Three Phase Transformers Information

Three phase transformers are designed to supply electric power to three-phase systems. These electrical devices have three circuit conductors and may or may not have a neutral wire. Three phase power is used by electric power distribution grids and to power large motors and other large loads. Three phase transformers carry many product specifications, including transformer type, winding turns, cooling method, core type, and mounting style or form factor. Performance specifications, regulatory approvals, and special features are also important parameters to consider.


There are many types of three phase transformers. Products include balun, cast coil, distribution, flyback (FBT), generator step-up (GSU), harmonic mitigating, high voltage, industrial control, and inverter transformers. Categories of three phase transformers also include isolation, multi-ratio, neutral grounding, power, rectifier, resonant, and substation transformers. Autotransformers are used mainly in low-power applications. They include variacs or variable autotransformers.

Like other types of transformers, three phase transformers are used to increase or decrease the voltage from one side of the transformer to the other. The turn ratio or number of windings on the primary and secondary sides of the device determines the change in voltage. One-to-one three phase transformers have a turn ratio of 1:1 or near 1:1. Variable transformers are three phase devices with a setting for changing the turn ratio as needed. Step-up transformers produce a secondary voltage that is larger than the primary voltage. Step-down transformers have a secondary voltage that is smaller than the primary voltage.

Core Type, Cooling Method, Output Voltage and Mounting

Core type, cooling method, output voltage, and mounting or form factor are additional product specifications to consider when selecting three phase transformers. Core types are listed as laminated, split, toroidal, and other. There are four choices for cooling method: dry or air cooled, oil filled, water cooled, and other. There are a variety of form factors or mounting styles to choose from. Choices for three phase transformers include chassis mount, chip, dish or disk, H-frame, modular jack, pad mounted, printed circuit board (PCB), and pole mounted.

Selecting Three Phase Transformers

Selecting three phase transformers requires an analysis of performance specifications, device configuration, features, and approvals. Performance specifications include operating temperature, power rating, operating frequency range, maximum primary voltage rating, maximum secondary voltage rating, and maximum secondary current rating. Configuration styles for three phase transformers consist of delta – delta, delta – wye (Y), wye (Y) – wye (Y), wye (Y) – delta, wye (Y) – single phase, delta – single phase, and international. With regard to features, some three phase transformers are waterproof or rated for outdoor use. Products sold in Europe must comply with RoHS and WEEE.