Electrical

Assuming that I knew what your L T Stabiliser was or what you meant by an HT AVR Transformer I would still have to know more about the problem with the source voltage. A variation from 380 to 460 v sounds like something about to fail. Then again, maybe your measurement equipment is defective.

All in all, I would have to recommend you try again with more details. And turn off the "Caps Lock" on your keyboard. Most people interpret all Caps as yelling and take offense to that.

Whichever is cost-effective - both the capital cost and the running cost

I feel he means by LT - low voltage side of the transformer & HT - high voltage/medium voltage side of the transformer , AVR - automatic voltage regulation.

Better option here is automatic voltage regulation - for better output voltage . I am not an expert in this. Let us wait for more comments on this.

I'm wondering if the term LT stands for "low tension"? I've heard of the term "high tension" used to mean high voltage as in greater than 25KV.

Using terms specific to region or field can be confusing. Perhaps it is the language of a specialist.

They say that the British and the American speak the same language, but I beg to differ.

define "LT stabiliser". what are its components?