Can a Transformer Make 3 Phase from Single Phase?

No. Hammond Power Solutions, a transformer maker, answers it in one sentence: "Transformers cannot convert a single-phase source to a three-phase source." A transformer changes voltage; it does not add a phase. People search for one anyway, and the people asking usually need one of three other things: a phase converter or a VFD to make 3 phase, a step-up transformer after a converter to reach 480V, or a buck boost transformer to trim a voltage that is a little off. This guide sorts out which one you need.

Can a transformer convert single phase to 3 phase?

Hammond's FAQ gives the whole answer in three sentences: "Single-phase power can be derived from a three-phase source. Transformers cannot convert a single-phase source to a three-phase source. The typical method to convert single-phase power to three-phase power is to utilize devices generally termed as rotary or static phase converters."

So the direction matters. Three phase to single phase: a transformer can do that. Single phase to 3 phase: no transformer can, and no wiring of one changes that.

What does the job instead?

Four devices make 3 phase from single phase. The guide to running 3 phase machines on single phase power covers all four; here they are in one line each.

• A static phase converter. Phoenix Phase Converters: "A static phase converter uses capacitors and a start relay to momentarily generate a third phase of power." About two thirds of the motor's horsepower, one machine.
• A rotary phase converter. Phoenix: it "uses an idler motor" and is "combined with a control panel to generate continuous, balanced three-phase power." Several machines from one unit.
• A digital phase converter. Phoenix: "also called an electronic phase converter", it uses power electronics to "synthesize the third phase digitally".
• A VFD with single phase input. One motor, with speed control. Lenze's application note on derating VFDs for single phase input: "Most manufacturers of VFDs only offer products up to 3 Horsepower (HP) for single phase input." Phoenix's CNC guide, on VFDs: "Cannot power multiple motors simultaneously".

Which one fits is a question of motors, machines and balance; rotary vs digital vs VFD walks through it.

Why do people search for one?

Three real needs hide behind the phrase.

The first is 3 phase itself. A used machine arrived with a 3 phase motor and the shop has single phase service. That is a converter or a VFD, above.

The second is voltage. The machine is 480V and the service is 240V. That takes a converter and a transformer, in that order, and it is the one case where a transformer belongs in the answer.

The third is a small correction. The service reads 208V and the machine wants 230V, or the other way round. That is a buck boost transformer, and it has limits.

Where a transformer does belong: a 480V machine on 240V service

A phase converter puts out the voltage it takes in. Phoenix's 480V page: "On its own, a rotary phase converter produces a three-phase voltage that matches the input voltage." Its answer for a 480V machine: "So, if you need to convert 240-volt single-phase power into 480-volt three-phase power, invest in a rotary phase converter and a step-up transformer." The converter makes 3 phase at 240V; the transformer raises it to 480V. Phoenix's description of the second step: "A step-up transformer accelerates the voltage of the electrical current, thus enabling you to power equipment with larger loads."

A 480V machine is a hand-off, not a chart lookup. The converter maker sizes the converter and the transformer as a package, and a licensed electrician installs both. Call (855) 923-2610 and we point you to the maker's line.

What about a buck boost transformer?

A buck boost transformer nudges voltage a little. Hammond's buck boost brochure: "Buck-boost transformers can correct line voltage within 5 to 25% of nominal." Acme's selection chart puts its range at "5–20%". Going from 240V to 480V is a 100% rise, four times the top of either range, so a buck boost transformer is not the 480V answer.

It has two other limits, in Hammond's words: "No circuit isolation" and "Cannot create a neutral". And one unit does not serve a 3 phase machine. Acme: "Three-phase applications require multiple separate single-phase buck boost transformers to be wired and mounted together."

What it is for: a 3 phase supply that is a few percent off what the machine wants, corrected after the converter has made 3 phase. Which unit, and how it connects, is the maker's chart and your electrician's job. Both makers publish the same sizing formula, "1 Phase kVA = Volts x Amps / 1000" in Acme's chart; Hammond's autotransformer version reads "Output Volts x Secondary Amps / 1000".

Do any converters or drives change voltage?

Two makers list units that do, and neither is a 480V answer without the maker's say-so.

Phase Technologies lists voltage doubling Phase Perfect models, PT207 through PT230, whose output the Gen4 manual gives as about twice the input voltage. What they are built for is a question for Phase Technologies; ask before you count on one for a 480V machine.

Invertek lists a small E3 line for low voltage input: "110V 1 Ph Input: 0.5–1.5HP (230V 3 Ph Output)". It raises 110V to 230V for a motor of 1.5 hp or less. It does not reach 480V.

Questions

Can I run a 3 phase transformer backwards to get 3 phase?

No. A transformer needs a 3 phase source to put out 3 phase, whichever way you connect it. Hammond: "Transformers cannot convert a single-phase source to a three-phase source."

Does a rotary phase converter change voltage?

No. Phoenix: "On its own, a rotary phase converter produces a three-phase voltage that matches the input voltage." Add a step-up transformer for a 480V machine.

Does a VFD change voltage?

The 230V single phase input drives in our reading put out 230V 3 phase. Invertek's 110V input E3 puts out 230V. None reaches 480V from 240V service.

Who sizes the transformer?

The converter maker, as part of the converter and transformer package, and a licensed electrician installs it. Phoenix's installation guide: "Phase converter installation should always be performed by a licensed electrician." The same goes for the transformer.

Sources named in this guide

Hammond Power Solutions' FAQ on converting single phase to three phase and its universal buck boost transformer brochure. Acme's buck boost transformer selection charts. Phoenix Phase Converters' 480V page, comparison of static, rotary and digital converters, complete guide to phase converters for CNC machines and installation guide. Lenze's application note on derating VFDs for single phase input. Invertek's Optidrive E3 specification. Phase Technologies' Phase Perfect Gen4 manual. We name maker documents and don't link maker sites.

Start with the guide to running 3 phase machines on single phase power, then size the converter in the calculator. More answers on the FAQ. Sizing help is free. Call (855) 923-2610 with the nameplate numbers.