Based Load and Peak Load in Power Plant
- Every generating station has to respond and supply the varying demand of power throughout the day. Hence, it is necessary that individual generators are required to bring into service or shut down from service depending on whether the load is increasing or decreasing.
- The peak-load on the station remains for a short duration, when some units are reserved for meeting the peak-load demand only they will be operated for this short period only. The cost of energy generated by such units will be high due to low load factor of these units.
- In the co-ordinated operation of hydro and thermal power stations, the available hydro energy and thermal plant capacity are fitted into the system load curve. Output of hydro-electric plant is determined from the data of river flow or the number of units a hydro plant can produce per hour/day is thus fixed.
- The capacity of the hydro-station to carry peak-load demand is thus dependent upon the number of hours the station operates. When thermal plant carry the base-load, the hydro plants operating hours are reduced, which will increase the peak-load carrying capacity of the latter. The total maximum demand which can be met, Increases due to decrease in load factor of the hydro-electric plant.
A hydro electric plant can work as a peak-load station in any of the following conditions :
- By storing the natural run-off from a catchment area during hours of light load and using the water to operate the plant at full capacity during peak-load periods.
- Pumped storage system : In this system water is pumped into a high level reservoir at off peak periods and is utilized to drive turbines and generate power, when the peak of the system occurs. Such a system is installed at Jayakwadi project.
- The plant consists of a synchronous motor or induction motor coupled on one side to a multistage centrifugal pump on the other side to a turbine. During off-peak-load period, the motor drives the pump and pumps the water in the reservoir.
- When the system peak occurs the motor runs as an alternator or an induction generator driven by the turbine.
- The plant can change over from one function to another (pumping to generating) and vice versa very quickly and the whole sequence of operations is automatically controlled. As the Induction generator always supplies load at leading p.f. it improves the p.f. of the system also.
- An overall efficiency of a pumped storage system is of the order of about 60 to 65%. Use of such systems are justified because it permits available energy to be stored for later use when it is required i.e. at the times of peak-loads. Hence, pumped storage system enables a lesser steam plant capacity to be used, making pumped storage system economical.