so generator room is kept away from the patient buildings so the 11kV generator is adopted for the ease of distribution. The generators are inside the building not outdoor. The outgoing feeder cables are lay through tunnels using cable trays. My question is

1. Is it need to install a surge arrestor in the parallelling switchgear or is there any chance of voltage surge during transformer switching. If required is it sufficient if we provide only one number in the main bus of the parallelling switchgear?

2. Secondary side of the transformers are connected to inductive loads also (HVAC/VFDs) and each transformers are provided with capacitor banks for the power factor improvement. There will be harmonics THD% generated in the secondary side of the transformer within the limit of 415V system, does it make any impact in the primary sided of the transformer (11kV generators)?.

The 6nos. generator neutral is earthed using a common NGR where only one generator neutral will be closed at time to avoid circulating current. Is it needed to provide any harmonic filters in the parallellling switchgear busbars?

Thank you