How do you select transformers?

  1. Determine primary voltage and frequency.
  2. Determine secondary voltage required.
  3. Determine the capacity required in volt-amperes.
    • This is done by multiplying the load current (amperes) by the load voltage (volts) for single phase.
    • For example: if the load is 40 amperes, such as a motor, and the secondary voltage is 240 volts, then 240 x 40 equals 9600 VA. A 10 KVA (10,000 volt-amperes) transformer is required.
    • ALWAYS SELECT  THE TRANSFORMER LARGER THAN THE ACTUAL LOAD. This is done for safety purposes and allows for expansion, in case more load is added at a later date. For 3 phase KVA, multiply rated volts x load amps x 1.73 (square root of 3) then divide by 1000.
  4. Determine whether taps are required. Taps are usually specified on larger transformers.
  5. Use the selection charts found on the website.

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