Satyajeet Sahoo presented a seminar on underground cables. The presentation covered the construction of underground cables including their cores or conductors, insulation, metallic sheath, bedding, armouring, and serving. It discussed insulating materials like XLPE and classified cables as low, high, super, or extra high tension. Single core low tension cables were described. Methods of laying underground cables like direct laying and draw-in systems were also covered. Common cable faults and a comparison of underground and overhead systems concluded the presentation.

1. A Seminar Presentation
on
“Underground cable”
Presented By:
Satyajeet sahoo
Semester: 7th
Branch: EE
Registration Number: 2021219124
Guided By:
Mr. Biswapriti Mishra
Assistant Professor.
College of Engineering Bhubaneswar

2. CONTENT
 ABSTRACT
 INTRODUCTION
 UNDERGROUND CABLES
 CONSTRUCTION OF CABLES
 VARIOUS PART OF CABLES
 INSULATING MATERIAL FOR CABLES
 CLASSIFICATION OF CABLE
 SINGLE CORE LOW-TENSION CABLE
 LAYING OF UNDERGROUND CABLE
 TYPES OF CABLE FAULT
 COMPARISON BETWEEN OVERHEAD AND UNDERGROUND
CABLE
 ADVANTAGES AND DISADVANTAGES OF CABLES
 REFERENCES
 CONCLUSION
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3. ABSTRACT
 Underground cable are the electric
power transmission cables. Because of
their reliability on transmitting, they used
in congested urban areas and in thick
population areas, where overhead
transmission is dangerous underground
cable have low maintenance cost, less
chances of faults, similar voltage drop. In
recent improvements in design and
manufacture have led to development of
cables suitable for use at high voltage.
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4. INTRODUCTION
The underground system of electrical
distribution of power in large cities in
increasingly being adopted. Although it is
costly system of distribution as compared
to overhead system, it ensures the
continuity of supply apart from the
following advantages :
 Its maintenance is less
 It has a long life
 Its appearance is good
 It eliminates hazards of electrocution
due to breakage of over head
conductors..
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5. UNDERGROUND CABLE
 An underground cable consists of
one or more conductors covered with
some suitable insulating material and
surrounded by a protecting cover.
The cable is laid underground to
transmit electric power.
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6. CONSTRUCTION OF CABLE
 Cores or Conductors
 Insulation
 Metallic sheath
 Bedding
 Armouring
 Serving
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v
FIG.1 SHOWS THE GENERAL
CONSTRUCTION OF A 3-CONDUCTOR
CABLE.

7. VARIOUS PARTS OF CABLE
 Cores or Conductors- A cable may have one or more than one core (conductor)
depending upon the type of service for which it is intended. For instance, the 3-
conductor cable shown in Figure is used for 3-phase service. The conductors are made
of tinned copper or aluminium and are usually stranded in order to provide flexibility to
the cable.
 Insulation- Each core or conductor is provided with a suitable thickness of insulation,
the thickness of layer depending upon the voltage to be withstood by the cable. The
commonly used materials for insulation are impregnated paper, varnished cambric or
rubber mineral compound.
 Metallic sheath- In order to protect the cable from moisture, gases or other damaging
liquids (acids or alkalies) in the soil and atmosphere, a metallic sheath of lead or
aluminium is provided over the insulation as shown in Figure.
 Bedding- Over the metallic sheath is applied a layer of bedding which consists of a
fibrous material like jute or hessian tape. The purpose of bedding is to protect the
metallic sheath against corrosion and from mechanical injury due to armouring.
 Armouring - Over the bedding, armouring is provided which consists of one or two
layers of galvanized steel wire or steel tape. Its purpose is to protect the cable from
mechanical injury while laying it and during the course of handling. Armouring may not
be done in the case of some cables.
 Serving- In order to protect armouring from atmospheric conditions, a layer of fibrous
material (like jute) similar to bedding is provided over the armouring. This is known as
serving .
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8. INSULATING MATERIAL FOR CABLE
XLPE Cables (Cross Linked Poly-ethene)
 This material has temperature range
beyond 250 – 300 C
 This material gives good insulating
properties
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GFIG.2: XLPE MATERIAL FOR CABLE

9. CLASSIFICATION OF CABLE
1. Low-tension (L.T.) cables — up to 1000 V
2. High-tension (H.T.) cables — up to 11,000 V
3. Super-tension (S.T.) cables — from 22 kV to
33 kV
4. Extra high-tension (E.H.T.) cables — from 33
kV to 66 kV
5. Extra super voltage cables — beyond 132
kV
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10. SINGLE-CORE LOW TENSION CABLE
A cable may have one or more than one core depending upon
the type of service for which it is intended. It may be
 Single-core
 Two-core
 Three-core
 Four-core etc.
Single core low tension cable:-
The cable has ordinary construction
because the stresses developed in the
cable for low voltages (up to 6600 V)
are generally small.
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FIG.3: SINGLE CORE
LOW- TENSION
CABLE

11. LAYING OF UNDERGROUND CABLE
The reliability of underground cable
network depends to a considerable
extent upon the proper laying and
attachment of fittings i.e. cable end
boxes, etc. There are three methods of
laying underground cables
 Direct laying
 Draw-in-system
 Solid-system
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12. TYPES OF CABLE FAULT
Cables are generally laid in the ground
or in ducts in the underground
distribution system. For this reason,
there are little chances of faults in
underground cables, the following are
the faults most likely to occur in
underground cables:-
 Open circuit fault
 Short circuit fault
 Earth fault 12

13. COMPARISON BETWEEN
UNDERGROUND & OVERHEAD
SYSTEM
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14. ADVANTAGES & DISADVANTAGES
Advantages:-
1. Better general appearance
2. Less liable to damage through storms or lighting
3. Low maintenance cost
4. Less chances of faults
5. Small voltage drops
Disadvantages:-
The major drawback is that they have greater installation cost
and introduce insulation problems at high voltages compared
with equivalent overhead system.
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15. CONCLUSION
Underground cables are the ultimate
solution of over head transmission lines
.In recent past the electric transmission
system is completely destroyed in
thunder storms and cyclones .Using
underground cable those destruction are
eliminated. But it has high initial cost for
installation.
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16. REFERENCES
 Power system analysis & design by
B.R Gupta,S.Chand publications,3rd
editions
 Power system by V.K Mehta
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17. THANK YOU
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