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1
SCADA System
by
Anil Sinha, Consultant/ Advisor
(anilsinha@live.in)
© Anil Sinha
ContentsSCADA Applications
Power System
General
Data Acquisition
Protection
Automation Systems
SCADA Functions
SCADA Screens
2
Notice� Some of the diagrams and the text have
been taken from the World-wide-web, purely for illustrative purposes. These remain the copyright/ property of their respective owners
© Anil Sinha
SCADA APPLICATIONS
© Anil Sinha
3
SCADA
SSSSupervisory
CCCControl
AAAAnd
DDDData
AAAAcquisition
© Anil Sinha
SCADA Applications� SCADA System may be applied to any
process, which:� Is largely continuous
� Is physically spread out
� Requires common monitoring/ control
� Is amiable to a centralised database
� Needs historical data
� Can interface to online instrumentation
� Needs operator intervention from time-to-time
© Anil Sinha
4
SCADA Applications� Target Segments:
� Power Sector
� Railways
� Manufacturing Industry
� Petro-chemicals and Pipelines
� Chemicals and Fertilisers
� Road Traffic
� Water Supply
© Anil Sinha
SCADA Applications� Some selected users of SCADA Systems
� Power Distribution
� Power Transmission
� Captive Power Distribution
� Oil/ Gas Pipelines
� Railway Traction
� City Water Supply
© Anil Sinha
5
Captive Power Distribution� Manage Grid supply and Captive generation
� Separate loads on different busses in the case of duel-mode supply
� Power factor correction
� Manage Power supply contracts
� Manage load restrictions
� Metering/ Billing
� …
© Anil Sinha
Oil/ Gas Pipeline SCADA� Regular Monitoring and Control of the Valves
� On-demand diversions and re-routing
� Leak-detection
� Pressure profile
� Volume monitoring
� Cleaning & Scrubbing operations
© Anil Sinha
6
Railway Traction� Monitoring of Voltage profile and supply dips
� Auto-switchovers to alternate supply
� Switching –in and –out of track sections
� Emergency tripping and restore
� Metering
� Condition Monitoring
� …
© Anil Sinha
City Water Supply� General Monitoring & Control of pipeline and
Valves
� Leak-detection
� Pressure profile
� Supply-side management
� Schedules
� Metering for Audit
� …
© Anil Sinha
7
POWER SYSTEM
© Anil Sinha
Power System Constituents� Generation
� To produce Power, with minimum inputs
� Transmission� To transport bulk power economically
� Distribution� To satisfactorily cater to end-consumer’s needs
The sum-total of the three is the Grid
© Anil Sinha
8
Power System - Expanded� Other Important Functionaries are:
� Ministry of Power
� Central Electricity Authority
� State Load Despatch Centres
� National/ Regional Load Despatch Centres
� Central/ state Electricity Regulatory Commissions
� Power Finance Corporation
� Power Trading Corporation
� Power Exchanges
� Public/ Private-sector Power-sector Companies
© Anil Sinha
SCADA System in Power Sector� Distribution
� Distribution Management System (DMS)
� Transmission
� Load Dispatch Control (LDC)
� Generation
� Plant Control System (PCS)
© Anil Sinha
9
GENERAL
© Anil Sinha
© Anil Sinha
SCADA System Schematic
D1
D2
D3
D4
D5
D6
DnControl
Room
10
SCADA Schematic
© Anil Sinha
POWER SYSTEM (GRID/ PLANT/ NETWORK)
TRANSDUCERS/ SENSORS/ CONTACTS/ ETC.
Human-Machine INTERFACE 1
PROGRAMMABLE
LOGIC
CONTROLLERS
(PLC)
REMOTE TERMINAL UNIT (RTU)
FRONTEND PROCESSOR
SCADA SERVERS (Redundant Configuration) (Distributed Servers)
HMI 2
OTHER SERVERS FOR
ADD-ON FNs
OPTION-1 OPTION-2
(Multiple
Locations/
Nos.)
………..
(May be integrated with the SCADA Servers)
(More HMIs)
External Links
Example: PCS Configuration
© Anil Sinha
11
Advantage SCADA System� A properly designed SCADA System reduces
labor costs by minimizing site visits for:� Inspection
� Data collection/logging
� Making adjustments
� SCADA Systems allow:� Real-time monitoring from your PC system – settings and
modifications
� Troubleshooting from your PC
� Increased equipment life – better preventive maintenance
� Automatic report generating feature
© Anil Sinha
DATA ACQUISITION
© Anil Sinha
12
Logical Data Flow
© Anil Sinha
Conceptual Architecture
of a Plant Automation
Scheme
Field Equipment
RTU/ PLC/ DCS
Comm. Server
SCADA Server
Bi-Directional Data Movement
- Information from Field to SCADA
System
- Commands from SCADA System
to Field
(Many)
(Many)
(A Few)
Terminology� Sensor/ Transducer
� Converts Process parameter for automated processing
� Programmable Logic Controller (PLC)/ Remote Terminal Unit (RTU)/ Distributed Control System (DCS)� Processes/ Multiplexes multiple process information &
routes it over one link to the Servers
� Server� Optimized Computer & Software for Central Functions,
e.g. Database
� Human-Machine Interface (HMI/MMI)� Operator’s Interface to the Servers
© Anil Sinha
13
Process Data� Represents the current status of the process
� Binary: status of a process parameter
� Circuit Breaker, Isolator, Limit switch, Gate status
� Fleeting: Temporary change of state
� Process alarms
� Analog: Current value of a process parameter
� Linier: Voltage, Current, Power, Frequency, RPM
� Non-linier: Temperature, Flow
� Count: Cumulative value of process parameter
� Energy, Production Inventory, Fuel Consumption
� One-of-N: One selection out of multiple options
� Transformer Tap Position
© Anil Sinha
Transducer/ Sensor/ Contact� Instrumentation: Data Input
� Sensors/ Transducers for Analog Process Values
� Relays/ Contacts for status or limits
� Temperature Sensors: e.g. Bimetallic, RTD
� Position Sensors: e.g. Micro-switch, Capacitive
� Proximity Sensors: e.g. Magnetic, Hall-effect
� Flow Transducers: e.g. Rotary wheel, Manometer
� Motion/ Acceleration Sensors: e.g. Inductive
� Others: e.g. echo based, induction based, Venturi
© Anil Sinha
14
Actuator/ Stepper/ Motor� Instrumentation: Command Output
� Device-specific
� Motors for Rotation
� Stepper Motor for incremental motion
� Hydraulic Pump to move a piston
� Linier Motor for straight-line movement
� others
© Anil Sinha
Telemetry� To communicate specific Process Data,
from:� Field Equipment to Sensors
� Sensors to Data Concentrator
� Data Concentrator to Central Control
� Requires:� Accuracy of Data transmission
� Reliability of Communication
� Error Avoidance
© Anil Sinha
15
Acquiring Data� Remote Terminal Units (RTU)
� Data acquisition at a remote location
� Limited Connectivity
� Generally lower speeds/ less data
� Programmable Logic Controllers (PLC)� Located logically close to the SCADA Servers
� Data interface for SCADA System & other independent Functions
� Generally High Speed Processing
� Distributed Control System� Specific Function modules & Data Acquisition for SCADA
System
© Anil Sinha
Communication Interface� Field Equipment to Sensor
� Direct wiring for Analog Signals (e.g. CT/ PT)
� Current Loop for Binary Signals (e.g. Relay)
� Wiring Consideration� Electrical/ Mechanical Shielding
� Impedance Matching
� Length Restriction
© Anil Sinha
16
Communication Interface� Sensor to Local Data Interface (e.g. PLC)
� Direct Copper Cable for Analog Signals/ Current
Loops
� Shielding/ Impedance/ Length
� Direct/ Bus/ Ring Cabling for Digitised
Information
� Length/ Impedance/ Shielding
� Limit on number of bus nodes
� Protocol and Speed Considerations
© Anil Sinha
Sending Data� Sending form
� Packet/ Datagram
� Header/ Tail
� Validation
� Sequencing
� Handshake
� Sending Procedure� Cyclic Transmission
� Spontaneous
Transmission
� Polling
© Anil Sinha
HEADER
ADDRESS
SEQUENCING
HANDSHAKE
DATA/ INFORMATION
TAIL/ VALIDATION
DA
TA
GR
AM
17
PROTECTION
© Anil Sinha
Power System Protection� Protection Philosophy: Safety of humans,
safety of power system, safety of power equipment
� Protection of Humans comes first
� Protection Systems mainly protect the overall power system against the failure/ malfunction of one or more equipment
� It also attempts to limit the damage to the costly equipment
© Anil Sinha
18
Electrical Protection� Type of Electrical Faults:
� Symmetrical
� All three phases are in fault
� Unbalanced/ Asymmetrical
� Phase-to-phase
� Phase-to-ground
© Anil Sinha
Protection Components� Fuses
� Suitable for small currents only
� Even ‘fast fuses’ are relatively slow
� Circuit Breaker� Act very fast to break current
� Available in various forms and sizes
� Can be used to break even very large currents
� Instrument Transformer� CT/ PT, to supply basic information to the Relays
© Anil Sinha
19
Protection Relays� Overcurrent Protection
� Due to Overload
� Due to Fault
� Earth Fault Protection� Vector sum of the balanced phase-currents is zero
� Differential Protection� Currents going-in & coming-out are compared
� Voltage/ Frequency Regulation
� Distance Protection: for long lines
© Anil Sinha
Equipment Protection� Generator
� Transformer
� Busbar
� Feeder
© Anil Sinha
20
Intelligent Electronic Device� A very versatile electronic equipment
� Undertakes:� Protection
� Control
� Monitoring
� Metering
� Communication
© Anil Sinha
PROGRAMMABLE LOGIC CONTROLLER
© Anil Sinha
21
Programmable Logic Controller� Relatively Higher Data Sampling Rate
� Higher Acquisition Rate
� Relatively Limited Area of Influence
� Possible Need for Independent Local Processing
� Need of Intermediate or Final Results
� Subject only to Supervision by SCADA System
� Modes: Fail-safe, Basic/ Standby Operation
© Anil Sinha
PLC Block Diagram
© Anil Sinha
Digital Input Digital Output Analog Input Analog Output Other Inputs Other Outputs
CENTRAL PROCESSING UNIT
PROCESS ELEMENTS (& TRANSDUCERS/ SENSORS/ CONTACTS/ ETC)
LOCAL PROGRAMME MEMORY LOCAL DATABASE
COMMUNICATION/ PROCESSOR
22
PLC Configurations� Independent Master PLC
� Simplest
� Independent Master with Remote I/O� More efficient layout
� Duplicated Masters (Standby/ Hot-standby)� For Redundancy/ better availability
� Combinations of the above� Addresses Real-Life situations
� Process Monitoring Stations� To serve as local HMI
© Anil Sinha
PLC Basic Functions� Data Acquisition: Sampling, quantisation
� Data Conversion: Modify range & domain
� Logic Control Function: Binary equations
� Open Loop Control/ Closed Loop Control
� Integration/ Differentiation based Control
� Look-up table based Control
� Plausibility check: Is the information valid?
© Anil Sinha
23
Uses of PLC (examples)� Automatic Bus transfers
� Automatic start/stop of the units and checking of
Interlocks
� Automatic synchronizing, loading/unloading of
the units
� Data monitoring and acquisition on real time
basis
� Emergency operation from Bay/ Unit control
boards
� Bi-directional communication with SCADA
system© Anil Sinha
DISTRIBUTED CONTROL SYSTEM
© Anil Sinha
24
Distributed Control System� Originally developed for Generating Units as
fast Analog Control Modules, before the era of Microprocessors
� Were near the controlled equipment for shorter cable-lengths
� Hence distributed in the Power Plant
� Needed unique communication bus to interconnect the modules
� Present designs are Microprocessor-based
© Anil Sinha
DCS� The present day DCS functions are a carry-
over from the earlier days
� Some Vendors consider DCS more reliable, as compared to PLC, others differ
� Very little now to distinguish the traditional DCS from a distributed instance of multiple PLCs
© Anil Sinha
25
© Anil Sinha
RTU
REMOTE TERMINAL UNIT
© Anil Sinha
26
Remote Terminal Unit� Low Data Volume
� Low Data Transmission Speed
� Long Physical or Logical Distances
� Need for Reliable Transmission
� Geographically Scattered Data acquisition
� No local processing required
© Anil Sinha
RTU Block Diagram
© Anil Sinha
Digital Input Digital Output Analog Input Analog Output Other Inputs Other Outputs
CENTRAL PROCESSING UNIT
PROCESS ELEMENTS (& TRANSDUCERS/ SENSORS/ CONTACTS/ ETC)
COMMUNICATION PROCESSOR PROCESS DATA IMAGE
COMMUNICATION MODULE
27
RTU Communication� Point-to-Point
� Point-to-Multipoint
� Polling Method� Allows use of common connecting cable
� Concentrator/ Multiplexer� Communicating on one side with Multiple RTUs
� Other direction goes to SCADA Server
� Master RTU/ Front-end� To reduce communication load on the server
© Anil Sinha
COMMUNICATION
© Anil Sinha
28
Communication Modes� Base-band Communication
� The frequency range starts at zero
� The signal has a DC component
� The communication link must have Galvanic connectivity
� Modulated Communication� The real signal is shifted higher in frequency space
(modulated) at the starting point, and shifted back to the
original frequency space (de-modulated) at the receiving
point
� The modulated signal does not have any DC component
� Galvanic connectivity is not required
� The modulated signal is suitable for multiplexing
© Anil Sinha
Communication Modes
© Anil Sinha
BASEBAND
MODULATED, DOUBLE SIDE BAND
MODULATED, SINGLE SIDE BAND
FREQUENCY ->0 Hz
AM
PL
ITU
DE
->
CARRIER FREQUENCY
29
Bandwidths� Telephone: 3.4 kHz/ 4 kHz
� AM Radio: 4.5 kHz
� FM Radio: 15 kHz
� Digital channel: 2x4 kHz x8 bits = 64 kbps
� Basic rate ISDN: 64+64+16= 144 kbps
� Primary rate ISDN: 30x64 + 2x64 = 2048 kbps = 2 Mbps
© Anil Sinha
Communication Link: SERIAL� Serial Connection
� Point-to-Point
connection
� Data Acquisition Unit is,
logically, directly
connected to the
SCADA server
� Represents a single
channel
� Usually, but not always,
a galvanic wire
connection
© Anil Sinha
Data Acquisition Unit
SCADA Server
Direct
Cable
30
Communication Link: BUS� Bus Based
Communication� Multiple Units
connected on the same
logical bus
� Enables Any-to-Any
communication
� Addition of new units on
the Bus is Possible
© Anil Sinha
DA Unit 1
DA Unit 1
DA Unit 1
SCADA ServerB
US
Communication Link: Ring� Ring-based
Communication� Multiple Units
connected in a ring form
� Communication from any unit to any
other, goes along the ring
� Every unit gets opportunity to use
the ring in turn© Anil Sinha
DA UNIT 2
SCADA Server
DA UNIT 1 DA UNIT 3
31
Communication Link: Star� Similar to BUS
� Addition of new Links is Simple
� Failure of one Link does not affect the other Links
© Anil Sinha
HUB
SCADA SERVER
DA Unit 1
DA Unit 2
DA Unit 3
DA Unit ..
(EMS SERVER)
Communication Link: Hybrid� Different Network Topologies can be
combined for site-specific solution
� The Combination may be Lateral or Hierarchical
� Multiple Busses/ Multiple Rings may be connected in Hierarchy
© Anil Sinha
32
OSI Model
© Anil Sinha
Application�Sender or receiver of data
Presentation�Transform formats as required
Session�Start/end a logical link
Transport�End-to-end protocol
Network�Unique Network address
Data Link�Bits & Bytes, local address
Physical�Cable, Wireless, etc.
Device 1
Application
Presentation
Session
Transport
Network
Data Link
Physical
Device 2
Communication Media� Copper Cable, Cat. 1-7
� Fiber Optic Cable
� Leased Telephone Lines with Modem
� PLCC (Power Line Carrier Communication)
� GSM/ CDMA Dial-up Modem
� Wireless/ Radio
� Microwave
� V-SAT
� Inmarsat© Anil Sinha
33
Fiber-Optic Communication� Two types: Mono mode/ Multi-mode
� Mono mode fiber dia. 9 micron
� Multi-mode/ Graded Index fiber dia. 50/62.5
micron
� Multi-mode/ fiber: varying op. density
� Multi-mode fiber: LED source
� Mono mode fiber: Laser source
� Multi-mode: 2 km practical length
� Mono mode: practical lengths > 50 km
� WDM: Wave Division Multiplexing© Anil Sinha
Communication Standards� RS 232/ RS 422/ RS 485
� DNP (Distributed Network Protocol)� Stated with 60870.5. series, developed separately
� IEC 60870.5.101/.104 series� Current Open Standard for Serial or LAN link
� IEC 61850 standard for Protection Devices� Being included in other equipment, as well
� OPC (OPen Connectivity via open standards)� Upcoming New Standard from OPC-foundation
© Anil Sinha
34
SCADA FUNCTIONS
© Anil Sinha
Basic SCADA Tasks� Input/ Output
� Data Acquisition/ Commands
� Alarms� Acknowledgement
� Including Events
� Displays (Real-Time Process Information)
� Reports� Scheduled/ Event-driven/ On Demand
� Trends (Monitoring of Data over a time period)
© Anil Sinha
35
SADA Functions� Conversion to physical quantities
� e.g. amp, kV, MW
� Limit checks� Usually two lower/ two upper limits
� Gradient check� Rate of change of data
� Summations� e.g. sum of power flow over all the feeders
� Averaging over data points� Improves reliability of data
© Anil Sinha
SCADA Functions� Averaging over time
� Reduces jitters in data presentation
� Accumulation over time� Pseudo-integrated value, e.g. Power to Energy
� Manual entry� Manually substitute missing field data
� Blocking/ de-blocking� Manage work permits/ maintenance schedules
� Active/ not active� Integrate system changes/ new configuration
© Anil Sinha
36
SCADA Functions� Count processing
� Server-level energy metering, if energy pulse is available
� Integration of ‘units’ to get ‘total quantity’
� Command Output for Process operation� Check-before-execute function; Result monitoring
� Calculation and logical tasks� Automation of control functions; Execution of multiple
steps
� Facility for SCADA data analysis� Data Interface to Higher Functions
� Trending based on Past Data
� Interface to Other Corporate Systems
© Anil Sinha
SCADA SCREENS
© Anil Sinha
37
Example: Control Room
Example of an SLD
© Anil Sinha
NHPC/ ABB
38
Another SLD example
© Anil Sinha
NHPC/ ABB
Example of a Panel Display
© Anil Sinha
NHPC/ ABB
39
Example of annunciation
© Anil Sinha
NHPC/ ABB
Example of a Trend Display
© Anil Sinha
NHPC/ ABB
40
Example of a Control Board
© Anil Sinha
Example: Siemens S7 PLC
41
Example: ABB AC500 PLC
Example: Allen Bradley PLC
42
Thank you
Anil Sinha, Consultant/ Advisor(anilsinha@live.in)
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