In a three-phase balanced star connected system, which of the following will hold true? [Ø is the angle between phase volage and phase current.]

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  1. The angle between line currents and the corresponding line voltages is 30° + ∅ for leading.
  2. The angle between line currents and the corresponding line voltages is 30° - ∅ for lagging.
  3. The angle between line currents and the corresponding line voltages is 30° + ∅ for lagging.
  4. The angle between line currents and the corresponding line voltages are in phase.

Answer (Detailed Solution Below)

Option 3 : The angle between line currents and the corresponding line voltages is 30° + ∅ for lagging.
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Detailed Solution

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Concept

In a three-phase balanced star-connected system,

Line current = Phase Current

IL = Ip

Phase voltage = Line voltage / √3

\(V_p={V_L\over √{3}}\)

Explanation

Consider a three-phase star-connected system as RYB.

qImage6595605bad01f2b5ebe84d8e

The phasor diagram for a three-phase balanced star-connected system is shown below:

qImage6595605bad01f2b5ebe84d93

The phase voltage is:

VR = V∠0° 

VY = V∠-120°

VB = V∠120°

For lagging load in star connection, (phase current = line current) lags phase voltage by ϕ° 

The line voltage between R and Y is:

VRY = VR - VY

VRY = V∠0° - V∠-120°

VRY = √3V∠30° 

The line voltage leads phase voltage by 30° and phase voltage leads line current by ϕ°.

Hence, line voltage leads line current by (30+ϕ°).

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