Shaft voltages and rotating machinery

In order to determine whether a machine is experiencing shaft voltage and current problems, recognition of the four types of damage is imperative. The four distinct types of shaft current damage, frosting, spark tracks, pitting, and welding are described. The four shaft voltage sources and their means of generation are discussed in detail. Methods for correction and/or elimination of these sources are reviewed, so that users can better understand how these voltages and currents are generated. Tests for the detection of shaft voltage sources and their potential circuits are outlined. The most promising, by far, in terms of identifying the potential voltage source, is the direct measurement of shaft voltage and currents. It appears that even though certain assumptions are necessary in this method of testing and analysis, when these measurements are combined with an adequate background of electrical theory, they are extremely useful in determining the health of the train with regards to circulating currents