Step up transformer and Hv cells

Hello everybody
In a power plant using Fuel Generators, I came across some technical things that I couldnt undertand
Well its a 4x2000KVA (4 generators 2000 KVA) , these 4 generators connected with Busbar to step-up transformers (410 V -> 11kV) , after that from the step-up transformer to HV cells switchgears and feeders to client.
The transformer are Y-D , the neutral in primary is grounded . and in the other side a homopolar generator is used to create neutral point wich is also grounded
My questions are :
1- Why the transfomer is not Y-Y in this case they would not buy and use homopolar generator ?
2- Why is it so important to ground neutral ?
3- What does the HV cells do exactly and what is INTERLOCKING ?
4- Why there is a resistor connected between 2 secondary phases at homopolar generator ?

thank you so much for your feedbacks

4. see :- https://www.schneider-electric.com/...cial-transformers/60984-homopolar-generators/
It looks like a high voltage DC generator to pass current down the neutral wire via the two resistors on the live phases.? For checking the continuity of the neutral/earth connection?
3. Interlocking, is normally a physical arrangement of locks and switches to ensure that apparatus can only be used in a certain sequence. i.e. cabinet opening lock, has its key trapped by the ON/OFF switch in the ON position, so you have to turn it off before the key becomes available to open the cabinet.
2. If you did not earth the neutral and bearing in mind that the whole electrical network has excellent insulation, the wires supplying power could float to any potential and flash across in a consumers premises. it also provides an earth return for lightning strokes.
1. The whole of power generation is determined by the immense cost, as the generators produce at 2KV (or 410V in your case?) and not 11KV, so I would guess its cheaper!.
Frank

Hi chuckey thanks so much for your feedback ,
I have some comments if u don't mind
1- Yes It's cheaper , but It would be more easy if the step-up transformer is Y-Y , then ground all neutrals.
4- I didn't see any rectifier in the homopolar generator , it looks exactly like a transformer. where the DC current is coming from , and how exactly passing DC current on live AC phases will check Neutral/eartch connection (Some theory please)
Thank you
Dxtr