470 Mr. Alexander Siemens [Feb. 26, 



passes round the support of the insulators, and also round a vertical 

 wire, which is connected to the running rails, and through them to 

 earth. 



This device is added for the case that a high tension wire breaks, 

 as the loop then comes in contact with the earthed wire, and prevents 

 any danger from high tension currents. 



"When the Allgemeine Elektricitats Gesellschaft car ran at its 

 highest speed one of the conductors broke and struck a man who 

 hajDpened to stand near, but luckily the earth connection proved to be 

 effective, and no harm was done. 



Excepting this accident, which was caused by the abnormal 

 swaying of the car, the method of suspending the conductors gave 

 every satisfaction, and the experiment on the Zossen line thus 

 confirmed the previous favourable experience gained at Gross- 

 Li chter fold e. 



The current for the experiments was supplied from the power 

 station of the Berlin Electricity Works, at Oberspree, through a 

 feeder about 13 km. (8 J statute miles) long, and it was generated by 

 a 3000 kw. three-phase alternator, driven direct by a steam engine. 



It was possible to regulate the output so as to give from 25 to 50 

 periods per second, which corresponded, after transforming up, with 

 a difference of potential of from 6000 to 14,000 volts at the station 

 end of the feeder. 



As the set is designed to give its full output at 50 periods, it was 

 rather over-loaded at the lower speeds, so that the motors could not 

 develop their full power during the acceleration period. 



The connection between the periods of the generator and the 

 speed of the car is determined by the diameter of the car wheels and 

 the number of poles of the motors. 



In this case, six-pole motors were employed, driving the axle 

 direct, and the diameter of the wheels is 1 • 25 metre. 



Consequently, the kilometres per hour are found by multiplying 

 the periods per second by 4*714. 



Thus : — 30 periods correspond to 141-42 km. per hour. 

 40 „ „ 188-56 „ 



50 „ „ 235-70 „ 



In other words, the speed of the cars, neglecting the slip, depends 

 on the generator, and not on the motor ; in this way the differences 

 in speed on different days and on the two cars are explained. 



One of the most difficult problems was to transfer the electric 

 current from the stationary conductor to the moving car at the very 

 high speeds which were eventually attained. 



Here again, the experience of Gross-Lichterfelde proved to be of 

 service, as the comparison between the collectors on the Lichterfelde 

 locomotive and on the Zossen line clearly shows. In fact, the 

 syndicate prescribed the adoption of this collector for both cars. 



During the first experiments the Lichterfelde collector proved 

 satisfactory, but at speeds of 176 km. and more per hour the mass 



