🔌 Transformer Sizing & Selection Calculator
Enter your connected load and get the standard transformer kVA, recommended model and a copper-linked reference price. Covers oil-immersed, dry-type, amorphous-alloy and box-type substations.
⚙️ Your Load & Specs
📊 Result
For electrical engineers, contractors and buyers sizing a distribution transformer from a load.
How it is calculated
· Sizing — kW mode: kVA = Load (kW) ÷ Power factor; kVA mode: kVA = Load; Amps mode: kVA = √3·U·I (3-phase).
· Design capacity: kVA_design = kVA × (1 + design margin %).
· Selection: next standard kVA from the IEC R10 preferred series; price = base × winding × efficiency × voltage factor, with ±3% per $1,000/t copper for copper windings.
Referenced standards
| Standard | Scope |
|---|---|
| IEC 60076-1 | Preferred kVA ratings (R10 series) for power transformers |
| GB/T 1094 | Chinese equivalent of IEC 60076, power transformer ratings |
Worked example — 500 kW load → 800 kVA transformer
1. Load 500 kW, power factor 0.85 → kVA = 500 ÷ 0.85 = 588 kVA.
2. Design margin 20% → kVA_design = 588 × 1.20 = 706 kVA.
3. Next standard R10 size = 800 kVA (dry-type SCB13, 10/0.4 kV, copper).
4. Reference price from the live price table, copper-linked to the LME price.
FAQ
How do I calculate the transformer kVA I need?
Transformer kVA = total load kW x demand factor / Power Factor. For 300 kW of load at 0.85 pf with 0.8 demand factor: 300 x 0.8 / 0.85 = 282 kVA, so select 315 kVA. Leave 15-20% headroom for growth and select the next standard rating per IEC 60076. The calculator does this and returns the model and price.
What is the difference between oil-immersed and dry-type transformers?
Oil-immersed units are cheaper (10-30% less), quieter under load and better cooled, suited to outdoor and larger ratings; dry-type cast-resin units are fire-safe, suited to indoor, hospitals and high-rises, but cost more and run hotter. Dry-type is mandatory for many indoor installations per fire codes. The calculator prices both types.
What does S13, SCB13 and S20 mean in a transformer model?
S-series is oil-immersed (S11/S13/S20/S22), SCB is dry-type cast-resin. The number is the efficiency/loss grade — higher numbers mean lower No-Load Loss. S13 cuts no-load loss ~20-30% versus S11; S20/S22 are the current GB 20052 energy-efficiency grades. The calculator lets you pick the grade and shows the price delta.
What vector group do I need — Dyn11 or Yyn0?
Dyn11 (delta primary, wye secondary, 30 deg shift) is standard for distribution because it blocks third-harmonic circulation and supports unbalanced load better. Yyn0 is used for small single-phase-heavy loads but passes zero-sequence harmonics. For most modern LV networks choose Dyn11; the calculator defaults to it.
How much does a 500 kVA transformer cost?
A 500 kVA oil-immersed S13 transformer runs roughly $12,000-18,000 FOB, and a dry-type SCB13 roughly $16,000-24,000, varying with copper price (base ~14,200 USD/t), winding material and tap-changer. The calculator returns a live reference FOB price from the QDTB pricing matrix, updated with copper.
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