ELECTRIFICATION AND O.L.E.
Keeping protection testing on track
Thomas Schossig of Omicron electronics Austria GmbH discusses standards in substation communications networks. T
he quality of the protection system has a direct influence on the performance and stability of any electrical power system.
The effectiveness of the protection provided in rail infrastructure plays a vital role in the economic success of the system. In the future, there will be more reliance on the communication networks incorporated in the substation protection system. The current standard for communication networks in substations is IEC 61850,1
the flexible and
future-proof solution for substation automation and protection systems.
Impact of engineering
Further to simply defining a set of services and communication protocols, IEC 61850 also specifies a common, vendor independent engineering concept. The concept uses configuration information in a standardised file format (Substation Configuration Language SCL IEC 61850-6)2
and software called system
configurator creates an SCD-file (Substation Configuration Description).
This file is the base for setting up test sets, provides information regarding all IEDs and is essential to testing in a substation.
Data model and client/server-services
One of the new concepts of IEC 61850 is the segregation of application and transport. The application is the data model of the substation; it consists of logical devices and logical nodes.3 These logical nodes contain data attributes and data object information, such as a logical node PTRC (Protection Trip Conditioning), which is the general trip of a protection device. After modelling, the next step is the definition of services. Possible services (such as get, set, report, control…) are defined in part 7-2 of the standard4
in an abstract manner (ACSI
Abstract Communication Service Interface). The services mentioned are already client/ server-services (C/S) that are to be used for SCADA purposes.
GOOSE
IEC 61850 provides two kinds of real time communication. The GOOSE (Generic Object Oriented Substation Event) was introduced5 the fast transmission of events in a substation.
for 52 | rail technology magazine Jun/Jul 12
Every GOOSE transmits the information of a dataset. A dataset refers to information stored in the logical nodes. The data in a GOOSE message is not only sent out after a data change, but is sent out with a repetition strategy and as an unconfirmed multicast. Currently GOOSEs are often used for: - -
Interlockings Reverse blockings Sampled values
As a second possibility of real-time communication, IEC 61850 specifies the transmission
of instantaneous values (for
example of voltages and currents) from a power system. These types of data are called Sampled Values and are defined in part 9 of the standard. IEC 61850-9-2 6
describes the
transmission as a multicast on the Ethernet. First implementations are available.
Testing setup
Omicron is the market leader in offering a wide range of products and services for testing in IEC 61850 substations, as shown in figure 1. IEDs of different vendors are connected to a substation network as well as circuit breaker IEDs and a merging unit to produce sampled values. Client/server communication can be tested with a test-client such as IEDScout. This tool can also be used for the visualisation of GOOSE messages. To check the real-time behaviour of a protection relay during testing, a test set is necessary. All Omicron test sets can subscribe to GOOSE messages and make measurements to verify GOOSE performance. They can also produce sampled values for testing merging units, which can be viewed using SVScout.
REFERENCES 1 IEC 61850-1:2003 Communication Networks and Systems in Substations; Introduction and Overview 2 IEC 61850-6:2004 Communication Networks and Systems in Substations; Configuration description language for communication in electrical substations related to IEDs 3 IEC 61850-7-4:2003 Communication Networks and Systems in Substations; Basic Communication Structure for Substation and Feeder Equipment – Compatible Logical Nodes Classes Introduction and Overview 4 IEC 61850-7-2:2003 Communication Networks and Systems in Substations in substations; Basic communication structure for substation and feeder equipment – Abstract communication service interface (ACSI) 5 IEC 61850-8-1:2004 Communication Networks and Systems in Substations; Specific Communication Service Mapping (SCSM) – Mappings to MMS (ISO/ IEC 9506 Part 1 and Part 2) 6 IEC 61850-9-2:2004 Communication Networks and Systems in Substations; Specific Communication Service Mapping (SCSM) – Sampled Values over ISO/EC 8803-3
FOR MORE INFORMATION
David Brazier, Omicron electronics UK T: 01785 251000 E:
david.brazier@
omicron.at W:
www.omicron.at
Conclusions
IEC 61850 has changed the world of protection testing dramatically and new approaches such as GOOSE and sampled values require a new testing solution – as a market leader in digital protection testing, Omicron offers just such a solution.
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