Size of plant

The size of plant depends on the purpose for which the plant is being set up. If it is being set up for aprivate industry; the size would be governed by the amount of power required by the various sections of the industry and the likely increase in power demand in future. If it is being planned as an emergency plant, the size would be governed by the load that must be supplied by the plant in the event of failure of grid supply.

The size of the plant for supplying power to a given area will depend on the power needs of the area at present and the likely increase in power demand in next 5-10 years.

More often than not the proposed plant is likely to feed a power grid which supplies power to large areas. The proposal for a hydro-plant for this purpose will depend on the amount of water available, the additional power necessary for the grid and the likely increase in power demand in the next 10-20 years or so. It may be possible that the proposed hydro-plant has a capability of meeting a huge power demand but the immediate prospects of power demand are low. In such a case the power plant size may be selected on the basis of the present and the immediate future requirements with provision for future extension. Alternatively it may be worthwhile to go in for the full plant capacity immediately because once cheap hydro power is available, the demand is likely to increase sharply. The power demands of the Northern region were low before the Bhakra plant came into being. But immediately after the plant was completed, the demand increased tremendously and this necessitated the planning of other hydro and steam stations in the region.

To assess the electricity requirements and to plan the generation forecasting the power demand is very important. The long term load forecasting can be carried out using the statistical data of previous years. From the statistical data, a general trend and the mean rate of annual increase can be established. To expand generation capacity in an optimum manner, for an estimated load growth, it is necessary to prepare a long term programme for a period of next 30 years or so. The importance of system reliability should also be taken into account. The optimum plan should include

(1) The addition in system generation in different years.

(2) The type of generation (hydro, coal or nuclear) to be developed in different years.

(3) The proposed location of plants.

(4) The sizes of the power plants.

 

The needs of power system security and reliability require that the generation systems should not be confined to one side of the area being fed but should instead be dispersed to different sides. The size of the steam plant to be added to the grid is, in addition to power demand, also governed by the fact whether the plant will be used as a base load station or as a peak load station and the extent to which it is required to contribute to increase the firm capacity of the hydro plants.

There are many advantages, mostly economic, in having a large plant size. Some of the costs are hardly affected by the size of the plant. The cost of office space, shops, docks and landscaping can be spread over more capacity. Coal handling equipment, cooling facilities and other appurtenances can also be operated at lesser cost per kilowatt-hour at larger installations. The problems of site acquisition and development are less severe for one large site than for two or more smaller ones. Broadly speaking a large capacity plant will generate energy at a lower cost.

However, some factors tend to limit the plant sizes. Thermal plants need lot of space (for coal storage, ash disposal, cooling towers) and large quantities of water. The amount of land and water required will prevent the use of many otherwise suitable plant sites. The system reliability is also affected by the plant size. The maximum size of plants and capability of system interconnection are also related. Finally the environmental pollution problems are more severe for large plants than for the smaller ones.

The advantages of large plants seem to outweigh the disadvantages. As a matter of fact, the increase in electricity demand has forced the utilities to go in for larger and larger plant sizes.

In India, the plant size has shown an increase over the last 3 decades. At the time of independence, the maximum plant size was around 50 MW. By 1960,the plant sizes had increased to around 300 MW and by 1970 the maximum plant size had increased to 420 MW. At present many plants of more than 500 MW capacity are operating. Some time back Govt. of India appointed a committee to select sites for setting up large thermal plants of 1000MW and above. Out of these six sites viz. Singrauli, Korba, Ramagundem, Fanakka, Rihand and Vindhyachal were recommended for super thermal stations of 2000 MW each.