Transformer Sizing Calculator Formula
Understand the math behind the transformer sizing calculator. Each variable explained with a worked example.
Formulas Used
Maximum Demand
demand_load = demand_kwRequired kVA (with growth)
required_kva = demand_kw / power_factor * (1 + growth_margin / 100)Variables
| Variable | Description | Default |
|---|---|---|
total_load_kw | Total Connected Load(kW) | 200 |
demand_factor | Demand Factor(%) | 80 |
power_factor | Average Power Factor | 0.85 |
growth_margin | Growth Margin(%) | 20 |
demand_kw | Derived value= total_load_kw * demand_factor / 100 | calculated |
How It Works
Transformer Sizing
The transformer must handle the maximum demand load with adequate margin.
Method
Maximum demand = Total connected load x Demand factor
Required kVA = Max demand (kW) / Power factor x (1 + Growth margin)
The demand factor accounts for the fact that not all loads operate simultaneously. The growth margin reserves capacity for future expansion (typically 15-25%).
Worked Example
200 kW total connected load, 80% demand factor, 0.85 PF, 20% growth.
total_load_kw = 200demand_factor = 80power_factor = 0.85growth_margin = 20
- 01Maximum demand = 200 x 0.80 = 160 kW
- 02Required kVA = 160 / 0.85 x 1.20 = 225.9 kVA
- 03Select the next standard size: 250 kVA transformer.
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Open Transformer Sizing Calculator