Overview of Voltage & current - magnitude & phase angle

Always set Voltage (red phase to neutral) as reference phasor.ie V_rn= |V_rn|/_0°

The next Voltage drawn in clockwise rotation (yellow phase to neutral, Vyn) is displaced by 120° with respect to reference phasor. So V_yn= |V_yn|/_120°

The next Voltage again drawn in clockwise rotation after Vyn is (blue phase to neutral, Vbn) displaced by 240° with respect to reference phasor. So V_bn= |V_bn|/_240°

Let's start calculating load currents.

Assume a balanced 3-phase load of 900kW is delivered from 415V_ac 3-phase source at power factor 0.8 lagging.

Load per phase = 900kW/3 =300kW

3-phase current magnitude = 900kW / (√3 x 0.415 kV x 0.8) = 1565 A

Load current always lags it's phase Voltage by an angle of cos ^-1pf where pf is power factor.

Angle = cos ^-1pf = cos ^-1 0.8 = 36.9 °

Phase current I_R= 1565 /_-36.9° A. The -ve sign shows that the current I_R lags phase Voltage |V_rn|/_0° by 36.9 °

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