ADVANTAGES AND DISADVANTAGES 35 



would be very desirable to standardize on one frequency 

 for electric-power apparatus, and if this were done in 

 America, there is no doubt that the frequency would be 

 60 cycles. This frequency is by far the most popular 

 for the supply of power to towns and cities. Generators, 

 transformers, and motors generally cost less when built 

 for the higher frequency, and most lighting devices, es- 

 pecially tungsten lamps and arc lamps, give much more 

 satisfactory results at 60 cycles than at 25 cycles. Per- 

 haps the most important class of load which must inher- 

 ently use low-frequency current is that of alternating- 

 current railways. But the fact that the load is often 

 single-phase, and that the momentary peaks of load are 

 very great, being sometimes of the order of 5,000 kilowatts 

 or more, would render advisable the use of A. C. motor- 

 generator sets, even when the 25-cycle load is to be 

 supplied from a 25-cycle high-tension power net- work 

 serving all classes of loads in the vicinity. If A. C. 

 motor-generator sets must be used, it is obvious that 

 a 25-cycle high-tension net- work would have no advan- 

 tage over a 6o-cycle one in supplying a 25-cycle rail- 

 way. Thus it is seen that the standardization of the 

 frequency of 60 cycles for transmission-line systems is 

 desirable and possible, and it would be greatly assisted 

 by the adoption of the principles of constant-voltage 

 transmission. 



A very attractive and practical feature of the 

 constant-voltage system is that any existing transmis- 

 sion line or net- work can be gradually and easily changed 

 over so as to operate, completely or in part, according 

 to the new method. For example, consider a varying- 

 voltage line which has 20 per cent regulation at the 



