281. A 50H z gener at i ng uni t has H -constant of 2 MJ/MVA. The machine is initially operating in steady state at synchronous speed, and producing 1 pu of real power. The initial value of the rotor angle δ is 5°, when a bolted three phase to ground short circuit fault occurs at the terminal of the generator. Assuming the input mechanical power to remain at 1 pu, the value of δ in degrees, 0.02 second after the fault is ________.

1. 1. 5.1

   
   
   

   2. 5.7 to 6.1

   
   
   

   3. 6

   
   
   

   4. None of the above

   
   
   

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   NA

   Correct Option: B

   NA

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282. A separately excited DC motor runs at 1000 rpm on no load when its armature terminals are connected to a 200V DC source and the rated voltage is applied to t he field winding. The armature resistance of this motor is 1Ω. The no-load armature current is negligible. With the motor developing its full load torque, the armature voltage is set so that the rotor speed is 500 rpm. When the load torque is reduced to 50% of the full load value under the same armature voltage conditions, the speed rises to 520 rpm. Neglecting the rotational losses, the full load armature current (in Ampere) is _______.
     

1. 1. 8

   
   
   

   2. 56

   
   
   

   3. 25

   
   
   

   4. 15

   
   
   

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   NA
   

   Correct Option: A

   NA
   

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283. A 200/400V, 50 Hz, two-winding transformer is rated at 20 kVA. Its windings are connected as an auto-transformer of rating 200/600V. A resistive load of 12 Ω is connected to the high voltage (600V) side of the auto-transformer. The value of equivalent load resistance (in Ohm) as seen from low voltage side is _________.

1. 1. 1.3 to 1.4

   
   
   

   2. 4

   
   
   

   3. 6.5

   
   
   

   4. 1.2

   
   
   

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   NA

   Correct Option: A

   NA

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284. Two single-phase transformers T₁ and T₂ each rated at 500 k VA are operated in parallel. Percentage impedances of T₁ & T₂ are (1 + j6) and (0.8 + j4.8) respectivel y. To share a load of 1000 k VA at 0.8 lagging power factor, the contribution of T₂ (in kVA) is _________.

1. 1. 614

   
   
   

   2. 525

   
   
   

   3. 555

   
   
   

   4. None of these

   
   
   

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   ST2 = S ×	z1
   	z1 + z2

   
   

   = 1000 ×	6.08 ∠ 80.53	= 555 KVA
   	10.94 ∠ 80.53

   Correct Option: C

   ST2 = S ×	z1
   	z1 + z2

   
   

   = 1000 ×	6.08 ∠ 80.53	= 555 KVA
   	10.94 ∠ 80.53

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285. A DC motor has the following specifications: 10hp, 37.5 A, 230V; flud/pole = 0.01Wb, number of poles = 4, number of conductors = 666, number of parallel paths = 2. Armature resistance = 0.267 &ohm. The armature reaction is negligible and rotational losses are 600W. The motor operates from a 230V DC supply. I f the motor runs at 1000 rpm, the output torque produced in (in Nm) is _________.

1. 1. 42

   
   
   

   2. 57 to 58

   
   
   

   3. 51

   
   
   

   4. 15

   
   
   

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   NA

   Correct Option: B

   NA

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