SCADA System, 2012.07.13-H

1

SCADA System

by

Anil Sinha, Consultant/ Advisor

([email protected])

© 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

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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

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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

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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

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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

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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

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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

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GENERAL

© Anil Sinha

© Anil Sinha

SCADA System Schematic

D1

D2

D3

D4

D5

D6

DnControl

Room

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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Intelligent Electronic Device� A very versatile electronic equipment

� Undertakes:� Protection

� Control

� Monitoring

� Metering

� Communication

© Anil Sinha

PROGRAMMABLE LOGIC CONTROLLER

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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

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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

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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

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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

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© Anil Sinha

RTU

REMOTE TERMINAL UNIT

© Anil Sinha

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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Example: Control Room

Example of an SLD

© Anil Sinha

NHPC/ ABB

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Another SLD example

© Anil Sinha

NHPC/ ABB

Example of a Panel Display

© Anil Sinha

NHPC/ ABB

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Example of annunciation

© Anil Sinha

NHPC/ ABB

Example of a Trend Display

© Anil Sinha

NHPC/ ABB

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Example of a Control Board

© Anil Sinha

Example: Siemens S7 PLC

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Example: ABB AC500 PLC

Example: Allen Bradley PLC

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Thank you

Anil Sinha, Consultant/ Advisor([email protected])