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# What are Load Curves?

## Load Curves

The graph which shows the variation of load on the power station with respect to time is called the **load curve** of the power station.

The load on a power station does not remain constant; it changes from time to time. These changes in the load on a power station during whole day (i.e. for 24 hours) are recorded half-hourly or hourly and are plotted with respect to time on the graph. The obtained graph is called the **daily load curve** of the power plant.

The daily load curve shows the variation of load with respect to time during the day. A typical daily load curve of a power station is shown in the figure. From the figure, it can be seen that the load on the power station is varying and being maximum at 6 pm.

The **monthly load curve** of the power station can be obtained from the daily load curves of that month. In order to plot the monthly load curve, average values of power over a month at different times of the day are calculated and then plotted on the graph. The monthly load curve of power station is mainly used to fix the rates of energy.

The **yearly load curve** can be obtained from the monthly load curves of that year. To plot the monthly load curves, average values of power over the year are calculated and then plotted on the graph. The yearly load curve is generally used to determine the annual load factor of the power station.

## Importance of Load Curves

Load curves are very important in generation of electrical power because they provide the following information −

The daily load curve shows the variation in the load on the power plant during the different hours of the day.

The peak point on the daily load curve represents the maximum demand on the power station on that day.

The load curves help in selecting the size and the number of generating units of the power station.

The load curves help in preparing the operation schedule of the power station. That means, to determine the sequence and time for which the various generating units in the power station will be put in operation.

The area under the daily load curve represents the number of units generated on that day, i.e.,

Units generated per day = Area (in kWh) under the daily load curve

The ratio of area under the daily load curve and the total number of hours gives the average load on the power station on that day, i.e.

$$\mathrm{Average\: load\: per\: day\, =\, \frac{Area\: under \: daily \: load \: curve(in kWh)}{24\: hours}}$$

The area under the load curve divided by the total area of the rectangle in which it is contained gives the load factor of the power station, i.e.,

$$\mathrm{Load\: Factor\, =\, \frac{Average\: load}{Maximum\: demand}\, =\, \frac{Average\: load \times \: 24\: hours}{Maximum \: demand \: \times 24 \: hours} }$$

$$\mathrm{\therefore Load\: Factor\, =\, \frac{Area\: under \: daily \: load \: curve\: (in kWh)}{Total\: area \: of\: rectangle \: in\: which \: the \: load \: curve\: is \: contained}}$$

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