A proposed wave shape standard
|Author(s):||Cassius M. Davis|
|Publisher:||IEEE - Institute of Electrical and Electronics Engineers, Inc.|
|Publication Date:||1 February 1913|
|Page(s):||235 - 244|
The present wave-shape standard has several objections, principal among which are the use of the oscillograph, the lengthy calculations necessary and the discrimination in favor of higher harmonics. The proposed standard makes use of the change of effective reactance of a condenser with change of wave shape. The important advantages are: the wave shape distortion can be determined very quickly; the distortion depends in a very definite way upon the harmonics present, both as to order and magnitude; the apparatus is very simple and the test easily manipulated. The disadvantage is that it does not show which harmonics are present. The ratio of the condenser reactance on a sine wave to the condenser reactance on the distorted wave is called the distortion ratio. It is conveniently determined by impressing the wave shape to be measured, first on a condenser with a large inductive reactance in series, and then on the condenser alone. The current and voltage at the condenser terminals in each case determine the reactance. The measurement of the distortion ratio on generating apparatus should be made at full voltage no-load, since the wave shape at load is indefinite. Several oscillograms show wave shapes recently observed and accompanying them are the distortion ratios, the deviations and the analyses. The paper concludes with proposed substitutes for the present A. I. E. E. Standardization Rules. The derivation of the theoretical formula for distortion ratio is given in the appendix. Tables are also given to serve as a guide in determining permissible distortion.