POWER SYSTEM ANALYSIS (utu previous year question papers)

POWER SYSTEM ANALYSIS
SEM-VI, 2012
B.TECH EXAMINATION
UTTARAKHAND TECHNICAL UNIVERSITY
(UTU)

Time :3 hours

Total Marks:100

Note: Attempt all questions

Attempt any four parts out of the following

1. Why do we prefer to analyze unsymmetrical faults by symmetrical component methods?
2. A single phase two-winding transformer is rated 20 kVA, 480/120 V, 60 Hz. The equivalent leakage impedance of the transformer referred to the 120V winding 2, is Z_eq2 = 0.0525 ∠ 78.13^oΩ. Using transformer ratings as base values determine the per unit leakage impedance referred to winding 2 and referred to winding 1.
3. Bus voltages at Bus-1 and Bus-2 in a two-bus system with a purely reactive transmission line between Bus-1 and Bus-2 are 1.00∠ 0^o and 1.05∠ -10^o ,respectively. In what directions real and reactive powers will flow? Explain why?
4. Transmission line between Bus-1 and Bus-2 of a two bus system has a serial impedance of R + JX and shunt admittance of jY. Find the Bus Admittance Matrix.
5. What is the need of a reference buses are there in an interconnected system?

Attempt any four parts out of the following

1. Define the following terms:
   (i) Surge Impedance
   (ii) Power System Stability
   (iii) Symmetrical Components
   (iv) One Line Diagram
   (v) Reactance Diagram
2. What is difference between load bus and voltage control bus?
3. What are the steps used to find Ybus matrix?
4. What are the advantages and disadvantages of Fast Decoupled method of load-flow analysis?
5. Write the swing equation describing the rotor dynamics of a synchronous machine connected to infinite bus through a transmission line. Explain the meaning of symbols used in the equation.

Attempt any two parts out of the following

1. Tap-setting of a 20 kVA, 50 Hz 2000/200 V transformer on primary side is 90%. If its leakage reactance is 5Ω, draw the π-equivalent circuit of this transformer and determine its bus admittance matrix. Use p.u system. Neglect winding resistance, core losses, and magnetizing reactance.
2. A three phase 20 MVA, 10 kV alternator has internal reactance of 5% and negligible resistance. Find the external reactance per phase to be connected in series with the alternator so that steady current on short circuit does not exceed 8 times the full load current.
3. Derive an expression for fault current for single line to ground fault by symmetrical components method.

Attempt any two parts out of the following

1. In a two-bus system with a slack bus (Bus-1) and a load bus (Bus-2), voltage at Bus-1 is 1.00∠ 0^o pu and power demand at Bus-2 is (0.01 + j 0.01) pu. No generator is connected at Bus-2 and no load is connected at Bus-1. Transmission line between Bus-1 and Bus-2 is lossless (and shunt-capacitance is also neglected) and has a series reactance of 0.1 p.u.
   (i) Use analytical method (direct calculations) to find the voltage at Bus-2 and power being generated by the generator at Bus-1.
   (ii) Show the calculations for one iteration of Newton-Raphson method after assuming suitable initial guess.
2. Mention two objectives of short circuit analysis. Draw the zero sequence network of a star connected generator with zero sequence impedance Z_go when the neutral is grounded through an impedance Z_n.
3. Derive the formula for fault current, fault-bus voltages and current through the lines for a 3 phase symmetrical fault at a bus in a power system using Z_bus. State the assumptions made in the derivation.

Attempt any two parts out of the following

1. A 11.2 kV, 10 MVA synchronous generator having a sub-transient reactance of 0.25 p.u supplies 4 MW at 0.8 pf leading to a 11.2 kV, 5 MVA synchronous motor having a sub-transient reactance of 0.2 p.u. through a line having a reactance of 0.2 p.u. through a line having a reactance of 0.05 p.u. The motor terminal voltage is 11.15 kV. Calculate the total fault current supplied by the generator and the motor when a three-phase dead short circuit occurs at generator terminals. Neglect all losses.
2. With a neat flow chart, explain the computational procedure for load flow solution using Newton-Raphson iterative method when the system contains all types of buses.
3. Assume a (0.8 + j0.4) per unit load at bus 2 is being supplied by a generator at bus 1 through transmission line with series impedance of (0.05 + j0.1) per unit. Assuming bus 1 is the swing bus with a fixed per unit voltage of 1.0∠0^o, use the Gauss-Seidel method to calculate the voltage at bus 2 after 1 iteration.

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