How Much Transformer Capacity Does a Factory Need?

This is the question behind most transformer enquiries. The answer comes from a load study, not a rule of thumb, but a few checks will tell you quickly whether your existing or proposed capacity is in the right range.

Here is the method, with the checks people most often forget.

This is the question behind most transformer enquiries. The answer comes from a load study, not a rule of thumb, but a few checks will tell you quickly whether your existing or proposed capacity is in the right range.

Here is the method, with the checks people most often forget.

Capacity (kVA) = connected kW × diversity ÷ power factor × (1 + growth margin).

Worked example: 2,000 kW connected, 0.65 diversity, 0.85 power factor, 25% margin → 2000 × 0.65 ÷ 0.85 × 1.25 = 1,912 kVA → select 2,000 kVA subject to motor starting and harmonic checks.

Using connected load without diversity is the single most common cause of grossly oversized transformers. Diversity is real: machines idle, shifts change, and process steps rarely coincide perfectly.

A large direct-on-line motor start causes a voltage dip. If the dip would affect other equipment, either increase capacity or specify soft starting or a variable speed drive.

If drives and rectifiers are a large share of load, add harmonic heating to the assessment. Ignoring it is how correctly sized transformers end up running hot.

Capacity planning is not a one-time exercise. Re-measure load annually and before adding any significant new equipment.

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.