CHAPTER V 



DISADVANTAGES OF VOLTAGE VARIATION 



VOLTAGE variation has been stated in a previous 

 paragraph to be one of the main features to be taken into 

 account in designing an electric-power system. A short 

 description will be given of some of the disadvantages 

 of variation in the voltage. 



Where electric power is being supplied to customers 

 in a city, a large part of the power is used for lamps. 

 These, perhaps more than any other type of commercial 

 power-consuming apparatus, require a very constant 

 voltage. If the voltage is lowered a small percentage 

 below normal, the brightness of an incandescent lamp is 

 decreased by a much greater percentage. If, on the 

 other hand, poor line regulation causes a rise of voltage 

 above normal late at night when the total load is low, 

 the disadvantage is encountered that the lamp deterior- 

 ates at a rapid rate and its life is shortened. This is a 

 matter of considerable commercial importance in con- 

 nection with expensive modern metal-filament lamps. 

 Mercury vapor lamps also require a voltage very close 

 to that for which they were designed, for satisfactory 

 operation. Even heating and cooking devices, such as 

 are used on lighting circuits, operate best at their normal 

 voltage, and separate types are manufactured for nor- 

 mal voltages of 105, no, 115, etc. Since there will often 

 be two or three volts drop in the local no- volt circuit, 

 it is evidently necessary to maintain practically constant 



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