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Professer N.P .Singh Final Exams

1.A three bus system having a regulating transformer(RT) in the line 1-2 near bus 1 is shown in
figure,the complex ratio of RT IS ‘a’.The per unit(PU) in the line admittances are indicated in the
figure.The lines resistance and shunt admittances are negligible.Determine the Y bus matrix for ‘a’
=1.05<-2°, and changes in real power flow p12 and reactive power flow Q12 when ‘changes from
1.0<0° to 1.0<-3°
1.Compare and contrast between Newton-Raphson,decoupled load flow and fast decoupled load flow
method of load flow analysis.
2.Describe the algorithm for solving aload flow problem using the Newton-Raphson method
2. A synchronous generator is feeding 250 MW to a large 50 Hz network over a double circuit
transmission line.The maximum steady state power that can be transmitted over the line with both
circuit in operation is 500 MW with any one of the circuits. A solid three phase fault occurring at the
new -end of one of the lines causes it to trip.estimate the critical angle in which the circuit breakers
must trip and isolate faulty line so that synchronism is not lost.
3. A synchronous generator has balanced emfs induced in its three phases and its neutral grounded
trough a reactance Xn.The generator has positive,negative and zero sequence reactance x1,x2 and
x0,respectively such that x0<<x1=x2.
A,Draw the sequence networks of the generator as seen from the terminals,
B,Prove that,if the neutral is solidly grounded,the line-to-ground fault current will be more than the
solid three-phase short circuit fault current.
4. A 30 MVA,13.2KV alternator with its neutral grounded through a reactance of 2.5 ohms has a
sub-transient reactance of 35 percent.The negative and zero sequence reactance of the alternator are
25% and 10% respectively.A line to line fault occurs at the terminal of unloaded alternator.Determine
the fault current and the line to line voltages under faulted condition.
5. For the system shown below ,the rating of components are,
Generator: 25MVA,12.4KV,10% sub-transient reactance
Motor: 20MVA,3.8KV,15% sub-transient reactance
Transformer T1:25MVA,11/33KV,5% reactance
Transformer T2:20MVA,33/3.8KV,10% reactance
The reactance of the line is 60 ohms and the system is loaded so that the motor is drawing 15 MW at
0.9 leading power factor.the motor terminal voltage being 3.2KV.find the sub transient current in
generator and motor for three phase fault at the generator bus.