The solution was the slip ring motor, a variation of the asynchronous motor in which the short circuit of the rotor is opened and guided to the outside via sliprings. By connecting various external resistors, Dolivo-Dobrovolsky was able to introduce an asynchronous motor with high starting torque in 1891. At the beginning of 1889, the first AEG three-phase motors were in operation, and in the following year they already produced 2 to 3 horsepower. Dolivo-Dobrovolsky paid attention to well distributed windings, a low dispersion of the lines of force and as uniform a force field as possible and achieved a satisfactory result. In 1891, he also developed the first Delta-wye transformer for this purpose. First remote transmission of electrical energy At AEG and the Swiss cooperation partner Maschinenfabrik Oerlikon (MFO), all components for a three-phase network were available, but until now they had only been in trial operation. At this time, Oskar von Miller made the extremely daring proposal to present the three-phase current transmission system Lauffen-Frankfurt at the International Electrotechnical Exhibition planned for 1891 in Frankfurt at the MFO, where Dolivo-Dobrovolsky and his chief electrician partner Charles E. L. Brown realized the project: A 300 HP three-phase AC generator of the MFO was to be driven by the water turbine of the cement plant in Lauffen am Neckar, generating a voltage of about 50 V and 40 Hz, transforming it up to 15 kV (later 25 kV) and then transmitting it via 175 km of overhead line to Frankfurt and transforming it down again to supply a 100 HP asynchronous motor and several small three-phase motors as well as about 1000 incandescent lamps. The power output of the motors, which had previously been in test operation, was still only 2 to 3 hp. Nevertheless, the plant was put into operation on the evening of 24 August 1891, and a test committee determined that 75% of the energy generated in Lauffen arrived in Frankfurt. This proved that, on the one hand, alternating current was profitable for a large-scale public electricity supply and, on the other hand, that the three-phase components were now of the same quality as those of direct current technology. The image-boosting effect of the demonstration at the World Expo finally led to the breakthrough of three-phase AC technology. At Siemens and Edison, however, AC technology only slowly gained acceptance, which enabled AEG to become a global company.