Transformer Sizing & Derating Reference Card
Free download · 85 × 54mm (credit card size)
Transformer sizing involves more than just adding up the loads. This pocket card covers the essential formulas and derating rules. The front presents the kVA sizing formula S = P_total / (PF × η), demand factor application S_design = Σ(kW × DF) / PF_avg, temperature derating at -1%/°C above rated ambient (typically 40°C), and altitude derating at -3% per 1000m above 1000m ASL. The reverse covers K-factor transformers for harmonic loads: K = Σ(Ih² × h²) / ΣIh² with typical values K-1 (linear), K-4 (minor harmonics), K-13 (VFDs/computers), plus an impedance %Zk effect on fault level quick lookup table. QR links to ECalPro Transformer Calculator.
What's Included
How to Print
- ●Recommended paper: 250–300gsm cardstock
- ●Print double-sided, flip on short edge
- ●Cut along crop marks with a paper trimmer
- ●Laminate with 80–125 micron pouches for durability
- ●Fits in wallet, toolbox, or pocket
Try the Interactive Calculator
Need precise calculations beyond quick reference? Try our free online calculator with full clause references and professional report output.
Open CalculatorRelated Downloads
Short Circuit
Free printable short-circuit calculation reference card. IEC 60909 formulas, voltage factor c table, impedance correction factors, peak current calculations. Credit-card size.
PF Correction
Free printable power factor correction calculation reference card. Reactive power formula, capacitor sizing, kVAr/kW correction factors table, harmonic derating rules.
Frequently Asked Questions
What paper should I print this on?
Print on 250–300gsm cardstock for durability. Use duplex (double-sided) printing and cut along the crop marks. Laminate with 80–125 micron pouches for long-term site use.
Can I distribute this to my team?
Yes. All ECalPro reference cards are free to download, print, and distribute within your organization. Keep the ECalPro branding and QR code intact.
What standard does this reference?
This card references IEC 60076 (power transformer standards) and IEEE C57.12 (transformer general requirements). K-factor ratings per UL 1561.
How often is this updated?
Updated when transformer standards are revised. Sizing formulas are fundamental and change rarely.