8/19/2019 Electrical Lecture 13

1/3

Page 1 of 3 

LECTURE 5: IEC61850 Standard for SCADA

5.1 Introduction to IEC 61850 IEC 61850  is a standard for the design of substation automation and a part of the International Electro-technical Commission’s (IEC) Technical Committee 57 (TC57) reference architecture for electric powersystems. Its is essentially a set of abstract data models which can be mapped onto a number of protocols.Multiple protocols exist for substation automation, which include many proprietary protocols with custom

communication links. Interoperation of devices from different vendors would be an advantage to users ofsubstation automation devices. Hence a ‘standard’ for protocols was formed in the mid-90s – IEC 61850.

5.2 IEC 61850 - FundamentalsIEC 61850 was developed using this in mind; hence fits the workability of IEDs like a glove! ‘Fundamentalarchitectural construct – “abstraction” of data items, which are independent of any underlying protocols. Theabstract definitions then allow “mapping” of the data objects and services to any other protocol that can meetthe data and service requirements. It was ‘Inspired’ by OSI 7 layered model. Fundamental architecturalconstruct – “abstraction” of data items, which are independent of any underlying protocols. The abstractdefinitions then allow “mapping” of the data objects and services to any other protocol that can meet the dataand service requirements.

5.3 Intelligent Electronic Devices (IEDs) 

In the earlier years, low bandwidth led to DAS comm. protocol optimizations; cost was the time it took toconfigure, map and locate the various data-bits received. With increased bandwidth, emphasis shifted to thecomponents being able to “describe” themselves. With growing number of vendors and protocols, pertainingto standards became a necessity – especially one which caters to the requirements for SA.IEC 61850 wasdeveloped using this in mind; hence fits the workability of IEDs like a glove!

Intelligent Electronic Devices (IEDs) have been installed in the substations for more than a decade forcomplete monitoring and control of power networks. Earlier Programmable Logic Controllers (PLCs) werevery popular in performing different monitoring, automation and control tasks in the substation. Now- a-days,they are being replaced by IEDs. New Substation installations are equipped with IEDs which essentiallyconsists of microprocessor based protective relays, metering devices, programmable logic controllers, faultand event recorders, etc. Power System Automation using IEDs help technology continuously monitor powersystems include modular hardware design, programmable logic capabilities, built in relay software testingfeatures and the availability of continuously increasing non-protective functions. The improved sampling rate,processor speed, memory and other parameters, allow the relays to become indeed "intelligent", and workwith full capacity not only during system faults but also under "normal" system conditions, thus becoming thelowest level in the distributed intelligence based Power System Integration System. Substation architecturefor data acquisition, protection and control architecture shown in Fig. _ below.

5.4 IED and SCADASCADA (Supervisory Control And Data Acquisition) is a combination of Telemetry and Data Acquisition.Telemetry is a technique used for transmission and receiving of measured parameters such as voltage,current, power, speed etc., Data Acquisition Method used to access and control information/data from theequipment that is being controlled and monitored. Distributed Controlled System (DCS) is a specific type ofSCADA system for process control.

Difference between SCADA and DCS is that SCADA covers larger geographical areas involving a variety of

Telecommunication links such as radio and telephone on the other hand DCS is more confined to a particularplant/process and mostly uses LAN for communication

The main components of a SCADA System are the following1. Field Instrumentation2. Remote Stations3. Communications Network4. Central Monitoring Station

8/19/2019 Electrical Lecture 13

2/3

Page 2 of 3 

5.5 IED Based Substation AutomationIntelligent Electronic Devices are most widely used in the substation for monitoring and protective relaying.They provide the bottom layer of intelligence in the substation and power system integration systems. IEDs ,as protective relays perform the essential processing of the analog data from the substation environment,such as currents and voltages. Analog or digital filtering techniques are applied to obtain the fundamentalcomponents of current and voltage wave forms. These are further processed for protective relaying functions.Typical functions of protective relaying are differential protection, inverse-time over current, etc. The main

advantages of IEDs are their ability to exhibit multi function relaying property. An IED based multifunctionalprotective relay consists of sequence component filters, which will help generate the positive, negative andzero sequence currents and/or voltages used in different protection schemes. These IEDs provide the realtime monitoring and forms the ‘intelligence’ to the substation. IEDs can also be used as devices for powerquality monitoring, real time control and advanced protection functions.

5.6 Substation Automation System (SAS) using IED:The important requirements for SAS using IEDs are the following

High-speed IED to IED communication and Networking throughout the utility enterpriseHigh-availability, Guaranteed delivery times and Multi-vendor interoperabilitySupport for Voltage / Current samples data and Support for File Transfer

 Auto-configurable / configuration support and Support for security.With growing number of vendors and protocols, pertaining to standards became a necessity – especially

one which caters to the requirements for SA.

IEC 61850 – Object StructureEach element of data within the logical node conforms to the specification of a common data class (CDC) perIEC 61850-7-3. Each CDC describes the type and structure of the data within the logical node. Each CDC hasa defined name and a set of CDC attributes each with a defined name, defined type, and specific purpose.Each individual attribute of a CDC belongs to a set of functional constraints (FC) that groups the attributesinto categories

 ACSI and MMSThe Abstract Communication Service Interface (ACSI) models of IEC 61850 define a set of services and theresponses to those services that enables all IEDs to behave in an identical manner from the network behaviorperspective. IEC 61850-8-1 maps the abstract objects and services to the Manufacturing Message

Specification (MMS) protocols, a public and ISO standard protocol, of ISO9506.

IEC 61850 – Other featuresThe Sampled Values and GOOSE applications map directly into the Ethernet data frame for time-criticalprocesses. the MMS Connection Oriented layer can operate over TCP/IP or ISO; the Generic SubstationStatus Event (GSSE) is the identical implementation as the UCA GOOSE and operates over connectionlessISO services. All data maps onto an Ethernet data frame using either the data type “Ethertype” in the case ofSampled Values, GOOSE, TimeSync, and TCP/IP or “802.3” data type for the ISO and GSSE messages.

The Process BusThe Process layer of the substation is related to gathering information, such as Voltage, Current, and statusinformation, from the transformers and transducers connected to the primary power system process – thetransmission of electricity.IEC 61850 defines the collection of this data via two different protocol definitions,namely, Part 9.1 which defines a Unidirectional Multidrop Point-to-Point fi xed link carrying a fixed datasetand Part 9.2 which defines a “ configurable” dataset that can be transmitted on a multi-cast basis from onepublisher to multiple subscribers. Hence, possible to remotely acquire status information of IEDs too! (apartfrom the Sampled Values)

SCL Substation Configuration Language (SCLSubstation Configuration Language (SCL), based on XML, specified by IEC 61850-6-1 to describeconfigurations. The various SCL files include: system specification description (SSD) files, IED capabilitydescription (ICD) files, substation configuration description (SCD) files, configured IED description (CID) files.

8/19/2019 Electrical Lecture 13

3/3

Page 3 of 3 

SCL – BenefitsThe benefits of SCL are   Automation, Remote Configuration, Offline Configurations, Sharing of IEDconfigurations, Custom configurations, Elimination of discrepancies 

Key Features and of IEC 61850 Abstract Model - Protocol Independent, Descriptive Strings for all data, Standardized Object Names, Self-Describing Devices, Wide Range of High-level Services and SCL (Substation Communications Language)

Major Benefits of IEC 61850Eliminates Procurement Ambiguity, Lower Installation cost, Lower Transducer cost, Lower Commissioning,Migrations, Integration and Extension costs, Inter-device operability, Implementation of New capabilities

Current challenges with IEDInitial integration efforts by most vendors focused solely on providing data access and control of SCADA typedata to replace separate SCADA hardware like RTUs. Choosing to use SCADA protocols like Modbus, DNPand UCA led to the problem that data not supported by these protocols were “trapped” inside IEDs and madeunavailable. As a result, IEDs tended to get underutilized.