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I need a 3 phase power supply for Lab purpose. Since using 220 V x 3 phase is dangerous, I'm searching for a three phase step down transformer and that seems not available. Am I asking something which is not commonly used?

  • Input : 3 phase, RYB, 220 V AC
  • Output : 3 phase, RYB, 12 V AC

I'm looking for a transformer just like the power companies do - 11 kV to 220 V, 3 phase - similar transformer from 220 VAC to 12 VAC, 3 phase.

Any directions? Pros / Cons - why not available easily, any references?

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    \$\begingroup\$ Three-phase power is pretty much exclusively used at high voltages; you rarely see three-phase below about 200V. So transformers specifically for three-phase designed to output such low voltage are rare; try using three single-phase transformers if you really need 12V three phase. But this sounds like a bit of an XY problem to me; why do you need 12V three phase? \$\endgroup\$ – Hearth Dec 11 '18 at 17:17
  • \$\begingroup\$ I'm developing a product which needs 3 phase AC input, and need to run a control circuit (microcontroller based and a couple of other integrated circuits which work on 12v) on each phase. I can control using high value resistors, but i prefer to have a galvanic isolated transformer so that we can work on the unit without turning the power off... \$\endgroup\$ – Vinay Sathyanarayana Dec 11 '18 at 17:42
  • \$\begingroup\$ then simply use three single-phase measurement transformers. \$\endgroup\$ – Marcus Müller Dec 11 '18 at 18:16
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Option 1

schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. A low-voltage 3-phase supply made from single-phase transformers.

Option 2

I have seen 24 V DC industrial power supplies which were 400 V primary and probably about 18 V secondaries feeding a rectifier. The rectified 3-phase supply has very little ripple so no smoothing capacitors are required. If you can find one of these you could tap in before the rectifier to get your three phases but they will be wired in delta so there will be no star / wye point for a neutral.

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  • \$\begingroup\$ I had indeed thought about this option, however i need an input without neutral. Let me check this and get back. Thanks. \$\endgroup\$ – Vinay Sathyanarayana Dec 12 '18 at 2:27
  • \$\begingroup\$ Then use Option 1a and don't connect the neutral or use option 1b. \$\endgroup\$ – Transistor Dec 12 '18 at 7:00
  • \$\begingroup\$ Will try this and let you know the result. thanks much. \$\endgroup\$ – Vinay Sathyanarayana Dec 12 '18 at 8:06
  • \$\begingroup\$ Got 3 transformers - 400V AC in, 12V AC out, connected both - primary and secondary in delta, now I get 12V AC 3 phase in the output. Thanks for all your inputs. \$\endgroup\$ – Vinay Sathyanarayana Dec 15 '18 at 16:20

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