Drive Electric

E.ON study: Smart equipment, such as voltage regulation distribution transformers, can ensure that grids are able to cope with people charging their electric cars.

Marten Bunnemann is the CEO of Avacon AG. He is convinced that VRDTs are the way forward when it comes to overcoming the challenges associated with e-mobility.

Electromobility is on the rise all around the world. But this raises the question whether our power grids can cope with this trend. E.ON, Germany’s largest distribution grid operator, recently pub­lished a high-profile study looking into the grids of its four regional grid operators (Avacon Netz, Bayernwerk Netz, E.DIS Netz, and Schleswig-Holstein Netz). And the results confirmed that it would be possible to charge all cars electrically within the area served by the grids by 2045.

Voltage regulation distribution transformers (VRDTs) are an important part of the technical infrastructure required. Leading the way in the use of this equipment, which was developed in partnership with Maschinenfabrik Reinhausen, Helmstedt-based Avacon Netz GmbH has a particularly impressive repertoire of experience in terms of implementation and operation. We talked with CEO Marten Bunnemann about what the study covered and the technical solutions

Mr. Bunnemann, what do you see as the main problems when integrating electromobility into the grid?

All of our research into grid integration has revealed that the main prob­lem is how drivers will go about charging their vehicles since we have to predict these patterns of behavior 15 or 20 years in advance. The key questions to consider are: How many cars will realistically be charged at once and how can we make sure that the grids are able to cope with this level of demand? We looked into this as part of the large-scale study mentioned above, but also in many other studies. We gave particular emphasis to those looking at rural grids since our rural spaces (villages and small and medium-sized towns) have the most cars.

Proposition one:
A full switch to e-mobility is a possibility

And we determined that, on the basis of the knowledge available to us now, there won’t be any major problems for our grids if we are smart in our preparations for electromobility and stay ahead of the game. We want to be able to stand out from the crowd and not force specific charging times on our customers. They should all be able to charge their vehicles at home whenever they wish to. This is the promise we have made to ourselves.

To what extent do voltage regulation distribution transformers (VRDTs) feature in your plans for the upgrade work required in the future?

Transformers and lines are known for being the main components of power grids. According to our findings, prob­lems mainly occur in the transformers and lines in the low-voltage grid, which is the part of the grid that is closest to the customers. Here, the first problems that almost always arise are transformers being overload­ed and line voltages being too low. Any other issues are much less common.

What this means is that we will replace small, unregulated transformers with larger voltage regulation distribution transformers (VRDTs). And we will also make them intelligent. This largely cuts out the need for line reinforcements, which often used to be required to the detriment of the general public.

A lot of demand would be placed on the power grid if everyone were to start charging their cars at the same time. VRDTs help to keep the voltage constant. (© Timo Müller)

What benefits do you expect from the use of voltage regulation distribution transformers?

To put it simply, the use of VRDTs large­ly rules out voltage problems in the low-voltage grid, and potentially also the medium-voltage grid, depend­ing on the specifications. This is a very quick and efficient way of ensuring that we don’t have to subject the gen­eral public to unnecessary cable in­stallation work.

Proposition two:
There are no longer any technical obstacles standing in the way of full e-mobility.

Instead, we can limit ourselves to work that is usually required as a result of age and to major new connections that have always required grid development. This is how we can fit electromobility into the existing grid—especially when we are able to look ahead and make plans for the future.

But we mustn’t forget that costs are still involved. We included cost considerations in our study with the results showing a one-time charge of around EUR 400 on average per vehicle for expanding the grid. But as far as we are concerned, these investments are absolutely worthwhile. It’s all relative, after all: Around EUR 25,000 has to be invested in a car every seven years on average.

Which specific measures does the study call for?

Perhaps we should cover one thing first of all: We are often asked why we assume that the automotive segment will become fully electric. We know that this is a bold assumption but it is based on internal and external analyses of the mobility sector, with a particular focus on sustainability and efficiency. The crucial thing for us is what we now take away from the results. And we have to say that we have put together an excellent package.

Proposition three:
Grids can be made fit for the future without having to undergo major restructuring.

What this means for our customers and communities first off is that we will be supporting electromobility in every way. Instead of complaining, we’ll be motivating because we believe this is the right direction to be heading in and we take the issue of CO2 very seriously. As far as our grids are concerned, we will be focusing on intelligent secondary substations with VRDTs and on larger line cross-sections. But this will only be when replacements are needed, usually owing to age. This requires an incredibly strategic approach when allocating expansion work but it stops us pressing pause on a future issue that we don’t want to abandon.

The ECOTAP® VPD® is the key component in the quest to have e-mobility rolled out exclusively. (©Timo Müller)

That was sadly what many grid operators did ten years ago when the first solar boom occurred before this VRDT technology even existed. And we don’t want to be faced with an impossible task in ten years’ time. Another point worth mention­ing is that we will also have more solar power within our grids, potentially including heat pumps, and VRDTs are ideal here. This technology therefore helps move the energy transition in all directions.

VRDTs are still quite rare around the world. What’s your experience with using them?

Our operating experience has been very positive. It goes without saying that there were a few start-up and development problems with the first series delivered years ago. But the VRDTs we have today work in exactly the same way as standard transformers. But, figuratively speak­ing, they can do twice as much!

Proposition four:
VRDT technology is key to the energy revolution.

And there is not even much more material required—just the regulator. For us this means efficiency, intelligence, and sustainability. Obviously all of that cannot replace strategy and expertise, including on the part of colleagues working on the grid. But our experience has been so positive that over 90% of our new transformer acquisitions in 2019 have been VRDTs.


A full switch to electromobility represents a major challenge for distribution grids—especially if the power has to come from sustainable sources. The technology needs to compensate for fluctuations in medium voltage and must be able to respond dynamically to changes in feed-in and load at the low-voltage level. In both cases, grid operators can rely on the ECOTAP® VPD®.

It combines the expertise that MR has accumulated over decades of working with vacuum on-load tap-changers in high-speed resistor-type tap-changer technology with experience in voltage regulation distribution transformers to guarantee a stable, maintenance-free performance of 500,000 tap-change operations. The ECOTAP® VPD® is so compact that it does not make the distribution transformer any larger.


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