A Senior Capstone Design Team of the University of Idaho is in the process of developing an OPC XML-DA Client solution that connects to a network of Synchrophasor devices and allows the use of OPC to retrieve data from the devices. The goal of the project is to create a “product” that power and electrical distribution companies can use to monitor their networks of Synchrophasor devices. The University of Idaho in partnership with SEL (Schweitzer Engineering Laboratories) selected the OPC Linux Toolbox from Softing AG, based near Munich, Germany, and with North American offices in Newburyport, Mass., for implementing a customizable OPC XML-DA client. The OPC Linux Toolbox enables the Design Team to concentrate on the project goal and not on learning the intricacies of DCOM, SOAP, or other technologies.The main goals of the project are to:Monitor a Synchrophasor network in near real-time Visualize the Synchrophasor dataArchive Synchrophasor data for further analysisMonitor the health of SynchrophasorsIn addition to the main requirements the proposed solution must: Be easy-to-useWork through firewallsRun on cross-platform systemsHowever, what is a Synchrophasor? SEL refers to Synchrophasors as “time-synchronized phasor measurements of electrical power in a power system. A phasor measurement is a measurement of the voltage or current at a particular time and place. Power engineers analyze the Synchrophasor measurements […] to understand the state of the power system. In a Synchrophasor system, these measurements are taken at many different places on a power system grid at the same time. Analysis of this information helps to prevent many power system problems such as rolling blackouts.”Synchrophasors adhere to the IEEE C37.118 standard. This standard defines (a) the synchronized phasor measurements that are used in a power system and (b) the communications protocol for transmitting the data points in real-time. Furthermore, the C37.118 specifies the format of the transmitted phasor data. With C37.118, data frames are usually transmitted as a binary stream of values. The format of the data can vary and is defined during runtime by a so called “configuration frame,” which is the first frame sent to a client. The configuration frame contains information about the data format to enable a client to correctly interpret subsequent data frames. This method of communication is, understandably, not well suited for the human observer interested in the data.Typically, C37.118 data frames are transmitted either over a serial link or over a data connection using the IP protocol. With the IP protocol the number of simultaneous connections to SEL’s Phasor Data Concentrator (PDC) is limited to six, each with a dedicated IP address.There are numerous cases when engineers and/or other software applications need to have easy access to measurements taken by the Phasor Measurement Units (PMUs) in a Synchrophasor network without occupying one of the six dedicated connections. It is also important that phasor data can easily be visualized at multiple locations with off-the-shelve software packages. For these reasons, the Design Team decided on OPC XML-DA as an additional protocol that circumvents most of the limiting factors mentioned above. The OPC XML-DA Client connects to an OPC Server that translates C37.118 messages and provides the information to attached Clients. Softing’s XML-DA Linux Toolbox enables the Design Team to develop an application that is able to communicate across different operating system platforms. Standard OPC DA clients are based on Microsoft’s DCOM technology and are consequently restricted to the Windows operating system. In addition, DCOM communication is blocked by firewalls that prevent clients from accessing data over a wide-area network and the World Wide Web. The OPC XML-DA specification defines an alternative mechanism for remote OPC communications. XML-DA is based on SOAP (Simple Object Access Protocol), and generally uses HTTP as its transport layer. As a result, XML-DA is likely to work through firewalls, and offers the possibility of cross-platform OPC communication. Using Softing’s OPC Toolbox, the Design Team is currently in the process of developing a web application that is able to connect to an OPC server. The partnering company SEL stated that Softing’s OPC Toolbox is very useful in the development of the Web application. “With the Toolbox, a developer does not necessarily need to have expertise in SOAP or even the OPC protocol and can focus, instead, on the non-OPC-specific components of the application.”With the introduction of the XML-DA specification, OPC has become a widely accepted protocol for exchanging data with devices. This is one of the main reasons why it was important to SEL to evaluate the technology for its product line. Today, a user already has access to several OPC clients for visualization and other purposes that support OPC XML-DA and OPC DA. Specialized OPC Client applications, like the Web application for Synchrophasor devices, are easily developed for different operating systems by using software libraries like Softing’s comprehensive cross-platform OPC Toolbox suite, allowing the developer to concentrate on transmitting data and not on learning the ins and outs of DCOM, SOAP, or other technologies.Softing, a member of the European Steering Committee of the OPC Foundation and author of the OPC Book, actively contributes to the success of OPC by providing high quality OPC products that enable our customers to stay in the lead. For more information on how Softing can assist you, please visit www.softing.us.
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