180 BELL SYSTEM TECHNICAL JOURNAL 



Service Taps on Transmission Lines. — In some rural situations, it has 

 been found economically impracticable to initiate distribution lines 

 clue to distances involved. However, in many such situations immedi- 

 ate electric service is urgently required and in some of these cases, 

 transmission lines may be located relatively close to the point where 

 service is desired. In such cases the only alternative to a long distri- 

 bution line is to tap the high tension transmission line when this can be 

 done by some less expensive method. Such methods have been devel- 

 oped and applied to a limited extent. More study and field experience 

 are needed to determine the effects of these installations on inductive 

 coordination should they become extensively employed. 



Transformer Connections. — In distribution practise, the trend toward 

 higher primary voltages has been accompanied by the use of the "Y" 

 connection of the primaries of transformers as a step in the transition 

 from one voltage class to another. Thus 2300-volt delta systems have 

 become 2300/4000-volt "Y "connected systems, 6600-volt delta sys- 

 tems have become 11,000-volt "Y" systems, and the 7620/13,200- 

 volt "Y" connection is being used. The use of the "Y" connection 

 of the primary of distribution transformer banks is sometimes necessa- 

 rily accompanied by a similar connection of the secondary. Such 

 " YY" connections are usually in urban situations. Also, these banks 

 usually represent only a small portion of the total transformer capac- 

 ity on the circuits. 



On large transformer banks and in the higher voltages delta-Y con- 

 nections have long been the prevailing practise. However, where the 

 " YY" connection is used for purposes of grounding, especial attention 

 has been given to controlling the effects of this connection in situations 

 of coordination, and for the absorption of triple harmonic currents it is 

 common practise to use delta-connected tertiary windings in such in- 

 stallations. This subject is discussed more fully in another paper in 

 this symposium. 



Wave Shape. — The connection of primary circuits directly to gener- 

 ating station busses results in service and economic advantages by 

 eliminating transformations thereby improving voltage regulation and 

 aiding system simplification. This practise, however, tends to make 

 coordination more difficult as those harmonics which may be present 

 in the generated voltage can flow directly out over these circuits. 

 However, the important bearing of the wave shape of generators and 

 apparatus of various kinds on the coordination problem has long been 

 realized and is receiving increasing attention. Even before the forma- 

 tion of the Joint General Committee the general problem of apparatus 

 wave shape was being studied both as to the amounts of various har- 



