What is a grid? It is a common transmission network through which all electricity runs and loads are connected. How does the grid system in the country operate? Currently,the northern,western,eastern and northeastern regions are integrally connected through strong synchronous AC transmission links and there is a free flow of power between one region and another. The southern region,however,is hooked up with the rest of the country through an asynchronous HVDC (high voltage direct current) transmission link,which puts constraints on wheeling capacity,thereby limiting the free flow of power from the southern region to the rest of the country. What is an asynchronous interconnection? It has two independent grids joined with the help of HDVC terminals so that the disturbance of one grid is not passed on to the other grid. What is a synchronous interconnection? Here,two independent grids are joined through AC transmission links that enable operations at a synchronised frequency. The largest such grid is the synchronous grid of Continental Europe (ENTSO-E) with generation capacity 667 gigawatts,and the widest region served is that of the IPS/UPS system serving countries of the former Soviet Union. Indias combined generation capacity integrated north,west,east and southern grids would be about 232 GW. What is the advantage of having a very large grid? It has more electrical inertia and hence is inherently considered more stable. Is there a disadvantage too? If there is a serious disturbance leading to the collapse of a key line in even a specific region,the consequences could be more widespread. For instance,in July 2012,a grid collapse was triggered by excessive line loading on the Agra-Gwalior-Bina transmission link,which connects the northern region with the west. When that line snapped,it set off cascade tripping. The impact was felt by states that form part of the eastern grid too,simply because the east was synchronously connected to the northern and the western grids.
