Undergrounding is the replacement of overhead cables that provide including underground cables which are electrical power or telecommunications. It demonstrates superior technology in developed countries to prevent fire and to make power lines less susceptible to scattering during high wind thunderstorms or heavy snow or ice storms.
An additional advantage of undergrounding is the aesthetic quality of the landscape without power lines. Undergrounding can increase the initial cost of electrical transmission and distribution, but can also reduce the lifetime operational cost of wires.
History Underground cable
Early uses of undergrounding were a basis for detonating mineral explosives, and underside telegraph cables Had power cables were used in Russia in 1812 to detonate mine explosives and in 1850 to carry telegraph signals across the English Channel.
Undergrounding also began to increase with the expansion of early electrical power systems. Thomas Edison used underground DC “street pipes” in his early distribution networks; these were first heated with jute before rubber insulation was introduced in 1882.
Subsequent events occurred in both insulation and fabrication techniques:
- 1925: Pressurized paper insulation is used in wires
- 1930: PVC insulation is used in cables
- 1942: First used on polyethylene insulating wire
- 1962: Insulated cables of Ethylene propylene rubber-
- become commercially available
- 1963: Preformed wire accessories become available
- The 1970s: Compressed cable accessories available
- In the twentieth century, the directly buried cable became common.
Benefits of Underground cable, electrical wire
- Fewer causes of damage due to severe weather (mainly thunderstorms, cyclones/cyclones/typhoons, tornadoes, other winds, and freezing)
- The electromagnetic field (EMF) emission range in the surrounding area has decreased. However, depending on the depth of the underground cable; Larger EMFs can be experienced on the surface. The electric current in the wire conductor creates a magnetic field but grouping closer to the underground power cables reduces the external magnetic field and can provide more magnetic ideal. See Electromagnetic Radiation and Health.
- Installing underground cables requires a narrow strip around 1-10 miles (up to 30 meters for 400 kV cable during construction), while a strip around 20-200 meters wide of an overhead line is to be kept permanently clean for protection, maintenance, and repair.
- Underground cables pose no risk to low-flying aircraft or wildlife.
- By human activities, damage from underground cables is greatly easily to reduced such as theft, illegal connections,  sabotage, and accidents.
- Burying the utility line gives way to larger trees on the sidewalk, making the trees more environmentally friendly and increasing property value.
- Undergrounding is more expensive since the cost of burying wires at transmission voltages is several times higher than that of overhead power lines and the life cycle cost of underground power cables is two to four times more than the cost of an overhead power line. The above-ground lines cost 10 per foot and the underground lines cost from 20 to 40 per foot. In high urban areas, the cost of group transmission can be 10-15 times more expensive than overhead. However, these calculations may neglect the expenditure of power constraints. For low-voltage distribution networks, the lifetime cost difference is less in the range of 12-28% higher than the overhead line of equivalent voltage.
- Overhead cable break detection and repair can be ok within hours, underground restoration can take days or weeks, and this is why unnecessary lines are wielded.
- The locations of underground wires are not always explicit, which can damage irrational digging wires or electrified of electrical.
- The high reactive power of the underground cable creates large charging currents and therefore makes the voltage control are more difficult that’s why the operations are a lot of hard.
Larger charging currents arise due to higher capacitance from underground power lines and thus limit how long an AC line can last. When undergrounding long-distance transmission lines, it avoids capacitance problems. HVDC lines can be used as they do not suffer from the same problem.
- By modifying line clearance overhead lines can be easily improved and power poles to carry more power, and undergrounding all cables cannot be operated and need to increase capacity. Transmission and distribution companies usually install high-rated cables while still being future-underground lines.
- Underground cables do more damage to ground movement. The 2011 Christchurch earthquake, caused New Zealand 360 kilometers (220 miles) of high voltage underground cable and large parts of the city of Christchurch would subsequently lose cut power. It was Since only a few kilometers of the overhead line that was damaged, mainly due to the polar foundation being compromised.
- The advantages may in some cases outweigh the higher investment costs and more costly maintenance and management difficulties.
Methods of Underground cable
Horizontal annoyance – This is a method that uses a drill bit to create an arch underground to start horizontally at one stage of the soil surface and return to the surface. This method is used if the minimum surface damage is preferred.
The UK Regulatory Office of Gas and Electricity Markets (FGEM) allows transmission companies to recover the cost of undergrounding their prices to customers. To qualify, undergrounding must be in designated areas of national parks or designated natural beauty.
The most noticeable overhead cables of the main transmission network have been excluded from this project. By national lottery earnings, Some undergrounding projects are funded. All low and medium voltage electrical power (<50 kV) in the Netherlands is now supplied underground.
In Germany, 73% of medium voltage cables are underground and 87% of low voltage cables are underground. The high percentage of underground cables contributes to very high grid reliability
(SAIDI <20). By comparison, the SAIDI standard in the Netherlands (minutes per year without electricity) is about 30 and in the UK it is about 70.
In the United States, Rule 20 of the California Public Utilities Commission (CPUC) allows the undergrounding of electric power cables under certain circumstances. Rule 20A All customers of utility companies pay for projects. Rule BB projects are partially funded in this way and cover the cost of equivalent overhead systems. Rule 20C enables project property owners to fund undergrounding.
Most of Japan’s electrical energy is still distributing by wind cables. In 23 wards in Tokyo, only 7.3 percent of the cable is lying underground as of March 2008, according to Japan’s Ministry of Construction and Transportation Equipment.
One compromise between undergrounding and overhead line use is to install air cables. For telecommunication services or power transmission, Aerial cables are insulated cables to cut between poles and used. One advantage of aerial wires is that their insulation eliminates the risk of electric shock (only if the wires are not damaged). Another advantage is the cost of burying them – especially in rocky areas. The disadvantages of aerial wires are that they have the same aesthetic problems as standard overhead lines and can be affected by storms. However, there is no interruption of service if the insulation is not destroyed during pylon failure or injury to a tree. Electrical risk is reduced and it is possible to re-hang cables without power outages.