Understanding Transformer Sizing

Transformer sizing ensures efficient energy transfer without overloading or underutilization.

Formulas

Single-Phase:

\[ \text{kVA} = \frac{I \times V}{1000} \]

Three-Phase:

\[ \text{kVA} = \frac{\sqrt{3} \times I \times V}{1000} \]

Why Transformer Sizing Matters

Choosing the correct transformer size is crucial for efficient operation. An undersized transformer can overheat, reducing its lifespan, while an oversized transformer can increase costs unnecessarily.

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 transformers for similar loads.

Example Calculations

Example 1: Single-Phase Transformer

For a load of 100 A at 240 V:

\[ \text{kVA} = \frac{100 \times 240}{1000} = 24 \, \text{kVA} \]

Example 2: Three-Phase Transformer

For a load of 100 A at 400 V:

\[ \text{kVA} = \frac{\sqrt{3} \times 100 \times 400}{1000} = 69.3 \, \text{kVA} \]

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: For a calculated size of 24 kVA with a safety factor of 0.85:

\[ \text{kVA} = \frac{24}{0.85} \approx 28.2 \, \text{kVA} \]