What Is The Structure Of Electrical Cable? | Advantage Of XLPE Cable - MS3 Naveen Kumar

What is the structure of Electrical Cable? | Advantage of XLPE Cable

Reading time 7 Min

Electrical Cable

An Electrical cable is an assembly of one or more wires running side by side or bundled, which is used to carry electric current. It is used to connect two or more devices, enabling to transfer the electrical signals or electrons from one device to the other.

Types of Electrical Cable

PVC Electrical Cable

If we talk about the PVC cable then first of all we have to understand what is PVC. So let me explain that in PVC cable PVC stands for Poly Vinyl Chloride. It is a thermoplastic resin, which means it can be softened by heating and is produced by a process known as polymerization.

PVC is resistant to corrosion, shock proof, scratch proof, PVC not change their properties with climate change, and even chemical decomposing. It is entirely non-toxic, and it has been deemed for having no more effect on the environment.

PVC will burn when exposed to fire but, it is self extinguishing that means if the external source of fire is taken away it will self extinguish. The maximum operating temperature of PVC Cable is 70 degree Celsius.

Since the maximum operating temperature of PVC is only 70 degree Celsius, hence it is only used in low and medium line voltage.

XLPE Electrical Cable

Electric Cable

Before going for the XLPE cable first of all we have to know about XLPE. XLPE stands for Cross Linked Poly Ethylene. XLPE have better resistivity and also having higher thermal property. Due to excellent thermal tolerance properties, the current carrying capacity of XLPE cable is higher than conventional cable.

These cables have better resistance to salinity of water in the ground, chemicals, oil, corrosion and have longer life. Maximum operating temperature of XLPE cable is 90 degree Celsius which is suitable for high voltage and extra high voltage.

XLPE cable consists of one or more conductors covered with suitable insulation and is surrounded by protecting cover. Conductors used in cable should be tinned stranded copper or aluminum of high conductivity. Stranding is done so that conductor may become flexible and carry more current.

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 so that it may withstand the rough use in laying it.

XLPE cable cable can also be use for over head network, in fact if we for 11 KV the current carrying capacity of cable will increase. The only thing we have to remember that we have to run a messenger wire to support the cable.

AB Cable

Electric Cable
Electric Cable

AB Cable (Aerial Bunched Cables) is a very common concept for Over Head Power distribution. it is mainly used in rural distribution and specially for installation in hilly areas, forest area and coastal area. As compared to the conventional bare conductor over head distribution system,  ABC provides higher safety and reliability, lower power losses and ultimate system economy by reducing installation, maintenance and operative cost.

Construction of Electrical Cable

Construction of cable

As we know Electric cable is made of different layers, if count all the layer or parts of HT cable you will found there is total 9 layer in any HT cables. All type of cable are manufactured as Indian

Core or Conductor

A cable may have one or more than one core depending upon the type of service for which it is used. The conductors are made of tinned copper or aluminium and are usually stranded in order to provide flexibility to the cable

Conductor Screen

Material used for conductor screen is Extruded Thermoset Semi Conducting compound, carbon paper and carbon loaded polymer. The purpose of conductor screen is to maintain a uniformly divergent of electric field and to contain the electric field within the cable cores. It  also reduces voltage stress at the interface between the conducting and insulating components. It provides a cylindrical, smooth surface between the conductor and insulation.

Insulation

Each core or conductor is provided with suitable thickness of insulation. The thickness of layer depends upon the voltage to be withstood by the cable.

Insulation Screen

Material used for conductor screen is Extruded Thermoset Semi Conducting compound, carbon paper and carbon loaded polymer. A semi conducting layer is applied over the insulation layer to ensure that the electric stress is homogenous around the insulated core. While doing any termination or cable joint work, it is necessary to remove that insulation screen.

Metallic Sheath

The metallic sheath needs to be electrically continuous over a cable length. The purpose of metallic screen is to nullify the electric field outside of the cable. this sheath needs to be continuous over the length of cable. This metallic screen needs to connect to earth at least at one point along the route to provide a path for fault and leakage current.

The other function of metallic sheaths is to block water and form a radial barrier to prevent humidity from penetrating the cable insulation system.

Fillers

Before telling about filler let me clear one point that there is no any technical reason in terms of electrical, behind providing the filler. The purpose of providing the filler is to only maintaining the roundness of cable. The material used for filler is PVC.

PVC Inner sheath

The purpose of providing PVC Inner sheath to provide the circular shape to cable and it also provides bedding for armouring. Inner sheath is made up by wrapping thermoplastic tape. All multi core cable have either extruded PVC inner sheath or thermoplastic wrapped inner sheath, which is compatible with insulation material and removable without any damage to insulation.

Armour

Armour provides the protection against external mechanical forces and carries current during asymmetrical fault conditions.

When talking about armour we often seen that, in three core or multi core cable galvanized steel wire or strip used and for single core cable Aluminium armour used.  So let clear this point for three core or multi core Core cables the vector sum of current in conductor is zero and there is virtually no resultant magnetic flux.

But in single core cable eddy current heating would occur if magnetic material was used for armoring, and this may lead to failure of cable. Hence for single core cable non magnetic material (Aluminium) is used for armoring the cable.

PVC Outer Sheath

It is the outer protection part of cable against the surrounding environment, weather, chemical and electrical protection. It is made of PVC.

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