This document discusses various concepts related to power system operation and control including load curves, load duration curves, connected load, maximum demand, average load, load factor, capacity factor, and categories of loads. Load curves show the variation of load with time on a daily, monthly, or yearly basis. Connected load is the sum of ratings of all equipment, while maximum demand is the greatest short-term average load. Load factor is the ratio of average load to maximum demand and indicates how uniformly the load is distributed over time. There are five broad categories of loads from a system perspective: domestic, commercial, industrial, agricultural, and others.

1. V. KALAIRAJAN (AP/EEE)
KONGUNADU COLLEGE OF ENGINEERING AND TECHNOLOGY
TRICHY
Power System Operation and Control

2. Load Curve:
Curve between load variation on power station with respect to time.
1. Daily load curve.(load variation for 24hrs)
2. Monthly load curve .(load variation for month)
3. Yearly or Annual load curve .(load variation for year)
Needs of Load curves:
 Load variation
 Total number of power generated.
 Maximum demand.
 Average load.
 Load factor (curve Area and total rectangle area(Max Demand)).
Power System Operation and Control

3. Load duration curve:
 It is also load variation curve, but with loads arranged in
descending order of magnitude.
 Can find load factor.
Power System Operation and Control

4. Connected Load :
Sum of continuous ratings of all electrical equipments connected to
supply system.
Maximum Demand:
Greatest of all short time interval averaged.
It determines cost and size of installation.
Power System Operation and Control

5. Average Load or Demand:
LoadConnectedTotal
DemandMaximumActual
FactorDemand
24
dayinasuppliedKWhr
DemandAvgorLoadAvgDaily 
30x24
monthainsuppliedKWhr
DemandAvgorLoadAvgMonthly 
365x24
yearainsuppliedKWhr
DemandAvgorLoadAvgAnnual 
Power System Operation and Control

6. Load Factor: (<1)
Coincidence Factor: 1/ Diversity Factor
StationpowerofdemandMaximum
demandsmaximumindividualofSum
FactorDiversity
periodtimesametheduringLoadPeak
periodgiven timeaoverLoadAverage
rLoad Facto
DemandMaximum
DemandAverage
rLoad Facto
(T)periodtimesametheduringDemandMaximum
(T)periodgiven timeaoverGeneratedUnits
rLoad Facto
Power System Operation and Control

7. Capacity factor:
Reserve Capacity = Plant Capacity – M.D
plantpowerofCapacityRated
DemandAverage
FactorCapacitor
HoursofNoCapacity xPlant
GeneratedKWhrorUnits
FactorCapacitor
StationPowertheofCapacityRated
SatationPoweron theMax.Demand
n FactorUtilisatio
Power System Operation and Control

8.  Installed Reserves
 Spinning reserves
 Cold and Hot Reserves.
Power System Operation and Control

9. • From system’s point of view, there are 5 broad category of loads: Domestic,
Commercial, Industrial, Agriculture and others
Domestic:
lights, fans, domestic appliances like heaters, refrigerators, air conditioners, mixers,
ovens, small motors etc.
Demand factor = 0.7 to 1.0; Diversity factor = 1.2 to 1.3; Load factor = 0.1 to 0.15
Commercial:
Lightings for shops, advertising hoardings, fans, AC etc.
Demand factor = 0.9 to 1.0; Diversity factor = 1.1 to 1.2; Load factor = 0.25 to 0.3
Industrial:
Small scale industries: 0-20kW
Medium scale industries: 20-100kW
Large scale industries: above 100kW

10. Industrial loads need power over a longer period which remains fairly uniform
throughout the day
For heavy industries:
Demand factor = 0.85 to 0.9; Load factor = 0.7 to 0.8
Agriculture:
Supplying water for irrigation using pumps driven by motors
Demand factor = 0.9 to 1; Diversity factor = 1.0 to 1.5; Load factor = 0.15 to 0.25
Other Loads:
Bulk supplies, street lights, traction, government loads which have their own
peculiar characteristics