Current Ratio

Voltage Ratio - h1011v4_50

Three-Phase Transformer Connections

Electrical Science Volume 4 of 4
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Transformers TRANSFORMER THEORY Current Ratio The current in the windings of a transformer is inversely proportional to the voltage in the windings. This relationship is expressed in Equation (13-5). (13-5) V_P V_S I_S I_P where I_P = primary coil current I_S = secondary coil current Since the voltage ratio is equal to the turns ratio, we can express the current ratio in terms of the turns ratio, as in Equation (13-6). (13-6) N_P N_S I_S I_P Example 1: When operated at 120 V in the primary of an iron core transformer, the current in the primary is 4 amps. Find the current in the secondary if the voltage is stepped up to 500 V. Solution: V_P V_S I_S I_P Next, we solve for I_S. I_S V_P V_S I_P I_S 120 500 4 amps I_S 0.96 amps Example 2: A transformer with 480 turns on the primary and 60 turns on the secondary draws 0.6 amps from a 120 V line. Find I_S. Solution: N_P N_S I_S I_P Rev. 0 Page 7 ES-13

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