1. DATTA MEGHE INSTITUTE OF ENGINEERING
TECHNOLOGY AND RESEARCH,WARDHA.
MR. SURYAKANT B. MOREY
DEPARTMENT OF ELECTRICAL ENGINEERING
CABLES AND DISTRIBUTION LINES
An electric cable is a group of one, two or more wires or optical fibers bound
together, in a common protective jacket or sheath. Individual cables or fibers inside the
jacket are usually covered or insulated. There are combination cables, made by
manufacturers and may contain both electrical wires and optical fibers. Copper electrical
wires are most commonly used because of its excellent conductivity. Aluminum electrical
wires are also used as they are less expensive.
Electrical cables are sometimes made more flexible by stranding the wires. The process
involves twisting or braiding the smaller individual wires to produce larger wires that are
far more flexible. Small electrical wires are also bunched before concentric stranding,
thereby adding more flexibility.
3. MATERIALS FOR ELECTRICAL
The electrical cables we use are made of various types of materials. A electrical
cable has several layers and different layers are made from different materials. The
conductors in the electric cables are usually made of metals or metallic alloys because
metals are good conductor of electricity and also they are strong, ductile and durable.
Similarly, the insulation of cables are made of such materials which are heat resistant,
flexible, durable and non conducting. So we can categorize the electric cables on the
basis of materials with which they are made.
Copper Electric Cables
•Aluminum Electric Cables
•Tungsten Electric Cables
•Teflon Electric Cables
Why Aluminum is suitable for making Electric Cable?
High electrical conductivity: Aluminum has very high electrical conductivity. So it is good for
making electrical cables.
High ductility: Its ductility is very high which makes it perfect for drawing large wires.
Light weight: Aluminum weighs about one third of copper, nickel, brass, and steel. Its specific
gravity is 2.7. So the cables made of them are very light weight, hence suitable for long distance
cabling. They are also useful in overhead cabling.
High resistance to corrosion: Aluminum is resistant to corrosion which makes it perfect for
manufacturing underwater cables.
High strength: The high strength of aluminum prevent it from creeping even under high load.
Economical: Aluminum is the most economical element and hence the cables are cheaper than
copper, their nearest competitor.
Physical properties: Aluminum is silvery white metal and highly reflective to heat and light. It is
easily machinable and can have various surface finishes. It is easily recyclable.
Non magnetic: Aluminum is non-magnetic in nature which is an important property for making
armors and raceways.
5. COAXIAL CABLES -
Coaxial cables are a type of electrical cables, which consist of a round conducting
wire that is surrounded by an insulating spacer, and which is again surrounded by a
cylindrical conducting sheath. All these layers are surrounded by a final insulating layer.
Coaxial cable is used as a high-frequency transmission line for carrying a high-frequency or
6. UNDERGROUND Vs OVERHEAD
Electric power can also be transmitted by underground power cables instead of overhead power
lines. They can assist the transmission of power across:
1.Densely populated urban areas
2.Areas where land is unavailable or planning consent is difficult
3.Rivers and other natural obstacles
4.Land with outstanding natural or environmental heritage
5.Areas of significant or prestigious infrastructural development
6.Land whose value must be maintained for future urban expansion and rural development
Some other advantages of underground power cables:
1. Less subject to damage from severe weather conditions (mainly wind and freezing)
2.Greatly reduced emission, into the surrounding area, of electromagnetic fields (EMF). All electric
currents generate EMF, but the shielding provided by the earth surrounding underground cables
restricts their range and power.
3. Underground cables need a narrower surrounding strip of about 1- 10 meters to install, whereas an
overhead line requires a surrounding strip of about 20- 200 meters wide to be kept permanently clear
for safety, maintenance and repair.
Some disadvantages of underground power cables:
1.Under grounding is more expensive, since the cost of burying cables at
transmission voltages is several times greater than 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. This is mainly due to the limit of the physical properties of the
insulation placed during installation, keeping the runs to hundreds of meters
between splices, which are most commonly placed in manholes or splice-boxes for
2.Whereas finding and repairing overhead wire breaks can be accomplished in
hours, underground repairs can take days or weeks, and for this reason
redundant lines are run.
3.Operations are more difficult since the high reactive power of underground
cables produces large charging currents and so makes voltage control more
An insulator, also called a dielectric, is a material that resists the flow of electric current. An
insulating material has atoms with tightly bonded valence electrons. These materials are used in
parts of electrical equipment, also called insulators or insulation, intended to support or separate
electrical conductors without passing current through themselves. The term is also used more
specifically to refer to insulating supports that attach electric power transmission wires to utility
poles or pylons.
Some materials such as glass or Teflon are very good electrical insulators. A much larger class of
materials, for example rubber-like polymers and most plastics are still "good enough" to insulate
electrical wiring and cables even though they may have lower bulk resistivity. These materials can
serve as practical and safe insulators for low to moderate voltages.
The various types of insulators available are –
1.Pin type insulators
2.Suspension type insulators
• A strain insulator is an insulator
that provides both large
electrical insulation and a large
load-bearing capacity. Strain
insulators were first used in
telegraph systems to isolate
the signal wire from ground
while still supporting the wire.
• Strain insulators are used to
support radio antennas and
overhead power lines.