Packaged Underground Cables Underground Smart Grid

The replacement of overhead cables providing an electrical power with underground cables is undergrounding. This serves the significant purpose of avoiding power lines from outages due to high wind thunderstorms or heavy snowfall or ice storms…

The Indian National grid is the electric power transmission network of high voltage. The state owned Powergrid Corporation of India operates and maintains the national grid. The installed power generation capacity is 329.23 GW as on 30 June 2017, one of the largest synchronized operational grids in the world.

  The existing Indian grid has electric power transmission and distribution lines, to transmit energy is an overhead power line (conductor) which is suspended by towers/poles. Use of the area below an overhead line is restricted as the objects should not come too close to energized conductors.

Future Prospective Of India, Underground Cables

  The replacement of overhead cables providing an electrical power with underground cables is undergrounding. This serves the significant purpose of avoiding power lines from outages due to high wind thunderstorms or heavy snowfall or ice storms. Overhead power lines are generally used as most of the insulation is provided by air, this reduces the cost of power transmission for large quantities of electric energy. The initial cost of overhead lines might be less but the operational cost may be large. Undergrounding of electric power lines can increase the initial cost but may reduce the operational cost of the cables over the lifetime.
The present National (India) Grid consists of an overhead transmission lines. Looking at the history of blackouts or the power outages in India, it shows that a continuous observation and maintenance is required. The line men are to be ready at all the times to work on the lines as fault may occur at any point of time for any reason. The main reason for the fault is either the poor quality of conductors/cables used for transmission/distribution or due to the electrical theft/ man handling.

  We can observe the negligence of lines handled. When the fault is occurred due to the line breakage, the fault is cleared just by twisting lines instead of providing a joint. In some cases, the conductors are needed to be replaced during fault, at that time the low quality conductors are placed, this may cause fault in future. As such low quality conductors will not be able to withstand the voltage for longer duration and the life span of such materials will be low which results in the replacement again.

  The other main reason of power outage is an electrical theft. As the transmission/distribution lines are barely available, it can be hooked easily and get the power to run their equipment. However, there are lots of studies taking place like HVDS to avoid such faults. Techniques to identify the exact location of fault on the line are possible but the power drawn at the mid of transmission/distribution lines by hooking has not been identified as a fault. These kinds of faults are identified as the particular feeder line draws more than the agreed power.

  As the present, power network is becoming a smart grid this may also lead to a huge blackout if the complete system lines are and stations are not analyzed properly with authorized standard materials and proper network connections. The system seems to be investigated at all the main supply lines and then at the subway (distribution lines) and feeders. This is really not an easy task. If we go for replacement of the system, it is better to opt an undergrounding.

  The electrical accident is also a major cause as we look at the death rate of person or animal or birds due to electrical accidents. The accident may happen either while working on the lines or due to unidentified broken lines laid on the ground. The death rate due to electrical accidents can be reduced by proper undergrounding of cables.

  The Indian grid is divided into five major sections (regional power grids); Eastern grid, Western grid, Northern grid, Southern grid, and North-eastern grid. All these grids can be replaced one by one section completely. But India being a developing country, it is very difficult to replace completely at once. Some of the Indian villages are still not electrified. At this stage, instead of providing electricity supply to these villages if we go in replacement process for existing working electrical transmission/distribution lines makes no sense.

  The undergrounding of electrical lines can be erected stage by stage. Base stage is to start directly erecting underground lines to non-electrified villages instead of overhead lines. Then the remaining all villages are undergrounded. Once all such villages are electrified, then the cities which are surrounded to such villages, in particular to the less dense cities. At later stages in all remaining dense cities lines can be replaced from overhead to underground.
It is easy if the replacement of lines is started from feeder side. So, this method can also be used. Once all the feeders connected to a particular distribution or sub-station are undergrounded. As most of the theft occurs at the distribution line side so that it can be buried first. Later burying of transmission lines connecting receiving station to distribution/ sub-station can be done. The on ground stations (receiving station, sub-station/distribution stations) can be kept as it is or than can also be undergrounded in final stages.

  However, the undergrounding of cables/lines/conductors or even a station can be built, each and every materials used for construction/erection/conduction and for all the purposes including the manhole utmost care has to be taken. If the complete system is built with all positive intension, it lives healthy for a longer period of time.

  The future India with underground electrical power lines

• Enriches the beauty of the nation
• Avoids electrical theft
• Reduces interruption of power supply to the consumer
• Reduced requirement of maintenance
• Reduces the death rate due to electrical accidents
• It is also a step to be a developed nation

Pros & Cons of Underground Cables

Pros

• Damage of conductor from severe weather conditions such as lightning, wind and freezing are reduced.
• Underground cables are less subject to conductor theft, illegal connections.
• The surrounding area is less subjected to electromagnetic fields (EMF). Greater emf may be experienced depending on the depth of the underground cable. The closer grouping of underground power cables results in the reduction of resultant external magnetic field and provides magnetic shielding.
• For the purpose of safety, repair and maintenance, an overhead line requires a surrounding strip of about 20–200 meters wide, whereas a narrower surrounding strip of about 1–10 meters to install (upto 30 m for 400 kV cables during construction) is needed for underground cables.
• No hazard to low flying aircraft or to wildlife from undergrounded cables.
• Burying of cables avoids clearing of trees this convey the environmental benefits.

Cons

• The cost to burry cables at transmission voltages is several times greater compared to overhead power lines. The lifecycle cost of an underground power cable is 2-4 times the cost of an overhead power line. In highly urbanized areas, the cost of underground transmission can be 10-14 times as expensive as overhead. 
• Finding a fault and repairing of overhead lines can be accomplished in hours, whereas underground repairs can take days or weeks.
• The unwary diggers may damage cables as underground cable locations are not always obvious.

  The large charging currents are produced due to high reactive power of underground cables; this makes the operation more difficult and also difficult the voltage control.

  Generally, transmission and distribution companies future-proof underground lines with the highest-rated cables to install, this being still cost-effective.

  In some cases, the advantages can outweigh the disadvantages of the investment cost, maintenance and management.


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