Convert three-phase to a single-phase

Question

For a local power grid powered by a 20 kW diesel generator, I want to feed a set of single-phase loads.

But I have problem with imbalance.

I have equally divided consumers between each phases as much as possible, but due to the lack of coordination of consumer use, imbalances occur.

The load of each line is about 1 to 2 kW, but consumers are very important and expensive so it require a constant voltage.

Therefore, load imbalance and the destructive effects of load imbalance are not acceptable.

The solution that seemed to me was this to use a transformer to convert three input phases to single phase and then use a single phase stabilizer with 10 kW capacity. And for this solution I want to use Scott transformer to convert three phase to single phase.

But I'm looking for a solution that is more industrial.

If you have done some thing like this before, please share your experience or suggest a solution.

Answer 1

I don't believe you can do this.

You will notice that in 3 and 2- phase systems there is always at least one phase supplying current at any instant. In single- phase output the current drops to zero twice per mains cycle and that means you have no load on the poly-phase supply at those times.

I think your best hope is a star (wye) supply with a decent neutral connection to each load.

Perhaps @CharlesCowie will prove me wrong with an illustration from his library of ancient and forgotten electrical inventions.

Answer 2

The Le Blanc (or Leblanc) transformer connection is a 3-phase to 2-phase conversion connection that has one phase using three secondary windings as shown below. The second phase, not shown, uses only two secondary windings.

For the phase shown below, the secondary winding voltages for the A and B secondaries are not necessarily the same as the C phase winding. The desired secondary output voltage can be obtained with any A/B and C voltage selection desired. It seems to me that one selection of secondary voltages will result in balancing the real power among the three phases and another will result in balancing the apparent power and primary current. The load power factor may also need to be considered.

For a 2-phase secondary it may be possible to balance both real and apparent power.

The user of a scheme like this may also need to investigate the effect of any harmonic components in the load current.

Depending on the details of the load power requirements, it might be preferable to rectify the generator output and distribute DC to the loads. Another alternative would be to supply DC to an inverter.

There are research papers and other resources available for Leblanc transformer information. For example:

Tsai-Hsiang Chen, Comparison of Scott and Leblanc transformers for supplying unbalanced electric railway demands, Electric Power Systems Research, Volume 28, Issue 3, 1994, Pages 235-240, ISSN 0378-7796, https://doi.org/10.1016/0378-7796(94)90038-8.