Overhead transmission lines transmit power using bare conductors suspended by towers, while underground cables transmit power below ground using insulated conductors inside protective casing. Underground cables are more expensive to install due to excavation costs but have fewer transmission losses and are unaffected by weather. Overhead lines are cheaper but more vulnerable to outages from lightning and damage. Underground cables can transmit up to 33kV while overhead lines can transmit higher voltages. Basic cable laying involves excavating trenches, laying cables in protective casing, backfilling trenches. There are different cable and transmission line types for varying voltages.

1. NAME: SURYA PRATAP BHANJA
ROLL NO- 2158006
Overhead
Transmission Lines Vs
Under Ground Cabling

2.  An overhead power line is a structure used in electric power
transmission and distribution to transmit electrical energy across
large distances.
 It consists of one or more uninsulated ACC/AAAC/ACSR conductor
starting from 35sqmm to up to 232sqmm size for 11KV & 33KV line
transmission.
 Commonly they are transmitted multiples of three for three-phase
power suspended by towers or poles.
 Short transmission line – Here the length is upto 50 KM,
Voltage is completely low <20 kV
 Medium transmission line – Here the length of the line
between 50 km to 150 km
Voltage is line voltage is between 20 kV to 100 kV
 Long transmission line – Here the length of the
transmission line is more than 150 km
And Voltage is more than 100Kv.
Overhead Transmission Lines

3. ⦁ A cable is basically an insulated conductor and is used for
underground (UG) transmission and distribution of electricity.
Insulation is used to cover the conductor and provides isolation
from the surroundings. It should possess high resistance, high
dielectric strength, high mechanical strength and long durability.
⦁ An underground cable consists of one or more conductors &
surrounded by a protecting cover.
⦁ The cable is laid underground to transmit electric power.
Under ground Cabling

4. Under ground Cabling
Cables for underground service may be classified in two ways
according to
(i)The type of insulating material used in their manufacture.
(ii)The voltage for which they are manufactured. However, the
latter method of classification is generally preferred, according
to which cables can be divided into the following groups :
A) Low-tension (L.T.) Cables......upto 1000V .
B) High-tension (H.T.) Cables....upto 11000V.
C) Super-tension (S.T.) Cables....from 22kV to 33kV.
D) Extra-high Tension (E.H.T) Cables.......from 33kV to 66
kV.
E) Extra Super Voltage Cables.........beyond 132 kV.

5. For 11Kv Cable Laying
Under ground Cable Laying Methodology:

6. Major Differences Between OH & UG

7. Major Differences Between OH & UG

8. ⦁ Underground cables offer an affordable and
justifiable solution for critical parts, and in
some cases the entire length, of overhead
high voltage power lines. With appropriate
technology used in appropriate places, the
environmental impact of underground cables
can be minimized.
⦁ It has lesser transmission losses
⦁ It is less affected by extreme weather
conditions and hence increases reliability of
supply of power

9. A Comparison of Overhead & Underground
Transmission

10. • Electric Power needs to be carried over long distances from the point of
generation to the point of consumption. This Transmission is done either through
overhead lines or underground cables. Each of these two methods of transmission
has its own advantages and disadvantages.
• Overhead Transmission lines are cheaper as the insulation cost is lesser and the
conductor material cost is lesser too. They also have better heat dissipation.
• However, they have significant dis-advantages. Overhead lines are vulnerable to
lightning strikes which can cause interruption. Overhead lines use bare conductors
and can cause damage if they break. They are considered to be unsightly as they
mar the scenery of the landscape. The maintenance cost of overhead lines is more
and the voltage drop in overhead lines is more.
A Comparison of Overhead & Underground
Transmission

11. ⦁ Underground transmission due to cables is costlier than overhead transmission as
the ground needs to be excavated. This can be difficult when passing though
geographic obstructions such as hills, marshes and rivers. Special trenches need to
be constructed when passing through loose soil. Besides, heat dissipation in
underground cables is an issue. Hence, the conductors have to be thicker. The
insulation required for the cables is expensive. Hence, it is difficult to use
underground cables for voltages at HV levels (> 33 kV).
⦁ Underground cables may have to be rerouted to accommodate other underground
structures such as pipelines, sewage lines, etc. It is necessary that the routes of
underground lines are clearly marked with sign boards to prevent accidents when
excavations are carried out for other reasons at a later date.
A Comparison of Overhead & Underground
Transmission

12. ⦁ Basic Difference between UG cabling & OH transmission line in power distribution
⦁ Up to what Kv, UG cabling is suitable for transmission ?
⦁ What is the basic procedure for 11Kv cable laying?
⦁ What are the different kind of cables & OH transmission lines present ?
Questions & Answers