Track/Trolley System Transients

Application of fuse protection to mine electrical dc power systems requires knowledge of the resistance and inductance of the dc track/trolley systems. Analytical methods developed to date, relying on several simplifying assumptions, lead to results that do not closely match those obtained through measurements. More sophisticated yet mathematically simple models are incorporated with the analytical methods presented by the author to produce results that show superior agreement with measured values. Simple equations are developed which account for the increased internal inductance and resistance of rails constructed of ferromagnetic material. Modeling the earth as a conducting cylinder within which the track/trolley system is located, allows more accurate estimation of the mutual resistance seen by earth return currents. This model also provides a better estimate of the external self- and mutual-inductive voltage drops due to the pattern of time-varying flux linkage caused by currents in the track/trolley system as well as those within the earth. The equations developed permit the calculation of the division of return current through all return paths. A comparison of the results obtained from this approach with data measured in practice shows good agreement. Results obtained using these equations support the conclusion that a large portion of the transient return current flows through the earth.