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The Application of XML in the Substation Automation Based on IEC 61850

The Application of XML in the Substation Automation Based on IEC 61850

Huangwei Changhong Huangwenhua Tangshengan

School of Electrical Engineering, Xi’an Jiaotong University

28 West Xianning Road, Xi’an 710049, P.R.China

E-mail: Huangwei.email@163.com

Abstract：The paper presents the application of XML in the substation automation based on IEC 61850. Expatiate how to use SCL (Substation Configuration description Language) for self-description of IED and system, the procession of respective configuration, and advance a processing model of using XML/HTTP to realize an IEC 61850 non-real-time communication system, and simply discuss the problems of XML security and XML parsing. An application of XML/HTTP demo is given in the end of paper.

Keywords：IEC 61850; SCL; XML; Substation Automation

INTRODUCTION

In the substation automation, due to using a lot of different communications protocols which are responsible for enormous costs for components from different manufacturers and long-term maintenance of the devices is difficult, worldwide of acceptance a single integrated communication standard is very important, IEC (International Electrotechnical Commission) advances IEC 61850, “one world - one technology - one standard”. The aim of it is achieving interoperability between all devices in substations with a common protocol.

XML (eXtensible Markup Language) more rich restricted from of SGML (Standard for General Markup Language), is becoming a widespread method for creating, controlling, and managing data on the web. The IEC 61850 defines a formal, standardized description of devices and the system in SCL (Substation Configuration description Language) which based on XML. IEDs (Intelligent Electronic Devices) made by different manufacturers can exchange SCL configuration information with system configuration tools, which realizes vendor-independent. Moreover, XML/HTTP provides a simple, powerful interface to IED, we can monitor and access to remote data or configuration parameters directly from web browser tools. In this paper, an application of XML/HTTP model will be given.

SCL AND CONFIGURATION

XML is a clearly defined way to structure, describe, and interchange data. SCL bases on XML1.0, and especially is used in substation configuration. We will give an example to show that how to describe the substation in SCL.

</Bay>

</VoltageLevel>

</Substation>

In this SCL file, we can get the information that, there is a bay E1Q1in the substation AB, which includes a breaker QA1 and a switch QB1. The two IEDs connect at Node L1. Thanks to XML, we can easily to describe all different elements and their relationships. In a substation automation system, it is important to configure the primary and secondary equipment in the substation. SCL can help us to resolve this problem with a formalized format. We can describe the structure of substation, IED capability and system specification in SCL.

In the processing of configuration, the IED capability description file(.icd) describes the capabilities and the preconfigured data model of the IED; the system specification description file(.ssd) describes the single line diagram of the substation with the associated logical nodes; the substation configuration description file(.scd) describes the complete substation configuration; the configured IED description file(.cid) describes a instantiated IED with all configuration parameters relevant for the IED. Although these description files have different file types, they all format as XML files. It is easily to comprehend the procession from figure1. Firstly, IEDs create ICD files by IED configuration tools which are offered by respective manufacturers. Then, all these ICD files and SSD files will be given to system configuration tool to create SCD files. At last, according to SCD file, IED configuration tools can create CID files for each IED, which can be downloaded in IED to finish configuring the IED.

Fig. 1 the Procession of Configuration

The APPLICATION OF XML/HTTP

XML/HTTP Model Based on IEC 61850

HTTP (HyperText Transfer Protocol) is an application level protocol for distributed, collaborative, hypermedia systems. It is the standard protocol used to access web pages and other information over the Internet. Http also can transfer XML documents; we can use HTTP post/get requests to realize accessing to remote data. Fig. 2 shows an application of XML/HTTP Model based on IEC 61850. IEC 61850 defines ACSI mapped to MMS, If IED’s data or services are not real time, we can also map IED Data Model to XML service and access to these remote data from web browser. In this model, we should firstly realize mapping Data Model to XML DTD file, and according to the XML DTD file, create XML files. For instance, an electric energy metering device often adopts some databases, such as Microsoft’s ACCESS, as data buffer pool. We can transform the structure of access database into XML DTD file. According to the DTD file and the data gotten from access database, we can create XML files, which maybe include some data, such as phase active power, phase voltages or configuration parameters. So, IED can also be seen as a HTTP web server, we can access to remote data and configuration parameters. Even in some embedded IED, we can realize an embedded MMS/IEC 61850 server, which will be low-cost configuration tools and better user interfaces.

XML Security and XML Encryption

The security of communication data is a very important problem in SAS (Substation Automation System). Thanks to XML, we can easily to comprehend the information in a XML file, but which induces some confidential data will also be easily monitored. Thus, we must encrypt the confidential data. Recent years, SSL/TLS protocol is wildly used in network communication field, which can afford a secure end to end session. But this is a complete encrypt manner, which must encrypt all parts of the file. Maybe some parts in the XML file are not confidential, if we encrypt all the parts, which will induce more time to unencrypt the whole file and cause the file more complex. Thus, we hope to only encrypt XML elements or its contents, not the whole file. W3C offers two ways to involve the security of XML, XML Signature and XML Encryption. XML Signature can be used to validate that the information of the XML file is not be changed. Firstly, the sender produces a unique signature, which is a special relation with the data of the XML file. After the files are received, the receiver starts to compute the signature of the XML file. The integrality of data can be confirmed by comparing with the signature.

Fig. 2 an Application of XML/HTTP Model

Fig. 3 Encrypting Communication IP Address in a Substation Configuration File

XML Encryption can realize the encryption of the whole XML file, XML elements or the contents of XML elements. Figure 3 shows that, in an IEC 61850 SCL file, a XML element is encrypted; the red font codes realize the encryption of communication address, <Address> 192.168.255.25 </Address>. We also can realize contents of XML elements individually encrypted. For instance, we can only encrypt the IP value of Address, 192.168.255.25. Then, EncryptedData Type now will become “http://www.w3.org/2001/04/xmlenc#Content”. Using the XML signature and XML encryption, the coherence of sending data and receiving data can be insured effectively, and the data can be safely transmitted.

Implement a Demo

In this demo, we study an electric energy metering device, which is used to gather and cumulate many data, phase to ground voltages, phase to ground currents, phase active power and so on. The real device often adopts Windows OS and a small database for data buffer pooling. We use Window98 OS and Microsoft’s ACCESS as IED running environment, and implement a JAVA program running in the IED, which realizes to create XML files according to DTD files and offers HTTP web service. Meanwhile, a java applet running in the client, will access to IED data by parsing XML file which transferred by HTTP. The applet will be parsing XML file every 5 seconds, because created XML files will change with data gathered in IED buffer database. We can monitor the data changing through the applet in the web browser. In our test, the parsing interval is 5 seconds, but in real device, the refreshing database cycle maybe 5 minutes or even 10 minutes. Due to such data is not critical to time; using XML/HTML to access to IED non-real-time information is a good manner.

How to create and parse XML files is a mainly problem in this demo. Creating and parsing is a reverse procession. There are two ways to deal with XML files, one is parsing with XML document structure, and the other is data binding. We adopt the latter way, which is a more simple way to deal with XML files. Castor is public software, which can automatically create parsing code according to XML schema given. It maps elements in the XML schema to classes in java codes, and implements the structure of XML file mapped. After mapping, we can use get or set method to get or set values in the XML files, and use unmarshal or marshal method to implement parsing XML files or creating XML files.

Example codes:

...................................................

URL IEDserver = new URL("http:// 192.168.255.25 /JSEPRI_IED1.xml"); // HTTP transfers XML documents

BufferedReader parseXML = new BufferedReader( new InputStreamReader(IEDserver.openStream()));

JSEPRI_IED1 DNIED1 = JSEPRI_IED1.unmarshal(parseXML); // Castor parses the XML documents

phsA=DNIED1.getMMUX().getMX().getV().getphsA(); // We can Get phsA value by get method

.....................................................

Fig. 4 an Applet for Accessing to Remote Data

Fig.4 shows that the demo java applet which implements to monitor 3 phases to ground voltages and currents changes in IE web browser. We also can implement to set configuration parameters in this way and achieve web configuration tools.

CONCLUSION

In this paper, we mainly study the application of XML in the substation automation based on IEC 61850. We have given a procession of substation configuration, and given an example to explain how to use SCL describe substation structure. Because the security of communication data is very important, we use the XML signature and XML encryption to realize XML files safely transmitted and encrypt the confidential data of Substation configuration files. Moreover, an application of XML/HTTP Model is proposed and we have realized a demo to test the model. We believe that XML/HTTP is

a good way to accessing non-real-time information of IED. In the future, we hope to implement both MMS, IEC 61850 support and XML/HTML access in embedded system.

REFERENCES

[1] IEC 61850-6 Configuration description language for communication in electrical substations related to IEDs 2002.08.30CDV

[2] Alexander Apostolov, “XML Applications to UCA2.0/IEC 61850 Object Modeling”, 2002 IEEE

[3] Chiristoph Brunner, “IEC61850 Object Model and Configuration Language”,ABB 2002

[4]MMSd plus Web Technologies http://www.nettedautomation.com

[5] Bilal Siddiqui, “Exploring XML Encryption” , IBM developworks 2002 3

china.huangwei 发表于 2004-07-12 10:05 引用(Trackback0)