Lauffen–Frankfurt Power Transmission: Bringing Distant Hydropower to the City

In 1891, the International Electrotechnical Exhibition in Frankfurt brought competition over lighting, motive power, and supply systems into a public exhibition space. Cities building power stations had to choose systems, while many potential hydropower sources lay far from factories and consumers. The Lauffen–Frankfurt experiment promoted by Oskar von Miller addressed a specific question: could electricity generated beside the Neckar be transmitted roughly 175 kilometers to a city and actually light lamps and drive machinery at the receiving end?

The generating end at Lauffen stood at a cement works' hydropower site, while the exhibition grounds formed the receiving end. The link was not a short line for visitors to inspect but a long-distance engineering project crossing towns and depending on poles and insulation. This account uses 1891, the year of the exhibition and experiment, as its chronological anchor. Initial energization, lighting groups of lamps, and continuously powering exhibits were separate operations.

References: [1] [3]

Miller promoted and organized the system. Mikhail Dolivo-Dobrovolsky of Berlin's AEG specialized in three-phase motors and transformers, while Charles Eugene Lancelot Brown of Switzerland's Oerlikon machine works contributed to generating equipment and high-voltage technology. The demonstration consequently depended on connecting equipment from different companies, rather than simply scaling up a single inventor's small experiment.

Building the line also required cooperation from postal, telegraph, and railway authorities. Engineering records mention telegraph administrations supplying poles and companies lending copper wire, with the route following railway corridors and the Neckar region. Starting construction, borrowing materials, erection, and testing each had scheduling requirements. Even if the generator was finished, any incomplete section of transmission or insulation work would prevent usable electricity from reaching the exhibition.

References: [1] [3]

At Lauffen, a water turbine drove a three-phase alternating-current generator. The three currents were staggered in time, creating a phase difference of 120 degrees. Transformers raised the relatively low generating voltage before power traveled through three overhead conductors. At Frankfurt, receiving transformers lowered the voltage to the range required by lamps and motors.

For a given transmitted power, increasing voltage reduces the required current and therefore the heating losses caused by conductor resistance. Higher voltage, however, makes insulation between conductors, supports, and the ground more difficult. Engineering could not simply maximize voltage; it had to coordinate transformers, insulation components, material supplies, and safety measures.

Transmission during the exhibition used approximately 15,000 volts. Soberski's engineering retrospective records that delays in delivering all the larger oil insulators were one reason the originally planned higher voltage was not used immediately. After the exhibition, tests were also conducted at 25,000 volts. Public operating parameters and subsequent test parameters therefore must not be conflated.

References: [1] [2]

Electricity from Lauffen began reaching the exhibition in August 1891. An installation of approximately one thousand incandescent lamps and a motor-driven artificial waterfall subsequently gave visitors directly observable results. A pump raised water and let it fall, demonstrating how power from a distant water turbine passed through generation, transmission, and an electric motor to become mechanical movement of water again.

Operating a pump with a motor of roughly one hundred horsepower demanded more than proving that a single bulb could light. It required sufficient starting and sustained torque and stable operation as the load changed. Hering's article that year used the demonstration as a context for explaining polyphase currents and rotating magnetic fields, including how a three-phase system supplied power through three conductors.

Technicians measured power at both ends to examine losses at each stage from the prime mover to the receiving end. Efficiency figures require an explanation of the load and measurement boundaries: measuring only the line's input and output is not the same as including the generator, transformers, and motor. The exhibition's value lay in enabling measurement and comparison under load, not merely announcing successful long-distance transmission.

References: [1] [2]

The Lauffen–Frankfurt system showed that high-voltage transformation and three-phase machines could form a practical long-distance transmission chain, connecting remote hydropower with urban electricity use. Generator, line, insulation, and receiving equipment jointly supplied the demonstration, encouraging engineers to consider greater distances and capacities.

One exhibition did not mean every city immediately made the same choice. Power-station development still depended on existing equipment, finance, concessions, and the composition of demand. After the exhibition, the Lauffen plant supplied nearby areas, showing that a temporary demonstration could leave facilities with continuing uses. Broader three-phase networks subsequently emerged through long-term improvements in equipment and operating organizations.

References: [1] [3]