Load Forecasting is an important function in power system operation.  Load forecasting is projecting the estimated load in advance.  Load forecasting can be done for a range of time periods from a few hours to many years. 

Load forecasting is done to decide which power generating units need to be taken in line in a certain period of time.  This is done to determine the best mix of generating units which will give the lowest cost of generation. 

The maintenance activities of the various power plants are also planned based on the load forecasting.  Investments for new power plants which may be required a few years down the line are also planned based on the load forecasting.

The load forecasting is done using historical data and factors, such as seasonal variations, projected economic activity, population growth, etc


Shunt Capacitors  Series Capacitors 
 Shunt Capacitors are used to improve the power factor of the system.  They are used to offset the effect of the series reactance in the line.
 Shunt capacitors are not effective in situations where
the line reactance of the line is high.
 Series capacitors are useful in conditions of high series reactance.
 Shunt Capacitors are connected as a single bank
connected to the bus or individually near the loads.
 Series Capacitors are connected in series with the load



A bus is a set of conductors in which electrical power flows and is then distributed to different lines.
In Power Flow Analysis, buses are classified into three main types.

They are
  • The Generator Bus
  • The Load Bus and the 
  • Slack, Swing or Reference bus
The Generator Bus
As the name suggests, the generator bus is the bus producing power.  For the generator bus, the values of P, the active power and the voltage, V are given.  The reactive power, Q and the load angle, delta should be found.

The Load Bus
The load bus consumes active and reactive power.  For this bus, the active power, P and the reactive power, Q are given.  The voltage and the phase angle should be calculated.

The Swing Bus
The swing bus is the bus which has been made to take the additional active and reactive power which are used to supply the transmission losses.  Therefore, the active and reactive powers are unknown for this bus.  Only the voltage,V and the load angle, delta are given.


Bus Type Quantities Specified  Quantities to be found 
 Generator Bus  P,V  Q, load angle
 Load Bus  P,Q  V, load angle
 Swing Bus  V, load angle  P,Q



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Static Compensators are electric circuits which are used to compensate the surge impedance in a circuit.  They are also used for load compensation.  Static compensators are used to maintain a constant voltage during varying loads.  They are also used during sudden reduction in the loads or during tripping of the source. 

Static Compensators improve the power factor and,consequently, the system stability

A simple static compensator consists of an variable inductor and a capacitor connected in parallel.  The reactive power in the system can thus be compensated using these two elements.

Thyristors are often used in series with the inductor and compensator to precisely control the reactor power flow to and from the static compensator. 


A load curve is a plot of the load in a network against time.  Load is plotted along the Y axis and time on the X-axis.

The curve shows the variation of load with time.  There can be daily load curves, monthly load curves and yearly load curve.

The area under the load curve shows the total units generated.  The tallest point in the curve shows the maximum demand.  The average load can be deduced by dividing the area under the curve by the total number of hours.

The load factor can be calculated by dividing the area under the curve by the area of the rectangle enclosing the curve.





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A Load Duration curve (LDC) is a curve formed by placing the loads in descending order of their magnitude.



The curve is essentially a bar graph.  Each bar represents a specific load.  The taller bars indicating the higher loads are placed to the left.  The area under the load curve indicates the total units generated. 

The Load Duration Curve can be used in economic dispatching, system planning and reliability.


If the load on a power system is not constant but has steep variations, the cost of power generation will increase. 

More generators will have to be connected to handle the high peak loads of the system.  These generators will be idle when the load drops or they may have to operate at low loads.  This will reduce the efficiency of the prime mover and increase the fuel costs.

Increase in capital cost

More generators will have to be added to deliver the peak load.  This will result in higher capital cost.