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| underground distribution system |
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| overhead distribution system |
1.public safety
If we comment about public safety keeping in view both underground and overhead then it is obvious that underground system is more safe publicly as all the distribution wiring is underground.
2.flexibility
The overhead system is more flexible as compared to underground as we can modify overhead system whenever needed but underground once place then its modification is not possible for modification new instrumentation is required.
3.initial cost
The components used in underground like cables,manholes and other components are more expensive as compared to overhead.So underground is more expensive.Normally underground system has five to ten times more cost than overhead system.
4.faults
The probability of faults in underground is least as qualitative insulation is provided here.But faults occurrence will be more for the overhead distribution system as many environmental factors affect the overhead distribution system.
5.appearance
The appearance of underground system is better as compared with overhead as in underground all wiring system is invisible so public is forcing different companies to turn overhead to underground system.
Less subject to damage from severe weather conditions (mainly lightning, wind and freezing)
Reduced range of electromagnetic fields (EMF) emission, into the surrounding area. However depending on the depth of the underground cable, greater emf may be experienced. The electric current in the cable conductor produces a magnetic field, but the closer grouping of underground power cables reduces the resultant external magnetic field and further magnetic shielding may be provided. See Electromagnetic radiation and health.
Underground cables need a narrower surrounding strip of about 1–10 meters to install (up to 30 m for 400 kV cables during construction), whereas an overhead line requires a surrounding strip of about 20–200 meters wide to be kept permanently clear for safety, maintenance and repair.
Underground cables pose no hazard to low flying aircraft or to wildlife.
Much less subject to conductor theft, illegal connections, sabotage, and damage from armed conflict.
Burying utility lines makes room for more large trees on sidewalks which convey environmental benefits and increase property values
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.
Underground cable locations are not always obvious, which can lead to unwary diggers damaging cables or being electrocuted.
Operations are more difficult since the high reactive power of underground cables produces large charging currents and so makes voltage control more difficult.
Whereas overhead lines can easily be uprated by modifying line clearances and power poles to carry more power, underground cables cannot be uprated and must be supplemented or replaced to increase capacity. Transmission and distribution companies generally future-proof underground lines by installing the highest-rated cables while being still cost-effective.
Underground cables are more subject to damage by ground movement. The 2011 Christchurch earthquake in New Zealand caused damage to 360 kilometres (220 mi) of high voltage underground cables and subsequently cut power to large parts of Christchurch city, whereas only a few kilometres of overhead lines were damaged, largely due to pole foundations being compromised by liquefaction.
Courtesy of wikipedia....
6.fault location and repairs
Normally in underground system fault location is extremely tough task and furthermore after fault location fault repairing is further difficult task but in overhead fault location and repairing is much easy and simple.7.interference with communication circuits
The electromagnetic interference occurs in overhead of the system with telephones lines.But such interference is not associate with underground system.8.maintenance cost
The maintenance cost for underground system is very negligible as chance of fault due to various factors are small and this cost is associated to overhead system to the considerable amount.9.useful life
The useful life for overhead system is less whereas for underground this is more and more long.The useful life for underground system is almost 50 years and almost 25 years for overhead distribution system.10.current carrying capacity and voltage drop
An overhead system has considerably large amount of current carrying capacity as compared with underground system of the same conductor material and same area of cross section.Comparison
The aerial cables that carry high-voltage electricity and are supported by large pylons are generally considered an unattractive feature of the countryside. Underground cables can transmit power across densely populated or areas where land is costly or environmentally or aesthetically sensitive. Underground and underwater crossings may be a practical alternative for crossing rivers.
Advantages
Less subject to damage from severe weather conditions (mainly lightning, wind and freezing)Reduced range of electromagnetic fields (EMF) emission, into the surrounding area. However depending on the depth of the underground cable, greater emf may be experienced. The electric current in the cable conductor produces a magnetic field, but the closer grouping of underground power cables reduces the resultant external magnetic field and further magnetic shielding may be provided. See Electromagnetic radiation and health.
Underground cables need a narrower surrounding strip of about 1–10 meters to install (up to 30 m for 400 kV cables during construction), whereas an overhead line requires a surrounding strip of about 20–200 meters wide to be kept permanently clear for safety, maintenance and repair.
Underground cables pose no hazard to low flying aircraft or to wildlife.
Much less subject to conductor theft, illegal connections, sabotage, and damage from armed conflict.
Burying utility lines makes room for more large trees on sidewalks which convey environmental benefits and increase property values
Disadvantages
Undergrounding 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. Above ground lines cost around $10 per foot and underground lines cost in the range of $20 to $40 per foot In highly urbanized areas the cost of underground transmission can be 10-14 times as expensive as overhead.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.
Underground cable locations are not always obvious, which can lead to unwary diggers damaging cables or being electrocuted.
Operations are more difficult since the high reactive power of underground cables produces large charging currents and so makes voltage control more difficult.
Whereas overhead lines can easily be uprated by modifying line clearances and power poles to carry more power, underground cables cannot be uprated and must be supplemented or replaced to increase capacity. Transmission and distribution companies generally future-proof underground lines by installing the highest-rated cables while being still cost-effective.
Underground cables are more subject to damage by ground movement. The 2011 Christchurch earthquake in New Zealand caused damage to 360 kilometres (220 mi) of high voltage underground cables and subsequently cut power to large parts of Christchurch city, whereas only a few kilometres of overhead lines were damaged, largely due to pole foundations being compromised by liquefaction.
Courtesy of wikipedia....
Very usefull
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