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Transformer Examples

These worked examples apply the turns ratio formula and the kVA-based current relationships used to size and check transformers.

  1. Step 1

    A transformer has 480 V on the primary and 120 V on the secondary. Find the turns ratio.

    a = Vp ÷ Vs = 480 ÷ 120 = 4 : 1

  2. Step 2

    A transformer is rated at 480 V, 20 A on the primary. Find its kVA rating.

    kVA = (V × I) ÷ 1000 = (480 × 20) ÷ 1000 = 9.6 kVA

  3. Step 3

    A 9.6 kVA transformer has a 120 V secondary. Find the secondary current.

    Is = (kVA × 1000) ÷ Vs = (9.6 × 1000) ÷ 120 = 80 A

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