Code No: V3110/R07 III B.Tech I Semester Regular & Supplementary Examinations, November 2011 POWER SYSTEMS-II (Electrical and Electronics Engineering) Time: 3 Hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ***** 1. a) Briefly describe the VARIOUS types of conductors b) Find the inductance of line consisting two ACSR conductors spaced between conductors is 1.2m as shown in below Figure. The outer diameter of the single layer of aluminum strand is 45mm and the radius of each strand is 7mm. Assuming neglect the effect of the central strand of steel on inductance. 2. a) Define regulation, efficiency, losses and power factor at each end of the line and explain how these characteristics are affected by the constants of the line b) A short 3-phase transmission line with an impedance of (4+j7) ohm per phase has sending end and receiving end voltages of 125kV and 112kV respectively for some receiving end load at a power factor of 0.85 lagging. Determine (i) power output and (ii) sending end power factor. 3. a) Derive the expressions for voltage and current distribution over a long line. Explain the significance of characteristic impedance loading in connection with the long lines. Deduce the above voltage and current relations in the hyperbolic form and obtain the element values of an equivalent to represent the long lines. b) A three-phase transmission line is 300km long and delivers a load of 150MVA, 0.85p.f lag at 220kV. The ABCD constants of the line are A=D=0.7∠1.8 0 ; B=150∠80 0 ; C =0.001∠90 0 mhos. Determine the following under full load and no load conditions i) Sending-end line to neutral voltage, ii) The sending-end current, and iii) The percent voltage regulation. 1 of 2 Set No:1 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
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Code No: V3110/R07
III B.Tech I Semester Regular & Supplementary Examinations, November 2011
POWER SYSTEMS-II
(Electrical and Electronics Engineering)
Time: 3 Hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
*****
1. a) Briefly describe the VARIOUS types of conductors
b) Find the inductance of line consisting two ACSR conductors spaced between
conductors is 1.2m as shown in below Figure. The outer diameter of the single
layer of aluminum strand is 45mm and the radius of each strand is 7mm. Assuming
neglect the effect of the central strand of steel on inductance.
2. a) Define regulation, efficiency, losses and power factor at each end of the line and
explain how these characteristics are affected by the constants of the line
b) A short 3-phase transmission line with an impedance of (4+j7) ohm per phase has
sending end and receiving end voltages of 125kV and 112kV respectively for some
receiving end load at a power factor of 0.85 lagging. Determine (i) power output
and (ii) sending end power factor.
3. a) Derive the expressions for voltage and current distribution over a long line. Explain
the significance of characteristic impedance loading in connection with the long
lines. Deduce the above voltage and current relations in the hyperbolic form and
obtain the element values of an equivalent to represent the long lines.
b) A three-phase transmission line is 300km long and delivers a load of 150MVA,
0.85p.f lag at 220kV. The ABCD constants of the line are A=D=0.7∠1.80;
B=150∠800;
C =0.001∠900 mhos. Determine the following under full load and no load
conditions
i) Sending-end line to neutral voltage,
ii) The sending-end current, and
iii) The percent voltage regulation.
1 of 2
Set No:1
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Code No: V3110/R07
4. a) Starting from first principles show that surges behave as travelling waves. Find
expressions for surge impedance and wave velocity
b) A 220 kV surge travels on a transmission line of 410 ohms surge impedance and
reaches a junction where two branch lines of surge impedances of 600 ohms and
350 ohms respectively are connected with the transmission line. Find the surge
voltage and current transmitted into each branch line. Also find the reflected
voltage and current.
5. a) Explain the Ferranti effect on EHV transmission lines with neat phasor diagram
b) Estimate the corona loss for a 3-phase, 130 kV, 50 Hz, 250 km long transmission
line consisting of three conductors, each of 12 mm diameter and spaced 2.8 meter
apart in an equilateral triangle formation. The temperature of air is 350C and the
atmospheric pressure is 750 mm of mercury. Taking the irregularity factor as 0.85.
6. a) Explain the strain and shackle insulators with the help of neat sketches
b) A string of four insulators has a self-capacitance of ‘C’ Farads. The shunting
capacitance of the connecting metal work of each insulator is 0.3 C to earth and 0.2
C to the line. A guard ring increases the capacitance to the line of the metal work of
the lowest insulator to 0.5 C. Determine the string efficiency of this arrangement
with the guard ring.
7. a) Explain the importance of conductor spacing and ground clearance of overhead
transmission lines
b) A copper conductor is suspended between two points at the same height and strung
to a tension of 1250 kg the load on the conductor is 1.8 kg/ m and its cross section
area 1.8 sq cm, the load on the conductor is increased to 2.8 kg/m. Calculate the
tension in the conductor and a sag under this move conditions the span is 200 m
and the modulus of the elasticity of the copper is 12.5 510× kg/sq cm
Use the approximate method, assuming the curve to be a parabola.
8. a)What are the factors determining the size of power cables? On which factors does
the current carrying condition depend
b) A single core cable has a conductor diameter of 2.5 cm and a sheath of inside
diameter 6 cm. Calculate the maximum stress. It is desired to reduce the maximum
stress by using two inter-sheaths. Determine their best positions, the maximum
stress and the voltage on each. System voltage is 66kV, 3-phase.
*****
2 of 2
Set No:1
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Code No: V3110/R07
III B.Tech I Semester Regular & Supplementary Examinations, November 2011
POWER SYSTEMS-II
(Electrical and Electronics Engineering)
Time: 3 Hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
*****
1. a) Derive an expression for the inductance per phase for a 3-phase overhead transmission
line when conductors are unsymmetrical placed but lines are un-transposed.
b) A three-phase, three-wire, 132 kV, 50 Hz overhead line conductor is placed in
horizontal plane as shown in the below Figure. The conductor diameter is 1.5 cm. If
the length of the line is 120 km, calculate (i) Capacitance per phase per meter,
(ii) Charging current per phase.
2. a)Explain how transmission lines are classified into short, medium and long lines and
explain their characteristics
b)The per-phase impedance of a short transmission line is (0.3 + j 0.6) ohm. The sending-
end line-to-line voltage is 3300 V, and the load at the receiving end is 320 kilowatts
per phase at 0.85 power factor lagging. Calculate (i) the receiving end voltage; (ii) the
line current; (iii) sending end power factor and (iv) power loss.
3. a) Explain the interpretation of the long line equations
b) A three phase, 50 Hz, 700 km long transmission line has the following line constants
per phase per km uniformly distributed r = 0.3 Ω ; x = 0.6 Ω ; g = 4 910× and b =
2.53 s6
10−
× . Find the auxiliary constants (i) by using convergent series of complex
angles ii) by using convergent series of real angles.
4. a) How can the analysis of a wave travelling on a line terminated by an inductance be
carried out? Derive the expression for the voltage across the terminating inductance
connected at the end of a line on which a step wave of magnitude ‘V’ is travelling.
b)Two stations are connected together by an underground cable having a surge
impedance of 50 ohms joined to an overhead line with a surge impedance of 300 ohms.
If a surge having a maximum valve of 120 kV travels along the cable towards the
junction with the overhead line, determine the value of the reflected and transmitted
wave of voltage and current at the junction.
5. a)Explain briefly the factors which affect corona
b) An overload transmission line operates at 220 kV between phases at 50 Hz. The
conductors are arranged in a 4 meter delta formation. What is the maximum diameter
of conductor that can be used for no corona loss under fair weather conditions?
Assume an air density factor of 0.9 and irregularity factor of 0.82. The critical voltage
is 230 kV. Find also the power loss under storm conditions.
1 of 2
Set No:2
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Code No : V3110/R07
6. a) Explain different types of insulators used in overhead line? Give their field of
application.
b) A three phase over head transmission line is suspended by a suspension type insulator
which consists of three units. The potential across top unit and middle unit are 8 kV
and 12 kV respectively. Calculate (i) The ratio of capacitance between pin and earth to
the self capacitance of the each unit (ii) The line voltage and (iii) String efficiency
7. a) Show that an overhead line conductors strung between two level supports takes up the
shape of a parabola. Obtain expressions for the san and maximum tension when the
supports are at the same level.
b) An overhead line consists of 7 strands of copper, having a cross sectional area of 2.2 cm2