A new dimension in power grid reliability and efficiency
Measurement of voltages and currents is necessary for protection. Currently sensors, delivering analog values, are directly wired to the protection devices. Since the relays in a substation are normally situated in a central building this wiring has to cover a distance. In an EMC critical area like ahigh voltage substation this demands high power signals resulting in big copper cables. For conventional instrument transformers this is proven technology.In process bus a new approach is used. Instead of wiring the protection devices to the sensors a Merging Unit is placed near the sensor. The Merging Unit digitalizes the analog values and sends them via a Sampled Measured Value stream to one or more protection devices. The SampledMeasured Value stream is transmitted using fiber optical Ethernet, where EMC is no issue. As an additional advantage this enables new sensors that are not capable of generating high power signals. The relays no longer have to sample the analog values but directly use the digital values out of the Sampled Value Stream.Today's conventional instrument transformers provide an analog signal representing the high voltage signal. This is interoperable by definition. Measurement is done directly in the relays.In process bus the interoperable interface is generated by the Merging Unit. The Merging unit works as a converting device. It converts proprietary sensor outputs to a standardized Ethernet based output. This additionally supports non conventional instrument transformer.To fashion interoperable devices in Energy Automation systems IEC 61850 was created. The standard not only covers message interchange based on IEC 61850-8-1 which is nowadays state of the art technology. In IEC 61850-9-2 the digital representation of analog values is standardized. This standard is the base for an interoperable process bus. Siemens supports IEC 61850-9-2 interface and focuses on interoperable solutions.Benefits
Minimize wiring by measuring directly at the sensors, operating at a central position and use of fiber optical Ethernet
Enhanced safety by avoiding open wire condition at relays
Easier extension / maintenance, adding a device only connection to the network necessary. No direct connection to the sensors required
Maximum network reliability, through seamless redundancy protocols
Interoperability ensured, standardized in IEC 61850-9-2
Merging Units for conventional CT/VT offer process bus advantages without change in primary equipment
Safe and fast communication is the key for reliable electrical energy automation systems. The Ethernet redundancy protocol “High Availability Seamless Redundancy” (HSR) was developed in accordance with standard IEC 62439-3 in order to fulfill the requirements of important and time-critical substation automation applications. HSR allows full redundancy of the communication without depending on reconfiguration times of the network. Even in the event of a fault in the communication network, the application still has full connectivity.
Question: Hello Mr. Heine, at Siemens you have been strongly involved in the development of HSR (High-Availability Seamless Redundancy). How did the protocol come into being? [H. Heine]: HSR was developed with various manufacturers from the area of energy automation in the framework of a research project by the Zurich University of Applied Sciences (ZHAW). Aim of the project was creating a method for realizing the most critical applications via Ethernet. This scope was chosen in order to realize an interoperable solution right from the beginning. Question: Back then, you represented Siemens as an expert for communication in protection devices. Which applications did you focus on at the time?[H. Heine]: At Siemens we mostly focused on the transfer of trip signals and Reverse interlocking via IEC 61850 GOOSE, this means a transfer of individual information from device to device on field level. It is essential for these applications not to lose any information - or a telegram, to be more precise - even if there is a network fault. An additional application we had in mind was the process bus. If we were able to generate redundancy without changeover (seamless), then this would be the foundation for a reliable process bus. Question: The first HSR prototypes were presented at Cigré 2010 in Paris. What do you associate with this event?[H. Heine]: Cigré 2010 was a lot of fun. After hard weeks of preparation with us often programming until late at night, we actually had a functioning, interoperable HSR system. In this system, we not only transferred IEC 61850 GOOSE messages between devices of different manufacturers. We also integrated an IP camera and a projector. To simulate the interruption, a cable was chopped through at one point. This was a lot of fun! Interested persons could watch the demo and then, as the highlight, so to say, interrupt part of the ring with an axe. To prove that the interruption of the cable would not impact the application, you could watch yourself via the camera and projector. Question: After CIGRE, the prototype was to become a series product. How do you evaluate this decision in hindsight, from the point of view of the responsible developer? [H. Heine]: It was only logical to do this. For me it was important not only to develop prototypes, but to supervise the idea up to the commercial product. After all, we had demonstrated that the technology works. Yet, it was still a long way to go to make reliable products, more so because we were developing PRP (Parallel Redundancy Protocol) as a sibling protocol of HSR simultaneously. Endurance tests with many devices gave us especially hard fights. We used more than 100 SIPROTEC devices at our large system testing facility in Nuremberg to test such scenarios. When a telegram was missing in one of the devices, I was often close to flying to Nuremberg to find it. Question: Is one lost telegram really such a big deal?[H. Heine]: We do not develop a protocol for seamless communication and then lose telegrams. Our customers’ claim is highest reliability and this is our objective as well. Communication must be available under all circumstances. This is essential if we want to realize even the most critical applications via Ethernet. "Communication must be available under all circumstances." Question: You have mentioned that in the original project, interoperability was among the focus points. Have you followed up on this? [H. Heine]: To ensure interoperability, we have continued to cooperate with ZHAW which was extremely valuable as a neutral partner and which has been critically reviewing the compatibility of the implementation. Moreover, we were able to substantially contribute our experiences to the standardization of HSR and the revised version of PRP in IEC 62439. I remember quite well two standardization meetings in Korea and Canada, in which I participated. Such meetings always give birth to new ideas, which I discussed with the other participants there. When we were in doubt, we could directly and realistically carry out tests at our large test facility in Germany, in parallel to our standardization meetings. That was exhausting for all involved, but time difference helped a lot. Question: The importance of this development project for our customers and for Siemens was highlighted with the “Best R&D Project 2012” award by the Siemens Smart Grid Division. I’m sure you were quite proud.[H. Heine]: It is of course nice when efforts are appreciated. More important for me, however, is that we were the first manufacturer to be able to offer HSR in our products. At the end of the project, we had integrated both seamless redundancy protocols PRP and HSR not only in the complete SIPROTEC 4 product family, but also in the SIPROTEC Compact family. We were the first ones to provide complete substations with this technology. This makes me very proud. Question: And that is what you presented at Cigré 2012? [H. Heine]: Exactly. I was at the Cigré in Paris with our products in the framework of a UCA interop test. To return there exactly two years after the first prototypes, but this time with a system tested and released product, was a great feeling. It took me quite a while to get the prototype running in 2010. Quite a lot of last-minute adaptations had to be made at the time. In 2012, this was a lot better! The device came directly from the manufacturing plant. I unpacked the device, connected it, activated HSR and everything was up and running within 5 minutes. The fact that HSR is parameter-free, just like PRP, reduces configuration efforts tremendously. This not only helps on the building site, when our devices are commissioned, but also at an industry fair like Cigré. Question: Then, both protocols were also integrated in SIPROTEC 5. Was that a great challenge?[H. Heine]: No, we re-used the algorithms in the subsequent integration in SIPROTEC 5 as they had been tried and tested. Moreover, at the same time the vast field experience of SIPROTEC 4 can be used. Question: In which area of use do you see most advantages of the new technology for our customers?[H. Heine]: I believe in the process bus. I believe, that the advantages of this technology will bring our customers huge advantages. The reduction of copper cables in substations and the introduction of non-conventional converters are only two arguments in favor of the process bus. Shifting measurements directly to the process makes maintenance works at the protection devices much safer. By the way: HSR and PRP are integral parts of Siemens process bus solution.