Combined Operation of Power Plant
- Electrical power is being generated in large generating stations, which are either hydro thermal, nuclear power stations. These generating stations are mostly far away from the load centres (i.e, where the load is required).
- Hence, it is required to erect large and long transmission network to feed the electricity from the generating end (i.e. sending end) to place of load centre, (i.e. receiving end) of electrical supply.
- It needs several electrical equipments to be connected for proper transmission of generating power.
- The transmission system of an area is known as a grid. Different grids are interconnected through the tie lines to form a regional grid.
- Number of such regional grids are further interconnected to form a national grid. Each grid (regional) operates independently, but at times of requirement and agreement between regional grids power can be exchanged between them.
- In an interconnected power system, which consists of number of power stations of different types operating in parallel it is required to direct different stations to operate for their best possible economic operation i.e. to decide which type of plant is to be used for which plant factor depending upon the availability of fuel and other resources at the site of plant and in the vast scense availability of fuel etc. In the country.
- The types of generating stations that are usually available in India are: Hydro-electric, steam thermal power, gas plants. Diesel plants and nuclear plants, these have to be used either as base-load plants or peak-load plants or sometimes both for coordinated operation to supply load demand.
- Base-load plants run throughout the year and operate at high load factor. The economic characteristics of base-load plants should be such that they supply power at high capital cost but have low cost of operation.
- As such nuclear power plants and hydro power plants will fulfill the above conditions. Peak-load plants run for a few hours in the year and work at low load factors.
- They should supply power at lower capital cost though their cost of operation may be high. Such power plant must be capable of quick starting and should be inexpensive in starting and shutting down operation.
- Hydro-electric power stations with ample storage of water are used for base-load operation. In a similar way run-off river plants during river flow period mainly rainy season in India are also used to meet the base-load required.
- Hydro-electric plants with limited storage are used to meet the peak load demand of a system, Pumped storage plants are always used as peak-load plants. The example being a Jayakwadi project.
- Nuclear power stations are used as base-load stations and they operate at high load factor which is more than 80%. They supply the load at the bottom of the load curve, such loads are called ‘Block loads’.
- Steam stations can operate as base-load stations and peak-load stations also, depending upon the co-ordination with other types of stations in the grid system. They can operate at load factor which varies from 40% to 80%.
- Diesel and gas turbine plants are mostly used as peak-load plants only because of their high cost of generation and shortage of fuel material. They work at low load factors of 25% or so. When the load factor is less than 25% it is preferred to use Gas turbine plant. Gas turbine plants cost is low for installation as compared to thermal (steam) power stations of the same size. Fixed changes on a gas plant are also lower than a steam plant, but the thermal efficiency of a gas plant is low as compared to steam plant.
- Diesel plant have low capacity which may be in the range of 1000 kW to 3000 kW, they are mostly used as peak-load plant. Now due to shortage of electricity, factories etc. using such sets as standby or emergency plant. As peak-load plant it is required to use it at load factors above 25%.