UNDER GROUND CABLES
LAXMI INSTITUTION OF
Sr. no. Name Enrollment No.
1 Kulkarni Ajay A. 150863109004
1 Nakum Dharmesh M. 150863109005
2 Nayakvade Ragini B. 150863109006
3 Parmar Ashish V. 150863109007
Sub: Electrical Power
A Power cable is an assembly of two or
more electrical conductors, usually held together with an
overall sheath. The assembly is used for transmission
of electrical power. Power cables may be installed as
permanent wiring within buildings, buried in the ground, run
overhead, or exposed.
Flexible power cables are used for portable devices, mobile
tools and machinery.
General Constructions of Cable.
Types of Cables
◦ Belted Cables
◦ Screened Type Cables
◦ Super Tension Cables
◦ Oil Filled Cables
◦ Gas Pressure Cables
The types of cables basically
decided based on the voltage
level for which it is
manufactured and material used
for the insulation such as paper,
cotton, rubber etc. the
classification of cables
according to the voltage levels
◦ Low Tension Cables (L.T. Cables)
◦ Medium and High tension Cables
◦ H.T. Cables)
These cables are used for the
voltage level up to 11 kV. The
construction of belted cable is
shown in fig.
◦ The cores are not in circular shape.
◦ The cores are insulated from each
other by use of impregnated paper.
◦ The gaps are filled with fibrous
material like jute.
◦ The belt is covered with lead sheath.
These cables are used for the voltage levels of
22 kV and 33 kV. The two types of screened
◦ H-Type cables
◦ S.L. Type cables
H- Type cables :
◦ Designed by M.
Hochstetler and hence
named H-type cable.
◦ No paper belt in this type
◦ Each conductor is insulated
with a paper, covered with
a metallic screen.
S.L. Cables :
◦ S.L. leads for Separate Lead
◦ Each lead is insulated with
an impregnated paper than
covered by separate sheath
◦ Due to individual lead sheath, core to core fault
possibility gets minimized.
◦ Electrical stresses are radial in nature.
◦ Bending of cable is easy.
◦ Uses solid insulation only like paper.
◦ Mechanical shock can cause voids.
The S.T. cables are intended
for 132 kV to 275 kV voltage
In such cables, the following
methods are specially used to
eliminate the possibility of
◦ Instead of solid type insulation,
low viscosity oils under pressure is
used for impregnation.
◦ Using inert gas at high pressure in
b/w the lead sheath & dielectric.
In case of oil filled
cables, the channels or
ducts are provided
within or adjacent to the
cores, through which oil
under pressure is
◦ It consists of concentric
standard conductor but
built around a hollow
cylindrical steel spiral
core, which acts as a
channel for oil.
◦ Thickness of insulation required is
◦ Thermal resistance is less.
◦ Possibility of voids is completely
◦ Temperature range is high.
◦ Perfect impregnation is possible.
◦ Initial cost is very high.
◦ Long lengths are not possible.
◦ Oil leakage is serious problem.
◦ Complicated maintenance.
An inert gas like N at high
pressure is introduced
lead sheath and dielectric.
Gas like SF6 is also used in
Pressure is about 12-15
Working power factors is
◦ These can carry 1.5 times of the normal load
◦ Maintenance cost is small.
◦ No reservoirs or tanks required.
◦ Power factor is improved.
◦ Ionization and possible void completely eliminated.
◦ The only disadvantage is that the initial cost is