Xd,X’d and X”d are steady state d-axis synchronous reactances, transient d-axis reactance and sub-transient d-reactance of a synchronous machine respectively. Which of the following statement is true    

1.  Xd, >X’d> X”d         

2.     X”d>,X’d> Xd                 

3.    X’d> X”d> Xd               

4.      Xd, > X”d> X’d                   

View Answer  
4
Correct Answer :

Xd, >X’d> X”d         


Explanation :
No Explanation available for this question

A 50 Hz balanced three-phase, Y-connecteed supply is connected to a balanced three-phase Y-connected load. If the instantaneous phase a of the supply voltage is Vcos(wt) and the phase a of load current is Icos(wt-), the instantaneous three phase power is    

1.  A constant with a magnitude of VI cos            

2.  A constant with a magnitude of (3/2) VI cos?

3.  Time varying with an average value of (3/2) VI cos? and a frequency of 100Hz

4.  Time varying with an average value of VI cos? and a frequency of 50 Hz

View Answer  
4
Correct Answer :

A constant with a magnitude of (3/2) VI cos?


Explanation :
No Explanation available for this question

A fault occurring at the terminals of an unloaded synchronous generator operating at its rated voltage has resulted in the following values of the current and voltage Ia0=j2.37 p.u Ia1=j3.05p.u Ia2=j0.68 p.u Va0=Va1=Va2=j2.37 p.u The fault that has occurred is    

1.  L-L fault  

2.  L-L-G fault  

3.  L-G fault  

4.  None of these

View Answer  
4
Correct Answer :

L-L-G fault

 


Explanation :
No Explanation available for this question

If the excitation of the synchronous generator fails, it acts as a

1.  Synchronous motor  

2.  Synchronous generator  

3.  induction motor  

4.   induction generator

View Answer  
4
Correct Answer :

 induction generator


Explanation :
No Explanation available for this question

The positive, negative and zero sequence impedance of a solidly grounded system under steady state condition always follow the relation

1.  Z1

2.  Z1

3.  Z0

4.  none of these

View Answer  
4
Correct Answer :

Z1<Z2<Z0


Explanation :
No Explanation available for this question

The positive sequence current for a L-L fault of a 2 KV system is 1400 A, and corresponding current for a L-L-G fault is 2220A. The zero sequence impedance of the system is    

1.  62.75      

2.    4.5275 ?      

3.     5.275 ?     

4.   0.5275 ?

View Answer  
4
Correct Answer :

 0.5275 ?


Explanation :
No Explanation available for this question

A power system network with the capacity at 100 MVA has a source impedance at 10% at a point. The fault at that point is

1.  10 MVA        

2.   30 MVA            

3.  3000 MVA              

4.  1000 MVA 

View Answer  
4
Correct Answer :

1000 MVA 


Explanation :
No Explanation available for this question

Four identical alternators each rated for 20 MVA, 11 KV having a subtransient  reactance of 16 % are working in parallel. The short-circuit level at the bus bar is    

1.  500 MVA           

2.  400 MVA         

3.  125 MVA          

4.  80 MVA 

View Answer  
4
Correct Answer :

500 MVA           


Explanation :
No Explanation available for this question

A single line to ground fault occurs on a three-phase isolated neutral system with a line to neutral voltage of V KV. The potential on the healthy phase rise to a value equal to    

1.  √2 V kV                

2.  √3 V kV                   

3.  3 V kV                   

4.  1/√3 V kV       

View Answer  
4
Correct Answer :

√3 V kV                   


Explanation :
No Explanation available for this question

A large ac generator, supplying power to an infinite bus, has a sudden short-circuit occurring at its terminals. Assuming the prime mover input and the voltage behind the transient reactance to remain constant immediately after the fault, the acceleration of the generator rotor is

1.  Inversely proportional to the moment of inertia of the machine

2.  Inversely proportional to the square of the voltage

3.  Directly proportional to the square of the short-circuit current

4.  Directly proportional to the short-circuit power 

View Answer  
4
Correct Answer :

Inversely proportional to the moment of inertia of the machine


Explanation :
No Explanation available for this question
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