| 摘要 |
An earth-leakage monitoring method for a power distribution system, and in particular a DC 4-rail traction system, incorporating a pair of current-conductors (current rails) and an earth reference (a pair of running rails or an earthing system), comprises measuring the conductor-to-earth voltage for each conductor; forming a ratio of these voltages; connecting a known resistance between one conductor and earth; re-measuring the two conductor-to-earth voltages; forming a new voltage ratio, and calculating the value of leakage resistance existing between each conductor and earth using the known resistance value and the two voltage ratios. An earth-leakage fault method is also disclosed in which the earth-leakage monitoring arrangement is adapted to continuously display the value of conductor-to-earth voltage of the two conductors, the power-distribution system having a number of such monitoring arrangements along its length; the behaviour of this displayed voltage is monitored, and the monitor with the fastest indicated voltage rise time is taken to be the monitor lying in the same section of the distribution system as the fault.
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