DEPARTMENT OF ENGINEERING
ELECTRICAL POWER, COMPUTER & TELECOMMUNICATIONS SECTION
Higher College of Technology, P O BOX 74, Al-KHUWAIR, CODE 133 24473600 Fx 24485364
Specialization: Electrical power engineering Level: Baccalaureate EEPW4256: Power stations Chapter 1: Load curves & its relevant factors
Prepared by: Jayanna k Lecturer: Electrical power Engineering
Student name: Student ID:
Chapter 1 Load curves & its relevant factors
Contents: 1.1 Analysis of Load curves 1.2 Important terms & Factors 1.2.1 Connected Load 1.2.2 Maximum demand 1.2.3 Demand Factor 1.2.4 Average Load 1.2.5 Load Factor 1.2.6 Diversity Factor 1.2.7 Plant Capacity Factor 1.2.8 Plant Factor 1.3 Problems on load curves & its factors
References:  V.K. Mehta & Rohit Mehta, “Principles of Power System,” Third Edition, S.Chand & Company Ltd., INDIA, 2003, pp.41-55
1.1 Analysis of Load curves The load on a power station is never constant; it varies from time to time. These load variations during the whole day are recorded half-hourly or hourly and are plotted against time on the graph called daily load curves. Fig.1 shows a daily load curve of a power station.
The curve showing the variation of load on the power station with respect to time is known as a load curve. The curve shows the variation of load with respect to time during the day is known as daily load curve. The monthly load curve can be obtained from the daily load curves of that month. The yearly load curve can be obtained from the monthly load curves of that particular year. The load on power station is varying, being maximum at 6 PM (Fig.1). The daily load curves are important in generation as they provide following information: (i) The daily load curves shows the variations of load on the power station during different hours of the day (ii) The area under the daily load curve gives the number of units generated in the day. (iii)The highest point on the daily load curve represents the maximum demand on the station on that day
(iv)The area under the daily load curve divided by the total number of hours gives the average load on the station in that day Average load = Area (in KWh) under daily load curve/ 24 hours (v) The ratio of average load to maximum demand gives load factor. (vi)The load curve helps in selecting the size and number of generating units (vii) The load curve helps in preparing the operating schedule of the station
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. The load duration curve is obtained from the same data as the load curve but the ordinate are arranged in the order of descending magnitudes. The maximum load is represented to the left & decreasing loads are represented to the right in the descending order. Hence area under load duration curve & area under load curve are equal. Fig.2 (i) shows the daily load curve. The daily load duration curve can be obtained from load curve. In Fig.2 (ii), load elements in order of descending magnitude are; 20MW for 8 hours; 15MW for 4 hours & 5 MW for 12 hours. Plotting these loads in order of descending magnitude to get daily load duration curve shown in fig.2 (ii). The following points may be noted for load duration curve: (i) The load duration curve gives the data in a more presentable form. 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. The area under daily load duration curve will give the units generated on that day (iii)The load duration curve can be extended to include any period of time. If we extend abscissa (x-axis) from 0 to 8760 hours, the annual load duration curve can be obtained.
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