What are power cables and types of power cable

What is a Power cable

Power cables are used for the transmission of electric power they are used to transmit power from substations to required locations. Power cables can be installed as overhead or underground according to the needs, it is an assembly of two or more conductors and it is protected with an outer coating and this protective coating is called as insulation.

Types of the power cable

Belted cables

In this type, the conductors are wrapped with oil-impregnated paper and then the cores are assembled with filler material after that the assembly is enclosed by a paper insulating belt. It is used for voltage range up to 11kv in some cases it could be used up to 22KV. Voltages above 22KV, tangential stress should be considered

Because of the low insulation strength of the paper the tangential stress will set up and it will create leakage current and it can cause local heating which may result in braking of insulation

Screened cables

These cables can be used up to the voltage range of 33KV, but in certain cases, it can be extended up to 66KV. Screened type cables are divided into two types they are

H-type cable

In this type each core is insulated by a layer of impregnated paper, each core insulation is covered with a metallic screen and it is usually of perforated aluminum foil and the core is laid in a manner that metallic screen would make contact with one another. The metallic screen is the advantage of H-type because it can assist in complete impregnation of the cable with compound, so by that, it can eliminate the air pockets or voids in the dielectric. The metallic screen can also increase the heat dissipation power of the cable

S.L type

Each core insulation is covered with its own lead sheath and because of that it has certain advantages like minimizing the possibility of the core to core breakdown and another advantage is that the cable bending is easy due to the elimination of overall sheath. This type of cable is thinner than the H-type so greater care is needed for manufacturing

Pressurized type cables

In this cable the cable pressure is maintained above atmosphere by using oil or gas, gas pressure cables are used up to 275KV and oil-filled cables are used up to 500KV

Oil-filled cables

Low viscosity oil is used and it is kept under pressure and it fills the voids in the oil-impregnated paper under all conditions of varying load. Oil-filled cables are divided into three types they are self-contained circular type, self-contained flat type, and pipe type cables

Advantages of oil-filled cables

  • Greater operating dielectric stress
  • Greater working temperature and current carrying capacity
  • Better impregnation
  • Impregnation is possible after sheath
  • .no void formation
  • Cable size is small due to reduced dielectric thickness
  • Defects can be detected by oil leakage

Gas pressure cables

In this type inert gases like nitrogen is used to exert pressure on paper dielectric to avoid void formation they are also called compression cables and its insulated core is similar to solid type. The cable is inserted in a pressure vessel which could be rigid steel type and it is mostly known as pipeline compression cables

Gas-insulated cables

In this type high-pressure sulphur hexafluoride is used to fill the small spaces in oil-impregnated paper insulation and it will suppress the ionization. Mostly EHV and UHV lines are filled with SF6  which is used widely for voltages above 132KV – 1200KV. These cables are mostly used for short lengths such as river and highway crossing

Advantages of Gas-insulated cables

  •  Efficient heat transfer so it can carry more current
  • Low capacitance and low dielectric loss
  • SF6 gas is non-toxic, non-flammable and chemically stable

  • Termination of these cables are simpler and cheaper

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