POWER SYSTEM ANALYSIS

POWER SYSTEM ANALYSIS
SEM-VI, 2010
B.TECH EXAMINATION
UTTARAKHAND TECHNICAL UNIVERSITY

Time: 3 hours
Total Marks:100
Attempt any four of the following:
  1. One conductor of a three phase line is open. The current flowing to the connected load through a line is 10A. With the current in line a as reference and assuming that line c is open, find the symmetrical components of the line currents.
  2. The line to ground voltages on the high voltage sides of a step up transformer are 100 kV, 33 kV and 38 kV on phases a, b and c respectively. The voltage of phase a leads that of phase b by 100o and lags that of phase c by 176.5o. Determine analytically the symmetricalcomponents of voltage.
  3. The line currents in amperes in phase a, b and c respectively is 500+j150, 100-j600 and -300+j600 referred to the same reference vector. Find thesymmetrical components of the currents.
  4. Three identical Y connected resistors from a load bank with a three phase rating of 2300 V and 500 kVA. If the load bank has applied voltages |Vab| = 1840 V, |Vbc| = 2760 V and |Vca| = 2300 V, find the line voltages and currents in per unit into the load. Assume that the neutral system and select a base of 2300 V, 500 kVA.
  5. A 25 MVA, 13.2 kV alternators with solidly grounded neutral has a sub transient reactance of 0.25 pu. The negative and zero sequence reactance are 0.35 and 0.1 pu. A single line to ground fault occurs at the terminals of an unloaded alternator, determine the fault current.
  6. Draw the zero sequence equivalent circuit of 3 phase transformer for various possible combinations.
Attempt any four of the following:
  1. Find out the average three phase power in terms ofsymmetrical components.
  2. A 500 kV 2μ sec rectangular of 350 ohms approaches a station at which the concentrated earth capacitance is 3000 pF. Determine the maximum value of the transmitted wave.
  3. Explain the variation of current and voltage on an overheated line when one end of the line is
    (a) short circuited and (b) open circuited and at the other end a source of constant e.m.f V is switched on.
  4. Differentiate between steady state stability and transient stability and transient stability of a power system. Discuss the factors that affect
    (a) Steady state stability and
    (b) Transient state stability of the system.
  5. What is the load flow solution? Explain its significance in power system analysis.
  6. Explain the principle of operation of Ferranti surge absorber.
Attempt any two of the following:
  1. Classes the various types of buses in power system for load flow studies. Justify the classification.
  2. What is equal area criterion? Discuss its applications and limitations in the study of power system stability.
  3. Show that a travelling wave moves with a velocity of light on the overhead line and its speed is proportional to 1 /√εr on a cable with dielectric material of permittivity εr.
Attempt any two of the following:
  1. Derive an expression for the maximum power transfer between two nodes. Show that this power is maximum when X = √3R, where X is the reactance and R is the resistance of the system.
  2. Develop load flow equations suitable for solution by
    (i) Gauss Seideal method
    (ii) Newton-Raphson method using nodal admittance approach.
  3. Explain the point by point method of solving the swing equation. Compare this method with the equal area criterion method.
Attempt any two of the following:
  1. A 50 Hz four pole turbo generator rated 20 MVA, 13.2 kV has an inertia constant of H = 9.0 kW-sec/kVA. Determine the K.E stored in the rotor at the synchronous speed. Determine the acceleration if the input less the rotational losses is 2500 HP and the electric power developed is 15000 kW. If the acceleration computed for the generated is constant for a period of 15 cycles. Determine the change in torque angle in that period and the rpm at the end of 15 cycles. Assume that the generator is synchronized with a large system and has no accelerating torque before the 15 cycle period.
  2. Two generating stations having short circuit capacities of 1200 MVA and 800 MVA respectively and operating at 11kV are linked by an interconnected cable having a reactance of 0.5 Ohm per phase. Determine the short circuit capacity of each station.
  3. The following is the system data for a load flow solution:

    Determine the voltage at the end of first iteration using Gauss-Seidel method. Take α = 1.6.
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