Smart Substations Are Shedding Light on the Distribution Grid

Industry News – February 20, 2023
Mitnetz Strom looks after more than 16,000 transformer stations in its grid area. Across Germany, there are around 600,000 of them.

As the energy transition progresses, power distribution is becoming more and more complex. Smart grids are needed in order to monitor power grids and control the flow of energy. This is where digital transformer stations come in. Join us on a tour of a smart substation.

Burladingen, Germany, a town about an hour south of Stuttgart, will soon see a pioneering electrical substation connected to the grid. Distribution grid operator Netze BW plans to put the transformer station into operation by the end of 2023. The station will be transforming electricity from the trans-regional 110,000-volt high-voltage grid to the regional grid’s medium-voltage. In the future, larger producers feeding in electricity (as set out in the German Renewable Energy Sources Act) can be directly integrated into the grid. The new hub for the transport and the distribution grid will be equipped with two transformers featuring state-of-the-art protection and control technology and weigh around 70 metric tons. In addition to glass fiber communication, integrated sensors will supply a cloud-based digital twin with real-time status data. What’s more, the high-voltage installation uses purified and compressed air instead of sulfur hexafluoride (SF6), a greenhouse gas commonly used in modern electrical switchgear, transformers and substations. To enable this, the grid operator invested €11 million.

More diversity – more challenges for the power grid

The energy transition comes with enormous challenges for grid operators. On one side, an increasing number of prosumers generates decentralized electricity through PV systems on their roofs, some of which is consumed on-site, some of which is fed into the grid. On the other side, the electricity produced by offshore wind power, for instance, needs to be transported to urban agglomerations over large distances. What’s more, the growing share of renewable energies renders power generation more volatile, while the energy demand is continuously growing due to the electrification of the transport and heat sectors.

As more and more producers and consumers are connected to the distribution grid, there is an urgent need for more intelligent solutions to manage it. “The energy transition is happening in the low-voltage grid,” Ulrich Hempen, Vice President Business Unit Solutions at WAGO Kontakttechnik, recently said on the The smarter E Podcast. This is why the low voltage grid level needs to become transparent, and that’s where transformer stations play a key role. So if all homeowners in a village went ahead and installed a PV system tomorrow, then a conventional transformer station would not be able to handle the bidirectional flows of energy,” Hempen explains. This is why transformers need to be digital.

In Germany alone, there are estimated to be around 600,000 transformer or local substations. What separates one from another is the extent to which they are digitalized and how they are used. Simple systems are limited to monitoring operational data to enable condition-based maintenance. “More advanced systems can actually support operators in their day-to-day operational decisions,” explains grid specialist Lasse Kleinjohann, Head of Customer Operations & Engagement, Digital Grid, IoT & Edge at Siemens Energy.

From transformer stations to digital secondary substations

Digital secondary substations (DSS) are essential for smart grids at medium and low voltage levels and differ considerably from conventional secondary substations. “It has become important for the switchgear in medium voltage cells to be controllable,” says Carsten Ziegler, spokesperson for the distribution grid operator Mitteldeutsche Netzgesellschaft (Mitnetz) Strom, which is part of the E.ON Group and describes itself as one of the largest distribution grid operators in Europe. The medium voltage cells are part of the switchgear and connect it to the existing supply system. According to Ziegler, this makes it possible to issue central commands to open or close load break switches. In addition, measurement technology maps all cable outlets, both at medium and at low-voltage levels.

Digital secondary substations (DSS) are essential for smart grids at medium and low voltage levels and differ considerably from conventional secondary substations

Just one in five stations needs to be “smart”

Such measurements form the basis for a comprehensive overview of loads across the power grid. Without this data, technicians will be unable to properly control the volatile renewable energies. One big challenge lies in processing this data in order to manage the power flows within the grid.

“Not all secondary substations need to be digitalized to allow to control and monitor all of the power grids,” Ziegler explains. Mitnetz Strom is planning to enable the complete monitoring of its medium-voltage grid by 2026. According to current estimations, equipping just 20 percent of all secondary substations with DSS would be sufficient. Another ten percent of standard transformers would require an update in order to provide measurement data. The grid operator additionally uses measurements gathered by the customers. The measurement points is selected so that not all secondary substations need to provide measurement data in order to make the medium-voltage grid completely monitorable. “Complex Algorithms can simulate those parts of the grid that have no intelligent measurement technology, making them monitorable – provided there is an appropriate selection of measurement points,” Ziegler clarifies. In addition to the complete transparency of the medium-voltage grid, the network operator also aims to make thirty percent of the low-voltage grid monitorable. Equipping just thirty percent of the transformer stations with intelligent measurement technology is sufficient in this case.

“The DSS that are used by the E.ON Group all have the same functionalities,” Ziegler reports. As the distribution grid operator acquires them from several different component manufacturers, their components may vary, but this affects service and maintenance rather than functionalities. DSS always come in a completely modular design, so each component can be replaced according to a plug-and-play principle, minimizing trouble-shooting.

Digitalizing transformer stations step by step

Some of the existing conventional transformer stations can and will be digitalized, too, provided they meet certain technical requirements. To digitalize existing transformer stations, so-called retrofit kits are used. Gradual retrofitting is also possible. According to Ziegler, “retrofitted transformer stations will rarely have all of the functionalities of a DSS, though. The main focus will be on monitoring the low-voltage grid.”

The first step to take regarding existing transformer stations is assessing the installed technologies, such as sensor and communication equipment, to decide which retrofitting elements are needed. “For some functions, we need the manufacturer’s design data, which can be near impossible for transformer models that are over 15 years old,” as Siemens Manager Kleinjohann reports from experience.

High demand makes for longer delivery time

The demand for digitalization of the power grid is high, which is leading to significantly longer delivery periods for smart transformers. “The demand for transformers and components is increasing drastically as grid operators are now ordering large quantities from us, as well. Our delivery time for transformers is about twelve weeks, for transformer stations it is 16 to 18 weeks,” Gerhard Irlesberger confirms. Irlesberger is head of project planning and management at Troja Europe, a company that supplies and connects transformers, transformer stations and large substations. Other suppliers currently have delivery times of more than one year.

Fortunately, long delivery times are not a problem for Mitnetz Strom. “We placed the order early, so we have received all smart transformers as planned,” Ziegler states with satisfaction. As a result, his company was able to install around 200 DSS into the power grid of the enviaM Group in East Germany in 2022 – and are planning to install as many again in 2023. “Our realistic, forward-looking planning makes it very likely for us to achieve our goal of installing the projected amount,” he says. The plans to retrofit the transformers are accompanied by the expansion of renewable-energy power plants, heat pumps and charging infrastructure for e-mobility. As Ziegler explains, all of these measures go hand in hand.

Switching and operating intelligently

Intelligent transformers continuously gather data to create a clear picture of a system’s status, operating data and thermal load. The information gathered includes ageing, malfunctions and required maintenance work. Virtual models (digital twins) of the transformers are created in order to simulate operating points, load profiles and overload scenarios based on current operating values. This allows for decisions to be based on data, while at the same time, their impact on service life and maintenance work is recorded. The grid operator collates all data regarding the power grid, like demand forecasts.

More transparency for more flexible operation

In the future, an even more closely connected network of grid operators and consumers will be crucial for automatic intelligent decisions based on demand and generation. “Intelligent, digitalized transformers or secondary substations are helping grid operators provide more operational transparency as well as a flexible operation,” Kleinjohann from Siemens Energy states.

Smart technology now sheds light on the previously untransparent distribution grid. By simulating operating points, grid fluctuations can be controlled and balanced. According to Kleinjohann, one of the advantages is that “it is even possible to operate transformers under controlled overload conditions without risking damage to the devices.” He recommends equipping all new transformers to be retrofittable into digital and intelligent transformers, even if those functions are not yet needed in their entirety. Siemens is currently making use of machine learning in pilot projects to gather more information from existing data. One of these projects is the aforementioned switchgear, which will soon be put into operation.

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