computer applications in power systems - scada · computer applications in power systems - scada...

© 2003 by Michael Leslie 1

Computer Applications in Power Systems -

SCADA

Michael Leslie, P.Eng.Manager of OperationsHydro Ottawa Limited

For the IEEE Ottawa SectionFor the IEEE Ottawa SectionPES, RS, EA and Algonquin College Student BranchPES, RS, EA and Algonquin College Student BranchDecember 17, 2003, at Algonquin CollegeDecember 17, 2003, at Algonquin College


WelcomeTopics:

Introduction to Hydro Ottawa Electric DistributionWhat is SCADA and how is it used by Hydro Ottawa?Key SCADA elements.SCADA EvolutionCommunication options.Next Generation SCADA


Hydro Ottawa LimitedPart of the Hydro Ottawa family of companies:

Telecom Ottawa

Energy Ottawa

Hydro Ottawa Limited

Hydro Ottawa Holding


Hydro Ottawa LimitedAbout us:

Formed in November 2000 under the OBCA. Merger of the former Ottawa Hydro, Nepean Hydro, Gloucester Hydro, Kanata Hydro, and GoulbournHydro93% of the assets of the Hydro Ottawa family of companiesThe core business of Hydro Ottawa Holding IncRegulated by the Ontario Energy Board and the Independent Market Operator


Hydro Ottawa Limited

OttawaKINBURN

MARATHON

ANTRIM

GALETTA

WOODLAWN

KILMAURS

DIRLETON

RICHMOND

MUNSTER HAMLET

ASHTON

AERODROME

STITTSVILLE

CARP

OSGOODE

CARSONBY

MANOTICK

KARS

GREELY

OTTAWA AIRPORT

SPRING HILL

MARIONVILLE

VERNON

KENMORE

METCALFE

BEARBROOK

VARS

EDWARDS

LEONARD

SARSFIELD

NAVAN

CUMBERLAND

MOHR CORNERS

FITZROY HARBOUR

FITZROYPROVINCIAL

PARK

CARP AIRPORT

MOORES CORNERS

PIERCES CORNERS

BECKETTS LANDING

NORTH GOWER

RIDEAU RIVER PROVIN

CIAL PARK

WATTERSON CORNERS

BAXTERS CORNERS

LANSDOWNEPARK

OTTAWA

GLOUCESTER

ROCKCLIFFE AIRFIELD

GLOUCESTER

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ConstanceLake

BritanniaBay

Graham

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Chats

Deschenes

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Bay

BayShirleys

BayCrystal

River

North Gower

Carsonby

Manotick

Kars

Osgoode

Vernon

Spring Hill

Marionville

KenmoreMetcalfe

Greely

Edwards

Vars

Bearbrook

Leonard

Sarsfield

Notre-Dame Navan

Stittsville

Richmond

Ashton

Carp AirportAerodrome

Carp

Woodlawn

Kilmaurs

Dirleton

Kinburn

Antrim

Galetta

Marathon

Watterson Corners

BaxtersCorners

MooresCorners

MunsterHamlet

PiercesCorners

BeckettsLanding

MaclarensLanding

FitzroyHarbour

MohrCorners

Champs

Cumberland

Macdonald-CartierInternational

Airport

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VANIER

BayMooneys

DowsLake

FallsChaudiere

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MadawaskaLake

KANATA

GOULBOURN

NEPEAN

OTTAWA

GLOUCESTER

HYDRO OTTAWA SERVICE AREACITY OF OTTAWA LIMITS

OSGOODE

CUMBERLAND

CARLETON

WEST

RIDEAU


Hydro Ottawa LimitedAbout us:

We deliver 7,500,000 KWh to 265,000 customers90% of the total customer base in the amalgamated city

Number of Customers Energy Use

Comme rcia l70%

Re side ntia l30%

Comme rcia l10%

Re side ntia l90%


Substations:Transform voltage from higher level tolower levelUsually from Transmission voltage to Distribution voltage

(eg. 115kV/27.6kV)Sub-transmission Voltage (44kV) is also common.Two ‘flavours’ of substation:

1. Terminal Station (TS), and2. Distribution Substation (DS)

Range from very simple to very complex

Electric Power Distribution System


Electric Power Distribution System

Distribution Circuits:Medium Voltage (4.16 to 35kV);4.16/8.32/12.47/13.2/27.6kV in Ottawa;Protected by circuit breakers at substations;Reclosers, switches, fuses can be found at substations and on the lines;Distribution transformers lower the voltage to a utilization level

(120/240V or 600Y/347V).


SCADA – Supervisory ControlAnd Data Acquisition

Provides a means to monitor power system activity and control substations and other distribution devices.Also common in Petroleum and Water/Wastewater industries.Relatively mature technology.Operational efficiencies gained through upgrading manned substations to monitored substations has largely been achieved.Long time to get to this point.Still plenty of opportunity for future advancement.


SCADA – Key Elements

RTU (Remote Terminal Unit)Monitors, measures, controls, digitizesUsually within substation although distribution automation increasingly commonEquipment interface CT’s, PT’s, relays, transducers

Control Centre (SCADA Master, MTU, etc)Collects, stores, displays, processes RTU data

Communication PathProvides the link – copper wire, fiber, wirelessInterface – modems, transceivers, radios


Communication Devices

Encoder / Decoder / Processor

SCADA “Master Station”

Human Interface

Operation CentreCommunications Device

Encoder / Decoder

Measuring Device

Power Station

State Monitor

Control Device

Equipment Interface

SCADA Remote Terminal


SCADA – Basic Functions

RTU collects measurements of power system parameters and transports over communication pathway to the SCADA Master where the data is presented to the Operator.SCADA system will provide the Operator a means to control devices.Master station stores operational data for historical reference.SCADA Master monitors data stream and flags (alarms) abnormal conditions.


Measuring Systems – ‘Analogs’

Continuously variable quantities like AC current, voltage, temperature, pressure, etc.RTU transforms physical quantities to digital through A/D converters.Instrument transformers (CT’s, PT’s) scale currents and voltages to manageable levels.Early RTU’s required transducers that produce 0-1ma signal proportional to IT output.


Real-Time State Information –‘Status’

RTU senses On/Off or Open/Close positions of breakers, switches, etc.Interfaced to substation equipment via auxiliary contacts or interposing relays.Early RTU’s reported equipment status only when ‘polled’ by Master. Depending on polling frequency, state transitions could be missed.Newer RTU’s have state change detect, and time stamping features.GPS time synchronization is possible.


Control

RTU traditionally interfaced to interposing relays that are hardwired into the control circuits of substation power equipment.Necessary due to the high voltages and currents associated with operating these devices.It is possible to interface with newer microprocessor-based protective relays. RTU control outputs wired directly to relay or software control.


Control Center

Control Room is responsible for the real-time management of the electric distribution system. SCADA is an Operations tool used to help maintain the health of the distribution system, quickly identify problems when they occur, and aid in the power restoration efforts.Accomplished by collecting data from substations, storing this data, populating Operator displays and graphics with data, alerting Operators to abnormal conditions, maintaining event and alarm summaries.


SCADA Configuration

Communication Front-end

MMI

Application Server 1 Application Server 2

MMI

dual LAN

CommunicationServer

Mimic BoardControler

to other ControlCenters

RTU


SCADA Evolution

Pre-computer systems used electromechanical switches and were based on telephone technology.Computer based systems began to appear around 1970 with the advent of real-time (interrupt driven) operating systems.Mainframe systems (IBM, Honeywell, Digital Equipment) with SCADA software (Westinghouse, General Electric)Very few suppliers of these specialized systems.


SCADA penetration into the Utility industry increased alongside growth in the Computer Industry. Especially after the introduction of mini-computers like Digital’s PDP-11 and VAX lines. Smaller SCADA vendors enter the market.SCADA software is still custom but based on industry programming languages such as FORTRAN and PL-1.SCADA vendors supply both Master and RTU equipment and data exchange is based on proprietary protocols.Many of these legacy protocols are still in use today. L&G 8979, PG&E 2179, QUICSIV .

SCADA Evolution (cont’d)


Early systems presented data and allowed control functions via tabular displays. A graphics engine has now been added to display information in a more user friendly manner (one line substation schematics). Fully geographic systems are now common.Today, SCADA systems are based on client-server architecture, connected via local area networks. UNIX operating systems common, however, Windows (NT, 2000) making inroads.SCADA considered mission critical and must be available at all times - dual redundancy and hot-standby components.




As computing horsepower increased and costs decreased, and as SCADA matured, advanced applications became available.Transmission system state estimators and EMS (Energy Management Systems).DMS – Distribution Management Systems.Data Warehouses, Data Historians, contingency planning, network modeling c/w circuit connectivity, switch order preparation, smart (hierarchical) alarming, short-term load forecasting, etc.


In the past, SCADA systems were stand-alone and isolated. Now usually connected to the Corporate LAN through a router and firewall. This allows many new SCADA uses and users.System and capacity planning Engineers.Protection Engineers – Sequence of Events.Maintenance Engineers – Underperforming circuits, Autorecloses, Condition based maintenance and condition monitoring.Regulatory reporting – SAIDI, SAIFI, CAIDI.Outage management, Public Relations, Call Centre, Claims agents, etc.

New Users


CommunicationHistory

Early communication between Master and remote based on telephone technology. Used a telecommunication carrier (Bell) or private exchange.Copper lines (leased or private) linked the Control Room to the substation and operated at 300-4000Hz.Noisy.Serial data transfer rates, 60bps (teletype), 300-9600 bps with modems (Bell 202 common).9600 bps is still ‘state of the art’Ground Potential Rise (GPR) problem with Telco’s and electrical substations.


Communication

History cont’dDue to the low data rates SCADA vendors had to be extremely efficient with bandwidth. Compressed data and report by exception. Very specialized communication protocols.Vendor specific hardware designed for noise immunity.Vendors designed their own serial to parallel data converters.Legacy protocols are still with us. Some have been published (open) but many are still proprietary.


Communication

Communication options and bandwidth has increased steadily. Utilities have been slow to adopt new technologies but this is changing. LAN/WAN – Ubiquitous 10/100Mbs or higher Ethernet.Fiber Optic, Microwave, Frame Relay, Radio, Power line carrier, etc.Public Cellular .9600 bps is still ‘state of the art’.


CommunicationWireless

Point to Point and Point to Multi-point Radio. Multiple Address Systems (MAS). Used extensively – mostly for pole-mounted RTU’s. Usually 800/900Mhz licensed. Unlicensed (spread spectrum) radio’s use frequency hopping techniques. Low Power – 1 Watt. Up to 512 kbs throughput with both Ethernet and serial ports.Variation of the spread spectrum radio is the ‘store and forward’ device. Radios act as repeaters. Redundancy through multiple communication paths. Useful where response times not critical.


Communication

Wireless cont’dCellular and PCS – connect field devices using digital modems and messaging services.Wireless Ethernet solutions‘Public’ Internet – DSL, Cable, Satellite


Communication

High Speed (Backbone)Fiber Optic – Electric Utilities blessed as owners of right or ways, pole lines, and U/G ducts. Can cost effectively install a private fiber network. This may change due to industry restructuring and a ‘competitive’ market.Hydro Ottawa has 30 substations communicating over a self-healing fiber ring. Uses add/drop multiplexing and ‘terminal server’ like technology. Serial communication to RTU at 9600bps. Not the most efficient use of the fiber.


Communication

High Speed (Backbone) cont’dMicrowave – networks can transport voice and data. Hydro One operates at provincial level.SONNET, Frame Relay, DSL, ISDN, ATM, VPN, and Public Internet are increasingly available and can be cost effective if moving a large amount of data.Security issues when moving from private to ‘public’ systems.


Substation Automation

New breed of equipment is fundamentally changing the way SCADA is interfaced into the substation environment.IED – Intelligent End Device.Legacy RTU’s rely on transducers and on-board A/D to obtain analog measurements. Status and control functions have been hardwired. Protection Relays and Power Metering Equipment (Revenue & Monitoring) have traditionally be isolated from SCADA for reliability and security reasons.


Substation AutomationThe IED – Intelligent End Device

MicroProcessor based relays and digital power meters contain their own A/D conversion. Why duplicate this at the RTU?Protection Relays are also capable of controlling specific devices like breakers duplicating some SCADA functions.The challenge is to get the RTU to ‘talk’ to the IED to read analogs and status, and to ‘command’ the IED to take some action (control). Requires industry standard communication protocols and the ability to link IED’s together and to the RTU.


Substation AutomationThe Substation Communication Bus

RTU’s and IED’s have built in serial communication portsSerial RS232 is point to point. IED’s generally use RS232 to connect to a PC for local interrogation or to configure the device.Standard RTU has 1-4 serial ports. Additional ports may be added to allow connection to multiple IED’s. Switching and multiplexing arrangements but can become unwieldy due to serial cabling required.Most IED’s offer RS485 to ‘daisy-chain’ serial devices reducing cabling requirements but single device failure will result in lost communication to all.



The Substation Communication Bus cont’d.IED’s on a common communication line must all ‘talk’ the same language and the RTU must understand this language. Protocol translation has had limited success.‘Defacto’ standards have developed but it is not uncommon to find various ‘flavours’ of a particular protocol. MODBUS (Allen Bradley) is a PLC protocol that has some acceptance by IED manufacturer’s.



The Substation Communication Bus cont’d.IEEE Substation Working Groups have developed some ‘hard’ protocol standards.

DNP 3.0 and IEC870-5.DNP (Distributed Network Protocol) was originally developed by Harris and has been adapted by IEEE. It is now the most common SCADA protocol. It is possible to mix and match IED’s, and RTU’s from different vendors into the SCADA environment.DNP3.0 is a feature rich protocol but with a high overhead when compared to proprietary protocols. This is less a problem with higher bandwidths.



Substation LANBeginning to see the establishment of local area networks into substations.Substation LAN is connected to the Corporate LAN through Wide Area Network (WAN) or Metropolitan Area Network (MAN). Video, Voice over IP (VOIP), and other Network resources and applications are available at the substation.Just beginning to see Ethernet enabled RTU’s and IED’s.



Substation LAN cont’dRTU’s, IED’s, and SCADA Servers are connected via Ethernet (802.xx).MODBUS, DNP3.0, and a new protocol ‘UCA’ (Utility Communication Architecture) are embedded into the IP transport. Devices no longer need to be daisy chained with serial cables. Standard UTP (Cat5) cabling and Ethernet hubs are used.Everyday network devices like routers, switches, hubs, bridges, and terminal servers greatly simplify substation device connectivity. Now Plug and Play.


ReferencesIEEE Std C37.1-1994 - IEEE Standard Definition, Specification, and Analysis of Systems Used for Supervisory Control, Data Acquisition, and Automatic Control

IEEE Tutorial Course Text EHO 337-6 PWR

IEEE/PES Substations Committee and Data Acquisition, Processing, and Control Systems Subcommittee.

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