How to Choose a Transformer for a Factory
Choosing a factory transformer is a load, environment and growth decision, not a catalogue pick. This guide works through the checks in order — load, supply, harmonics, cooling, growth and protection — so the unit you order still fits the factory in five years, not just on the day it arrives.
Start with a real load list
List every load with running demand, starting demand, and which loads run together. Factories are where diversity is most often guessed wrong: motors, welders, furnaces and HVAC rarely peak together, but when they do, the transformer must handle it. A load list built from nameplates alone, without starting currents and simultaneity, will size either too small for the real peak or too large for the real load — and both cost money.
Supply, harmonics and voltage
Confirm the supply voltage, fault level and earthing arrangement with the utility before choosing a vector group or impedance. Then check harmonics: variable-speed drives, rectifiers and welders add harmonic heating that a plain kVA total ignores, and may call for a higher rating or a different winding design. Check voltage drop at the farthest load under motor starting, not only at steady full load, because a factory that starts a large motor and sags the whole plant will blame the transformer even when the rating was right.
Cooling, environment and growth
A rating assumes stated cooling conditions: ambient temperature, ventilation, altitude and whether the unit sits indoors or in dust, heat or corrosive air. A factory environment that is hotter, dirtier or less ventilated than standard conditions derates what the nameplate promises. Plan growth honestly — a documented margin plus a physical route to a larger unit beats a unit that cannot be replaced without rebuilding its room.
Protection and the order decision
Coordinate protection so inrush and motor starts do not trip the plant, while genuine faults still clear fast. Before ordering, confirm in writing: rating, ratio, vector group, impedance, cooling, tap range, standards, test scope, delivery and warranty terms. A transformer ordered on a one-line specification is a dispute waiting for delivery day.
If you want a second pair of eyes on your own numbers or drawings before you decide, see the remote transformer services — documents only, fixed price, fixed turnaround, no site visit. For the wider testing picture, start with the transformer testing and commissioning guide.