Load Duration Curves

Load  Duration  Curve:

When the load elements of a load curve are arranged in the order of descending magnitudes, the curve thus obtained is called a  load duration curve.

Load Duration Curves

The load duration curve is obtained from the same data as the load curve but the ordinates are arranged in the order of descending magnitudes. In other words, the maximum load is represented to the left and decreasing loads are represented to the right in the descending order. Hence the area under the load duration curve and the area under the load curve are equal.Fig.( i) shows the daily load curve.The daily load duration curve can be readily obtained from it.  It is clear from daily load curve [See Fig. (i)], that load elements in order of descending magnitude are: 20 MW for 8 hours; 15 MW for 4 hours and 5 MW for 12 hours. Plotting these loads in order of descending magnitude, we get the daily load duration curve as shown in Fig.(ii ).

The following points may be noted about load duration curve :

(i) The load duration curve gives the data in a more presentable form.In other words, it readily shows the number of hours during which the given load has prevailed.

(ii) The area under the load duration curve is equal to that of the corresponding load curve.

Obviously, area under daily load duration curve (in kWh) will give the units generated on that day.

(iii) The load duration curve can be extended to include any period of time.By laying out the abscissa from 0 hour to 8760 hours, the variation and distribution of demand for an entire year can be summarized in one curve.The curve thus obtained is called the annual load duration curve.