Transformer Basics

Specifying the Correct Transformer

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  • 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, each line 120 degrees out of phase with the other two.
  • kVA is kilovolt ampere or thousand volt amperes. This is how transformers are rated.

NOTE: If motors are started more than once per hour, increase minimum transformer kVA by 20%. To determine the size of the transformer you need, use the chart at the right.

Transformer Selection Formula

  1. Determine the proper kVA based on the required load voltage, line voltage and load current.
    For an example: Load voltage = 480 volts, Load current = 80 Amps and Line voltage = 208 volts.

  2. Choose the appropriate style of transformer for the application. For example, if you need a transformer for a three phase industrial application you can choose the Three Phase Ventilated style.
  3. Find the appropriate section in the Product list.
  4. Select the options such as mounting brackets to assist your installation.