AJAY KUMAR GARG ENGINEERING COLLEGE GHAZIABAD AKGEC/IAP/FM/01

PRE-UNIVERSITY EXAMINATION

Course: B. Tech. Subject Code: EEE-601 Branch: EN Subject Name: Power System Analysis Date: 26/04/12 Time Allowed: 3 HoursMax. Marks: 100 Instructions: Attempt all the questions.----------------------------------------------------------------------------------------------------------------Q1. Attempt any four parts: (5*4=20)

(a) Describe single line diagram representing synchronous machines transformers and feeders from generating end to disturbing end. Discuss about impedance and reactance diagram with examples.

(b) For the three-phase power network shown in fig. below, the ratings of the various components are:G1: 100 MVA, 0.30 pu reactanceG2: 60 MVA, 0.18 pu reactanceTransformer (each): 50 MVA, 0.10 pu reactanceInductive reactor X: 0.20 pu on a base of 100 MVATL (each): 80 ohms (reactive); neglect resistance.With the network initially unloaded and a line voltage of 110 kV, a symmetrical short circuit occurs at mid point F of line L2. Calculate the short circuit MVA to be interrupted by the circuit breakers A & B at the ends of the line.

T1 L1 T3

X A L2 B

Bus T2 F T4 Bus

(c) A 3-phase line supplies a Δ connected load. The line current in 1 is 100 Amps. Taking the current in line-1 as reference, find the symmetrical components of line current if phase-3 is only switched off.

(d) Derive an expression for maximum momentary current, if transient takes place on a transmission line; also draw the waveform of short circuit on a transmission line. Assume the conditions.

(e) Discuss the various strategic locational aspects of reactors for limiting the fault current and their advantages.

(f) Draw the positive, negative & zero sequence impedance networks for the power system shown in figure

j 50Ω j50Ω

G1

G2

G1

GG2

Choose a base of 50MVA, 220 kV in the 50Ω transmission lines & mark all reactance in per unit. The ratings of the generators & transformers are:

G1: 25 MVA, 11 kV, X”=20%, X’=10%, X0=5%G2: 25 MVA, 11 kV, X”=20%, X’=10%, X0=5%

3-phase transformer (each): 20 MVA, 11/220 kV, X=15%

Q2. Attempt any two parts: (10*2=20)

(a) What do you understand by sequence networks? What is their importance in unsymmetrical fault calculation?An 11 kV, 10MVA alternator has positive, negative and zero sequence reactance of 0.19, 0.17 and 0.06 per unit respectively. The generator neutral is grounded through a reactance of 0.04 per unit. Determine the fault current and line to line voltages at the fault when a double line fault occurs at generator terminal. Assume generator was unloaded before the fault.

(b) Derive an expression of fault current for Double line to ground fault by symmetrical component method. 5Calculate the sequence components of the fault current and the neutral fault current, if the line-to-line-to-ground fault occurs at bus q shown in fig. all the reactance are given in p.u on the generator base.5

G: Xd”=j0.16, X2=0.17, X0=0.06

T1, T2: X1=X2=X0=j0.10M: X2

”=j0.20, X2=0.22, X0=0.15TL: X1=j0.11, X2=j0.11, X0=j0.33

(c) Describe in detail with flow chart diagram, the computational method for short circuits calculations.

Q3. Attempt any two parts: (10*2=20)(a) Draw the flowchart and write the algorithm for Newton-Raphson Load Flow Method.

Also compare the Gauss-Siedel and Newton Raphson methods of load flow.(b) A four bus system is shown in figure. Values of real & reactive powers are listed in

table. All buses other than the slack bus are PQ type. Assuming a flat voltage start, find the voltages at the three buses at the end of the first iteration using G-S method.

Bus No

Type Bus voltage

PL(pu) QL(pu) Vi (pu) δi deg 1 Slack ? ? 1.06 0 2 PQ 0.5 0.2 ? ? 3 PQ 0.4 0.3 ? ? 4 PQ 0.3 0.1 ? ?

Line Admittance1-2 2.0-j8.01-3 1.0-j4.02-3 0.666-j2.6642-4 1.0-j4.03-4 2.0-j8.0

Line Admittance1-2 2.0-j8.01-3 1.0-j4.02-3 0.666-j2.6642-4 1.0-j4.03-4 2.0-j8.0

G

M

G

G G

G

(c) (i) Discuss the decoupled and fast decoupled method of load flow analysis.(ii) How the magnitude & phase angle of voltage at a bus is controlled by regulating transformer?

Q4. Attempt any two parts: (10*2=20)

(a) A three-phase, 60 Hz, 500 MVA, 13.8 kV, 4-pole steam turbine generating unit has an H constant of 5.0 pu-s. Determine:-(i) ωsyn and ωmsyn;(ii) The kinetic energy in joules stored in the rotating masses at synchronous speed.(iii) The mechanical angular acceleration αm and electrical angular acceleration α if

the unit is operating at synchronous speed with an acceleration power of 500 MW.

(b) Find the critical clearing angle for the system shown in the figure for a three phase fault at point ‘P’. The generator is delivering 1.0 p.u. power under pre-fault conditions.

j0.25pu X’=j0.3pu j0.15pu j0.15pu j0.15pu

j0.15pu j0.15pu E’=1.2pu P j0.25pu V=1.0 pu *

(c) (i) Describe the point by point method solution technique of swing equation for the transient stability of a power system.(ii) Discuss the methods for improving the transient state stability of a power system.

Q5. Attempt any two parts: (10*2=20)(a) Derive the expressions for reflection and refraction coefficients of voltage and current

waves when a line is(i) Terminated through a resistance(ii) Through a capacitance

(b) Obtain an expression for the surge impedance of a transmission line and for the velocity of propagation of electric waves in terms of the line inductance and capacitance. An overhead line with surge impedance 500 ohm bifurcates into two lines of surge impedance 500 ohm and 50 ohm, respectively. If a surge of 25 kV is incident on the overhead line, determine the magnitudes of voltage and current which enter the bifurcated lines.

(c) Explain how lightning produces over-voltages in transmission lines. Discuss different methods of protecting the line against over-voltages caused by lightning.

Line Admittance1-2 2.0-j8.01-3 1.0-j4.02-3 0.666-j2.6642-4 1.0-j4.03-4 2.0-j8.0

G