The biggest questions on Iberian blackout answered by experts ...Middle East

National blackouts across Spain and Portugal ground much of the two nations to a halt, with Spanish Prime Minister Pedro Sanchez blaming a “strong oscillation” in the grid for the extraordinary incident.

While Sanchez insisted the specific cause of the power failure was still unclear, his Portuguese counterpart, Luis Montenegro, said there was “no indication” that a cyber attack took place.

Portugal’s grid operator REN went further, blaming the Spanish electricity grid and a “rare atmospheric phenomenon”.

The operator said that extreme temperature variations in the country led to “anomalous oscillations” in very high-voltage lines.

But what does that actually mean? And why did the blackout impact a whole peninsula? The i Paper spoke to energy experts to find out.

Sanchez said officials did “not yet have conclusive information on the reasons” behind the massive power cut.

Professor Jacopo Torriti from the University of Reading said it was “premature” for REN to publicly state the blackout’s cause. “It takes days for you to know the causes of a blackout… I would take what the Portuguese said with a pinch of salt,” he told The i Paper.

University of Bath’s Professor Chenghong Gu said the “anomalous oscillations” phenomenon is “quite a normal effect”, also treating REN’s hypothesis with scepticism.

“These electricity systems should be designed for these oscillations and these weather conditions, even extreme weather conditions,” he said.

Meanwhile, Gu’s colleague at Bath University, Dr Jenny Bake,r emphasised that “we don’t know if it was just one thing” that caused the power cut or “if there were multiple things”.

Operators are expected to be “N-1 secure”, Gu explained, meaning they can deal with any single outage and absorb one problem into the system. A greater problem may arise if there are several issues at play.

What do anomalous oscillations mean in layman’s terms?

Anomalous oscillations take place when there are extreme changes in temperature, which lead to a volatility of air pressure around overhead cables.

Torriti said: “With a sudden change in temperature, you would experience a change in pressure in the air and that would then trigger almost as a physical pressure and movement on the cable. They could stretch and tear.”

“Power cables are quite often the cause [of blackouts], like during a storm,” he added. “They are out in the open and vulnerable.”

Torriti, though, warned that the cables “are very secure”, again stressing they should be made to withstand such temperature changes.

Gu said that high temperature, in particular, could cause something known as the “corona effect” on transmission lines. This effect can produce vibrations in conductors, which connect power lines to pylons.

“This vibration can cause fatigue of conductors, the change in their parameters, and in very extreme cases, failures of conductors.

“The stability of power systems is very sensitive to these [vibrations]… In the worst case, system frequency could drop too low, and customers must be cut off to re-balance the supply and demand.”

Torriti said the Spanish and Portuguese operate on the same grid system, adding: “It is not surprising at all that Portugal would be affected by a generation issue in Spain.”

Baker, meanwhile, said grid operators are “trying to keep to a very small margin of frequencies, around 50 Hz”. If the frequency drops too low, she explains, then the operator has to disconnect customers.

She said that if the grid was already “near the edge”, in terms of the Hz limit – because of low electricity supply, for instance – then an issue such as anomalous oscillations could have a wide-ranging knock-on effect.

Gu described a “domino effect” whereby, if the grid’s frequency is outside the desired 50 Hz, then a localised customer base will be cut off from the grid, to bring the frequency back to the right level.

If the frequency is still not brought back to around 50 Hz, then a larger area will be cut off from the grid, and so on and so forth until, potentially, a whole peninsula loses power.

A restaurant has no lights on during a power outage in Lisbon, Portugal (Photo: Adri Salido/Getty Images)

“The power grids in EU countries are interconnected,” he added. “It means all grids are synchronised. If there are any failures somewhere in one part of the system, the consequence can immediately propagate to other regions.

Gu explained how these disconnections of households to the grid occur “automatically”, as soon as the frequency deviates too far from 50 Hz. “You cannot control this disconnection. All the settings were set a long time ago.”

Why was there no fallback?

Interconnected grids, like the ones in Spain and Portugal, should, in theory, mean there are reliable backup solutions.

“If there are any issues in one grid, other grids can provide backup supply very quickly,” Gu said. “Interconnected grids can enjoy higher reliability, because resources in the whole system can be shared by all grids in these countries.”

While there is no official explanation for why there was not a sufficient fallback system in place, he said it could be explained by an “operational error” or backup systems being “under maintenance”.

Torriti said the mass blackout seen on the Iberian Peninsula could, potentially, occur in the UK. However, he said, this was less likely.

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“We have two mechanisms to alleviate the impact of such events. One is the capacity market, which is launching this summer in Spain, but we have had it since 2012.

“In extreme conditions, [the UK’s] National Grid would issue a capacity notification, and so any available power that we have would be turned on – like gas power plants that we keep on standby if demand is not being met.

“The cause may still be there, but you could generate sufficient power… It reduces the chance right after the event [of a blackout] of not having enough energy.”

He also said the UK has access to a “black start process”, which helps restore electrical power stations without relying on external electrical power from the grid to recover.

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