It is related to transmission and distribution of Underground cables and its advantages & disadvanatges

1. UNDERGROUNDCABLESCONSTRUCTIONANDTYPES
EASWARI ENGINEERING COLLEGE
(AUTONOMOUS)
Bharathi Salai, Ramapuram, Chennai – 89
DEPARTMENT OF ELECTRICALAND ELECTRONICS
ENGINEERING
Subject : TRANSMISSION AND DISTRIBUTION
BATCH 5:
MANOJ V-310620105025
MURATH BASHA K -310620105025
JEEVAPANDIYAN S – 310620105015
VIKAS V - 310620105051
DHRUV K-3106201050302

2. CONTENT:
INTRODUCTION.
REQUIREMENTS OF UNDERGROUND CABLES.
CONSTRUCTION OF UNDERGROUND CABLES.
TYPES OF UNDERGROUND AND IT’S VARIOUS CALSSIFICATION.
ADVANTAGES AND DISADVANTAGES OF UNDERGROUND
CABLES.

3. INTRODUCTION:
 An underground cable is a cable that is buried below the ground. They
distribute electrical power or telecommunications. Such cables are an
alternative to overhead cables, which are several meters above the
ground.
 Normally, electric power can either be transmitted using over head lines
or underground cables
 The essential of an underground cable are the conductor, the
insulation, the screening, the sheathing, the bedding, the protection
and the serving.
 Underground cables are employed for transmission and distribution of
electric power where it becomes impracticable to make use of
overhead construction.

4. Requirements of underground cables:
 The conductor used in cables should be tinned stranded copper or
aluminium of high conductivity.
 The conductor size should be such that the cable carries the desired load
current without overheating and voltage drop within permissible limits.
 The cable must have proper thickness of insulation in order to give high
degree of safety and reliability at the voltage for which it is designed.
 The cable must be provided with suitable mechanical protection to
withstand the rough use in laying it.
 The materials used in manufacture of cables should be such that there is
complete chemical and physical stability throughout.

5. CONSTRUCTION OF UNDER GROUND CABLES
 A typical underground cable will consist of a conductor/s covered by a
number of insulating and protective layers necessary for its satisfactory
operation. Underground cables construction is explained below:

6. Parts of the underground cables:
Cores or Conductors.
Insulation.
Metallic sheath.
Bedding.
Armouring.
Serving

7. 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. 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.

8. METTALIC 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 fig.
 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.
BEDDING:

9. ARMOURING:
 The armoured cable is a common cable with an extra protective layer
to keep it away from unwanted cut or damage. The armour increases
cable life thus improves the performance, reliability, and safety of the
cable core..
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.

10. CLASSIFICATION OF UNDERGROUND CABLES:
The classification of Underground cables can be done on the basis
of several criteria follows :
1.Number of conductors in the cable
2.Voltage rating of the cable
3.Type and thickness of insulation used
4.Installation and Laying of the cables
ClassificationBasedUponNumberOf ConductorsInTheCable
1.Single core cable
2.Three core cable

11. Classification BasedUpon Voltage Rating Of The Cable
1.Low tension cables: These have a maximum voltage handling capacity of
1000 V (1 kV)
2.High tension cables: These have a maximum voltage handling capacity of
11 kV.
3.Super tension cables: These have a maximum voltage handling capacity of
33 kV.
4.Extra high tension cables: These have a maximum voltage handling
capacity of 66 kV.
5.Extra super voltage cables: These are used for applications with voltage
requirement above 132 kV.
Classification BasedUpon InsulationOf The Cable
Various insulating materials used in cable construction are Rubber, Paper,
PVC, XLPE (Cross linked Polyethene) etc. Such classification is based upon
operating temperature limitations. Following are some insulating materials
used and their maximum operating temperatures.(porcelin)-HIGH VOLTAGE

12. Insulation material Max. operating temperature
PVC TYPE A 75°C
PVC TYPE B 85°C
PVC TYPE C 85°C
XLPE 90°C
RUBBER 90°C
RUBBER – EPR IE-2, EPR IE-3,
EPR IE-4, SILICON IE-5
150°C
ClassificationBasedUponInstallationAndLayingOf TheCable
 Direct Buried
 Trough
 Tunnels
 Gas Insulated Lines

13. Advantages of underground cables:
 Longer Life Expectancy
Underground systems normally last much longer than overhead wiring.
 Reduced Maintenance Costs
Components of underground systems, not being exposed, require less
maintenance.
 Service Uninterrupted by Storms
Underground systems are protected from ice storms, lightning, and
high winds.
 Conserve Valuable Land
Land is a valuable resource, particularly in urban areas. Underground
systems permit the construction of buildings and other structures over
and around them.
 Reduced Fire Fighting Hazards
Fire departments are not hampered, or endangered, by poles and
overhead wires, when erecting their fire-fighting apparatus.

14. Disadvantages of underground cables:
 The installation process through various geographic areas has high
difficulties, because of ground excavation.
 The installation cost of Underground transmission is high, as it requires a
continuous trench or concrete ducts for cable installation. Also, it has a high
material cost due to the requirement of thick and insulated conductors.
 High complications in fault detection.
 Limited by thermal capacity.