Overhead And Underground Electrical Distribution System|Overhead Lines Vs Underground Cables

Contents

What is an Electrical distribution system?

The electrical system, which distributes electrical energy to the consumers, is known as a distribution system.

The electrical system between the substations and service mains is known as a distribution system.

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There are two types of distribution systems: primary and secondary distributions.

The power, which is received at 33 kV, 66 kV or 110 kV, is stepped down to 11 kV, where the power is distributed along main roads and is called the primary distribution system.

The power is distributed through distribution lines called distributors, which run along the streets of consumers.

The distribution lines, which feed the power from primary distribution to the distributor, are called feeders.

The power is then distributed to the consumers from the distributors using service lines.

Therefore, feeders, along with service lines, make up the secondary distribution system.

Essential Components of Transmission and Distribution Systems

Both transmission and distribution of electrical energy from generating stations to consumers can be done using overhead lines or underground cables.

Components of Overhead Lines

The essential components of overhead lines, which can be used for transmitting or distributing electrical energy are:

Conductors, which are used to carry electrical power from the sending-end to the receiving-end of a particular station.
Support, which is provided using poles or towers, helps in keeping the conductors at a suitable height from the ground.
Insulators, which are used to insulate the conductors from the ground.
Cross-arms are used to provide support to the insulators.
Miscellaneous items like lightning arrestors, phase plates and so on.

Components of Underground Cables

Schematic Diagram of an Underground able

The essential components of underground cables are shown in Figure which can be used for transmitting or distributing electrical energy.

The various components of the cables are explained as follows:

Cores or conductors, which are made up of stranded tinned copper or aluminium to provide flexibility to the cable.
Insulation is a layer, which is placed above the conductor, with a suitable thickness that decides the maximum voltage that can be transmitted through the cable.
Metallic sheath is provided in the cable to protect the cable from moisture, gases or other liquids, which could damage the cable.
Bedding, which is made up of fibrous material like jute or hessian tape, is provided over the metallic sheath to prevent it from corrosion and other mechanical injuries.
Armouring, which is made up of galvanized steel wire or steel tape, to protect the cable while it is being laid or handled.
Serving is used for protecting the armouring from atmospheric conditions and is made up of a fibrous material called jute.

Comparison Between Overhead Lines and Underground Cables

Even though the electrical energy can be transmitted or distributed using overhead lines and underground cables, the selection of one over the other is based on the following reasons listed in Table below.

Overhead Lines Vs Underground Cables

Parameter	Overhead Lines	Underground Cables
Public safety	More dangerous to the public	Less hazardous to the public
Initial cost	Less costly	It is 10 times the cost of an overhead line
Flexibility	More flexible and can be modified easily	Less flexible
Faults	Chance of fault occurrence is more	Less chance of fault occurrence
Appearance	Bad, since the wiring is visible	Good, since the wiring is not visible
Fault location and repair	Easier to locate the fault and repair it	Difficult to locate the fault and repair it
Useful life	Less	More
Maintenance cost	High	Very low
Interference with communication circuits	Faces problems due to interference	No interference with the communication circuits
Lightning	Liable to hazards from lightning	Not liable to hazards from lightning
Submarine crossings	Cannot be used	Can be used
Transmission	Used for long-distance transmission	Used for short-distance transmission