Formula & Calculator
Transformer kVA Rating
Calculates a transformer's apparent power rating from its rated voltage and current.
Variables
| Symbol | Quantity | Unit |
|---|---|---|
| kVA | Transformer apparent power rating | kVA |
| V | RMS voltage (primary or secondary winding) | V |
| I | RMS current (corresponding winding) | A |
What it means
The kVA rating of a single‑phase transformer is the product of the primary (or secondary) voltage and current, divided by 1000: kVA = (V × I) / 1000. For a three‑phase transformer, it is kVA = (√3 × V_L × I_L) / 1000. This rating represents the apparent power the transformer can handle. It is used to size transformers for a given load. Example: A single‑phase transformer with primary voltage 440V and primary current 50A has a rating of 440 × 50 / 1000 = 22 kVA. This means it can deliver 22 kVA to the load. The actual kW output depends on the load’s power factor.
Worked example
Transformer kVA Rating – Practical Example
Real‑World| Parameter | Value |
|---|---|
| V | 240 V |
| I | 20.8 A |
| Formula | kVA = (V × I) / 1000 |
Common mistakes
Watch for unit mismatches (W vs kW, single- vs three-phase) and remember to include power factor or efficiency where the formula requires it.Applications
Transformer kVA rating: kVA = (V × I)/1000 for single‑phase, or √3·V_L·I_L/1000 for three‑phase, gives the apparent power capacity. This is the primary rating for transformers. Engineers use it to select transformers for loads, to design substations, and to ensure capacity meets demand. Understanding kVA rating is essential for power system design.
- Transformer selection and specification
- Substation and distribution system design
- Load capacity planning
- Transformer protection and coordination
- Educational understanding of transformer ratings