266. For an existing ac transmission line, the string efficiency is 80%, if dc voltage is supplied for the same set up, the string efficiency will be ______%

1. 1. 70

   
   
   

   2. 80

   
   
   

   3. 90

   
   
   

   4. 100

   
   
   

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1. View Hint View Answer Discuss in Forum

   Since there are no currents flowing in any part of the insulator circuit (assuming infinite leakage resistance), the voltage across each of the equal capacitance units is equal, i.e. uniform voltage distribution exists, the string efficiency becomes 100%.

   Correct Option: D

   Since there are no currents flowing in any part of the insulator circuit (assuming infinite leakage resistance), the voltage across each of the equal capacitance units is equal, i.e. uniform voltage distribution exists, the string efficiency becomes 100%.

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267. To increase the visual critical voltage of cporona for an overhead line, one solid phase-conductor is replaced by a “bundle” of four smaller conductors per phase, having an aggregate cross-sectional area equal to that of the solid conductor. If the radius of the solid conductor is 40 mm, then the radius of each of the bundle conductors would be _______ mm

1. 1. 2.0 mm.

   
   
   

   2. 0.020 mm.

   
   
   

   3. 0.20 mm.

   
   
   

   4. 20 mm.

   
   
   

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1. View Hint View Answer Discuss in Forum

   πR² = nπr²
   ∴ r = R √n = 40 √4 = 20 mm.

   Correct Option: D

   πR² = nπr²
   ∴ r = R √n = 40 √4 = 20 mm.

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268. A 220 kV, 20 km long, 3-phase transmission line has the following A, B, C, D constants:
     A = D = 0.96/∠3°, B = 55∠65∠ Ω/ phase, C = 0.05 D = 04 ∠80° S/phase. Its charging current per phase will be ________A

1. 1. 10

      √3

   
   
   

   2. 3

      √11

   
   
   

   3. 11

      √3

   
   
   

   4. 9

      √2

   
   
   

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1. View Hint View Answer Discuss in Forum

   I_S = CV_r + D I_r
   Here, V_r = 220/√3
   Let I_r = 0,
   

   ∴ Ir = 0.05 ×	22	=	11	A
   	√3		√3

   Correct Option: C

   I_S = CV_r + D I_r
   Here, V_r = 220/√3
   Let I_r = 0,
   

   ∴ Ir = 0.05 ×	22	=	11	A
   	√3		√3

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269. A 3-phase, 11 kV, 50 Hz, 200 kW load has a power factor of 0.8 lag. A delta connected 3-phase capacitor is used to improve the power factor to unity. The capacitance per-phase of the capacitor in microfarads is __________

1. 1. 1216

   
   
   

   2. 1316

   
   
   

   3. 1612

   
   
   

   4. 1613

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: B

   NA

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270. The per unit impedance of a circuit element is 0.15. If the base kV and base MVA are halved, then the new value of the per unit impedance of the circuit element will be __________
     

1. 1. 30.0

   
   
   

   2. 0.03

   
   
   

   3. 0.30

   
   
   

   4. 3.00

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: C

   NA

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