Delta Star Transformation MCQ [Free PDF] – Objective Question Answer for Delta Star Transformation Quiz

11. If a resistor ZR is connected between R and N, ZBR between R and B, ZRY between R and Y, and ZBY between B and Y form a delta connection, then after transformation to star, the impedance at R is?

A. (ZBRZBY)/(ZRY + ZBY + ZBR)
B. (ZRYZBR)/(ZRY + ZBY + ZBR)
C. (ZRYZBY)/(ZRY + ZBY + ZBR)
D. (ZRY)/(ZRY + ZBY + ZBR)

Answer: B

After transformation to star, the impedance at R is

(ZRYZBR)/(ZRY + ZBY + ZBR).

 

12. If a resistor ZR is connected between R and N, ZBR between R and B, ZRY between R and Y, and ZBY between B and Y form a delta connection, then after transformation to star, the impedance at Y is?

A. (ZRY)/(ZRY + ZBY + ZBR)
B. (ZBY)/(ZRY + ZBY + ZBR)
C. (ZRYZBY)/(ZRY + ZBY + ZBR)
D. (ZRYZBR)/(ZRY + ZBY + ZBR)

Answer: C

After transformation to star, the impedance at Y is

(ZRYZBY)/(ZRY + ZBY + ZBR).

 

13. If a resistor ZR is connected between R and N, ZBR between R and B, ZRY between R and Y, and ZBY between B and Y form a delta connection, then after transformation to star, the impedance at B is?

A. (ZBRZBY)/(ZRY + ZBY + ZBR)
B. (ZRYZBY)/(ZRY + ZBY + ZBR)
C. (ZBY)/(ZRY + ZBY + ZBR)
D. (ZBR)/(ZRY + ZBY + ZBR)

Answer: A

After transformation to star, the impedance at Y is

(ZBRZBY)/(ZRY + ZBY + ZBR).

 

14. If the resistors of star connected system are ZR, ZY, ZB then the impedance ZRY in delta connected system will be?

A. (ZRZY  + ZYZB  + ZBZR)/ZB
B. (ZRZY  + ZYZB  + ZBZR)/ZY
C. (ZRZY  + ZYZB  + ZBZR)/ZR
D. (ZRZY  + ZYZB  + ZBZR)/(ZR + ZY)

Answer: A

After transformation to delta, the impedance ZRY in delta connected system will be

(ZRZY  + ZYZB  + ZBZR)/ZB.

 

15. If the resistors of star connected system are ZR, ZY, ZB then the impedance ZBY in delta connected system will be?

A. (ZRZY  + ZYZB  + ZBZR)/(ZB + ZY)
B. (ZRZY  + ZYZB  + ZBZR)/ZB
C. (ZRZY  + ZYZB  + ZBZR)/ZY
D. (ZRZY  + ZYZB  + ZBZR)/ZR

Answer: D

After transformation to delta, the impedance ZBY in delta connected system will be

(ZRZY  + ZYZB  + ZBZR)/ZR.

 

16. If the resistors of star connected system are ZR, ZY, ZB then the impedance ZBR in delta connected system will be?

A. (ZRZY  + ZYZB  + ZBZR)/ZY
B. (ZRZY  + ZYZB  + ZBZR)/R
C. (ZRZY  + ZYZB  + ZBZR)/ZB
D. (ZRZY  + ZYZB  + ZBZR)/(ZB + ZR)

Answer: A

After transformation to delta, the impedance ZBR in delta connected system will be

(ZRZY  + ZYZB  + ZBZR)/ZY.

 

17. Asymmetrical three-phase, three-wire 440V supply is connected to star-connected load. The impedances in each branch are ZR  = (2 + j3) Ω, ZY  = (1 − j2) Ω, ZB  = (3 + j4) Ω. Find ZRY.

A. (5.22 − j0.82) Ω
B. ( − 3.02 + j8) Ω
C. (3.8 − j0.38) Ω
D. ( − 5.22 + j0.82) Ω

Answer: C

ZRY  = (ZRZY  + ZYZB  + ZBZR)/ZB

= (3.8 − j0.38) Ω.

 

18. A symmetrical three-phase, three-wire 440V supply is connected to star − connected load. The impedances in each branch are ZR  = (2 + j3) Ω, ZY  = (1 − j2) Ω, ZB  = (3 + j4) Ω. Find ZBY.

A. ( − 5.22 + j0.82) Ω
B. (5.22 − j0.82) Ω
C. (3.8 − j0.38) Ω
D. ( − 3.02 + j8) Ω

Answer: B

ZBY  = (ZRZY  + ZYZB  + ZBZR)/ZR

= (5.22 − j0.82)Ω.

 

19. A symmetrical three-phase, three-wire 440V supply is connected to star − connected load. The impedances in each branch are ZR  = (2 + j3) Ω, ZY  = (1 − j2) Ω, ZB  = (3 + j4) Ω. Find ZBR.

A. (5.22 − j0.82) Ω
B. ( − 3.02 + j8) Ω
C. ( − 5.22 + j0.82) Ω
D. (3.8 − j0.38) Ω

Answer: B

ZBR  = (ZRZY  + ZYZB  + ZBZR)/ZY

= ( − 3.02 + j8) Ω.

 

20. 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

Answer: C

If a star-connected system has equal impedances Z1, then after converting into delta connected system having equal impedances Z2, Z2  = 3Z1.

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