IEC 60870-5-104 - the new solution for communication in substationsMichael Eckl, Reinhard Krug

VA TECH SAT

Austria

VA TECH SAT GmbH & Co, Ruthnergasse 1, A-1210 Vienna, Austria

Abstract

Communication to and within substations iscurrently one of the main issues in substationautomation. Existing protocol standards, based onthe IEC 60870-5-1 to 5 Stds., i.e. IEC 60870-5-101Telecontrol tasks [Load Dispatch Centre (LDC) tosubstation] and IEC 60870-5-103 Informativeinterface to protection equipment, are well defined,mature and used world-wide. The recently releasedIEC 60870-5-104 combines the experience gainedwith IEC 60870-5-101 with the modern protocol ofTCP/IP over Ethernet. New tools can supportexisting object oriented engineering combined with astation bus based on IEC 60870-5-104.

Communication Standards

When Remote terminal units (RTUs) wereintroduced, communication between substationsand the LDC was required. Due to the lack ofstandards and limited communication technology,equipment vendors used proprietary protocolsoptimised to make maximum use of the availablebandwidth. Utilities became dependent on a chosenvendor’s equipment resulting in the need forexpensive gateways to interface between differentequipments in system extensions. The need forstandardisation became evident, consequentlyinternational standards were defined, the IEC 60870-5-1 to 5 series, which covered the basic methods forremote communication and defined important issueslike interoperability and data integrity, also defininga profile for RTUs in IEC ..-101 and consequentlycreating a standard for interfacing protection relaysi.e. IEC ..-103. These two standards are now appliedall over the world and are supported by nearly allmajor vendors of RTUs, substation automationsystems, and protection relays. The informationavailable via communication became moresophisticated when microprocessors were employedand Intelligent Electronic Devices (IEDs) started tochange the architecture of control equipment insubstations.

The increasing information available from modernIEDs and higher level functionality at the bay levellike interlocking schemes covering several bays,make the need for a more intensive communicationbetween the different substation functions evident.

The station bus meets this need providing an openand reliable method of transport that is highlyavailable and which provides scaleable solutions forsubstations of different size and importance at MV,HV and EHV levels. In addition a solution has beenprovided for the refurbishment / expansion ofexisting substations, taking into account that60870-5-101/103 Stds. are used in manyinstallations and gateways have been avoided.

During the last decade the design of LANs (LocalArea Network) typically used for office automationhas changed dramatically. Modern concepts, basedon high speed (up to 1 GBit/s) switched Ethernetmakes state of the art network design a reliable andscaleable solution. The use of TCP/IP protocol andEthernet guarantees a stable and very wellstandardised platform for both users and vendors.Today Ethernet is superceding other existing LANand bus-solutions, practically becoming the world-wide LAN standard.

This well proven network platform was, therefore,chosen to be used also for Utility applications. Inalmost all primary substations fibre opticconnections and new LAN/WAN technologies areavailable. The need to adapt the existing and provenIEC..-101 protocol to TCP/IP based communicationin order to make use of new communicationtechnology was evident.

IEC 60870-5-104 published by IEC TC57 / WG 3offers a homogenous transition from the provenIEC..-101 to TCP/IP over Ethernet. Many alreadysuccessfully completed projects using WAN showthe benefit of employing this standard. Due to therapid development in LAN technology, switchedEthernet can be applied in the substationautomation as station bus, at a reasonable price.

Switched Ethernet combined with the TCP/IP basedprotocol IEC..-104 offers state of the artcommunication technology also for substationautomation. The available baud rates can satisfyeven the highest demands for data rate in largeEHV-substations.

Scaleable solutions to meet the users needs

Substation automation can be used implementedwith different levels of complexity. The variety ofsubstations (AIS/GIS,indoor/outdoor, MV/HV/EHV,refurbishment/new) puts extremely high demands onsubstation automation in terms of flexibility. Veryhigh demands are usually put on substationautomation for the highest voltage levels. This is truenot only for the IEDs, but also for the availability ofthe station bus. Industrial switched Ethernetsolutions can provide redundant configurations andextremely fast redundancy switching algorithms:starting with multipoint star configurations with fibreoptic for indoor switchgear, but also redundant ringstructure based on fibre optics when used in EHVoutdoor switchgear with relay kiosks (see figures 1& 2).Modularity is the key to provide a system thatmeets the users needs. Stand-alone functionalityguarantees highest availability even at the bay level.Rugged hardware design guarantees that thesystem can be used even within outdoor controlcubicles without additional housing. An IECcompliant system architecture guarantees that allfunctions defined by the Standard can beengineered within a very short time using only oneconfiguration tool.

Object oriented engineering - a new paradigmfor engineering

Today’s existing standards like IEC 60870-5 arebased on an ”anonymous datapoint oriented model”in order to identify addressed IEDs. This means thesource is always identified by a structured numericaddress within an RTU regardless of the analogue ordigital input or output concerned. New dataprocessing approaches support an object orientedmethod, now its not bits and bytes to be exchangedbut objects identified by their names and attributes!The new draft IEC 61850, defines a Standard forCommunication Networks and Systems inSubstations, using object oriented models todescribe the process to be controlled e.g.substation, feeder or circuit breaker etc. This objectoriented approach is aimed at simplification ofengineering. Significant savings can be obtained bycombining substation standardisation and bycreating an object library.

To express it in other words: Up to now it has beenimportant "how" to communicate between IEDs butin the future it will be important "what" kind ofinformation is to be exchanged.

Configuration Tool

In order to cope with an object oriented data-modelas proposed by the new IEC 61850 drafts, objectoriented tools are required. Figure 3 shows how astate of the art configuration tool supports IEC61850-7 compliant modelling of a substation. At theleft is a substation consisting of several feeders.One feeder (AD03) is divided into severalcomponents (object circuit breaker, two-disconnectors, current and voltage transducers). Inthe middle window all detail-objects of a circuitbreaker can be seen. In the window to the right allattributes concerning the object "pressure-valuecircuit breaker" are listed.

But does this mean that IEC 60870-5-10Xstandards are out of date?Certainly not, TCP/IP protocol over Ethernet allowsboth IEC..-104 and IEC 61850 data frames to becommunicated, thus providing the advantages ofboth approaches and maintaining an upgrade path.Using a modern object oriented configuration toolmeans ”bridging the gap” between a very effectiveand future proof engineering method and gaining thebenefits of an existing open and well provencommunication standard.

Conclusion

With a station bus based on IEC 60870-5-104 theadvantages of state-of-the-art communicationtechnology such as switched Ethernet can beemployed in combination with well defined andproven standard communication in substations. Byadding an object oriented engineering approachfurther savings can be obtained. This concept allowsfor a consistent communication from bay level to thedispatcher centres and provides object orienteddesign of substation automation systems now andfor the future. A further advantage is that noadditional gateway needs to be installed in order toconnect with existing devices that are not compliantwith the object oriented IEC 61850. State of the artengineering tools are narrowing the gap between thetraditional data point oriented way of engineeringand new approaches as proposed by the draft IEC61850 Standards. Until these become fullInternational Standards, which will probably takesome more years, the existing IEC 60870-5-104 isthe first choice for an open and efficient standard forthe substation bus.

VA TECH SAT1

Configuration with Stationbus

N-00115e.ppt / 2000 10 03 by M. Eckl, B. Steininger / Copyright (c) by VA TECH SAT GmbH & Co Vienna

Router

(ETHERNET)

IEC 60870-5-104

IEC 60870-5-103

IEC 60870-5-104

WAN

IEC 60870-5-101 and/orIEC 60870-5-104

IEC 60870-5-101

Bay ControleDevice

Station Automation

Control centre

Other RTU

Small RTU

Station Control Device

Active / stand-by

digitalProtection

Bay ControleDevice

digitalProtection

Compact BayControl Device

digitalProtection Feeder Manager

High Voltage Bays Medium Voltage BaysBAY 1 BAY 2 BAY 1

S I E M E N S S I E M E N S S I E M E N S

VA TECH SAT2

100 Mbps Station Bus-LAN (IEC 60870-5-104), fibre optic

SAT NLSA Extra High Voltage

N-00144e.ppt / 2001 01 29 by M. Eckl, B. Steininger / Copyright (c) by VA TECH SAT GmbH & Co Vienna

Router

AM 1703

SAT 200

remotemaintenance

network controlcentres

printer

High Voltage Bays(bay control devices, protective devices)

Station Control Device(active / stand-by)

Station Automationand Disturbance Archive

AK 1703

Sta

tio

n L

evel

Bay

Lev

el

AM 1703 AM 1703

PSactive /stand-by

IEC 60870-5-103 IEC 60870-5-103 IEC 60870-5-103

VA TECH SAT3

Object Oriented Engineering

N-00116e.ppt / 2000 10 10 by M. Eckl, B. Steininger / Copyright (c) by VA TECH SAT GmbH & Co Vienna

IEC 61850 compliant data model