“You Can Never Fully Rule Out a Blackout”

Hello Tom, hello Marcel. On April 28, a massive power outage affected large parts of Spain and Portugal, with the impact still being felt the following day. What’s your assessment of what happened?

Tom Janson: So far, the exact cause of the blackout is unknown. What has been measured, however, is a significant frequency drop in the power grid.
 

What does that mean?

Tom Janson: It means that either too little electricity was being generated—so not enough power was available in the grid—or that there was too much demand, putting the system under stress. This can happen, for example, if a major generator suddenly and unexpectedly goes offline. Or if a sudden spike in consumption overloads the grid.

Marcel Karell: You can imagine grid frequency like a balance scale. Ideally, in the European interconnected grid, we have 50 hertz. On one side of the scale is demand—the energy being consumed. On the other side is generation—supplied by renewables, conventional power plants, and so on. Both sides must stay balanced to maintain the 50 hertz frequency—that’s the normal operating state.
 

How do grid operators normally ensure stability?

Marcel Karell: Transmission system operators in Germany and across Europe use congestion management, power plant scheduling, and continuous forecasting to keep the frequency stable. The European grid is essentially the conductor. We also have an increasing number of inverters in the grid. Especially renewable energy sources are equipped with frequency protection. If the frequency moves too far out of range, these sources automatically disconnect from the grid.

In this case, the frequency imbalance seems to have occurred in the southern part of the network, triggering the outage.
 

So you think a supply-demand imbalance is more likely than a weather event or cyberattack?

Tom Janson: We can’t say for certain at this point. Natural events can definitely cause frequency drops, either by increasing load or taking generators offline. But such effects could also be triggered by a targeted cyberattack. Given the current data, we can’t draw firm conclusions yet.
 

Spain’s grid is now said to be about 90% restored. Portugal is still behind. How do you restart the grid after a blackout like this—and why is it so difficult?

Marcel Karell: Large-scale outages like this are complex to manage. It’s like a blackout at home: if every light is on, the oven’s running, and then the washing machine starts, the demand might trip the fuse. You can’t just flip the fuse back on unless you first turn everything off. You need to restart the system gradually, bit by bit, so it doesn’t overload again. That’s exactly the challenge in Spain and Portugal now.

Tom Janson: Right. The recovery is managed via so-called "island systems"—small, independent grid segments that are reconnected to the main grid step by step. And that takes time.
 

Now the root cause needs to be analyzed. How is that done—and how important are measurement data and instruments, especially those with local memory and backup power?

Tom Janson: Root cause analysis is always challenging in these cases. Measurement data is essential—it’s the foundation for any diagnosis. Devices with buffer batteries and internal memory are crucial. If there’s no power, data can’t be recorded or transmitted. Measurement devices need to be able to bridge that gap. Right now, experts need log files from medium-voltage protection systems: where did the protection trip, and what were the threshold violations?

Marcel Karell: Detailed measurement values are the basis of any fault analysis. It’s like an aircraft accident—everyone looks for the black box. And it takes experts to interpret the data. That’s true here too. Even with data recorded by Janitza meters, we’d need to overlay and compare data sets to trace the root cause. It’s a complex task, but one where we at Janitza can contribute with our know-how and software tools. The analysis can take weeks.
 

Doesn’t that make reliable measurement data even more important for preventing such failures in the first place?

Tom Janson: Absolutely. Without accurate data, you simply can’t manage a power grid—whether medium or high voltage. Grid operation and development must be based on facts—on measurable values.

Marcel Karell: And ideally, you also learn from these incidents. Each scenario adds to our understanding. We analyze what led to the failure and use that to introduce new protections and monitoring. That’s what will happen this time as well.
 

Looking ahead—how likely is such a blackout in other countries?

Tom Janson: You can never fully rule out a blackout like this, even in Germany. There was reportedly a frequency dip in Germany during the event, which makes sense in an interconnected European grid. But the situation in Germany is different. Spain and Portugal are on a peninsula, with just one main connection to the continental grid via France and Andorra. Germany is connected in all directions to neighboring countries.
 

So the risk is more spread out?

Tom Janson: Exactly. The European grid can absorb a certain level of disturbance. And Germany simply has more interconnections than the Iberian countries.

Secondly, Germany probably has one of the most reliable grids in the world. It’s highly meshed, with many redundancies, and equipped with modern protection systems. Compared to other EU countries, we’re in a strong position. So while the likelihood is low, you can never say "never."

Tom Janson is International Business Development Manager for Utilities at Janitza.
Marcel Karell is Account Manager for Utilities at Janitza.

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Interview: Joachim Bär