CON TIN UO US-C URREN T D YNA MOS. 317 



reservoirs on the mountain river Gorzente and distributed to 

 Genoa and the Polcevera Valley. The fall is divided into 

 three portions, each of which has its own station : the 

 system employed in all alike is the high-tension continuous 

 current with the generators and the motors in series, and 

 they therefore closely resemble one another in their main 

 features. Each turbine of 140 horsepower is directly con- 

 nected by Raffard insulating" couplings to two Thury 

 dynamos and runs at a speed of 475 revolutions per 

 minute. The dynamos are six-pole machines with drum 

 armatures, and are designed to give a constant current of 

 45 amperes with a maximum pressure of 1 100 volts. They 

 are coupled together in series so that the voltage at full 

 load amounts to about 6000 volts per circuit, and owing 

 to this high pressure the insulation of the windings has 

 received great attention. The bedplates of the dynamos 

 are insulated from the ground by means of porcelain in- 

 sulators filled with rosin oil, and not only are the armature 

 shafts insulated from the turbine by the coupling as men- 

 tioned, but, in addition, the actual iron core of the armature 

 is insulated from the shaft itself. 1 From the above it may 

 be seen wherein lies the disadvantage of the continuous 

 current for the transmission of power over very long dis- 

 tances. The nature of the commutator of the dynamo 

 does not permit of more than at the most about 2000 volts 

 being generated in any one machine, and we are therefore 

 compelled to couple several machines in series in order to 

 obtain the high voltage which alone will render the trans- 

 mission efficient. It is then only by the most careful 

 precautions that the complete insulation of the system can 

 be secured, since the windings of running machines form 

 part of it ; whereas with the alternating system it is easy 

 to generate the electrical power at low pressures and sub- 

 sequently to transform it up to high pressures by means of 

 stationary transformers. 



As might have been anticipated, the list of transmissions 

 of power includes but few cases within the British Isles. 



1 Journal Inst. EL Eng., No. 107, vol. xxii., 1893. 



