1. Power System Operation & Control
(KEN-070)
Unit – I
Introduction to PSOC
Mr. Gaurav Srivastava
Asst. Professor
EN Department
AKGEC, Ghaziabad
2. Contents
Structure of Power System
Significance of Voltage and Frequency Control
Energy Control Centre
Level Decomposition in Power System
SCADA
EMS
Real Time Computer-Control
PMU- concept of Synchrophasor
PowerSystem Security
Operational Stages of Power System
Power Scenario in Indian Grid
Installed Capacity in India
3. Structure of Power System
• Generating stations, transmission lines and the distribution
systems are the main components of an electric power
system.
• Generating stations and a distribution system are connected
through transmission lines, which also connect one power
system (grid, area) to another.
• A distribution system connects all the loads in a particular
area to the transmission lines.
• For economical and technological reasons, individual power
systems are organized in the form of electrically connected
areas or regional grids (also called power pools).
• Each area or regional grid operates technically and
economically independently, but these are Eventually
interconnected to form a national grid (which may even form
an international grid) so that each area is contractually tied to
4. Structure of Power System
• Power station siting depends on many factors like—
technical, economical and environmental.
• As it is considerably cheaper to transport bulk electric
energy over extra high voltage (EHV)
• transmission lines than to transport equivalent
quantities of coal over rail road, the recent trends in
India has been to build super (large) thermal power
stations near coal mines.
• Bulk power can be transmitted to fairly long
distances over transmission lines of 400/765 kV and
above.
• Transmission capability of a line is proportional to the
square of its voltage. The voltages are expected to
5. Structure of Power System cont..
• In India, 400 kV lines are already in
operation.
• Several 765 kV lines have been built so
far in India.
• For very long distances (over 600 km), it
is economical to transmit bulk power by
DC transmission.
• Electric power is generated at a voltage
of 11 to 25 kV which then is stepped up
to the transmission levels in the range of
66 to 765 kV (or higher).
• The first stepdown of voltage from
transmission level is at the bulk power
substation, where the reduction is to a
range of 33 to 132 kV, depending on the
transmission line voltage. Some
industries may require power at these
voltage levels. Schematic diagram depicting
power system structure
6. Structure of Power System cont..
• The next stepdown in voltage is at
the distribution substation.
Normally, two distribution voltage
levels are employed: -
1. The primary or feeder voltage
(11 kV).
2. The secondary or consumer
voltage (415 V 3/230 V 1.
• The distribution system, fed from
the distribution transformer
stations, supplies power to the
domestic or industrial and
commercial consumers.
• Thus, the power system operates
at various voltage levels
separated by transformer
Schematic diagram depicting
power system structure
7. Significance of Voltage and Frequency Control
• The stability of electrical grid is maintained by frequency and voltage control.
• The only possible ways of storage.
– Transform AC into DC and then store it.
– Transform the electric energy into the form of energy.
• In the long run, storage in hydrogen could contribute to the management of electric
system.
• Since storage is difficult, two separate equilibriums should be kept on the grid.
• Frequency Control = Active Power Control
• The active power generated should always equal to the active power consumed. A
deviation from this equilibrium results in a deviation from the 50 Hz frequency. So
keeping this equilibrium between active policy and generation means maintaining
frequency.
• Consumption of active power varies strongly according to the time of the day, the
season, or weather conditions.
• The reserve capacity is kept in power plants to be able to react quickly and deliver extra
power when necessary.
8. Significance of Voltage and Frequency Control cont..
• In a power system the load demand continuously changes, in accordance with it the
power input also varies.
• If the input - output balance is not maintained a change in frequency will occur.
• The control of frequency is achieved primarily through speed governor mechanism
aided by supplementary means for precise control.
• Voltage Control = Reactive Power Control
• The objective of system voltage control is to maintain a satisfactory voltage profile in the
system during both periods of maximum and minimum loadings.
• The reactive power on the grid should be kept in equilibrium as well. Reactive power is
an extra load for the grid, leaving less capacity for active power, resulting in a local
voltage drop. So keeping reactive power in equilibrium means maintaining voltage.
• Reactive power is inextricably related with active power, and oscillates between
generator, inductive elements (motors, transformers) and capacitive elements (capacitor
batteries) on the grid.
• Capacitor banks, synchronous generators are responsible for compensating reactive
power.
9. Energy Control Centre
• The energy control center (ECC) has traditionally been the decision-center for
the electric transmission and generation interconnected system.
• The ECC provides the functions necessary for monitoring and coordinating the
minute-by-minute physical and economic operation of the power system.
• In order to have an efficient power system operation and control, various
control centers have to be operated in a hierarchical manner.
• There has been level decomposition of control centers in the power system.
• There are 4 types of control centers.
1. Local Control Centre
2. Area Load Dispatch Centre
3. State Load Dispatch Centre
4. Regional Control Centre.
10. Level Decomposition in Power System
• National Load Dispatch Centre
(NLDC) has been setup at New
Delhi and became operational
in January 2014.
• Below this, five Regional level
Load Dispatch Centers (RLDC)
have been shown.
• The role of the NRLDC is to
monitor and supervise the grid
and power generation of the
region.
• It focuses attention on the
regional interconnected
network.
• By using 'Energy Management
System' (EMS) and advanced
application programmes,
NRLDC coordinates with all
inter-region and inter-state
power exchange.
11. Level Decomposition cont..
• Below NRLDC, State level SLDCs and Central Project Coordination & Control Centre
(CPCC) have been shown.
• The primary role of SLDCs is to monitor, control and coordinate the generation,
transmission and distribution of power within the State while ensuring safety and
continuity of its transmission and sub-transmission power networks.
• CPCC (North) coordinates with all Central sector projects of northern region such as
those of NTPC, NHPC, Power Grid, Tehri, etc. CPCC gets data from Central Sector
projects and that data is added at regional level.
• Each RLDC has the ability to exchange data with other RLDCs as well as with NLDC,
but direct data transmission does not take place between SLDC of one State with SLDC
of another State.
12. Responsibilities of NLDC
• The National Load Dispatch Centre shall be Apex Body to ensure
integrated operation of the national Power System and discharge
the following functions.
• Supervision over the RLDCs.
• Scheduling and dispatch of electricity over inter-regional links in
accordance with Grid standards specified by the Authority and
Grid Code specified by the Central Commission in coordination
with RLDCs.
• Coordination with RLDCs for achieving maximum economy and
efficiency in operation of National Grid.
• Monitoring of operations and grid security of the National Grid.
• Dissemination of information relating to operations of transmission
system in accordance with directions or regulations issued by the
Central Commission and the Central Government from time to
time.
13. Responsibilities of NLDC
• Supervision and control over the inter regional links as may be
required for ensuring stability of the power system under its control.
• Co-ordination with Regional Power Committees for regional outage
schedule in the national perspective to ensure optimum utilization of
power resources.
• Coordination with RLDCs for the energy accounting of inter-regional
exchange of power.
• Coordination for restoration of synchronous operation of National
Grid with RLDCs.
• Co-ordination for trans-national exchange of Powers.
• Providing operational feed-back for National Grid planning to the
Authority and the Central Transmission Utility.
• Levy and collection of such fee and charges from the Generating
Companies or the licensees involved in the power system as may
be specified by the Central Commission.
14. Responsibilities of NRLDC
• NRLDC: Northern Region Load Dispatch Center
• To ensure the integrated operation of the power system in the Northern
Region.
• Monitoring of system parameters and system security.
• Daily scheduling and operational planning.
• Facilitating bilateral and inter-regional exchanges of power.
• Analysis of tripping/disturbances and facilitating immediate remedial
measures.
• System studies, planning and contingency analysis.
• Augmentation of telemetry, computing and communication facilities.
• Computation of energy dispatch and drawls values using SEMs.
15. Responsibilities of SLDC
• SLDC: State load Dispatch centre
• Be responsible for optimum scheduling and dispatch of electricity within a
State in accordance with the contracts entered into with the licensees or the
generating Companies operating in that State.
• Monitor grid operation.
• Keep accounts of the quantity of electricity transmitted through State grid.
• Exercise supervision and control over the inter-State transmission system.
• Be responsible for carrying out real time operation for grid control and
dispatch of electricity within the State through secure and economic
operation of the State Grid in accordance with the Grid standards and State
Grid Code.
16. RTU
• RTU (Remote Terminal Unit): The system gets information from
remote terminal unit (RTU) that encode measurement transducer
outputs and opened/closed status information into digital signals
which are sent to the operation center over communications circuits
• Main operations of RTU:
Each sub-LDC collects data from various RTUs, installed at important sub-
stations (400KV, 220KV and few 132KV) and powerhouses.
So far in UPPTCL, 72 RTUs have already been integrated with the system.
Each RTU automatically picks up required information (MW, MVAr, KV, Hz,
Circuit breaker & isolator status) of the sub-station/powerhouse and transmit it
to its sub-LDC through communication system.
This information is processed in the data Server of sub-LDC.
Data in the form of binary stream of pulses are sent by RTU at the speed of
300, 600 or 1200 bits per second rate (baud).
At sub-LDC, the information is updated within 10 sec.
17. Components of Energy Control Centre
• The system control function traditionally used in electric utility
operation consists of three main integrated subsystems:
– The energy management system (EMS),
– The supervisory control and data acquisition (SCADA),
– The communications interconnecting the EMS and the SCADA
(which is often thought of as part of the SCADA itself).
• Figure on next slide provides a block diagram illustration of modern
Energy management system comprising of Initial load forecast and
scheduling, SCADA, Security assessment and analysis; and finally
the optimal power flow/constrained economic dispatch.
19. SCADA cont..
• In SCADA system measured values, i.e. analogue (measured value) data (MW,
MVAR, V, Hz Transformer tap position), and Open/Closed status information,
i.e. digital data (Circuit Breakers/Isolators position i.e. on/off status), are
transmitted through telecommunication channels to respective sub-LDCs.
• Secondary side of Current Transformers (CT) and Potential Transformer (PT)
are connected with 'Transducers’.
• The output of transducers is available in dc current form (in the range of 4mA
to 20mA).
• A/D converter converts this current into binary pulses.
• Different inputs are interleaved in a sequential form and are fed into the CPU of
the RTU.
• The output of RTU, containing information in the form of digital pulses, is sent
to sub LDC.
• At sub LDC end, data received from RTU is fed into the data servers.
• In general, a SCADA system consists of a database, displays and supporting
programs.
20. SCADA cont..
1. Communications - Sub-LDC's computer communicates with all
RTU stations under its control, through a communication system.
RTU polling, message formatting, polynomial checking and
message retransmission on failure are the activities of
'Communications' functional area.
2. Data Processing - After receipt of data through communication
system it is processed. Data process function has three sub-
functions i.e. (i) Measurements, (ii) Counters and (iii) Indications.
'Measurements' retrieved from a RTU are converted to
engineering units and linearized, if necessary. The
measurement are then placed in database and are checked
against various limits which if exceeded generate high or low
limit alarms.
21. SCADA cont..
Counters: The system has been set-up to collect 'Counters' at
regular intervals: typically 5 or 10 minutes. At the end of the
hour the units is transferred into appropriate hour slot in a 24-
hour archive/history.
'Indications' are associated with status changes and
protection. For those statuses that are not classified as
'alarms', logs the change on the appropriate printer and also
enter it into a cyclic event list. For those statuses, which are
defined as an 'alarms' and the indication goes into alarm, an
entry is made into the appropriate alarm list, as well as in the
event list and an audible alarm is generated in the sub-LDC.
22. SCADA cont..
3. Alarm/Event Logging - The alarm and event logging facilities are
used by SCADA data processing system. Alarms are grouped into
different categories and are given different priorities. Quality codes
are assigned to the recently received data for any 'limit violation' and
'status changes'. Alarms are acknowledged from single line diagram
(or alarm lists) on display terminal in LDCs.
4. Manual Entry - There is a provision of manual entry of measured
values, counters and indications for the important
sub-station/powerhouse, which are uncovered by an RTU or some
problem is going on in its RTU, equipment, communication path, etc.
23. SCADA cont..
5. Averaging of Measured Values - As an option, the SCADA
system supports averaging of all analogue measurements. Typically,
the averaging of measured values over a period of 15 minutes is
stored to provide 24 hours trend.
6. Historical Data Recording (HDR) - The HDR, i.e. 'archive',
subsystem maintains a history of selected system parameters over a
period of time. These are sampled at a pre-selected interval and are
placed in historical database. At the end of the day, the data is saved
for later analysis and for report generation.
24. SCADA cont..
7. Interactive Database Generation - Facilities have been provided in such
a way that an off-line copy of the SCADA database can be modified allowing
the addition of new RTUs, pickup points and communication channels.
8. Supervisory Control/Remote Command - This function enables the
issue of 'remote control' commands to the sub-station/powerhouse
equipment e.g. circuit breaker trip command.
9. Fail-over - A 'Fail-over' subsystem is also provided to secure and
maintain a database of devices and their backups. The state of the device is
maintained indicating whether it is 'on-line' or 'failed'. There is a 'backup'
system, which maintains database on a backup computer and the system is
duplicated.
25. EMS & Real Time Computer-Control
• EMS: ENERGY MANAGEMENT SYSTEM
• For energy management of the power system, control personnel
and application software engineers use SCADA data available in the
database by using EMS software. Important features are as below:
1. The Data Base Compiler provides a consistent source of data
usable for the applications in an efficient form. The Data Base
Compiler does final checking for completeness and consistency of
the entries for a specific application and prepares those special
tables which are needed for the efficiency of specific application
programes.
26. EMS & Real Time Computer-Control
2. Recording of 'Sequence of Events' (SOEs) is the most innovative feature
provided in this system. A RTU has the ability to accurately time tag status
change and report this information to sub-LDC. All RTUs in the system are 'time
synchronized' with the master station. In the event of any tripping, sequence of
events can be well established on time scale with a resolution of 10 ms.
3. Normally, 'Automatic Generation Control' (AGC) function issues control
commands to generating plants using the concept of Area Control Error (ACE). It
is based on deviations in 'standard frequency (50 Hz)' and 'scheduled area
interchanges' from that of the 'actual frequency' and 'actual area interchanges' In
the event of unavailability of sufficient generation to satisfy the AGC
requirement, the System Control Officer can enforce required quantum of load
shedding.
27. EMS & Real Time Computer-Control cont..
4. For 'Operation Scheduling' the application software has 'short-
term' and 'long-term' 'System Load Forecasting' functions to assist
dispatching Engineer/control Officer in estimating the loads that are
expected to exist for one to several days in advance. This function
provides a scientific and logical way of scheduling of resources in a
very effective manner.
Under 'Short-term Load Forecasting' function, application
software engineers are able to forecast weekly peak demands
and load duration curves for several months into the future.
Under 'Long-Term Load Forecasting' function, forecasting of
monthly peak demands and load duration curves for several
years into the future can done for the use of 'Power System
Planner'.
28. EMS & Real Time Computer-Control cont..
5. The other functions like economic dispatch, reserve monitoring, production
costing, inter system transactions scheduling, etc. are available to guide
System Control Officer to optimally use available resources.
6. Power System Control Officer/Analyst would be able to use contingency
analysis function to assess the impact of specified contingencies that
would cause line (s) overloads, abnormal voltages, and reactive limit
violations.
7. The EMS software system may have many other applications for use,
which include network topology, performing of state estimation, optimal
power flow (OPW) & stability program, Power Flow/Help/
Instructional/Tabular/Single Line Diagram Displays etc.
29. PowerSystem Security
• An overriding factor in the operation of a power system is the desire to
maintain system security.
• System security involves practices designed to keep the system
operating when components fail.
• All equipment in a power system is designed such that it can be
disconnected from the network. The reasons for these disconnections
are generally divided into two categories:
Scheduled Outages
Forced Outages.
30. PowerSystem Security
• Scheduled outages are typically done to perform maintenance or
replacement of the equipment, and, as its name implies, the time
of disconnect is scheduled by operators to minimize the impact on
the reliability of the system.
• Forced outages are those that happen at random and may be due
to internal component failures or outside influences such as
lightning, wind storms, ice build-up, etc.
31. PowerSystem Security cont..
• If a forced outage occurs on a system that leaves it operating with limits violated on
other components, the event may be followed by a series of further actions that switch
other equipment out of service. If this process of cascading failures continues, the entire
system or large parts of it may completely collapse. This is usually referred to as a
system blackout.
• Most large power systems install equipment to allow operations personnel to monitor
and operate the system in a reliable manner.
• System security can be broken down into three major functions that are carried out in an
operations control centre:
1. System monitoring
2. Contingency analysis
3. Security-constrained optimal power flow
32. System Monitoring
• System monitoring provides the operators of the power system
with pertinent up-to-date information on the conditions on the
power system.
• Generally speaking, it is the most important function of the three.
• From the time that utilities went beyond systems of one unit
supplying a group of loads, effective operation of the system
required that critical quantities be measured and the values of the
measurements be transmitted to a central location.
• Such systems of measurement and data transmission, called
energy management systems (EMS), have evolved to schemes
that can monitor voltages, currents, power flows, and the status of
circuit breakers and switches in every substation in a power
system transmission network.
33. System Monitoring
• The power system as seen by power system operators,
whether at the highest level or individual level at a small
electric company, all have to deal with the power system
in what has been characterized as one of four modes:
– Normal
– Alert
– Emergency
– Restoration
34. System Monitoring cont..
• Normal usually means that there are no alarms being
presented and contingency analysis is not reporting any
contingencies that would cause overloads or voltage
violations.
• Alert means that either an alarm has been presented to
the operator or the contingency analysis programs have
presented the possibility of a contingency problem.
35. System Monitoring cont..
• Emergency would indicate serious alarm messages that the
operators must act on immediately and threaten to cause major
shutdowns of power system equipment or even parts of the system.
• Restoration comes if the system does in fact lose equipment or
part of the system or even most of it is shut down or blacked out. In
restoration, equipment must be investigated to see if it can be
brought back on line and then switched back into the system. Loads
that were dropped are brought back on line, sometimes in small
blocks. Restoration can take many hours especially if large
generators are involved.
36. Contingency Analysis
• The results of this type of analysis allow systems to be
operated defensively.
• Many of the problems that occur on a power system can
cause serious trouble within such a quick time period
that the operator cannot take action fast enough once
the process is started. This is often the case with
cascading failures.
• Because of this aspect of systems operation, modern
operations computers are equipped with contingency
analysis programs that model possible system troubles
before they arise.
37. Contingency Analysis
• These programs are based on a model of the power system
and are used to study outage events and alarm the
operators to any potential overloads or out-of-limit voltages.
• For example, the simplest form of contingency analysis can
be put together with a standard power flow program together
with procedures to set up the power flow data for each
outage to be studied by the power flow program.
• Several variations of this type of contingency analysis
scheme involve fast solution methods, automatic
contingency event selection, and automatic initializing of the
contingency power flows using actual system data and state
estimation procedures.
38. Security-Constrained Optimal Power Flow
• In this function, a contingency analysis is combined with an optimal power flow
that seeks to make changes to the optimal dispatch of generation, as well as
other adjustments, so that when a security analysis is run, no contingencies
result in violations.
• To show how this can be done, power system is divided into four operating
objectives.
• Normal state dispatch: This is the state that the power system is in prior to
any contingency. It is optimal with respect to economic operation, but it may not
be secure.
• Post-contingency: This is the objective after a contingency has occurred. We
shall assume here that this condition has a security violation (line or
transformer beyond its flow limit or a bus voltage outside the limit).
• Secure dispatch: This is the objective with no contingency outages is to
correct the operating parameters to account for security violations.
• Secure post-contingency: The objective is to re-mediate the contingency as
applied to the base-operating condition with corrections.
39. Operational Stages of Power System
• A normal (secure) state is the ideal
operating condition, wherein all the
equipment operate within their design
limits.
• Also, the power system can withstand a
contingency without violation of any of the
constraints.
• The system is said to be in the alert
(insecure) state, if voltage and frequency
are reaching beyond the specified limits.
The system is "weaker" and may not be
able to withstand a contingency.
40. Operational Stages of Power System cont..
• Preventive Control actions like shifting generation (re-scheduling), load
shedding are required to get the system back to the normal state.
• If preventive control actions do not succeed, a power system remains insecure
(in the alert state).
• If a contingency occurs, the system may go into the emergency state where
overloading of equipment (above the short term ratings of the equipment)
occurs.
• The system can still be intact and can be brought back to the alert state by
Emergency Control actions like fault tripping, generator tripping, load tripping,
HVDC power control etc.
• If these measures do not work, integrated system operation becomes unviable
and a major part of the system may be shutdown due to equipment outages.
• Load shedding and islanding is necessary to prevent spreading of
disturbances and a total grid failure.
• The small power systems (islands) are reconnected to restore the power
system to normal state (Restorative Control).
41. Power Scenario in Indian Grid
• Total Installed Capacity (As on 31.05.2023) - Source : Central
Electricity Authority (CEA)
• INSTALLED GENERATION CAPACITY (SECTOR WISE) AS ON 31.05.2023
Sector MW % of Total
Central Sector 1,00,055 24.0%
State Sector 1,05,726 25.3%
Private Sector 2,11,887 50.7%
Total 4,17,668 100 %
45. Cont.…
• PERFORMANCE OF GENERATION
FROM THERMAL, HYDRO,
NUCLEAR
• The electricity generation target
(Including RE) for the year 2023-
24 has been fixed as 1750 Billion
Unit (BU). i.e. growth of around
7.2% over actual generation of
1624.158 BU for the previous year
(2022-23). The generation during
2022-23 was 1624.158 BU as
compared to 1491.859 BU
generated during 2021-22,
representing a growth of about
8.87%.
• The electricity generation target
of thermal, hydro, nuclear &
Bhutan import for the year 2021-
22 has been fixed as 1356 Billion
Unit (BU). i.e. growth of around
CATAGORY INSTALLED
GENERATION
CAPACITY (MW)
% of
SHARE IN
Total
Fossil Fuel
Coal 2,05,235 49.1%
Lignite 6,620 1.6%
Gas 24,824 6.0%
Diesel 589 0.1%
Total Fossil Fuel 2,37,269 56.8%
Non-Fossil Fuel
RES (Incl. Hydro) 1,73,619 41.4%
Hydro 46,850 11.2 %
Wind, Solar & Other ER 1,25,692 30.2 %
Solar 67,078 16.1 %
BM Power/Cogen 10,248 2.5 %
Waste to Energy 554 0.1 %
Small Hydro Power 4,944 1.2 %
Nuclear 6,780 1.6%
Total Non-Fossil Fuel 1,79,322 43.0%
Total Installed Capacity
(Fossil Fuel & Non-Fossil Fuel)
4,17,668 100%
Installed Generation Capacity (Fuel
wise) as on 31.05.2023
46. Cont.…
• Total Generation and growth over previous year in the country during 2009-10 to 2023-24 :-
• The electricity generation target for the year 2023-24 was fixed at 1750 BU comprising of 1324.110 BU
Thermal; 156.700 BU Hydro; 46.190 Nuclear; 8 BU Import from Bhutan and 215 BU RES (Excl. Large Hydro)
Year
Total Generation
(Including Renewable Sources) (BU)
% of growth
2009-10 808.498 7.56
2010-11 850.387 5.59
2011-12 928.113 9.14
2012-13 969.506 4.46
2013-14 1,020.200 5.23
2014-15 1,110.392 8.84
2015-16 1,173.603 5.69
2016-17 1,241.689 5.80
2017-18 1,308.146 5.35
2018-19 1,376.095 5.19
2019-20 1,389.102 0.95
2020-21 1,381.855 -0.52
2021-22 1,491.859 7.96
2022-23 1,624.158 8.87
2023-24* 286.176 -0.72
