ppt

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DEPARTMENT OF TECHNICAL EDUCATION
ANDHRA PRADESH
Name : G.Venkateswara Rao
Designation : Lecturer
Branch : Electrical & Electronic Engg.
Institute :G.P.T,Hyderabad
Year/semester :v Semester
Subject :Power systems-II
( Transmission & Distribution)
Subject code :EE-504
Topic :Different conductor materials
Sub topic :Types of transmission line conductor, relative
merits & demerits of conductors; current
distortion effects.
Duration :50 min
Teaching Aids :ppt, diagrams.

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RECAP
• The Empirical formula for determine the
system voltage.
• Importance of H.V.D.C transmission of power and
requirements of conductor material.
In the previous class, we have learnt about

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OBJECTIVES
• Solid, stranded, hallow and bundled conductors.
• Relative merits of different types of conductors
• Current distortion effects.
On completion of this period you would be able
to know

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TYPES OF TRANSMISSION LINE
CONDUCTOR
1. Solid conductors.
2. Stranded conductors.
3. Hallow conductors.
4. Bundled conductors.

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SOLID CONDUCTORS
Solid conductor
• Solid conductors are mainly available in the form of
solid copper and copper clad steel.

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• Over weight as compared to other conductors
• Solid wires except of smaller sizes are difficult
to handle and transport.
• Skin effect is more
• They are only used for smaller cross sections.
• Solid aluminum conductors are not used
because of mechanical reasons.

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STRANDED CONDUCTORS
Steel
Aluminium
• Standard conductors have greater flexibility and
mechanical strength as compared to single
conductor of same cross section.

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• Stranded conductors usually have a central wire around
which there are successive layers of 6, 12, 18, 24… wires.
• The number of strands is given by the formula
N = 3n(n+1)+1
where ‘n’ is the number of layers.

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• Diameter of the stranded conductor can be
determined by
D = (2n+1)d
where ‘d’ is the diameter of the each stranded.
‘n’ is the no. of layers
• In manufacture process, adjacent layers are
spiraled in opposite directions, so that the
layers are bound together.
• Stranded conductors are easier to handle
and transport.

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• Standard conductors are mainly available in the
following forms
• ACSR ( Aluminium Conductors Steel Reinforced )
• AAC ( All Aluminium Conductors )
• AAAC (All Aluminium Alloy Conductors )
• ACAR (Aluminium Conductors Alloy Reinforced )
• Out of the above ACSR conductors are used for
transmission lines

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HALLOW CONDUCTORS
• Hallow conductors gives large diameter.
Hollow Conductors

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• Tensile strength and flexibility are less.
• Corona loss is reduced.
• Skin effect is less.
• Major portion of the conductor surface is exposed to
atmosphere causes more wind pressure and too much
ice formation on surface

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BUNDLED CONDUCTORS
• Generally there is no difference in construction between
stranded and bundled conductors.
• Only difference is Bundled conductors have very large
number of strands than stranded conductors.

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Limited
Trans. Lines
Limited
Applications
7
Less
High
Less
Mech.
strength
6
Low
Moderate
Low
Resistance
5
Less
Less than
solid
More
Corona loss
4
Very less
Less than
solid
More
Skin effect
3
Moderate
Easy
Difficult
Handling
&transport
2
Less than solid
& Standard
Less than
solid
More
Weight of
conductor
1
Hollow
Standard
Solid
Characteristic
S.No
Relative merits between solid, stranded
and hallow conductors

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CURRENT DISTORTION EFFECTS
• When a conductor is carrying a steady current (D.C) it will
be distribute uniformly over the whole cross section.
• In practice the alternating current does not distribute
uniformly over the whole cross section of the conductor, but
it is distorted due to,
a) Skin, b) Proximity and c) spirality effects.

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SKIN EFFECT
• The distribution of alternating currents through a conductor
is not uniform, because the current density increases from
the middle towards the outer layers.
• Due to A.C flux, the reactance of the central core of the
conductor increase, therefore the impedance increases.
• Hence current confines to the upper layers of the
conductor.

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• This crowding of current towards the surface of the
conductor is known as skin effect.
No current flow
Crowding of current
over the surface

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EFFECTS OF SKIN EFFECT
• At lower frequencies the effect is very small.
• For higher frequencies or solid conductors of large
diameter, the effect is considerable.
• Due skin effect the effective area of conductor through
which current flow is reduced, which increases resistance.
• This effect is much smaller for stranded conductor.
• This effect facilitate to use hallow conductors.

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PROXIMITY EFFECT
• Consider two conductors placed side by side one is
going and other one is for return of current.
• The fluxes are not distribute uniformly, the currents are
also not distribute uniformly, so that the currents are
crowded to one side of the conductors.

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B A
Concentration of current due to conductor B on A
•This effect is known as proximity effect as shown.

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EFFECTS OF PROXIMITY EFFECT
1. Like skin effect, the proximity effect increases the
resistance and decreases the reactance of the conductor.
2. The effect is more for a)Large diameter conductors,
b) high frequencies and c) closeness of the conductors.
3. At normal frequency and for wide spacing
of conductors, this effect is negligible.
4. This effect is eliminated for stranded conductors.

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SPIRALITY EFFECT
• This effect is associated only for stranded conductors,
where the effecting length of the conductor is increased,
which is known as spirality effect.
• The magnitude of this effect depends on the size and
method of construction of the conductor.

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• Due to this effect the effective length of the
conductor increases.
• Spirality effect increases both resistance and internal
reactance of the standard conductors
• This effect is very small at normal frequency such as
at
50 Hz frequency and can be ignored in the case of non-
magnetic conductors.
EFFECTS OF SPIRALITY EFFECT

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SUMMARY
• Types of transmission line conductors
• Relative merits of various types of conductors.
• Different types of current distortion effects.
We have discussed about

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1. In D.C transmission, full cross section of the conductor is
utilized because of no ----
a) Inductance effect
b) Capacitance effect
c) Phase displacement effect
d) Skin effect
QUIZ

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2. Stranded conductors are easier to ----
a) Handle
b) Transport
c) Handle and transport
d) None
QUIZ

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3.A.C.S.R conductor consist of central core of
a) copper
b) steel
c) aluminum
d) cadmium
QUIZ

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4. Crowding of current towards the surface of the
conductor is known as
a) skin effect
b) proximity effect
c) ferranti effect
d) spirality effect
QUIZ

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FREQUENTLY ASKED QUESTIONS
1. Explain the different types of transmission line
conductors ?
2. State the relative merits of different types of line
conductors ?
3. Explain the current distortion effects ?

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