Where does transmission end and distribution start voltage levels?
Answers
Preferrable depends on a lot of things. For someone looking at minimizing cost, a medium level voltage such as 34.5 or 69kV would probably be preferred due to the distance.
This type of line is relatively cheap (when built overhead, not buried), but may still be beyond what its' worth for only 3 MW. The voltage level you'd choose would be the same as is available nearest you, in my opinion - so you can minimize how far you must build, which minimizes long term, land ownership costs.
Since this is a fairly small load, the I^2*R losses would be fairly low through 34.5 or 69kV lines. Metering will most typically be done at the utility's end (if you own the line), so this may be important to maximize power that is being metered, resulting in a maximized payout to you.
The basic balance is up front cost vs. long term cost vs. what other equipment must be upgraded to accommodate this addition. The higher the voltage, the higher the upfront cost will be; also the higher the fault currents can be, and the more complex relaying can be.
Lower cost up front will result in more line loss, higher power transfer limitations, possibly extra equipment such as cap banks that you may be able to avoid at higher voltage (but not guarunteed).
You may need to do your own research on this; the utility you are interfacing with should be very knowledgable about this sort of thing - discussion with protection and controls, system planning, and special study groups at the utility may be necessary to fully answer your question as each location in the power grid presents unique challenges to adding generation, and different codes apply to different voltage levels and areas (which they will know).