A method for determining the distance to a fault on power transmission lines from the time of propagation of electromagnetic waves along the line, in which at least at one point on the line the timer interval is measured between the instant of arrival of the leading edge of a wave occurring at the fault and propagated towards said point on the line around the loop formed by the line wires, and the instant of arrival of another wave occurring likewise at the fault and propagated towards said point around the loop formed by the line wires and earth, after which the distance to the fault is found as a function of the measured time interval. A device for applying the above-disclosed method on d.c. power transmission lines, comprising a series combination of a wave-receiving unit connected to the power transmission line via voltage dividers and a time-interval measuring unit, with the wave-receiving unit incorporating at least two transformers whose primaries are connected via voltage dividers to the unlike poles of the power transmission line and whose corresponding secondaries are combined in pairs and connected via rectifiers to said time-interval measuring unit, with some secondaries being connected series-aiding so that they develop a signal proportional to the electromagnetic wave propagated from the fault around one of the two said loops and the remaining secondaries being connected in series opposition so that they develop a signal proportional to the electromagnetic wave propagated from the fault around the other loop.
The distance from the end of the cable to the dielectric weak point of said cable is measured by applying a D.C. high voltage to said cable and generating a discharge at the dielectric weak point, obtaining a pair of pulse signals one by differentiating a surge signal generated and the other reflected at said dielectric weak point, limiting the amplitude of said pair of pulse signals, and measuring the interval between said pair of pulse signals.
A simple and inexpensive device which is suited for real-time location of a fault occurring anywhere in a residential distribution system by analysis of the propogating fault signal considering the predetermined propagating velocity of the cable.
A method of measurement for fault distance determination on two or more parallel HVDC lines connected between two stations with a line fault locator is provided. The fault distance determination is performed by determining the difference in time, via synchronous clocks at each station, between travelling waves, which arise when a fault occurs, reach the two stations. The difference in time is determined by measuring the current associated with the travelling waves and detecting the current at the two stations and on each of the parallel connected lines.
The faulted cable is connected in a loop with a spark gap at one end. Voltage is applied until the spark gap breaks down and the arrival time of the resultant forward wave is measured at both ends of the loop to measure total cable length. Next, the spark gap is opened and the voltage is built up until the fault breaks down. The time of receipt of the wavefront at the two ends of the loop is measured to determine the location of the fault. The apparatus comprises the power supply equipment, the spark gap and the time measuring equipment with its voltage divider and clamp.
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.
