Q and A: IEC61850
Our Questions and Answers section in this edition of Electrical Tester is a little different from those that have appeared in past issues. That’s because this time we’re dealing with a more complex and demanding issue than usual: IEC 61850, the standard that relates to communications between intelligent electronic devices in electrical substations. The Megger Technical Support Group receives a lot of questions on this topic, so we’ve allowed rather more space than usual so that Andrea Bonetti and Marius Spitzer, both engineers with wide experience in this field, can clear up some common misconceptions and to provide some useful answers.
Q: Is IEC 61850 a communications protocol?
A: IEC 61850 is a standard that defines communications protocols and much more. In reality, IEC 61850 is built on three pillars:
- Standard Signal List
- Standard Information Exchange
- Standard System Engineering
The Standard Signal List provides a standardized approach for modelling the system, the equipment and the signals associated with the system and the equipment. It does this by defining ‘elementary functions’ called Logical Nodes (LN), their signals (Data Objects, DOs), and their descriptions in System Configuration Language (SCL).
Standard Information Exchange defines the services and protocols used for the exchange of information. These include: GOOSE (Generic Object Oriented System Event) messages, sampled values, disturbance recorder file formats – COMTRADE – and the protocols to access the files (MMS and FTP). It is useful to note that the communication protocols are described in SCL.
Standard System Engineering provides a standardized approach to designing IEC 61850 communication structures and describing them in SCL. It promotes a top-down engineering approach and is also related to the definition of IED Configuration Tools (ICTs) and System Configuration Tools (SCTs).
Because its structure is based on these three pillars, IEC 61850 is robust and future proof.
To illustrate this, let us assume that future technology produces a new real-time protocol that performs better than GOOSE. If the power system has been modelled and described in SCL (and, of course, correctly implemented), the information that’s being sent around the system is known, along with the sources and destinations. So all that needs to be done is to change the communication section of the SCL file to show that some messages will be sent with the new protocol rather than with GOOSE. The modelling strategy in IEC 61850 is the power of the standard.
Once these changes have been made in SCL, it is the task of the IED Configuration Tools (ICTs) to read the SCL file and instruct the IEDs to send and receive the information using the new protocol. The SCL file is provided by the System Configuration Tool (SCT) and typically is named as System/Substation Configuration Description (SCD).
This example is not, of course, entirely complete because the new protocol must also be implemented in the devices, but it shows that the entire concept is robust and sufficiently open to support future developments.
Q: How important is IEC 61850 for the implementation of the Smart Grid?
A: According to the IEC, IEC 61850 is one of seven core standards for the Smart Grid, and it would not be possible to implement the Smart Grid without using it. More information can be found on the IEC website at https://www.iec.ch/smartgrid/standards/.
Q: What is meant by IEC 61850 Edition 2?
A: This is potentially a very misleading description because there is no overall ‘edition’ for the whole IEC 61850 standard – each part of the standard has its own edition. All of the original parts of the standard have now reached Edition 2, while parts that have been added more recently have not. For example, the part dealing with time synchronisation (IEC 61850-9-3) is availabe at Edition 1. This means that it’s very dangerous to refer to ‘IEC 61850 Edition 2 devices’ without clarifying exactly what is meant by this simplistic description.
In the protection field, there’s a high probability that an ‘Edition 2’ device is one that supports zero recovery time Ethernet redundancy (PRP, HSR), as well as test and simulation modes, and SCL Edition 2. Unfortunately, there’s nothing to guarantee this, so the description ‘Edition 2’ should be used with great caution. Ideally, this description should not be used at all, but in practice its use is so widespread that compromise is necessary, and those using it should at least be prepared to answer the question “What do you mean by Edition 2?”.
Q: Does Megger have products and tools for IEC 61850 applications?
A: Yes! Megger is very active in this field, and the company released its first products for IEC 61850 applications as early as 2009. Today, Megger offers the FREJA and SMRT relay test sets with embedded IEC 61850 GOOSE sniffer technology that eliminates the need to connect a computer to the IEC 61850 network and therefore enhances cyber security.
Megger products also support IEC 61850 Sampled Values, which are associated with the so-called process bus. With Megger test sets, it is possible to generate analog quantities (voltages and currents) in the digital standardized IEC 61850 Sampled Values (SV) format, in line with the Light Edition profile (IEC 61850-9-2 LE). And with the Megger SV Analyzer Software, it is possible to ‘see’ the Sampled Values in electrotechnical format – that is, as rms voltages and currents, phase angles, waveforms in time domain, and so on.
A feature unique to Megger equipment is the ability to compare GOOSE messages in the substation network with their descriptions in the formal SCD file, in the standardized IEC 61850 SCL. The algorithm that provides this functionality is implemented in Megger’s MGC software, which is available on board the company’s relay test sets and as a standalone version for use on a PC. This concept, which was patented by Megger in 2009, facilitates commissioning tests, diagnosis of interoperability problems and field acceptance testing.
Please refer to the following link for a recent IEEE paper from Megger on this subject: https://ieeexplore.ieee.org/document/8778541
Q: What is the Megger GOOSER?
A: GOOSER was the first dedicated product from Megger for looking at IEC 61850 GOOSE messages. It was released in 2009 and discontinued in 2013, but it has some characteristics that purportedly similar devices still can’t match when performing special tests, like the 0.6 ms ‘full chain’ conversion time of GOOSE messages into contact signals. Similar equipment on the market today typically takes between 4 ms and 8 ms for this conversion.
Thanks to its ability to convert GOOSE messages into contact signals and binary inputs into GOOSE messages in just 0.6 ms, and thanks to the substation performance of its binary
input/output interfaces – the breaking capacity of the binary outputs of the GOOSER was the same as that for the binary outputs of a protection relay – GOOSER was a very good example of what is today called switchgear control unit (SCU).
The GOOSER was also a good solution from the point of view of cyber security, especially where there was a need to record GOOSE messages from the IEC 61850 network by using a GOOSE sniffer installed on a PC without connecting the PC to the network itself.
The GOOSER had a front port and a rear port. It was designed to detect GOOSE messages on the rear port and forward them to the front port. It was impossible to send any type of message in the reverse direction – from the front port to the rear port – because this functionality was not provided. In effect, GOOSER was an ‘Ethernet diode’. An engineer could safely connect a PC to the front port of the GOOSER and read messages available to the rear port, which was connected to the IEC 61850 network, with absolutely no risk of interaction with the substation bus.
Today, the GOOSE sniffing functionality provided by the GOOSER is integrated into Megger test sets, offering a safe environment that can be connected to the IEC 61850 bus with absolutely no risk of introducing malware. In addition, this arrangement makes it unnecessary to use a PC for monitoring GOOSE messages.
About the author
Andrea Bonetti graduated as electrotechnical engineer from Sapienza University of Rome, Italy, in 1993, after having carried out his first two years of engineering studies at Universitá di Trento, Italy.
After five years with ABB Italy as a protection engineer, Andrea worked for 10 years as an HV relay protection specialist with HV relay protection manufacturer ABB Grid Automation Products in Västerås, Sweden. His work involved relay post-fault analysis, relay settings, commissioning support, as well as training for distance protection and line differential protection in IEC 61850 and conventional applications.
From 2008 to 2013 Andrea worked at Megger in Stockholm, as product manager and technical specialist for relay test equipment, dealing with the development of IEC 61850 test set and tools, test algorithms for distance protection and transformer differential protection relays.
From 2013 to 2018, he worked as consultant in Relay Protection and IEC 61850 Applications. This involved procurement specification for TSOs, IEC 61850 specification and attendance for FAT/SAT, IEC 61850 troubleshooting in operative substations, training, IEC 61850 top down specification and engineering process, development of IEC 61850 test equipment and tools. Subsequently, Andrea has been working with Megger in Stockholm as senior specialist in relay protection and IEC 61850 applications.
Andrea holds a patent for IEC 61850 testing tools and algorithms. Since 2006, he has been an active member of the IEC TC 95/MT 4 and sub-group leader for the development of the IEC 60255-121 standard. He received the IEC 1906 Award in 2013. Since 2008 Andrea has been a guest lecturer at KTH (Royal Institute of Technology, Stockholm) for IEC 61850 for Substation Automation applications.
