About Distribution Transformer Characteristics

Who is "we"? Normally when the secondary line voltage is out of specs. (too low), the power company can step this up with the distribution line transformer (the ones on the poles) Call them.

To answer your question: your transformer should have 190 Volts primary and 230 volts secundary with minimal the power rating of your load. It is a cost you can avoid with a telephone call.

You cannot just do that, because the problem can be in the supply by the power company and adding your transformer just makes their (eventual) problem bigger.

Stepping up the voltage is handy if you have voltage drop issues on site (there are legal requirements about the power transmission company providing voltage regulation within a certain tolerance like 10% for example, but I won't go into this as you have not mentioned your country or site details, so I will assume this is your voltage drop problem to fix and not the power or lines company's).

Be aware however that if you step up the voltage with a transformer by 21% then if the supply voltage jumps back up to 230V (for example the load on the 230V line reduces, which is what is causing the voltage drop in the first place) you will be running your equipment at 278V which is likely to cause damage.

Consider instead using voltage regulators or UPS's on sensitive (light load) equipment that cannot handle the 21% voltage drop (many pieces of equipment will work fine so you shouldn't need to protect everything depending on what is on your site), adding or replacing the high voltage transformer with a suitably sized one to combat the voltage drop on the 230V supply side (if you are talking about a large site), adding voltage regulation or power factor correction (depending on the type and duration of the 230V voltage sags), checking the legal obligations of your power or lines company to see if they have to fix it instead, etc.

From what you stated it seems that you are on the tail end of supplier's transformer and it is the transmission loss and you need to improve conductor size to reduce transmissions loss. If your voltage is fluctuating from 230 to 190 volts, it means the voltage is dropping depending on the load conditions of customers who are ahead of you. In that case solution is to install voltage stabiliser using auto transformer and voltage sensing circuit and operate the position of the transformer by a servomotor operated by voltage sensor. Such servo voltage controllers are available in the market . Buy and install one with correct kVA rating depending on your load.