In a balanced three-phase star connected system, if the line current is 30 A, then its phase current is:

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ALP CBT 2 Electrician Official Paper (Held On: 23 Jan 2019 Shift 3)
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  1. 15 A
  2. 17.3 A
  3. 30 A
  4. 51.9 A

Answer (Detailed Solution Below)

Option 3 : 30 A
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Detailed Solution

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Concept:

In a three-phase load, three different impedances are connected together in a star or delta fashion.

The delta in a three-phase system is formed by connecting one end of the winding to the starting end of other winding and the connections are continued to form a closed loop.

The star in the three-phase system is formed by connecting one end of all three impedances are connected together.

Important Points:

In a star-connected three-phase system,

  • VL = √3 × Vph
  • IL = Iph
  • \({I_{ph}} = \frac{{{V_L}}}{{\surd 3Z}}\)

 

In a delta connected three-phase system,

  • VL = Vph
  • IL = √3 × Iph
  • \({I_{ph}} = \;\frac{{{V_L}}}{Z}\)

Where,

VL is line voltage

Vph is phase voltage

IL is line current

Iph is the phase current

Application:

Given-

IL = 30 A
As given 3-ϕ system is star connected system, then phase current is

Iph IL = 30 A

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