Aryabhatta Knowledge University
Sem. iv 2013 Time 3hr Full marks: 70
POWER SYSTEM -1
Attempt any five questions in which question no 1 is
compulsory
1.
Choose the correct answer (any seven) :
(a)
In India ,high voltage transmission is mostly by
(i)
Overhead system
(ii)
Underground system
(iii)
Both (i) and (ii)
(iv)
None of the above
(b)
The volume of copper required for an a.c
transmission line id inversely proportional to
(i)
Current
(ii)
Voltage
(iii)
P.f.
(iv)
Both (ii) and (iii)
(c)
The function of steel wire in an ACSR conductor
is
(i)
Compensate for skin effect
(ii)
Take care of surges
(iii)
Provide additional mechanical strength
(iv)
Reduce inductance
(d)
In transmission line ,sag depends upon
(i)
Span length
(ii)
Tension in conductor
(iii)
Weight of conductor
(iv)
All of the above
(e)
The diameter of each strand is d, then the
diameter of n-layer stranded conductor will be
(i)
(2n+1)d
(ii)
3(n+1)d
(iii)
(2n-1)d
(iv)
(3n-1)d
(f)
The ratio
of line to line to line capacitance and line to neutral capacitance is
(i)
½
(ii)
¼
(iii)
2
(iv)
4
(g)
A 25 km 33 kv transmission line is considered to
be
(i)
Short transmission line
(ii)
Medium transmission line
(iii)
Long transmission line
(iv)
High power line
(h)
Which of the following regulation is considered
as best?
(i)
21/2%
(ii)
155
(iii)
25%
(iv) 40%
(i)
The material commonly used for sheaths of
underground cable is
(i)
Copper
(ii)
Lead
(iii)
Steel
(iv) Rubber
(j)
The dielectric stress in a cable is maximum at
(i)
Conductor surface
(ii)
Bedding
(iii)
Lead sheath
(iv)
Armour
2.
(a) Explain in detail the factors on which
transmission line voltage is chosen.
(b) The daily load cycle of a 3-Φ,110 kV
transmission line can be approximated as follows:
(i)
24 mW for 6 hours
(ii)
8 mW for 6 hours
(iii)
4 mW for 12 hours
The load p.f is 0.8 lagging.
Determine the most economical cross –section ,of the cost of line including erection is Rs (12000+8000a) per
Km, where a is the cross section of each conductor in sq.cm the line is in used
through year . the resistance per Km of each conductor is 0.19a/a ohm .energy
cost 8 paisa per unit.
Assume any additional data if required.
3.
The following data refers to a1-Φ short ;one operating
oat 50Hz with the following condition:
Line length=10Km
Line impedance=0.5(60°)Ω/Km
Load side power= 316.8 Kw
Load side p.f.=0.8(lag)
Load bus voltage=3.3Kv
Find % voltage reduction regulation and
sending –end voltage, line loss and sending-end voltage, line loss and
sending-end p.f.
4.
A 3-Φ,
3-core metal sheathed cable gave the following results on test for capacitance:
(i)
Capacitance between two conductors bunched with
the sheath and the third conductor 0.4 μF/km
(ii)
Capacitance between bunched conductors and
sheath 0.625μF/km
(a)
Determine the capacitance between any two
conductor
(b)
Determine the capacitance between any two
bunched conductors and the third conductor if the sheath is insulated.
(c)
Also calculate the charging current per phase
per km when it is connected to 19 KV supply.
5.
(a) What is grading of cable? Explain
(b) What is intersheath grading? Explain in
detail. Derive the formula for maximum vol. Gradient and compare it with it
with without ‘grading’.
6.
Prove that the shape of conductor between two
supports in case of overhead line is ‘catenary’.
7.
(a) Explain different types of vibration in
overhead transmission line .
(b) An overhead line at a river crossing is
supported from two towers of height 30 meters and 90 meters above water level
with a span of 300 meters. The weight of the conductor is 1 kg/m and the
working tension is 2000kg . determine the clearance between the water level
midway between the towers.
8.
Determine the inductance per km of a transposed
double- circuit 3-Φ line shown in the figure below . each circuit of the line
remains on its own side. The dia of the conductor is 2.532 cm:
9.
Prove that the capacitance per phase of a double
–circuit transposed line having the following specification as shown in the
figure is given by
C=
ε˳/[ln 3√2 d/r(g/f)2/3]F/meter/phase
ε˳/[ln 3√2 d/r(g/f)2/3]F/meter/phase
Where r is the radius of conductor:
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