Not If but When
by Alex Apostolov, Editor-in-Chief
It was not that long ago when people were asking should we build a digital substation and the answer to this question is already obvious – yes, we should. Now the frequently asked question is when we should build a digital substation.
And the answer to this question is as usual starting with “It depends!” First of all, it depends on what do we mean by a digital substation. For many people any substation that uses some form of digital technology like microprocessor based multi-functional IEDs may be considered a digital substation. This is not what I understand by this term.
To me, a digital substation is the substation in which all interfaces to the electric power system and between the protection, automation and control devices exchanging information to implement different protection schemes are digitized. So, in a digital substation the only copper wiring is to the power supply of the protection and control devices – everything else is communications based and in reality, this communication interface uses the IEC 61850 client-server and peer-to-peer communication services.
Based on this understanding of what a digital substation is we can say that the electric power industry has made a significant progress. While not that long ago most of the digital substations around the world were part of pilot projects by forward looking utilities that were trying to gain experience and see how they can use them in the most efficient way to solve the challenges of the changing electric power industry, today we can say that many utilities have already concluded that this is the way to go and other are in different stages of standardizing their protection, automation and control systems as digital substations based on IEC 61850 station in process bus.
When we look at the different articles included in this issue of the magazine, we can see that this is not an isolated event in some part of the world but is definitely a global trend showing that there is no turning back.
Before the pandemic hit the world, I have been traveling to many countries to participate in different conferences, seminars, workshops or working group meetings and in many cases I was lucky enough to have the opportunity to visit digital substations all over the world.
When you ask people why they have made the decision to switch from conventional to digital substations you may get a wide range of answers. In one utility they told me that they had to start using low power instrument transformers with IEC 61850 sampled values for safety reasons – they had several instances of conventional current transformers exploding which presented a very dangerous safety hazard. In another utility the answer was that they had an aging infrastructure and they had to upgrade hundreds of old substations and it was impossible to accomplish that by replacing the existing hard-wired interfaces simply by new hard-wired interfaces – the only possible way of accomplishing this task was by replacing the hard wiring with optical cables carrying sampled values and GOOSE messages.
For some other people the reason was the possibility to replace the time-based maintenance testing with condition-based maintenance testing using the monitoring capabilities that a digital substation provides.
At the same time throughout the years, we have observed the evolution of the protection, automation and control technology delivered by the leading global manufacturers that have seen the benefits of this technology and invested heavily in its development. We not only see multifunctional IEDs with sampled values and GOOSE interfaces but also a wide variety of different process interface devices. The early versions of digital substations typically used merging units for the digitization of the analog signals and some form of a switchgear interface units. In today’s digital substations we can see process interface units integrating both the analog and the binary interface to the primary equipment, but also in some cases adding local intelligence, such as synchrophasor calculations or overcurrent and distance protection functions. Today we are also talking about centralized digital substations and virtual IEDs that can further improve the efficiency of the PAC systems.
From reading the articles in this issue it is obvious that we have made significant progress in the development and implementation of digital substations and we have learned some important lessons that can help us make another step forward to a time when we will not be even asking the question when we are going to have a digital substation because every knew or refurbished substation will be digital.
“Digital transformation is more about humans than digital”
Brian Solis
