This document discusses the operation and control of electrical power systems. It covers topics like the structure of power systems, variable loads on power stations, load curves, load characteristics, and the effects of variable loading. Load curves show how demand varies over time. Variable loading increases generation costs and requires additional control equipment to regulate frequency. Load characteristics include terms like maximum demand, average load, load factor, diversity factor, and plant capacity factor. Different types of loads like domestic, commercial, industrial, and agricultural loads are also described. Examples problems are provided to illustrate calculations related to load factors, demand factors, and energy generated.

1. DEPARTMENT OF
ELECTRICALAND ELECTRONICS ENGINEERING
19EEC11 – OPERATION AND CONTROL OF
ELECTRICAL POWER SYSTEM
COURSE FACULTY
M.SWATHISRIRANJANI
AP/EEE

2.  Introduction
Structure of Electric Power system
 Variable load on power stations
Load curves
Load Characteristics
Load duration curves
Load curves and selection of generating units
2

3. The power demands of different
consumers vary in accordance with their
activities.
The result of this variation in demand is
that load on a power station is never
constant rather it varies from time to time
3

4. 4
• The load on a power station varies from time to
time due to uncertain demands of the consumers
and is known as variable load on the station.

5. 5
Effects Of Variable Loading On Power System:
Generation of power becomes costly:
For obvious reasons of optimum operation,
alternators are designed in such a way that
maximum efficiency occurs at (or very close to)
their rated capacity.
Hence, when the load varies and becomes low,
the alternator will not be loaded up to its rated
capacity and its working efficiency is reduced.
This consequently increases the cost of
production.

6. 6
Effects Of Variable Loading On Power System: [cont..]
When the load changes, the frequency of the
system also varies.
For proper operation, the frequency must be
within the permissible limits. (Generally ± 1%
deviation is permissible)
In order to keep the frequency within limits,
additional control equipments are required.
Such equipments increase the cost and
complexity of the system.

7. 7
Effects Of Variable Loading On Power System: [cont..]
• Requirement of additional equipment:
Variable loading necessitates the use of speed
governors, voltage and frequency sensors,
microcontrollers and other closed loop control
equipments to exert control over the system and
maintain all parameters within permissible
ranges.

8. 8
Effects Of Variable Loading On Power System: [cont..]
Due to variation in loading conditions, various
machines like transformers, electronic devices
and other machines show increased losses due to
magnetization characteristics,
variation in parameters. This
saturation and
decreases the
overall efficiency of the system.

9. 9
The load characteristic plays an important role in
Determining the total power and energy
requirements of the system
planning the installed capacity of a power plant
selection of suitable generating
capacity for each unit of the plant..

10. Demand Interval
It is the period over which the load is
averaged.
3/25/2017 Power System Operation and Control 8

11. Load Curve
• The curve showing the variation of load on the
power station with respect to time is known as a
load curve
11

12. 12

13. P & Q
13

14. Load Curve
• Area under active power curve in MWh equals
number of units generated per day
• The highest point on active power curve
represents the maximum (peak) demand on the
station on this specific day
• Average load on station equals area under daily
load curve divided by total hours.
14

15. Load Curve
Load factor equals the ratio of the area under the
daily load curve to the total area of the rectangle
in which the curve is contained
15

16. 16
Load Curve
• Size & Number of generating units
• Operation schedule

17. 17
Load Characteristics
• Terms used commonly:
1. Connected load: Sum of the continuous rating of
the entire load consuming apparatus connected to
the system.
2. Maximum demand : It is the greatest demand
of load on the power station during a given period.

18. Load Characteristics
3. Demand factor. It is the ratio of maximum
demand on the power station to its connected
load
The value of demand factor is always less than 1
18

19. Average load: The average of loads occurring on
the power station in a given period (day or month or
year) is known as average load or average
demand.
19

20. • Load factor. The ratio of average load to the
maximum demand during a given period
20

21. 21
• The load factor may be daily load factor, monthly
load factor or annual load factor
• Load factor is always less than 1
• Higher the load factor of the power station, lesser
will be the cost per unit generated.

22. • Diversity factor: The ratio of the sum of
individual maximum
maximum demand on
demands
power
to the
station is
known as diversity factor
• Always greater than 1.
• The greater the diversity factor, the lesser is
the cost of generation of power
22

23. • Plant capacity factor: It is the ratio of actual
energy produced to the maximum possible
energy that could have been produced during a
given period
23

24. • Reserve capacity = Plant capacity − Max. demand
24

25. • Plant use factor: It is ratio of kWh generated
to the product of plant capacity and the
number of hours for which the plant was in
operation
25

26. Load Duration Curve
• When
elements
the load
of a load
curve are arranged in
the order of
descending
magnitudes, the curve
thus obtained is called
a load duration curve
26

27. 27

28. 28
(i) Domestic load:
Domestic load consists of lights, fans, refrigerators,
heaters, television, small motors for pumping water
etc. Most of the residential load occurs only for
some hours during the day (i.e., 24 hours) e.g.,
lighting load occurs during night time and domestic
appliance load occurs for only a few hours. For this
reason, the load factor is low (10% to 12%).

29. 29
Types of Loads [cont..]
(ii) Commercial load: Commercial load consists of
lighting for shops, fans and electric appliances
used in restaurants etc. This class of load occurs
for more hours during the day as compared to the
domestic load. The commercial load has seasonal
variations due to the extensive use of
airconditioners and space heaters.

30. 30
Types of Loads [cont..]
(iii) Industrial load: Industrial load consists of load
demand by industries. The magnitude of industrial
load depends upon the type of industry. Thus
small scale industry requires load upto 25 kW,
medium scale industry between 25kW and
100 kW and large-scale industry requires load
above 500 kW. Industrial loads are generally not
weather dependent.

31. 31
Types of Loads [cont..]
(iv) Municipal load: Municipal load consists of
street lighting, power required for water supply
and drainage purposes. Street lighting load is
practically constant throughout the hours of the
night. For water supply, water is pumped to
overhead tanks by pumps driven by electric
motors. Pumping is carried out during the off-
peak period, usually occurring during the night.
This helps to improve the load factor of the power
system.

32. 32
Types of Loads [cont..]
(v) Irrigation/Agricultural load: This type of load is
the electric power needed for pumps driven by
motors to supply water to fields. Generally this
type of load is supplied for 12 hours during night.

33. 33
(vi) Traction load: This type of load includes tram
cars, trolley buses, railways etc. This class of load
has wide variation. During the morning hour, it
reaches peak value because people have to go to
their work place. After morning hours, the load
starts decreasing and again rises during evening
since the people start coming to their homes.

37. 37
Eg1: The maximum demand on a power station is
100 MW. If
the annual
load factor is
40% ,
calculate the total energy generated in a year.
Sol:
• Energy
generated/year

38. Eg2: A generating station has a connected load of
43MW and a maximum demand of 20 MW; the
units generated being 61·5 × 10^6 per annum.
(i) the demand factor and (ii) load
Calculate
factor.
Sol:
38

39. Eg3: A 100 MW power station delivers 100 MW for
2 hours, 50 MW for 6 hours and is shut down for
the rest of each day. It is also shut down for
maintenance for 45 days each year. Calculate its
annual load factor.
Sol:
39

40. 40
Eg4: A generating station has a maximum demand
of 25MW, a load factor of 60%, a plant capacity
factor of 50% and a plant use factor of 72%. Find
(i) the reserve capacity of the plant (ii) the daily
energy produced and (iii) maximum energy that
could be produced daily if the plant while running
as per schedule, were fully loaded.

41. 41

42. 42

43.  Industrial consumer = 1500 kW ; Commercial
establishment = 750 kW Domestic power =
100 kW; Domestic light = 450 kW
 If the maximum demand on the station
is 2500 kW and the number of kWh
generated per year is 45 × 105,
determine (i) the diversity factor and (ii)
annual load factor
43

44. 44