Network Theory Questions and Answers – Star to Delta and Delta to Star Transformation

This set of Network Theory Multiple Choice Questions & Answers (MCQs) focuses on “Star to Delta and Delta to Star Transformation”.

1. If a resistor Z_R is connected between R and N, Z_BR between R and B, Z_RY between R and Y and Z_BY between B and Y form a delta connection, then after transformation to star, the impedance at R is?
a) (Z_BRZ_BY)/(Z_RY+Z_BY+Z_BR)
b) (Z_RYZ_BR)/(Z_RY+Z_BY+Z_BR)
c) (Z_RYZ_BY)/(Z_RY+Z_BY+Z_BR)
d) (Z_RY)/(Z_RY+Z_BY+Z_BR)
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2. If a resistor Z_R is connected between R and N, Z_BR between R and B, Z_RY between R and Y and Z_BY between B and Y form a delta connection, then after transformation to star, the impedance at Y is?
a) (Z_RY)/(Z_RY+Z_BY+Z_BR)
b) (Z_BY)/(Z_RY+Z_BY+Z_BR)
c) (Z_RYZ_BY)/(Z_RY+Z_BY+Z_BR)
d) (Z_RYZ_BR)/(Z_RY+Z_BY+Z_BR)
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3. If a resistor Z_R is connected between R and N, Z_BR between R and B, Z_RY between R and Y and Z_BY between B and Y form a delta connection, then after transformation to star, the impedance at B is?
a) (Z_BRZ_BY)/(Z_RY+Z_BY+Z_BR)
b) (Z_RYZ_BY)/(Z_RY+Z_BY+Z_BR)
c) (Z_BY)/(Z_RY+Z_BY+Z_BR)
d) (Z_BR)/(Z_RY+Z_BY+Z_BR)
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4. If the resistors of star connected system are Z_R, Z_Y, Z_B then the impedance Z_RY in delta connected system will be?
a) (Z_RZ_Y + Z_YZ_B + Z_BZ_R)/Z_B
b) (Z_RZ_Y + Z_YZ_B + Z_BZ_R)/Z_Y
c) (Z_RZ_Y + Z_YZ_B + Z_BZ_R)/Z_R
d) (Z_RZ_Y + Z_YZ_B + Z_BZ_R)/(Z_R+Z_Y)
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5. If the resistors of star connected system are Z_R, Z_Y, Z_B then the impedance Z_BY in delta connected system will be?
a) (Z_RZ_Y + Z_YZ_B + Z_BZ_R)/(Z_B+Z_Y)
b) (Z_RZ_Y + Z_YZ_B + Z_BZ_R)/Z_B
c) (Z_RZ_Y + Z_YZ_B + Z_BZ_R)/Z_Y
d) (Z_RZ_Y + Z_YZ_B + Z_BZ_R)/Z_R
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6. If the resistors of star connected system are Z_R, Z_Y, Z_B then the impedance Z_BR in delta connected system will be?
a) (Z_RZ_Y + Z_YZ_B + Z_BZ_R)/Z_Y
b) (Z_RZ_Y + Z_YZ_B + Z_BZ_R)/_R
c) (Z_RZ_Y + Z_YZ_B + Z_BZ_R)/Z_B
d) (Z_RZ_Y + Z_YZ_B + Z_BZ_R)/(Z_B+Z_R)
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7. A symmetrical three-phase, three-wire 440V supply is connected to star-connected load. The impedances in each branch are Z_R = (2+j3) Ω, Z_Y = (1-j2) Ω, Z_B = (3+j4) Ω. Find Z_RY.
a) (5.22-j0.82) Ω
b) (-3.02+j8) Ω
c) (3.8-j0.38) Ω
d) (-5.22+j0.82) Ω
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8. A symmetrical three-phase, three-wire 440V supply is connected to star-connected load. The impedances in each branch are Z_R = (2+j3) Ω, Z_Y = (1-j2) Ω, Z_B = (3+j4) Ω. Find Z_BY.
a) (-5.22+j0.82) Ω
b) (5.22-j0.82) Ω
c) (3.8-j0.38) Ω
d) (-3.02+j8) Ω
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9. A symmetrical three-phase, three-wire 440V supply is connected to star-connected load. The impedances in each branch are Z_R = (2+j3) Ω, Z_Y = (1-j2) Ω, Z_B = (3+j4) Ω. Find Z_BR.
a) (5.22-j0.82) Ω
b) (-3.02+j8) Ω
c) (-5.22+j0.82) Ω
d) (3.8-j0.38) Ω
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10. If a star connected system has equal impedances Z₁, then after converting into delta connected system having equal impedances Z₂, then?
a) Z₂ = Z₁
b) Z₂ = 2Z₁
c) Z₂ = 3Z₁
d) Z₂ = 4Z₁
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Sanfoundry Global Education & Learning Series – Network Theory.

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