UNDERGROUND CABLES
A FUTURE TRANSMISSION LINES
CONTENTS
INTRODUCTION
COMPARISION BETWEEN OVER HEAD
LINES AND UNDER GROUND CABLES
DIFFERENT IMAGES FOR CABLES
CLASSIFICATION OF CABLES
TYPES OF CABLES
MERITS & DEMERITS
CONCLUSION

INTRODUCTION
CABLE: A conductor for transmitting electrical
or optical signals or electric power.
Electrical energy can be transmitted and
distributed with the overhead transmission or by
underground cables. Among these two
underground is more preferred than over head
transmission.
OVERHEAD LINES v/s
UNDERGROUND CABLES
OVERHEAD LINES
Inductance plays predominant
role in overhead lines.
Insulation cost is less in
overhead lines.
Erection cost is also less.
OVERHEAD LINES v/s
UNDERGROUND CABLES...
UNDERGROUND CABLES
Greater safety to the public
and better out look to the
city.
Used in submarine crossings.
Less
interference
with
amenities.
Different images for cables
CLASSIFICATION OF CABLES
 UG cables may be classified according to:
a) Type of insulating material used.
b) Voltage for which they are used. They are:
 Low tension cables {LT} – up to 1000V
 High tension cables{HT} – up to 11kV
 Super tension cables{ST} – up to 33kV
 Extra high tension cables{EHT}–up to 66kV
 Extra super voltage cables – beyond 132kV
TYPES OF CABLES FOR
THREE PHASE SERVICE
In practice, UG cables are used to deliver 3-phase
power. For this purpose, three core cable or three
single core cables may be used.
3-core cable is preferred up to 66kV due to
economic reasons. Different types are:
1)
2)
3)
Belted cables – up to 11kV
Screened cables – from 22kV to 66kV
Pressure cables – beyond 66kV
BELTED CABLE
THREE CORE H-TYPE CABLE
THREE CORE SL TYPE CABLE
THREE CORE FILLER SPACE
CHANNEL OIL FILLED CABLE
SINGLE CORE & THREE
CORE OIL FILLED CABLE
IMPREGNTED PRESSURE
CABLE
ADVANTAGES
1)Less subject to damage from severe weather
conditions (mainly lightning, wind and
freezing).
2)Underground cables pose no hazard to low
flying aircraft or to wildlife.
3)Much less subject to conductor theft, illegal
connections, sabotage and damage from
armed conflict.
DISADVANTAGES
1)UG cable locations are not always obvious,
which can lead to unwary diggers damaging
cables or being electrocuted.
2)Operations are more difficult since the high
reactive power of cables produces large
charging currents and so makes voltage
control more difficult.
DISADVANTAGES...
3) Undergrounding is more expensive,
since the cost of burying cables at
transmission voltages is several times
greater than the overhead power lines
and the life-cycle cost of an underground
power cable is two to four times the cost
of an overhead power line.
CONCLUSION
 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
minimised.