3 _B] PREDETERMINATION. IOI 



APPENDIX III. 

 MISCELLANEOUS NOTES. 



56. Transmission Line Regulation. In the electromotive force 

 method, 16-22, a complete treatment is given of the effect upon 

 delivered voltage of resistance drop and reactance drop in the arma- 

 ture of an alternator. The treatment, however, is general and is not 

 limited to alternators. The same treatment will apply to any resist- 

 ance and reactance drop, wherever located, and may accordingly be 

 applied to the case of a transmission line. In the geometrical treat- 

 ment of any problem, resistance drop is always in phase with the 

 current, reactance drop in quadrature. 



Example I. Given a transmission line in which RI drop = 7.4 ; XI 

 drop = 233.9. What must be the voltage Eo applied at the sending end of 

 the line to maintain a voltage of 575 at the receiver for a load of 43.4 

 amperes, at unity power factor, at power factor 0.866 (current lagging 

 30), and at power factor 0.866 (current leading 30) ? Figs. 3, 4 and 5 

 show that 627, 726 and 508 volts, respectively, are required at the sending 

 end in the three cases, the corresponding line regulation being 9, 26.3 

 and 12 per cent. In this example the same numerical values have been 

 used for a transmission line as were used in Figs. 3, 4 and 5 for an alter- 

 nator. Practical values for a transmission line would give a relatively 

 greater resistance drop and smaller reactance drop, as in example 2. 



Example 2. A transmission line gives 1,000 volts at the receiver. The 

 resistance drop is 100 volts, reactance drop is 200 volts ; what is the regula- 

 tion for different power factors? 



Curves as shown in Figs. 6 and 7 can be drawn for a transmission 

 line. These curves have been discussed for an alternator; the discus- 

 sion can, however, be applied to a transmission line. 



In calculating the regulation of a transmission line, the values of 

 resistance and reactance can be taken from tables in various hand- 

 books and elsewhere. 



In testing a transmission line, the reactance drop can be found by 

 an open-circuit test and a short-circuit test, as in the case of alterna- 

 tors. With a low voltage, short-circuit the line and measure /s ; open- 

 circuit the line and measure Eo. The line impedance is Z = EO -=- 7 S ; 

 the line reactance is X = \J~Z Z R". 



In the laboratory a line with resistance and reactance can be tested 

 in this way as a transmission line; the regulation for loads of dif- 

 ferent power factors can be predetermined (Figs. 6 and 7) and com- 

 pared with actual load tests. 



