Transformer Basics

How to Size a Transformer

• Transformer size is determined by the kVA of the load.
• Load voltage, or secondary voltage, is the voltage needed to operate the load.
• Line voltage, or primary voltage, is the voltage from the source.
• Single-Phase has two lines of AC power.
• Three-Phase has three lines of AC power, with each line 120 degrees out of phase with the other two.
• kVA is kilovolt ampere or thousand volt ampere. This is how transformers are rated.

To determine the size of the transformer you need, determine the following requirements for your transformer:

1. Load Voltage
2. Load Current/Amps
3. Line Voltage

Next, determine if your application is single-phase or three-phase, and use this corresponding formula:

The kVA of the transformer should be equal to or greater than the kVA of the load to handle present requirements and to account for future expansion.

As a service to you, we offer a transformer specifier to help you find your transformers quickly and easily.