[Q:-01]
What do you mean by low pressure aerial line ?
Ans
:
Low pressure aerial line means the low
tension overhead line upto 250 volts.
[Q:-02]
What are the points to be taken into consideration for selecting the materials
of overhead lines ?
Ans
:
(i) Type of
load,
(ii)
Conductivity,
(iii) Tensile
strength,
(iv) Wind
pressure,
(v)
Atmospheric conditions,
(vi) Ease of
operation,
(vii) Cost of
erection and maintenance,
(viii)
Flexibility of future expansion.
[Q:-03]
What are the various component parts of an overhead line ?
Ans
:
The component parts of an overhead line
are as follows :—
(i) Line
supports,
(ii)
Insulators,
(iii)
Conductors,
(iv) Cross
arms & brackets,
(v) Stays and
Struts,
(vi) Guarding
and safety devices,
(vii) Armours,
(viii)
Jointing and termination materials,
(ix) Dampers,
(x) Barded
wire,
(xi) Danger
notice,
(xii) Earthing
materials,
(xiii)
Lightning arrestors,
(xiv) Fuses
and isolating switches,
(xv) Bird
guard &
(xvi)
Foundation.
[Q:-04]
What should be the characteristics of the line supports ?
Ans
:
(i) High
mechanical strength,
(ii) Cheap in
cost,
(iii) Light in
weight,
(iv) Low
maintenance cost,
(v) Longer
life,
(vi) Easily
accessible for painting and erection of line Conductors &
(vii) Good
appearance.
[Q:-05]
What are the various types of line supports normally used ?
Ans
:
(i) Wooden
pole,
(ii) Concrete
pole,
(iii) Steel
tubular pole,
(iv) Rail
pole,
(v) Lattice
steel masts,
(vi) Steel
towers.
[Q:-06]
What are the other accessories used with poles ?
Ans
:
(i) Cross arms
and brackets,
(ii) Clamps,
(iii) Earth
clamp,
(iv) Stay
clamp,
(v) D-iron
clamp,
(vi)
Insulators,
(vii) Pole cap
(in case of tubular pole) &
(viii) Stay
sets.
[Q:-07]
What are the uses of different poles ?
Ans
:
Wooden
pole—for L.T. lines and H.T. lines upto 11 kV.
Concrete pole —
as above—
Steel tubular
pole—for L.T. lines and H.T. lines upto 33 kV.
Rail pole—for
33 kV H.T. lines.
Steel
tower—for extra high voltage lines.
[Q:-08]
What types of poles are generally used for distribution purpose ?
Ans
:
(i) Wooden
poles,
(ii) Concrete
poles &
(iii) Steel
tubular poles.
[Q:-09]
What are the factors affecting the height of the Poles or towers ?
Ans
:
(i) Line
voltage,
(ii) Size,
weight, consequent sag of the conductor and
(iii) Minimum
ground clearance required.
[Q:-10]
What do you mean by the setting depth of the pole ?
Ans
:
The depth of the pole which is buried
under the ground is caned planting depth or setting depth of the pole. The
setting depth is equal to 1/6th of the pole length.
[Q:-11]
What do you mean by end poles ?
Ans
:
The poles at the beginning and finishing
end of the line are known as terminal or end poles.
[Q:-12]
What do you mean by angle poles ?
Ans
:
The poles at the point where the line
makes an angle are called as angle poles.
[Q:-13]
What do you mean by tangent poles ?
Ans
:
The poles used
in a straight line are called as tangent poles.
[Q:-14]
What do you mean by cross-arm ?
Ans
:
The cross pieces of wood or m.s. angles or
m.s. channels used on the poles to hold the insulators and keep the conductors
of line at a safe distance are known as cross-arms.
[Q:-15]
What are the various types of conductors used in overhead lines ?
Ans
:
(i) Copper
conductor,
(ii)
All-Aluminium conductor (AAC),
(iii)
Aluminium Alloy stranded comductor (MSC),
(iv) Aluminium
conductor steel reinforced (ACSR),
(v) Cadmium
copper conductor,
(vi) Phosphor
Bronze. &
(vii)
Galvanised steel conductor.
[Q:-16]
What are the properties of a good conductor ?
Ans
:
The conductor must have the following
properties :—
(i) High
conductivity i.e. low specific resistance,
(ii) High
tensile strength in order to withstand mechanical stress,
(iii) Low
specific gravity in order to give low weight per unit volume,
(iv) Should
not be brittle and
(v) Low cost.
[Q:-17]
What Is meant by "ACSR" conductor ?
Ans
:
"ACSR" means aluminium conductor
steel reinforced. It has a core of one or two layers of galvanised steel
strands surrounded by one, two or three layers of aluminium strands.
[Q:-18]
What are the advantages and disadvantages of using ACSR conductor for power
transmission ?
Ans
:
Advantages :—
(i) It has
much lighter weight as compared with copper conductors and greater tensile
strength.
(ii) The sag
can be reduced and accordingly shorter towers or longer spans may be used which
in turn reduce the cost of transmission tower along with its accessories.
(iii) The
failure in operation is very much less.
(iv)
Maintenance cost is less.
(v) It has
higher corona limit.
Disadvantages :—
(i) Due to its
lower electrical conductivity the relative cross sectional area will be more
than that of copper.
(ii) It necessitates
stronger supporting structures.
(iii) These
conductors are susceptible to corrosion.
[Q:-19]
Why are A.C.S.R. conductors preferred over copper conductors for transmission
& distribution lines ?
Ans
:
For the same conductivity since A.C.S.R.
conductors are both fighter and stronger than copper and also for lower cost
A.C.S.R. conductors are preferred over copper conductors.
[Q:-20]
What do you mean by "A.A.C." ?
Ans
:
A.A.C. means all aluminium conductor.
These are stranded conductors made of aluminium wires.
[Q:-21]
Where are A.A.C. conductors used ?
Ans
:
All aluminium stranded conductors are
mainly used on low voltage distribution system employing relatively shorter
spans.
[Q:-22]
What are the minimum section of A.A.C. and A.C.S.R. conductor that may be used
in O.H. line satisfying the requirement of I.E. rules ?
Ans
:
A.A.C.
conductor - 7/2.21 mm A.A.C.
A.C.S.R.
conductor - 6/2.35 mm Al. and 1/2.35 mm steel.
[Q:-23]
What do you mean by A.A.S.C. ? Where is it used?
Ans
:
A.A.S.C. means aluminium alloy stranded
conductor which is also known as all aluminium alloy conductor (A.A.A.C). These
are stranded conductors made of aluminium-magnesium-silicon type alloy.
These conductors are mainly used for low
and medium voltage overhead power transmission purpose.
[Q:-24]
What do you mean by lay ratio of stranded conductor?
Ans
:
Ratio of the axial length of one complete
turn of the helix formed by an individual wire in a stranded' conductor to the
external diameter of the helix is called as the lay ratio of that stranded
conductor.
[Q:-25]
How the ACSR conductor sizes are specified according to the use of different
voltage levels of transmission lines ?
Ans
:
The ACSR conductors used in transmission
lines are identified by the names of different animals. Dog type ACSR conductor
is used for 33kV system, Lark ACSR and Panther ACSR conductors are used for 132
kV system, Deer ACSR and Zebra ACSR conductors are used for 220 kV system &
Moose ACSR conductor is used for 400 kV system.
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