The phase impedance of a balanced star connected load is ZY = 40 + j30 Ω. What will be the phase impedance of the equivalent Δ-connected load?

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MPPGCL JE Electrical 19 March 2019 Shift 2 Official Paper
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  1. ZΔ = 40 + j30 Ω
  2. ZΔ = 120 + j90 Ω
  3. ZΔ = (40+j30) × √3 Ω
  4. ZΔ = (120 + j90)/3 Ω

Answer (Detailed Solution Below)

Option 2 : ZΔ = 120 + j90 Ω
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Detailed Solution

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Star to Delta Conversion

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The delta equivalent of a star connected resistor is:

\(R_A={R_1R_2+R_2R_3+R_1R_3\over R_3}\)

\(R_B={R_1R_2+R_2R_3+R_1R_3\over R_2}\)

\(R_C={R_1R_2+R_2R_3+R_1R_3\over R_1}\)

If all resistances connected in the star are equal to  'R', then the delta equivalent resistance is:

\(R_A=R_B=R_C={3R}\)

Calculation

Given, ZY = 40 + j30 Ω

ZΔ = 3 × (40 + j30)

ZΔ = 120 + j90 Ω

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