Measurements of the Electrical Niose Produced in the Carrier Band by a DC Converter

As part of a program to develop better tools for predicting noise levels from DC converters, a series of measurements were made of the noise levels produced by the Arrowhead converter of the Square Butte project. In this paper both measurement techniques and measurement results are presented. Voltages were measured on both the ac and the dc systems and on both the line and valve sides of the smoothing reactor and converter transformers. Valve side measurements were made possible by a divider that uses a bushing as the high voltage element. Operation of a noise meter is discussed and a circuit shown that allows quasi-peak levels to be measured with an instrument that normally does not provide a quasi-peak function. Quasi-peak levels are shown to be 7-12 dB higher than average levels. Effects of meter bandwidth are discussed. Internal resonances in the smoothing reactor are shown to be the cause of pronounced peaks and valleys noted on line side measurements. The data suggests that a simple 1/f curve of appropriate magnitude may be a sufficient model of the frequency dependent noise produced by the valves.