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-> home > question and answers > iec 61850 > mappings > The Layers of IEC 61850 and IEC 61400-25.

IEC 61850 Mappings

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Communication networks and systems in Power System Automation


Comprehensive Overview of the many different layers in the definition of IEC 61850: Models, services, mapping to MMS services and protocols, ANS.1, ASN.1. BER, ... This presentation provides a lot of details and and examples.

  1. Abbreviations
  2. Hierarchy of definitions, protocols, …
  3. Model (Standard)
  4. Model (SCL)
  5. Model (IED)
  6. Services (ACSI)
  7. Model and Service Mapping
  8. Services and Protocols (MMS)
  9. ASN.1 BER (Basic Encoding Rule)
  10. Encoded MMS Message


Abbreviation

Description

ACSI Abstract Communication Service Interface
ASG Analogue Setting Common Data Class
ASN.1 Abstract Syntax Notation One
BER Basic Encoding Rules
MMS Manufacturing Message Specification
MV Measured Value Common Data Class
SCL System Configuration Language
SPS Single Point Status Common Data Class
STMP

Temperature Supervisory Logical Node


The following comprehensive set of figures (taken from one of the 50+ seminar modules) provide an introduction into the many different layers of IEC 61850 (IEC 61400-25). Most of the 2,000+ people I have educated in these standards have a problem with the many layers of definitions from abstract Information models down to the messages on tghe wire.

These slides are included here with detailed description and explanation. Many crucial aspects can be understood without additional information - at least people that know the basics of IEC 61850 will understand these slides. The following slide has three colums. The first contains the different layers, the second depicts examples, the third references to the corresponding documents or real world entities.

The highest layer are the Logical Nodes. The example shows the LN STMP (Supervison of Temperature). Note - This LN has been published in Editon 2 of IEC 61850-7-4 (2010). We focus on the three Data Objects Tmp, Alm and TmpAlmSpt.

The Common Data Classes can be found in IEC 61850-7-3. MV stands for Measured Value, SPS for Single Point Status and ASG for Analogue Setpoint.

The three Data Objects Tmp, Alm and TmpAlmSpt can be used to Monitor the temperature for reaching the alarm level or trip level. In case the value reaches the TmpAlmSpt, a report with the Alarm could be sent or the value could be logged in the local log of the IED.

The setpoint could be programmed, configured locally, configured by an SCL file or be set by a communication service.

The Data Attribute STMP1.Tmp.mag.i is described with the SCL File (upper part). This reference STMP1.Tmp.mag.i needs to be mapped to the real value (memory location). This is done by a simple table with the <Private> element with 5 Fields (Field1, Field2, ...).

This mapping is used in the application program and by the IEC 61850 stack to access the real values.

This mapping is, e.g., contained in the Beck IPC Chip supporting IEC 61850.

Once the IEC 61850 Stack on the Chip has read the corresponding SCL file it interprets the file and builds the information models and links the leafs of the model to the real values (by Private fields). A client can immediately retrieve the self description of the server and can Get the current value of the temperature.

The service for getting the value is GetDataValues. This service is defiend as an abstract service in IEC 61859-7-2. Tis service cannot yet be encoded with this definition.

The Logical Device mapps to an MMS Domain, the Logocal Node maps to a NamedVariable as do the Data Objects.

Further details of the mapping can be found in the following figure.

The next level is the MMS service Read. The Read service table is shown in the next figure. Further details on MMS services and protocol can be found here.

The MMS Read-Request protocol (Syntax - similar to an XML Schema) is depicted in the following figure. For electrical engineers it is not eays to read these syntaxes. They are usually more familiar with tables like for IEC 608750-5-10x. The ASN.1 schema for the services is still abstract - the schema needs to be mapped to a concrete transfer syntax.

The main building blocks for the ASN.1 Syntax are shcown in the following figure. These definitions cover almost a good part of the MMS protocol syntax.

The abstract syntax of MMS is encoded with the ASN.1 BER. An example is given in the next slide.

A trace of a MMS message (as payload of an Ethernet frame, carrying IP, TCP, Session, and Presentation protocol information) is shown in the following figure.

The concrete encoding of the message InvokeID is shown in the figure below. The Tag according to the MMS message is "02", the length of the value is "01", and the value is "58" hex.

Further layers and many more details of MMS and below MMS are presented and discussed in our comprehensive and neutral seminars.

02.08.2010


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