THE QUIET INVENTION THAT SETS THE PULSE OF ENERGY
How an unassuming technical principle from Regensburg made modern power supply possible – and why its legacy is more important than ever in the age of the energy transition.
Prologue: When Technology Must Not Stand Out
There are technologies that shine. And there are technologies that work perfectly precisely when no one notices them. The high-speed resistor-type tap-changer belongs to the second category. It isn’t found in control centers, it doesn’t send data to displays, it has no screen and no user interface. It operates in secret – deep inside the transformer. And yet, for a century, it has determined whether power grids remain stable or become unstable, whether voltage is kept stable or fluctuates, and energy flows safely or must be interrupted.
Inventor and CEO of OBAG – a lifelong partner of Maschiennfabrik Reinhausen
Exactly 100 years ago, Dr.-Ing. Bernhard Jansen filed the patent for the highspeed resistor-type tap-changer – an invention that would quietly but fundamentally transform power engineering. For Reinhausen (MR), this patent marks the origin of an engineering lineage that remains relevant to this day: on-load switching as the foundation of modern grids.
The era before the patent: Electricity as an unstable quantity
To understand the significance of the Jansen patent, one must look back to a time when electricity was far from the reliable lifeline we know today. In the early decades of the 20th century, power grids were fragmented. Isolated networks dominated, voltage regulation was crude, and grids reacted sensitively to load changes. Every major consumer, every industrial machine, posed a risk to grid stability.
Transformers could change voltages—but not under load. Every switchover meant: shutdowns, interruptions, wear and tear, operational risks. It was a time when the grid dictated to consumers what was possible – not the other way around.
Dr. -Ing. Bernhard Jansen: Engineer, Visionary, Enabler
Dr. Jansen was not an inventor in the grand, dramatic sense. He did not seek the limelight. He was an engineer, with a deep understanding of grids and their practical limitations. As technical director of an energy utility, he recognized early on: If power grids were to grow, they had to become controllable – under real operating conditions.
His approach was as pragmatic as it was ingenious: Instead of avoiding voltage under load, he made it controllable. The principle of the resistor-type tap-changer routed transient currents in a controlled manner through resistors, smoothed switching operations over time, and thus created a solution that was mechanically robust and electrically safe.
This principle was ahead of its time—and at the same time so fundamental that it remains relevant to this day. Wilfried Breuer, a member of Reinhausen’s Executive Board, describes this invention in retrospect as follows: “The rapid-acting resistor switch is a groundbreaking invention – comparable to Carl Benz’s automobile or Thomas Alva Edison’s light bulb. It is invisible inside the transformer, but of equally fundamental importance to our industry.”
A patent – and the beginning of a partnership with Reinhausen
The patent alone would have remained meaningless without industrial implementation. Only through the collaboration with Maschinenfabrik Reinhausen and the Scheubeck brothers turned the idea into a reliable, reproducible product.
What emerged here was more than just technology: it was a dynamic triangle formed by the operator’s (Dr. Jansen and OWAG) need for a solution for the transformer manufacturers’ products, and the development and production of that solution by Maschinenfabrik Reinhausen and Dr. Jansen, with constant exchange and communication among all three corners of this collaboration.
This constellation continues to shape the company to this day. And it explains why the Jansen patent is not viewed at Reinhausen as a historical footnote, but as a cultural origin.
The First Grids – and the Birth of Mesh Networks
The rapid-acting resistance switch fundamentally changed grid architecture. For the first time, voltages could be adjusted during operation. This made it possible to distribute loads, interconnect grids, and systematically increase supply reliability.
The meshing of grids – now taken for granted – was conceivable without this technology, but could not be reliably implemented. The switch became the invisible pacemaker of electrification.
From a single grid to a global infrastructure
1950s to 1970s: Growth and industrialization:
In the post-war period, energy demand exploded. Industry, households, transportation – everything demanded stable electrical power. MR consistently further developed the tap changer, increasing service life, reliability, and standardization. Products like the OILTAP® M marked the beginning of the international break through. The tap changer evolved from a specialty product into a key global component.
1980s to 2000s: Power density and new technologies:
Higher voltages, larger transformers, and more demanding grids led to further innovations. The introduction of vacuum technologies (VACUTAP® VV®) reduced maintenance requirements and increased operational reliability.
But while the mechanics became increasingly sophisticated, a new challenge began to emerge: dynamics.
Grids are changing – and with them, the role of the tap-changer
With the increasing feed-in of renewable energy, the relationship between generation and consumption shifted. Consumers became producers, so-called “prosumers.” Grids became volatile, unpredictable, and subject to asymmetric loads. Tap-changers no longer regulated only slowly drifting voltages – they were suddenly part of highly dynamic systems.
The classic question “Can the switch handle this?” evolved into: “How often does it switch?” “Under what load profiles?” “With what aging mechanisms?” “In what overall context ?”
This marked the beginning of a new phase: from component to system. And in this phase, too, MR is the industry pioneer – true to the spirit of the great inventor.
ETOS®: When the transformer learns to speak
With ETOS® (Embedded Transformer Operating System), MR began digitally mapping the mechanical reality of the transformer. Sensors, actuators, data analysis, and communication were not simply added on, but systemically integrated. Into an operating system that reveals what was previously hidden: switching frequencies, thermal loads, load peaks, operating histories. This enables Reinhausen to provide condition-based maintenance. Switching operations are thus planned proactively, and for the first time, transformers are no longer operated statically but dynamically and according to demand.
COTAP® VPD®: Regulation where it used to be impossible
While much attention was focused on high-voltage grids, MR recognized the importance of distribution grids early on. As consumers began feeding power back into the grid, it became necessary to regulate the grid even right there. With the ECOTAP® VPD®, the company launched a load tap changer for the low-voltage level – long before “active distribution grids” became a buzzword. Today, the ECOTAP® VPD® is a key element for decentralized power generation, photovoltaics, electromobility, and voltage quality all the way down to the local grid level.
VACUTAP® VI: The Jansen principle reimagined
With the VACUTAP® VI, MR is launching a new cycle of innovation. The OLTC implements the resistor-type tap-changer in a material-efficient, sustainable form – optimized for modern requirements.
The VACUTAP® VI is the most contemporary interpretation of Dr. Jansen’s invention – less material, lower CO₂ footprint, with unchanged high reliability.
TESSA® APM 2.0: From Individual Device to Fleet Intelligence
Building on the proven foundation of ETOS®, TESSA® APM 2.0, Asset Performance Management enables the leap to the fleet level. Enhanced with inspection and test data, TESSA® APM 2.0 creates a comprehensive, data-driven view of your assets. The central platform enables advanced condition monitoring and performance assessment of transformers and other electrical assets across the grid. By transforming raw data into actionable insights, operators are empowered to make informed decisions, increase system reliability, and ensure long-term asset availability.
This changes decision-making logic: maintenance becomes condition-based, investments are prioritized based on data, and lifespans are actively managed. In a world of constrained resources, this system-level intelligence becomes a decisive advantage.
Industrialization in the Age of the Supercycle
The global energy transition has created a demand cycle the industry has rarely experienced. Transformers, tap-changers, and testing and control technology are in demand – now, not in five years. MR is responding with one of the largest investment programs in the company’s history to strengthen capacity and reduce delivery times:
- Increase staffing levels
- Produce more flexibly
- Activate resources
- Expand facilities
- Digitize testing technology
- Leverage automation
“As the market leader, we were the first to be hit by the wave of demand. That’s why we’ve invested consistently – regionally and for the long term,” says Holger Michalka, Managing Director of Operations at Reinhausen. Delivery capability thus becomes a strategic competency in its own right.
“As our customers have been accustomed to for decades, we have done everything in our power to shorten our delivery times,” says Thorsten Stohr (Executive Sales Director at Reinhausen). “The days of bottlenecks are over and the 10-week* delivery capability is in place. In extraordinary cases, even faster delivery times are possible.”
100 Years – and the Next Chapter
The Jansen patent is not an endpoint. It is a benchmark. A reminder that robust technical principles can endure for decades – if they are well-conceived. For Reinhausen, the anniversary is therefore less a retrospective than a starting point:
“We are driving the market forward by ensuring a reliable, economical, and sustainable power supply through our innovations. Through the further development of tap-changers. Through digitalization and asset management. And through power electronics. Today, tomorrow, and the day after,” says Dr. Nicolas Maier-Scheubeck, spokesperson for the Reinhausen Executive Board, summarizing the company’s aspirations, promises, and vision for the future.
Epilouge: The Art of Working Behind the Scenes
The high-speed resistor-type tape-changer will continue to stay out of the head lines. It will operate quietly, switch precisely, and maintain voltages. It will not draw attention – and that is precisely where its strength lies.
For 100 years. And for 100 years to come.
Dr. Bernhard Jansen (1899–1958)
Dr. Bernhard Jansen was born on 31 August 1899 in Wissen, Germany, as the son of a master watchmaker. After completing his secondary education, he studied electrical engineering at the Technical University of Hanover from 1919 to 1923. In 1925, hereceived his doctorate with a dissertation on the economic efficiency of interconnecting large power supply areas – at a time when the technical prerequisites for interconnected grids were still largely undeveloped.
On 13 July 1926, Jansen filed a patent for a device enabling the switching of transformer taps under load using resistor-based switching elements. Granted in 1929 (German patent no. 474613), this invention laid the technological foundation of the resistor-type on-load tap-changer and became a defining element in the regulation of power transformers worldwide. In the same year Dr. Jansen started the life long cooperation with the brothers Scheubeck and the Maschinenfabrik Reinhausen (today Reinhausen).
Alongside his inventive work, Jansen pursued a professional
career in power supply companies. In 1928, he became Technical Director of Oberpfalzwerke AG in Regensburg, where he systematically developed regional electricity networks into an interconnected system. From 1956, he served as Chairman of the Board of Energieversorgung Ostbayern AG (OBAG).
He died on 15 October 1958 in a traffic accident following a heart attack.
Learn more about the Jansen patent and the history of the resistor-type tap-changer at 100years.reinhausen.com
This article was originally published in the June 2026 issue of the Grid Modernization and Flexibility magazine.
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