Understanding Transformer Sizing

Select the type of transformer (Single-Phase or Three-Phase) and input the load current and voltage to calculate the minimum kVA size required.

Single-Phase Formula:

Formula: kVA = (I × V) / 1000

Example: If the load is 100 A at 240 V:

kVA = (100 × 240) / 1000 = 24 kVA

Three-Phase Formula:

Formula: kVA = (√3 × I × V) / 1000

Example: For a load of 100 A at 400 V three-phase:

kVA = (√3 × 100 × 400) / 1000 = 69.3 kVA

Why Transformer Sizing Matters:

Selecting the right transformer size is crucial to ensure efficiency and avoid overloading or underutilization. An undersized transformer can overheat and reduce the lifespan, while an oversized transformer may increase costs unnecessarily.

Load Factor Consideration:

It’s common practice to apply a safety factor (e.g., 80-85%) to the calculated kVA to account for peak load conditions and ensure reliable performance.

Example: If you calculate 24 kVA based on maximum demand and apply a 0.85 load factor:

kVA = 24 kVA / 0.85 ≈ 28.2 kVA

Three-Phase vs. Single-Phase:

Three-phase transformers are typically used for larger loads (greater than 10 kVA) due to their higher efficiency and lower cost compared to single-phase for similar loads.