Calculate kVA Size for Single & Three Phase Transformers
Easily calculate transformer kVA size for single-phase and three-phase loads using kW, power factor, voltage, and current with formulas and tables.
three phase kVA conversion
To determine the size of transformer kVA, take the real power (kW)/power factor, single-phase, or the formula is √3 × Voltage × Current /1000, three-phase. Increase by 10-25 percent and then always round off to the nearest standard kVA rating.
Formula & Table Summary:
- Single-phase: kVA = (kW) / (Power Factor)
- Three-phase: kVA = (kW) / (Power Factor) OR kVA = (√3 × V_L × I_L) / 1000
- From amps (3φ): kVA = (√3 × V_L × I) / 1000
- From amps (1φ): kVA = (V × I) / 1000
Converter: Input → Output
| Input | Formula | Output |
|---|---|---|
| kW & PF (1φ) | kVA = kW / PF | kVA |
| kW & PF (3φ) | kVA = kW / PF | kVA |
| V, I (3φ) | kVA = √3 × V_L × I / 1000 | kVA |
| V, I (1φ) | kVA = V × I / 1000 | kVA |
calculate transformer load
The appropriate transformer kVA size will improve the efficient operation of electrical systems and guarantee safety. Transformer size is determined by load power (kW), power factor (PF), and supply voltage. To obtain kVA of a single-phase transformer, the load kW is divided by the PF of the load. In three-phase transformers, the formula is calculated by dividing by PF or the formula using 1/pf, line voltage (V), line current (I), and the square root of three. Proper computing of transformer size helps avoid overloading, minimizes losses, and enhances the reliability of a system. A margin of 1025 percent is usually added by the engineers to accommodate future load increase and efficiency. Typical kVA ratings are selected by increasing the calculated value to the nearest existing size. This manual will give a stepwise formula overview, an input-output converter, and sample tables as a reference. It also comprises the FAQs, terms to be used in the search engine optimization, and a text description of the image. This kVA calculation method is applicable in residential systems, commercial systems, or even industrial systems, and it will provide a correct selection of the transformer.
residential transformer kVA
| Single-phase motor | kW = 5, PF = 0.9 | kVA = 5 / 0.9 = 5.56 | 6 kVA |
| Three-phase load | kW = 50, PF = 0.85 | kVA = 50 / 0.85 = 58.82 | 60 kVA |
| 3φ from amps | V_L = 400 V, I = 72 A | kVA = 1.732×400×72/1000 = 49.92 | 50 kVA |
Frequently Asked Questions - Calculate kVA Size for Single & Three Phase Transformers:
How do I calculate kVA for a single-phase transformer?
Divide kW by power factor: kVA = kW / PF.
How to calculate kVA for a three-phase load?
Use kVA = kW / PF or kVA = √3 × V × I ÷ 1000.
What margin should I add?
Add 10–25% extra capacity for safety and future growth.
Can I calculate kVA from current?
Yes, use kVA = V × I ÷ 1000 (1φ) or √3 × V × I ÷ 1000 (3φ).
Does power factor affect kVA?
Yes, lower PF increases required kVA for same kW.
Should I round up transformer kVA?
Always round up to the next standard kVA rating.
Do transformer losses affect kVA size?
Yes, consider efficiency and select slightly larger capacity.
How does voltage affect kVA calculation?
Higher voltage reduces current for same kVA rating.
What about motor loads?
Allow extra kVA for starting currents and motor inrush.
What are common transformer kVA sizes?
Typical ratings: 5, 10, 15, 25, 50, 75, 100 kVA, etc.
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