Load Curve and Load Duration Curve

Load curve and Load duration curve

Load Curve

Load curve (or chronological curve) is the graphical representation of load (in kW or MW) in proper time of sequence and the time in hours. The load on a power station is never constant; it varies from time to time. If this curve is plotted over a time period of 24 hours, it is known as daily load curve. If its plotted for a week, month, or a year, then its named as the weekly, monthly or yearly load curve respectively.

Daily Load Curve
Daily Load Curve

The following information is obtained from Load Curve.

  1. Load variation during different hours of the day
  2. Peak load in a load curve indicates the maximum demand on the system.
  3. Area under the Load curve gives the total energy generated in the period under consideration.
  4. Area under the load curve divided by total number of hours gives the average load.
  5. The ratio of area under the load curve to the total area of the rectangle in which it is contained gives the load factor.

Load curve helps us in deciding the installed capacity of a power station, economical size of various generating units, generating cost and operational schedule of the Power station.

Load Duration Curve

A Load duration curve is a graph between load and time in hours, in which the ordinate representing the load are plotted in the order of descending magnitude i.e. with the greatest load at the left, lesser loads towards the right and lowest load at extreme right. Load duration curve is obtained from Load curve. The area under the load duration curve and the area under the load curve are equal.

Load Duration curve
Load Curve and Load Duration Curve

The following points may be noted about load duration curve.

  1. 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.
  2. 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.
  3. 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 summarised in one curve. The curve thus obtained is called the annual load duration curve.

Procedure for Plotting The Load Duration Curve

  1. From the data available from the Load curve, determine the maximum load on the system and the duration for which it occurs.
  2. Take the next lower load and determine the total time, during which this and the previous greater load occurs.
  3. Plot the load against time during which it occurs

Information Obtained from Load Duration Curve

  1. It gives the minimum Load present throughout the given period.
  2. It enables the section of base load and peak load power plants
  3. Any point on the load duration curve gives the total duration in hours for the corresponding load and all loads of greater value.
  4. The area under load curve and corresponding load duration curve are equal. Both these areas represent the same associated energy, during the period under consideration.
  5. the average demand during some specified time period such as day or month or year can be obtained from the load duration curve as follows\\\;\;\;\;\;\;\;\;\; Average demand = (Energy (KWh or MWh) consumed in a given time period) / (hours in the time period)\\\;\;\;\;\;\;\;\;\;Average demand = Area under the Load duration curve / base of the load duration curve.

Read Also

  1. Load | Maximum Demand | Demand Factor | Average Load | Diversity Factors | Plant capacity Factor | Utilization factor
  2. Generating Stations | Power plant | Coal Power Plant | Steam power plant | Hydro electric power plant | Nuclear power plant | Diesel power plant | Thermal Power plant
  3. Introduction to Electrical Power System


AJAZ UL HAQ has above 8 years of Experience in Electrical Power Transmission, Distribution and Substation. Presently He is working with KEI Industries Limited as Engineer-EPC/EHV.

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