201. Consider a HVDC link whcih uses thyristor based line-cooutated converters as shown in the figure. For a power flow of 750 MW from System 1 to System2, the voltages at the two ends, and the current, are given by: V₁ = 500kV, V₂ = 485kV and I = 1.5kA. If the direction of power flow is to be reversed (that is, from System 2 to System1) without changing the electrical connections, then which one of the following combinations id feasible ?
     
     If power is to be reversed

1. 1. V₁ = – 500kV, V₂ = – 485kV and I = 1.5kA

   
   
   

   2. V₁ = – 485kV, V₂ = – 500kV and I = 1.5kA

   
   
   

   3. V₁ = 500kV, V₂ = 485kV and O = – 1.5kA

   
   
   

   4. V₁ = – 500kV, V₂ = – 485kV and I = – .5kA

   
   
   

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1. View Hint View Answer Discuss in Forum

   
   

   I =	V1 - V2
   	R

   
   For power to be reversed
   

   I =	V2 - V1	(+V)
   	R

   
   V₁ = – 485kV, V₁ = – 500kV
   I = 1.5kA

   Correct Option: B

   
   

   I =	V1 - V2
   	R

   
   For power to be reversed
   

   I =	V2 - V1	(+V)
   	R

   
   V₁ = – 485kV, V₁ = – 500kV
   I = 1.5kA

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202. The primary mmf is least affect ed by the secondary terminal conditions in a

1. 1. power transformer

   
   
   

   2. potential transformer

   
   
   

   3. current transformer

   
   
   

   4. distribution transformer.

   
   
   

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1. View Hint View Answer Discuss in Forum

   The primary mmf is least affected by the secondary terminal conditions in a current transformer. It is required for voltage stability.

   Correct Option: C

   The primary mmf is least affected by the secondary terminal conditions in a current transformer. It is required for voltage stability.

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203. The inertia constant H of a machine of 200 MVA is 2 p.u. Its value corresponding to 400 MVA will be _________

1. 1. 1

   
   
   

   2. 0.1

   
   
   

   3. 0.001

   
   
   

   4. 1.1

   
   
   

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1. View Hint View Answer Discuss in Forum

   As H (p.U) ∝ 1	1
   	(MVA)Rating,

   
   thus, new value of H corresponding to 400 MVA is 1 p.u.

   Correct Option: A

   As H (p.U) ∝ 1	1
   	(MVA)Rating,

   
   thus, new value of H corresponding to 400 MVA is 1 p.u.

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204. If a 75 MVA, 10 kV synchronous generator has X_d = 0.4 p.u, then X_d value (in p.u.) to a base of 100 MVA, 11 kV is ___________

1. 1. 44

   
   
   

   2. 0.44

   
   
   

   3. 4.4

   
   
   

   4. 0.04

   
   
   

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1. View Hint View Answer Discuss in Forum

   Xd(new) = Xd(old) ×		KVold,base		²	×		MVAnew,base
   		KVnew,base					MVAold,base

   
   

   = 0.4 ×		11		²	×	100	= 0.44 pu.
   		11				75

   Correct Option: B

   Xd(new) = Xd(old) ×		KVold,base		²	×		MVAnew,base
   		KVnew,base					MVAold,base

   
   

   = 0.4 ×		11		²	×	100	= 0.44 pu.
   		11				75

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205. A 3-phase transformer has rating of 20MVA, 220 kV (star) + 33 kV (delta) with leakage reactance of 12%. The transformer reactance (in ohms) referred to each phase of the L.V. delta-connected side is _________

1. 1. 19.6

   
   
   

   2. 196

   
   
   

   3. 15.8

   
   
   

   4. 152.6

   
   
   

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1. View Hint View Answer Discuss in Forum

   From Δ sides, Z(in ohms) = 3	(33KV)²	× 0.12
   	20 MVA

   
   = 19.6

   Correct Option: A

   From Δ sides, Z(in ohms) = 3	(33KV)²	× 0.12
   	20 MVA

   
   = 19.6

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