SUBJECT : Feild Theory TOPIC : Transmission Line

1. SHRI SAD VIDHYA
MANDAL INSTITUTE OF
TECHNOLOGY
SUB: FIELD THEORY
CLASS: ELECTRICAL 2ND
YEAR
TOPIC:TRANSMISSION LINES
Presented
By:
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NO NAME ENROLLMENT NO.
1. Patel Shivam 150450109036

2. CONTENTS:
Introduction
Types of transmission lines
Transmission line parameters
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3. A WAVE IS AN OSCILLATION
ACCOMPANIED BY A TRANSFER
OF ENERGY THAT TRAVELS
THROUGH A MEDIUM (SPACE OR
MASS).

5. INTRODUCTION
• The electrical lines which are used to transmit the electrical waves
along them are called transmission line.
• The transmission line theory is the theory of propagation of the electric
waves which are transmitted along the transmission line .
• e.g.:- telephone message and electrical power signals.
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6. • The transmission line are assumed to consist of a pair of wires
which are uniform throughout the whole length .
• The transmission line parameters like resistance, inductance
and capacitance are not physically separable unlike circuit
elements of a lamped circuit.
• In the analysis of transmission lines ,only steady state currents
and voltage are considered .
• The analysis includes the finding of current and voltage at any
point along the length of the line ,when a known voltage is
continuously applied at one end.
• The end to which the voltage is applied is called sending end
while the end at which the signal are received is called
receiving end . 06/08/17 6

7. TYPES OF TRANSMISSION
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8. 1.OPEN-WIRE LINE
• These lines are the parallel conductors open to air hence called open
wire lines.
• The conductors separated by air as the dielectric and mountain on the
towers.
• Example:
1.Telephone lines
2.Electrical power lines
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9. Advantages:
1.Less capacitance compare to underground cable
Disadvantages:
1.Requirement of towers/poles
2.High initial cost
3.Affected by atmospheric condition. (like wind, air, ice)
4.Shorting by flying objects
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10. 2.CABELS
• These are underground lines.
• Telephone cables consist hundred of conductors which are
individually insulated with paper.
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11. • Electrical transmission cables consists two or three large conductor
which insulated with oil impregnated paper or other solid dielectric
materials.
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12. Advantages:
1.Reduced range of electromagnetic filed (EMF) emission, into the
surrounding area.
2.Underground cables pose no hazard to low flying aircraft or to wildlife.
3.Much less subject to conductor theft, illegal connections.
Disadvantages:
1.Undergrounding is more expensive.
2.Whereas finding and repairing overhead wire breaks can be
accomplished in hours, underground repairs can take days or weeks.
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13. 3.CO-AXIAL LINES
• As the name suggests, there are two conductors which are co-axially
placed.
• One conductor is hollow and other placed co-axially inside the first
conductor.
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14. • The dielectric may be solid or gaseous.
• These lines use for high voltage levels.
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15. Advantages:
1.Lower error rates.
2.Coaxial cable shielding reduces noise .
Disadvantages:
1.More expensive to install compare to twisted pair cable.
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16. 4.WAVE GUIDES
• These type of transmission lines are used to transmit the electrical
waves at micro frequencies.
• Constructionally these are the hollow conducting tubes having uniform
cross section.
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17. • The energy is transmitted from inner walls of the tube by the
phenomenon of total internal reflection.
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18. Advantages:
1.Fiber optic cables have a much greater bandwidth than metal
cables.
2. Low Power Loss.
3.Since the fiber is a dielectric, it does not present a spark hazard.
4. Optical fibers are difficult to tap.
Disadvantages:
1.Cables are expensive to install but last longer than copper cables.
2.Transmission on optical fiber requires repeating at distance intervals.
3.Optical fibers require more protection around the cable compared to
copper. 06/08/17 18

19. TRANSMISSION LINE PARAMETERS
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20. • Inductance
• Resistance
• Capacitance
• Conductance
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21. INDUCTANCE
What is inductance ?
• If a changing flux is linked with a coil of a conductor there would be an
emf induced in it. The property of the coil of inducing emf due to the
changing flux linked with coil. it is known as inductance
Its presents role in transmission line
• When the conductor carry the current the magnetic flux is produce
around the conductors.
• It depends on the magnitude of the current flowing through the
conductors.
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22. 06/08/17 22

23. RESISTANCE
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• What is resistance ?
• Resistance is the opposition that a substance offers to the flow of
electric current.
• Its present role in transmission line.
• Depending upon the cross section area of the conductors, the
transmission line have the resistance associated with them.

24. • The resistance is uniformly distributed all along the length of the
transmission line.
• Its total value depends on the overall length of the transmission line.
• Hence its value is given per unit length of the transmission line. It is
depend as R and given in ohm per unit length.
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25. CAPACITANCE
What is capacitance ?
• Capacitance is the ability of a body to store an electric charge
Its present role in transmission line.
• The transmission line consist of two parallel conductors separated by
a dielectric like air .
• Such parallel conductors separated by an insulating dielectric
produces a capacitive effect. Due to this there exists a capacitance
associated with the transmission line which is also distributed along
the length of the conductor.
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26. • It is denoted as C and measured in farads per unit length of the
transmission line.
• In the transmission lines, air acts as a dielectric medium. This
dielectric medium constitutes the capacitor between the conductors,
which store the electrical energy, or increase the capacitance of the
line. The capacitance of the conductor is defined as the present of
charge per unit of potential difference.
• Capacitance is negligible in short transmission lines whereas in long
transmission; it is the most important parameter. It affects the
efficiency, voltage regulation, power factor and stability of the system.
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27. CONDUCTANCE
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What is conductance ?
• Conductance is an expression of the ease with which electric current
flows through a substance.
Its present role in transmission line.
• The dielectric in between the conductors is not perfect. Hence a very
small amount flows through the dielectric called displacement current.
• This is nothing but a leakage current and this gives rise to a leakage
conductance associated with the transmission line.

28. • It exists between the conductors and distributed along the
length of the transmission line. It is denoted as G and
measured in mho per unit length of the transmission line.
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29. THANK
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