Electrical Engineering Power System Operation and Control

1. Power System Operation and
Control
by
Dr. Deependra Kumar Jha
ME (Power Systems), PhD (Electric Power System Engineering)
Professor, Department of Electrical Engineering
School of Engineering & Technology, Galgotias University

2. Introduction
• In 1831, Michael Faraday’s many years of efforts rewarded when he
discovered electromagnetic induction
• Later, he invented the first generator
• Today, electric energy technologies have a central role in social and
economic development at all scales
• Energy is closely linked to environmental pollution and degradation, to
economic development and quality of life
• Today, we are mostly dependent on nonrenewable fossil fuels that have
been and will continue to be a major cause of pollution and climate
change
• Finding sustainable alternatives is becoming increasingly urgent
• Operation and control of power system is an extremely complex task

3. Definitions
• Electric Capacity is a term that defines the rated continuous load-
carrying ability, expressed in megawatts (MW) or megavolt-amperes
(MVA) of generation, transmission, or other electrical equipment
• Electric Energy is the term that defines the generation or use of electric
power by a device over a period of time. It is expressed in kilowatt-hours
(kWh), megawatt-hours (MWh), or gigawatt-hours (GWh)
• In context of electric circuits, the term ‘load’ refers to any device in which
power is being dissipated (i.e. consumed)
• In larger context of the power system, loads are usually modeled in an
aggregated way rather than an individual appliance. Load may refer to
an entire household, a city block or all the customers within a certain
region

4. Type of loads
• Resistive loads (25%): Heating and lighting equipments
e.g. Toaster, iron, electric blankets, Incandescent
lamps
• Motors (70%): Compressors (air conditioner, refrigerator)
Pumps (well, pool), Fans
Household appliances (washer, mixer, vacuum
cleaner)
Large commercial 3-phase motors (grocery store
chiller)
Power tools (hand drill, lawn mower)
Electric street cars
Basically ‘anything’ that moves!
• Electronic devices (5%): Power supplies for computers etc.
Transformers (adapter, battery charger)

5. Definitions
• The term ‘demand’ refers to physical quantity of power, NOT energy
• Serving the instantaneous demand under diverse circumstances is the
central challenge in designing and operating power systems and the one
that calls for majority of investment and effort
• Load curves (Load profiles):
Instantaneous demand varies over the course of a day and is
represented by Load profile
A load profile is drawn at any level of aggregation: for an individual user,
a distribution feeder or an entire grid
It may represent an actual day or a statistical average over typical days
in a given month or season
The maximum demand which is of greatest interest to the service
provider is termed as peak load or peak demand or simply peak

6. Definitions
• In warmer climates where air conditioning dominates electrical usage,
demand will tend to be ‘summer peaking’; conversely, heating
dominated regions will see ‘winter peaking’
• Load Duration Curves:
A different way to represent the load profile
Rearranging of the load profile in descending order of magnitude
Indicates how many hours a certain load has been required in the
course of the day
• The ratio between average and peak demand is called ‘load factor’: flat
load duration curve desired from economical standpoint
• The load factor clearly depends upon climate but also it depends upon
the diversity within the customer base or load diversity

7. Calculations
Load
Connected
Total
Demand
Maximum
Actual

Factor
Demand
system
the
of
Peak
Actual
demands
maximum
individual
of
Sum

Factor
Diversity
period
time
same
the
during
Load
Peak
period
given time
a
over
Load
Average

r
Load Facto

8. Type of loads
• 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

9. Type of loads ……Contd
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
• “Load” is an externally given quantity, a variable beyond control, in a
completely unselfconscious manner.

10. Electric Power System Operation.
• Operational objectives of a power system have been to provide a
continuous quality service with minimum cost to the user. These
objectives are:
• The term “continuous service” can be translated to mean “secure and
reliable service”
 First Objective: Supplying the energy user with quality service, i.e.,
at acceptable voltage and frequency
 Second Objective: Meeting the first objective with acceptable
impact upon the environment.
 Third Objective: Meeting the first and second objectives
continuously, i.e., with adequate security and reliability.
 Fourth Objective: Meeting the first, second, and third objectives
with optimum economy, i.e., minimum cost to the energy user.

11. Integrated Objectives
• The direction of the arrows indicates the priority in which the objectives
are implemented
Interrelated objectives of operation of a power system
Economically constrained operation of a power system.

12. Task Division
1) Operations planning
2) Operations control
3) Operations accounting
Interrelated tasks of planned scheduling operation

13. Operation planning
• The facilities of a large power system consist of many generating units,
transmission lines, transformers, circuit breakers, DC/DC converters &
DC/ AC converters which are to scheduled for orderly operation &
maintenance
• The energy resources of a large power system consist of hydro, nuclear,
fossil power and renewable energy sources such as wind farm,
photovoltaic and micro turbines.
• These facilities are to be managed and utilized to satisfy load demand of
a power system.
• The load demand of a power system is cyclic in nature and has a daily
peak demand over a week period, weekly peak demand over a month
period, and monthly peak demand over a year period.
• Overall objectives of planned scheduling operation are to manage
facilities and optimize resources for satisfying the peak demand of each
load cycle, such that the total cost of operation is minimized.

14. Operation Control
• The primary functions of operations control are satisfying the
instantaneous load on a second-to-second and minute-to-minute basis.
Some of these functions are:
 Load Frequency Control
 On-Line Load Flow
 Economic Dispatch Calculation (EDC)
 Operating Reserve Calculation (ORC)

15. Operation Control……Contd.
• Load Frequency Control (LFC). This function is also referred to as
governor response. As the load demand of the power system increases,
the speed of generators will decrease and this will reduce the system
frequency. Similarly, as system load demand decreases, the speed of
the system generators would increase and this will increase the system
frequency. The power system frequency control must be maintained for
the power system grid to remain stable.
• Online Load Flow (OLF): This function generally utilizes the output of
network topology, i.e. the real time network model, and the bus
injections from state estimation for purpose of security monitoring,
security analysis and penalty factor calculations. This function performs
“if then condition” to determine the possible system states (voltages) in
face of system outages such as loss of a line due to weather condition
or sudden loss of a generator.

16. Operation Control……Contd.
• Economic Dispatch Calculation: Economic dispatch calculation of a
power system determines the loading of each generator on a minute-by-
minute basis so as to minimize the operating costs.
• Operating Reserve Calculation: The objective of operating reserve
calculation is to calculate the actual reserve carried by each unit and to
check whether or not there is a sufficient reserve in a system. The
operating reserve consists of spinning reserve (synchronized), non-
spinning reserve (non-synchronized), and interruptible load.

17. Unit Commitment and Economic
Load Dispatch

18. Economic Dispatch
 With a given set of units running, how of the load much should
be generated at each to cover the load and losses? This is the
question of Economic dispatch.
 The solution is for the current state of the network and does not
typically consider future time periods.
G
G
G
G
G
G
G
G G

19. Deciding which units to “commit”
 When should the generating units (G) be run for most economic
operation?
 Concern must be given to environmental effects
 How does one define “economic operation”? Profit maximizing?
Cost minimizing? Depends on the market you’re in.
G
G
G
G
G
G
G
G G

20. What is Unit Commitment?
 We have a few generators (units)
 Also we have some forecasted load
 Besides the cost of running the units we have additional costs
and constraints
 start-up cost
 shut-down cost
 spinning reserve
 ... and more

21. What is Unit Commitment?
 It turns out that we cannot just flip the switch of certain units on and
use them!
 We need to think ahead, and based on the forecasted load and unit
constraints, determine which units to turn on (commit) and which
ones to keep down
 Minimize cost, cheap units play first
 Expensive ones run only when demand is high

22. How Do We Solve the Problem?
 If a unit is on, we designate this with 1 and respectively, the off unit is
0
 So, somehow we decide that for the next hour we will have "0 1 1 0
1" if we have five units
 Based on that, we solve the economic dispatch problem for unit 2, 3
and 5
 We start turning on U2, U3, U5
 When the next hour comes, we have them up and running

23. To Come Up With Unit Commitment
 The question is, _how_ do we come up with this unit commitment
"0 1 1 0 1" ?
 One very simplistic way: if we have very few units, go over all
combinations from hour to hour
 For each combination at a given hour, solve the economic dispatch
 For each hour, pick the combination giving the lowest cost!