DISADVANTAGES OF VOLTAGE VARIATION 23 



cal experience in increasing the load of transmission 

 lines that good operation cannot be obtained when the 

 variation in voltage from no load to full load is more 

 than 20 or 25 per cent. A small percentage variation in 

 the load, such as is liable to occur suddenly on any 

 power system, should not cause a fluctuation in the de- 

 livered voltage sufficient to be a detriment to the service. 

 It is found with a line whose total variation in voltage 

 is as great as the percentages mentioned above, that 

 ordinary changes in load produce noticeable changes in 

 voltage at the load which are too rapid and too great to 

 be satisfactorily corrected by either hand regulation or 

 automatic regulators. In other words, the line has poor 

 regulation. 



In many systems, hand regulation of the generator 

 voltage is used rather than automatic regulation. In 

 such cases, practical difficulty is experienced in compen- 

 sating for large gradual changes in load, where the line 

 has a large percentage regulation. The operator in the 

 generating station must estimate from the readings of 

 his ammeters and power-factor meter what his volt- 

 meter reading and his rheostat setting ought to be. The 

 result of his efforts is frequently unsatisfactory to the 

 station receiving power, and readjustments of the volt- 

 age can only be obtained, after considerable delay, by 

 using the long-distance telephone. 



The disadvantages and difficulties described above in 

 operating a transmission line with a large voltage regu- 

 lation between no load and full load have been apparently 

 insurmountable in many cases. As a result, when the 

 regulation, due to increases in load, has reached 20 or 

 25 per cent, or sometimes a smaller percentage, new du- 



