Inductance calculations for earth-return trolley systems

The calculation of the inductance of tack/trolley haulage systems with parallel rail and earth-current-return paths is difficult because of the frequency dependence of the earth-return inductance and resistance. A simple iterative technique is discussed which allows the system time constant and inductance to be calculated easily. The method is tested against a large amount of measured data and compared with a simplified method for time constant calculation. The method is shown to give results which are quite accurate when the model used takes into account the nonideal mine DC network conditions. An additional comparison is made between measured results and an EMTP (electromagnetic transient pulse) simulation of an underground mine track/trolley short circuit transient. The technique is simple enough to have a short execution time on a personal computer.<>