3. Communication Needs of Power System and an
Introduction to SCADA Fundamentals
and Implementation
Supervisory Control And Data Acquisition
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4. Operation Control Room:
Reliability.
Stability.
Security.
Quality.
Economy.
•Main target is to provide electric energy to the loads in
an appropriate Voltage & Frequency levels considering
circuits loading & tie lines exchange.
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5. Voltage Control
Transformers tap changer.
Capacitor Banks & inductors .
Excitation of Generating Units
Synchronous Condenser.
Circuit paralleling.
Voltages to be maintained:
±5% for 400 kV
±10% for 132 kV
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Reactive Droop Curves
6. Frequency Control
The power system
frequency
according grid code
Interconnected)
)
49.90 Hz- 50.10 Hz
(Isolated)
49.95 Hz- 50.05 Hz
Mainly the Egyptian system is the primary controller
of the unified frequency.
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7. Frequency Demand Control
Reduction in Demand would be required when:
• insufficient generation from available Generating Units on the Power
System or transfers across Interconnectors, or
• Transmission Network not being able to meet the Demand requirements
of Users due to operational constraints
Demand control methods include:
•Automatic under frequency load shedding (UFLS) scheme.
•Demand Control initiated by the transmission system operation (TSO).
•Consumer Demand Management (CDM).
Demand control is implemented according to the Grid Code
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8. SUPERVISORY CONTROL AND DATA ACQUISITION
There are two parts to the term SCADA:
Supervisory control (SC): indicates that the operator
in energy control center (ECC), has the ability to
control remote equipment.
Data acquisition (DA) : indicates that information is
gathered characterizing the state of the remote
equipment, and sent to the ECC for monitoring purposes.
The monitoring equipment is normally located in the
substations (slave) and is consolidated in what is known as
the remote terminal unit (RTU).
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(SCADA)
10. RTU
SCADA : Data communication architecture
computer
Panel
Multi-port
Stallion
Adapters
Panel
multi-Port
Stallion
adapters
Splitter
Modem
computer
Modem
Modem
Modem
RTU
Modem
RTU
Modem Modem
Modem
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master station
Communication system
Slave
11. Mainly a SCADA system consists of :
1- master station : Communicates with remote terminal
units (RTUs) that allowing operators to observe and
control physical plants.
2- Communication system : generally is via circuits
operating in the range of 600 to 4800 bits/s with the
RTU responding to periodic requests, initiated from the
master station every 2 to 10 s, depending on the criticality
of the data.
3- RTUs transmit device (Slave) : responsible to status and
measurements , and receive control commands and set
point data from, the master station.
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14. 1) Data acquisition: Provides telemetered measurements and
status information to operator.
2) Supervisory control: Allows operator to remotely control
devices, (open and close circuit breakers).
3) Tagging: Identifies a device as specific operating
restrictions , and prevents unauthorized operation.
4) Alarms: for unplanned events and undesirable
operating conditions. (Alarms are sorted by criticality area
of responsibility. Acknowledgment may be required).
5) Logging: Logs all operator entry, all alarms, and selected
information.
6) Load shed: Provides both automatic and operator
initiated tripping of load in response to system
emergencies.
7) Trending: Plots measurements on selected time scales.
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The traditional functions of SCADA systems are summarized:
15. Master Station Mainly Function
The master station in SCADA system functions mainly are:
• Manage communication circuit configuration.
• Down line load RTU files.
• Check and correct message errors .
Convert to engineering units.
• Detect status and measurement changes.
• Monitor abnormal and out-of-limit conditions.
• Log and time-tag(label) sequence of events.
• Detect and annunciate alarms.
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16. Dr.Audih M.alfaoury 16
RTUs FUNCTION (slave)
RTUs are equipped with microprocessors having memory
and logic capability.
Older RTUs are equipped with modems to provide the
communication link back to the ECC, whereas newer RTUs
generally have intranet or internet capability .
Relays located within the RTU, on command from the
ECC, open or close selected control circuits to perform a
supervisory action.
18. RTU actions may include :
opening or closing of a circuit breaker or switch.
modifying a transformer tap setting.
raising or lowering generator MW output or terminal
voltage.
switching in or out a shunt capacitor or inductor.
starting or stopping of a synchronous condenser.
Information gathered by the RTU and communicated to the
ECC includes both:
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a) Analog information: This includes frequency, voltages,
currents, real and reactive power flows , etc.
b) Status indicators : Which includes alarm signals (over-
temperature, low relay battery voltage, illegal entry) and
whether switches and circuit breakers are open or closed.
Such information is provided to the ECC through a periodic
scan of all RTUs. Two second scan cycle is typical.
19. MONITORING FUNCTIONS OF SCADA
Measurement and displaying of :current, voltage, frequency,
active and reactive power, energy, temperature, also storage
and evaluation of time stamped events and archiving of
measurements ,collection ,evaluation of maintenance data. As
well as disturbance recording and evaluation.
PROTECTION FUNCTIONS OF SCADA
Substation protection functions :
This includes monitoring of events (like start or trip
indication) , relay operating time , setting and reading of relay
parameters ,protection of bus bars, line feeders, transformers,
generators, protection monitoring (status, events,
measurements, parameters, recorders).
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20. COMMUNICATION TECHNOLOGIES OF SCADA
The form of communication required for SCADA is
telemetry.
Telemetry: is the measurement of a quantity to allow
interpretation of that measurement at a distance from the
primary detector. The feature of telemetry is the nature of
the translating (means, converting the measure into a
representative quantity of another kind). Telemetry may be
analog or digital.
IN ANALOG TELEMETRY :
Voltage, current, or frequency proportional to the quantity
being measured is developed and transmitted on a
communication channel to the receiving location, where
the received signal is applied to indicate the quantity
being measured, forms of analog telemetry include
variable current, pulse-amplitude and pulse-length.
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21. IN DIGITAL TELEMETRY:
The quantity being measured is converted to a code in
which the sequence of pulses transmitted indicates the
quantity.
One of the advantages to digital telemetering is
accuracy of data (is not lost in transmitting the data
from one location to another).
Digital telemetry requires analog to digital (A/D) and
possible digital to analog (D/A) converters as illustrated
in the next figure.
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23. COMMUNICATION BETWEEN MASTER CONTROL
STATION AND REMOTE CONTROL STATION:
a)Leased-wire : means a standard telephone (careful
coordination between the user and the telephone company).
b)Power-line carrier (PLC) offers an inexpensive and
typically more reliable alternative to leased-wire. (the
transmission circuit itself is used to modulate a
communication signal at a frequency occurs in the range
of 30-500 kHz. The security of PLC is very high since
the communication equipment is located inside the
substations.
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24. TYPICAL PLC ARRANGEMENT PHASE-GROUND COUPLING
CD
CKT-I
E/W
B
R
Y
E/W
B
R
Y
CVT/CC
CD
CVT/CC
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25. c) Microwave radio : refers to ultra-high-frequency (UHF)
radio systems operating above 1 GHz. (microwave
telemetry was analog, but digital microwave
communication is now quite common for EMS/SCADA
applications
d) Fiber optic cable : A more recent development has
concerned the use of fiber optic cable, a technology
capable of extremely fast communication speeds. Although
cost. ( Fiber optics may be run underground power cables
or to overhead transmission line towers just below the lines or
be run within the shield wire suspended above the
transmission lines).
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26. e) VSAT Communication : Very small aperture terminals
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36,000 km
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UTILITY
CONTROL
CENTER
SHARED HUB
SATELLITE
VSATs
NETWORK
MANAGEMENT
CENTER
Various frequency bands:
C-band (4/6 GHz), Ku-band (12/14 GHz),Ka-band(30/20 GHz)
Advantages
Near-universal coverage
Good reliability
Fast installation
Disadvantages
Cost
Transmission delays
Blackout periods due to eclipses
Attenuation in heavy rain (Ku band)
27. f) Mobile Communication
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Several competing technologies
Use of control channel on analog AMPS (Advanced
Mobile Phone Service), 800 MHz CDPD (Cellular
Digital Packet Data)
Recently also being offered for applications in feeder
automation
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30. 1. Normal state
2. Alert state
3. Emergency state
4. Extremis state
5. Restorative state
Normal state:
A system is said to be in normal if both load and
operating constraints are satisfied .It is one in which the
total demand on the system is met by satisfying all the
operating constraints.
Alert state:
A normal state of the system said to be in alert state
if one or more of the postulated contingency states,
consists of the constraint limits violated.
When the system security level falls below a certain
level or the probability of disturbance increases, the
system may be in alert state .
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31. If severe disturbance occurs, the system will push into
emergency state. To bring back the system to secure
state, preventive control action is carried out.
Emergency state:
The system is said to be in emergency state if one or
more operating constraints are violated, but the load
constraint is satisfied .
In this state, the equality constraints are unchanged.
The system will return to the normal or alert state by
means of corrective actions , disconnection of faulted
section or load sharing.
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32. Extremis state:
When the system is in emergency, if no proper
corrective action is taken in time, then it goes to either
emergency state or extremis state.
In this regard neither the load or nor the operating
constraint is satisfied, this result is islanding.
Also the generating units are strained beyond their
capacity .
So emergency control action is done to bring back the
system state either to the emergency state or normal state.
Restorative state:
From this state, the system may be brought back either to
alert state or secure state .The latter is a slow process.
Hence, in certain cases, first the system is brought
back to alert state and then to the secure state .
This is done using restorative control action.
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