26 TRANSMISSION LINE FORMULAS 



These limits are clo.se enough for commercial work, so that 

 the K formulas can be recommended for all ordinary 

 engineering calculations of the performance of long power 

 transmission lines under steady conditions, where the 

 corona loss is small. The accuracy of the electrical calcu- 

 lations will be better than the accuracy with which the 

 resistance and the physical dimensions of the line are 

 generally known. 



The K formulas are well adapted to the solution of 

 long transmission lines which have substations at inter- 

 mediate points between the ends. In such cases each 

 section of the line between substations must be calculated 

 separately, beginning with the end where conditions are 

 known. The first step is to find the voltage, in-phase 

 current and quadrature current at the first substation. 

 The load taken by the substation, expressed as in-phase 

 current and quadrature current, must be added to, or sub- 

 tracted from, the above values of current. When condi- 

 tions are given at the receiver end and one is proceeding 

 toward the supply end, the substation load must be added 

 to the line load. When conditions are given at the supply 

 end, the substation load must be subtracted from the line 

 load, since one is proceeding away from the supply. Hav- 

 ing thus found complete conditions at one end of the 

 second section of the line, the calculation of this section 

 may be taken up in the same way as for the first section. 

 In this manner the entire line may be calculated and the 

 voltage and current at the unknown end may be deter- 

 mined. 



Examples are worked out, which will give a clear idea of 

 the manner in which the K formulas are used. Many 

 other such examples have been calculated and carefully 



