Electrical Engineering ⇒ Topic : Relation between line current and phase current
Relation between line current and phase current. In Y-connected supply system, each line conductor is connected in series to a separate phase as shown in Fig.(a). Therefore, current in a line conductor is the same as that in the phase to which the line conductor is connected.
Line current, IL = Iph .........in magnitude
For a balanced load, all the phase currents are equal in magnitude but displaced 120° from one another. Fig. (b) shows the phasor diagram for a balanced lagging load ; the phase angle being (Φ).Note that (Φ) is the angle between phase voltage and the corresponding phase current. However, the angle between the line current and the corresponding line voltage (say IR and VRY) is 30° + Φ. If the balanced load has a leading power factor of cos Φ, then the angle between the line current and the corresponding line voltage will be 30°- Φ.
Hence in a balanced 3-phase Y-connected supply system
(1) Line current, IL= Iph
(2) All the line currents are equal in magnitude (i.e.= Iph) but displaced 120° from one another
(3) The angle between the line currents and the corresponding line voltages is 300 + Φ ; + if pf is lagging and - if it is leading.
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