Comparison between Overhead Lines and Underground Cables

 

Comparison between Overhead Lines and Underground Cables

	Overhead Line	Underground cable
Fault location	As the overhead line is visible, it is easy to find the location of the fault.	As the underground cable is invisible, it is very difficult to find the location of the fault.
Initial cost	There is no requirement of digging, manholes, and trench. So, the overhead line system is cheaper than the underground system.	The initial cost of the underground transmission system is more compared to the overhead line because it needs digging, trenching, etc.
Chance of fault	As overhead line exposed to the environment, the chances of faults are more.	The cables are not exposed to the environment, there is less chance of fault.
Safety	This system is less safe as the conductors placed on the towers.	This system is safer as the cables placed underground.
Useful life	In this system, useful life is approximately 20 to 25 years.	Useful life is approximately 40 to 50 years.
Appearance	The general appearance of this system is not good because of all lines are visible.	The general appearance of this system is good because of all lines are invisible.
Maintenance cost	In this system, no need to dig at the time of maintenance. Hence, for the same number of faults, the maintenance cost is less.	In this system, to find the fault, digging is compulsory. It increases labor cost. Hence, for the same number of faults, the maintenance cost is more.
Flexibility	This system is more flexible. Because the expansion of the system is easily possible.	This system is not flexible. The expansion cost is nearly equal to the new erection of the system.
Conductor size	The conductors placed in atmosphere. So, the heat dissipation is better. Therefore the size of the conductor is small compared to the underground system.	Because of the poor heat dissipation, the size of the cables is more.
Interference with the communication line	The communication lines are run along the transmission line. In this case, it is possible to cause electromagnetic interference.	In this case, there is no chance of interference with communication lines.
Proximity effect	The distance between the conductor is very high. So, proximity effect does not affect.	As the distance between cables is very less, the proximity effect is very high.
Application	The cost of this system is low. Therefor overhead lines used in the long transmission system and in rural areas for the distribution system.	Because of the high cost, it uses in the short distance and in populated areas. Where space is a major problem for the overhead transmission line.

Standardization of Transmission System Voltage

 Standardization of Transmission System Voltage

There is much variation in transmission voltages in different countries. Each country have different voltage level as per there requirments. Earlier individual makes  an attempts to fix voltage levels for higher power transmission but such an attempt had resulted in wastage of time and higher cost because of designs of varied nature. Hence, the transmission voltages had to be standardized. The various advantages of standardization of transmission voltage are:

1.      Standardization provides better facilities for research and development.

2.      The equipments can be manufactured with greater economy and reliability.

3.      Systems are easily interconnected.

Hence standardization enables to carry out joint efforts to tackle Extra High Voltage (EHV) or Ultra High Voltage (UHV) problems. By standardizing, the voltage level can be adopted for a reasonable period of time before next change. The choice of the highest system voltage for a country is a matter of great significance. It is not merely the economic factors that influence the next higher voltage but the site of power station, location and density of load, and the technological developments are also kept in mind. The next higher voltage level should also be selected on the basis of future load enhancements. The interval between the existing and the proposed voltage level should be judiciously spaced, as too small interval between the voltages will result in a short life of the proposed voltage level. At the same time too large interval would lead to heavy expenditure. It is therefore desirable that the next voltage selected should be at least two steps higher than the existing one.  

The various AC voltages adopted by different countries above 220 kV are 275, 345, 380, 400, 500, 735, 765, 1000, 1100, 1200 kV etc. The AC transmission voltages adopted in India are 220 kV, 400 kV and 765 kV. The next higher AC transmission voltage selected is 1200 kV.

Smart Grids

     A Smart Grid is an electricity Network based on Digital Technology that is used to supply electricity to consumers via Two-Way Digital Communication. This system allows for monitoring, analysis, control and communication within the supply chain to help improve efficiency, reduce the energy consumption and cost and maximize the transparency and reliability of the energy supply chain.

    Smart grid is a large ‘System of Systems’, where each functional domain consists of three layers: 

(i) the power and energy layer, 

(ii) the communication layer, and 

(iii) the IT/computer layer.

     Layers (ii) and (iii) above are the enabling infrastructure that makes the existing power and energy infrastructure ‘smarter’.

It uses smart meters and appliances, renewable and efficient energy resources.

• The system delivers electricity via 2-way digital communication. It allows consumers to interact with the grid.
•  It reduces energy consumption and reduces cost to the consumers by smart means. Electric supply companies make efficient usage of energy and consecutively will be able to meet the varying load demands of the consumers.

Features of Smart Grid

    Smart grid has several positive features that give direct benefit to consumers:

• Real time monitoring.
• Automated outage management and faster restoration.
• Dynamic pricing mechanisms.
• Incentivize consumers to alter usage during different times of day based on pricing signals.
• Better energy management.
• In-house displays.
• Web portals and mobile apps.
• Track and manage energy usage.
• Opportunities to reduce and conserve electricity etc.

Benefits of Smart Grid Deployments

• Peak load management, improved QoS and reliability.
• Reduction in power purchase cost.
• Better asset management.
• Increased grid visibility and self-healing grids.
• Renewable integration and accessibility to electricity.
• Satisfied customers and financially sound utilities etc.

Smart Grid Architecture Components

The figure depicts generic Smart Grid Network Architecture components or modules with different reference points. As shown typical smart grid network consists of following components.

• Grid domain (Operations include bulk generation, distribution, transmission)

• Smart meters

• Consumer domain (HAN (Home Area Network) consists of smart appliances and more)

• Communication network (Connects smart meters with consumers and electricity company for energy monitoring and control operations, include various wireless technologies such as zigbee, wifi, HomePlug, cellular (GSM, GPRS, 3G, 4G-LTE) etc.

• Third party Service providers (system vendors, operators, web companies etc.)