218 ELECTRICAL ENERGY. 



As for line inductance in the two-phase and three-phase systems, there 

 is no question that the latter has an advantage in this respect. By- 

 suitable arrangement of circuits the line inductance can be brought to a 

 minimum, and this is of the utmost importance in long-distance trans- 

 mission. I will not take into account the supposed increased efficiency 

 of three-phase motors and dynamos as against two-phase apparatus, as 

 there is a question as to whether a superiority exists, but simply con- 

 sidering the decreased amount of copper required and the decreased 

 inductance of the line, there is no question in my mind that, for trans- 

 mission, the three-phase system is superior to the two phase. It is well 

 known, of course, that the inductance of the circuit can be in some 

 measure compensated for by the use of condensers or over- excited 

 synchronous motors. The first of these remedies is, however, a very 

 uncertain quantity commercially, while the second should be used as 

 much as possible, that is, as many synchronous motors should be con- 

 nected as is practicable. The best remedy, as things stand at present, 

 lies in the careful construction of the line and the apparatus, so that 

 the effects, although they exist, can be reduced to a minimum. 



It has been shown by Mr. Scott and others that it is possible to 

 transform a two-phase into a three-phase current, to transmit it and to 

 transform it back again to a two-phase current. This will allow us, if 

 we wish, to use two-phase dynamos for generating the current, to trans- 

 mit with the advantage incidental to the use of three-phases, and at 

 our reducing end to use two-phase circuits for transmission. This has 

 some advantages as far as balancing the voltage on the circuits go, and 

 it has been proposed in the case of several plants whose installation is 

 being considered. 



Looking broadly at the value of alternating transmission as against 

 continuous current transmission, we have a gain in the simplicity and 

 safety in the transmission, and at the distributing end the use of multi- 

 phase currents enables us to supply both lamps and power with an 

 economy and success comparable to that of the continuous current sys- 

 tem. If it is necessary to use continuous currents for certain types of 

 distribution at the receiving end, they can be obtained by the use of 

 rotary transformers, by which the alternating current is transformed 

 into a continuous current. These machines have approximately the 

 efficiency of corresponding continuous current dynamos, while the out- 

 put for a given size is 50 per cent greater. 



POSSIBLE VOLTAGES AND DISTANCES OF TRANSMISSION. 



A number of calculations have been made as to the possibility of 

 transmitting electrical energy to very long distances. If the question 

 of cost of transmission alone is considered, then where water powers 

 or culm heaps are within distances of 100 miles of some large center of 

 consumption, it has been shown that it would be profitable to generate 

 and transmit electrical energy. In these calculations, however, vol- 

 tages are assumed that have never been employed for commercial 

 plants, and whose availability is problematic, while sufficient stress is 



