Implementing effective monitoring measures could yield much more energy from the cable network—all without digging a single new trench. Just a dream scenario? No, it is entirely possible, say researchers.
This is the story of how cold calculation, and a collaboration between researchers and an entire industry, could save Norway billions in development costs.
It’s about squeezing more out of the tube.
Comparing the cable network and a toothpaste tube is imprecise for sure, but not entirely off the mark. Both cases involve a resource that we know is there and that we would like to use, but which is difficult to access.
Like getting the last bit of toothpaste out of the tube
A toothpaste tube contains about 5% to 10% residual toothpaste, which is almost impossible to squeeze out. The cable network might contain as much as 20% more capacity—which could be “squeezed out” if we apply effective measures, says Thinn, a research scientist at SINTEF Energy.
Temperature control inside the cables is the key in this project. That temperature is greatly affected by the environment. Cables can withstand temperatures up to 90 degrees Celsius but are sensitive to the environment. Both moisture and temperature play a role in how effectively the cables can move electricity.
There’s gold in those trenches
When it comes to cable performance, colder is better. This is an excellent fit in a country where more electricity is used for heating in the cold season than for cooling in the summer. Cables don’t function so well in the long, hot summer weeks, and in fact they perform best in arctic winter weather conditions.
Currently, no temperature sensors are connected to the power cables, and calculations have been based on what is guaranteed to be a safe internal temperature. A fixed load limit has then been set based on this temperature—as if every day was always the hottest, driest and most unfavorable day of the year. As seen from the cables’ point of view, that is.
But cables do not live in a constant “worst case” scenario. They lie in ground that changes temperature and humidity with the weather and season, and thereby impacts the cables’ internal temperature. Yet, the cable capacity is still treated as a fixed quantity. And this, Thinn explains, is where we can find the added values.
“INCA is a type of collaboration between industry and research that solves societal challenges—not just on paper, but actually out in the cable trenches,” says Thinn.
“At SINTEF we are developing the dynamic models and methods that make it possible to calculate the capacity of the cables in real time.
“If we exploit everything the grid can provide, we can extract more capacity when conditions allow it. And we’ll be able to do that without increasing the risk of overload, because we will know the real capacity,” he says.
“But without the cooperative efforts of all the players, we would not be able to create such great value. There’s a lot of gold to be found in the shallow trenches out there, and together we can dig it up.”
The project does in fact involve digging at various test sites around Norway. In several places, a number of sensors have joined the cables down in the trenches.
The sensors monitor temperature and humidity second by second. The information gained from these measurements is part of what will help squeeze more value out of the power grid.
More of everything, and faster too
“The value of 20% more capacity in the cable network lies primarily in everything we don’t have to do—and everything we can suddenly accomplish faster,” says Marius Engebrethsen from REN, who is the project manager for INCA.
On the one hand, you have investments that are avoided or postponed: billions in new cables and upgrades, licensing processes, environmental interventions and all the time these require. On the other hand, you have the value of what can be connected sooner: new industry, data centers, battery factories, electrification of transport and the continental shelf, and more renewable power into the grid without hitting the capacity limit.
From strict static limits to a living grid
In the research project, the researchers regard the power grid as a system in constant motion and interaction with the environment. The soil and gravel around the cables change both temperature and humidity, and the energy capacity follows suit.
“The grid can no longer be understood as a fixed limit, but as something that changes hour by hour,” Thinn says.
Earth becomes a winter blanket
Let’s say that a cable measures 70 degrees Celsius at 500 A (current). If the cable sand dries out, the thermal resistivity of the material adjacent to the cable increases. The sand then insulates the heat that the cable generates more, and the temperature in the cable rises. The surrounding earth becomes more and more like a thermos.
Then the cable temperature can rise to 80 degrees at 500 A current simply because the surrounding masses “change” and therefore insulate better—which is worse for the cable.
“It’s like switching from a summer blanket to a winter blanket,” says Thinn. “It gets a lot warmer.”
With real-time measurements from the sensors located around the cables, and at the same time from inside the cables themselves, the researchers get a precise picture. They see how temperature, humidity and the properties of the soil really affect how much current the cables can withstand before they reach their temperature limit.
What was previously hidden and unused capacity suddenly becomes visible—not as a theoretical possibility, but as room to maneuver that grid companies can use.
Down-to-earth work
To achieve this scenario, the calculation models and reality must meet. All the knowledge and data that is collected must be converted into a tool that grid operators can use. The project has several methods to determine what the cables can actually withstand.
One method involves using fiber optic cables inside existing power cables to calculate and monitor the cable’s internal temperature. The other pilot project involves measuring the moisture and temperature around the cable.
Tensio measures cable temperature
A third project will unite three worlds that normally do not coexist: road, water and power cables. Imagine a building or road construction site: Good drainage is critical because standing water is undesirable in these settings.
However, optimal conditions for power cables are exactly the opposite. Creating the best possible environment for both cables and other infrastructure in the same area thus requires a bit of creativity. Tensio is addressing this need by testing water-borne cooling as a potential solution.
In Trondheim, Tensio is using fiber-optic sensing technology to test temperature monitoring performance inside the cable and compare the measured values with calculated values.
“We’re doing this to learn about different measurement methods so that we can compare real-time values with calculated values,” says Jan Petter Svegård, the project manager for INCA at Tensio.
“Once we have established reliable measurements of cables in operation, we will also be able to check the effects of cooling cable connections by means of both air and water. “
Gauging capacity, minute by minute
Sensors collect data along numerous cables that are either buried in the trenches or measured using fiber-optic sensors within the cables. Information from the different parts of the project is gathered and used to further develop and fine-tune the calculation models that adjust and fine-tune the real capacity.
“We use a program that we call Trench Design (Norwegian: Grøft Design),” says Marius Engebrethsen from REN and the project manager for INCA.
“Trench Design is software for calculating transmission capacity, and a tool that the industry already knows and uses for operational decision support. So what we’re doing is testing a way to give industry the ability to make minute-by-minute decisions about how much each individual cable can handle,” he says.
The grid companies will then be able to adjust the maximum load accordingly. The maximum load is the highest load the grid can handle at any given moment before the capacity is used up and the network risks failures or outages.
The result is an objective basis for decision-making that makes it possible to increase the utilization of existing infrastructure, especially in periods when conditions provide extra cooling or lower thermal load. The tool also provides better control in pressure situations, because we will know more precisely where the limits actually are.
“In reality, a cable can actually tolerate short-term overloading above 90 degrees Celsius in a crisis situation,” says Engebrethsen. “And just how much we can push the network in an emergency situation is what we want to find out now.”
All of this is still in the experimental stage. Gradually, it will be tested at full scale—in hydropower plants, regional grids, and in distribution networks. Then it will be clear whether the models hold up. And when they do, it will be time to “squeeze the tube harder,” that is, to extract the true capacity from the cables we already have.
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