# Convert three-phase to a single-phase

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.

• of course not. it is a real problem for me. Nov 14, 2021 at 10:51
• What do you mean by "more industrial?" What exactly do you see as a problem with the Scott-T arrangement?
– user80875
Nov 14, 2021 at 12:05
• dear @Charles Cowie Do you agree with my method of converting 3-phase to single-phase power? Because the main application of Trans Scott is to convert 3-phase to 2-phase. Nov 14, 2021 at 12:46
• I believe there is a transformer arrangement that can provide single phase power with equal loading on the three phases. I have not assembled such an arrangement, but I believe that I worked out the required connection and transformer winding ratios. The required transformers may need to be custom made. I may have previously posted an answer about that.
– user80875
Nov 14, 2021 at 12:58
• I believe that some version of a Le Blanc connection will reduce the amount of imbalance. I will try to provide more information later.
– user80875
Nov 14, 2021 at 13:49

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.

• Thank you for your answer but give me a solution if you are saying this way is not work. The simplest way to describe my problem is this, I wanna supply a single-phase load, with a 3 phase supply, but my 3phase supply only accepts 20% unbalance, so because of that, I should find a way to make my system more balance. Nov 23, 2021 at 5:42
• What did you not understand about my answer? Nov 23, 2021 at 6:44
• I did understand your answer, and I told you to give me a solution to improve the imbalance. I can not change my supply scheme and it is a diesel generator that it can handle only 20% of the imbalance. so If you have any ideas, I will be thankful to share them. Nov 23, 2021 at 8:44
• "I told you to give me a solution ..." Sorry, that's not how it works here. You ask a question and hope for a solution. You don't tell me to do things for you. Nov 23, 2021 at 10:01
• I am sorry but do you really understand what I am saying?! did I ask you to do anything for me?!! I just describe my problem to you and asked you if you have any idea that is relative to my problem, not some words that don't help me, you shared it with me. I have never asked you to do anything. but still thank you for your attention. Nov 23, 2021 at 10:36

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.

• Thank you for your answer. I searched a lot about Scott and Leblanc and both of them gives me 2 single-phase that should be the same current flow at each single phase. and for now, I want to check out rectifying to dc and invert it to a single phase. Can you give me some real experience examples or a handbook name about it? Nov 23, 2021 at 6:08