Siemen's Paul Bancroft explains that power electronics are a key part of the transition to renewable energy. Gone are the days when the grid solely relied on a relatively small number of huge spinning machines, helping create stability.

“There are several key differences in the way renewable plant works. Most renewable energy sources are connected via power electronic inverters. There is the inertia issue, but also lower fault current contributions," he says.

"The systems protecting the transmission network offer amazing performance, which greatly help the power system's stability. Faults on the 400kV network are fully cleared in 80 milliseconds; maintaining this level of performance as the network evolves could be a challenge."

Under fault conditions traditional generation provides big spikes in current that let operators know there is a fault and act. “On the transmission system, historically there have been very high fault levels. The protection system has somewhat been designed with that underlying assumption. The system sits there trying to distinguish between when things are normal or abnormal. When you look at the current and see big spikes, that’s the trigger letting you know something is wrong.

“The relationships between the voltages and currents allow the system to home in on where the fault has occurred.”

The smaller current levels and different voltage profiles produced by DERs have the potential to make it harder to detect problems and shutdown the part of the system that is failing quickly, Bancroft explains.

That’s where digitalisation can help by alerting protection engineers to potential problems and enabling them to run simulations of different scenarios on networks to assess their impact. The modular software portfolio of Gridscale X, for example, can simulate the way windfarms, solar installations and battery storage respond to faults on the network. This helps to ensure assets and networks comply with NESO’s Grid Code.

Gridscale X Advanced Protection Assessment software – for example - supports protection engineers at transmission owners, networks and generators in managing the entire workflow related to their assets. This includes detailed protection data, management of electronic settings, setting calculations, and validation. The software features an extensive library of more than 7,300 detailed relay models and an array of modular protection tools that enable engineers to seamlessly manage large volumes of complex network data, uncovering potential problems and examining alternative solutions.

“Renewables and their integration may not affect frequency of faults or where they occur. The challenge is that what happens during a fault changes, with different relationships between the voltages and currents that the protection relays rely on to clear the faults,” says Bancroft. Gridscale X Advanced Protection Assessment allows network protection relays to be modelled in much more depth – down to an algorithmic level. The software provides a digital means for studying protection systems on the network, along with tools for simulating load flows and short circuits. It collects both real-time and static data from sources including smart meters, SCADA systems, and GIS data, among others.

Modern protection relays, Bancroft explains, are “like little computers featuring PLC controllers, associated with a single circuit breaker”. The algorithms on which the protection relays rely to make decisions can be modelled in fine detail in Gridscale X. “For a specific relay, its algorithm is modelled within Gridscale X Advanced Protection Assessment. This gives you much more confidence when it comes to simulating the way something is going to behave; the system is going to identify any foibles in the way that particular relay would respond to the event.”

As system conditions start to become more unpredictable, this is where Gridscale X comes into its own, spotting potential issues in the way the protection system is going to react. “Obviously if we can find those differences in a simulation, it’s infinitely better than finding out about a problem after we’ve just had a blackout,” says Bancroft. “An outage might be due to something unexpected happening with a relay that 20 years ago wouldn’t have been a problem.

“But because the fault looks different on the system, the protection didn’t work as we would want it to.”

As protection evolves with the grid, there will be a need to analyse the performance of not just transmission but also distribution networks in much greater detail. “Everybody is modelling the primary system, and that is well understood. What we’re doing is modelling the secondary system: these little computers that are making decisions about what to do in the primary system in real time.” This could have advantages in terms of predictive maintenance. “It could help feed into pre-emptively identifying ways we need to change protection engineering on the system.”

Among many use cases, Gridscale X modular software can also help solve issues with the connection of many more distributed energy resources to networks. One of the scenarios the software simulates is connection requests, says Bancroft. “Thanks to the core, which is the digital grid model, you can execute multiple use cases. One of them is connection requests management.”

For example, if a connection request is registered on a utility CRM, Gridscale X software can identify where the connection should be located. It can also run multiple simulations of the impact of the connection on the network. “With our system the operator can immediately understand if a voltage or current violation will occur if you connect that specific asset, and how to anticipate and solve problems by reconfiguring the grid,” Bancroft explains. The software can also indicate if a section of the grid needs reinforcement. Siemens is working on incorporating data about vibration and temperature into the digital grid model to help predict failure.

The addition of extra sources of data helps with applications such as Gridscale X Dynamic Line Rating. This application optimises the capacity of overhead power lines by adjusting their capacity based on real-time weather conditions. It’s a different approach to static line ratings that assume worst-case conditions, potentially leading to underutilisation of grid capacity.

Bancroft explains: “Traditionally, power systems have been designed for worst-case assumptions, and we haven’t used adaptive technology like Gridscale X Dynamic Line Rating. How much power you can send down an overhead line ultimately comes down to how hot you can make it before it gets dangerous.” Overheating power lines have the potential to sag, which can cause safety issues. While all this is problematic, power systems have been designed to reflect extremes.

“If there is a loading limit of 1,000 amps on an overhead line, this maximum could be based on the onerous assumption that it’s 39°C outside and there’s no wind. If it’s January and 2°C outside, and you have a strong wind, you might be able to put 1,400 amps down the line because the heat dissipates into the environment.”

The widespread availability of accurate data about temperature and wind speed in local areas means a different approach. “We can take advantage of knowing the conditions to give the line a rating for the day – and that’s where this software is focused.”

Bancroft adds that in general, digitalisation is enabling grid operators to “push the grid to its limits”. “The more data you have that you can digest in real time, or near real-time, the more actions you can execute on the grid.” This enables networks to “reconfigure the grid on the fly”, he adds. “In the past, the only way to operate the grid was to make some assumptions to keep it as stable as possible. With the advent of the digital twin, that changes.”

It's not a case of replacing activities such as reinforcement but making that reinforcement more precise based on the detailed information now available, he adds. “Because of the scale of the challenge, we have to use everything at our disposal.

“The capabilities of the modular software as part of Gridscale X complement an intelligent approach to operation of and investment into the grid.”