TREXnS IX /'RACTISK AS AFFECTING COORDIXATIOX 163 



In the power industry one of the most important items in the im- 

 provement of service has been the stead>' decrease in the number of 

 service interruptions. This has been brought about mainly by better 

 standards of construction, including more systematic mechanical and 

 electrical arrangements of circuits and apparatus, and increased num- 

 bers of circuits and sources of supply. The interconnection of power 

 systems has figured largely in the last mentioned factor contributing to 

 service reliability, by making available greater numbers of sources and 

 by multiplying the routes over which power can be recieved at specific 

 locations. While the increasing numbers of interconnecting and other 

 types of lines bring new conditions for the coordination of power and 

 telephone plants, improved construction and increased security of 

 circuits and apparatus have a definitely beneficial effect upon matters 

 of coordination by reducing the number of abnormal conditions of 

 operation. 



Other items in the improvement of the service given by the power in- 

 dustry are better voltage regulation and a great increase in the number 

 of types of power consuming appliances and apparatus made available 

 for the customer. Accompanying better voltage regulation are certain 

 factors which definitely aid coordination, among these being better 

 balance of currents in the separate phases of the circuits and more 

 effective arrangements minimizing the tendency for currents to flow in 

 the earth. The effect of increased numbers of types of utilization 

 apparatus on coordination is problematical, though probably not of 

 sufficient magnitude to be of practical importance. 



Other trends which have a bearing on the improvement of power 

 service are discussed in the section of this paper devoted to the power 

 system. 



While in some respects the general trends indicated above, namely, 

 the extent and rapid growth of the two utilities, and the improvement 

 of service standards, have by themselves tended to increase the im- 

 portance and the difficulties of coordination work, these adverse ten- 

 dencies have been offset by beneficial effects of improvements in plant 

 design and construction and by the cooperative endeavor which has 

 been carried on by the two utilities during recent years. It is a tribute 

 to the effectiveness of this cooperative work that the degree of satis- 

 factory coordination between the two systems is steadily improving. 

 Fig. 4 shows that during the past 10 years the mileage of telephone 

 toll circuits has increased 250 per cent and the mileage of power trans- 

 mission lines over 100 per cent. The effect of such growth on the num- 

 ber of situations of proximity is illustrated by the fact that during the 

 past three years the exposures of interest from a noise standpoint have 



