chapter  4
52 Pages

Calculating Currents in Three-Phase Circuits

WithJoseph E. Fleckenstein

Calculations applicable to balanced three-phase circuits are more easily performed than those applicable to unbalanced three-phase circuits. This chapter shows how currents in a balanced delta circuit with resistive loads are determined. Resistive loads in single-phase circuits are necessarily in phase with the applied voltage. If all three phases of a three-phase circuit have resistive loads of equal magnitude, the phase current would likewise be in phase with the respective phase voltage. As may often happen, a three-phase circuit will serve a mixture of delta and wye loads that could be both balanced and unbalanced loads. A common problem is to calculate line currents in the conductors of a three-phase circuit that serves a variety of loads. In many instances, calculations are not required to determine line currents for some loads as the line currents may already be provided. For example, motor nameplates will state the motor's full load current.