Three-phase transformers

Our three-phase range, from 1 to 1,000 kVA

A three-phase transformer matches the voltage of a three-phase supply to that of a machine or an installation: it creates a neutral, isolates an installation from the mains, powers a machine built for another country's supply, or provides 230 V single-phase from a 400 V network. We manufacture dry-type three-phase transformers. From 1 to 100 kVA, every rating is for sale online, with a price shown for each protection rating (IP00, IP23 or IP54). Above that, from 125 to 1,000 kVA (125, 160, 200, 250, 315, 400, 500, 630, 800 and 1,000 kVA), we build them on request.

Three-phase isolation transformers (Dyn11)

• 400 V / 400 V + N isolation transformer: isolates an installation from the mains and creates a neutral, with 230 V between each phase and neutral.
• 400 V to 230 V + N transformer: supplies machines designed for a 3 × 230 V network.
• 230 V to 400 V + N transformer: runs 400 V machines on a 3 × 230 V network.
• 230 V / 230 V + N isolation transformer: isolates a 3 × 230 V network and adds a neutral.
• 400 V to 208 V + N and 208 V to 400 V + N: North American machines in Europe, and the reverse.

Other configurations

• Three-phase to single-phase transformer: a 230 V single-phase output from a 3 × 400 V supply.
• 400 V / 230 V + N three-phase autotransformer, without galvanic isolation.
• A three-phase transformer for HP printers, and the custom three-phase transformer for any other voltage, up to 1,000 V between phases.

What is a three-phase transformer?

A three-phase (3-phase) transformer works on all three phases of an AC supply. Its magnetic core has three limbs, with one coil per phase; each coil carries a primary and a secondary winding. It changes the voltage without changing the frequency. For the same power, it shares the load across three phases, which is why it is the power transformer found in workshops, on machinery and in industrial installations.

Our three-phase transformers are dry-type, naturally cooled units with insulation class H (180 °C), designed for an ambient temperature of up to 40 °C. They are low-voltage to low-voltage (LV/LV) transformers, up to 1,000 V between phases. For single-phase supplies up to 20 kVA, see our single-phase transformers.

The main types

Three-phase isolation transformer

The primary and secondary are two separate windings with no electrical connection between them, so the connected installation is isolated from the supply. With a Dyn11 connection, it brings out a neutral on the secondary: this is how you obtain a 3 × 400 V + N network from a 3 × 400 V supply that has no neutral. Our three-phase transformers with separate windings have an electrostatic shield as standard, connected to earth, which limits the transfer of interference between primary and secondary. See also our isolation transformers.

Three-phase autotransformer

It has a single winding per phase, shared by input and output. More compact, it does not separate the installation from the supply: it is suitable when galvanic isolation is not required and the voltage difference is moderate, for example between 400 V and 230 V. See our autotransformers.

Three-phase to single-phase transformer

It connects to a 3 × 400 V supply and delivers a 230 V single-phase output, for a single-phase machine or piece of equipment on a site without a neutral.

MV/LV distribution transformers

Substation transformers, which step down the medium voltage of the distribution network, are either oil-immersed or dry-type, cast-resin units. We handle these on a quotation basis: see our special transformers.

Vector groups and wiring diagram

The winding connection describes how the three windings are linked together, on the primary and on the secondary. It determines whether a neutral is available and which voltages you can use.

• Delta (D on the primary, d on the secondary): the three windings are connected end to end. There is no neutral; this connection handles unbalanced loads well.
• Star (Y, y): the three windings are joined at a common point, the neutral. With the neutral brought out (N, n), two voltages are available: line-to-line and line-to-neutral.
• Zigzag (Z, z): each phase is split across two limbs, which gives a stable neutral when single-phase loads are unbalanced.

Vector group Dyn11, used on our standard three-phase isolation transformers, combines a delta primary with a star secondary and a brought-out neutral; the clock number 11 denotes a 30° phase shift between primary and secondary. It is the most widely used vector group in low-voltage distribution. Other vector groups are available on request: Dd0, Yyn0, YNyn0, Yd11 and YNd11.

On a three-phase transformer wiring diagram, the supply comes in on primary terminals 1U, 1V and 1W, with earth on PE; the outgoing circuits leave from secondary terminals 2U, 2V and 2W, and the neutral from terminal 2N. The wiring diagram and the enclosure drawing of each model are on its product page.

How to choose a three-phase transformer

Voltages and neutral

Note the line-to-line voltage of your supply and that of the machine. Check the neutral as well: a 400 V / 400 V + N unit gives 230 V between each phase and neutral, whereas a 400 V / 230 V + N unit gives 230 V between two phases and 133 V between a phase and neutral, for machines designed for a 3 × 230 V network.

Power rating

Multiply the machine's current per phase by the line-to-line voltage and by √3, then divide by 1,000 to get kVA. Choose the next standard rating up. Example: 10 A per phase at 230 V gives about 4 kVA.

Protection rating

IP00 for a cabinet or an enclosed electrical room; IP23 in a ventilated metal enclosure, for a plant room sheltered from water; IP54 in a closed enclosure, protected against dust and splashing water. See our page on IP and IK protection ratings.

Installation and protection

On the primary side, fit a type D circuit breaker or aM fuses, sized to the rated current: when it is switched on, a transformer draws a high inrush current. The recommended size for each power rating is given on the product page. Terminals are screw-type up to 55 A, with cable lugs above that. Connection must be carried out with the power off, by a qualified person. Units over 30 kg are shipped on a pallet.

Wound and tested in Gailhan, with a 5-year warranty

ABL Transfo has been manufacturing transformers since 1993 in its workshop in Gailhan, in the Gard (southern France). Every three-phase transformer is wound, wired and 100 % tested there before dispatch; it falls under EN IEC 61558-1 and EN IEC 61558-2-4 and carries a 5-year warranty. Built to order, models from 1 to 50 kVA leave the workshop within 3 working days, and those from 63 to 100 kVA within 6 working days.

Options on request: tappings at ±2.5 %, ±5 % or ±10 %, other voltages up to 1,000 V between phases, 60 Hz subject to confirmation, temperature sensors (bimetallic, PTC or PT100), forced ventilation, a primary-side isolator, and castors for large enclosures.

Professionals get an immediate 5 % discount and prices excluding VAT with a trade account.

Above 100 kVA or for another voltage

From 125 to 1,000 kVA, our three-phase transformers are made on request: tell us your voltages, power rating and installation, and we will reply within 48 hours with a free quote. For a voltage that is not in our standard range, the custom three-phase transformer can be configured online, with its price. All our non-standard models are grouped under custom-built transformers.

Compare all the options: 400 V to 230 V transformers.