Thus the earthing of an electrical installation have any effect on the low/high cost of electricity bill; Even though there is NO leakage current in the system?

Earthing (Grounding in US terms) is done for specific reasons. You ground the metal enclosure of electrical equipment for SAFETY as required by the Code. You ground the neutral of an electrical systems for various reasons and intentions including Code requirements. You may not ground the system neutral if your design do not require it to be grounded, if the Code allows. You can ground it through an impedance purposely if the design requires it. You ground your lightning arresters, surge arresters, and cable sheaths for specific reasons, and there are various reasons and requirement why you ground your system or your system components. I do not see any significant effect on cutting your electricity bill by grounding unless the revenue meter is not pilfered-proof ( old type of meters).

NO.
Has no effect on the bill. Only on the capital cost.

Edem grounding has no impact on electricity bills.

the essence of any electrical earthing for purpose of safety. earthing of every electrical installation is MUST because it is key to a reliable electrical installations.
Bill accumulation or decrease is product of power consumption within your household or industry, so it does has any relationship with earthing of electrical equipment. Regards.

can anyone tell me how to calculate MVA for a 11/33KV transformer?

As I understand your Transf. is step-up Transf.
Assume the primary line current is I1 while the secondary one is I2 in ampere.

Then, Transformer rated MVA can be calculated as follows:

MVA = (Root '3" X I1 X 11 X 10^3) X 10^-6 (based on the primary)
= (Root '3" X I2 X 33 X 10^3) X 10^-6 (based on the secondary)


Regards