Sizing a Distribution Transformer correctly is one of the most consequential decisions in project planning. An undersized unit overloads, overheats, and fails prematurely; an oversized unit wastes capital and runs at poor efficiency with higher no-load losses. The goal is a capacity that covers your actual demand with a reasonable margin for growth - no more, no less.
Load Power, Power Factor & Maximum Demand
Start with the total connected load in kW, then convert to kVA using your power factor: kVA = kW ÷ power factor. Do not size on connected load alone - use the maximum demand, the peak simultaneous load your facility will actually draw, which is often 60–80% of connected load. A facility with 320 kW of connected equipment at 0.8 power factor draws 400 kVA at full simultaneous operation; with a typical maximum demand of 75%, a 500 kVA Distribution Transformer provides comfortable headroom. For smaller operations with peak demand around 150–200 kW, a 200 kVA Distribution Transformer is usually the practical starting point.
Motor Starting Current & Future Expansion
Motor starting currents can reach 6–8 times rated running current, and simultaneous starts can cause voltage sags that trip other equipment. If your load is motor-heavy, add margin for starting rather than sizing only for steady-state demand. Separately, factor in future expansion: adding a production line or EV chargers later is far cheaper than replacing a transformer. A common rule is to reserve 20–30% spare capacity for planned growth.
Parameters to Confirm Before Requesting a Quote
Before contacting a supplier, confirm and provide: primary voltage and secondary voltage (e.g., 11 kV / 0.4 kV), frequency (50 Hz or 60 Hz), vector group (e.g., Dyn11), impedance if specified by your utility, tap changer range, installation environment (indoor/outdoor, altitude, ambient temperature), and applicable standards (IEC 60076, ANSI, or local codes). Providing a load list and single-line diagram shortens the engineering review considerably.
About Hebei Hozee Electric Co., Ltd.
Hebei Hozee Electric Co., Ltd. manufactures oil-immersed transformers, dry-type transformers, single-phase transformers, and transformer cores including laminated cores and single-phase wound cores. Our engineering team reviews customer load lists and drawings within 24–48 hours and can recommend a capacity based on your maximum demand, motor starting profile, and expansion plans. If you are sizing a Distribution Transformer for a new project, send us your load details and we will help you confirm the right rating before you order.