Over Head Lines vs Underground Cables │Electronicsinfos

Comparison between Underground And Overhead Cables 

overhead lines vs underground cables

There are two ways to transmit energy, one is an overhead system and the other is an underground system. In this article, we discuss the comparison of the Overhead system and the underground system of the electrical system. there are many benefits of underground cables. for example, underground cables save from external factors lightning, temperature etc the fault level of underground cables is low as compared to overhead transmission lines. underground cables do not interfere with a communication system. 

The voltage drop due to inductance is low. there are also some disadvantages of underground cables, for example, the initial cost of the system is high, the maintenance cost of the system is high, and the installation cost of the system is also high. there are many types of cables available on the market. the usage of cable depends on working voltage and the nature of services.


A Conductor is used to transmit electrical energy, whether is bare or insulated called a cable. the cable which is used to transmit electrical power in transmission and distribution is called a power cable. the cable which contains proper insulating material and is used underground is called underground cable. normally cable must contain the following property as described below

Properties of Cables

  • The conductor which is used in a cable is a good conductor of electrical energy. therefore we made stranded cables to increase the flexibility and current carrying capacity.
  • the size of the cable is flexible which allows the maximum current at a particular time without heating up.
  • the cable insulation is properly designed so its shows reliability in a system
  • cable provides proper mechanical protection
  • with the material of cable is  stable that not change their property concerning the time

underground cables

  1. underground cables are protected from the lightning effect
  2. the fault level of underground cable is low
  3. .the fault tracking is difficult in underground cables
  4. the maintenance cost plus fault tracking cost is high
  5. the possibility of a public accident is low
  6. bunching of underground cables is difficult.
  7. bunching cost of cable is high
  8. its appearance is good
  9. underground cable not interference in communication lines
  10. the inductive voltage is less as compared to others.
  11. not interfere in road crossing
  12. underground cables are not used for long-distance
  13. we use underground cables in Populated Areas
  14. underground cable is the most reliable and protected
  15. we use underground cables for low voltage to extra high voltages.
  16. the current carrying capacity is low
  17. underground cables have low inductance reactance
  18. the capacitive reactance of underground cable is high
  19. the lifetime of underground cables is long.
  20. tappings are difficult in underground cables.

overhead lines

  1. overhead lines are not protected from the lightning effect
  2. the fault level of overhead lines is higher as compared to underground cables
  3. fault tracking is easy in overhead lines
  4. the maintenance cost of overhead lines is low compared to underground cables
  5. the chance of a public accident is greater as compared to underground cables.
  6. the installation of overhead lines is easy compared to the underground system.
  7. this is low cost as compared to the underground system
  8. the appearance is not good compared to the underground system
  9. overhead lines interfere with communication lines
  10. the voltage drop of overhead lines is high
  11. in populated areas, the preference for overhead lines is not used.
  12. overhead lines system is reliable and durable
  13. they need more space in terms of line structure 
  14. the current carrying capacity is high
  15. the inductive reactance of the overhead system is high
  16. overhead lines system used low voltage to extra high voltage
  17. the capacitance reactance of the overhead system is low
  18. the working life of the overhead system is low compared to the underground system
  19. the voltage drop is high
  20. the installation cost of this system is low compared to the underground system.

Types of cables 

There are three types of cables which are described below

  1. types of cables concerning the core
  2. types of cables concerning voltage
  3. types of cables concerning insulation

w.r.t Core 

there are two types of cables concerning the core first is single-core and another one is three core

  1. Single-core cable
  2. three core cable

 Single-core cable

A single Core cable is made with a stranded conductor which consists of a circular form. we use impregnated insulation I the top of the conductor then we circulate the lead sheath at the insulating.  material. this lead sheath protects the insulation from humidity.in internal generating stations we used plain lead core cable.to protect from corrosion we use that tape as an insulating material.to reduce the eddy current losses we do not use armouring at the single-core cable.

Three core cable

Three core cables consist of the multi-core is called three core cable. we put three-conductor or three cores in a single lead sheath.to protect the three core cables we used steel armouring. we used a three-phase cable to transmit the electrical energy.to consider the economic condition we use three core cables at a voltage level of 66kv. if we increase the voltage above 66kv the cable length and size of the cable are increased.

Types of cables W.r.t voltages 

we divide the cables into different voltages
  1. Low tension cables
  2. High tension cables
  3. Super tension cables
  4. Extra high-voltage cables

Low tension Cables

low tension cables define as which are used up to 1000 voltages. we use paper, varnish cambric, volcanize bitumen, and rubber as insulation material. the low tension cables are also single-core cables.

High-tension cables up to 11 kV

the working voltage of the high-tension cable is up to 11 kV. this type of cable is paper insulated. three core belt type cable is a type of high-tension cable. every core is insulated in its core cable.to protect the cable insulation from the humidity we cover the lead sheath. we also use steel armouring to protect the mechanical strikes.

Super tension cables 22kv to 33 kV

the voltage range of super tension cables is 22kv to 33kv.in belt-type cable, the electrostatic stress is radial form. when the voltage is greater than 22kv the electrostatic stress destroys the insulation and produces a leakage current.to overcome this loss we use a screen-type cable in which the leakage current is earth via the metallic screen. there are three types of screen cables which are described below

  1. H-type cables
  2. S.L type cables
  3. H.S.L type cables

Extra-High voltage cables 

the voltage range is greater than 66kv.to avoid the voids in insulation we used some special cables which are from oil fields. there are two types of pressure cables defined below

  1. Oil-filled Cables
  2. Gas pressure cables

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