it is vey necessary for power enginner

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Real time or online applications
of computers in power system
CHAPTER TWO
INTRODUCTION
 The global electricity demand is growing at a rapid
pace, making the requirements for more reliable,
environment friendly, and efficient transmission and
distribution systems inevitable.
 The traditional grids and substations are no longer
acceptable for sustainable development and
environment-friendly power delivery.
 Electric power utilities worldwide are increasingly
adopting the computer aided monitoring, control and
management of electric power system to provide better
services to electric consumers.
 Therefore, Power engineering today is a combination of
the latest techniques in signal processing, wide area networks,
data communication, and advanced computer applications.
Power system automation TECHNIQUES
• Power system automation focuses use of transformers,
circuit breakers, relays, generators, capacitors, regulators,
monitoring, and control equipment in a efficient manner.
 Data Acquisition System :
 Data acquisition refers to collection of data in the
form of analog measured voltage and current
 Power system supervision
 Computer processes ,personnel supervises and monitor
 The status and condition of power system using the
acquired data.
 Power system control
 Control refers to sending messages to a device to
operate I&C and power system devices.

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Remote Terminal Unit :-
RTU is an IED which is installed at
the remote location and acts as a
termination point of network.Dedicated
pair of copper conductor is used to
sense every contacts and transducer
value.
 metering
It is an IED which is used for
measurement of accurate values of
voltage, current , power and power factor
and stores the historical data.
Contd …
Digital Fault Recorder
It is an IED which records
disturbances. It stores data like
frequency, voltage and
harmonics in digital format.
Protective Relays
A Protective relay is an IED used to sense power
disturbances and automatically control action on the power
system to protect the equipment.
Automated Meter Reading
It is a communication service which transfers data from
utility meters to control panel.
Contd …
 Automation is used worldwide in a variety of applications
ranging from the gas and petroleum industry, power
system automation, building automation, to small
manufacturing unit automation.
 SCADA systems are defined as a collection of equipment
that will provide an operator at a remote location with
sufficient information to determine the status of particular
equipment or a process and cause actions to take place
regarding that equipment or process without being
physically present.
 SCADA implementation thus involves two major
activities: data acquisition (monitoring) of a process or
equipment and the supervisory control of the process, thus
leading to complete automation.
Supervisory control and data acquisition
(SCADA) systems
 The complete automation of a process can be achieved by
automating the monitoring and
the control actions. This will involve the following steps:
 Collect the data from the field.
 Convert the data into transmittable form.
 Bundle the data into packets.
 Transmit the packets of data over the communication media.
 Receive the data at the control center.
 Decode the data.
 Display the data at the appropriate points on the display screens of
the operator.
• The operator initiates the control command.
• Bundle the control command as a data packet.
• Transmit the packet over the communication media.
• The field device receives and decodes the control command.
• Control action is initiated in the field using the appropriate device
actuation.

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• The monitoring and controlling process.
SCADA IN POWER SYSTEMS
 SCADA systems are in use in all spheres of power
system operations starting from generation, to
transmission, to distribution, and to utilization of
electrical energy.
 The SCADA functions can be classified as basic
and advanced application functions.
 The basic SCADA functions include data acquisition,
remote control, human-machine interface, historical
data analysis, and report writing, which are common to
generation, transmission, and distribution systems.
 Data acquisition is the function by which all
kinds of data analog, digital, and pulse are
acquired from the power system.
 This is accomplished by the use of sensors,
transducers, and status point information
acquired from the field.
 Remote control involves the control of all the
required variables by the operator from the
control room.
 In power systems, the control is switch
positions; such as circuit breaker and isolator
positions and equipment on and off positions.
Historical data analysis is an important
function performed by the power system
SCADA, where the post-event analysis is done
using the data available after the event has
happened.
the post outage analysis where the data
acquired by the SCADA system can
provide insights into such information as
the sequence of events during the
outage, malfunctioning of any device in
the system, and the action taken by the
operator.

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 Figure Use of SCADA in power systems.
A GENERATION SCADA APPLICATION FUNCTIONS
 Generation SCADA, in addition to the basic functions,
will include the following application functions.
• Automatic Generation Control (AGC): a set of
equipment and computer programs implementing
closed-loop feedback control of frequency and net
interchange
• Economic Dispatch Calculation (EDC): the
scheduling of power from all available sources in such
a way to minimize cost within some security limit
 Interchange Transaction Scheduling (ITS): ensures that
sufficient energy and capacity are available to satisfy
load energy and capacity requirements
A GENERATION SCADAAPPLICATION FUNCTIONS
 Transaction Evaluation (TE): evaluates economy of
transactions using the unit commitment results as the
base condition.
 Unit Commitment (UC): produces the hourly start-up
and loading schedule which minimizes the production
cost for up to one week in the future.
 Short-Term Load Forecasting (STLF): produces the
hourly system load for up to one week into the future
and is used as input to the unit commitment program
 Hydrothermal coordination: the scheduling of power
from all available hydro generation in such a way to
minimize cost within constraints
TRANSMISSION SCADA APPLICATION FUNCTIONS
 The transmission SCADA will include energy
management system (EMS) functions such as
 Network Configuration/Topology Processor:
analyzes the status of circuit breakers as well as
measurements to automatically determine the current
model of the power system.
 State Estimation: provides a means of processing a
set of redundant information to obtain an estimate of
the state variables of the system
 Contingency Analysis: simulates outages of
generating units and transmission facilities to study
their effect on bus voltages, power flows, and the
transient stability of the power system as a whole.

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TRANSMISSION SCADA APPLICATION FUNCTIONS
 Three-Phase Balanced Power Flow: obtains
complete voltage angle and magnitude information for
each bus in a power system for specified load and
generator real power and voltage conditions.
 Optimal Power Flow: optimize some system objective
function, such as production cost, losses, and so on,
subject to physical constraints on facilities and the
observation of the network laws.
DISTRIBUTION AUTOMATION APPLICATION FUNCTIONS
 Distribution automation/distribution management
systems (DA/DMS) include substation automation,
feeder automation, and customer automation. .
 Fault identification, isolation, and service restoration
 Network reconfiguration
 Load management/demand response
 Active and reactive power control
 Power factor control
 Short-term load forecasting
 Three-phase unbalanced power flow
 Interface to customer information systems (CISs)
 Interface to geographical information systems (GISs)
ADVANTAGES OF SCADA IN POWER SYSTEMS
 Increased reliability, as the system can be operated with less severe
contingencies and the outages are addressed quickly
 Lower operating costs, as there is less personnel involvement due
to automation
 Faster restoration of power in case of a breakdown, as the faults can be
detected faster and action taken
 Better active and reactive power management, as the values are accurately
captured in the automation system and appropriate action can
be taken
 Reduced maintenance cost, as the maintenance can be more effectively done
(transition from time-based to condition-based maintenance) with continuous
monitoring of the equipment
 Reduced human influence and errors, as the values are accessed
automatically, and the meter reading and related errors are avoided
 Faster decision making, as a wealth of information is made available
to the operator about the system conditions to assist the operator in
making accurate and appropriate decisions
 Optimized system operation, as optimization algorithms can be run
and appropriate performance parameters chosen
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TYPICAL SUPERVISORY SYSTEM
M
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m
M
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m
User
Interface
Analog
Output
Digital
Output
Intelligent
Electronic
Devices
User
Interface
Analog
Input
Digital
Input
Communications
Master
Station
Remote
Terminal
Units
Typical Supervisory System

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Real time applications can be classified under this category
 Control functions:
i) Load Frequency Control (LFC)
ii) Automatic Generation Control (AGC)
iii) Reactive Power Control (RPC)
iv) Voltage Control (VC)
v) Reactive Power and Voltage Control (QVC)
 Protection Functions: functions are the first which are
activated in a real time operation as a protective
measure.
i) Protective relaying ii) Primary protection iii) Secondary
protection or backup protection
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Real time applications
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i) On-line closed loop control
ii) On-line open loop control
iii) Off line study or simulation model
 On-line closed loop controls are those which are
performed without the presence of the operator like LFC,
AGC, etc.
 On-line open loop controls are those which are
performed with the presence of the operator for decision
making like Operation and Dispatch. Examples are
 Real power dispatch or active power dispatch (APD)
 Reactive Power Dispatch (RPD)
 Active and Reactive Power Dispatch .
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The important functions which are carried out based on the
real time functions
 Measurements: Measurements of important parameters
from the remote terminal unit (RTU) like three phase
voltage, current, power factor, power flows, etc.
 Monitoring: Real time monitoring of the above
parameters at frequent intervals of time. These values are
continuously monitored to check for any significant
deviations from normal values
 Control Actions: Important control functions or actions
like ‘preventive’, ‘corrective’, ‘emergency’ , ‘restorative’, etc.
 Network Topology Processing: Building a network
model based on real time measurements.
 The role of network topology processor is to update the
status of circuit breakers and in the real time model in the
simulation study.
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 State Estimator: Determining the best estimate from
real time measurements.
 The output of state estimation is used along with the
output network topology processor.
 Power Flow: Load flow analysis or Determining
voltages and phase angles.
 Security Assessment: Determining the ‘secure’ or
‘insecure’ state of a system.
 The result of security analysis is used for dispatch and
optimization functions like generation dispatch and
voltage and reactive power optimization.
 Contingency Analysis: Impact of a set of
contingencies to identify harmful ones.
 Optimal Power Flow: Optimization of a specified
objective function with constraints.
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 Short Circuit Analysis: Determination of fault
currents for various faults on the network
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