Power System II (Operation and Control) 2025

(a) Power system stability for continuous and small variation of load is studied by:

1. Transient stability
2. Dynamic stability
3. Steady state stability
4. Marginal state stability

(b) The following fault has highest probability of occurrence in power system:

1. L-L-L-G fault
2. L-G fault
3. L-L-G fault
4. All have same probability of occurrence

(c) The current flowing through the neutral wire for a 3 phase 4 wire system under a single line to ground fault has:

1. Only zero sequence component
2. Zero & negative sequence component
3. Zero & positive sequence component
4. Positive & negative sequence component

(d) The ______ matrix is a sparse matrix for a practical sized power system.

1. Admittance matrix
2. Impedance matrix
3. Bus matrix
4. None of the above

(e) The per unit impedances of a transformer referred from the primary and secondary side are:

1. Equal
2. Same as their actual value in ohm
3. Proportional to the transformation ratio of transformer
4. None of the above

(f) The full form of SCADA is:

1. Supervisory Control and Data Acquisition
2. Supervisory Control and Document Acquisition
3. Supervisory Column and Data Assessment
4. None of the above

(g) Which of the following quantities are to be determined in slack bus?

1. Q and |V|
2. P and Q
3. |V| and δ
4. Q and δ

(h) The % reactance of a 100 kVA, 5 kV, 5 ohm reactance is given by:

1. 2%
2. 20%
3. 40%
4. 4%

(i) Advantage of Gauss-Seidel method over Newton-Raphson method is:

1. Suitable for large power system
2. Calculation time for each iteration is less
3. Number of iterations less
4. All of the above

(j) LFC studies the variation of ______ due to the variation of ______ in power system.

1. Frequency, Voltage
2. Load, Voltage
3. Frequency, Load
4. Load, Voltage

(a) The line to neutral voltages of a three phase system are:

Va = 90∠0° kV

Vb = 66∠−100° kV

Vc = 22∠−85° kV

Determine the symmetrical components:

Va₀, Va₁, Va₂, Vb₁, Vb₂, Vc₁ and Vc₂.

(b) Draw the zero sequence equivalent circuit for the transformers for following connections:

1. Star-Star bank (both neutrals grounded)
2. Star-Delta bank (star grounded)

(a) For a short lossless transmission line, determine the expression of both active and reactive power transferred to the load when sending end and receiving end voltages are Vs and Vr.

(b) The sending end and receiving end voltages of a three phase transmission line at 200 MW load are equal at 230 kV. The per phase line impedance is (0 + j15) Ω. Calculate the maximum steady-state power that can be transmitted over the line.

(a) Write down the algorithm of Gauss-Seidel power flow method.

(b) What are the assumptions made for Fast Decoupled load flow?

(a) Two generators rated 350 MW and 450 MW are operating in parallel. The droop characteristics of the governor are 3% and 4% respectively. How would a load of 650 MW be shared between them? What will be the system frequency? Assume nominal system frequency is 50 Hz and no governing action.

(b) A 30 MVA, 13.2 kV synchronous generator has a solidly grounded neutral. Its positive, negative and zero sequence impedances are 0.35, 0.35 and 0.10 pu respectively. Determine the following:

1. What value of reactance must be placed in the generator neutral so that the fault current for a line-to-ground fault of zero fault impedance shall not exceed the rated line current?
2. What value of resistance in the neutral will serve the same purpose?

(a) Calculate the bus admittance matrix for the given data.

(b) Write advantages of PU system in application of power system.

(a) Describe the working principle of STATCOM with neat schematic diagram.

(b) What are the three different states of power system for contingency analysis? Explain.

(a) A 400 MVA alternator has H = 4.6 MJ/MVA and a 1200 MVA machine has H = 2 MJ/MVA. These two machines operate in parallel. Find the equivalent H in 100 MVA base.

(b) Draw the reactance diagram for the power system shown in figure below. Use a base of 100 MVA, 33 kV in the transmission line. The ratings of the generator, motor and transformer are:

• Generator: 50 MVA, 33 kV, X = 20%
• Motor: 50 MVA, 11 kV, X = 30%
• Transformer T1: 100 MVA, 33/220 kV, X = 15%
• Transformer T2: 50 MVA, 11/220 kV, X = 15%

(a) A generator operating at 60 Hz delivers 1.0 pu MW power. Suddenly a three phase fault takes place reducing the maximum power transferable to 0.40 pu MW whereas before the fault, this power was 1.80 pu MW and after the clearance of the fault it is 1.30 pu MW. Determine the critical clearing angle.

(b) Write short note on:

• Critical clearing angle
• Critical clearing time