Directly from 30 kV to 0.4 kV? Or step down the voltage in stages, typically from 30 kV to 6 kV, then from 6 kV to 0.4 kV.

[Jpascp]

In most cases, it's standard to not go directly from 30 kV to 0.4 kV. The more common practice is to step down the voltage in stages, typically from 30 kV to 6 kV, then from 6 kV to 0.4 kV.

Any advantages (economical, technical) of it?

Attached example.

 

[davidbeach]

Lots and lots of installations with 34.5kV to 690V or 480V transformers, so "most cases" is probably not accurate. Probably depends on many factors including local custom.

 

[dpc]

I agree with David - if you don't plan to use the intermediate voltage for anything, best practice would be direct conversion from 30 kV to 400 V. Simpler and lower losses. A quick chat with a transformer manufacturer might help dispel any of your concerns.

 

[waross]

34kV to 120/240 Volt residential is common.

 

[7anoter4]

In a power station of 700 MW coal fired steam turbine where the most of equipment
Is of 1 to 20 MW rated power-see the boiler air draft fan, for instance- the main auxiliary distribution is 6 or 10 kV and not the low voltage [0.4-0.48-0.690] so you have here 6 kV already. But, if you have to supply a 1000 square km [or more] rural region, an overhead distribution you need of 30[or 35 kV] rated transformers in order to reduce the supply grid losses. By the way, the main losses in a transformer are from current level and not from dielectric losses. The medium voltage equipment expenses are, more or less, the same.

 

[Jpascp]

I agree with David - if you don't plan to use the intermediate voltage for anything, best practice would be direct conversion from 30 kV to 400 V. Simpler and lower losses. A quick chat with a transformer manufacturer might help dispel any of your concerns.

Agreed. Attached economical evaluation. Best option is to go directly from 30 to 0,4 kV

 

[Jpascp]

In a power station of 700 MW coal fired steam turbine where the most of equipment
Is of 1 to 20 MW rated power-see the boiler air draft fan, for instance- the main auxiliary distribution is 6 or 10 kV and not the low voltage [0.4-0.48-0.690] so you have here 6 kV already. But, if you have to supply a 1000 square km [or more] rural region, an overhead distribution you need of 30[or 35 kV] rated transformers in order to reduce the supply grid losses. By the way, the main losses in a transformer are from current level and not from dielectric losses. The medium voltage equipment expenses are, more or less, the same.

Yes it is clear that if we need to transport more power we need o increase the voltage.

I am mentioned for case study shown in image. I believe the best option is going directly from 30 kV to 0,4 kV. If we need 6 kV voltage level we add a transformer for that loads.

 

[Jpascp]

Lots and lots of installations with 34.5kV to 690V or 480V transformers, so "most cases" is probably not accurate. Probably depends on many factors including local custom.

Yes. It is possible to compare in terms of technical and economical.

 

[waross]

Common practice in large industrial plants is to step down to 489V, 600V or 690V.
That is the greatest portion of the load.
Small local transformers are used to supply 120/240av and other lighting voltages.
Often each lighting panel will be fed from an individual transformer mounted close to the panel.
But these are utilization voltages, not an intermediate voltage, just because.