1. Meaning

National Grid may be perceived as a mesh of interlinked transmission lines, interconnecting different electrical regions, viz., Northern, Eastern, Western, Southern and North - Eastern regions of the country. This is required to optimally harness the generating resources, confined to certain regions of the country, by facilitating transfer of power from such regions to the other regions which are not adequately endowed.

Prior to independence, small generating stations were used to supply power to local loads through small haphazard radial transmission system, which gradually progressed towards the formation of State grids in 60's, regional grids in mid 70's, progressively moving on a long and arduous journey to provide a backbone for formation of a "National Grid", by way of integration of the existing regional grids, with suitable augmentations.

The installed generating capacity of the country has increased from a mere 1713 MW in 1950 to more than 1,04,000 today MW. The growth in transmission system is characterized not only by the physical growth in the reach of the transmission network but also the superior technology like introduction of higher transmission voltage land also state-of-the art technologies for bulk power transmission. Some of the features of the Indian Power Sector are as follows :

For quite sometime, planning of generation and transmission system in India was being done on a regional concept. Over a period of time, this regional concept of planning had yielded good dividends. However, a number of overriding factors, like uneven disposition of energy resources, unbalanced growth of different regions, need for optimisation of generation capacity addition to consume the resources etc., have necessitated integration of regional grids.

powergrid, a Central Transmission Utility, was established in 1989 with the mandate of "Establishment and Operation of Regional and National Grids to facilitate transfer of power within and across the regions with reliability, security and economy on sound commercial principles." In view of this, powergrid has evolved a perspective transmission Plan for short, medium and long-term for strengthening the regional grids with ultimate objective of establishment of National Grid in a phased manner.

In order to transfer energy across various regions, many AC interconnections at 220 kV and 400 kV level exist. However, due to numerous factors, the regional grids operate at off-nominal parameters most of the time, thus making it difficult to connect them in synchronous mode. Keeping this in view, in the first phase, HVDC back-to-back interconnections (which connect in asynchronous mode) were planned, however, keeping the Eastern and North-Eastern regions connected in synchronous mode. As envisaged, the interconnections between North & West (with 500 MW HVDC Back-to-back at Vindyachal), West & South (with 1000 MW HVDC Back-to-back at Chandrapur) and East & South (with 500 MW HVDC Back-to-back at Gazuwaka) have already been established. The first phase of the much needed National Grid will be accomplished with the completion of 500 MW HVDC back to back at Sasaram connecting Eastern and Northern Region by October, 2002, thus, the cumulative power transfer capacity will reach to a level of 4850 MW.

With the converted efforts of powergrid, the energy exchange from Eastern Region has increased from 500 MU in 1992 - 1993 to about 7,200 MU at present. This has benefited Eastern region, as generating companies were not forced to back-down their available generation, as also the importing regions, which could save the investments that would have been necessitated, otherwise.

During this phase, high capacity synchronous HVAC links have also been planned between the regions together with asynchronous HVDC links, associated with certain mega-sized generation projects like Talcher-II (2000 MW), Tala HEP (1020 MW). The major inter-regional links contemplated in this phase are :

Powergrid has given special emphasis to its prestigious 2000 MW East-South Interconnector-II HVDC Bipole link (Talcher-Kolar), for which a dedicated team is striving hard to complete this project ahead of schedule. This project shall not only be instrumental in evacuation of bulk power from Talcher STPP stage-II (4X500 MW) but also facilitate transfer of surplus power from Eastern region to power-starved Southern Region, due to advancement of its completion. The 7500 MW super highway link shall provide the flexibility to cope with the uncertainties associated with siting of new generation projects.

With the completion of this phase, the inter-regional power transfer capacity will increase to about 23,000 MW by year 2006-07.

In the ultimate phase, a strong National Grid has been envisaged to evacuate the power from major generating resources that include hydro projects in North-East Region and large sized Thermal Power Plants in Bihar, Orissa and Madhya Pradesh. The scheme for ultimate National Grid would involve development of high capacity transmission corridor in chicken-neck area (falling between Nepal & Bangladesh) and establishment of a ring of 765 kV lines interconnecting Eastern-Western and Northern region. Cumulative inter-regional transmission capacity of the proposed ultimate National-Grid would be increased to about 130,000 MW by the year 2012.

While developing the National Grid, various factors, like, conservation of Right of Way, flexibility to cope with the uncertainties associated with growth of load and siting of new generating station, high cost, high initial tariff, etc., pose challenges to the power system planners.

The efforts of powergrid have already come to fruition, as, already, existing interconnections are facilitating transfer of power among the regions resulting in improved grid parameters, like voltage, frequency etc. and optimal utilization of generating resources.

The success of National Grid shall largely depend upon the strength and performance of the underlying network to wheel power upto the consumer end. Therefore, to extend the benefits of National Grid to the ultimate consumer, it is essential that development of sub-transmission and distribution system is commensurate with the development of National Grid.

In order to assist the SEBs in the development of sub-transmission and distribution system, Powergrid has undertaken about 30 nos. of critical state schemes, vital for entire grid, at an estimated cost of Rs. 2,000 crores in states of Bihar, Orissa, West Bengal, Uttar Pradesh, Goa. Among these, four schemes are already under operation and six are under advanced stage of construction. It is a welcome effort on part of many SEBs/utilities who are taking up sweeping reforms and improve the distribution system in order to check the losses in Transmission & Distribution. As the unbundling and restructuring of the (SEBs) is taking place all over the country, the weaknesses in sub-transmission and distribution system are likely to perish.