# 3-phase 380 V to 3-phase 230 V

I have a portable bearing heater which works with 3-phase 230 V power supply.

My power supply is 3-phase 380 V. Is there any way to convert the 3-phase 380 V to 3-phase 230 V? Please note that since the equipment is portable, it is important that the solution be portable too.

I added the picture of wiring diagram of the equipment. The manual indicates: The equipment is designed for 3 phase 230V power supply (Between each hot wire, 220 volts can be measured) when 2 phases are connected. it means 2 phases out of 3 phases are connected.

The supply power is 3-phase 380V,which means between each hot wire, 380 volts can be measured and between the neutral and any of hot wires, 220 volts can be measured

• Is the heater Delta or Wye? And the supply? – Tom Carpenter Nov 3 '18 at 8:55
• Technically, this can be easy to do with a three-phase transformer. However, these transformers can be heavy and expensive. How much power does your heater require? Are both your power supply and heater using the same frequency? (both 50Hz, or both 60Hz?) – bitsmack Nov 3 '18 at 8:56
• Actually the equipment use 2 phases out of 3-phase 230V power. both equipment and supply are 50Hz and the power that equipment needs is 23.2 KVA. I have found a transformer that does this job but the weight is 150Kg. I'm looking for a solution which can be used as portable. – Kayvan Milani Nov 3 '18 at 9:04
• The heater and supply both are Delta – Kayvan Milani Nov 3 '18 at 9:08
• If you have 3-phase 380 V in delta configuration, you have also 3-phase 220 V in star configuration requiring an additional neutral connector. But if you want 230 V, you need 400 V. Of course you may use 3 phase power transformer, primary in delta, secondary in star. It will be portable for very low power. – Uwe Nov 3 '18 at 16:24

Figure 1. Coloured up version for single-phase 230 V + N wiring.

It appears from the wiring diagram that you can just connect L3 to neutral instead with no internal modification.

The only concern should be that the components' insulation now has to withstand 230 V instead of $$\ \frac {230}{\sqrt 3} \ \text V\$$. You should check, if possible, that they are rated for that.

Most likely your heater expects supply of three phases at 230 V(rms) phase-to-neutral, and the supply you have is three phases at 380 V(rms) phase-to-phase.

Fortunately these are the same* thing! So most likely you won't need any conversion, except perhaps a plug adapter.

(*: Within a few percent that can be chalked up to rounding; and utilities seemingly redefining their nominal voltage by 10 V up or down every several decades without non-electricians in the populance noticing; and is dwarfed by tolerances anyway).

It is quite rare and nonstandard to find three-phase AC at 230 V measured phase-to-phase or 380 V measured phase-to-neutral, so it would require extraordinary evidence to believe your heater or supply is one of those.

• I added wiring diagram and additional information to the question. – Kayvan Milani Nov 4 '18 at 5:53
• You have either 220 V phase-to-neutral and 380 V phase-to-phase or you have 230 V phase-to-neutral and 400 V phase-to-phase. But you don't have 230 V phase-to-neutral and 380 V phase-to-phase. The factor is sqrt(3) for both cases. – Uwe Nov 4 '18 at 9:59
• @KayvanMilani: I see no reason to assume from your diagram that the "230 V" it speaks about would be measured between the phases. Quite on the contrary. it's om German, and in all German-speaking countries a supply of three-phase 230V phase-to-neutral is the standard whereas 230V phase-to-phase is a weird nonstandard thing that it would, as I said, require extraordinary evidence to believe any German-speaking engineer would design an appliance to require. – Henning Makholm Nov 4 '18 at 10:01
• @Uwe: I did see your comment on the question and added the third paragraph to this answer especially to respond to that. – Henning Makholm Nov 4 '18 at 10:01

There may be a simple solution to this depending on the connection, If the load is connected between the two phases and no neutral connection as you have indicated in the comments section, you can connect the bearing heater between L1 and the neutral from your 380v supply. This will give you a voltage of approximately 220v and de-rate the output power by about 1KVA. The only other option without knowing the internal connections would be a big transformer on a trolley.

Looking at your wiring diagram it appears that what I suggested above will work. The only problem that I can see is if the 230v neutral wire is used by any monitoring electronics not shown on the diagram.

simulate this circuit – Schematic created using CircuitLab

The best way to do this would be a 3 wire connection as shown above by replacing the existing plug with a 380v one, or if you need to keep the 230v compatibility an adaptor box that is clearly marked for use with only this unit.

• I added wiring diagram and additional information to the question. – Kayvan Milani Nov 4 '18 at 5:51

simulate this circuit – Schematic created using CircuitLab

You have only to rewire heating elements from wye to delta connection.

EDIT:

You said:

Actually the equipment use 2 phases out of 3-phase 230

simulate this circuit

All you have to do is to connect your load between phase to neutral, and not phase to phase anymore. But 22kVA seems huge power for single phase operation. You'd better dismount your device and post some pictures. For exaple you could separate the electronic part which needs low voltage by means of SMPS or transformer and the power part by replacing two phase graetz diode bridge with 3 phase diode bridge.

Check if L1, L2 and L3 are series connected as shown in schematics. There is a notation: 3x6mm^2 or 3x10mm^2 at 2x220V, which means that sections are made for different voltage, combining them series or parallel.

You have to use phase to neutral voltage for control unit. This can be easily done by rewiring L3 control supply to N.

The next thing is to check if the coils are really connected in series. IMO, by combining L2 and L3 in series or parallel you can get 380V/220V. So they shold be connected parallel right now.

simulate this circuit

Another possibility for combining multiple voltages. Watch if the windings are wound in same direction or they are connected anti series, dectructing their magnetic field.

simulate this circuit

• Are you sure about that? Isn't first circuit 3x380V? The voltage between phases is 380V/400V and voltage between phase and neutral is 230V – Chupacabras Nov 3 '18 at 13:35
• First circuit is 220 V phase to phase. The second circuit is 220 V phase to neutral. The OP says in the comments that the load is connected between two phases though so this diagram is not accurate. The one load would have to be wired phase-neutral. – Transistor Nov 3 '18 at 16:15
• Each element has nominal voltage of 220V. 1st picture: the mains network is 3x220V (phase to neutral is 127V). 2nd picture: the mains network is 3x380V (phase to neutral is 220V). The OP made a question with very poor description, he should edit the question with details to get an answer. – Marko Buršič Nov 3 '18 at 16:38
• @MarkoBuršič phase to neutral is not 127V. Phase to neutral is 230V (in Europe). Phase to phase is 400V. – Chupacabras Nov 3 '18 at 17:37
• @Chupacabras Has the OP said that he's from EU? In EU there is no 3x220V mains that OP is asking for. Those are totally different networks 3x220v, 3x380V and 3x400V. The europe is 3x400V, others not. – Marko Buršič Nov 3 '18 at 18:30