Power Systems Stability

What do you understand by Interconnection of Power Systems? Describe its advantages & disadvantages.Name the various power grids in India.

A worldwide trend in the development of power systems is to build interconnections with the goal to achieve economical benefits. Such large interconnected systems can cover many countries or even wide continental areas. Interconnections of power systems may offer significant technical, economical and environmental advantages, such as pooling of large power generation stations, sharing of spinning reserve and use of most economic energy resources taking into account also ecological constraints: nuclear power stations at special locations, hydro energy from remote areas, solar energy from desert areas and connection of large off-shore wind farms.

The liberalization in the power industry also supports more interconnections to enable the exchange of power among the regions or countries and to transport cheaper energy over long distances to the load centers. Examples for such interconnections are systems in Russia, North America, Europe and Asia. However, there are technical and economical limitations in the interconnections if the energy has to be transmitted over extremely long distances. In future, the situation can, however, change if ecological and political terms change or the present cost conditions alternate.

The interconnections are mostly realized by synchronous links where such solutions are technically feasible and economically justified. On the other hand HVDC links often offer technically better and more economical solutions. A large number of examples worldwide shows, that HVDC is a quite suitable solution. However, in many situations, hybrid solutions for interconnection are more advantageous: a synchronous high voltage AC link, supported by an additional HVDC link. In cases where the synchronous interconnection is technically at the limit, HVDC can support the operation of the interconnected systems and thus makes the synchronous AC link more reliable.

In case of an isolated plant, a considerable amount of the reserve capacity would be required to ensure the continuity of the supply, to provide an uninterrupted power supply. This would naturally increase the capital cost of the power station resulting in increase in the fixed cost owing to interest and depreciation.

In some parts of the country there are large resources of generating power but their requirement is low whereas in other parts power requirement is large as compared to available resources of power.

These above difficulties can be overcome by interconnecting power stations. Interconnection of power stations increases the reliability of the supply, reduces the reserve capacity required, improves the load factor, diversity factor and efficiency, makes use of more efficient plants as base load plants and less efficient plants as peak load plants possible and reduces the capital cost per kW and overall cost per unit generated.

However, the problems of load and frequency control are more difficult in large interconnected systems with many power stations scattered over a wide area in comparison with a system having one or two generating stations.

1 | P a g e Submitted by : Rohan Sharma

Power Systems Stability

Power Grids in INDIA:

The objective of Power Grid Corporation of India Ltd is to create a strong and vibrant National Grid in the country to ensure the optimum utilization of generating resources, conservation of an eco-sensitive right of way and the flexibility to accommodate the uncertainty of generation plans.With the modernization of RLDCs and implementation of various inter-regional links, inter-regional power exchange has grown manifold. During FY 2007-08, about 43,000 MUs of inter-regional energy transfer was facilitated--an increase of about 13% compared to the previous year (about 38,000 MU). Growth of inter-regional power exchange has helped in meeting more demand in energy deficit regions besides achieving overall economy. Inter-regional power transfer capacity of the National Grid has been enhanced to about 17,000 MW in FY 2007-08. Four major power regions of the country namely, North-Eastern, Eastern, Western and Northern are now operating as one synchronous grid (same frequency). Southern Regional grid is connected to this synchronous grid through HVDC links. A transmission plan has also been evolved for strengthening the regional grids and to support the generation capacity addition program of about 78,000 MW during XI Plan. In line with the perspective plan, various inter-regional transmission schemes have been undertaken for implementation by POWERGRID. Several milestones have been achieved by The Power Grid Corporation of India Ltd as a part of the development of the National Grid such as the implementation of Asia’s longest Talcher-Kolar HVDC Bipole link including its upgradation, Sasaram HVDC back-to-back link, 400 kV D/C Synchronous interconnection between Eastern and Western Region including series compensation, Augmentation of Gazuwaka HVDC, Muzaffarpur-Gorakhpur400 kV D/c line under Tala Transmission System, Agra-Gwalior 765 kV S/C line (operating at 400 kV), Patna-Balia 400 kV D/c line, Biharshariff-Balia 400 kV D/c line, etc. Establishment of the ultimate National Grid is on fast track and a number of projects are under implementation/ planned which would enhance Inter-regional power transfer capacity of the National Grid to more than 37,000 MW by year 2012.

Thus there are five power grids in India - Eastern Grid Western Grid Southern Grid Northern Grid North-Eastern Grid

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Power Systems Stability

References:[1] A Course in Electrical Power by J. B. Gupta[2] Solutions for large Power System Interconnections by W. Breuer, D. Povh, D. Retzmann, E. Teltsch

(Siemens AG, Germany) & X. Lei (XJ Group, China)[3] http://www.powergridindia.com

3 | P a g e Submitted by : Rohan Sharma