How to Choose a Transformer for an Industrial Plant?

Choosing a transformer for an industrial plant is a system decision. The unit has to match the network fault level, the protection philosophy, the plant load profile and the physical constraints of the substation.

This guide covers the checks that most often get missed at specification stage.

Choosing a transformer for an industrial plant is a system decision. The unit has to match the network fault level, the protection philosophy, the plant load profile and the physical constraints of the substation.

This guide covers the checks that most often get missed at specification stage.

Get the utility’s declared supply voltage, frequency, fault level and earthing arrangement at the point of connection. The transformer’s insulation level (BIL) and short-circuit withstand capability follow directly from this data.

Impedance is a compromise. Higher impedance reduces prospective fault current, which allows lower rated switchgear and reduces mechanical stress on windings. Lower impedance improves voltage regulation and reduces voltage dip on motor starting.

Typical distribution values are 4–6%; large industrial units sometimes go to 8% where fault level is a constraint.

Dyn11 is the usual choice: a delta primary blocks third harmonic currents from the network, and the star secondary gives an accessible neutral. If you plan to parallel with an existing transformer, the vector groups must match.

ONAN is standard. ONAF (fans) raises the continuous rating, typically by 25–33%. Dry type equivalents are AN and AF. Match the cooling to the load profile and to the ventilation available at the site.

For critical process, consider two transformers each able to carry the essential load with automatic changeover. This increases the fault level on the bus, so switchgear ratings must be checked.

Large drive and rectifier populations distort current waveforms and heat windings beyond what the fundamental current suggests. Provide the drive share of load to your supplier, and consider a K-rated or de-rated design.

Confirm bushing type, cable box arrangement, cable entry direction, and the signals required by protection and monitoring (winding temperature, Buchholz, oil level, pressure relief).

Not sure which rating fits your project? Send us your load list and we will size it for you, or email info@xsdfftransformer.com, call +86 158 6789 7761 or WhatsApp +852 5416 2620.