What Size Transformer Does a Factory Need?

There is no single answer, but there is a reliable method. Factory transformer sizing comes down to five numbers: connected load, diversity factor, power factor, the largest motor and your growth plans.

This guide shows the method and gives indicative ratings by factory type so you can sanity-check whatever number you arrive at.

There is no single answer, but there is a reliable method. Factory transformer sizing comes down to five numbers: connected load, diversity factor, power factor, the largest motor and your growth plans.

This guide shows the method and gives indicative ratings by factory type so you can sanity-check whatever number you arrive at.

Transformer kVA = (Maximum demand in kW) ÷ (Power factor) × (1 + growth margin).

Maximum demand itself is connected load × diversity factor. Every input matters: a 0.6 diversity assumption instead of 0.8 changes the answer by 25%.

A factory has 1,600 kW of connected load. Assessment shows that at peak about 70% of it runs together, so maximum demand is 1,120 kW. Power factor is 0.85 after correction. Growth margin is 25%.

kVA = 1,120 ÷ 0.85 × 1.25 = 1,647 kVA → select the next standard rating up, typically 1,600 kVA or 2,000 kVA depending on the motor starting check.

The largest motor is a common reason to upsize. A direct-on-line start can draw six to eight times full load current and cause a voltage dip of 10–20% on a weak transformer. If a dip of that size affects other equipment, either increase the rating or change the starting method.

If variable speed drives, rectifiers or large UPS systems make up a significant share of load, harmonic currents add heating that the kVA calculation does not capture. Tell your supplier the drive share of load so the design can account for it.

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.