21. Buses for load flow studies are classified as (i) the load bus (ii) the generator bus (iii) the slace bus The correct combination of the pair of quantities specified having their usual meaning for different buses is
    Load Bus Generator Slace bus

1. 1. P, |V| P, Q P, δ

   
   
   

   2. P, Q P, |V| |V| ,δ

   
   
   

   3. |V|, Q P, δ P, Q

   
   
   

   4. P, δ Q, |V Q, δ

   
   
   

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1. View Hint View Answer Discuss in Forum

   Load bus = P, Q
   Generator bus = P, |V|
   Slack bus = |V|, δ

   Correct Option: B

   Load bus = P, Q
   Generator bus = P, |V|
   Slack bus = |V|, δ

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22. A power system network consists of three elements 0 - 1, 1 - 2 and 2 - 0 of per unit impedance 0.2, 0.4 respectively. Its bus impedance matrix is given by

1. 1. 		1		2
      1		7.5		-2.5
      2		-2.5		5.0

   
   
   

   2. 		1		2
      1		0.16		0.08
      2		0.08		0.24

   
   
   

   3. 		1		2
      1		0.16		-0.08
      2		-0.08		0.24

   
   
   

   4. 		1		2
      1		0.6		0.4
      2		0.4		0.8

   
   
   

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1. View Hint View Answer Discuss in Forum

   The Bus impedance matrix Z_BUS can be formed by using circuit theory knowledge
   

   Correct Option: B

   The Bus impedance matrix Z_BUS can be formed by using circuit theory knowledge
   

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23. In a synchronous machine, in case the axis of field flux is in line with the armature flux, the machine is working

1. 1. as synchronous moter

   
   
   

   2. as synchronous generator

   
   
   

   3. as floating machine

   
   
   

   4. the machine will not work

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: C

   NA

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24. It x is the system reactance and r is its resistance, the power transferred is maximum when

1. 1. x = r

   
   
   

   2. x = √2r

   
   
   

   3. x = √3r

   
   
   

   4. x = 2r

   
   
   

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1. View Hint View Answer Discuss in Forum

   
   

   I =	V1∠δ - V2∠0
   	Z∠θ

   
   

   =	V1	∠(δ - ∠0) -	V2	∠- θ
   	Z		Z

   
   Power received, P₂ = Re [V₂I*]
   

   = Re		V2		V1	∠(θ - δ) -	V2	∠θ
   				Z		Z

   
   

   =	V1V2	cos(θ - δ) -	V²2	cos θ
   	Z		Z

   
   Let θ = 90° – α, then
   

   =	V1V2	cos(90° - α - δ) -	V²2	cos(90° - α)
   	Z		Z

   
   

   =	V1V2	sin(α + δ) -	V²2	sin α
   	Z		Z

   
   

   P2 max =	V1V2	-	V²2	sin α[α + δ = 90°]
   	Z		Z

   
   

   As, sin α =	r	, then
   	Z

   
   

   P2 max =	V1V2	-	V²2	.	r
   	√r² + x²		√r² + x²		√r² + x²

   
   For P_{2 max} to be maximum,
   

   dP2 max	= 0
   dx

   
   

   or V²2		x1	-	2xr		= 0
   		(r² + x²)2/3		(r² + x²)²

   
   Here V₁ = V₂
   ∴ r² + x² = 4r²
   or x = √3r

   Correct Option: C

   
   

   I =	V1∠δ - V2∠0
   	Z∠θ

   
   

   =	V1	∠(δ - ∠0) -	V2	∠- θ
   	Z		Z

   
   Power received, P₂ = Re [V₂I*]
   

   = Re		V2		V1	∠(θ - δ) -	V2	∠θ
   				Z		Z

   
   

   =	V1V2	cos(θ - δ) -	V²2	cos θ
   	Z		Z

   
   Let θ = 90° – α, then
   

   =	V1V2	cos(90° - α - δ) -	V²2	cos(90° - α)
   	Z		Z

   
   

   =	V1V2	sin(α + δ) -	V²2	sin α
   	Z		Z

   
   

   P2 max =	V1V2	-	V²2	sin α[α + δ = 90°]
   	Z		Z

   
   

   As, sin α =	r	, then
   	Z

   
   

   P2 max =	V1V2	-	V²2	.	r
   	√r² + x²		√r² + x²		√r² + x²

   
   For P_{2 max} to be maximum,
   

   dP2 max	= 0
   dx

   
   

   or V²2		x1	-	2xr		= 0
   		(r² + x²)2/3		(r² + x²)²

   
   Here V₁ = V₂
   ∴ r² + x² = 4r²
   or x = √3r

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25. The voltage of generator and an infinite bus are given as 0.92 ∠10° and 1.0∠0° respectively. The generator acts as a

1. 1. shunt coil

   
   
   

   2. shunt capacitor

   
   
   

   3. the data is insufficient to judge

   
   
   

   4. none of these

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: A

   NA

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